The Detection And Active Mitigation Methods For Power System Harmonics

The development of power electronics brings convenience to energy conversion and utilization on one hand and also causes harmonics and reactive power problems on the other hand. So the study on active power filter for compensating harmonics and reactive power becomes an important issue in the fields of power electronics. The initial investment of active power filter is very high, which limits the development and application of active power filter. The hybrid active power filter, which combines active power filter and passive power filter, can availably reduce the capacity of active power filter and is more appropriate for engineering applications. First the detection method of harmonics and reactive power is studied in this paper. Then the shunt active power filters and hybrid active power filters are detailed in two aspects of control strategies and system parameters design in order to compensate harmonic and reactive power. The investigated contents are shown as follows.The study on a novel detection method of harmonic and reactive current is carried out. The selection of the step-size in conventional adaptive harmonic detection method will make a compromise between convergence speed and steady precision, which restrict its practicability. In order to conquer this disadvantage, an improved variable step-size method is proposed in this paper. This proposed method adopts a sliding integrator to obtain the real tracing error and then uses a fuzzy adjustor with a self-adjustable factor to modify the step- size, so it can obtain both fast convergence speed and high steady precision. For simplifying system design and realization with DSP, the method of non-uniform quantization is adopted during the process of fuzzification and defuzzification in the proposed fuzzy adjustor. The self-adjustable factor can regulate in the whole region and modify the adjusting strategies according to the system state instantaneously, which assures good robustness and excellent dynamic responses. Finally the applications of the proposed adaptive harmonic detection method in three-phase system and some other situations are investigated, which generalizes the application range of the proposed algorithm. The control strategies of active power filter are investigated. In order to realize zero-error-control, the generalized integrator is introduced into the current controller of active power filter. The control strategies of active power filter and its zero-error characteristics are detailed. Additionally, a fuzzy adjustor is designed to improve the robustness of current controller through modifying parameters of the generalized generator, thus both excellent steady performance and fast dynamic response can be obtained.Another control issue for active power filter is the control of DC-link voltage. In order to maintain the DC-link voltage value and realize soft startup, a combined controller, containing conventional PI and fuzzy controllers, is designed to control DC-link voltage. This combined controller absorbs the merits of PI and fuzzy controllers, so it has high accuracy in steady state and strong robustness and excellent self-adaptability in transient state.The optimal design of single-tuned hybrid active power filter is developed. In this paper the capacities and DC-link voltage characteristics of active power filters in hybrid active power filters are derived, and the capacities of several hybrid active power filters are compared in detail. Based on that, a novel optimal design method is proposed for the single-tuned hybrid active power filters in order to minimize the capacity of its active power filters. Additionally, a combined controller is designed for the novel hybrid topology, which contributes to both filtering characteristics and system stability.The multi-objective optimal design of hybrid active power filter set at medium and high voltage bus is developed. A hybrid active power filter is designed for a project. And the design of parameters for this hybrid active power filter is turned into a multi-objective optimal problem with restrictions. The factors of system investment, filtering performance, reactive power compensation, and detuning effects are all considered in this optimal design. And the particle swarm optimization algorithm is first introduced into the optimal design of hybrid active power filter. Through the optimal design method proposed in this paper, the parameters can be designed better so the hybrid active power filter can gain more excellent performance.