Load side energy storage cooperation voltage control model and strategy

Abstract

The invention discloses a load side energy storage cooperative voltage control model and strategy, which takes a PQ node model as an equivalent model of an energy storage access power distribution network system, analyzes an energy storage droop control strategy, controls an output link of energy storage and further controls output power during energy storage grid connection so as to achieve a control effect of system voltage quality. Comprising a PQ control strategy and a droop control strategy, the PQ control strategy achieves voltage control through adjustment of active power and reactive power, and the droop control strategy simulates the similar frequency of a traditional generator and the relation between the active power amplitude and the reactive power and the relation between the voltage amplitude and the reactive power. Stable frequency and voltage output are obtained through P-f droop control and Q-V droop control respectively, and active power and reactive power output by a distributed power supply in the system are controlled respectively. The method has the advantages of being simple, reliable, adjustable and controllable in voltage and good in voltage control quality.

Description

Technical Field

[0001] The present invention belongs to the technical field of load-side energy storage coordinated voltage quality control in distribution networks, and specifically relates to a load-side energy storage coordinated voltage control model and strategy. Background Art

[0002] With the steady improvement of the global economy and the rapid development of the power industry, while the total electricity consumption in various countries has increased significantly, the difference between the peak and valley of power load has also been expanding, increasingly highlighting the imbalance of power supply and demand. As an important technical support for energy transformation, energy storage technology can effectively solve the contradiction between power grid supply and demand. Among them, load-side energy storage is widely used in distribution networks. It can be used as an uninterruptible power supply to provide power support for important loads, and participate in demand response to reduce load-side electricity costs, improve system power utilization, reduce network losses, and improve power quality.

[0003] In the actual operation of the power grid, the distribution network has problems such as voltage fluctuation, voltage deviation, and harmonics. These problems will affect the stable operation of the user's electrical equipment, so it is necessary to study and control the voltage quality. Energy storage technologies such as battery energy storage and supercapacitor energy storage can store excess electrical energy and release it when the load is large or unstable, so as to improve the stability and voltage quality of the distribution network. In order to effectively link them together, it is necessary to consider the voltage control model and strategy of load-side energy storage coordination.

[0004] The widespread application of distributed energy storage on the load side can effectively solve the problems of randomness and large system load fluctuations caused by distributed power sources, while also reducing line losses and system investment pressure, and improving the peak-shaving and valley-filling capabilities of the distribution network. At present, the total installed capacity of load-side energy storage is relatively small, and it is still in its infancy. However, with the continuous maturity of technology, the corresponding costs are also continuously reduced, and the development prospects are broad. Load-side energy storage technology faces the following challenges in the process of development:

[0005] (1) In terms of the configuration of energy storage systems on the load side of the distribution network, in order to ensure economy, it is necessary to obtain the optimal configuration of the energy storage system, but there is currently no universal and effective economic model for load-side energy storage systems;

[0006] (2) Regarding the research on the coordinated control of load-side energy storage and distribution network voltage quality, there is currently no accurate model for energy storage access to the distribution network, nor an effective control strategy.

[0007] In order to solve the above problems, it is necessary to develop a load-side energy storage coordinated voltage control model and strategy. Summary of the invention

[0008] The purpose of the present invention is to overcome the deficiencies of the prior art and to provide a load-side energy storage coordinated voltage control model and strategy that is simple and reliable, has adjustable and controllable voltage, and has good voltage control quality.

[0009] The purpose of the present invention is achieved as follows: a load-side energy storage coordinated voltage control model and strategy, using the PQ node model as an equivalent model of the energy storage access distribution network system, and analyzing the energy storage droop control strategy, controlling the output link of the energy storage and then controlling the output power when the energy storage is connected to the grid, so as to achieve the control effect of the system voltage quality, including two steps: PQ control strategy and droop control strategy.

[0010] Furthermore, the PQ control strategy is to control the voltage by adjusting the active power and reactive power, and the output active power and reactive power are their reference values ​​P ref and Q ref , the power given value is subtracted from the measured value, and the current reference signal i is obtained through the proportional integral controller dref and i qref , thereby controlling the constant power output of distributed power sources, including establishing a PQ node model and using the PQ node output to control the voltage.

[0011] Furthermore, the establishment of the PQ node model and the use of the PQ node output to control the voltage are specifically as follows: the output voltage is converted from a three-phase static coordinate system to a rotating two-phase coordinate system by transformation, and the active and reactive power in the three-phase static coordinate system can be expressed as follows:

[0012] P=u a i a +u b i b +u c i c ;

[0013]

[0014] The dq rotation coordinate system output by park transformation is as follows:

[0015]

[0016]

[0017] By setting the output active power and reactive power, the reference current in the two-phase coordinate system can be calculated as shown in the following formula:

[0018]

[0019] The reference current is processed by the current inner loop to output the voltage reference value, which is inverted into the abc coordinate form through park transformation, and then modulated to output a three-phase modulation wave of the corresponding frequency.

[0020] Furthermore, the droop control strategy is to simulate the relationship between frequency and active power, and voltage amplitude and reactive power similar to that of a traditional generator as a control method, and to obtain stable frequency and voltage outputs through Pf droop control and QV droop control, respectively, to control the active and reactive power output of the distributed power sources in the system.

[0021] Furthermore, the method of obtaining stable frequency and voltage output through Pf droop control and QV droop control is as follows: in the load-side energy storage network, the system voltage quality is adjusted by controlling the stable output of power; when the system voltage and frequency are reduced, the node output voltage is increased by reducing the output active or reactive power, and the voltage of the distribution network system is regulated.

[0022] Due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] (1) The present invention uses the PQ node model as an equivalent model of the energy storage access distribution network system, and analyzes the energy storage droop control strategy to control the output link of the energy storage and then control the output power of the energy storage when it is connected to the grid, so as to achieve the control effect of the system voltage quality, support the stable operation of the power grid and respond to emergencies, reduce the losses caused by power outages, and thus improve the stability and reliability of the distribution network;

[0024] (2) The present invention performs dual control through the PQ control strategy and the droop control strategy, which can realize dynamic regulation and stabilization of voltage, effectively solve the problem of excessively high or low voltage, reduce the impact of voltage fluctuations on user equipment, and thus improve the voltage quality of the distribution network;

[0025] (3) The present invention can reduce the loss and load of electrical equipment by improving the voltage quality, reduce equipment failures caused by excessively high or low voltage, and thus extend the service life of the equipment;

[0026] (4) The present invention will improve users’ satisfaction with power services and user experience by optimizing voltage quality and power stability;

[0027] In general, the present invention has the advantages of being simple and reliable, having adjustable and controllable voltage, and having good voltage control quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the control method of the present invention.

[0029] Figure 2 It is a control principle diagram of the PQ control strategy of the present invention.

[0030] Figure 3 It is a droop characteristic curve diagram of the droop control strategy of the present invention. DETAILED DESCRIPTION

[0031] To explain, the distribution network is affected by load-side fluctuations, and there are a large number of distributed power sources in the system that affect the power quality of the power grid. The analysis of the system voltage quality can be considered from the active power P, reactive power Q, voltage amplitude V, and voltage angle θ contained in the node, and is divided into PQ nodes, PV nodes, and Vθ nodes. The system can select strategies based on the selection of different nodes to achieve effective control of voltage quality. The present invention specifically adopts the PQ node.

[0032] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0033] like Figure 1 , Figure 2 and Figure 3 As shown, the present invention provides a load-side energy storage coordinated voltage control model and strategy, takes the PQ node model as the equivalent model of the energy storage access distribution network system, and analyzes the energy storage droop control strategy, controls the output link of the energy storage and then controls the output power when the energy storage is connected to the grid, so as to achieve the control effect of the system voltage quality, including two steps: PQ control strategy and droop control strategy.

[0034] The PQ control strategy is to control the voltage by adjusting the active power and reactive power. The output active power and reactive power are their reference values ​​P and ref and Q ref , the power given value is subtracted from the measured value, and the current reference signal i is obtained through the proportional integral (PI) controller dref and i qref , thereby controlling the constant power output of distributed power sources, including establishing a PQ node model and using the PQ node output to control the voltage.

[0035] Among them, the proportional integral (PI) controller is a commonly used feedback controller, in which the proportional control of the proportional part (P) changes the control amount in proportion to the current error value (the difference between the set value and the actual value), can respond to the error quickly, and adjust the distribution network system in the direction of reducing the error. However, a single proportional control may have a steady-state error, and after the system is stable, there is still a deviation between the actual value and the set value; the integral control of the integral part (I) operates on the integral of the error to eliminate static errors. As time goes by, even if the error is very small, the integral term will continue to accumulate and continuously adjust the control amount until the steady-state error is zero; therefore, the combination of the two can enable the distribution network system to respond to errors quickly and ultimately eliminate steady-state errors.

[0036] The PQ node model is established, and the voltage is controlled by using the PQ node output. Specifically, the output voltage is converted from the three-phase static coordinate system to the rotating two-phase coordinate system by transformation. The active and reactive power in the three-phase static coordinate system can be expressed as follows:

[0037] P=u a i a +u b i b +u c i c ;

[0038]

[0039] The dq rotation coordinate system output by park transformation is as follows:

[0040]

[0041] By setting the output active power and reactive power, the reference current in the two-phase coordinate system can be calculated as shown in the following formula:

[0042]

[0043]

[0044] The reference current is processed by the current inner loop to output the voltage reference value, which is inverted into the abc coordinate form through park transformation, and then modulated to output the three-phase modulation wave of the corresponding frequency, which is fed back to the power grid to realize the control of the power grid voltage.

[0045] PQ control includes active power (P) control and reactive power (Q) control. P control mainly adjusts the output of the inverter so that the distributed power source can output according to the given active power instruction. For example, in a photovoltaic power station, the output value of active power is set according to the conditions such as light and load demand. The inverter adjusts its own output according to this set value to ensure that the active power output to the grid or local load meets the requirements. Q control adjusts the output of reactive power. Through PQ control, the distributed power source can provide or absorb reactive power to the grid, thereby adjusting the voltage of the grid. For example, when the grid voltage is low, the distributed power source can output reactive power to increase the voltage.

[0046] The droop control strategy is to simulate the relationship between frequency and active power, voltage amplitude and reactive power similar to that of traditional generators as a control method, and obtain stable frequency and voltage output through Pf droop control and QV droop control respectively, and control the active power and reactive power output of distributed power sources in the system respectively. This control method can control the active power and reactive power output of distributed power sources in the system respectively, and realize the adjustable and controllable power grid system on a stable basis, which is simple and reliable.

[0047] Droop control is based on simulating the droop characteristics of a conventional synchronous motor, for which the frequency decreases when the active power increases and the voltage decreases when the reactive power increases.

[0048] The specific method of obtaining stable frequency and voltage output through Pf droop control and QV droop control is as follows: in the load-side energy storage network, the system voltage quality is adjusted by controlling the stable output of power; when the system voltage and frequency decrease, the node output voltage is increased by reducing the output active or reactive power, and the voltage of the distribution network system is regulated.

[0049] In summary, PQ control accurately controls the active power and reactive power output of distributed power sources, and droop control realizes automatic distribution and adjustment of power through the droop characteristic curve. PQ control and droop control work together. PQ control is used when the system is operating normally to provide stable active power and reactive power supply to the power grid according to the predetermined power. When the system fails or the load changes significantly, the droop control adjusts the power output according to its own droop characteristics, thereby maintaining the frequency and voltage stability of the system and realizing reasonable power distribution in the multi-power system.

[0050] In summary, the coordinated control of voltage quality based on load-side energy storage will further improve the operation mode of the distribution network, further enhance the controllability of voltage quality, and thus effectively improve voltage stability.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A load-side energy storage coordinated voltage control model and strategy, characterized by: The PQ node model is used as an equivalent model of the energy storage access distribution network system, and the energy storage droop control strategy is analyzed to control the output link of the energy storage and then control the output power of the energy storage when it is connected to the grid, so as to achieve the control effect of the system voltage quality, including two steps: PQ control strategy and droop control strategy.

2. The load-side energy storage coordinated voltage control model and strategy according to claim 1 is characterized by: The PQ control strategy is to control the voltage by adjusting the active power and reactive power. The output active power and reactive power are their reference values ​​P and ref and Q ref , the power given value is subtracted from the measured value, and the current reference signal i is obtained through the proportional integral controller dref and i qref , thereby controlling the constant power output of distributed power sources, including establishing a PQ node model and using the PQ node output to control the voltage.

3. The load-side energy storage coordinated voltage control model and strategy according to claim 2 is characterized in that: The establishment of the PQ node model and the use of the PQ node output to control the voltage are specifically as follows: the output voltage is converted from the three-phase static coordinate system to the rotating two-phase coordinate system by transformation, and the active and reactive power in the three-phase static coordinate system can be expressed as follows: P=u a and a +in b and b +in c and c ; The dq rotation coordinate system output by park transformation is as follows: By setting the output active power and reactive power, the reference current in the two-phase coordinate system can be calculated as shown in the following formula: The reference current is processed by the current inner loop to output the voltage reference value, which is inverted into the abc coordinate form through park transformation, and then modulated to output a three-phase modulation wave of the corresponding frequency.

4. The load-side energy storage coordinated voltage control model and strategy according to claim 1 is characterized by: The droop control strategy is to simulate the relationship between frequency and active power, voltage amplitude and reactive power similar to that of traditional generators as a control method, and obtain stable frequency and voltage output through Pf droop control and QV droop control respectively, and control the active and reactive power output of distributed power sources in the system respectively.

5. The load-side energy storage coordinated voltage control model and strategy according to claim 4 is characterized in that: The method of obtaining stable frequency and voltage output through Pf droop control and QV droop control is specifically as follows: in the load-side energy storage network, the system voltage quality is adjusted by controlling the stable output of power; when the system voltage and frequency are reduced, the node output voltage is increased by reducing the output active or reactive power, and the voltage of the distribution network system is regulated.

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