High Power Density GaN-Based Power Converters for Grid-Tied Energy Storage

Power generation and transmission limits manifest themselves in the inability to respond to dynamic peak power demand. Load leveling can effectively support dynamic demand changes by having additional standby power generating capabilities. This is achieved by either 1) having a generation and distribution infrastructure that matches the peak demand and it is operated under its full capacity spinning reserve) or 2) having additional power plants that can be brought online to provide additional power. These methods, though effective, are economically costly because power generators are underutilized, likely operating at a lower efficiency point, or because power generating infrastructures are left unused for large portions of time. Grid-connected energy storage systems are intended to enhance performance and reliability of the utility infrastructure. Unlike load-leveling methods, grid-tied energy storage solutions can provide the flexibility to react to dynamic peak power demands in an economical manner. By storing energy during off-peak power demand and releasing it during peak demand, grid-tied energy storage systems can effectively shift the dynamic power demand profile seen by the grid infrastructure. In this regard, grid-tied energy storage systems are an attractive alternative to improve the performance of the current grid infrastructure. The trend in energy storage systems is to package the energy storage element alongside the power electronics into a standard shipping container. A containerized energy storage system yields many logistical advantages for transportation and deployment. Containerized energy storage solutions require the minimization of the associated power electronics in order to provide more volume for energy storage devices. The power electronics minimization requirement is exacerbated by the need to still operate at high efficiency to minimize power loss and therefore minimize operating cost. There is currently a need to develop minimal volume power electronics to interface with grid-tied energy storage systems in the physical confinement of a containerized application. Consequently, APEI is proposing to develop a high efficiency, high power density >75 kW at > 2 state-of-the-art designs), transformer-less, GaN- based three-phase > 480Vac output, grid-tied inverter for interfacing with containerized energy storage systems. A GaN-based power topology will be designed to enable bi-directional power flow to support energy storage. As such, there is an incentive to pursue size reduction of the passive components associated with switched- mode power conversion. GaN power switches can efficiently operate at high switching frequencies. One of the key benefits of high frequency operation is the significant reduction in size of the transformer used in the power conversion system. APEI has successfully implemented GaN-based systems capable of operating in the MHz range while still providing high efficiency as seen in Error! Reference source not found.. Furthermore, since GaN die have the capability to operate at higher temperatures, simpler cooling systems can be utilized to further reduce packaging size and complexity. The United States consumed approximately 3,800 TWh of electricity in 2012. At such a massive level, even small increases in efficiency can have a prominent impact. Assuming that 30% of the yearly total is processed by power electronics at 85% efficiency, for every 1% average efficiency increase, there would be an annual cost savings of over $2 billion at $0.15 per kWh [ ]) and a reduction of 25 billion lbm of CO2 emissions assuming 1.77 lbm of CO2 per kWh) in the United States alone [ ]. The significance of efficiency is accelerated even further as the proliferation of available sources for readily harvestable energy increases and a growing focus is placed on renewable electric resources such as wind, solar, and tidal. Improvements in the efficiency and power density of the requisite power converters in electric systems ranging from grid-tied energy generation and storage to transportation-based power systems will have a substantial impact as less energy is wasted and more weight and volume in a system may be utilized elsewhere additional battery capacity, etc.).