Research On Key Technology Of Single-Phase Three-Level PWM Rectifier

Rectifier is the key component of the new generation power system,and its performance is directly related to the efficiency and reliability of the whole system.Three-level rectifiers are widely used in various new power systems because of their good output waveform quality,low harmonic content and high voltage resistance.Traditional three level neutral clamped three-level(TL-NPC)rectifier has the problem of uneven loss distribution,which limits its capacity growth,while three level active neutral clamped(TL-ANPC)rectifier can reduce the uneven loss distribution of power devices.In addition,compared with the three-phase grid-connected system,the grid voltage in the single-phase grid-connected system only includes one input voltage phasor.While there are two unknowns,amplitude and phase.Phase-locked loop technology is more complicated to implement.This paper takes single-phase three-level ANPC rectifier as the research object,combined with the domestic and foreign scholars on single-phase three-level rectifier modulation and control research.Using transient current control strategy and a new improved three-order generalized integrator single-phase locked loop scheme,a total of six modulation schemes for SPWM and SVPWM are studied.At the same time,the power device loss model is established,and the results and performance of six modulation methods is analyzed by simulation.This paper analyzes the principle of three-level ANPC rectifier and lists four different zero-level state paths,which provides the basis for solving the problem of loss imbalance on each power device.The total loss of the device is divided into two parts: conduction loss and switching loss,and the loss model is built.According to the simulation situation,the current value flowing through the power device is substituted into the established loss power expression to obtain the average loss power in a modulation cycle,and the loss unbalance degree of six power switch tubes in each phase is calculated.The results and performance of the six modulation strategies are compared and the appropriate scheme is selected.Aiming at the shortcomings of traditional second-order generalized integrator phase-locked loop(SOGI-PLL)in single-phase complex power network environment,an improved third-order generalized integrator phase-locked loop(IDSC-TOGI-IPLL)based on improved delay signal cancellation method and feedforward compensation is proposed.The TOGI structure eliminates DC bias,and the IDSC structure can filter out the harmonic component,improve the anti-interference ability of the PLL,and the feedforward compensation can improve the dynamic performance of the system.Simulation results verify the effectiveness of the proposed IDSC-TOGI-IPLL.To solve the problem of double frequency fluctuation of DC voltage which affects the current control of the network side,the midpoint potential control algorithm of power flow to the midpoint and the moving average filter MAF are added to the outer loop voltage control.While controlling the balance of the midpoint,the AC component is effectively and smoothly filtered out,and only the DC component flows through,reducing the current distortion on the network side.Build Matlab/Simulink simulation to verify phase locking and control.Finally,a low-power experimental platform was built based on TMS320F28377 and HIL semi-physical hardware-in-the-loop real-time simulator.The hardware circuit design,the semi-physical simulator and the software circuit design of the experimental platform are introduced in detail,and the feasibility and practicability of the six modulation strategies,improved single-phase locked loop and control strategy are verified by the experimental platform.