Energy storage inverter is a kind of grid-connected inverter suitable for smart grid construction, applied in energy storage, with bidirectional inverter as the basic feature, and a series of special performance and functions. The energy storage link in the smart grid can effectively regulate power resources, balance the difference in power consumption between day and night and different seasons, adjust the surplus and shortage, and ensure the security of the power grid.
1. Four common functions of the energy storage inverter system
1.1 Unbalanced output
In the application scenarios of three-phase household electricity consumption in foreign countries, three-phase photovoltaic energy storage systems such as parking lots, station shopping centers, etc. are the best choices. But to power single-phase loads in the system, different amounts of power need to be delivered on each phase. We call this the "unbalanced output function".
In the anti-backflow scenario, if the uplink power control is phase-by-phase (single-phase level control), the unbalanced output function will be crucial, because the uplink power on each phase will be limited separately. This requires the inverter to be able to output different power according to the load consumption of each phase.
1.2 Power failure seamless switching
Off-grid output capability or backup power capability is an important function of photovoltaic energy storage system. This is especially the case where the public grid supply is unstable or where critical household loads require uninterrupted power supply. In this case, the energy storage inverter should also have off-grid output capability and seamless switching capability from grid-connected state to power-off state.
1.3 Remote Control
Photovoltaic systems usually require long-term and continuous operation and maintenance services. Nowadays, 10-year warranty is popular all over the world, so convenient operation and maintenance solutions are very important in energy storage inverter systems. The function of remote control can greatly reduce the time cost of on-site after-sales service and the cost of the service itself.
1.4 Protocol matching
Generally speaking, a photovoltaic energy storage system is a combined system that integrates all equipment in the entire photovoltaic storage system, including batteries, photovoltaic modules, inverters, brackets, meters, and control systems. Inverter manufacturers obviously cannot provide all the equipment needed for an entire energy storage system. In a complete photovoltaic storage system, it may also require other components to achieve intelligent energy management, including EMS controllers, multi-functional smart meters, thermal controllers, pump controllers, etc., to maximize the photovoltaic self-use rate or specific load control.
2. Main functions and performance indicators of energy storage inverters
2.1 The active control method of power stabilization is suitable for the short-term fluctuation of intermittent energy output power;
2.2 Passive control mode for power stabilization, accepting the control of the power grid dispatching system, and participating in the peak-shaving and valley-filling of the power grid;
2.3 Integrated charging and discharging design, the charging and discharging strategy can be selected according to the characteristics of energy storage components (such as constant current charging and discharging, constant power charging and discharging, automatic charging and discharging, etc.).
2.4 Grid-connected operation, reactive power automatic or dispatch compensation function, low voltage ride through function.
2.5 Off-grid operation: independent power supply, adjustable voltage and frequency; multi-machine parallel combined power supply, power can be automatically distributed between multiple machines.
2.6 It has Ethernet, CAN and RS485 interfaces, and provides open communication protocols to facilitate information exchange between BMS (battery management system) and monitoring systems.
2.7 Complete protection functions can protect the safety of converters and energy storage components under various fault conditions.
The main function and role of the energy storage inverter is to realize the bidirectional energy transfer between the AC power grid and the energy storage battery. It is also a bidirectional converter that can be adapted to a variety of DC energy storage units, such as super capacitor banks, Battery packs, flywheel batteries, etc., which can not only quickly and effectively stabilize the fluctuations of random power or power flows in distributed power generation systems, but also improve the grid's ability to accept large-scale renewable energy power generation (wind energy, photovoltaics), and can accept dispatching instructions.
Absorb or supplement the peak and valley electric energy of the grid, and provide reactive power to improve the power supply quality and economic benefits of the grid. In the event of grid failure or power outage, it also has the function of independent network power supply to improve the safety of power supply for loads.