Study Of Cascaded H-Bridge APF Based On DSP+FPGA

With the development of modern industrial technology,a variety of power electronic devices have been widely used.Harmonic pollution which is caused by nonlinear load makes serious impact on the power quality of the grid system.As a real-time compensation of harmonic and reactive devices,the application of active power filter(APF)plays an important role in the improvement of power quality.But in high voltage and high power occasion,Due to the contradiction between the capacity of power devices and the switching frequency,the application of APF is restricted.Combining H-bridge Cascaded multi-level converter with Carrier phase shift SPWM technology,It can be achieved at a lower switching frequency to get a higher equivalent switching frequency,and makes the low voltage capability of the power device applicate in high-voltage occasion.In this paper,the Cascade H-bridge APF based on DSP+FPGA has been studied.First of all,this paper introduces the basic principles of the APF,the Common harmonic current detection method and the Multi-level inverter topology.Then it analyzes the basic principles of the CPS-SPWM technology and the transmission bandwidth,At the same time,analysis and contrasts the bipolar and unipolar CPS-SPWM modulation output waveform by mathematical methods.Through analyzes the operating mode of cascaded H-bridge APF,unipolar CPS-SPWM technology applies to cascaded H-bridge topology.Secondly,After analyzing the mechanism of DC voltage imbalance,a three-layer control strategy of global voltage regulation,phase-to-phase voltage equalization and voltage equalization in the phase is proposed to achieve voltage balance.At the same time,in order to make the APF can get good compensation characteristics,the APF output filter inductor and DC side discrete capacitors were designed in this paper.Then based on the ip-iq algorithm of instantaneous reactive power theory and the direct current control of triangular carrier,the simulation model of cascaded H-bridge APF system is built in Simulink environment to verify the control strategy and parameter design.Finally,this paper analyzes and introduces the design of cascaded H-bridge APF control system,including Peripheral hardware circuit design and software flow design of control system.The hardware structure and implementation method of the DSP + FPGA Multiple PWM pulse generator are emphatically analyzed.