At present, China has become the world’s largest energy consumer, but due to the late start of power grid construction, there is a certain gap in economic and living aspects compared to other developed countries; At the same time, changes in the power grid structure also affect the size of power generation capacity and the improvement and stability of voltage levels. The research on this topic contributes to solving current power grid planning problems and has profound theoretical value.
1. Energy storage power supply and grid dispatch coordination system
In order to meet the safe operation of the power grid within the capacity and temperature range of energy storage devices, it is necessary to configure and optimize control them reasonably. A coordinated control system based on state space model will be introduced, and a mathematical model of the system will be established to achieve the scheduling problem of the system.
(1) The Analytic Hierarchy Process (AHP) is one of the effective tools for solving complex system descriptive planning research. It transforms multi-objective decision-making problems into a composite of single criteria and multiple options. By decomposing the factors at each level and giving weight values for each indicator, several evaluation matrices are combined to form a fuzzy network with multiple inputs and single variables. After gaining a profound understanding of the problem through the use of Analytic Hierarchy Process, this method has become an important part of the algorithm used in this article.
(2) The application and development prospects of particle swarm optimization algorithm. Due to the immaturity of current power industry technology and its high computational complexity, the focus of this chapter is on how to utilize the advantages of graphical software and numerical computers to solve multi parameter problems.
2. Operation mode of energy storage power supply and grid dispatch coordination system
In order to improve the coordinated control effect between energy storage power sources and power grid scheduling, it is necessary to establish certain constraints and optimize the operation mode of the system.
(1) Coordinated control requires an increase in energy management and load balancing requirements for the system when the capacity and scale of energy storage devices are constant. Under the premise of ensuring the safe and stable operation of the system, a comprehensive analysis of the entire system should be conducted to ensure its good flexibility, economy, reliability, etc.
(2) The goal of coordinated control is to adopt different control methods for different operating conditions under the constraint of energy storage equipment capacity. When the power frequency in the system is greater than the maximum limit value, centralized regulation shall be adopted; When the low-frequency signal in the system exceeds the critical value, priority should be given to the dispersed peak shaving method. If we want to fully leverage the advantages of distributed power generation and renewable energy, we need to reduce the range of load fluctuations to achieve coordinated operation between the two. So it is necessary to establish a scheduling controller that can automatically adjust according to changes in demand.
(3) The design principles of algorithms and the simplification of programs. For traditional optimization problems, the assumption of the model is usually made first and then solved, but this approach often increases the computational workload, so it must be solved through simplified mathematical tools.
3. Factors affecting the coordination system between energy storage power sources and power grid dispatch
In the process of coordinated control between energy storage power sources and the power grid, the main factors affecting the system are:
(1) Load characteristics. In actual operating conditions, when the capacity and frequency of the energy storage power supply are the same, the amplitude of its output power is fixed; When the load changes, the input active and reactive power will vary with the fluctuation of voltage. Therefore, in order to achieve stable and safe power supply to the power system, it is necessary to carry out reasonable planning and design.
(2) Technical level. Due to the different economic development conditions in different regions, the demand for electricity is not entirely the same. For some developed coastal cities, their power grid construction is relatively complete and can meet the electricity requirements of users. On the contrary, the construction of power grids at the city and county levels in many places is lacking.
(3) Equipment performance. If we want to improve the efficiency and stability of the entire system, we must consider the interference of various electrical quantities.
4. Design of Energy Storage Power Supply and Grid Dispatching Coordination Control System
At present, the main power generation method used in China’s energy storage system is the operation mode of thermal power units driving the power grid, which includes photovoltaic, hydropower, wind farms, and tidal turbines driven by thermal power units. Due to the small power fluctuation of wind turbines, the utilization rate of wind energy resources is high, and it can effectively reduce the peak valley difference of the power grid, improving the stability and reliability of the power grid. However, in the actual scheduling process, due to the influence of various factors and different operating conditions, the required power supply cannot be exactly the same. Therefore, when scheduling power supply, it is not possible to schedule it solely based on a single capacity. It is necessary to make reasonable arrangements and coordinate control based on specific situations.
4.1 Energy storage power sources and grid scheduling benefits
For the coordinated control system between energy storage system and power grid scheduling, its main task is to meet the constraints of control objects (thermal power, renewable energy, etc.), so that the entire scheduling process can achieve both energy-saving and environmental protection requirements:
(1) Reduce operating costs. On the basis of ensuring the objective function, corresponding optimization algorithms are adopted for different operating conditions to minimize the installed capacity and total energy loss of power generation and transmission equipment.
(2) Increase the load rate. When the capacity of the energy storage device used is less than the maximum required power value, it is necessary to consider the consumption of other power sources in the grid, and achieve the “how much load” through reasonable planning and design.
(3) Reduce waste and pollution of electric energy. Due to the increasingly severe environmental problems, the country advocates green transportation, therefore, it is necessary to vigorously develop new clean and low-carbon lifestyles, such as new energy sources such as solar and wind energy; As a new type of renewable resource, wind power can effectively solve the serious problems of air pollution and soil erosion.
4.2 System Implementation
Based on the analysis and research above, the functions of the energy storage scheduling coordination control system include:
(1) Manage batteries. On the premise of safe and stable operation of the full factory battery, make its charging and discharging process more reliable, and make the network structure of the system simpler and easier to implement.
(2) Balanced control of batteries. When the system load changes, the regulating controller can make corresponding adjustment measures based on the load changes to ensure the stability and economy of the entire power system.
(3) Protection and filtering of inverters. Inverter is a nonlinear component whose output characteristics are related to the parameters of its power frequency rectification and filter. Therefore, it is necessary to design a current transformer with strong filtering ability and fast dynamic response to ensure that the switching tube can act accurately in the event of a fault and provide good isolation conditions for the inverter. At the same time, it is necessary to consider the voltage resistance performance of the device, such as using low resistance materials and chips with low dielectric loss. (4) Selection of auxiliary equipment. To improve the reliability and flexibility of the system, it is necessary to choose components with high power density, such as capacitors, inductors, etc.
4.3 Power grid planning
From the perspective of power supply reliability and economy, the establishment of energy storage systems must meet the following conditions:
(1) The frequency of the power grid is within the allowable range. Due to significant power fluctuations in the power grid, voltage stability is required.
(2) The changes in network topology should be minimal. In order to ensure the charging and discharging of energy storage devices under different loads, it is necessary to choose appropriate primary and secondary current carrying components.
(3) In the main circuit, there should be sufficient capacity to balance the load of the entire communication line. When the main wiring of the power grid fails, it can be quickly restored through backup power sources. At the same time, it also reduces interference and impact on other devices.
(4) Has high anti-interference ability. When there are many branches in the power grid, it will lead to a decrease in the stability of the entire distribution automation system. If the sub wiring is incorrect, it can cause damage to the sub busbar or distribution equipment. So it should be avoided as much as possible. In addition, it should be noted that there may be some unstable factors on the DC bus, such as a large number of inductive appliances on the bus and abnormal rotor excitation current. These issues will have adverse consequences on power quality. When designing for this, it is necessary to fully understand various situations and take corresponding measures.
4.4 Distribution Transformers
Distribution transformers are one of the main electrical equipment in substations, responsible for the transformation and transmission of electrical energy. Its basic function is to convert voltage, converting AC power in the power system into DC power, and supplying power to the load with the high-voltage AC power after voltage reduction. In terms of power grid structure, the role of distribution transformers is very important, and their performance directly affects the quality and efficiency of the economic operation of the entire power grid.
(1) Isolate the fault. When accidents such as power frequency interference and unsafe operations occur, corresponding protective devices need to be configured to ensure the normal operation of users.
(2) Control and regulation. Timely switch or cut off power frequency wiring according to load changes to improve the reliability of the power grid; When a power outage occurs, it automatically cuts off and sends instructions to trip the circuit breaker and resume production.
(3) Maintenance. Install a status monitor on the main switch to monitor the closing status of the main switch at any time and remotely monitor it online. By observation, it is possible to understand the on/off current of the main switch and whether there is any abnormal heating phenomenon. If a short circuit is found in the circuit or above, it is possible to replace the iron core immediately to prevent damage.
4.5 Voltage regulation
When the output power of the power grid exceeds the demand of the load, or the capacity of the power system is less than the energy of the power source, different adjustment methods are adopted to ensure that it is within a safe range while meeting the control objectives, in order to achieve the best dynamic characteristics.
(1) Changing the regulation method to adjust the voltage appropriately is the most common regulation method and currently the most widely used form of regulation. For example, changing high current AC voltage regulation to DC voltage regulation can improve the transmission capacity of the power grid and improve voltage stability.
(2) Reasonably choose the adjustment time and frequency to achieve the best adjustment effect. Due to the uncertainty of loads in practice, it is necessary to flexibly configure the parameters and corresponding proportional relationships of various power sources according to specific situations, usually including maximum load fluctuations, changes in power frequency ratio, and the impact of active and reactive power compensation. These factors will all exert a certain force on the stability of voltage, so it is necessary to consider their interactions, as well as their connections and constraints. Additionally, it should be noted that in order to achieve the optimal number of switch groups, it is necessary to increase or decrease the number of controllers.
4.6 Determination of Energy Storage System Parameters
Due to the difference between energy storage systems and other power generation technologies, they have the characteristics of high energy density, high power, and small size. Therefore, in the design, these characteristics need to be taken into consideration.
(1) Capacity: The capacity of an energy storage system is a finite order of magnitude, mainly estimated based on its own maximum output power. When the operating time of energy storage equipment exceeds its rated working current, corresponding protective measures should be taken to prevent serious accidents from occurring; When the stored voltage is less than a certain value, it should be allowed to charge or discharge to ensure continuous power supply under normal load.
(2) Temperature: In the entire system, there are significant influencing factors on changes in operating conditions, so there are also high requirements for controlling operating conditions; For power electronic devices, it is necessary to meet the performance indicators of steady-state and thermal stability.
(3) Load: As the charging and discharging process of the battery is related to the grid connection, it is necessary to fully utilize the charging and discharging capacity of the battery to withstand greater pressure and corona. At the same time, it is also important to note that electric arcs should not be generated directly to prevent ignition and damage. If it cannot be completely avoided, appropriate safety measures should also be taken.
5. Conclusion
In today’s world, energy and environmental problems are becoming increasingly serious. In order to cope with this severe situation and challenge, China vigorously develops new energy generation technology. Energy storage systems, as an important component of the new power industry, play a huge role in improving the safe operation level of the power grid and improving economic benefits; This article briefly analyzes and studies the models in the current energy storage scheduling coordination control system, and proposes a multi-objective optimization scheduling method based on state feedback control algorithm.