Harmonie Suppression Strategy of Grid Side Current for DC-Link Small Capacitor Permanent Magnet Synchronous Motor Drive System

Traditional permanent magnet synchronous motor (PMSM) drive Systems often use large-capacity electrolytic capacitors to keep the dc-link voltage constant. However, DC-link electrolytic capacitors have disadvantages of short life and large volume, leading to drive System failure. The small-capacity film capacitor instead of the dc-link large electrolytic capacitor is a trend to reduce the size and enhance System reliability. However, due to the substantial reduction of the dc-link capacitance, the energy coupling between the input side of the grid and the Output side of the inverter is severe. When the System operates normally, the grid-side current generates a large number of harmonics, affecting the power quality of the grid side. This paper proposes an active damping control method based on impedance reshaping to suppress grid-side current harmonics.Firstly, the small-capacity PMSM drive System is modeled, and the factors affecting the grid-side current are obtained by analyzing the drive System impedance. Secondly, the harmonic characteristics of the grid-side current are analyzed, and the mathematical relationship between the dc-link current and the grid-side current is established. Then, an active damping control method based on Virtual impedance is adopted, and a band-pass filter is used to extract the harmonic signal of the DC-link voltage. The feedback loop is constructed as optimal voltage compensation, the equivalent impedance at a specific frequency of the drive System is reshaped, and the grid-side current harmonics are improved. Finally, a cascaded dual-frequency notch filter for the current loop is designed to suppress the voltage compensation module's influence on current inner loop disturbances.The Simulation analysis shows that when the motor runs at 270 Hz and the load torque is 20 N-m, the grid side current THD decreases from 52.2% to 36.6%, finally decreasing to 32.7%. At the same time, the dc-link voltage ripple is reduced by 58.3%. The Performance of the proposed control strategy is still good when the speed and load torque change dynamically. Based on the air-conditioning compressor drive System, the THD of a-phase current using the traditional active damping control method is 39.1%, the 5th harmonic has no apparent change, and the 7th harmonic is reduced by 78.8%. In contrast, the THD of a-phase current using the proposed voltage compensation is 37.8%, and the 5th and 7th harmonics are reduced by 5.8% and 84.3%, respectively. Using the proposed disturbance filtering, the a-phase current THD is reduced to 33.6 %, and the 5th and 7th harmonics are decreased by 19.8% and 88.8%, respectively.The following conclusions can be drawn from the Simulation analysis and experimental verification: (1) The harmonic components in the dc-link current greatly affect the grid-side current. Increasing the impedance at the grid-side harmonic frequency can reduce the harmonic electric current. (2) Combined with the active damping voltage compensation and disturbance filtering control, the proposed method does not change the control structure of the System and is simple to implement. (3) Compared with the traditional active damping control method, the proposed control strategy significantly reduces the grid-side current THD and the dc-link voltage ripple. © 2024 China Machine Press. All rights reserved.