Research On The Control Method Of Active Power Filter

With the large increase of rectifiers, switching power supplies in the distribution network, harmonic pollution is worsening and power quality has become a hot topic. Active power filters (APF) has drawn much attention since the 1970s, because they can suppress the harmonic current and compensate reactive power in real time. In this thesis, a widely used three-phase three-wire shunt APF is analyzed. The main works are the following:First, the mathematical model of APF under ABC coordinates is derived, which is a nonlinear and strong coupling system. The design of its controller is complex. To simplify the control system, the mathematical models under αβ coordinates and dq coordinates are obtained by coordinate transformation.Second, the principle and characteristic of common harmonic current detection and current control method are introduced and pointed out. The issues of inaccurate in the harmonic detection and current control which are often used in conventional control strategies are solved. A new control scheme based on VPI is proposed, which has the feature of less measurements, simple control structure, no harmonic detection and selective harmonic compensation. Theoretical analysis shows that it has an excellent compensation performance.Third, hardware and software design of the experimental prototype. The main circuit parameters and the hardware and software design are described and selected in detail, the flow chart of main program and interrupt program are also showed.Finally, a simulation model and an experimental prototype are built. A large number of simulation results based on the proposed control strategy show that it has better compensation effect. Compensation results, which got by using the proposed control strategy, show it can achieve selective harmonic compensation and have good dynamic responses and steady-state performance, compared hysteresis control and triangle comparison control.