Low Voltage, Low Frequency, Distributed Multi Level Power Conversion for HV Battery and Hybrid Energy Storage

A low voltage, low frequency (50/60Hz) distributed multi level power converter (LV-LF-DMLPC) is introduced for battery and hybrid (battery plus PV) energy storage systems (ESS). The architecture has targeted replacement of ESS central power conversion system (PCS) by battery module power conversion for cost, performance, safety, and reliability improvements. In the proposed architecture, each battery module is integrated with a low voltage, low frequency magnetic less full bridge converter. In the LV-LF-DMLPC the power MOSFETs are turned On/Off at grid frequency to generate a 50/60Hz semi-sine wave equivalent to grid voltage. The modular power converter will be integrated with the battery module to form an AC battery module. Each AC battery module generates a 50 or 60Hz AC voltage (pulse voltage) with an amplitude equal to the battery voltage and along with a zero state current mode. The zero state current mode, puts the battery at rest (zero current) at a short peiod of of the 50 or 60Hz duty cycle (e.g. ~30%) which helps and improves the battery module thermal releaf and life. A number of AC battery modules will be connected in series and turned on and off in a phase shifted manner relative to each other to form a DMLPC and generate a 50 or 60Hz semi-sine voltage. The output voltage of the DMLPC is a semi-sine voltage with very low total harmonic distortion but before it is paralleled with grid, it will be connected in series with a series active power filter (SAPF). This SAPF offers the DMLPC with several features such as smoothing out voltage steps and removing output current harmonics, power flow direction control, power quality control, buffering and balancing active and reactive power during short transients, and communicating with battery modules. The SAPF will be a low voltage high frequency full bridge converter and does ESS current, voltage, and power regulation. Replacement of the ESS central high voltage power converter with modular low voltage, low frequency, high efficient and magnetic less power converters are the backbone of cost reduction. Additionally, no DC cabling, distributed thermal management, and feasibility of integration of the battery modules cells BMS board with the battery module power conversion are the next level of cost reduction. As an essential achievement, additionally, this solution offers highly efficient battery module active balancing along with power conversion with the same power converter, this feature alone is a remarkable improvement of the batteries life. Significant efficiency improvement is achieved because of low voltage MOSFETs with very low Rdson, no switching loss, and no magnetics loss. Additionally, battery module level monitoring, control, active balancing, fault protection and bypassing improves battery module safety, reliability and life. The proposed solution by connecting the phase shifted AC battery modules and the low voltage SAPF in series, form a LV-LF- DMLPC which can remove the central PCS and offers remarkable cost, performance, safety, reliability, scalability and maintainability improvement. This architecture can be utilized for residential, commercial, industrial and utility scale, off grid and on grid ESS. As a proof of concept a 3KW, 1-phase, 240V, 60Hz LV-LF-DMLPC is designed and developed in power laboratory at Jabil.