Network construction type energy storage variable power factor control method considering reduction of network loss demand

Abstract

The invention discloses a network construction type energy storage variable power factor control method considering reduction of a network loss demand, and the method comprises the steps: changing a control target of an energy storage converter: controlling the voltage of a DC bus through a chopper, controlling the power output of energy storage through the converter, designing a power synchronization link in the control of the converter, and controlling the power output of the energy storage through the converter; the inertia and damping characteristics are realized; an energy storage target power factor is determined according to system network loss, a virtual impedance value is calculated, corresponding voltage is compensated to a converter voltage control ring, and output power is adjusted. According to the invention, network construction transformation is carried out for traditional network following type energy storage, the target power is utilized to calculate the virtual impedance before the virtual impedance is fed to the voltage environment, the virtual impedance is matched with the internal potential dq-axis component, and the output power is adjusted, so that the wide-range operation capability of the energy storage power factor is improved, and the reduction of the system network loss is facilitated.

Description

Technical Field

[0001] The present application relates to the field of energy storage control technology, and in particular to a grid-type energy storage variable power factor control method that takes into account the need to reduce network losses. Background Art

[0002] As the penetration rate of clean energy increases, the proportion of grid-connected inverters continues to rise, and the inertia and damping of the power grid continue to decrease. This not only increases the safety risk of equipment, but also reduces the stability margin of the system. To address this problem, based on the characteristics of traditional synchronous generators, flexible regulation resources such as energy storage can be transformed to enhance the system's inertia capacity and damping level, giving it the ability to build a power grid.

[0003] However, the power change of the grid-type energy storage affects the voltage and current dual-loop input through the synthesized internal potential, and the regulation is not flexible enough, making it difficult to meet the distribution network's demand for reducing network losses by flexibly changing the generator power factor. Existing technologies often consider switching the control of the grid-type energy storage to grid-following control, or mixing multiple grid-following / grid-type energy storages to perform power regulation. However, grid-following control inevitably relies on the dynamic characteristics of the phase-locked loop, resulting in insufficient system inertia and poor anti-interference ability. Summary of the invention

[0004] In order to solve the problems of low inertia level and poor anti-interference ability of the original grid-following energy storage, poor current control ability of the existing grid-building energy storage, and inability to quickly adjust the power factor, the present application proposes a grid-building energy storage variable power factor control method that takes into account the need to reduce network losses. The present application performs grid-building transformation on traditional grid-following energy storage, and uses the target power to calculate the virtual impedance before feeding it into the voltage environment, and cooperates with the dq-axis component of the internal potential to adjust the output power, so as to improve the wide range operation capability of the energy storage power factor and help reduce system network losses.

[0005] This application is implemented through the following technical solutions:

[0006] A grid-type energy storage variable power factor control method considering the need to reduce network loss, the control method comprising:

[0007] Change the control target of the energy storage converter: control the DC bus voltage through the chopper, control the power output of the energy storage through the converter, and design the power synchronization link in the converter control to make it have inertia and damping characteristics;

[0008] The target power factor of energy storage is determined according to the system network loss, and the virtual impedance value is calculated from it. The corresponding voltage is compensated to the converter voltage control loop to adjust the output power.

[0009] In some embodiments, the power output of the energy storage is controlled by the converter, and a power synchronization link is designed in the converter control so that it has inertia and damping characteristics, specifically including:

[0010] The rotor swing equation of the synchronous generator is simulated by the converter, so that it has inertia and damping characteristics:

[0011]

[0012] θ=∫ωdt

[0013] Among them, J and D P are the inertia coefficient and damping coefficient of active power, K P and K Q are the droop coefficients of active power and reactive power, ω * and ω are the reference angular velocity and the actual angular velocity of the converter, respectively. * and P are the reference value and actual value of the energy storage output active power, θ is the internal potential phase, E* and E are the internal potential amplitude and the converter terminal voltage, respectively;

[0014] In converter control, when the active power output changes, the synchronous angular velocity of the virtual axis will also change, causing a change in the internal potential phase, thereby affecting the decomposition of the converter control command and power output.

[0015] In some implementations, the DC bus voltage is controlled by a chopper, and the control equation is:

[0016]

[0017] Among them, U dc is the actual value of DC bus voltage, i dc is the DC bus current, U dc * is the DC bus voltage reference value, i md is the modulation signal.

[0018] In some embodiments, the virtual impedance is equivalent to an impedance connected in series in the circuit, and the voltage drop across the impedance is:

[0019]

[0020] Among them, ΔU d , ΔU q are the d-axis and q-axis components of the voltage drop on the virtual impedance, i Ld 、i Lq are the d-axis and q-axis components of the converter output current, respectively, and R v , X v are virtual resistance and virtual reactance respectively;

[0021] The compensation voltage can be calculated based on the virtual resistance and the converter output current.

[0022] In some implementations, the virtual resistance is obtained as follows:

[0023] Determine a target power factor according to the system network loss requirement, and calculate a reactive power reference value according to the target power factor;

[0024] According to the equivalent circuit of series impedance, the calculation equation of energy storage output reactive power is obtained;

[0025] Substitute the reactive power reference value into the energy storage output reactive power calculation equation to calculate the virtual impedance.

[0026] In some implementations, the energy storage output reactive power calculation equation is:

[0027]

[0028] Among them, Q is the reactive power output of energy storage, E v is the voltage before the virtual impedance, X f is the filter reactance, X g is the grid reactance, R g Grid resistance, R f is the filter resistance, R v , X v are virtual resistance and virtual reactance respectively.

[0029] In the second aspect, the present application also proposes a grid-type energy storage variable power factor control system that takes into account the need to reduce network loss, and the control system includes:

[0030] A converter control unit, which controls the power output of the energy storage through the converter, and also realizes power synchronization through converter control, and has inertia and damping characteristics; the converter control unit determines the target power factor according to the system network loss, and calculates the virtual impedance value according to the target power factor, compensates the corresponding voltage to the converter voltage control loop, and adjusts the output power;

[0031] and a chopper control unit, wherein the chopper control unit controls the DC bus voltage through the chopper.

[0032] In some embodiments, the converter control unit comprises:

[0033] A virtual impedance loop, wherein the virtual impedance loop determines a virtual impedance value according to the target power factor, calculates a voltage drop on the virtual impedance according to the virtual impedance value and an output current of the converter, and compensates for an internal potential amplitude to obtain a voltage reference value;

[0034] A voltage control loop, wherein the voltage control loop controls the voltage reference value to obtain a current reference value;

[0035] And, a current control and signal modulation loop, which controls the current reference value, performs dq conversion in combination with the internal potential phase, and modulates to obtain a modulation waveform of the converter.

[0036] In some implementations, the internal potential amplitude and the internal potential phase are obtained by controlling the power outer loop.

[0037] In some implementations, the chopper control unit controls and modulates the DC bus voltage according to a reference value and an actual value of the DC bus voltage, and obtains a modulation waveform of the chopper.

[0038] The present application proposes a grid-type energy storage variable power factor control method that takes into account the need to reduce network loss. By transforming the traditional grid-type energy storage control and introducing virtual impedance to achieve variable power output of the grid-type energy storage, the output power can be flexibly adjusted through virtual impedance to meet the power requirements in various operating scenarios, thereby broadening the operating range of the grid-type energy storage power factor and reducing system network losses.

[0039] The present application proposes a grid-type energy storage variable power factor control method that takes into account the need to reduce network losses. Through virtual impedance control, it can achieve internal power balance and stable target power output, and has high engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The drawings described herein are used to provide a further understanding of the embodiments of the present application, constitute a part of the present application, and do not constitute a limitation on the embodiments of the present application. In the drawings:

[0041] Figure 1 This is a schematic diagram of the control system architecture proposed in the embodiment of the present application;

[0042] Figure 2 This is a control principle block diagram of the energy storage converter according to an embodiment of the present application;

[0043] Figure 3 This is the simulation result diagram of the traditional grid-type control strategy for 2MW power energy storage;

[0044] Figure 4 This is a simulation result diagram of the improved grid-type control strategy proposed in the embodiment of the present application for 2MW power energy storage. DETAILED DESCRIPTION

[0045] Hereinafter, the term "include" or "may include" used in various embodiments of the present application indicates the presence of the invented function, operation or element, and does not limit the addition of one or more functions, operations or elements. In addition, as used in various embodiments of the present application, the terms "include", "have" and their cognates are intended only to indicate specific features, numbers, steps, operations, elements, components or a combination of the foregoing items, and should not be understood as first excluding the presence of one or more other features, numbers, steps, operations, elements, components or a combination of the foregoing items or the possibility of adding one or more features, numbers, steps, operations, elements, components or a combination of the foregoing items.

[0046] In various embodiments of the present application, the expression "or" or "at least one of A or / and B" includes any combination or all combinations of the words listed at the same time. For example, the expression "A or B" or "at least one of A or / and B" may include A, may include B, or may include both A and B.

[0047] The expressions (such as "first", "second", etc.) used in the various embodiments of the present application may modify the various constituent elements in the various embodiments, but may not limit the corresponding constituent elements. For example, the above expressions do not limit the order and / or importance of the elements. The above expressions are only used for the purpose of distinguishing one element from other elements. For example, the first user device and the second user device indicate different user devices, although both are user devices. For example, without departing from the scope of the various embodiments of the present application, the first element may be referred to as the second element, and similarly, the second element may also be referred to as the first element.

[0048] It should be noted that if it is described that one component element is “connected” to another component element, the first component element may be directly connected to the second component element, and a third component element may be “connected” between the first component element and the second component element. Conversely, when one component element is “directly connected” to another component element, it can be understood that there is no third component element between the first component element and the second component element.

[0049] The terms used in the various embodiments of the application are only used to describe the purpose of specific embodiments and are not intended to limit the various embodiments of the application. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. Unless otherwise limited, all terms used here (including technical terms and scientific terms) have the same meaning as the meanings commonly understood by ordinary technicians in the field of the various embodiments of the application. The terms (such as the terms defined in the dictionary generally used) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or an overly formal meaning, unless clearly defined in the various embodiments of the application.

[0050] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with examples and drawings. The illustrative implementation scheme of the present application and its description are only used to explain the present application and are not intended to limit the present application.

[0051] Embodiment 1:

[0052] Grid-type energy storage is based on power decoupling control and has a wide power factor operating range, but it has problems such as low inertia level and poor anti-interference ability. Existing grid-type energy storage has a high inertia level and strong anti-interference ability similar to that of synchronous machines, but the power regulation method is relatively single, and is mainly used to meet the frequency regulation requirements of the power grid, resulting in its power control capability not being fully utilized. In response to this, this embodiment proposes a variable power factor control method for grid-type energy storage that takes into account the need to reduce network losses. This embodiment performs grid-type transformation on traditional grid-type energy storage, uses the target power to calculate the virtual impedance before feeding it to the voltage link, and cooperates with the internal potential dq-axis component to adjust the output power. This can broaden the operating range of the power factor of the grid-type energy storage and reduce system network losses, and has certain engineering application value.

[0053] The control method proposed in this embodiment includes the following steps:

[0054] Step 1: Change the control target of the energy storage converter: control the DC bus voltage through the chopper; control the power output of the energy storage through the converter, and design a power synchronization link in the converter control to give it inertia and damping characteristics to improve the stability of the energy storage.

[0055] The traditional energy storage chopper is used to control the power output of the energy storage to achieve unity power factor operation; the converter is used to stabilize the DC bus voltage and realize the transmission of generator power. This control target allocation is suitable for maximizing the power absorption from the energy storage unit and stably transmitting it to the grid side. However, it also loses some power control capabilities and cannot meet the requirements of grid frequency construction, inertia support, damping compensation, etc. In view of this, this embodiment changes the control target of the energy storage converter, controls the DC bus voltage through the chopper, and controls the power output of the energy storage through the converter.

[0056] This embodiment starts with the energy storage converter, and uses it to simulate the rotor swing equation of the synchronous generator, so that it has inertia and damping characteristics:

[0057]

[0058] θ=∫ωdt (2)

[0059] Among them, J and D P are the inertia coefficient and damping coefficient of active power, KP and K Q are the droop coefficients of active power and reactive power, ω * and ω are the reference angular velocity and the actual angular velocity of the converter, respectively. * and P are the reference value and actual value of the energy storage output active power, θ is the internal potential phase, E* and E are the internal potential amplitude and the converter terminal voltage, respectively.

[0060] In the control of the energy storage converter, when the active power output changes, the synchronous angular velocity of the virtual axis will also change, causing a change in the internal potential phase, thereby affecting the decomposition of the converter control instructions and power output, and ultimately achieving a balance between power generation and consumption.

[0061] The modified chopper control is used to maintain the stability of the DC bus voltage, and its control equation can be expressed as:

[0062]

[0063] Among them, U dc is the actual value of DC bus voltage, i dc is the DC bus current, U dc * is the DC bus voltage reference value, i md is the modulation signal.

[0064] If the DC bus voltage can be kept stable, the converter can be regarded as a voltage source with power support function, similar to a traditional synchronous generator.

[0065] Step 2: Determine the target power factor of the energy storage according to the system network loss, calculate the virtual impedance value, compensate the corresponding voltage to the converter voltage control loop, and adjust the output power.

[0066] Since the grid-type energy storage converter cannot directly control the active and reactive power through the dq axis current instructions like the traditional grid-type energy storage, this embodiment considers the voltage source characteristics of the grid-type converter and changes its output power characteristics by adjusting the virtual impedance.

[0067] When virtual impedance is not considered, the active and reactive output power of energy storage can be expressed as:

[0068]

[0069] Among them, δ is the power angle, is the line impedance angle from the converter port to the grid connection point, Z is the line impedance from the converter port to the grid connection point, U is the voltage at the grid connection point, E is the voltage at the converter port, R is the resistance from the converter port to the grid connection point, and X is the reactance from the converter port to the grid connection point.

[0070] Assuming that the line is highly inductive, the attack angle of the grid control tends to 0 after grid pre-synchronization, then equation (4) can be simplified as:

[0071]

[0072] From formula (5), it can be seen that if the impedance is inductive, the active power is mainly determined by the power angle, and the reactive power is mainly determined by the voltage difference between the grid connection point and the converter port voltage. When considering the virtual impedance for power correction, the virtual impedance can be equivalent to connecting an impedance in series in the circuit, and the voltage drop across it is:

[0073]

[0074] Among them, i Ld 、i Lq are the d-axis and q-axis components of the converter output current, respectively, and R v , X v are virtual resistance and virtual reactance respectively.

[0075] After the introduction of virtual impedance, the output reactive power of energy storage can be calculated based on the equivalent circuit of series impedance:

[0076]

[0077] Among them, E v is the voltage before the virtual impedance, Q v is the reactive power consumed on the virtual impedance, X f is the filter reactance, X g is the grid reactance, R g is the grid resistance, R f is the filter resistance.

[0078] Considering the output power limit, the active power can be expressed as:

[0079]

[0080] Where S is the apparent power.

[0081] To simplify the calculation, we can use the inductance coefficient k v Determine the relationship between virtual reactance and virtual resistance:

[0082] X v =k v R v (9)

[0083] Therefore, formula (7) can be simplified to v The quadratic equation of :

[0084]

[0085] In the formula, R gf =R g +R f , X gf =X g +X f After substituting the corresponding values, R can be calculated by the root-finding formula v .

[0086] The reference output power factor is determined according to the network loss requirement, and the reactive power reference value can be further calculated according to the impedance triangle, and then the virtual impedance is calculated by formula (10).

[0087] Compared with the previous problem that grid-type energy storage is difficult to reduce demand according to network losses and perform variable power factor operation, the control method proposed in this embodiment can achieve variable power output of grid-type energy storage by designing appropriate virtual impedance, meet the power requirements in various operating scenarios, thereby broadening the operating range of the power factor of the grid-type energy storage and reducing system network losses.

[0088] This embodiment also proposes a grid-type energy storage variable power factor control system that takes into account the need to reduce network loss, such as Figure 1 As shown, the control system proposed in this embodiment includes:

[0089] The converter control unit controls the power output of the energy storage through the converter; the converter control unit also achieves power synchronization through converter control, and has inertia and damping characteristics to improve the stability of the energy storage. The converter control unit can determine the target power factor according to the system network loss, thereby calculating the virtual impedance value, compensating the corresponding voltage to the converter voltage control loop, and adjusting the output power.

[0090] and a chopper control unit, which controls the DC bus voltage through the chopper.

[0091] Figure 2 In the system, the energy storage unit (i.e., energy storage unit), chopper, and converter are directly connected to the power grid. The DC bus voltage is controlled by the chopper control, and the converter control is used to synchronize with the power grid, and the energy storage converter is given inertia and damping characteristics similar to those of a synchronous machine. The phase and amplitude are generated by the power outer loop (active power outer loop and reactive power outer loop) to synthesize the internal potential. After the internal potential is synchronized with the grid voltage, its phase can be used for the dq conversion of the converter. In the figure, I Lb 、i oabc are the output current of the energy storage unit and the three-phase current of the converter port respectively; i Labc The three-phase current of the converter is filtered, i Ld and i Lq is its dq axis component; L f , L T, L g , C f , R f are the converter filter inductance, the inductance from the energy storage converter to the grid connection point, the transmission line inductance, the filter capacitor, and the damping resistor; ω and θ are the internal potential phase and angular velocity, respectively; S b1 and S b2 is the switching function of the IGBT in the energy storage chopper; L b and C b is the inductance and capacitance in the energy storage chopper; P * and P are the reference value and actual value of the energy storage output active power respectively; Q * and Q are the reference value and actual value of the reactive power output of the energy storage respectively; P GSC , P G They represent the active power generated by the converter and the active power transmitted from the grid to the grid connection point respectively; E* and E are the internal potential amplitude and the converter terminal voltage respectively.

[0092] Furthermore, the control system proposed in this embodiment also includes:

[0093] An active power outer loop, which is used to control the internal potential phase according to the active power reference value and actual value output by the energy storage;

[0094] And, a reactive power outer loop, which is used to control the internal potential amplitude according to the reactive power reference value and actual value of the energy storage output. The control equation is specifically shown in equations (1) and (2).

[0095] Furthermore, if Figure 2 As shown, the converter control unit mainly includes:

[0096] A virtual impedance loop, wherein the virtual impedance loop determines the virtual impedance value according to the target power factor (as shown in formula (10)), calculates the voltage drop dq axis component on the virtual impedance according to the virtual impedance value and the dq axis component of the converter output current (as shown in formula (6)), and compensates the internal potential amplitude to obtain the voltage reference value dq axis component;

[0097] A voltage control loop controls the dq-axis components of the voltage reference value to obtain the dq-axis components of the current reference value;

[0098] And, a current control and signal adjustment loop, which controls the dq axis components of the current reference value, performs dq conversion in combination with the internal potential phase, and modulates to obtain a modulation waveform (control waveform) of the converter.

[0099] Furthermore, the chopper control unit mainly performs PI control according to the DC bus voltage reference value and actual value, and the DC bus current (the control equation is shown in formula (3)) and modulates to obtain the modulation waveform (control waveform) of the chopper.

[0100] Example 2

[0101] This embodiment takes 2MW power energy storage as an example to simulate and verify the control method or control system proposed in the above embodiment 1, and compares it with the traditional grid-type energy storage control. The simulation results are as follows: Figure 3 and Figure 4 As shown, Figure 3 It is a traditional grid-type energy storage waveform controlled according to unity power factor. Figure 4 It is an improved grid-type energy storage waveform for power factor change control.

[0102] Depend on Figure 3 It can be seen that the energy storage initially maintained unity power factor operation, with an active power output of 2MW and a reactive power output of 0MW. At 2.5s, the power factor changed to 0.6, the active power was 1.29MW, and the reactive power was 0.71MW. However, since the traditional grid-type energy storage is controlled according to the unity power factor, the internal active power and reactive power are unbalanced, and the converter eventually loses control at around 5.5s, causing instability, and the DC bus voltage, converter current, output power, etc. all oscillate to a large extent. It can be seen that the traditional grid-type energy storage control can temporarily bring the power close to the reference value, and the DC bus voltage and converter current do not exceed the limit.

[0103] Depend on Figure 4 It can be seen that the improved grid-type energy storage control maintains unity power factor control before 2.5s, the active power output is 2MW, and the reactive power output is 0MW. The power factor is adjusted at 6.5s, 10.5s, and 14.5s, respectively, and the active power / reactive power are 1.29 / 0.71MW, 1.65 / 0.24MW, and 1.05 / 1.24MW, respectively. During the power adjustment process, the DC bus voltage and the converter current have a certain stability margin. At the moment of power adjustment, the DC bus voltage suddenly increased, but did not exceed 1.15pu, and quickly stabilized near the rated value. It can be seen that the control strategy proposed in the embodiment of the present application can achieve internal power balance and stable target power output through the proposed virtual impedance control. Even when the grid-type energy storage outputs active power of 1.05MW and reactive power of 1.24MW (power factor of 0.398), it can still operate stably, and key parameters such as DC bus voltage and converter current have a large stability margin under the premise of ensuring safety. This shows that the control strategy proposed in the embodiment of the present application can effectively broaden the operating range of the grid-type energy storage power factor, reduce the network loss of the system, and has a high engineering application value.

[0104] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0105] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0106] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0107] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0108] The specific implementation methods described above further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only the specific implementation method of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A grid-type energy storage variable power factor control method considering the need to reduce network loss, characterized in that: The control method comprises: Change the control target of the energy storage converter: control the DC bus voltage through the chopper, control the power output of the energy storage through the converter, and design the power synchronization link in the converter control to make it have inertia and damping characteristics; The target power factor of energy storage is determined according to the system network loss, and the virtual impedance value is calculated from it. The corresponding voltage is compensated to the converter voltage control loop to adjust the output power.

2. According to claim 1, a grid-connected energy storage variable power factor control method considering the need to reduce network loss is characterized in that: The power output of the energy storage is controlled by the converter, and a power synchronization link is designed in the converter control so that it has inertia and damping characteristics, specifically including: The rotor swing equation of the synchronous generator is simulated by the converter, so that it has inertia and damping characteristics: θ=∫ωdt Among them, J and D P are the inertia coefficient and damping coefficient of active power, K P and K Q are the droop coefficients of active power and reactive power, ω * and ω are the reference angular velocity and the actual angular velocity of the converter, respectively. * and P are the reference value and actual value of the energy storage output active power, θ is the internal potential phase, E* and E are the internal potential amplitude and the converter terminal voltage, respectively; In converter control, when the active power output changes, the synchronous angular velocity of the virtual axis will also change, causing a change in the internal potential phase, thereby affecting the decomposition of the converter control command and power output.

3. A grid-connected energy storage variable power factor control method considering the need to reduce network loss according to claim 2, characterized in that: The control equation for controlling the DC bus voltage by the chopper is: Among them, U dc is the actual value of DC bus voltage, i dc is the DC bus current, U dc * is the DC bus voltage reference value, i md is the modulation signal.

4. A grid-connected energy storage variable power factor control method considering the need to reduce network loss according to any one of claims 1 to 3, characterized in that: The virtual impedance is equivalent to connecting an impedance in series in the circuit, and the voltage drop across the impedance is: Among them, ΔU d , ΔU q are the d-axis and q-axis components of the voltage drop on the virtual impedance, i Ld 、i Lq are the d-axis and q-axis components of the converter output current, respectively, and R v , X v are virtual resistance and virtual reactance respectively; The compensation voltage can be calculated based on the virtual resistance and the converter output current.

5. A grid-connected energy storage variable power factor control method considering the need to reduce network loss according to claim 4, characterized in that: The virtual resistance is obtained as follows: Determine a target power factor according to the system network loss requirement, and calculate a reactive power reference value according to the target power factor; According to the equivalent circuit of series impedance, the calculation equation of reactive power output by energy storage is obtained; Substitute the reactive power reference value into the energy storage output reactive power calculation equation to calculate the virtual impedance.

6. A grid-connected energy storage variable power factor control method considering the need to reduce network loss according to claim 5, characterized in that: The energy storage output reactive power calculation equation is: Among them, Q is the reactive power output of energy storage, E v is the voltage before the virtual impedance, X f is the filter reactance, X g is the grid reactance, R g Grid resistance, R f is the filter resistance, R v , X v are virtual resistance and virtual reactance respectively.

7. A grid-type energy storage variable power factor control system that takes into account the need to reduce network losses, characterized in that: The control system comprises: A converter control unit, which controls the power output of the energy storage through the converter, and also realizes power synchronization through converter control, and has inertia and damping characteristics; the converter control unit determines the target power factor according to the system network loss, and calculates the virtual impedance value according to the target power factor, compensates the corresponding voltage to the converter voltage control loop, and adjusts the output power; and a chopper control unit, wherein the chopper control unit controls the DC bus voltage through the chopper.

8. A grid-connected energy storage variable power factor control system that takes into account the need to reduce network losses according to claim 7, characterized in that: The converter control unit comprises: A virtual impedance loop, wherein the virtual impedance loop determines a virtual impedance value according to the target power factor, calculates a voltage drop on the virtual impedance according to the virtual impedance value and an output current of the converter, and compensates for an internal potential amplitude to obtain a voltage reference value; A voltage control loop, wherein the voltage control loop controls the voltage reference value to obtain a current reference value; And, a current control and signal modulation loop, which controls the current reference value, performs dq conversion in combination with the internal potential phase, and modulates to obtain a modulation waveform of the converter.

9. A grid-connected energy storage variable power factor control system that takes into account the need to reduce network losses according to claim 8, characterized in that: The inner potential amplitude and the inner potential phase are obtained through power outer loop control.

10. A grid-connected energy storage variable power factor control system that takes into account the need to reduce network losses according to any one of claims 7 to 9, characterized in that: The chopper control unit controls and modulates the DC bus voltage according to the reference value and actual value of the DC bus voltage, and obtains a modulation waveform of the chopper.

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