Firing angle control

The concept of Firing angle controls are explained in this presentation

1. Firing angle control 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 V c control signal for required firing angle α for valves. Firing angle generator generates the firing angle α with respect to V c . 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, individual phase control.(IPC) 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 Constant α control 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 Isolated load 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, Where 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 .   Kongunadunadu College of Engineering and Technology Department of EEE Firing Angle Control

11. Converter . Where, 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