Power Quality Detection And Control Method Research In Distribution System Of Enterprise

Power industry is a basic industry relative to the people’s livelihood. With the development of national economy and the improvement of people’s living standards, the people’s demand for electric power have rapid growth, and there are more and more requests for the power quality of distribution network.In this paper the real-time detection method and dynamic compensation method as well as synthesis compensation technique are proposed. The characteristics, innovation and beneficial conclusion are mainly embodied in the following aspects:1. In this chapter the adaptive noise cancellation principle and conventional LMS (Least Mean Square) algorithm are introduced firstly. An improved LMS algorithm based on normalized LMS is further proposed, and it owns a better convergence speed comparing with conventional LMS algorithm and good stability. Improved LMS algorithm is applied to adjust the weights of adaptive filters, and this dissertation proposes two adaptive detection algorithms of harmonic and reactive current with invariable step-length. Two proposed detection methods are tested and compared in single-phase system simulation and harmonic compensation control simulation of three-phase filter system. Simulation results show that the filter system with the second detection algorithm possesses a good dynamic response performance, but steady precision of using it still needs to be improved. An adaptive detection method of harmonic and reactive current based on fuzzy algorithm optimization is further proposed. The step-length of algorithm is adjusted through establishing the corresponding fuzzy rules and using fuzzy inference, which result in the improvement of compensation precision of filter. Finally the adaptive detection method of harmonic and reactive current based on fuzzy optimization is applied in simulation of three-phase filter system, and the simulation results have shown that the proposed method is correct and effective.2. In this chapter IHAPF (Hybrid Active Power Filter with Injection Circuit) is regarded as research object. A novel current tracking control method, which is based on n compensation smith predictor and neural network with a modified weight algorithm, is proposed. The use of π compensation smith predictor, which can transfer the system delay to external of control closed-loop from inside of closed-loop, has some advantages such as eliminating system delay effectively, as well as improving system stability and response speed. The neural network, which is based on PSO-BP (Particle Swarm Optimization and BP Neural Network) algorithm, is used for optimizing PI controller parameters and then improving control system precision. PSO-BP algorithm can not only overcome the problems such as slow convergence speed and sinking into the local extremum easily, but also has higher control precision and better learning ability of BP Neural Network. Meanwhile, after obtaining the relation of π compensation smith predictor parameters and PI controller parameters by ITAE (Integrated Time Absolute Error) criterion, parameter estimation of two controllers can be got, which avoids the case of identifying two controller parameters separately, and reduces the sensitive dependence on the grid parameters of two controllers. Simulation and experimental results have verified the effectiveness of proposed method.3. In this chapter, it makes an intensive study for the reactive current dynamic compensation method of SVC (Static Var Compensator). A compound control method composed of the voltage stability control and the compensation method of imbalance load in SVC system is proposed. The proposed method is easily carried out and the calculation with the method is small, so it is worth using for reference. In the paper, it introduces the topology structure of SVC, and designs the whole controller of SVC, then introduces the voltage control method and compensation method of the imbalance load respectively. In the voltage control method, an improved Ziegler-Nichols method is applied to optimize the parameters of controller and get a good control performance, and the method is easy to be realized and its calculation is small. In the compensation control of three-phase imbalance load, a calculation method of electrical susceptance based on synchronization reference rotating coordinate transformation of structuring symmetrical three-phase system is proposed. Proposed computing method has the advantage of small computation. The SVC system based on the proposed computing method can acquire synchronous rotation angle of not using phaselocked loop, and it can compensate reactive power of load quickly and accurately. Simulation results have verified the feasibility and effectiveness of proposed method.4. In this chapter a control technology of IHPQC (Injection Hybrid Power Quality Compensator) is studied, and control method composed of SVC mode control and IHAPF current control is proposed. In the paper, SVC mode control method consists of proposed reactive power control method in the fourth chapter and the grid power factor correction method proposed in this chapter. Stabilizing voltage of distribution system and compensating negative sequence components of load current as well as improving power factor can be realized by SVC mode control method, and it is easy to be realized and has reference value for large-scale SVC engineering application. IHAPF current control mainly consists of detection method of harmonic and reactive current and tracking compensation control. The detection method of detecting selected harmonic and compensating phase can realize the accurate detection of the harmonic component in the power grid, and can reduce the influence of detection delay. Proposed detection method can be used not only in three-phase symmetric system, but also for three-phase asymmetric system. Current tracking control method based on feedback-feedforward control is proposed to realize the dynamic compensation of harmonic in the power grid. An improved iterative learning control algorithm is applied in current feedback control, and proposed iterative algorithm avoids some defects of conventional iterative algorithm. In order to improve the control performance for tracking harmonic, the simplex method is used to optimize parameters of iterative controller. A feedforward link based on derivative learning law of harmonic current error as the control input is presented to the iterative feedback controller, which can improve the response performance of tracking harmonic. Simulation and experimental results have confirmed that IHPQC system with the proposed control method can effectively realize dynamic supression for load harmonic current and TCR harmonic, and dynamic compensation for reactive power of power grid.