Stability analysis and self-excited oscillation suppression of DC charging pile under wide charging power range

• This paper completes systematic modelling of the main circuit parameters as well as the control strategy of DC charging pile in different charging stages, and finds that the same set of control parameters is difficult to meet the stability needs of multiple charging stages. • In the constant voltage charging mode, when the DC charging unit is in a discontinuous current state, the system is stable when the number of positive and negative crossings of the phase-frequency characteristic curve of its open-loop transfer function is equal. However, it is prone to insufficient phase margin at the cutoff frequency, which can cause positive feedback at the cut-off frequency to induce self-oscillation, resulting in medium and low-frequency pulsations in the charging current at this time, and the frequency of this pulsation decreases with the decrease of the charging current. • It is possible to increase the cut-off frequency by increasing the voltage loop gain, thereby increasing the corresponding phase margin, effectively suppressing self-oscillation phenomena. • The work in this paper is important for the charging pile to provide stable charging current in the process of providing charging service for electric vehicles, and to provide a solution to the stability problem of the charging pile after a long period of time after some of the circuit parameters have been aging and offsetting. Aiming at the characteristics of phase-shifting DC charging pile with wide charging power range and multiple charging modes, The main circuit and its loop small-signal model for continuous and intermittent current states under constant-current and constant-voltage charging modes were established, the influence of compensation network parameters on the stability of the system was analyzed, and the amplitude-phase curves under different charging states were plotted using MATLAB simulation software. The causes of the low and medium frequency charging current pulsation and its relationship with the compensation network parameters are revealed, and the design rules of the control loop parameters are optimized. Finally, in the 20 kW phase-shifted charging module experimental platform, the charging current under constant voltage charging mode is compared when the voltage loop gain is 12 dB and 40 dB respectively, and the loop optimization scheme summarized in this paper effectively suppresses the self-excited oscillation of the charging current, and proves that the theoretical analysis results are correct and the optimization method is effective.