Equipment Development Of Modular Active Power Filter

In recent years, as the increasing number of non-linear loads connected to grid, power system harmonics pollution is worsening, harmonic flooding affecting the safe operation of the grid. With the national energy conservation and emission reduction strategy, the power grid harmonic control has become an important part of green energy. Active power filter (APF) to counteract the load generated by the dynamic harmonic current and reactive current through injecting the compensation current into the grid, widely used in various industrial and civil applications. Modular equipment gradually replacing the traditional cabinet APF with the advantages of easy capacity expansion, accounting for small, large power density and good versatility, furthermore, it greatly reduce the cost and ease of maintenance. In this paper, as the background of 380V/100A modular three-phase three-wire APF device research, the design of sampling filter circuit parameters, the control method of APF inner current loop, the problem of design of device hardware circuit and control system is studied.Firstly, the equivalent mathematical model of the APF current inner loop in the continuous domain is derived which in consideration of APF output current feedback loop. However, in the design of filter circuit in the feedback loop, the selection of the resistance and capacitance parameters directly determines the cut-off frequency of the sampling channel. When the cut-off frequency is not chosen, the resonant peak value will be introduced, which will affect the performance of APF and the stability of the device. In this paper, it detailed analysis the order selection of the feedback loop filter circuit and R, C parameter selection on APF inner current loop through BODE diagram, which made the parameter design method of RC filter circuit.Secondly, it describes the principle of traditional deadbeat control method, taking into account the inevitable existence of the control delay, the article analyzes the discrete deadbeat control model with time delay in z-domain, and discussed the impact of system robustness of inductance deviation. Furthermore, the delay controller will largely affect the performance of APF compensating device. In this regard, a predictive current control method is presented, and make a two-sample forecast of grid voltage and inverter output current, the influence of delay and the change of inductance on the system is reduced, and the robustness of the system is enhanced. Moreover, according to the transfer function of current loop in the z domain, system stability is analyzed, and given the range of control parameters selection. For this control method, set up the APF simulation prototype, the simulation results demonstrate the effectiveness and feasibility of the control strategy.Thirdly, the article completes the design of main circuit parameters, three-phase output filter inductor, and cooling systems of the modular APF. Moreover, the hardware design and software programming of the control system are described in detail, and a main controller based on DSP+FPGA dual core architecture is constructed. As well as, the design of hardware protection circuit, LCD display controlling circuit, the grid voltage zero crossing circuit are described. Last but not least, the 380V/100A modular active filter device is developed, and the experimental results verify the effectiveness and feasibility of the research.