With the transformation of the global energy structure and the rapid development of renewable energy, energy storage system plays an increasingly important role in the stable operation of the power grid and energy management. An energy storage PCS (Power Conversion System, Power Conversion System) as the core component of the energy storage system, bears the important mission of power conversion and control. Today, let us gain an in-depth understanding of the classification and characteristics of energy storage PCS.
Energy storage PCS in the energy storage system is like a “power wizard”, it has two main skills: First, when charging, it can be the grid AC power cleverly converted to DC power for the storage battery charging, so that the power can be stored; Second, when discharging, and can be the output of the DC battery DC power accurately reversed into alternating current (AC) power, transported back to the grid or directly to the power equipment. Grid or directly supply power equipment to ensure a stable supply of electricity.
Household energy storage systems are mainly used in domestic scenarios. The power of this kind of energy storage system is relatively small, usually around 5 to 10 kilowatts, the good thing is that it is relatively small in size and can be perfectly matched with distributed energy systems such as home solar panels. It can store solar power during the day for home use at night, which not only saves you money on your electricity bill but also serves as a backup power source when the grid goes down, ensuring your family's basic power needs and creating a stable and reliable microgrid environment for your home.
Industrial and commercial energy storage systems serve industrial enterprises and commercial sites. The power of such PCS is usually between 50kW - 500kW. It must face more complex power demands and working conditions, with higher conversion efficiency and greater stability. It can help enterprises cut peaks and fill valleys, i.e., store electricity in the trough and release it in the peak, which reduces the cost of electricity, and also improves the reliability of electricity consumption, avoiding the impact on production and operation due to fluctuations in the power grid or power outages, and is a powerful assistant for enterprise energy management.
Large-scale energy storage power stations are critical in the power system, playing the role of frequency regulation, voltage regulation and backup. The power of the storage converter (PCS) of these power stations usually reaches a megawatt level or even higher. The PCSs in large-scale energy storage plants need to have ultra-fast response speeds and high-precision control capabilities to ensure stable and efficient operation of the power system during large-scale power conversion. In addition, they must be able to smoothly connect to the grid and support parallel operation of multiple machines. In short, large-scale energy storage power plants are an indispensable part of building a modern smart grid.
Single-stage PCS has a relatively simple structure, with the rectifier and inverter functions integrated into a power conversion unit. The single-stage PCS adopts the DC/AC single-stage conversion structure of a three-phase full-bridge circuit, and the series-connected battery pack is directly connected to the DC bus. Its advantages include relatively easy control, simple structure high efficiency, and easier realization of off-grid parallel operation of multiple converters. However, due to the presence of the battery pack, the outlet voltage is generally higher.
The two-stage PCS consists of independent rectifier and inverter modules. The two-stage PCS, on the other hand, adopts a DC/DC+DC/AC two-stage structure, which is capable of accessing a wider range of DC-side voltages and improving battery utilization by adding a DC/DC DC chopper conversion link. However, this also leads to a relatively complex control algorithm.
String power conversion system (PCS) with its support for multi-branch battery access, cluster management and independent control features, significantly improves the battery utilization rate, operation and maintenance are simple and easy to expand, although the cost is higher, but the long-term benefits are significant; at the same time, the system effectively solves the problem of the battery cluster parallel loop current, the impact of the failure of a single PCS cabinet range is small, easy to operate and maintain, to ensure that the energy storage system of high reliability and Maintainability.
Centralized PCS is popular in the field of energy storage due to its mature technology, low cost, simple structure and convenient regulation. However, the challenge is that the voltage tolerance of the switching device limits the system expansion, and often requires a step-up transformer to connect to the grid; the battery pack make it difficult to control the fine equalization, which affects the system performance; and the whole machine is shut down in case of a failure, with high operation and maintenance costs, which affects the on-line rate and the utilization rate, and increases the burden of operation and maintenance in the later stage.
Distributed PCS is a kind of power conversion system with secondary AC/DC+DC/DC topology, which solves the problem of parallel loop current of battery clusters by adding DC/DC isolation before each battery cluster is connected to the DC bus in parallel and improves the battery utilization rate and system efficiency. At the same time, the clustered PCS has high flexibility and scalability, which facilitates operation and management. However, due to the addition of DC/DC isolation, its power conversion loss may increase, and the system structure is relatively complex, with higher requirements for safety and stability.
Its main advantage lies in its ability to eliminate the step-up transformer, thus directly improving the overall efficiency of the system. In addition, the system significantly reduces the physical space occupied by the batteries, allowing the integrated capacity to become larger. Since the battery clusters are not directly connected in parallel, the cascaded PCS is able to effectively avoid the circulating current problem that may arise when the clusters are connected in parallel. However, cascaded PCS also has some challenges. Its relatively complex structure makes it difficult to achieve a high degree of modularity, which may lead to a relatively slow project delivery. At the same time, the complexity of the structure puts higher requirements on operation and maintenance at a later stage.
As an important part of new energy sources, energy storage technology is gradually changing the way we use energy. As the core brain of the energy storage system, the power conversion system (PCS) plays a pivotal role. Different types of PCS systems have different characteristics, and the selection of PCS is a complex and detailed process that requires comprehensive review and careful consideration. Only by closely combining the actual needs and technical conditions of the project and comprehensively evaluating the advantages and disadvantages of different types of PCS systems can we ensure that the selected solution is the most compatible and appropriate. This will lay a solid foundation for the efficient and stable operation of the energy storage system and promote the continuous development and application of energy storage technology.
