The concept of Firing angle controls are explained in this presentation

1. Firinganglecontrol
content
 Types of firing angle control
 IPC Control
 EPC Control
Prepared By
Mr.K.Jawahar, M.E.,
Assistant Professor
Department of EEE
Firing Angle Control
Kongunadunadu College of Engineering and Technology Department of EEE

2. Firing angle control
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

3. • The operation of Constant CURRENT(CC) and Constant
Extinction Angle(CEA) controllers is closely linked with method
of generation of gate pulses for the values in a converter.
• It gives Vc control signal for required firing angle α for valves.
• Firing angle generator generates the firing angle α with respect to
Vc.
• The selector picks the smaller value of α determined by CC and
CEA controllers.
• Electrically triggered thyristors (ETT) or Light triggered
thyristors(LTT) switches are used for valves.
Two basic firing angle control schemes,
1. individual phase control.(IPC)
2. Equidistant phase control.(EPC)
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

4. Individual phase control.(IPC)
• The main feature of this scheme is that the firing pulse generation
for each phase is independent of each other and the firing pulses
are rigidly synchronized with the commutation voltages.
• It can be achieved by two ways
(i) Constant α control
(ii) Inverse cosine Control
Constant α control
• In this scheme six timing commutation voltages are derived from
the converter AC bus via voltage transformers.
• the six gate pulses are generated at nominally identical delay
times subsequent to the respective voltage zero crossings.
• The delay are produced by independent delay circuits and
controlled by a common control voltage derived from the
current/extinction angle controllers.
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

5. Inverse cosine control
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

6. Equidistant pulse control(EPC)
The firing angle are generated in steady state at equal intervals
through a ring counter.
• Pulse Frequency Control
• Pulse period control
• Pulse Phase control
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

7. Higher level controller
• The power in a DC link can also be controlled in response to the
quantities derived from the AC system in order to improve the
security of the overall system.
• This is achieved by an additional power order derived from an
emergency power controller or auxiliary controller.
• Frequency and Power/Frequency control
The frequency control can be used in the case of
(i) Isolated load
(ii) Isolated generation
• The objective is to improve the damping and reduce the wear of the
generator and governor system.
• The nuclear power stations are very sensitive to output power and
frequency fluctuations.
• The frequency variations both during steady state and transient
conditions can be minimized.
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

8. Stabilization of AC Ties
• When a DC tie is connected to a system with weak AC ties to
neighboring systems, DC link power can be varied quickly and
automatically to balance the load flows and maintain stability if
one of the AC tie trips.
• A DC tie used in parallel with an AC tie can be employed to damp
the low frequency inter area oscillations in the AC tie.
Emergency control
• In general, with suitable control, a disturbance originating in either
system can be share in a predetermined manner and the oscillations
occurring in the two systems can be damped simultaneously.
• Substantial damping can be achieved with a very small amount of
DC power modulation.
• If a large degree of modulation is required with the DC line already
operating close to its fully capacity, it is found that significant
results can be achieved simply by reduction of DC power at the
appropriate instants.
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

9. Reactive power control
• In weak AC systems it is used to reduce the dynamic over voltages.
• In inverters the fast reactive power control can help in allowing the
injection of increased power at time of need to improve the
stability of the receiving end AC system.
Sub synchronous damping control
• A radial HVDC link connected to a thermal generating station can
contribute to the negative damping of the torsional oscillations at
synchronous frequency due to interconnections with the current
controller.
• The power modulation controller is designed to damp low
frequency rotor oscillations, can aggravate the problem.
• However, a suitably designed sub synchronous damping
controller(SSDC) with control signal derived from the rotor
velocity can help to damp torsional frequency oscillations.
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

10. Control of VSC based HVDC link
A VSC used in a HVDC link injects a controllable voltage at the AC
terminals given by,
𝐸 = 𝑚𝐸 𝑎0 < 𝜃 + 𝛼
Where
𝐸 𝑎0 = 𝑘𝑉𝑑𝑐
𝑘 =
√6
𝜋
They are two level converters are
1. m ( normalized modulation index)
2. α (phase angle) are control variables used to control power and
reactive power.
𝜃 → 𝑎𝑛𝑔𝑙𝑒 𝑜𝑓 𝑡ℎ𝑒 𝐴𝐶 𝑏𝑢𝑠 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑒𝑟, 𝑚 < 1
𝛼 → +𝑣𝑒 𝑜𝑟 −𝑣𝑒 𝑑𝑒𝑝𝑒𝑛𝑑𝑖𝑛𝑔 𝑜𝑛 𝑤ℎ𝑒𝑡ℎ𝑒𝑟 𝑡ℎ𝑒 𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑒𝑟
𝑖𝑠 𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔 𝑎𝑠 𝑎𝑛 𝑖𝑛𝑣𝑒𝑟𝑡𝑒𝑟 𝑜𝑟 𝑟𝑒𝑐𝑡𝑖𝑓𝑖𝑒𝑟.
Kongunadunadu College of Engineering and Technology Department of EEE
Firing Angle Control

11. 𝑖 𝑝 𝑎𝑛𝑑 𝑖 𝑟 → 𝑎𝑐𝑡𝑖𝑣𝑒 𝑎𝑛𝑑 𝑟𝑒𝑎𝑐𝑡𝑖𝑣𝑒 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠 𝑜𝑓 𝑡ℎ𝑒 𝐴𝐶 𝑐𝑢𝑟𝑟𝑒𝑛𝑡
𝑑𝑟𝑎𝑤𝑛 𝑏𝑦 𝑡ℎ𝑒 Converter.
Where,
𝑖 𝑝 =
𝑃
𝑉𝑠
, 𝑖 𝑟 =
𝑄
𝑉𝑠
𝑖 𝑝
∗ = 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑣𝑎𝑙𝑢𝑒𝑠 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑎𝑐𝑡𝑖𝑣𝑒 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑠 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑒𝑖𝑡ℎ𝑒𝑟 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒
𝑝𝑜𝑤𝑒𝑟 𝑐𝑜𝑛𝑡𝑟𝑜𝑙𝑙𝑒𝑟 𝑜𝑟 𝐷𝐶 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑐𝑜𝑛𝑡𝑟𝑜𝑙𝑙𝑒𝑟
𝑖 𝑟
∗ = 𝑟𝑒𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝑣𝑎𝑙𝑢𝑒𝑠 𝑓𝑜𝑟 𝑡ℎ𝑒 𝑟𝑒𝑎𝑐𝑡𝑖𝑣𝑒 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑠 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒
𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑒𝑑 𝑟𝑒𝑎𝑐𝑡𝑖𝑣𝑒 𝑝𝑜𝑤𝑒𝑟 𝑜𝑟 𝐴𝐶 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑐𝑜𝑛𝑡𝑟𝑜𝑙𝑙𝑒𝑟
𝑒 𝑝, 𝑒 𝑟 → 𝑐𝑜𝑛𝑣𝑒𝑟𝑡𝑒𝑟 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡𝑠
• The reactive power injected by the converter is a function of V, the
bus voltage magnitude.
• Line commutated thyristors based converter can only draw reactive
power depending on the power flow through the converter.
Kongunadunadu College of Engineering and Technology Department of EEE

12. Reference:
• Padiyar, K. R., “HVDC power transmission system”, New Age
International (P) Ltd., New Delhi, Second Edition, 2010.
Firing Angle Control
Kongunadunadu College of Engineering and Technology Department of EEE