Distributed Hybrid Energy Storage Power Conversion And Control

The global energy crisis and environmental pollution vigorously promote the application of renewable and green energy sources such as wind and photovoltaic. But the power generation of them are unpredictable and intermittent.Thus, the usage of energy storage to make the reneawable energy power generation reliable and controlabe has become an important academic research field in the recent years. The study of this paper is mainly focused on the bidirectional DC-DC converter topology and control, hybrid energy storage control.1. A improved isolated winding-coupled bidirectional dc-dc converter is proposed for the energy storage power conversion. The parallel structure in the low voltage side is employed to share the large current and reduce the current ripple. The series half bridge structure in the high voltage side is adopted to reduce the voltage stress of the high side switches to half of the DC bus voltage. What’s more, PWM plus phase shift control strategy is used in this topology, which makes ZVS conditon always met, circulating power loss reduced and voltage input range wider.2. The bidirectional DC-DC converter small signal model is derived by state space averagy method. The obtained model is very complexed and verifed by simulation result. Then the simplifed2’rd older model deduced by some assumptions. The control loop is analyzed by using the simplified model. Experimental results validated the small signal model further. Moreover, a simplified system level model of the bidirectional dc-dc converter is proposed by anlyzing the electric characteristics of the converter low-votage and high-voltage ports, which simplify the control anlysis of the hybrid energy storage system.3. A control strategy which adopts super-capacitor to control the DC bus voltage and battery to control the super-capacitor voltage, is anlyzed for the hybrid energy storage system. The control strategy indirectly sets up low-pass, band-pass and high-pass filters by DC bus voltage controller and super-capacitor voltage controller. The power response of the battery, super-capacitor and DC bus capacitor is coordinated automatically by these filters. The cut-off frequencies of these filters are decided by the crossover frequency of the DC bus voltage loop and super-capacitor volage loop. Finally, the experimental results verified the analysis.