Research On Theories And Technologies Of Combined Power Quality Controlling Device

Reactive power compensation and harmonic currents elimination are the two important problems to the power distribution system, based on analysis of the Hybrid Active Power Filter (HAPF) for reactive power compensation and harmonic currents suppression, a comprehensive power quality controller for power distribution system combined with Static Var Compensator (SVC) and HAPF is proposed in this paper, named Shunt Power Quality Combined Compensator (SPQCC). The system mentioned has merits of SVC and HAPF, which overcomes the shortcomings of the SVC or APF operation respectively, it not only can improve the voltage fluctuation and flicker, but also can eliminate the negative currents arising from unbalanced load and the harmonic currents generated by nonlinear load and SVC, so can improve the power quality of the power system. The topology structure and model of SPQCC, the scheme of voltage control, the technology of unbalance compensation, the detection of harmonics and reactive current, the stability of the system mentioned in the paper and the technology of current tracing control are described in detail.Firstly, two types of topology structure of SPQCC are proposed based on analysis of the structure of HAPF, their operation principle are introduced, and the general model of the SPQCC are constructed and analyzed in this paper. Then take an example of SPQCC, which composed of Thyristor Controlled Reactors (TCR) and Resonant Impedance Type Hybrid Active Filter (RITHAF), also the model of the system is analyzed in detail and the complex control scheme is proposed. In which the passive filters of the RITHAF is divided to two parts, one is the fixed capacitors composed of 2 order harmonics filter and the high order filter, the other is composed of 3, 5 order filter series thyristor respectively. The reactive power of SPQCC can be controlled from inductive to capacitive smoothly, but also the shortcomings of the supply of the fixed capacitive reactive power of the HAPF and the harmonic currents coming from the TCR are avoided, and the VA of the APF is reduced greatly. Simulation results show that the SPQCC not only compensate the voltage fluctuation and the harmonic currents of the power system, but also can compensate the reactive components and harmonics of the load, and has a wide use in the power distribution system.Secondly, Considering of easy realization but dependence on the accurate mathematical model and difficult to fit to the variation of the load in traditional PI controller used in the SVC, the optimal recursive integral method was mentioned when maintain the voltage stability of the power system, and the recursive integral PI method was used in SVC. The recursive integral PI control method based on improved simplex method (SPX) optimization, the algorithm using ITAE of optimized object function is presented to adjust and optimize the Kp,Ki, parameters of PI controller real-time, which makes transient response procedure of SVC optimum, so it is able to track voltage set values of SVC fast and ensure the performance of the SPQCC. According to unbalanced load compensation, in order to overcome the shortcomings of the compensation susceptance calculation affected by the distortion of the voltage and current of the power system, a new type of compensation susceptance calculation of SVC based on virtual symmetrical three phase synchronous reference frame transform is presented. A single-phase voltage is derived and used to form the virtual symmetrical three-phase system, so the compensation susceptance is calculated accurately. The method of susceptance calculation presented needs simple calculation, the SVC based on the method proposed without Phase Locked Loop (PLL) of hardware and can compensate reactive power accurately.In consideration of the accuracy of the harmonic currents detection and no fundamental component included, an improved adaptive harmonic detection method based on adaptive noise cancelling technology was presented in the paper based on the analysis of the other harmonic currents detection method, its'stability is proved by averaging theorem of dynamical system theory. The proposed method conquers the limitation of the average adaptive harmonic detection methods and is able to detect harmonic as well as extract distortion of currents. The transient speed of the novel adaptive is improved through chose of learning rate. Due to its excellent tracking performance, the improved adaptive one is good at time-varying harmonic's detection. The simulation results show that the proposed approach is faster than the previous average one for synchronous detection of harmonic and extraction of fundamental component, and satisfy the power system's needs for harmonic current or harmonic voltage detection.At last, according to the phase delay of output current of the SPQCC, the reason causing the phase delay is analyzed in detail, the phase delay mentioned above is called as generalized delay here, which is variable with different frequency. At the same time, the equation of the generalized impedance and the stability of necessary and sufficient condition of the system proposed are given. In order to eliminate the effects of generalized delay, a novel -aimed Smith predictor is established based on the fact that there is a delay between output current and load and thyristor controlled reactor (TCR) harmonic current, which are negative in polarity. Applying generalized integrators with excellent performances of frequency division, a generalized integral control based on predictive compensation at different frequency for generalized delay is proposed. The feasibility and effectiveness of this control method is verified by PSIM simulation, also no error performance of stability is analyzed in the paper.Under the guidance of the above theories and technologies, a +120kvar—100kvar SPQCC prototype is developed in the lab. A large number of experiments are implemented on the experimental prototype. The experimental results match with the simulation results. The correction and effective of the theories and technologies are verified by the experimental results.