Research On Control Strategy Of Electrolytic Capacitor-Less PMSM Drive System Based On Asymmetric Split-Capacitor Converter

The electrolytic capacitor-less(ECL)motor drive system is based on the active power decoupling circuit(APDC)of small capacitance film capacitors.It has the advantages of long service life and high reliability,and is currently one of the hot research directions in motor drive systems.However,due to the significant reduction in the capacitance of film capacitors,the ECL drive system has drawbacks such as DC-link voltage fluctuations and large motor torque ripple.In addition,it can also cause coupling interference between the power grid,capacitors and motor power,leading to a decrease in the dynamic performance of the drive system and the quality of the power grid.In order to solve the above problems and promote the application of such drive systems,this paper studies an ECL motor drive system based on asymmetric split-capacitor structure,proposes a fast-tracking control strategy for grid current and a suppression strategy for DC-link voltage ripple.The main research contents are as follows:Firstly,studying the topology and working principle of asymmetric split-capacitor structure APDC,establishing the mathematical model of DC-link voltage of the APDC.The requirements for obtaining stable DC-link voltage through complementary split-capacitor voltage is analyzed,and a PIR controller is constructed to achieve high-precision control of capacitor voltage.Therefore,the DC-link voltage ripple is effectively suppressed.Secondly,in response to the problems of high DC-link voltage ripple and poor dynamic performance of the ECL drive system under dynamic conditions,a model predictive control(MPC)strategy of grid current based on motor power changes is proposed.The relationship between grid current,motor power,and DC-link voltage is analyzed,and a grid current prediction model based on motor power change is established.Meanwhile,the motor power change is introduced into the cost function to achieve fast and accurate tracking of motor power change in the grid power.Thirdly,a predictive current model for the inductance of the asymmetric split-capacitor structure APDC is constructed.Combined with PIR ripple voltage control,the high-precision complementary control of the split-capacitor voltages is realized under both steady conditions and dynamic conditions.Combining the above grid current model predictive control strategy,it effectively suppresses the significant changes in DC-link voltage of the ECL drive system under dynamic conditions,achieving high-performance operation of the motor.Finally,an experimental platform of ECL motor drive system is constructed and the effectiveness of the proposed control strategy is verified through experiments.The experimental results show that under the proposed control strategy,the DC-link voltage ripple suppression and dynamic motor speed performance of the ECL drive system reach or exceed the level of traditional large capacitance drive systems.Therefore,the model predictive current control strategy based on motor power change proposed in this paper is significantly superior to the existing control strategies.