A Novel Control Technology Research For The Series Hybrid Active Power Filter

This dissertation is mainly in the field of the power quality control. The research of the power quality improvement is of the great significance and of the most important in the electrical engineering. With the increment of the electric power requirement, the electric power network composition bearings in the increasingly complex. The proliferation of electronic loads in commercial and industrial installations has created a serious concern in the field of electric power engineering due to harmonic distortion produced in the mains. The compensation for harmonic and reactive currents becomes increasingly important both for utilities and industries to feed their sensitive equipment with a quality power. Active power filters are presently the most versatile and effective equipments to confront the challenge of reducing disturbances in power system. They are applicable of compensating current-based distortions such as current harmonics, reactive and neutral current. They are also used for voltage-based distortions such as shunt, series, and hybrid and unified power quality conditioners that have been proposed by many researchers. The dilemma between the electricity requirement and the control energy level of the power electronic device encourages the application of the hybrid active power filters. The purpose of the research in this dissertation is the circuit topology, filter characteristic, the control system and the problem application of the hybrid series active power filter, and this will lay a foundation for promoting its practical use as soon as possible.Firstly, this dissertation summarizes and reveals the presented basic active power filters based on the preceding observation and circuitry duality. These two types of harmonic suppressing devices have completed distinctive based on the dual properties of the current source nonlinear loads and the voltage source nonlinear loads. Among them some novel filter configurations are also proposed. A comprehensive comparison of all configurations is made in terms of required ratings, costs, performance and control.Quick and Accurate harmonic detection and its digital realization are the key technology for the active power filter. A unified positive and negative sequence math model of the synchronous frame harmonic detection method is constructed in this dissertation. Its harmonic detection characteristic is analyzed and the parameter optimization of the low power filter is given. The contradiction between the sample settling time delay and the coefficient quantization error, when the synchronous frame harmonic detection method is realized in DSP, is discussed in detail. A multi-cascade exponential mean digital low pass filter based on high sampling-rate is proposed to solve the problem. It can attain the small coefficient quantization error, high precision with the high rate sampling frequency, and can provide the optimize parameter design of the synchronous frame harmonic detection method.The filter performance of the series hybrid active power filter is confine to its control stability. In order to coordinate their problem, a state-space averaging model of the series hybrid active power filter is constructed to analyze its stability mechanism and parameters design based on the unified positive and negative sequence math model of the synchronous frame harmonic detection method, the effect of the power system, the main circuit of the hybrid active power filter and its control circuit. Taking into account the effect of the time delay to the system stability, a phase-lead compensation control strategy is proposed to improve the stability and filter performance of the series hybrid active power filter. A novel damping control strategy of the output filter is proposed, which solves the loss of the damping resistor and favorably applies in the high voltage and high power grids.The circuit topology and control strategy of the series-in series hybrid active power filter is also study in this dissertation. The improved-type series-in series hybrid active power filter is proposed. They have the same excellent filter performance and are better than traditional series hybrid active power filter. Several control strategies either harmonic detection method or no harmonic detection methods are presented for the series-in series hybrid active power filter and its improved circuit topology.Finally, the current-source nonlinear load is normally composed of the thyristor or diode rectifier, but the process of the commutation will cause the line current rush for the series hybrid active filter. In order to solve this problem, a method of the rush current inductor that a large inductor is series in between passive filters and rectifier, and a series-in series hybrid active power filter are proposed to suppress the line rush current. For the rush current inductor, a larger inductor is added to increase the impedance under the condition of the short commutation, while the shortcoming of the method is that it increases the size and cost of the whole system. The series-in series hybrid active filter which a fundamental frequency series resonance circuit is series in the AC side of the inverter can suppress the rush line current, improve the filtering performance and reduce the rating of the inverter in spite of the increment of the size and cost of the passive components. For the important characteristic of the source system impedance applied in active power filter, a novel method of on-line measurement for the source system impedance is proposed, which utilized the dynamic process of spontaneous short-circuit of the rectifier current transition.