The document provides a third quarter report on the creation of a custom PSCAD library component for renewable energy systems. Key accomplishments include successfully designing wind, solar, and battery storage models and integrating them into a custom library. Future work identified is improving the battery control system. The custom library allows users to easily design renewable energy systems in PSCAD.

1. Senior Design 2014-2015
SCE PSCAD Library Component
Third Quarter Report
Prepared by: Student Team
5/29/15
Supported by:

2. 1
SCE PSCAD Library Component
Senior Design 2014-2015
Design Review
5/31/15
Student Team Members:
Cho Wai Leung, Eric Hy, Jeff Ge, Adolfo San Juan Santiago
Advisor & Liaison:
Dr. Nagy Abed
ABSTRACT:
Power system computer aided design or PSCAD is a professional simulation tool used for
analyzing power system transients. It allows engineers to construct circuits, run simulations,
and analyze the results in a highly efficient way. From the previous winter quarter, the student
team was successful in designing wind and solar generation models integrated with a battery
storage element to smooth the fluctuating power output generated by renewable energy. The
objective of this quarter is to create a custom library that contains the models of wind, solar,
battery storage, and previous designs by utilizing PSCAD’s custom module techniques. The
report concludes that the custom library component was created successfully and any user
interested in designing a renewable system, can use the library created by the team to aid them
in their design. Future work that will be passed onto the next student team will be to
investigate and improve the control systems of the battery element.

3. 2
Table of Contents
1 Background and Requirements………………………………………………………………………………………..3-4
2 Technical Progress…………………………………………………………………………………………………………..4-7
3 System Components…………………………………………………………………………………………………………..7
- 3.1: Unbalanced Distribution Lines………………………………………………………………………………………8-9
- 3.2: Loads Model…………………………………………………………………………………………………………….9-11
- 3.3: Voltage Regulators and Controls…………………………………………………………………………….11-13
- 3.4: Photovoltaic Transient Modeling……………………………………………………………………………13-26
- 3.5: Wind Generation System……………………………………………………………………………………….26-45
- 3.6: Battery Energy Storage System………………………………………………………………………………45-57
4 Project Planning……………………………………………………………………………………………………………….58
5 Conclusion…………………………………………………………………………………………………………………….….59
6 Reference…………………………………………………………………………………………………………………….60-61

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1. BACKGROUND AND REQUIREMENT
Before it was known as PSCAD, it was known as Electromagnetic transients including
direct current, or EMTDC. It was initially used to study the Nelson River High Voltage Direct
Current Power system. Due to the success of that study, further advancement of EMTDC was
passed on and led to PSCAD. PSCAD stands for Power Systems Computer Aided Design which is
a powerful and flexible graphical user interface to the EMTDC engine. PSCAD enables the user
to schematically construct a circuit, run a simulation, analyze the results, and manage the data
in a completely integrated, graphical environment.
From PSCAD, a collection of components can be dragged from the library tab and be
paste onto to workspace to model a circuit. These components include the following and the
master library from PSCAD is shown below in Figure 1.1.
Network Components:
 RLC components  Transmission lines models
 induction machines  Transformers with saturation
 Synchronous machines  Motors with exciter governor and turbine
models
 Faults  Circuit Breakers
 Surge arresters  Current voltage sources
 Multiple harmonic injectors  Underground cables models
Power Electronics Components:
•Thyristors •Diodes •GTOs •HVDC valve group •SVS •FACTS devices
Control Blocks:
•Derivative •Delay •Differential lag •Integrator •Limit •Complex pole
•Real pole •Lead lag •Filter •Amplifier •Switch •Boolean functions
Meters:
•Voltmeters •Ammeters •Real reactive power meters •Peak detectors
•Phase angle •Frequency meters

5. 4
Figure 1.1: Master Library in PSCAD
Due to the increase penetration of renewable energy into utilities networks, the need for
a way to store this energy during off peak periods is in demand. This project intends to create a
component library to simulate and integrate renewable energy with battery energy storage
system. One of the important factors with renewable energy such as wind and solar is the power
output variation to the utility grid due to unpredictable input from nature resources. The power
output quality and variability can be simulated and evaluated by utilizing PSCAD applications to
investigate the case.
2. TECHNICAL PROGRESS
As the project title implies, the student team is creating a custom component library that
any user of PSCAD can utilize to aid in their design process. The reason of creating custom
components is that it is useful in simplifying and organizing the overall project. However, data
signals and electrical nodes that once connected the module circuit to the greater circuit will
sever, and these must be reconnected.
The process of transporting data and connecting nodes between a module circuit and the
greater circuit, is referred to as porting. A method the student team has selected to create these
custom modules is by using the component wizard application of PSCAD, which is shown below
in Figure 2.1.

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Figure 2.1: Component Wizard used to create custom modules
As you can see from Figure 2.1, we can model components, transmission lines, and
cables by using this technique. The component wizard generates a new definition, and then
creates a single instance of it for placement on the Schematic canvas. After entering the
desired parameters, a custom module can be created and an example of how the student team
created a custom module will be represented below in Figure 2.2. Furthermore, clicking into the
custom module box, an external node component is shown inside where it can be used to make
an external electrical connection to an electrical system from within a module.
Figure 2.2: Custom Module

7. 6
Shown below in Figure 2.3, an example of how we can connect the greater circuit to a
node shown by ‘a’ to represent the module that we create.
Figure 2.3: Example of utilizing component wizard
Through this technique, the student team came up with the main three custom
component library which contains the solar, wind, and battery storage elements which are
shown below in Figure 2.4. These custom components’ models and control systems will be
described in further detail within the report.

8. 7
Figure 2.4: Custom Component Libraries of Wind, Solar, and Battery element
3. SYSTEM COMPONENTS
To validate the necessity of integrating a battery storage to a renewable system, the IEEE
34-Bus Feeder was used as the testing benchmark. However, due to limitations of the student
team’s educational version of PSCAD, modifications had to be done in order to simulate our
design. Displayed in Figure 3.1, is the modified IEEE Bus which contains 23 Buses and the varying
components modeled in PSCAD.

9. 8
Figure 3.1: IEEE Modified Bus System with system parameters
As with any system, the IEEE Bus system contains important system components that allow
the system to operate efficiently and correctly. These components includes unbalanced
distribution lines, load types, voltage regulators, wind/solar generation, and battery storage
elements.
Next, our report will introduce a more in depth discussion of each system component and
custom component library models in sections that were studied and designed by each of our
team members.
UNBALANCED DISTRIBUTION LINE
Starting off with the unbalanced distribution line, it is design in PSCAD by Figure 3.2 shown
below,
Figure 3.2: Unbalanced Line modeled in PSCAD.
This component models two wires that are mutually coupled where Z & B matrices are
directly entered as shown below in Figure 3.3,

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Figure 3.3: Configuration of unbalanced lines
Each type of standard construction was modeled and six types of construction models that
are included are 300, 301, 302, 303, 304, and 305. The difference between each model was the
configuration that was inputted in each model.
LOADS MODEL
The generic term for a load is anything in the circuit that consumes power. These loads can
either be reactive, capacitive, or inductive, but more commonly a combination of all. The ones
that were focused on for the IEEE Bus includes phase loads and phase to phase loads, where the
difference between them is simply the rated voltage. Starting off with phase loads, these loads
can be constant power loads, constant impedance loads, and constant current loads.
A constant power load is a load that varies its impedance to change of input to keep its power
constant. A constant impedance load is simply a load that presents unchanging impedance like a
resistor. Lastly, a constant current load is a load that varies its internal resistance to achieve a
constant current, regardless of the input voltage that is fed to the load. In the real world and
shown in the IEEE system, the combinations of these loads are present.
These loads are modeled in PSCAD by Figure 3.4, which represents the load characteristics
as a function of voltage and frequency.

11. 10
Figure 3.4: Load connected to the system in Different configurations in PSCAD
Also, some important relations to these loads are the following equations that are a
function of voltage and frequency:
𝑃 = 𝑃𝑜 (
𝑉
𝑉𝑜
)
𝑁𝑃
∗ (1 + 𝐾 𝑃𝐹 ∗ 𝑑𝐹) (1)
𝑄 = 𝑄 𝑜 (
𝑉
𝑉𝑜
)
𝑁𝑄
∗ (1 + 𝐾 𝑄𝐹 ∗ 𝑑𝐹) (2)
Constant Power: Constant Z: Constant Current:
-Np=Nq=0 -Np=Nq=2 -Np=Nq=1
-Kpf=kqf=0 -Kpf=Kqf=0 -Kpf=Kqf=0
Where the following variables are represented by the following:
P = Equivalent load real power
Po = Rated real power per phase
V = Load Voltage
Vo = Rated load voltage (RMS L-G)
NP = dP/dV Voltage index for real power
KPF = dP/dF Frequency index for real power

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Q = Equivalent load reactive power
Qo = Rated reactive power (+inductive) per phase
NQ = dQ/dV Voltage index for reactive power
KQF = dQ/dF Frequency Index for reactive power
As we can see from Eq. (1) and (2), by entering different values for the variables, the
presence of different load types is seen. Real life application of a constant power load can be a
motor load with variable frequency drive, a constant impedance load can be an incandescent
lightbulb, and a constant current load can be an electronic load.
Frequency and voltage dependent loads are loads that their active and reactive power
requirements are functions of the system voltage and frequency. In PSCAD it is modeled by a
variable resistor and inductor and is shown in Figure 3.5.
Figure 3.5: Phase to Phase load representation in PSCAD
The variable resistor is a resistor whose electrical resistance can be varied to a required
value. It’s commonly used to allow for finer control over current by changing the amount of
resistance [1], so as you increase resistance, current would decrease giving an overall voltage
gain. Likewise, a variable inductor varies its inductance to a desired value to oppose changes in
current.
VOLTAGE REGULATORS AND ITS CONTROLS
An important system component included in the IEEE Bus is the regulator and its control,
where its main function is maintaining a relatively constant output voltage within a range of

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varying input voltage [2]. In PSCAD a custom design is created and is represented with a tap
changer with its regulation control, shown below in Figure 3.6.
Figure 3.6: Regulator and its controls modeled in PSCAD
The importance of the regulator is to measure how efficient the system is performing and
gives an indication of whether any adjustments are needed to improve the system. A tap changer
is a device within a power transformer to regulate the output voltage to a required level. This is
normally achieved by changing the turn ratios of the transformer by changing the turn ratios of
one side of the windings.
Regulator Controls includes:
Table 3.1: Additional functions of the Regulator control
Set Voltage Control time delay
Initial tap setting Tap position calculator
Bandwidth Timer reset
Out-of-band detector Line compensation
Now that the types of loads and regulators have been selected, now we will introduce
and discussed how to integrate battery storage component and how to use it in smoothing the

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power output for wind and solar generation. Before the integrating of the solar and wind with
battery storage, their full transient models designed will be presented and discussed. This
include the hardware (e.g. Inverter, Induction generators and solar plans) and the control
system.
PHOTOVOLTAIC TRANSIENT MODELING
We now start describing the custom component library that we have developed from
PSCAD starting with the solar generation. Represented below in Figure 3.7, is the custom
component library and a discussion of its components within the library will be explained.
Figure 3.7: Solar Generation Library with its components
Photovoltaic system is the most popular and efficiency solar system conversion method
recently. This system can transfer the solar energy to the electricity directly. Compared to
thermal power system and nuclear power system, photovoltaic panel system cannot cause
environment pollution. Figure 3.8, shows the world largest solar farm, Desert Sun light located
in the center of the desert in Riverside County. This solar farm can provide 550 MW power to
support 170,000 homes. Furthermore, it can reduce 614,000 tons of carbon-dioxide emission.

15. 14
Figure 3.8: Desert Sun light Farm World largest solar farm [3]
The solar farm is just a large scale photovoltaic system designed for supply of merchant
power into electricity grid. The detail photovoltaic system model is shown in Figure 3.9.
Figure 3.9: PV transient model in PSCAD
This transient model contains controllable photovoltaic panel, DC-DC converter, DC-AC
inverter, transformer and equivalent load. The photovoltaic panel, DC-DC converter and DC-AC
inverter are the three main parts in this model.
Photovoltaic Panel
All the photovoltaic panels are made by semiconductor material and they are combined
with photovoltaic cells. The equivalent circuit of the PV cell can be shown in Figure 3.10.
Figure 3.10: Photovoltaic cell equivalent circuit [4]

16. 15
The process of transferring solar energy to electricity is called photovoltaic effect. When
the sunlight hits the surface of the panels, the electrons present in the valence band absorb
energy, and being excited, jumping to the conduction band and become free. These highly
excited, non-thermal electrons diffuse, and some reach a junction where they are accelerated
into a different material by a built-in potential. This generates an electromotive force, and thus
some of the light energy is converted into electric energy. From Figure 3.10, the Eq. 3 of output
current (I) can be expressed as:
I=ISC-Idiode*(e(q*(V+I*Rseries)/n*k*t)-1)-(V+I*Rseries)/Rshunt (3)
Where, Idiode is diode saturation current, q is electron charge, k is Boltzmann constant (1.38*10-
23 J/K), n is ideal factor (1~2) and T is cells temperature. ISC is the photo current and it is a function
of the solar radiation on the plane of the solar cell G and the cell temperature TC. The photo
current Eq. 4 is as follows:
ISC=ISCR*G/GR[1+αT*(TC-TCR)] (4)
Where, ISCR is the short circuit current at the reference solar radiation GR and the reference cell
temperature. The parameter αT is the temperature coefficient of photo current.
Photovoltaic panel has a long life time because all parts in the panel are fixed. Also, the
most efficiency photovoltaic panel can improve the conversion rate to 24%. Figure 3.11 below
shows the photovoltaic panel model in PSCAD.
Figure 3.11: Photovoltaic panel represented in PSCAD
Figure 3.12 below shows the parameters in photovoltaic panel model in PSCAD.

17. 16
Figure 3.12: Photovoltaic panel parameter from PSCAD
We can set the number of cells to a large amount to make the photovoltaic panel model
act as a solar farm.
DC-DC Converter
The core component in the DC-DC converter is called maximum power point track or
(MPPT). The output power from photovoltaic panels changes based on the solar radiation, cells
temperature and also the value of the loads. Figure 3.13 below represents the relationship
between output voltage and output current from photovoltaic panels under 600 W/m2, 800
W/m2 and 1000 W/m2 and figure 3.14 represents the relationship between output voltage and
output current from photovoltaic panels under 25 Celsius, 50 Celsius and 75 Celsius. The
increasing solar radiation increases the short circuit current and the increasing cells
temperature decreases the open circuit voltage.

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Figure 3.13: Relationship between voltage and current under different solar radiation [4]
Figure 3.14: Relationship between voltage and current under different cells temperature [4]
Figure 3.15 below shows that under certain cells temperature and solar radiation,
different values of load affect the output power from the photovoltaic panel.
Figure 3.15: Relationship between photovoltac panel output power and values of load [4]

19. 18
The main benefit of maximum power point track (MPPT) is that it can make the
photovoltaic panels ignore the effect of loads and find the maximum power on the power curve
under certain solar radiation and cells temperature. Then it helps the system generate the
corresponding power. From Figure 3.16 below, shows the procedure of tracking maximum
power point.
Figure 3.16: Relationship between photovoltac panel output power and values of load [5]
Figure 3.17 below shows the MPPT custom library component represented in PSCAD.
Figure 3.17: Maximum power point component in PSCAD
There are two algorithm options which are the Perturb and Observe (P&O) and Incremental
Conductance. The concept behind P&O algorithm is based on observation of PV array output
power and its perturbation by changing the current or the voltage of PV array operation. The
algorithm increments or decrements continuously the reference voltage or current based on
the previous value of power until it reaches the maximum power point. When the dP/dV>0, it
means the perturbation moves the operating point of PV array to the maximum power point
and P&O method will continue to perturb the PV voltage in the same direction. When the
dP/dV<0 which means the perturbation moves the operating point of PV array away from the
maximum power point and P&O method will reverse the direction of the perturbation. Figure
3.18 below shows the state flow chart implementation of P&O method.

20. 19
Figure 3.18: P&O algorithm stateflow chat [6]
The other algorithm, Incremental Conductance is based on the derivative of PV output
power and the equations are shown below in (5) and (6),
(5)
(6)
I/V is the instantaneous conductance of PV array and dI/dV is the instantaneous change in
Incremental Conductance. Comparing these two quantities, it shows the position of the
currently operating point in relation with maximum power point. The flowchart is shown in
Figure 3.19 below,

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Figure 3.19: Incremental Conductance flowchat [7]
The results of these simulation for tthe two algorithms are shown below in Figure 3.20.
Figure 3.20: Simulation result of P&O and incremental conductance for step irradiance [6]
The advantage of Incremental Conductance over P&O, is that it can stop and determine
when the maximum power point is reached without having to oscillate around this value. Also,
it can perform MPPT under rapidly varying radiation conditions with higher accuracy than the
P&O method. Due to the advantages and results of the simulation, the Incremental
Conductance algorithm is selected in our solar generation. From PSCAD simulation, when
radiation, temperature, and algorithm is incremental conductance, the results between the
system with MPPT and without MPPT have an obvious difference. Figure 3.21 below shows the
output power from photovoltaic panel of the system with and without MPPT.

22. 21
Figure 3.21: Output power difference between the system with MPPT and without MPPT
The data above is exported from the original graphs made using excel. When the time
increases, the PV panel which contains MPPT generates more and more power than the one
without MPPT. The results from the simulation identifies how important MPPT techniques are
for a PV system.
DC-AC Inverter
In order to use the power from solar generation, the DC-AC converter is necessary and is
placed between the grid and DC-DC converter. There are six high frequency switches which are
called insulated-gate bipolar transistors or IGBT which converts DC to AC. These IGBTs are
controlled by a controller which is the core component in the inverter. Before we go through
the control system in the inverter, the inputs of the control systems should be introduced.
Figure 3.22 shows the simple real power (P) and reactive power (Q) regulation in our solar
generation.
Figure 3.22: Simple P and Q regulation in PSCAD

23. 22
For real power regulation, the measuring DC voltage is compared to the reference DC
voltage. The error between the two values is processed as an angle voltage (Ang) through a
proportional-integral (PI) controller. Similarly for reactive power regulation, the error is
compared between the desired and actual value of reactive power, then processed into
magnitude voltage (Mag) through a proportional-integral (PI) controller [8]. After that, the
angle voltage and magnitude voltage signals are sent to the controller in the inverter. Now, the
controller in the inverter will be introduced.
There are two methods of controller to control the IGBTs in the inverter in our system. The
first method is called firing pulse generation which is shown in Figure 3.23 below and it shows
the firing pulse generation model used in our solar generation.
Figure 3.23: Firing pulse generation in PSCAD
The controller starts with creating three sinusoidal modulating waves with a frequency of
60 Hz and a phase shift equal to the output of the previous PI controller (Ang) with additional
shifting of -120 and 120 degrees. The magnitude of the modulating waves is equal to (Mag)
from the previous PI controller. Then, the three sinusoidal modulating waves are compared
with a triangular carrier wave with magnitude ranging between -1 and 1. Switching signals gt1,
gt3 and gt5 were generated by setting the output of the comparator to 1 whenever the
modulating wave is greater than the carrier wave and 0 otherwise. Since the operation of the
two switches in each of the three legs of the inverter bridge should be complementary to
produce the final sinusoidal wave, the switching signals gt4, gt6 and gt2 were generated by
inverting the switching signals gt1, gt3 and gt5, respectively [9].

24. 23
The other method is called phase locked loop controller. Figure 3.24 below shows the
phase locked loop controller used in our solar generation.
Figure 3.24: Phase looked loop controller in PSCAD
The greatest advantage of the phase locked loop controller, is that it can constantly
synchronize the output frequency and phase of grid voltage with grid current. This means the
output phase and input phase are always matched up. This will improve the quality of output
power to the grid and Figure 3.25 below shows the results of two methods.
Figure 3.25: Simulation result by different control methods in PSCAD

25. 24
The red line represents the output power by using the phase locked loop controller. The
blue line represents the output power by using firing pulse generation. The DC-AC converter
which is controlled by phase locked loop generates more power than the firing pulse
generation. Due to the advantages and results of the simulation, the phase looked loop
controller is selected in our solar generation.
Solar Radiation representation
Lastly, the solar radiation variation over the full day cycle and its effects on the power
generated from the photovoltaic system will be modeled in PSCAD and discussed. Although
solar PV system is an important source for renewable energy with great advantages, it also has
its disadvantages. A disadvantage is that the PV panels can only generate power when the solar
radiation is present. Figure 3.26 below is the simulation from PSCAD, which shows the output
power from the solar panel in a 24 hour time frame.
Figure 3.26: Output power from solar panel
Referring again to Figure 3.26, before 6 A.M and after 6 P.M, the solar panel doesn’t
generate any power and the highest power that is generated is around 12 p.m. This is due to
the fact that before 6 A.M and after 6 P.M, there is no sun light at all and solar intensity reaches
the highest peak value during noon time. Our indication of output power from the solar panel is
that the more solar radiation the solar panel can detect, the more power it can generate and
vice versa. To prove this indication, a real time data graph of the power produced by solar
radiation is used, which is shown in Figure 3.27.

26. 25
Figure 3.27: Daily power that the renewable sources generate [10]
This graph is from California Independent System Operator (CAISO) website which shows
the daily output power that the renewable sources generated on May 29, 2015. Notice that
there is no power generated from solar panel before 5 A.M and after 9 P.M, which identifies
that the results from simulation matches up with real world data.
Now that the modeling of solar generation using PSCAD has been discussed, another
renewable energy model that will be introduced is wind generation and its controls.
WIND GENERATION SYSTEM (WGS)
People started using wind power centuries ago with windmills, which pumped water,
ground grain, and did other work. Today’s wind turbine is a highly evolved version of a
windmill. A modern wind turbine takes the wind’s kinetic energy and converts it into
mechanical energy and then in electricity. Wind power is an affordable, efficient and abundant
source of domestic electricity. For Southern California Edison (SCE), it has been 30 years since
the first wind turbines were installed in the Tehachapi-Mojave Wind Resource Area shown in
Figure 3.28 [11].This location is considered one of the premier places in the nation for wind
power generation, and it is one of the windiest places in the world.

27. 26
Figure 3.28: SCE wind Farm Located in Tehachapi, CA [11]
The Tehachapi Renewable Transmission Project (TRTP) is a critical piece of infrastructure
necessary to bring clean, renewable energy to customers throughout Southern California.
However, this is still only one part of SCE’s effort to achieve this important goal. SCE officially
began the construction of its Tehachapi Renewable Transmission Project (TRTP) in 2008. The
first phase of the project is high-voltage transmission system capable of delivering 4,500 MW of
clean energy into the Los Angeles area.
The following design, represented below by Figure 3.29, represents the wind generation
library component model designed using PSCAD. The parameters needed in PSCAD were
specified based on the functions and ratings for each of these components. Among these parts,
the wind turbine component and double-fed induction generator (DFIG) component are
available in the PSCAD library directly. The model in the PSCAD library was used with proper
parameters based on the ratings.

28. 27
Figure 3.29: Wind Generation Library Component Module Designed in PSCAD with DFIG
In recent years, wind energy has become one of the most important and promising
sources of renewable energy, which demands additional transmission capacity and system
stability. Therefore, for our project, we used the 34 bus system to test the integration of a wind
generation system with the implementation of a Double-Fed Induction Generator (DFIG). Our
focus was to comprehend the electromagnetic transient analysis behavior of the given system

29. 28
for utility applications through different simulations. Figure 3.30 below, represents the PSCAD
design for a wind turbine model. Three models related to wind energy are available in the
PSCAD library as shown in Figure 3.30, including the wind source model, wind turbine model
and wind governor model. In our project, the wind source model and the wind turbine model
were used. In PSCAD, the wind source model generates the wind speed variable. The wind
speed variable can be composed by four components as shown in equation (7). The values of
those four components can be independently set when necessary.
The wind turbine governor in the PSCAD library is designed for enabling the pitch
control function when necessary. Its output pitch angle value denoted as beta (β) is shown in
Figure 3.30.
Figure 3.30: Wind Turbine Model from PSCAD
Wind power equation:
Vwind= Vbase + Vgust + Vramp + Vnoise (7)
Where;
Vbase= base wind speed (m/s)
Vgust= gust wind component (m/s)
Vramp= ramp wind component (m/s)
Vnoise= noise wind component (m/s)

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𝑃𝑚 = (
1
2
) 𝜌𝐴𝐶 𝑝 𝑉𝑤
2
(8)
Where;
Pm: Output mechanical power [W],
𝜌: Air density (1.225 kg/m3),
A: Rotor’s Blades area [m2],
Cp: Power coefficient,
Vw: Wind speed [m/s] represented in (Figure: 3.31)
From equation 8, one can find the mechanical power output.
The following equations, Cp depends on two parameters:
1. Tip Speed ratio (λ)
2. Blade pitch Angle (β)
Cp= 0.5(λ-0.02 2 β2-5.6) 𝑒−.17𝜆
(9)
λ = (
1
𝑉 𝑤
) 𝑊𝑡 𝑅𝑡 (10)
Where:
𝑊𝑡 is the Turbine Speed [rad/sec]
Rt is the Radius of the blade [m].
Figure 3.31: Variations of power coefficient vs. tip speed ratio for β = 0 [18]

31. 30
In order to obtain the maximum Cp we have to control λ to be λopt so 𝑊𝑡 must be controlled in
each wind speed shown below in Figure 3.32.
Wind Turbine V-I Characteristic
The wind turbine control implements the V-I characteristic illustrated in Figure 3.33
below. As long as the reactive current stays within the maximum current values (-Imax, Imax)
imposed by the converter rating, the voltage is regulated at the reference voltage verve. A
voltage drop equation is used for the V-I characteristic (3% at maximum reactive power
output).
V= Vref. + I* Xs (11)
Where;
V Positive sequence voltage (p.u.)
I Reactive current (p.u./PNOM) (I > 0 indicates an inductive current)
XS Slope or drop reactance (p.u./PNOM)
PNOM Three-phase nominal power of the converter specified in the block dialog
box
Figure 3.32: Output power of the wind turbine vs. rotor speed. [16]

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Figure 3.33: Wind Turbine V-I Characteristic [13]
We used an example simulation in PSCAD where we used the standard 60Hz as our
frequency. The circuit simulates a low voltage system with an induction generator to analyze
each component and find the variation of the active and reactive power based on the variability
of the wind speed and pitch angle of the wind turbine Figure 3.34. We also analyze the
components of the wind source, their effect on the active and reactive power, and the response
of the control system. Each input and output is indicated on Table 3.2.
Figure 3.34: PSCAD Simulation design for an induction generator

33. 32
Shown below in Figure 3.35, is the typical layout of a wind turbine.
The main purpose of the transient analysis simulation is to reduce the wind turbine
power output fluctuation to less than ten percent for a low voltage ride through. In our
simulation we used a constant wind speed at 15 m/s. Our results indicate that as the wind
speed increases, the pitch angle must be adjusted also for maximum power output. Since the
generator starts in the per unit control mode, the active and reactive power fluctuate until the
control switches to the torque control mode and the machine rotates at a constant speed.
When the speed and pitch angle are constant, the active and reactive power also become
constant as shown in Figure 3.36 and Figure 3.37.
Wind Generator
Input/output Turbine Inputs Turbine Outputs Wind Parameters
W: Speed control mode
of the machine [p.u.
speed]
Vw: Wind speed (must
be a positive value)
[m/s]
Tm: Output torque of
the turbine [pu]
Mean Wind Speed
T: Torque control
mode. Speed calculated
based on machine’s
inertia
W: Machine
mechanical speed
[rad/s]
P: Output power of
the turbine [pu]
Gust
S: Switch to select the
speed mode. Beta: Pitch angle [deg]
Ramp/Ramp
Figure 3.35: Major components of a typical horizontal axis, three-bladed, upwind wind turbine
Table 3.2: Wind generator components input
[7]and output. [6]

34. 33
The power is controlled in order to follow a pre-defined power-speed characteristic,
named tracking characteristic. This characteristic is illustrated by the ABCD curve shown in
Figure 3.38 below.
Figure 3.36: PSCAD Simulation design for an induction generator
Figure 3.37: PSCAD Simulation design for an induction generator

35. 34
Figure 3.38: Turbine Characteristics and Tracking Characteristic [13]
The actual speed of the turbine ωr is measured and the corresponding mechanical
power of the tracking characteristic is used as the reference power for the power control loop.
The tracking characteristic is defined by four points: A, B, C and D. From zero speed to speed of
point A the reference power is zero. Between point A and point B the tracking characteristic is a
straight line. Between point B and point C the tracking characteristic is the focus of the
maximum power of the turbine (maxima of the turbine power vs turbine speed curves). The
tracking characteristic is a straight line from point C and point D. The power at point D is one
per unit and beyond point D; the reference power is a constant equal to one per unit.
Wind Turbine Generator
The generator is the component of the wind turbine responsible for converting the
mechanical motion of the rotor into electrical energy. There are many different types and sizes
of electric generators for a wide range of applications. Depending on the size of the rotor and
the amount of mechanical energy removed from the wind, a generator may be chosen to
produce either AC or DC voltage over a variety of power outputs. There are four major types of
electrical generators for converting mechanical energy; the squirrel cage induction generator,
the wounded-rotor induction generator, the doubly-fed induction generator, and the
synchronous generator. For our project, we decided to use the doubly-fed induction generator
simply because it can perform as well as the synchronous generator in controlling the active
and reactive power for variable wind speed, and it is less expensive.

36. 35
Double-Fed Induction Generator
To control the wind power efficiently, the most reliable system in the present era is the
grid connected DFIG. There are some important characteristics of the DFIG that we must take
into consideration. The DFIG brings the advantage of utilizing the turns ratio of the machine, so
the converter does not need to be rated for the machine’s full rated power. The rotor-side
converter (RSC) usually provides active and reactive power control of the machine while the
grid-side converter (GSC) keeps the voltage of the DC-link constant. The DFIG technology allows
extracting maximum energy from the wind for low wind speeds by optimizing the turbine
speed, while minimizing mechanical stresses on the turbine during gusts of wind. The optimum
turbine speed producing maximum mechanical energy for a given wind speed is proportional to
the wind speed. Another advantage of the DFIG technology is the ability for power electronic
converters to generate or absorb reactive power, thus eliminating the need for installing
capacitor banks [12].
The main electronic component controllers of the DFIG is shown in Figure 3.39 are:
 The Rotor Side Converter (RSC)
 The Grid Side Converter (GSC)
 The DC-Link
 The Crowbar
Figure 3.39: Double-Fed Induction generator Diagram
The following design represented below by Figure 3.40, represents the wind generation
model designed using PSCAD.

37. 36
Figure 3.40: Wind Generation Module in PSCAD with DFIG
Wind Generator Control System
In this section, aspects of implementing the control systems of the DFIG are named.
Controlling of DFIG depends upon the requirement, type of study and method to be used. The
classical technique based on proportional integral control has been used for this system. A
cascade control structure has been used to command the rotor-side converter (RSC) and grid
side converter (GSC). The rotor-side converter provides the excitation for the induction
machine rotor and a varying excitation frequency depending on the wind speed conditions. The
control objectives must be achieved by the manipulation of currents, thus the inner control
loops are current loops as shown in Figure 3.41. With a pulse with modulation (PWM) converter
it is possible to control the torque, the speed of the DFIG, and also the power factor at the
stator terminals shown in Figure 3.42. They receive the reference from the outer control loop,
which relates to the process variable defined in the control objective.

38. 37
Figure 3.41: Generation of Current References Control System Model from PSCAD
Figure 3.42: Generation of Current References PMW Control System Model from PSCAD
The choice of a synchronously rotating reference frame has the advantage that all the
currents, voltages and flux-linkages associated with the stator and rotor dq-windings are DC in a
balanced sinusoidal steady state as presented in Figure 3.43. Since the objective of the grid-side
converter (GSC) is to keep the dc-link voltage constant regardless of the magnitude and
direction of the rotor power, a vector control method is used as well. This method enables
independent control of the active and reactive power flowing between the grid and the

39. 38
converter. The PWM converter is current regulated, with the d-axis current used to regulate the
dc-link voltage and the q-axis current component to regulate the reactive power. While the GSC
control scheme always uses grid voltage space vector alignment, two possibilities exist for the
alignment of the RSC reference frame.
Figure 3.43: Stator to Rotor Control System from PSCAD
It can be aligned with the stator flux space vector as shown in Figure 3.44. Its purpose
rely in the identification of main stator flux by integrating the stator voltage after the removal
of resistive drop.
Figure 3.44: Stator Flux Control System from PSCAD
The rotor position and slip angle control has a purpose of determining the relative
difference between stator flux and rotor position for resolving the rotor currents. The angle
resolver cleans the angle signal so that jumps of 2π do not show up as referenced in Figure
3.45.

40. 39
Figure 3.45: Rotor Position and Slip Angle Control from PSCAD
The vector control for the generator can be embedded in an optimal power tracking
controller for maximum energy capture in a wind power application. By controlling the active
power of the converter, it is possible to vary the rotational speed of the generator, and thus the
speed of the rotor of the wind turbine. This can then be used to track the optimum tip-speed
ratio as the incident wind speed changes thereby extracting the maximum power from the
incident wind. The grid-side converter control gives potential for optimizing the grid integration
with respect to steady-state operation conditions, power quality and voltage stability. The
optimal power tracking control referenced in Figure 3.46, determines the reference speed to
maintain the optimal tip speed ratio (Max. power tracking) Assuming constant tip speed ratio:
wind speed/Wpu = 12/1.1 = 10.909 = constant. The Initial wind speed is 12 m/s and the initial
speed of machine is 1.1 pu.
Figure 3.46: Optimal Power Tracking Control System Model from PSCAD
The Rotor-Side Converter (RSC)
The rotor-side converter representation in PSCAD is shown below in Figure 3.47, is used
to control the wind turbine output power and the voltage measured at the grid terminals. The
purpose of the rotor-side converter is to control the rotor currents such that the rotor flux
position is optimally oriented with respect to the stator flux in order that the desired torque is
developed at the shaft of the machine.

41. 40
Figure 3.47: Rotor Side Converter Model from PSCAD
The Grid-Side Converter (GSC)
The GSC model in PSCAD is shown in figure 3.48, is used to regulate the voltage of the
DC-Link between the two converters and allows generating or absorbing reactive power for
voltage support requirements. During the steady state, and low voltage periods, the GSC takes
place in the generation of reactive power. It supplies the reactive power quickly while the rotor
side converter results in delay as it passes the current trough the machine.
Figure 3.48: Grid Side Converter Model from PSCAD

42. 41
The DC-Link
The dc-link model describes the dc-link capacitor voltage variations as a function of the
input power to the dc-link. The energy stored in the dc capacitor is as followed in the equation,
Wdc = ∫ 𝑃𝑑𝑐 𝑑𝑡 =
1
2
𝐶𝑉𝑑𝑐
2
(12)
Where the following variables represents,
C: Capacitance
Vdc: Voltage
Wdc: Stored energy
Pdc: Input power to the dc link
The voltage and energy derivatives are as follows,
𝑑𝑉 𝑑𝑐
𝑑𝑡
=
𝑃 𝑑𝑐
𝐶𝑉 𝑑𝑐

𝑑𝑊 𝑑𝑐
𝑑𝑡
(13)
Where;
Pdc: Pdc = Pin –Pc.
Pin: Input power from rotor-side converter
Pc: Grid-side converter output power
The dc-link voltage varies as Pdc and is a constant when Pdc = 0 [15].
A braking resistor is provided in the dc-link bus shown in Figure 3.49 below, as a form of
protection to dissipate excess energy during a grid fault. The resistor is connected to the dc-link
bus in series with an insulated gate bipolar transistor (IGBT), and is referred as either the dc-link
chopper or the dc crowbar. The IGBT can control the amount of energy dissipated in the
resistor, with the resistor or set of parallel resistors, sized to handle a specific amount of energy
during a grid fault. The larger the fault that is desirable to ride through, the larger the physical
size of the resistor or resistors must be. This design decision can be a function of utility
requirements for fault ride through, as the energy dissipation during a fault is a function of the
voltage dip magnitude and fault duration [12].
Figure 3.49: DC-Link model From PSCAD

43. 42
The AC Crowbar
An AC crowbar modeled in PSCAD is shown in Figure 3.50, is implemented on the rotor
side of the RSC, which acts to bypass the RSC by applying short-circuit to the rotor terminals. This
acts to protect the RSC from over currents as well as to protect the DC-link from over voltages.
The crowbar is an important aspect in not only the protection of the converter components, but
in understanding the behavior of the DFIG machine during grid faults. The crowbar avoids the
voltage bus exceed its maximum value once the RSC loses current control providing a path for
the rotor currents. The crowbar short-circuits the rotor and the machine operates as a squirrel
cage machine.
Figure 3.50: AC Crowbar model From PSCAD
To avoid the bus voltage from reaching the converter limits, it is necessary to break this
energy flow, and the simplest method is to short-circuit the rotor when the bus voltage reaches
a limiting value. With a passive control, the crowbar act as a protection system; the time
necessary to open the stator breaker is approximately 100 milliseconds, causing at the end the
disconnection of the wind turbine. When the control objective is to keep the wind turbine
connected to the grid during fault, it is necessary to control the bus voltage. The simplest
technique consists of comparing the bus voltage with its maximum and normal operation
reference values and, depending on that comparison, keeping the crowbar circuit open or
closed.

44. 43
Low Voltage ride through (LVRT)
The performance of the DFIG during grid faults is attracting much interest due to the
proliferation of wind turbines that employ this technology. Grid codes specify that the
generator must exhibit a fault-ride-through (FRT) capability by remaining connected and
contributing to network stability during a fault. The classical solution to fulfill LVRT
requirements is the use of the rotor crowbar method referred to Figure 3.51. It is the
conventional system adopted by manufacturers to ride through grid faults. Although the
crowbar is a cost-effective method able to protect the generator and the converter during the
faults, it has some disadvantages that cannot be overlooked. Its major disadvantage is that, the
DFIG loses its controllability once the crowbar is triggered, due to the rotor-side converter
deactivating. In such a situation, the DFIG absorbs a large amount of reactive power from the
grid, leading to further grid voltage degradation [13].
Figure 3.51: Low Voltage Ride Through graph [16]
In order to reduce the operation time of the crowbar, an improved hysteresis control
strategy is adopted. The maximum absolute value of rotor current |Ir| max is compared with a
threshold value Ith and a safety value Isa. If |Ir| max is greater than Isa, the crowbar is activated
for protecting the power converters. Immediately after |Ir| max decreases to be less than Isa,
the crowbar cuts off [14]. During the grid fault the power converters remain connected in order

45. 44
to continuously control the reactive power. In this way the DFIG is able to supply reactive
power to the grid, as required by recent grid codes, to help the grid voltage recovery as seen in
Figure 3.52.
Figure 3.52: System Response under Fault Conditions
Now that the models of solar and wind generations have been presented, the
importance of the integration of the battery with these renewable energy source will be
presented.
BATTERY ENERGY STORAGE SYSTEM (BESS)
Advantages of BESS have already been briefly established in the beginning of the report.
Further research and simulations were conducted regarding battery’s characteristics and
integration in power grids. Simulations fulfilled the purpose of integration of battery storage in
power grids, which is to smooth the power output due to fluctuating nature of renewable
resources. In spring quarter, two battery models were finalized and put into a custom
component library.
California legislature put an energy storage revolution into motion with the passage of
AB 2514 to meet the goal of 1.3 gigawatts by 2022 [19]. In order to achieve the goal, Southern
California Edison (SCE) has been implementing energy storage years ago and especially the 32
megawatt-hours (MWh) battery energy storage system at SCE’s Monolith substation in
Tehachapi, California Figure 3.53. The area is where the Tehachapi wind resource area that is

46. 45
projected to generate up to 4,500 megawatts (MW) of wind energy by 2016 [20]. The battery
storage for wind integration can provide 8 MW for 4 hours.
Figure 3.53: SCE’s Monolith substation in Tehachapi
The electrochemical battery model in PSCAD was given by Dr. Abed Nagy in order to
study the implementation of BESS with Solar and Wind generations. This section of the report
introduces a battery component in PSCAD which is based on electrochemical battery model.
Here are the sections:
 Electrical characteristics of batteries: Description of battery main characteristics
of battery.
 Battery model in PSCAD: Description of battery model in PSCAD and its
parameters.
 Improvement to wind generation output: Battery integration smooth out power
output profile of wind generation.
 Improvement to solar generation output: Battery integration smooth out
voltage output profile during low sun radiance.
Electrical characteristics of batteries:
There are many different common types of batteries and other factors to be considered
regarding performance. The four main rechargeable battery cell types include Lithium-Ion, Lead
Acid, Nickel-Zinc (Ni-Zn), Nickel-Cadmium (Ni-Cd), and Nickel metal hydride (Ni-MH). They all
have very similar percentage of capacity discharge characteristic Figure 3.54. Lithium-ion (Li-
ion) battery type has better advantages over other types. It offers excellent performance, which
is related to their high specific energy, energy density, specific power, efficiency, and long life
[21].

47. 46
Figure 3.54: Percentage Capacity Discharged [22]
The battery model is created for PSCAD based on a research paper from IEEE [22]. The
model has a series of assumptions which includes constant resistance, same charge and
discharge characteristics, no effect on the capacity at different current, no temperature effect,
no self-discharge effect and no hysteresis. The reason for neglecting hysteresis effect is that the
charge and discharge characteristic for any generic battery is similar Figure 3.55. Fully charged
voltage at 100% as indicated in Figure 3.55 is higher than nominal or rated voltage. On the
hand, voltage after end of nominal zone is lower than rated voltage. In real life, it is common to
run battery between 40% and 80% of state of charge to extend battery lifespan and to obtain
more stable voltage output.

48. 47
Figure 3.55: Charge and discharge characteristic [22]
Before modeling the PSCAD battery model, one must understand the fundamental and the
important terminology of batteries:
1. Rated Capacity (ah): The ampere-hour when a battery is fully charged.
2. Nominal Voltage (V): Voltage that is under normal operating conditions.
3. State of Charge (SOC): SOC is in percentage and represents the instantaneous battery
capacity over the total rated capacity.
4. Charge Rate (C rate): The amount of current that a battery can deliver for 1 hour A
1000mah or 1ah battery that is rated at 1C means that it can be fully discharged in one
hour ideally.
5. Internal Resistance: The Thevenin resistance in the battery Figure 3.55. The internal
resistance varies based on manufacture’s datasheet.

49. 48
The equivalent circuit of a general battery is shown below in Figure 3.56,
Figure 3.56: Equivalent circuit of the battery [22]
The battery voltage equation can be written as:
𝐸 = 𝐸𝑜 − 𝐾 (
𝑄
𝑄−𝑖𝑡
) + 𝐴𝑒−𝐵𝑖𝑡
(14)
In the equation above:
E No-load voltage (v)
Eo Battery constant voltage (V)
K Polarization voltage (V)
Q Battery capacity (Ah)
∫ 𝑖. 𝑑𝑡 Actual battery charge (Ah)
A Exponential zone amplitude (V)
B Exponential zone time constant inverse 1/(Ah)
Vbat Battery Voltage (V)
Rbat Internal Resistance (Ω)
Ibat Battery current (A)

50. 49
The battery voltage equation can be modified as following in terms of State of Charge
(SOC):𝐸 = 𝐸𝑜 − 𝐾 (
1
𝑺𝑶𝑪
) + 𝐴𝑒−𝐵𝑄(1−𝑺𝑶𝑪)
(15)
Therefore, SOC will affect the battery voltage exponentially and non-linearly.
Battery model in PSCAD:
In order to form the voltage equation of battery, the model parameters can be obtained using
Table 3.3.
Table 3.3: Battery parameters
The parameters appeared in the equation above can be changed in PSCAD accordingly as
shown in Figure 3.57 and Figure 3.58.
Figure 3.57: PSCAD battery model menu 1 Figure 3.58: PSCAD battery model menu 2

51. 50
The battery component in PSCAD is shown in Figure 3.59:
Figure 3.59: Battery component in PSCAD
Improvement to wind generation output:
The battery model is integrated to wind generation’s module in order to smooth out the
wind generation power output as wind speed changes. The battery in red box in Figure 3.60 is
integrated in between Grid Side Converter (GSC) and Rotor Side Converter (RSC). GSC converts
Alternating Current (AC) voltage from the grid to Direct Current (DC) voltage to the rotor side.
Because electrochemical battery produces DC signal, it is a common practice to integrate
battery energy storage system in between GSC and RSC.
Figure 3.60: Wind generation with battery integration
In the Double-Fed Induction motor (DFIG) wind generator model, wind is speed is
varying over time and is affecting the output power shown in Figure 3.61. The simulation shows
that output active power fluctuate between 0.30 MW up to 0.7 MW. The fluctuation is 0.5 MW
GSCRSC

52. 51
Figure 3.61: Wind output power without battery support
However, simulations show a significant improvement and the output power is much
smoother after battery integration in Figure 3.62.The output power in Figure 3.62 varies
between 0.5MW and 0.65MW. The fluctuation is improved and reduced from 0.5MW to
0.15MW.
Figure 3.62 Wind output power with battery support

53. 52
Improvement to solar generation output:
Figure3.63:SolargenerationwithbatteryIntegration

54. 53
In Figure 3.63, battery is integrated to solar generation’s module to smooth out the
voltage output profile whenever sun radiance becomes low. The model is placed and indicated
by a red box in the circuit in Figure 3.63. This circuit has designated output Root Mean Squire
(RMS) voltage to be 11kV.
To demonstrate the effect of sun radiance on the output RMS voltage, sun radiance is
manually reduced during simulation from 622.22 (Watts/meter^2) to zero without battery
integration. Indicated in red box in Figure 3.64, the RMS voltage drops below rated 11kV when
sun radiance becomes 0 (W/M^2) at around 1.4 seconds.
Figure 3.64: Solar Generation without battery integration

55. 54
In order to mitigate and smooth out the output RMS voltage profile of solar generation,
simulation is repeated counting the effect of battery integration in Figure 3.65. At around 2
seconds where sun radiance becomes zero, the output RMS voltage remains close to rated
11kV as indicated. It is proven that battery integration helps smoothing the output profile of
solar generation.
Figure 3.65: Solar generation with battery integration

56. 55
Custom energy storage library
In this quarter, two battery models were put finalized and modulated into a custom
component library called battery energy storage library shown in Figure 3.66.
Figure 3.66: Battery Energy Storage
Upon expanding this module, the user will find two versions of battery model shown in
Figure 3.66. Battery version_1 is one chosen to be integrated with solar and wind generations
since it is a newer version and has better control regarding state of charge. On the other hand,
battery version_2 has charge protection and charge/discharge control as shown in Figure 3.67.
User can choose whichever version based on their applications.

57. 56
Figure 3.67: Charge protection and charge control of battery version_2

58. 57
4. PROJECT PLANNING
Overall, the student team was able to work effectively and efficiently to complete their
custom component library which included the solar, wind, and battery storage elements.
Represented below in Figure 4.1, is the organization chart that indicates who was responsible for
what.
Figure 4.1: Team Organization Chart
From Figure 4.1, each member was in charge of a specific task, but overall each member
helped one another to complete a task. This last quarter was more focused in synchronous work
due to the fact that every component had to be placed within a custom component library that
contained the wind, solar, and battery elements.

59. 58
YEAR-ROUNDSCHEDULE
Figure3.2.Yearroundschedule

60. 59
5. CONCLUSION
PSCAD is a powerful tool that can enable its user to analyze their system’s transient
behavior. With PSCAD, the student team was able to understand the transient behavior from
renewable energy and was able to develop custom component libraries which contained these
elements. These elements included solar generation, wind generation, and battery storage
elements. With the custom component libraries that has been developed, new users who decides
to model a renewable energy system, can just recall the libraries created by the student team to
help them develop their design. The student team has already validated their results by using the
IEEE Bus system to validate their results and the need for integration of a battery storage element
to smooth out the power fluctuations generated by renewable sources. If future work is involved
next quarter, the analysis and implementation of a more efficient control system should be
analyzed.

61. 60
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