Microgrid Durable Power Conversion System Electronic

PCS, also known as two-way energy storage inverter, its role is to convert the direct current of the battery into alternating current, which is transmitted to the power grid or other AC loads. The AC current of the power grid is rectified to direct current, and the battery is charged. PCS is the core component of the energy storage system and the power grid or micro-grid to realize the two-way flow of electric energy. PCS consists of hardware and software such as power, control, protection, monitoring, etc. Its main functions include power suppression, information interaction, protection, etc. PCS determines the output power quality and dynamic characteristics, and also greatly affects the battery life.

Main functions of PCS

• Flattening power

1. Active control mode: smooth intermittent energy output power short-term fluctuations

2. Passive control mode: accept the control of the power grid dispatching system and participate in the power grid peak cutting and valley filling

• Integration of charge and discharge

Combined with the BMS system, charge and discharge strategies can be selected according to the characteristics of energy storage components (such as constant current charge and discharge, constant power charge and discharge, automatic charge and discharge, etc.)

• And/or off-grid operation

1. Grid-connected operation: reactive power automatic or scheduling compensation function, low voltage crossing function

2. Off-grid operation: independent power supply, adjustable voltage and frequency; Multi-machine parallel combined power supply, multi-machine power can be automatically distributed

• Information interaction

With Ethernet, CAN and RS485 interfaces, providing open communication protocols to facilitate information exchange with BMS and other systems

• Protection function

Ensure the safety of converter and energy storage components under various fault conditions

The configuration of the energy storage converter is generally determined according to the actual load in the microgrid and the energy capacity of distributed generation. The load is divided into important load (computer room, office, monitoring load, etc.) and non-important load (air conditioning, lighting, boiler, gate guard load, etc.). The load data generally needs to be measured on the spot, and the time-sharing data of working days and holidays are generally measured, and the data of typical time in the four seasons are selected for comprehensive analysis.

1. Energy storage converter capacity matching

   The energy storage capacity is configured as 1.2 times the load capacity. For example, if the critical load is 200kW, a 250kW energy storage converter is recommended. If other loads need to be operated off the grid, the energy storage power ratio should be increased accordingly.

2. Energy storage converter transformer ratio

   The transformer ratio of the energy storage converter is determined by the DC voltage input range (that is, the battery voltage range). The calculation method is as follows: Transformer ratio =Ul(minimum battery voltage)/1.414. If the voltage range of the lithium iron battery is 360~480VDC, 360/1.414=254, the transformer ratio can be determined to 200.

3. Energy storage converter additional function configuration

   Since the same time function (S) : the energy storage converter can realize seamless and off-grid switching without other devices. Under the premise that the grid-connected switch can be remotely controlled, the energy storage converter issues instructions to make the grid-connected switch open when it is running from grid-connected to off-grid, and issues instructions to make the grid-connected switch close when it is running from off-grid to grid-connected (closing conditions are judged by the converter and cannot be manually closed). Supercapacitor charger function (C) : When connected to the supercapacitor product, the energy storage converter can charge the supercapacitor from 0 voltage, and charge and discharge the supercapacitor voltage when it reaches the operating voltage, replacing the traditional charger.