Research And Implementation On Three Phase Unbalance Suppression Of Emergency Power Supply

With the development of Ship Technology, national standards provide that more than a certain size vessel must be equipped with emergency power supply(EPS). When the ship’s main power grid does not work, EPS can give some important equipment supply. Under the condition of unbalanced three-phase load, the EPS shows asymmetric output and the voltage distortion and other issues. To solve above problems, this paper studies the technology of three-phase load imbalance from the aspects of the asymmetry mechanism, the topology of the three-phase output, control mode, hardware circuit design and other aspects of EPS.To improve the ability to inhibit EPS of load imbalance, the split capacitor three-phase inverter topology is used as the main inverter topology of the emergency power supply. In the case of a split capacitor voltage balance, which means that the neutral voltage is stable, the capacitive split phase inverter can be decoupled into three single-phase inverters. In theory, it can be operated on single-phase, therefore, it have a strong three-phase imbalance inhibition capacity.To improve the ability to divide a capacitive three-phase inverter with unbalanced load, a series capacitor voltage network with DC/DC transform is proposed. Taking the split capacitor three-phase inverter as the research object, the working mechanisms of the three-phase load balance and unbalance condition are analyzed, and the reasons for the unbalance of the series capacitor voltage are proposed. The DC / DC converter network is introduced into the inverter, and a split capacitor self-balance type three-phase inverter topology is obtained and the operation modes are analyzed in detail. The simulation results show that the topology can improve the three-phase unbalanced load suppression effectively, but there are many shortcomings, such as increasing DC link capacitor ripple current, large auxiliary transformer current level and the core easily saturated.To solve the existing problems of split capacitor self-balance type three-phase inverter topology, a new type inverter topology is proposed. The control method of the circuit is designed by the detailed working mode analysis in different modes. The simulation results show that the new circuit topology can not only improve the unbalanced load rejection capability further, but also reduce the ripple current of the DC bus capacitor and auxiliary transformer greatly and avoid the transformer core saturation effectively. Its steady-state characteristic analysis show that the new topology is not sensitive to split capacitance value, the transformer leakage inductance and resistance parameters, and is easy to implement.To verify the split capacitor self-balance type three-phase inverter topology for three-phase unbalanced load suppression effectiveness, a three-phase inverter system of EPS hardware test platform is established. There are three aspects designed: the three-phase inverter main circuit, the control detection circuit and the split capacitor self- voltage module. Hardware experiment results show that the split capacitor self-balance type three-phase inverter have stable and reliable effect on the three-phase load imbalance.