Large-signal Stability Criteria of AC/DC Hybrid Microgrid Based on AC Constant Power Loads

In the AC/DC hybrid microgrid system, a large number of motor loads and converter loads are connected to the AC bus by closed-loop controlled power electronic devices. These loads have negative impedance characteristics and can be regarded as AC constant power loads, similar to those under large disturbances. Positive feedback will enhance disturbance signals, reduce the stability of the system, and even cause the entire microgrid system to fail to work normally in severe cases. On the other hand, the energy storage unit is the inertial link of the system, and reasonable control can enhance the stability of the system. In order to ensure the large-signal stability of the grid-connected AC/DC hybrid microgrid system, the hybrid potential function method is applied to propose a stable control strategy for the energy storage unit interconnected converter to compensate for the dynamic performance of the AC constant power load. First, according to the abc-dq coordinate transformation, a simplified model of the charging and discharging state of the AC/DC hybrid microgrid system in the energy storage unit is obtained; then, a mixed potential function model of the system is established respectively; finally, the third stability theorem is applied to derive the obtained Large-signal stability criterion under different working modes of energy storage unit. The criterion gives the stability limiting conditions of filter parameters, AC constant power load power, energy storage unit charging and discharging power, energy storage unit AC/DC converter current inner loop proportional link coefficient, and voltage outer loop proportional link coefficient. Experimental results verify the correctness of the proposed large-signal stability criterion. © 2021, High Voltage Engineering Editorial Department of CEPRI. All right reserved.