An overall introduction to how PCS works

The most important task of the power system is to provide safe and reliable power supply to the load. The energy storage system has the characteristics of randomness, volatility, and intermittentness, which to some extent helps the power grid maintain the balance of power supply and demand all the time. When conventional power sources (hydropower, thermal power, nuclear power, gas power, etc.) cannot regulate themselves to smooth out fluctuations in new energy output.

A certain amount of energy storage needs to be configured to enhance the power supply's regulation capability. At this time, energy storage PCS is needed. So have you wondered how PCS works?

1. What is energy storage PCS

Before get to know how PCS works, we should first know that the reason why the energy storage system and grid power can be converted in both directions is because of the power conversion system, referred to as PCS, also known as the energy storage inverter. The energy storage inverter is the core component of the energy storage system, equivalent to the heart of the human body.

The energy storage converter is a bidirectional energy storage inverter that can control the charging and discharging process of the energy storage system and convert AC to DC. How PCS works can invert the DC power of the energy storage system into AC power and transmit it to the power grid or to the power grid. It can be used for AC loads, and also rectify the AC power of the power grid into DC power to charge the energy storage system.

2. Is energy storage PCS bidirectional or unidirectional?

The PCS is a bidirectional current controllable conversion device that connects the energy storage battery system and the power grid. It can accurately and quickly adjust voltage, frequency, and power between the power grid and the energy storage system to achieve constant power, constant current charge and discharge, and smooth fluctuating power output.

​ The energy storage converter can not only meet the inversion requirements of traditional grid-connected converters for converting DC power into AC power, but also meet the bidirectional current conversion requirements brought about by the "charging + discharging" of the energy storage system, and has the function of charging and discharging the battery. How PCS works can be used in photovoltaic, wind power generation power smoothing, peak shaving and valley filling, micro grid and other occasions.

• ​ In grid-connected mode: During the low load period, the energy storage converter rectifies the AC power from the grid into DC power to charge the LFP battery pack. During the peak load period, the energy storage converter inverts the DC power in the battery pack into AC power and sends it back to the power grid. ​
• In off-grid mode: the energy storage converter is disconnected from the main grid and provides local partial loads with electric energy that meets the power quality requirements of the grid. For further information, you can click to check the best batteries for solar off grid.

3. Composition of energy storage PCS

PCS is composed of IGBT (insulated gate bipolar transistor), PCB board (printed circuit board), wire and cable, etc., its main functions include power calming, information interaction, and protection. How PCS works determines the output power quality and dynamic characteristics, but also greatly affects the life of the battery. For the best batteries, you can check the top 10 lithium battery companies in the world.

4. Main functional characteristics of energy storage PCS

The main functions of PCS include protection against over-voltage and under-voltage, overload, over-current, short circuit, over-temperature, etc. It’s capable of mode switching with islanding detection capability, communication function to the superior control system and energy switch, and smooth switching control between grid-connected and off-grid. So how PCS works?

5. Working principle of energy storage PCS

The principle of how PCS works is a four-quadrant converter controlled by AC and DC side, which realizes the bidirectional conversion of electric energy. How PCS works is to carry out constant power or constant current control through microgrid monitoring instructions, charge or discharge the battery, and smooth the output of fluctuating power sources such as wind power and solar power.

6. Working modes of energy storage PCS

The modes of how PCS works are divided into grid-connected mode, off-grid mode and hybrid mode.

• Grid-connected mode

The grid-connected mode includes charging and discharging function, and users can choose automatic mode and manual mode. In the automatic mode, if the user chooses the grid-connected charging or discharging state, the energy storage inverter will charge or discharge the battery at the previously set value. In manual mode, the user can manually modify the charging or discharging current, voltage and time value to make how PCS works in the set state of charging or discharging.

In grid-connected mode, the energy storage inverter is connected to a large-capacity public power grid, and the large-capacity means that the total capacity of the grid is at least 10 times larger than the capacity of the energy storage inverter. The main feature of how PCS works in the grid-connected mode is that the energy storage inverter must be synchronized with the existing grid frequency.

To synchronize with the grid, the energy storage inverter acts as a current source relative to the grid. In some cases, the energy storage inverter must be able to provide voltage support to the grid through reactive power control. This mode is often used for peak cutting and valley filling, power load balancing and power quality regulation.

• Off-grid mode

An island system is one or more power generation systems connected in parallel to form a local "microgrid". The main feature of the island system is that the local power grid is separated from all the large power grids, and the rated power of the energy storage system is roughly equal to the total power generated by the local power grid.

In this system, the energy storage system must be able to act as a network power source, providing voltage and frequency control to the local grid. On the other hand, if a power generation device cannot be synchronized with other power generation devices, such as a diesel generator connected to the local grid, then the energy storage system must be used as a power source synchronization.

In some cases, the energy storage system also switches between serving as a power source and synchronizing with the power generation device. Isolated island systems are characterized by energy storage systems connected to local power grids, which may exist in remote mountainous areas or small islands.

Common applications include smoothing power fluctuations caused by variable loads on variable power supplies, stabilizing the grid, optimizing fuel use, and regulating power quality.

• Hybrid mode

The energy storage system can switch between grid-connected mode and off-grid mode. When it comes to how PCS works in the micro-grid, and the micro-grid is connected to the public power grid, and it operates as a grid-connected system under normal conditions of how PCS works.

If the micro-grid is disconnected from the public power grid, the energy storage system will work in off-grid mode to provide the main power for the micro-grid. Common applications include filtering, stabilizing power grids, regulating power quality and creating self-healing grids.

7. Application scenario of energy storage PCS

According to the different application scenarios, how PCS works can be divided into four categories: energy storage power station, centralized or cluster type, industrial and commercial use, and household use, and the main difference is the power size.

• The power of how PCS works in energy storage power station is generally greater than 10MW. The cascaded multilevel topology and IGBT module design are adopted. Generally, N alternators are installed inside the container to support parallel operation of multiple machines, and transformer boost is required to connect to the power grid.
• The power of centralized PCS is above 250KW. Currently, it mostly adopts two-level topology. It also adopts IGBT modular design and uses fewer power devices. The power of a single machine can reach MW level, which requires high system reliability.
• The power of industrial and commercial PCS is generally below 250KW, the current use of three-level topology, combined with distributed photovoltaic, can achieve self-use, but also use the power grid peak valley difference for profit.
• Household PCS power below 10KW, such as 2000w inverter or 3000w inverter, which is combined with household photovoltaics to serve as emergency power supply, electricity bill management, etc., and it has high requirements for safety norms and noise.

8. Development trend of energy storage PCS

From the technical perspective, it is divided into centralized inverters, string inverters, distributed inverters and micro-inverters. At present, the battery energy storage system in the industry mainly adopts centralized PCS. The parallel connection of multiple batteries will cause imbalance between battery clusters; the string PCS can realize cluster-level management, extend the system life, and increase the discharge capacity throughout the life cycle.

As the scale of the energy storage market continues to expand, energy storage system PCS equipment is no longer a simple conversion device, but requires higher integration capabilities. In the future, energy storage system PCS will increasingly tend to integrate equipment.

Through software development, upgrades, and optimization, intelligent control and safety performance guarantee of the energy storage system will be realized, thereby achieving better application of energy storage techno.

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