Research On Soft Startup And No-Load Performance Improvement Of VIENNA Rectifier

With the widely applied of power electronic devices in people's daily lives,it brings huge economic benefits,but brings serious harmonics and reactive pollution to the grid at the same time.Therefore,how to improve the power factor of the power electronic device,especially the rectifier,reduce the total harmonic distortion rate(THD)and improve the power quality has became the urgent problem in the field of power electronics.The VIENNA rectifier is a kind of three-level PWM rectifier which has the advantages of high power factor,low harmonic,output voltage controllable and possesses a good prospect of application.The topology can be equivalent to three single-phase BOOST converters in parallel.The converter without load is no discharge circuit,the input energy storage inductance only charge and no discharge.So there is soaring phenomenon of the output voltage when the convertor is no-load and excessive voltage will threaten the safety of the converter.Therefore,it is of great engineering significance to research its no-load and soft startup to improve its performance.This paper introduces the development and working principle of VIENNA rectifier topology,establishes the mathematical model,and lays the foundation for the study of its control strategy.The control method of voltage orientation and current decoupling is analyzed in detail,and a double closed-loop control block diagram which consists of outer voltage loop and inner current loop is established.On this basis,the soft startup control algorithm is added to solve the problem that the surge current is generated during the starting process of VIENNA rectifier.Aiming at the problem that the output voltage of the DC side will increase when the VIENNA rectifier is no-load,two methods of the no-load output voltage algorithm and the no-load output voltage regulation based on the hardware auxiliary circuit are adopted to make the output voltage is stabilized at the given value,and to solve the problem of VIENNA rectifier no-load output voltage surging.An experimental prototype with TMS320F2812 DSP as the main control chip is set up,the hardware and software design of the system is given.The hardware includes system input and output filter,driver circuit,sampling conditioning circuit as well as over-current and over-voltage protecting circuit.The software includes main program and interrupt service routine.The method is validated by the experimental prototype,and the experimental results show that the method has the following advantages:(1)Current decoupling control has a high power factor on the network side,and a good output voltage regulation performance;(2)The impact current can be suppressed when the VIENNA rectifier is started after the soft startup control algorithm is used;(3)The DC side output voltage of the VIENNA rectifier can be stabilized near the given value when the no-load control methods are added.