Research Of Energy Storage Charge And Discharge Control With Hybrid Cascade Multilevel Converter

With the continuous development of the economy, the demand for power of thewhole society is increasing quickly, while the energy consumption and environmentalpollution is becoming more and more serious at the same time. Therefore, energyconservation has become one of the world’s main research topics. Activelydeveloping new energy sources and using electrical vehicle have become the mosteffective measures to reduce pollution and energy saving, where the energy storagesystem is all necessary. At present, energy storage with super-capacitor and batteryenergy storage is more and more used, but limited by the voltage and current outputability, so both of them must be used in series or parallel to enlarge the power scale.And the added voltage balance circuit will reduce the energy storage systemefficiency and increase cost.In this paper, a novel charge and discharge circuit based on hybrid cascadedmulti-level converter is proposed, in which the direct-series cells is replaced by anovel bridge-arm-cascaded circuit. The circuit combines the traditional equalizationcircuit and the charging and discharging circuit as a single one, which is modular andis easy to be applied in hybrid energy storage system. Since each storage cell iscontrolled separately, by using the cascaded carrier-wave PWM modulation, thevoltage balance of the storage cells can be realized on-time. The utilization ratio ofthe storage cell can be improved while the over-charge and over-discharge can beavoided. In addition, the proposed circuit can output multi-level voltage on the load,changes in the voltage is only a single storage unit and the AC output is closer to thesine wave, thus the dv/dt and harmonic of the output voltage are reduced while thepower quality can be improved, reducing or eliminating the need for output filterswhen used in power system. The control strategies of single storage system and hybrid storage system areanalyzed in the paper. Using lead-acid batteries and super capacitors as an example,the simulation and experiment results of the charging and discharging are given toverify the effects of the proposed circuit.