Double-line-frequency Ripple Suppression Strategy Of Single-phase PWM Rectifier Based On APD Technology

Single-phase PWM rectifiers,which have a simple structure and superior power factor,are widely used in various power electronics fields such as electric traction drives,uninterruptible power supplies and renewable energy power conversion.However,when the rectifier is operating,the output voltage on the DC side contains double-line-frequency(100Hz)pulsation,and this ripple voltage will have a detrimental effect on both the DC side and the AC side.Taking Buck type active power decoupling(APD)circuit on AC side as an example,the double-line-frequency ripple suppression strategy of single-phase PWM rectifier based on APD technology is mainly considered,aiming to attenuate the impact of DC ripple voltage with lower cost,higher power density and operational efficiency.Mathematical model of the single-phase PWM rectifier without APD circuit is established,based on which the generation of ripple power is analyzed and the compensation principle of the decoupling capacitor is expounded.The technique of APD is introduced to suppress the double frequency pulsating voltage.Thus,the mathematical model of single-phase rectifier based on independent APD(IAPD)topology is constructed.After the introduction of the third leg,there is an inherent decoupling relationship between the APD branch and the main circuit.The ripple suppression method is designed based on dual voltage control strategy.The simulation verifies that the IAPD topology has a superior ripple compensation effect(the peak-to-peak value of the pulsating voltage is 0.95% of udc)under the ideal grid,and which can effectively reduce the supporting capacitor.A dependent APD(DAPD)topology is introduced to avoid the increase in system cost caused by additional legs in IAPD circuit.At this time,a small auxiliary capacitor is added to buffer the double-frequency ripple power,but the multiplexing of the leg results in a control-coupling link between the APD branch and the main circuit.The new mathematical model based on DAPD topology is established after analyzing the circuit topology.Afther than an automatic power decoupling control scheme based on PI controller is adopted for double-line-frequency ripple suppression.The simulation verified the feasibility of the DAPD circuit under PI controller.The pulsating voltage between both terminals of the DC load is attenuated effectively via the proposed scheme(the peak-to-peak value of the pulsating voltage1.4% of udc).There is a certain ripple buffer effect under the distorted grid.Considering the strong coupling in the DAPD and the difficulty in adjusting the coupling between multiple controller parameters,a model predictive control(MPC)method is proposed to realize parameter-free regulation of the inner loop.In addition,the waveform types of decoupling capacitor voltage are more abundant and the capacitor utilization is much higher under.To obtain a more ideal the steady-state performance,this paper further proposes an MPC scheme based on virtual voltage vector,which inserts four virtual vectors synthesized by two adjacent vectors in addition to the traditional four vectors.So that the design of control system is simplified while an excellent suppression precision of pulsating voltage is achieved.The simulations verify the feasibility and effectiveness of the proposed algorithm.Compared with traditional passive filtering,The DAPD topology under the proposed MPC strategy can decrease the total capacitance by 7.1 times under the same ripple buffering effect.The proposed strategy reduces the control system parameters by half while still ensuring the high power factor operation of the rectifier.The double-line-frequency ripple power is evident compensated and the DC voltage is maintained straight(the peak-to-peak value of the ripple voltage is less than 2% of udc)under various complex conditions such as load mutation,DC reference change and AC grid distortion.The APD topology is simplified and the controller parameters is decreased while the stability of the system are powerfully improved.