China has entered a new era of power development, and the power grid needs to gradually increase its development and construction to adapt to the proportion of new energy. The development of new energy has reached a critical juncture of quantitative to qualitative change, which has also brought many challenges to the power system. The new power system has made changes to this end, including increasing energy storage investment, improving the protection capacity of the power system, intelligent reform, and electricity marketization reform. Investment in the power grid will enter a new stage of growth.
Basic Introduction to Power System
The current power system in our country can be divided into four parts: power supply side, grid side, load side, and energy storage. The production and use of electricity refer to the three processes of power generation, transmission, and consumption. The power supply side is the power generation end, the grid side is the power transmission main body, and the load side is the power consumption end. Energy storage is a unique link in the new power system, which plays a role in ensuring the safety of the power system, maintaining the stable operation of the power system, and improving the quality of power.
Power supply side: Currently, electricity in China can be classified into thermal power, hydropower, wind power, photovoltaic power generation, and other types based on production methods. Structurally, thermal power is the primary power source in China, while hydropower is the second primary power source. In 2011, the proportion of thermal power/hydropower in China was 73%/22%, respectively; Wind solar new energy is the direction promoted by China's current policies. It has developed rapidly in recent years and has become the new two major power sources in China. The proportion of wind power/photovoltaic power increased from 4%/0% to 14%/13% respectively in 2011-2021.
Grid side: Its main function is to transport the electricity produced on the power side to the load side through transmission and transformation. The grid side in China consists of the State Grid and the Southern Power Grid.
Energy storage: In traditional power systems, energy storage is not included, while in new power systems, energy storage is necessary for construction. Energy storage serves as a controllable device for electricity consumption/generation, with the aim of ensuring stable operation of the power grid. In traditional power systems, the power sources are mainly thermal power and hydropower, which have relatively stable supply and high controllability. The power generation output can be adjusted based on the electricity demand on the load side. With the gradual integration of new energy into the grid, the instability and intermittent impact of new energy are becoming increasingly significant, which will make the voltage/current of the power grid unstable. Therefore, the power grid needs a special "power source" to digest electricity when there is excess power, and supplement electricity when there is insufficient power. Energy storage serves as this special "power source" to ensure the stable operation of the power grid.
The new power system will undergo transformation around three major directions
1) New energy storage construction will enhance the capacity for new energy consumption
Energy storage is a key supporting technology for the large-scale development of renewable energy, and can serve as an additional link in the new power system, affecting the entire power system. On the power side, energy storage can be used for power peak shaving, system allocation, and can also be matched with energy storage in wind and solar projects. By charging and discharging energy storage, the intermittency and instability of wind and solar power can be regulated, smoothing the output of new energy generation, improving power quality, and reducing wind and solar power curtailment. On the load side, energy storage can be used as a backup power source to ensure the power supply of users, and can also be used for arbitrage by taking advantage of peak valley price differences to reduce electricity costs. On the power grid side, when the power line is blocked and unable to transmit electricity, energy storage can reserve electricity, alleviate the problem of power grid blockage, and also alleviate the construction of new transmission and distribution facilities, shorten construction time, and reduce costs.
At present, energy storage in China is mainly applied in three aspects: centralized new energy storage supporting facilities, power side auxiliary services, and grid side.
2) Add protective equipment in the power system
The power system in our country can be divided into three lines of defense, namely preventive adjustment and relay protection, machine cutting and emergency voltage control. The complexity of new energy high proportion power grids has significantly increased compared to traditional power grids, but the prevention and control system can still learn from traditional defense line division. The complexity brought about by the integration of new energy into the grid actually challenges the first line of defense. The power supply of traditional power grids is adjusted according to the load side, with high controllability. The first line of defense mainly deals with some sudden accidents or drastic changes on the load side. The high proportion of new energy brings fluctuations on the power supply side, increases the difficulty of prevention and control, and also increases the frequency of accidents. Therefore, the demand for power equipment related to prevention and control, scheduling adjustment, and relay protection will increase with the increase of the proportion of new energy.
In terms of specific implementation, the reform approach includes three aspects: fault or disturbance isolation, active stability control, and prevention of collapse. Fault or disturbance isolation is mainly the first line of defense renovation. When a fault occurs, relay protection equipment is used to isolate the fault source and reduce the subsequent impact of the fault on the power grid, such as circuit breakers. Active stability control can start from faults and disturbance events, by taking control measures to trip the switch, integrating and intelligentizing the switching process. Preventing collapse involves the last line of defense, as some of the new energy sources are distributed microgrids with independent operating capabilities. By combining the main grid and microgrid decoupling, the scope of decoupling can be improved.
The demand for dynamic reactive power compensators, harmonic filters, and other components increases as the proportion of new energy increases. As mentioned earlier, new energy generation is prone to reactive power imbalance and harmonic problems. Therefore, as the proportion of new energy increases, the demand for reactive power compensators and harmonic filters to handle this problem will increase. The mainstream of reactive power compensation devices can be divided into two types: SVC and SVG. Among them, SVG has the advantages of adapting to low voltage, higher safety, small harmonic effects, and can suppress system harmonics. Therefore, it is more suitable for power systems with an increasing proportion of new energy. The working principle of SVG is to control the generation and absorption of reactive power by controlling the compensation current.
3) Intelligent power system
The purpose of the intelligent reform of the new power system is to improve the comprehensive utilization efficiency of energy, improve the reliability of power supply, and promote the utilization of new energy. The measure is to enable the diverse interaction of sources, storage, and grid loads in the power system, forming a coordinated organic ecosystem.
Specifically, the construction of smart grids can be divided into control type intelligence and collection type intelligence.
Control intelligence includes three parts: intelligent distributed distribution automation construction, demand side response of electricity load, and distributed energy. 1. The construction of distributed distribution automation mainly aims to achieve protection and control of the distribution network. Through relay protection automatic devices, the status information of the distribution network's lines or equipment can be detected. If a fault occurs, it can quickly diagnose and locate the fault, thereby quickly isolating the faulty section of the distribution network line. 2. Demand side response is to change the inherent electricity consumption habits of power users, reducing deviations between the electricity load curve and the power generation output curve. This part is actually an intelligent reform that connects the power supply side and the load side. 3. Distributed energy regulation (virtual grid) is a power coordination and management system that utilizes advanced information and communication technology and software systems to aggregate and optimize distributed power sources, energy storage systems, controllable loads, electric vehicles, and other decentralized control systems. It serves as a special power plant to participate in the power market and grid operation. Its composition includes a distributed power monitoring master station, a distributed power monitoring substation, a distributed power monitoring terminal, and a communication system.
The intelligent construction of collection includes advanced metering and smart grid big video applications. 1. The foundation of advanced metering is smart meters, which meet the needs of intelligent electricity consumption and personalized customer service by collecting electricity consumption information. On the enterprise side, smart meters collect electricity consumption information from industrial customers, providing support for energy efficiency management for enterprises; On the residential side, smart meters are like power grid routers, which can provide users with key electricity and price information to promote optimized electricity consumption, which can also drive the development of demand side response. 2. The application of smart grid big video is mainly to replace manual inspection and monitoring, thereby reducing the use of manpower and providing safety and reliability.
The construction of a new power system is a long-term process and a wide-ranging and profound transformation in the field of energy and electricity. The "new" of the new power system not only refers to the "new" in form, but also to a series of innovations in the power system, including traditional power sources, power grids, electricity consumption, energy storage and other innovations, as well as technological and management innovations.
