Analysis Of Main Circuit Topology And Research On Control Of H-Bridge Cascade SSSC

Static Synchronous Series Compensato(rSSSC) plays an important role in improving the system stability and increasing the available transfer capability for the power system. This dissertation, combining with the National Natural and Science Foundation of China (Study on modulation principle of SSSC based on nonorthogonal coordinates and research on the balance of DC voltage), deeply studied on the main circuit, mathematical models, modulation strategies and control methods and so on.The main topology research is the fundamental for analyzing the characteristic of H-bridge cascade SSSC. This dissertation compared some different coupled circuits and modes of connection of inverter, and concluded that H-bridge cascade topology is applicable for the SSSC . Also the concept of Impedance Compensation Domain, and quasi-steady mathematical model of output voltage were given firstly. Based on these work, a method for selecting the DC capacitance was deduced. Also the large-step dynamic phasor model of H-bridge cascade SSSC was explained.Modulation strategies is elementary for achieving the SSSC control function. Based on the Non-orthogonal KL coordinator multi-level SVPWM, an improved line voltage modulation method which is more concise and detailed was given. And an improved single phase modulation algorithm for symmetrical system and a generalized modulation method for three phase unsymmetrical system were proposed. Also the concept of PWM static modulation error (PWMSME) was first given. The calculation of PWMSME was deduced quantitively. And the harmonic regularities of distribution of H-bridge cascade SSSC based on carrier phase-shifting SPWM was analyzed detailedly.The balance and stability of DC capacitor voltage are decisive for the normal operation of H-bridge cascaded SSSC. In this paper ,the mechanisms of imbalance and instability of DC voltages are qualitatively analyzed from the aspect of energy distribution.and getting the conclusions that the maincircuit parameters , DC voltage value and modulation strategy all can affect DC voltages balance; on the other hand, the accumulation of energy imbalance and the error of detection can result in DC voltages instability. According to the idea of hierarchy control, the"Three Lines of Defence"control strategy of DC voltages balance and stability was first proposed, which consists of modulation strategy called CMDCB-SVPWM and stability control strategy.Also the control strategies of constant resistance and constant power with the output filters and without filters were designed under the normal operation condition and abnormal operation condition. A segment and variable structure Bang-bang controller of SSSC was given for the system transient stability. Simulation shows that SSSC has an advantage on the effects of power oscillation damping. And the speed difference and the power of line as the input signal were simulated. At last the self-excitation startup charge energy strategy of H-bridge Cascade SSSC were given also.The small step RTDS simulation model of H-bridge cascade SSSC was first set up in the standard four machines and two area systems. Some key technical problems of small step simulation were pointed out. Also the prototype of SSSC using the universal converter was built, and the controller of SSSC was realized using the DSP and FPGA. The experimental results shown the correctness of the control methods and modulation strategies.