SVG-containing virtual synchronous machine voltage support coordination control method and system

Abstract

The invention discloses a SVG-containing virtual synchronous machine voltage support coordination control method and system, and relates to the technical field of power system power distribution network control strategies, and the method comprises the steps: analyzing a control system of a virtual synchronous machine and a reactive compensation device SVG, and analyzing the output characteristics of an inverter under the asymmetric voltage drop of a power grid; according to the analysis condition, an inverter control target under the asymmetric voltage drop is formulated; based on different asymmetric fault operation scenes, a voltage support coordination control strategy is set for the SVG-containing virtual synchronization mechanism. According to the method, through coordination control of the SVG and the virtual synchronous machine, current limiting and voltage supporting are achieved, and the voltage supporting capacity of the new energy field station under the unbalanced voltage drop condition is improved; through control strategy optimization, the fault ride-through capability of the inverter is improved, and the system instability risk is reduced; through scene distinguishing, different voltage drop degrees can be adapted, a coordination control strategy is formulated for different scenes, and the adaptability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system distribution network control strategy, and in particular to a virtual synchronous machine voltage support coordination control method and system including SVG. Background Art

[0002] Renewable energy generation represented by photovoltaic and wind power is gradually replacing traditional thermal power generation. After a large number of distributed new energy sources are connected to the power grid, since most of them are connected to the grid through inverters, they often do not have the inertia and damping characteristics of conventional units, resulting in a relative reduction in the power system's rotational inertia and rotating standby characteristics. At this time, the power system is very susceptible to power fluctuations and various faults, causing system instability. The current-type virtual synchronous machine control strategy can simulate the synchronous generator, provide the system with rotational inertia, droop characteristics and damping characteristics, and is applied in the power grid. However, when the grid voltage drops, the control target cannot be met due to insufficient inverter capacity. Overcoming the control failure caused by insufficient capacity is the primary problem of the voltage support inverter control strategy.

[0003] However, three-phase unbalanced faults often occur in actual distribution network operation. Under faults, the output power quality of the virtual synchronous machine control strategy decreases significantly. In severe cases, it may cause the new energy generator set to be removed, endangering the stability of power grid operation. For power grids with high renewable energy penetration, considering the stability of operating voltage, reactive compensation devices are usually configured at new energy sites with larger capacity. Compared with renewable energy generators, SVG has good voltage support and voltage balance enhancement capabilities. Coordinated control of virtual synchronous machines and SVG can solve the problem of insufficient voltage compensation of single virtual synchronous machines. Therefore, the control target electrical quantity is set according to the relevant grid-connected standards of the power system. By developing distributed new energy coordinated control strategies, stronger fault ride-through capabilities are provided for new energy power generation units under voltage imbalance drops, which is of great significance to improving the operating stability of high-proportion new energy systems.

[0004] In addition, from the perspective of scenario differentiation, by dividing different scenarios and formulating different control strategies, the capacity of SVG and virtual synchronous machine can be fully utilized in various scenarios, ensuring that the control strategy effectively supports the voltage of the grid connection point and ensures the safety of the grid connection point. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problems solved by the present invention are: traditional new energy control strategies have insufficient voltage support capability and current overload; traditional coordinated control strategies have a single control target and cannot perform appropriate coordinated control according to different scenarios; and how to solve the problem of formulating voltage support coordinated control strategies for virtual synchronous machines containing SVG under different operating scenarios.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for coordinated control of voltage support of a virtual synchronous machine containing SVG, comprising analyzing the control system of the virtual synchronous machine and the reactive compensation device SVG, and analyzing the output characteristics of the inverter under the asymmetric voltage drop of the power grid; formulating the inverter control target under the asymmetric voltage drop according to the analysis results; and formulating a voltage support coordinated control strategy for the virtual synchronous machine containing SVG based on different asymmetric fault operation scenarios.

[0008] As a preferred solution of the method for coordinated control of voltage support of a virtual synchronous machine containing SVG described in the present invention, wherein: the control system includes a virtual synchronous machine control and an SVG topology structure;

[0009] The virtual synchronous machine control includes a current-controlled virtual synchronous machine that adds frequency regulation control based on conventional vector control technology and retains the current inner loop control structure. The current command is controlled to accurately control the output power. When an asymmetric voltage drop occurs in the power grid, a negative sequence component will appear in the current, resulting in three-phase imbalance. In order to achieve three-phase current balance, the balancing current in the classical current vector control is introduced to control the virtual synchronous machine, and a negative sequence current loop is added. By adjusting the positive and negative sequence reference commands, accurate control of the positive and negative sequence components of the power grid is achieved; the virtual synchronous machine reference current is calculated, which is expressed as:

[0010]

[0011] Among them, U n Indicates the rated phase voltage amplitude, U max represents the output phase voltage amplitude, K represents the inertia coefficient of the reactive power control loop, S represents the differential coefficient, U d + Represents the positive sequence voltage amplitude on the d-axis, P set Indicates the set power, Q set Indicates the set power level.

[0012] As a preferred solution of the voltage support coordinated control method of a virtual synchronous machine containing SVG described in the present invention, wherein: the SVG topology structure includes the topology of SVG and the control method adopting the control method similar to the principle of the new energy power generation unit, SVG on the DC side, the DC voltage U dcIt is controlled so that the SVG can absorb active power from the AC power grid to compensate for the active power loss. The inner loop current control link and PWM signal generation link are consistent with the virtual synchronous machine control.

[0013] As a preferred solution of the coordinated control method of the voltage support of the virtual synchronous machine containing SVG described in the present invention, wherein: the inverter output characteristics under the asymmetric voltage drop of the power grid include the coordinated reactive power control of the SVG and the virtual synchronous machine, and the control objects are all inverters. The inverter control system uses the real-time measurement of the grid connection point voltage, current and the set active power reference value to calculate the reference current in the dq coordinate system. In the case of asymmetric voltage drop, the positive and negative sequence voltage vectors of the AC system point k are expressed in the dq synchronous rotating coordinate system as follows:

[0014]

[0015] in, and represents the positive and negative sequence voltages at point m in the AC system, and Indicates the amplitude corresponding to the positive and negative sequence voltages, δ + and δ - Represents the initial phase angle of the positive sequence and negative sequence voltages; calculates the inverter output current in the dq coordinate system, expressed as:

[0016]

[0017] Among them, I d and I q represents the active and reactive current components, i + and i - Represents the positive and negative sequence current components; according to the topology, in the case of asymmetric voltage drop, the positive and negative sequence voltages at the inverter outlet are expressed as:

[0018]

[0019]

[0020] Among them, v + and v - Indicates the positive and negative sequence voltages at the PCC point, and Indicates the positive and negative sequence voltages of the grid-side busbar, L l represents the equivalent inductance of the line; calculate the voltage support equation expressed in terms of positive and negative sequence amplitudes, expressed as:

[0021]

[0022]

[0023] Among them, V + and V - Indicates the support voltage of positive sequence and negative sequence.

[0024] As a preferred solution of the voltage support coordinated control method of a virtual synchronous machine containing SVG described in the present invention, wherein: the inverter control target under the asymmetric voltage drop includes voltage support control and current limit control; the voltage support control includes the three-phase voltage amplitude of the busbar at the grid connection point when the voltage is asymmetric, expressed as:

[0025]

[0026] Where φ = δ + +δ - , φ represents the sum of the initial phase angles of the positive and negative sequence voltages, U + and U - Indicates the magnitude of the corresponding positive and negative sequence voltages, U a , U b , U c Respectively represent the voltage amplitudes of the three phases abc; in the case of an unbalanced fault, a constraint is established to ensure that the three-phase voltage does not exceed the limit after voltage support, which is expressed as:

[0027] U max =max(U a ,U b ,U c )≤U upper

[0028] Among them, U max Indicates the phase voltage with the largest amplitude, U upper Represents the upper limit of the phase voltage amplitude constraint, and calculates the phase voltage with the maximum amplitude, which is expressed as:

[0029]

[0030] in:

[0031]

[0032] Maximum phase voltage amplitude U max With positive sequence voltage U + The relationship between max Raised to U upper When the inverter does not exceed the limit of phase voltage amplitude, it realizes the maximum support of positive sequence voltage. Based on the unbalanced fault, a constraint is established to ensure that the three-phase voltage does not exceed the limit after voltage support. Assume U max =U upper , calculate the corresponding positive sequence reference voltage under the maximum voltage support, expressed as:

[0033]

[0034] Calculate the reactive reference current corresponding to the maximum voltage support, expressed as:

[0035]

[0036] The current limiting control includes limiting the output current of the inverter when the grid voltage drops significantly, which is expressed as:

[0037]

[0038] Where φ = δ + +δ - ; According to the current limiting requirements, the maximum output current of the inverter will be limited, expressed as:

[0039] max{I a ,I b ,I c}≤I lim

[0040] Among them, I lim Indicates the maximum output current, assuming I lim =1.2; Since the output current three-phase balance needs to be achieved, the negative sequence reference current needs to be set to 0:

[0041]

[0042]

[0043] in, Represents the negative sequence active reference current, Represents the negative sequence reactive reference current.

[0044] As a preferred solution of the coordinated control method for voltage support of a virtual synchronous machine containing SVG described in the present invention, wherein: the asymmetric fault operation scenarios are different, including that the priority control of the coordinated control is to increase the grid-connected voltage of the new energy station composed of SVG and the virtual synchronous machine, and the general principle of coordinated control includes that when SVG and the virtual synchronous machine exist at the same time, priority is given to fully utilizing SVG control to support the voltage, and when SVG cannot support the voltage independently, consider coordinating the control of SVG and the virtual synchronous machine to jointly support the grid-connected point voltage. Therefore, when considering scene differentiation, whether SVG independently meets the control requirements is used as the basis for scene differentiation; the scene differentiation method includes when the voltage drops, starting the scene differentiation algorithm, in order to ensure the active output of the new energy station, since the output power of the virtual synchronous machine has system inertia and stability, the active current reference value of the virtual synchronous machine is defined as 0.52; the positive sequence reactive reference current of the voltage support is calculated Computation Imax , when calculating I max Does not exceed the maximum inverter current limit I lim , using a separate SVG to implement the voltage support method, when the calculated I max Exceeds the maximum inverter current limit I lim , then SVG and virtual synchronous machine are controlled cooperatively, SVG outputs the maximum positive sequence reactive current, and the virtual synchronous machine output current is equal to I lim For comparison, if the current does not exceed the limit, the SVG and the virtual synchronous machine will output power as required. If the current of the virtual synchronous machine exceeds the limit, the virtual synchronous machine will reduce the active power output. When the current meets the requirements, the supporting voltage is the priority target.

[0045] As a preferred solution of the voltage support coordinated control method of a virtual synchronous machine containing SVG described in the present invention, the voltage support coordinated control strategy includes scenario 1, scenario 2 and scenario 3; scenario 1 includes a slight voltage drop, and SVG alone implements voltage support; in scenario 1, the voltage support only relies on SVG to output reactive power, and the virtual synchronous machine does not output reactive power, reserving space for the output of active power, and the respective reference currents are expressed as:

[0046]

[0047]

[0048] Wherein, subscript 1 represents a virtual synchronous machine, and subscript 2 represents an SVG; scenario 2 includes a moderate voltage drop, and coordinated control of the SVG and the virtual synchronous machine; in scenario 2, using the SVG alone to support the voltage will cause the current to exceed the limit, and ultimately fail to achieve the effect of voltage support and endanger the safety of the inverter. It is necessary to coordinate the output of the SVG and the virtual synchronous machine to jointly support the voltage and ensure that the output current of both does not exceed the limit. The respective reference currents are expressed as:

[0049]

[0050]

[0051] Wherein, subscript 1 represents the virtual synchronous machine, and subscript 2 represents the SVG; the scenario 3 includes severe voltage sag, and coordinated control of SVG and the virtual synchronous machine; in scenario 3, using SVG alone, or conventional coordinated control of SVG and the virtual synchronous machine will lead to current exceeding the limit, and the output active power of the virtual synchronous machine is appropriately reduced to give priority to the purpose of voltage support and meet the voltage requirements of the grid connection point. The respective reference currents are expressed as:

[0052]

[0053]

[0054] Among them, subscript 1 represents the virtual synchronous machine, and subscript 2 represents SVG.

[0055] Another object of the present invention is to provide a virtual synchronous machine voltage support coordination control system containing SVG, which can solve the problem that the current traditional coordination control strategy cannot perform appropriate coordination control according to different scenarios by formulating a voltage support coordination control strategy.

[0056] As a preferred solution of the voltage support coordination control system of the virtual synchronous machine containing SVG described in the present invention, it includes: an analysis module, an asymmetric voltage drop control module, and a coordination strategy module; the analysis module is used to analyze the control system of the virtual synchronous machine and the reactive compensation device SVG, and analyze the output characteristics of the inverter under the asymmetric voltage drop of the power grid; the asymmetric voltage drop control module is used to formulate the inverter control target under the asymmetric voltage drop according to the analysis situation; the coordination strategy module is used to formulate a voltage support coordination control strategy for the virtual synchronous machine containing SVG based on different asymmetric fault operation scenarios.

[0057] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of a method for voltage support coordination control of a virtual synchronous machine containing SVG.

[0058] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a method for coordinated control of voltage support of a virtual synchronous machine containing SVG.

[0059] Beneficial effects of the present invention: The coordinated control method for voltage support of a virtual synchronous machine containing SVG provided by the present invention can achieve current limiting and voltage support under different voltage drop conditions through coordinated control of SVG and the virtual synchronous machine, thereby improving the voltage support capability of new energy sites under unbalanced voltage drop conditions; through optimization of the control strategy, the fault ride-through capability of the inverter under unbalanced voltage drop is improved, and the risk of system instability caused by faults is reduced; through scenario differentiation, the present invention can adapt to different degrees of voltage drop, and formulate corresponding coordinated control strategies for different scenarios, ensuring that the control objectives can be achieved under various conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0061] Figure 1 An overall flow chart of a voltage support coordinated control method for a virtual synchronous machine including SVG provided in the first embodiment of the present invention.

[0062] Figure 2 A virtual synchronous machine control topology diagram of a virtual synchronous machine voltage support coordinated control method including SVG provided in the first embodiment of the present invention.

[0063] Figure 3 A SVG control topology system diagram of a virtual synchronous machine voltage support coordinated control method including SVG provided in the first embodiment of the present invention.

[0064] Figure 4 A diagram of an operation scenario differentiation method for a virtual synchronous machine voltage support coordinated control method including SVG provided in the first embodiment of the present invention.

[0065] Figure 5 An overall flow chart of a virtual synchronous machine voltage support coordinated control system including SVG provided in the third embodiment of the present invention. DETAILED DESCRIPTION

[0066] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0067] Example 1, reference Figure 1-Figure 4 , which is an embodiment of the present invention, provides a voltage support coordination control method for a virtual synchronous machine including SVG, comprising:

[0068] S1: Analyze the control system of the virtual synchronous machine and the reactive power compensation device SVG, and analyze the inverter output characteristics under the asymmetric voltage drop of the power grid.

[0069] Furthermore, the control system includes a virtual synchronous machine control and an SVG topology structure; the virtual synchronous machine control includes a current-controlled virtual synchronous machine based on conventional vector control technology with additional frequency regulation control and a current inner loop control structure retained, and the current command is controlled to accurately control the output power. When an asymmetric voltage drop occurs in the power grid, a negative sequence component will appear in the current, resulting in three-phase imbalance. In order to achieve three-phase current balance, the balancing current in the classical current vector control is introduced to perform virtual synchronous machine control, and a negative sequence current loop is added. By adjusting the positive and negative sequence reference commands, accurate control of the positive and negative sequence components of the power grid is achieved; the virtual synchronous machine reference current is calculated, which is expressed as:

[0070]

[0071] Among them, U n Indicates the rated phase voltage amplitude, U max represents the output phase voltage amplitude, K represents the inertia coefficient of the reactive power control loop, S represents the differential coefficient, U d + Represents the positive sequence voltage amplitude on the d-axis, P set Indicates the set power, Q set Indicates the set power level.

[0072] It should be noted that the SVG topology structure includes the topology and control of the SVG, which adopts a control method similar to that of the new energy power generation unit. On the DC side, the SVG dc It is controlled so that the SVG can absorb active power from the AC power grid to compensate for the active power loss. The inner loop current control link and PWM signal generation link are consistent with the virtual synchronous machine control.

[0073] It should also be noted that the inverter output characteristics under the asymmetric voltage drop of the power grid include the reactive coordination control of SVG and virtual synchronous machine. The control objects are all inverters. The inverter control system uses the real-time measured grid connection point voltage, current and set active power reference value to calculate the reference current in the dq coordinate system. Under the condition of asymmetric voltage drop, the positive and negative sequence voltage vectors at the AC system point k are expressed in the dq synchronous rotating coordinate system as follows:

[0074]

[0075] in, and represents the positive and negative sequence voltages at point m in the AC system, and Indicates the amplitude corresponding to the positive and negative sequence voltages, δ + and δ - Represents the initial phase angle of the positive sequence and negative sequence voltages; calculates the inverter output current in the dq coordinate system, expressed as:

[0076]

[0077] Among them, I d and I q represents the active and reactive current components, i + and i - Represents the positive and negative sequence current components; according to the topology, in the case of asymmetric voltage drop, the positive and negative sequence voltages at the inverter outlet are expressed as:

[0078]

[0079]

[0080] Among them, v + and v - Indicates the positive and negative sequence voltages at the PCC point, and Indicates the positive and negative sequence voltages of the grid-side busbar, L l represents the equivalent inductance of the line; calculate the voltage support equation expressed in terms of positive and negative sequence amplitudes, expressed as:

[0081]

[0082]

[0083] Among them, V + and V - Indicates the support voltage of positive sequence and negative sequence.

[0084] It should also be noted that the control objects of the virtual synchronous machine and SVG are both inverters, and studying the output characteristics of the inverter is the basis for achieving the control objectives.

[0085] S2: According to the analysis, formulate the inverter control target under asymmetric voltage drop.

[0086] Furthermore, the inverter control target under asymmetric voltage drop includes voltage support control and current limit control; the voltage support control includes the three-phase voltage amplitude of the busbar at the grid connection point when the voltage is asymmetric, expressed as:

[0087]

[0088] Where φ = δ + +δ - , φ represents the sum of the initial phase angles of the positive and negative sequence voltages, U + and U - Indicates the magnitude of the corresponding positive and negative sequence voltages, Ua, Ub, and Uc respectively represent the voltage amplitudes of the three phases abc; in the case of an unbalanced fault, a constraint is established to ensure that the three-phase voltage does not exceed the limit after voltage support, which is expressed as:

[0089] U max =max(U a ,U b ,U c )≤U upper

[0090] Among them, U max Indicates the phase voltage with the largest amplitude, U upper Represents the upper limit of the phase voltage amplitude constraint, and calculates the phase voltage with the maximum amplitude, which is expressed as:

[0091]

[0092] in:

[0093]

[0094] Maximum phase voltage amplitude U max With positive sequence voltage U + The relationship between max Raised to U upper When the inverter does not exceed the limit of phase voltage amplitude, it realizes the maximum support of positive sequence voltage. Based on the unbalanced fault, a constraint is established to ensure that the three-phase voltage does not exceed the limit after voltage support. Assume U max =U upper , calculate the corresponding positive sequence reference voltage under the maximum voltage support, expressed as:

[0095]

[0096] Calculate the reactive reference current corresponding to the maximum voltage support, expressed as:

[0097]

[0098] The current limit control includes limiting the output current of the inverter when the grid voltage drops significantly (such as under fault conditions), which is expressed as:

[0099]

[0100] Where φ = δ + +δ - ; According to the current limiting requirements, the maximum output current of the inverter will be limited, expressed as:

[0101] max{I a ,I b ,I c}≤I lim

[0102] Among them, I lim Indicates the maximum output current, assuming I lim =1.2; Since the output current three-phase balance needs to be achieved, the negative sequence reference current needs to be set to 0:

[0103]

[0104]

[0105] in, Represents the negative sequence active reference current, Represents the negative sequence reactive reference current.

[0106] It should be noted that the control target under asymmetric faults is to support the grid connection point voltage to the maximum extent and limit the current output during asymmetric faults while ensuring the safety of the virtual synchronous machine.

[0107] S3: Based on different asymmetric fault operation scenarios, a voltage support coordination control strategy is formulated for the virtual synchronous machine containing SVG.

[0108] Furthermore, the different operating scenarios of asymmetric faults include coordinated control, in which the priority control is to increase the grid-connected voltage of the new energy station composed of SVG and virtual synchronous machine. The general principle of coordinated control includes that when SVG and virtual synchronous machine exist at the same time, priority is given to fully utilizing SVG control to support the voltage. When SVG cannot support the voltage independently, consider coordinating the control of SVG and virtual synchronous machine to jointly support the grid connection point voltage. Therefore, when considering scenario differentiation, whether SVG can independently meet the control requirements is used as the basis for scenario differentiation; the scenario differentiation method includes starting the scenario differentiation algorithm when the voltage drops. In order to ensure the active output of the new energy station, since the output power of the virtual synchronous machine has system inertia and stability, the active current reference value of the virtual synchronous machine is defined as 0.52; the positive sequence reactive reference current I of the voltage support is calculated q + , calculate I max , when calculating I max Does not exceed the maximum inverter current limit I lim , using a separate SVG to implement the voltage support method, when the calculated I max Exceeds the maximum inverter current limit I lim , then SVG and virtual synchronous machine are controlled cooperatively, SVG outputs the maximum positive sequence reactive current, and the virtual synchronous machine output current is equal to I lim For comparison, if the current does not exceed the limit, the SVG and the virtual synchronous machine will output power as required. If the current of the virtual synchronous machine exceeds the limit, the virtual synchronous machine will reduce the active power output. When the current meets the requirements, the supporting voltage is the priority target.

[0109] It should be noted that the voltage support coordination control strategy includes scenario 1, scenario 2 and scenario 3; scenario 1 includes a slight voltage drop, and SVG alone implements voltage support; in scenario 1, the voltage support only relies on SVG to output reactive power, and the virtual synchronous machine does not output reactive power, reserving space for the output of active power. The respective reference currents are expressed as:

[0110]

[0111]

[0112] Wherein, subscript 1 represents a virtual synchronous machine, and subscript 2 represents an SVG; scenario 2 includes a moderate voltage drop, and coordinated control of the SVG and the virtual synchronous machine; in scenario 2, using the SVG alone to support the voltage will cause the current to exceed the limit, and ultimately fail to achieve the effect of voltage support and endanger the safety of the inverter. It is necessary to coordinate the output of the SVG and the virtual synchronous machine to jointly support the voltage and ensure that the output current of both does not exceed the limit. The respective reference currents are expressed as:

[0113]

[0114]

[0115] Wherein, subscript 1 represents the virtual synchronous machine, and subscript 2 represents the SVG; the scenario 3 includes severe voltage sag, and coordinated control of SVG and the virtual synchronous machine; in scenario 3, using SVG alone, or conventional coordinated control of SVG and the virtual synchronous machine will lead to current exceeding the limit, and the output active power of the virtual synchronous machine is appropriately reduced to give priority to the purpose of voltage support and meet the voltage requirements of the grid connection point. The respective reference currents are expressed as:

[0116]

[0117]

[0118] Among them, subscript 1 represents the virtual synchronous machine, and subscript 2 represents SVG.

[0119] It should also be noted that the distinction of operating scenarios includes the following steps: Step 1: Calculate the required reactive current support value under different scenarios based on the voltage support target; Step 2: Distinguish the operating scenarios and formulate a coordinated control strategy based on the inverter output current and the required reactive support current.

[0120] Embodiment 2, an embodiment of the present invention, provides a voltage support coordination control method for a virtual synchronous machine including SVG. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through economic benefit calculation and simulation experiments.

[0121] First, the scenario differentiation method is verified. After the voltage drops, the voltage drop degree is evaluated according to the comparison between the positive sequence reactive reference current and the current amplitude limit to achieve scenario division. The specific case settings and scenario differentiation results are shown in Table 1.

[0122] Table 1 Simulation example settings

[0123]

[0124] Secondly, conduct verification in specific scenarios.

[0125] Scenario 1: The voltage drops slightly and the SVG alone supports the voltage.

[0126] At a certain moment, a slight asymmetric voltage drop occurs on the grid side, the positive sequence voltage drops to 0.5pu, and the negative sequence voltage rises to 0.27pu. By adopting this coordinated control strategy, by adjusting the positive and negative sequence voltages at the grid connection point, the voltage of each phase can be adjusted and the maximum phase amplitude of the grid connection point voltage can be stabilized at 0.96pu, meeting the set voltage support requirements. When the voltage drops slightly, voltage support can be achieved by relying solely on the reactive power output of SVG.

[0127] Scenario 2: Moderate voltage sag, coordinated control by SVG and virtual synchronous machine.

[0128] At a certain moment, a slight asymmetric voltage drop occurs on the grid side, the positive sequence voltage drops to 0.5pu, and the negative sequence voltage rises to 0.27pu. By adopting this coordinated control strategy, by adjusting the positive and negative sequence voltages at the grid connection point, the voltage of each phase can be adjusted and the maximum phase amplitude of the grid connection point voltage can be stabilized at 1.03pu, meeting the set voltage support requirements. When the voltage drops moderately, the voltage support is achieved by relying on the coordinated control of the SVG and the virtual synchronous machine.

[0129] Scenario 3: Severe voltage sag, coordinated control by SVG and virtual synchronous machine.

[0130] At a certain moment, a slight asymmetric voltage drop occurs on the grid side, the positive sequence voltage drops to 0.2pu, and the negative sequence voltage rises to 0.25pu. By adopting this coordinated control strategy, by adjusting the positive and negative sequence voltages at the grid connection point, the voltage of each phase can be adjusted and the maximum phase amplitude of the grid connection point voltage can be stabilized at 0.81pu, meeting the set voltage support requirements. When the voltage drops severely, the coordinated control of SVG and the virtual synchronous machine simultaneously reduces the active output of the virtual synchronous machine to give priority to voltage support. The verification results of three specific scenarios are shown in Table 2.

[0131] Table 2 Summary of verification results

[0132]

[0133] Referring to Table 2, the verification results are analyzed, and it can be seen that the method of the present invention can effectively solve the problems of insufficient voltage support capacity and current overload existing in the prior art, and formulate corresponding coordinated control strategies for different voltage drop degrees through scene differentiation, thereby ensuring that the control objectives can be achieved under various circumstances, improving the voltage support capability of the new energy station under the condition of unbalanced voltage drop, and improving the fault ride-through capability of the inverter.

[0134] Example 3, reference Figure 5 , which is an embodiment of the present invention, provides a virtual synchronous machine voltage support coordination control system containing SVG, including an analysis module, an asymmetric voltage drop control module, and a coordination strategy module.

[0135] The analysis module is used to analyze the control systems of the virtual synchronous machine and the reactive power compensation device SVG, and to analyze the output characteristics of the inverter under asymmetric voltage drops in the power grid; the asymmetric voltage drop control module is used to formulate the inverter control target under asymmetric voltage drops according to the analysis results; the coordination strategy module is used to formulate a voltage support coordination control strategy for the virtual synchronous machine containing SVG based on different asymmetric fault operation scenarios.

[0136] If the function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the methods of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0137] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0138] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering, or processing in another suitable manner as necessary, and then stored in a computer memory.

[0139] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc. It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limited. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

[0140] 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 preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for coordinated control of voltage support of a virtual synchronous machine including SVG, characterized in that: include: Analyze the control system of virtual synchronous machine and reactive power compensation device SVG, and analyze the output characteristics of inverter under asymmetric voltage drop of power grid; According to the analysis, formulate the inverter control target under asymmetric voltage drop; Based on different asymmetric fault operation scenarios, a voltage support coordinated control strategy is formulated for the virtual synchronous machine containing SVG.

2. The method for coordinated control of voltage support of a virtual synchronous machine including SVG according to claim 1, characterized in that: The control system includes virtual synchronous machine control and SVG topology; The virtual synchronous machine control includes a current-controlled virtual synchronous machine, which adds frequency regulation control based on conventional vector control technology and retains the current inner loop control structure. The current command is controlled to accurately control the output power. When an asymmetric voltage drop occurs in the power grid, a negative sequence component will appear in the current, resulting in three-phase imbalance. In order to achieve three-phase current balance, the balancing current in the classical current vector control is introduced to control the virtual synchronous machine, and a negative sequence current loop is added. By adjusting the positive and negative sequence reference instructions, the positive and negative sequence components of the power grid are accurately controlled. The virtual synchronous machine reference current is calculated and expressed as: Among them, U n Indicates the rated phase voltage amplitude, U max represents the output phase voltage amplitude, K represents the inertia coefficient of the reactive power control loop, S represents the differential coefficient, U d + Represents the positive sequence voltage amplitude on the d-axis, P set Indicates the set power, Q set Indicates the set power level.

3. The method for coordinated control of voltage support of a virtual synchronous machine including SVG according to claim 2, characterized in that: The SVG topology structure includes the topology of SVG and the control method using the same principle as the new energy power generation unit. On the DC side, SVG controls the DC voltage U dc It is controlled so that the SVG can absorb active power from the AC power grid to compensate for the active power loss. The inner loop current control link and PWM signal generation link are consistent with the virtual synchronous machine control.

4. The method for coordinated control of voltage support of a virtual synchronous machine including SVG according to claim 3, characterized in that: The inverter output characteristics under the asymmetric voltage drop of the power grid include the reactive coordination control of SVG and virtual synchronous machine. The control objects are all inverters. The inverter control system uses the real-time measured grid connection point voltage, current and set active power reference value to calculate the reference current in the dq coordinate system. Under the condition of asymmetric voltage drop, the positive and negative sequence voltage vectors of the AC system point k are expressed in the dq synchronous rotating coordinate system as follows: in, and represents the positive and negative sequence voltages at point m in the AC system, and Indicates the amplitude corresponding to the positive and negative sequence voltages, δ + and δ - Indicates the initial phase angle of positive and negative sequence voltages; Calculate the inverter output current in the dq coordinate system, expressed as: Among them, I d and I q represents the active and reactive current components, i + and i - Represents positive and negative sequence current components; According to the topology, in the case of asymmetric voltage drop, the positive and negative sequence voltages at the inverter output are expressed as: Among them, v + and v - Indicates the positive and negative sequence voltages at the PCC point, and Indicates the positive and negative sequence voltages of the grid-side busbar, L l Indicates the equivalent inductance of the line; Calculate the voltage support equation in terms of positive and negative sequence amplitudes, expressed as: Among them, V + and V - Indicates the support voltage of positive sequence and negative sequence.

5. The method for coordinated control of voltage support of a virtual synchronous machine including SVG according to claim 4, characterized in that: The inverter control objectives under the asymmetric voltage drop include voltage support control and current limit control; The voltage support control includes the three-phase voltage amplitude of the busbar at the grid connection point when the voltage is asymmetric, which is expressed as: Where φ = δ + +δ - , φ represents the sum of the initial phase angles of the positive and negative sequence voltages, U + and U - Indicates the magnitude of the corresponding positive and negative sequence voltages, U a , U b , U c Respectively represent the voltage amplitudes of the three phases abc; In the case of unbalanced faults, constraints are established to ensure that the three-phase voltages do not exceed the limits after voltage support, expressed as: U max =max(U a ,U b ,U c )≤U upper Among them, U max Indicates the phase voltage with the largest amplitude, U upper Represents the upper limit of the phase voltage amplitude constraint, and calculates the phase voltage with the maximum amplitude, which is expressed as: in: Maximum phase voltage amplitude U max With positive sequence voltage U + The relationship between max Raised to U upper When the inverter does not exceed the limit of phase voltage amplitude, it realizes the maximum support of positive sequence voltage. Based on the unbalanced fault, a constraint is established to ensure that the three-phase voltage does not exceed the limit after voltage support. Assume U max =U upper , calculate the corresponding positive sequence reference voltage under the maximum voltage support, expressed as: Calculate the reactive reference current corresponding to the maximum voltage support, expressed as: The current limit control includes limiting the output current of the inverter when the grid voltage drops significantly (such as under fault conditions), which is expressed as: Where, φ=δ + +d - ; According to the current limiting requirements, the maximum output current of the inverter will be limited, expressed as: max{I a ,I b ,I c }≤I lim Among them, I lim Indicates the maximum output current, assuming I lim =1.2; Since the output current three-phase balance needs to be achieved, the negative sequence reference current needs to be set to 0: in, Represents the negative sequence active reference current, Represents the negative sequence reactive reference current.

6. The method for coordinated control of voltage support of a virtual synchronous machine including SVG according to claim 4, characterized in that: The different asymmetric fault operation scenarios include that the priority of coordinated control is to increase the grid-connected voltage of the new energy station composed of SVG and virtual synchronous machine. The general principle of coordinated control includes that when SVG and virtual synchronous machine exist at the same time, priority is given to fully utilizing SVG control to support the voltage. When SVG cannot support the voltage independently, consider coordinating the control of SVG and virtual synchronous machine to jointly support the grid-connected voltage. Therefore, when considering the scene differentiation, whether SVG can independently meet the control requirements is used as the basis for scene differentiation; The scenario differentiation method includes starting the scenario differentiation algorithm when the voltage drops. In order to ensure the active output of the new energy station, the active current reference value of the virtual synchronous machine is defined as 0.52 because the output power of the virtual synchronous machine has system inertia and stability; Calculation of positive sequence reactive reference current for voltage support Computation I max , when calculating I max Do not exceed the maximum inverter current limit I lim , using a separate SVG to implement the voltage support method, when the calculated I max Exceeds the maximum inverter current limit I lim , then SVG and virtual synchronous machine are controlled cooperatively, SVG outputs the maximum positive sequence reactive current, and the virtual synchronous machine output current is equal to I lim For comparison, if the current does not exceed the limit, the SVG and the virtual synchronous machine will output power as required. If the current of the virtual synchronous machine exceeds the limit, the virtual synchronous machine will reduce the active power output. When the current meets the requirements, the supporting voltage is the priority target.

7. The method for coordinated control of voltage support of a virtual synchronous machine including SVG according to claim 5, characterized in that: The voltage support coordinated control strategy includes scenario 1, scenario 2 and scenario 3; Scenario 1 includes a slight voltage drop, and SVG alone provides voltage support; In scenario 1, the voltage support relies only on the reactive power output of SVG, and the virtual synchronous machine does not output reactive power, leaving space for the output of active power. The respective reference currents are expressed as: Among them, subscript 1 represents the virtual synchronous machine, and subscript 2 represents SVG; The scenario 2 includes moderate voltage sag, coordinated control of SVG and virtual synchronous machine; In scenario 2, using SVG alone to support voltage will cause the current to exceed the limit, and ultimately fail to achieve the voltage support effect and endanger the inverter safety. It is necessary to coordinate the output of SVG and virtual synchronous machine to jointly support the voltage and ensure that the output current of both does not exceed the limit. The respective reference currents are expressed as: Among them, subscript 1 represents the virtual synchronous machine, and subscript 2 represents SVG; The scenario 3 includes severe voltage sag, coordinated control of SVG and virtual synchronous machine; In scenario 3, the use of SVG alone, SVG and conventional coordinated control of virtual synchronous machines will lead to current exceeding the limit. The virtual synchronous machine output active power is appropriately reduced to give priority to the purpose of voltage support and meet the voltage requirements of the grid connection point. The respective reference currents are expressed as: Among them, subscript 1 represents the virtual synchronous machine, and subscript 2 represents SVG.

8. A system using the method for coordinated control of voltage support of a virtual synchronous machine containing SVG as claimed in any one of claims 1 to 7, characterized in that: It includes analysis module, asymmetric voltage drop control module and coordination strategy module; The analysis module is used to analyze the control system of the virtual synchronous machine and the reactive power compensation device SVG, and analyze the output characteristics of the inverter under the asymmetric voltage drop of the power grid; The asymmetric voltage drop control module is used to formulate the inverter control target under asymmetric voltage drop according to the analysis situation; The coordination strategy module is used to formulate a voltage support coordination control strategy for a virtual synchronous machine including an SVG based on different asymmetric fault operation scenarios.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the voltage support coordinated control method of a virtual synchronous machine including an SVG according to any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the voltage support coordinated control method of a virtual synchronous machine containing SVG according to any one of claims 1 to 7 are implemented.

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