Energy storage converters, also known as bi-directional energy storage inverters, or PCS (Power Conversion System), are used in ac coupling energy storage systems such as grid-connected energy storage and micro-grid energy storage. They connect batteries and Power grids (or loads) to achieve bi-directional energy Conversion. It can invert the dc power of the battery into AC power, and send it to the power grid or ac load. It can also rectify the alternating current into direct current to charge the battery.
Energy storage converters (PCS) consist of power, control, protection, monitoring and other hardware and software electrical components. It is divided into single camera and three camera. Single-phase PCS is usually composed of two-way DC-DC lifting voltage device and DC/AC AC/DC converter device. The DC end is usually 48Vdc and the AC end is 220Vac. The three cameras are divided into two types. Low-power three-phase PCS consists of two-way DC-DC lifting voltage device and DC/AC AC/DC conversion two-stage device, while high-power three-phase PCS consists of DC/AC AC/DC conversion one-stage device. Energy storage converters are divided into high frequency isolation, power frequency isolation and non-isolation. Three-phase PCS with single-phase and small power below 20kW generally adopt high frequency isolation; PCS with 50kW to 250kW generally adopt power frequency isolation; PCS with more than 500kW generally adopt non-isolation.
Important technical parameters of energy storage converters: Due to different application situations, the functions and technical parameters of energy storage converters vary greatly, so attention should be paid to the system voltage, power factor, peak power, conversion efficiency, switching time, etc., when selecting these parameters, which have a great influence on the function of energy storage system.
System voltage
The voltage of the battery, the input voltage of the energy storage converter. For energy storage inverters with different technologies, the system voltage varies greatly. The single-phase two-stage structure energy storage converter is about 50V, and the three-phase two-stage structure energy storage converter is between 150V-550V. The three-phase energy storage converter with power frequency isolation transformer is between 500V-800V, and the three-phase energy storage converter without power frequency isolation transformer is between 600V-900V.
The power factor
When the energy storage inverter runs normally, the power factor should be greater than 0.99. When the system participates in power factor regulation, the range of power factor should be as wide as possible.
Switch time
Energy-storage there are two kinds of inverter switch time, one is the charging and discharging switch, the status of large energy storage flow should be able to quickly switch usually require rated power grid charging status at 90% and 90% rated power interconnection between discharge and switching time is not more than 200 ms, 2 it is applied in the interconnection mode and off-grid mode switch, switch time is not more than 100 ms.
Energy storage converters mainly have two working modes: grid-connected and off-grid. Grid-connected mode realizes bidirectional energy conversion between battery and power grid. PCS has the characteristics of grid-connected inverters, such as islanding prevention, automatic tracking of power grid voltage phase and frequency, low voltage crossing, etc. According to the requirements of power grid dispatching or local control, PCS can convert ac electric energy of power grid into DC electric energy, charge battery banks, and manage battery charge and discharge. In the peak load of the grid, it inverts the dc power of the battery into ac power and feeds back to the public grid. When the power quality is not good, it can feed or absorb active power to the grid and provide reactive power compensation. Off-grid mode, also known as isolated network operation, means that the energy conversion system (PCS) can be disconnected from the main power grid according to actual needs and meet the set requirements, so as to provide local part of the load with AC power that meets the power quality requirements of the power grid.
conclusion
Energy storage converters are the most core equipment in the micro-grid system composed of a variety of energy sources, because renewable energy, such as photovoltaic and wind power, fluctuates, as does the load. Oil-fired generators can only generate electricity, but cannot absorb it. If only solar, wind and fuel generator system, system operation may be unbalanced, when renewable energy power is greater than the load power, the system is likely to fail, so the photovoltaic (pv) grid inverter with fuel generator parallel operation, and energy storage converter can absorb energy, can also be generated energy, and reaction speed, balance in the system.