Research On Harmonic Detection And Control Strategy Of Active Power Filter Based On DSP

With the hyper growth of modern power electronics technology, electronics and electric devices are widely used in social production and daily life bringing great convenience and profits. But at the same time, a great deal of harmonics and reactive power produced by these non-linear devices are injected into power system, which seriously affects the quality of power supply and the reliable operation of power system. The traditional method of reactive compensation and harmonic suppression has not been able to satisfy the requirements of the modern power system. As a new kind of compensating device, APF (active power filter) is regarded as the most potential harmonic and reactive compensation device and becoming the hot spots of researching, becauae of its fast track and adaptive capacity to the changes of load and electricity grid parameters, and good compensation effect.An intensive study on the operating principle and the design of control system of APF is made in this paper, and the two key technologies of APF system are analyzed emphatically that is harmonic detection method and control strategy. Under the direction of the MATLAB simulation, the software and hardware related to the system are designed which also build the experimental platform, and the main contents of this study are as follows:The operating principle and topology of three-phase shunt active power filter are introduced, and the mathematical model of APF with voltage source topology is established. Then based on this, the main circuit parameters of the system are designed including the main circuit capacity, switching devices, inductance, capacitance and so on.The harmonic detection method and control strategy of APF are described. The ip-iq detection method based on instantaneous reactive power theory is determined as the harmonic detection method, and the triangular comparing control method is determined as the control strategy by comparing the advantages and disadvantages of various harmonic detection methods and control strategies.Then, a model of the whole APF system is built in MATLAB simulation environment, and simulated respectively on the condition of three phase load and three phase unbalanced load. The simulation results show that, in both of the above cases, the APF system can fulfill the filter function, which verifies the correctness and feasibility of the harmonic detection method and control strategy selected.Under the guidance of the system simulation, a hardware experimental platform with the intelligent power module (IPM) and the DSP TMS320F2812 as the core is built including the sampling circuit, control circuit, main circuit, drive circuit and protection circuit. Then on the basis of the hardware, the software is designed in development environment CCS2.2. According to the principle of modular programming, the system initialization program, main program, and each module subroutines (including capture interrupt subroutine, Timer T1 interrupt subroutine, A/D sampling procedure, harmonic calculation subroutine, PI program, PWM signal generation subroutine and protection program) are designed and programmed with C language and ultimately the APF system is debugged based on the platform of hardware and software. The experimental results show that, the system can quickly and accurately sample the grid current, voltage and the load current, complete the calculation of harmonic current and the generation of PWM control signal, and output the compensation current correctly, which proves the rationality and correctness of the hardware and software of APF system.