This document discusses issues related to interconnecting microgrids. It describes how a DC microgrid system utilizes a DC bus to distribute power from photovoltaic units and battery storage to local households. Interconnection can be done directly through switchgear or power electronic interfaces. Key issues that can arise include voltage and frequency fluctuations that occur due to imbalance between supply and demand, power factor correction needs, and harmonics produced by some loads. Unintentional islanding is also a safety concern that must be addressed when connecting microgrids to the main power grid.

1. -Prof. A S PANDEY
B.E, M.TECH (IPS), PhD Registered. (IITRAM)
1
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE,
Kopargaon
16/03/2021
MICRO GRID

2. MICROGRID
CONTENT
• DC Microgrid.
• Issues of interconnection.
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
2
16/03/2021

3. 16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
3

4. https://global-sei.com/technology/tr/bn75/pdf/75-25.pdf
• As per schematic view of the DC micro grid system.
• This system utilizes a DC bus as its backbone and
distributes power to a community that consists of
several dozens or a hundred of households in a
residential area.
• A 350 V DC bus is installed instead of 200 V / 100 V
lines in conventional AC distribution systems and
connected with a high voltage commercial grid through
the intermediary of a bidirectional AC/DC converter.
• All the PV units in the community are linked with the
DC bus through DC/DC converters.
16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
4

5. 16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
5
• These converters always track the maximum power point of the
DC power sources which fluctuates depending on the intensity
of solar radiation.
• Conventional appliances can be used as they are if an inverter
is installed in each house to change the DC power into 200 V /
100 V AC power, but DC power feeding will spread widely
because of its high efficiency, once safe and compact gears,
such as breakers and outlets, are standardized in the future.
• Storage batteries of the community are also linked to the DC
bus.
• The DC-based distribution system reduces facility costs and
energy dissipation associated with AC/DC conversion because
the PV units and battery are DC connected and most of the
current energy-saving appliances operate on DC due to the
progress of inverter technology.
• This is why we should push ahead with the DC system.

6. 16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
6
Interconnection methods and technologies
1. Directly through switchgear
2. Power electronic interfaces
3. Static switches
4. Directly through circuit breakers:
• Relatively simple and in expensive Slow (3 to 6 cycles to
achieve a complete disconnection).
• Since electrical characteristics on both sides of the circuit
breakers must be the same, then, electrical characteristics on the
micro-grid side are dependent on the grid characteristics.
• For example, use of a circuit breaker implicitly limits the micro-
grid to have, at least partially, an ac power distribution system in
order to match the grid’s electrical characteristics.
• Power flow through the PCC cannot be controlled.

7. Issues of interconnection in
MICROGRID
16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
7

8. Issues of interconnection
• Electricity grids must have standard conditions of supply to ensure that end-use
equipment and infrastructure can operate safely and effectively. These conditions
are commonly referred to as power quality requirements and are defined in
standards or by supply authorities .
• They most commonly relate to voltage and frequency regulation, power factor
correction and harmonics.
• In all distribution networks, challenges to maintaining these power quality
requirements arise from the technical characteristics and end-user operation of
electrical loads, and the network equipment and lines.
• Some loads have significant power demands that increase network current flows
pulling down line voltage (such as electric hot water heaters and large air-
conditioners).
• Some have very short-lived but major power draws on start-up (such as standard
induction motors) driving voltage fluctuations.
• Some have significant reactive power needs (again including motors) or create
significant harmonics (such as computer power supplies and fluorescent lighting).
• Power quality at different points of the distribution network at any time is impacted
by the aggregate impacts of loads and network equipment in highly complex ways.
16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
8

9. Issues of interconnection
(a) Voltage fluctuation and regulation: Voltage fluctuation is a
change or swing in voltage, and can be problematic if it moves
outside specified values.
(b) Power factor correction: Poor power factor on the grid
increases line losses and makes voltage regulation more
difficult.
(c) Frequency variation and regulation: Frequency is one of
the more important factors in power quality. The frequency is
controlled by maintaining a balance between the connected
loads and generation.
• Disruptions in the balance between supply and demand lead
to frequency fluctuation, it falls when demand exceeds
supply and rises when supply exceeds demand.
16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
9

10. Issues of interconnection
(d) Harmonics: Harmonics are currents or voltages with frequencies
that are integer multiples of the fundamental power frequency.
• The standard frequency's 50 or 60 Hz depending on t h e country,
and so harmonic in a 50 Hz country could be 100, 150, 200Hz, etc.
• Harmonics can also be eliminated using passive and active filters,
which are generally cheaper than inverters.
• Passive filters are composed of passive elements such as capacitors
or reactor s, and absorb harmonic current by providing a low-
impedance shunt for specific frequency domains
(e) Unintentional islanding: Unintentional islanding occurs when
distributed generation delivers power to the network even after circuit
breakers have disconnected that part of t h e network from the main
grid and associated generators
16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
10

11. 16/03/2021
DEPARTMENT OF ELECTRICAL
ENGINEERING, Sanjivani COE, Kopargaon
11

12. QUERIES??
Mail at :-
pandey.amarjeet73@gmail.com