Research On Control Of APF And TSC Harmonic And Reactive Power Synthesis Compensation System

How to provide consumers with safe, reliable, high-quality economic power is the main problem facing the power system. Reactive power compensation and harmonic suppression is one of the key technologies to achieve this goal. Active power filter (APF) is a new type device for reactive power and harmonic dynamical compensation. A united system of APF and the conventional resistance type compensator is the focus in the field of reactive power compensation and harmonic suppression, and research on stability, steady-state and dynamic performance of the united system is important for improving the applicatons of reactive power compensation and harmonic suppression technology in power system.This paper mainly researched on the control method of APF which is the core of the united system, to make system have good stability and robustness, and improve the system steady-state precision and dynamic performance. Specifically include the following:Reactive power and harmonic can be compensated by parallel compensation equipments simultaneously. This paper presented a united system of thyristor switched capacitor (TSC) and APF. TSC is consisted of multi-groups binary-coded capacitors, which is mainly used for large capacity reactive power compensation step by step. APF compensates small capacity reactive power continuously, and filters harmonics generated by the nonlinear load. APF made the united system have a better steady-state precision and a faster dynamic response then the conventional SVC, and the inductance of the TSC can also been reduced when the THD of the grid voltage is low. A closed-loop control strategy and an open-loop control strategy were proposed for the united system, and the system stability and compensation performance was analyzed. Finally the APF capability and main parameters were calculated.To ensure the integrated system has good compensation characteristics, the control methods of TSC and APF were studied. A novel method of TSC switching control was presented to ensure TSC switched fast, while avoiding switching oscillation when reactive power of load changes rapidly. APF switching frequency is limited by the sampling frequency of the DSP control system, when the time comparing PWM was executed using DSP. In theory, the maximum switching frequency is only half the sampling frequency. Time compare control can not be achieved in real-time compare as analog hysteresis, which led to lower switching frequency and large tracking error. Therefore a dual-sampling time compare control was presented, which improving the switching frequency effectively, and reducing the tracking error. Delay of APF system caused amplitude and phase errors between compensating current and reference current. An adaptive predictive control was presented to solve this issue. The coefficient of the adaptive predictive algorithm was adjusted according to the grid current error, and made the grid current error minimum.In order to obtain a better steady-state performance of APF, a novel control approach was presented for a LCL-filter-based active power filter, since the stability and steady-state error of the APF were influenced by grid parameter varying. The control approach consists of a novel generalized integrator and a novel active damping. The gain of traditional generalized integrator was attenuated at harmonic frequency by the grid frequency excursion, which made the steady-state error increase. This problem is solved by the novel generalized integrator based on parameter adjusted online. Otherwise a passive or active damping was needed to restrain the resonance of LCL filter, but the possible wide range of grid impedance values weakened the effectiveness of the damping, even challenged the stability of the LCL-filter-based APF system. Therefore the novel active damping based on sliding mode control was designed. The simulation and experiment results demonstrate that the control approach makes the APF system have a good robustness.Hybrid active power filter is suitable for medium-high voltage and large-capacity applications to compensate the non-linear load where reactive power fluctuats little. In this paper a novel sliding mode control approach was presented for a medium-high voltage hybrid shunt active power filter, since the harmonics suppression effect of the filter was restricted by the switching frequency of power semiconductor devices, and electromagnetic interference (EMI) caused by the filter was also related with the switching frequency nearly. The proposed control approach combines state variables tracking with pulse width modulation, in which source currents and the neutral point voltage of APF DC bus were decoupled and tracked simultaneously. With similar tracking accuracy, the switching frequency can be optimized and limited to a certain lower frequency band via the neutral point voltage control. The simulation and experiment results demonstrate that the proposed control strategy allows hybrid APF to eliminate harmonic currents caused by source voltage distorting and nonlinear loads effectively.