Development Of Single Phase PWM Rectifier With Harmonic Compensation Function

With the continuous development of modern life and social production,people’s demand for power quality is also increasing.Power electronic converter is to meet the needs of the times,not only to achieve the environmental maintenance of power systems,but also to make efficient and reasonable use of power energy.PWM rectifier is widely used in electric vehicle charging,renewable energy grid-connected power generation and so on,because it can run under the unity power factor and support two-way flow of energy.The single-phase PWM rectifier with harmonic compensation function is the research object of this paper.It is deeply studied in the control mode of single-phase PWM rectifier,DC side second harmonic suppression,harmonic detection and compensation.To decrease harmonic component in the q-axis component of traditional single phase-locked loop(PLL),a conclusion is drawn that the power frequency fluctuation is converted into harmonic disturbance due to coordinate transformation.To improve the precision of the phase-locked,the traditional low-pass filter(LPF)algorithm is usually used.Although LPF algorithm can filter this part of harmonic component,it will reduce the dynamic response speed of the system,even the phenomenon of delay.In this paper,starting with the principle of phase locked loop(PLL),we choose the second order differential circuit instead of the traditional LPF circuit,which can filter the harmonic component introduced by the coordinate transformation,and obtain the frequency of the power grid faster.To solve the current control problem of single-phase PWM rectifier,this paper adopts the double closed-loop control method which consists of voltage loop and current loop.To track the instruction current without static error,the current inner loop is controlled by the quasi-proportional resonance loop.The basic principle of the quasi-proportional resonance controller is analyzed.In order to ensure that the DC side voltage can reach the instruction value after the pre-charging,the outer voltage loop is controlled by the proportional integral link,which is convenient to be used in the control process and meets the experimental requirements.To solve the problem of the second harmonic voltage fluctuation in the DC side of single-phase PWM rectifier,this paper deduces the cause of voltage fluctuation in detail from the source and obtains several key factors that affect voltage fluctuation.The power decoupling circuit based on the full-bridge structure is selected by setting the instruction current of the filter inductor or the instruction voltage of the energy storage capacitor.The sum of the power of the inductor and the capacitor is equal to the power of the second frequency which causes the voltage fluctuation.To solve the problem of current harmonic in power network,the function of harmonic compensation is added to the single-phase PWM rectifier designed in this paper.And this paper analyzes the current detection scheme in detail and chooses the harmonic detection algorithm based on sine amplitude integral.This algorithm is simple in structure,easy to program,which can improve the current harmonic detection speed and can be more easily applied to single-phase system.And two kinds of current compensation mode are set to make the rectifier harmonic compensation function more flexible.