高压直流输电

TNA test of SSSC model
Control of SSSC
SSSC is often used to regulate power flow through line in high voltage system. Three-phase bridge could be adopted if three-phase voltage are symmetrical. Three single phase bridge can control three phase voltage separately even if threephase voltage are unsymmetrical. It is more flexible, but its cost is higher. The advantages of cascaded multilevel inverter are low switch frequency and high transition efficiency.
PWM control based on carrier phase shift
Voltages of A phase with PWM control based on carrier phase shift
Simulation and Analysis of SSSC
The SSSC injects a voltage of variable magnitude in quadrature with the line current, thereby emulating an inductive or capacitive reactance. This emulated variable reactance in series with the line can then influence the transmitted electric power. The SSSC is used to damp power oscillation on a power grid following a three-phase fault.
SSSC cascade H-bridge diagram
Control of SSSC
From convert 1 to convert 5,output of voltage reduces one by one with the reduce in firing angle. In facts, H-bridge will be controlled in turn to avoid the unbalance of voltage of every convert.
Model of SSSC
From fig4, If Uq>0, Power-Load Angle Characteristic curve rises compared with that without SSSC. If Uq<0, Power-Load Angle Characteristic curve falls compared with that without SSSC.
Simulation and Analysis of SSSC
SSSC Dynamic Response: Depending on the injected voltage, the power flow on line varies from 575 to 750 MW. In a real system the reference signal Vqref would typically be changed much more gradually in order to avoid the oscillation we see on the transmitted power (P_B2 signal).
From the Vector Graphics of pic3,the equation below could be founded.
Model of SSSC
When the Uq=0 (without SSSC),the largest transmission power could only be up to
Power-Load Angle Characteristic curve of Double-source Systems

Model of SSSC
Obviously, SSSC not only can change the ability of power transmission, but also can control the direction of power flow. At the same time, compared with TCSC, SSSC can change power flow more when the power-load angle is small.
Facts-SSSC
PPT
2016-6-7
SSSC



Introduction of SSSC Model of SSSC Control of SSSC Simulation and Analysis of SSSC HSSSC
Introduction of SSSC
The Static Synchronous Series Compensator (SSSC) is one of the most recent FACTS devices for power transmission line series compensation. It is implemented by a full controlled switch-based voltage source inverter (VSC) that can provide a controllable compensating voltage over an identical capacitive and inductive range, independent of the magnitude of the line current, which is different from Thyrisitor controlled Series Compensator(TCSC).
SSSC Model
Introduction of SSSC
Unlike other series compensators, an ideal SSSC is essentially a pure sinusoidal ac voltage source at the power system fundamental frequency. Its output impedance at other frequencies is ideally zero. SSSC does not resonate with the inductive line impedance to excite sub-synchronous system oscillations. SSSC can optimize the power flow of power grid swiftly and improve stability of power system considerably through controlling transmission line impedance. Although no stand-alone SSSC has been in service, it is the series converter of the unified power flow controller (UPFC) in the American Electric Power(AEP) system.
Modify the "Maximum rate of change for Vqref (pu/s)" parameter from 3 to 0.05.
The power oscillation on the active power is very small.
Initially Vqref is set to 0 pu; at t=2 s, Vqref is set to -0.08 pu (SSSC inductive); at t=6 s, Vqref is set to 0.08 pu (SSSC capacitive)
Model of SSSC
In the DC side of SSSC, the capacitor groups are used to support voltage. So active power won’t flow between SSSC and system except the self loss of SSSC. The angle between compensator voltage and current of line is 90 degrees. SSSC could be considered as a controlled as reactance. When K is negative, it is equal to capacitive. When K is positive, it is equal to inductive.
Voltages of invert bridges on A phase(1st period) Voltages of invert bridges on A phase(2nd period)
Control of SSSC
The other method is triangular carrier phase shift control. The frequency of triangular carrier is 250 Hz. The modeling wave is sinusoidal wave whose frequency is 50 Hz. The total switch frequency is 1250Hz,which could makes harmonic wave greatly reduced.