Study And Design Of Active Front End Converter Based On DSP

Active front end (AFE) converter possesses the merit of sinusoidal current on grid-side, controllable power factor and constant DC voltage, meanwhile, electricity feedback to the grid can be realized, therefore, AFE converter has profound prospect in active filter, reactive power compensation, grid-connected power generation of new energy and power feedback applications.The basic principle and topology of AFE converter operating at four quadrants are analyzed in this paper. The mathematic model of voltage and current in three phase static coordinate (abc), two phase static coordinate (ap)and synchronous rotating coordinate (dq) are built, and the power mathematic model in dq rotating coordinate is also established. Analysis is made for three control strategies, namely, PWM control with a fixed switching frequency, predictive control of current and double-loop PI control based on dq rotating coordinate.Direct power control is discussed in this paper and instantaneous power expression of complex power and vector multiplication definition in αβ and dq coordinate are deduced. As a substitute for switching table, the SVPWM algorithm overcomes the drawbacks of hysteresis controller based direct power control, typically known as fierce fluctuation of reactive power and varied switching frequency.According to mathematic model of power, the paper analyzes power decoupling control and grid voltage feedforward control, so as to realize the non-coupling independent control for active and reactive power. According to control equation, design requirements for PI regulator and its influence on system dynamic performance are analyzed. Reasons and remedies for overshoot of starting current are studied. Researches are made for phase locked loop (PLL) technology, the paper studies the principle of PLL based on single synchronous coordinate.Employing Matlab/Simulink to construct a simulation model, the validity of PLL and control system has been verified.Both the hardware and software of AFE converter are designed in this paper.For the hardware part, the paper mainly introduces the LC design in main circuit, IGBT driving protection circuit design and linearoptocoupler based sensor design. While designing filter inductance on grid-side, through constraining the current pulsating quantity in zero-crossing point, the parameter range of inductance reduces significantly and thus results in a more practical usage in engineering application.For the software part, taking TMS320F2812DSP of TI as MCU, blocking programming thought is employed and software design flow is provided in the paper.For the experiment part, a sample machine of AFE converter is constructed, debugging and evaluation are conducted in some research institute of national level, the experimental waveform and data analysis are available.The results shows that, in full-load cases, the system power factor can reach98%, efficiency is above95%, the total harmonic distortion (THD) of current is below3%, power can flow in bidirection.