Study On The Electrolytic Capacitor-free Single-phase PWM Rectifier With Dual Modulation SPWM

The single-phase PWM rectifier has the advantages of high power factor,low harmonic content and energy can flow in both directions.It is widely used in many scenarios such as UPS power supply and renewable energy power supply system.As a bidirectional AC-DC converter,the single-phase PWM rectifier needs to meet two key performance indicators: First of all,the harmonic content of the input current on the AC side needs to meet the network access standard;secondly,the output voltage on the DC side ought to meet the DC of the subsequent load or converter Power requirements.Under this background,this paper studies the modulation strategy of single-phase PWM rectifier and the electrolytic capacitor scheme on the DC bus.The content of this article is mainly composed of two parts: The first part analyzes the working mode of single-phase PWM rectifier.Through THD and loss calculation analysis,the best type of modulation is obtained among all possible modulations.Secondly,the problem of zero-crossing distortion in traditional unipolar modulation(UPWM)is specifically analyzed,and a dual-modulation wave SPWM modulation strategy is proposed in order to solve this problem.This method not only effectively solves the problem of zero-crossing distortion,but also the well preserves the advantages of low THD and low loss.Finally,simulation and experimental results verify the effectiveness of the proposed modulation method.Based on the idea of power decoupling,the second part proposes a method,which uses a boost active capacitor converter,to balance the DC bus ripple of the single-phase PWM rectifier.This paper explains the working principle of the active capacitor converter and reduces the capacitance requirement by the DC bus the capacitance value,in turn,overcomes the limitations of the power converter due to defects such as short service life of the electrolytic capacitor and poor thermal stability.The main circuit topology of the active capacitor converter is to connect a small capacitance capacitor in parallel with the input port of the synchronous boost converter.The working mode of the active capacitor converter is analyzed in detail and the main circuit parameters are quantitatively designed.Active capacitance conversion adopts double-loop control strategy.According to the design requirements,the controller design method of current inner loop and voltage outer loop is given.Finally,the feasibility of the scheme and the accuracy of parameter design are verified through simulation and experimental results.