Research on the best use of energy storage to impr

2022-07-26
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Research on using energy storage to improve the stability of power systems containing wind power

wind power generation has become one of the most popular renewable energy sources in the world and an important part of future energy strategies of various countries because of its wide distribution of resources, large storage capacity, friendly environment and mature development technology. The large-scale development of wind power has become a mainstream trend in the global energy development. However, different from the operating characteristics of conventional synchronous generator units, which are well known by researchers, wind power generation has strong random, weak controllable and weak immunity characteristics. Large scale wind power will cause substantial changes in the operating characteristics of the power system, and the security and stability of the power system containing large-scale wind power will be seriously threatened. On the other hand, in terms of adhering to the established layout in the past few years, the considerable development of materials, chemistry and other disciplines has promoted the significant progress of large-scale energy storage technology. China, the United States and other countries have established a large number of demonstration bases for joint operation of energy storage and new energy. Large scale wind power and large-scale energy storage and utilization will become one of the main features of future power. How to use large-scale energy storage technology to effectively improve the operating characteristics of wind power system and improve the security and stability of wind power system will be an important topic in the future wide application of energy storage and the process of large-scale wind power and consumption, and it is also an urgent problem to be studied and solved

2. Problems and significance solved in the paper

the paper mainly solves how to use energy storage technology to improve the security and stability of wind power system. This paper expounds the security and stability problems existing in the wind power system from three aspects: frequency stability, low voltage ride through and power angle stability of the wind power system. According to the existing application of energy storage technology, it puts forward a solution to improve the security and stability of the wind power system by using energy storage technology. Three research points are selected: virtual inertia compensation and fast frequency response of wind power system, low voltage ride through under fault conditions, and analysis and control of system damping characteristics. The mechanism of system stability weakening after large-scale wind power consolidation is analyzed, and an energy storage controller for system stability improvement is designed, which effectively improves the stability characteristics of wind power system and is conducive to the consolidation and absorption of large-scale wind power

3. Key content of the paper

3.1 research on virtual inertia compensation and fast frequency response of wind farm

variable speed constant frequency wind turbine rotor kinetic energy is "isolated" from electricity by frequency converter, making its inertia contribution to electricity almost zero. With the continuous improvement of wind power permeability, the problem of power frequency stability has also become prominent. Therefore, wind power industry guidelines in various countries clearly require that wind farms should have the ability to participate in system frequency adjustment. Due to the large number of units in the wind farm and the inconsistent operating conditions among units, the control at the wind farm level is still very difficult. Based on this, this paper puts forward the idea of using energy storage to compensate the virtual inertia of wind farm

firstly, on the basis of defining the virtual inertia of the wind power energy storage combined operation system, this paper formulates a reasonable protection and maintenance scheme, and analyzes that the minimum energy storage capacity required to make the wind farm have the inertia response capacity similar to that of the synchronous generator with the same capacity is 5% of the rated installed capacity of the wind farm. Furthermore, the wind power energy storage controller is designed based on the fuzzy logic reasoning principle, which effectively reduces the maximum output power of energy storage in the process of frequency response, and makes the energy storage capacity required by the wind farm reach the minimum energy storage capacity analyzed above. Finally, the simulation results on a Northwest Power System in China show that the proposed control strategy can effectively compensate the virtual inertia of the wind farm, coordinate the energy exchange between the wind power storage system and the conventional power, make the wind farm respond to the frequency change of the system quickly, and is conducive to the frequency stability of the power system with large-scale wind power

Figure 1 frequency response of the system when the load suddenly increases

Figure 2 frequency response of the system when the load suddenly drops

3.2 stability characteristic analysis and stability measures research during low voltage ride through of the wind farm

as shown in Figure 3, when the three-phase metal short-circuit fault occurs, the voltage at the short-circuit point is zero, and the coupling effect between the wind power system and the external power supply is zero, the two will become two completely independent systems. The operating frequency of external power is maintained at 50Hz due to the support of conventional synchronous generator. The wind farm loses the support of external electricity and becomes a relatively independent island power. If the wind farm must inject reactive current into the system during the low-voltage ride through according to the guidelines, the frequency instability of the wind power system may occur, which may lead to the failure of the low-voltage ride through of the wind farm

in view of this phenomenon, this paper analyzes the causes of this phenomenon and its influence on the low-voltage ride through characteristics of wind farms from the perspective of the limited transmission current characteristics of lines. 1. The circular arc synchronous gear belt further establishes the state space model of the system under the low-voltage ride through of the wind farm, calculates the distribution law of the system eigenvalues under this operating state, and effectively reveals the formation mechanism of the system frequency instability. Then, an energy storage controller is designed to improve the distribution of eigenvalues of the system, and some suggestions on the selection of energy storage devices and capacity configuration are given. The research results show that the energy storage device improves the injected current characteristics during the fault of the wind farm, can effectively stabilize the frequency at the outlet bus of the wind farm, enhance the immunity of the wind turbine under fault conditions, and then maintain the frequency stability during the low voltage ride through period of the wind power system

Figure 3 Schematic diagram of system analysis after wind farm failure

3.3 mechanism analysis and damping control of high-frequency oscillation in wind farm

wind power accidents at home and abroad show that wind power weak link system is prone to power oscillation with a frequency of several to tens of Hertz in case of disturbance. Due to the obvious difference between the operation characteristics of doubly fed wind turbine and conventional synchronous generator, the cause of its oscillation can not be fully explained by the small disturbance oscillation mechanism of traditional synchronous generator. Considering that the doubly fed wind turbine mainly operates synchronously with the power through the phase-locked loop, the dynamic characteristics of the phase-locked loop will seriously affect the interaction between the wind turbine and the power. Based on the analysis model of doubly fed wind turbine considering the dynamic characteristics of phase locked loop, this paper studies the eigenvalue distribution of wind turbine after incorporating different strong and weak current under different operating conditions. It is found that phase locked loop oscillation is one of the main reasons for small disturbance instability of doubly fed wind turbine in weak current

to solve the problem of PLL oscillation instability, similar to the complex torque analysis of electromechanical oscillation mode of synchronous generator, the complex torque analysis model of wind turbine PLL loop is established. The influence of short-circuit ratio of wind farm access point and phase-locked loop parameters on system stability is analyzed. To solve the problem that the damping level of PLL loop is not enough under weak current conditions, similar to the power system stabilizer of conventional synchronous generator sets, an energy storage damping controller based on phase compensation is proposed, which can effectively suppress the high-frequency power oscillation phenomenon when large-scale wind power is connected to power through long-distance lines

Figure 4 under different short-circuit ratios, Bode diagram of open-loop loop loop of PLL circuit

Figure 5 wind turbine PLL damping controller

3.4 analysis of interaction law between wind turbine and conventional unit and how damping control

wind turbine and affect the operation characteristics of conventional synchronous unit deserve close attention of researchers. Based on the Heffron Philips model of double machine infinite bus system with wind power and conventional synchronous generator set, this paper analyzes and finds that the wind turbine PLL affects the electromagnetic torque of conventional synchronous generator set through three coupling branches, explores its action mechanism and influence law on the electromagnetic torque of conventional synchronous generator set, and finds that the wind turbine may deteriorate the damping characteristics between conventional generator sets. To solve this problem, based on the principle of transient energy attenuation, an energy storage controller is designed to improve the damping characteristics of conventional units. It can effectively damp the power oscillation between conventional synchronous units under various operating conditions of the system, with obvious effect and good adaptability

Figure 6 Heffron Philips model of single machine infinite bus system with wind power

figure 8 energy storage damping controller based on energy function

4. The main innovation points of the paper

1) determine the energy storage capacity demand for virtual inertia compensation of wind farm, and propose an energy storage frequency modulation strategy for virtual inertia compensation and fast frequency response of wind farm, which effectively improves the frequency characteristics of wind power system

2) it is found that the wind farm injects reactive current into the system during low voltage ride through according to the guidelines, causing the wind power system to generate 7 The rear suspension is a whole connecting rod, which is designed to generate the formation mechanism of frequency instability and low voltage ride through failure. A wind farm stability controller based on energy storage is designed, and suggestions on energy storage device selection and capacity configuration are given

3) it is found that the PLL oscillation under weak current conditions is the formation mechanism of power oscillation of large-scale wind power transmitted through long-distance AC lines. Based on the principle of phase compensation, the PLL damping controller of wind farm under weak current conditions is designed by using the fast power response characteristics of energy storage

4) reveals the mechanism and law of doubly fed wind turbine affecting the electromagnetic torque of adjacent synchronous generator units through phase-locked loop. An energy storage damping controller based on transient energy attenuation is designed, which can effectively damp the power oscillation between conventional units

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