An improved grid support control method and system adapted to unbalanced grid voltage

Abstract

The present invention belongs to the technical field of power electronic systems and discloses an improved grid support control method and system adapted to unbalanced grid voltages. The method measures the grid's positive and negative sequence voltages #imgabs0# and #imgabs1# and equivalent impedance #imgabs2#, and derives, in a synchronously rotating coordinate system, a relationship between the positive and negative sequence voltages at a PCC point and the positive and negative sequence components of a given outer loop power. Given reference values for the negative sequence components of active and reactive power, the adjustable range of the positive sequence component #imgabs3# of reactive power is calculated according to national standards for grid-connected voltage deviation of photovoltaic inverters. A relationship is established between an index value μ representing the distance from the three-phase voltage to the nominal voltage and the positive sequence component of reactive power, and a reference value #imgabs4# of the positive sequence component of reactive power and a reference value #imgabs5# of the positive sequence voltage at the PCC point are calculated when the index value is minimum. The reference values #imgabs6# and #imgabs7# are used to set positive sequence voltage-reactive power control parameters, and adaptive additional control is used to maintain the index value near the minimum value.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronic systems, and in particular relates to an improved grid support control method and system adapted to unbalanced grid voltage. Background Art

[0002] Photovoltaic power generation is being integrated into the power grid on a large scale. However, as installed capacity increases, output shortfalls present new challenges to the grid. Consequently, photovoltaic grid-connected converters are required to proactively support grid voltage by flexibly adjusting converter output power to maintain voltage at the photovoltaic grid connection point. However, due to asymmetric loads and the occurrence of asymmetric faults, grid voltage becomes unbalanced, and existing voltage support strategies are unable to effectively support and control this unbalanced three-phase voltage.

[0003] Many current power grid standards require distributed grid-connected generation systems to remain connected and provide dynamic reactive power support despite voltage drops within a certain range. These standards also propose a voltage-reactive power control approach, which specifies that the output reference value for reactive power should be based on the change in the positive-sequence voltage or the average RMS value of the three-phase voltages at the connection point. When the grid voltage is balanced, the positive-sequence voltage or the average RMS value of the three-phase voltages at the connection point effectively represents the change in the three-phase voltages. Using this voltage-reactive power control approach can suppress over-limit voltages and reduce voltage drops. However, for unbalanced grid voltages, the presence of negative-sequence voltages prevents the existing control voltage from fully representing the change in each phase voltage, potentially causing a phase voltage to exceed the limit and worsening voltage imbalance at the connection point. Furthermore, under traditional grid-following current control, the presence of negative-sequence reactive current can lead to changes in the negative-sequence voltage when using reactive power to suppress overvoltages, further exacerbating the voltage imbalance at the connection point.

[0004] To address the issue of voltage support under unbalanced grid voltage, some literature has proposed allocating positive-sequence active and reactive currents based on the line impedance ratio to effectively support the minimum phase voltage. This method can effectively support the minimum phase voltage when an asymmetric fault occurs in the grid, but it ignores the changes in the voltages of the other two phases and does not consider reducing the negative-sequence voltage. Therefore, some literature has suppressed the negative-sequence voltage, with the primary goal of raising the positive-sequence voltage. This can not only effectively support the PCC point voltage but also reduce the degree of grid voltage imbalance. However, the above method mainly considers the voltage drop caused by asymmetric faults in the grid and ignores the voltage limit problem caused by large-capacity photovoltaic connection in unbalanced load scenarios. Therefore, a flexible voltage support strategy is needed to effectively support the three-phase voltage in different grid voltage imbalance scenarios.

[0005] Through the above analysis, the problems and defects of the existing technology are: the existing technology ignores the voltage limit problem caused by large-capacity photovoltaic access in unbalanced load scenarios. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides an improved grid support control method and system that adapts to unbalanced grid voltage, aiming to achieve optimal support of the three-phase voltage at the PCC point under different unbalanced scenarios.

[0007] The present invention is implemented as follows: an improved grid support control method adapted to unbalanced grid voltage, comprising:

[0008] 1) Measure the positive and negative sequence voltages of the power grid 、 and equivalent impedance , derive the relationship between the positive and negative sequence voltages at the PCC point and the positive and negative sequence components of the given power in the outer loop in a synchronous rotating coordinate system;

[0009] 2) Given the reference values of the negative sequence components of active and reactive power, calculate the positive sequence component of reactive power according to the national standard requirements for the grid-connected voltage deviation of photovoltaic inverters. Adjustable range;

[0010] 3) Establish the relationship between the index value μ representing the distance from the three-phase voltage to the nominal voltage and the reactive power positive sequence component, and calculate the reference value of the reactive power positive sequence component when the index value is minimum And PCC point positive sequence voltage reference value ;

[0011] 4) Using reference values and Set the positive sequence voltage-reactive power control parameters and use adaptive additional control to keep the index value near the minimum value.

[0012] Furthermore, the relationship between the positive and negative sequence voltages at the PCC point and the reference values of the positive and negative sequence components of the outer loop given power is:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019] in, 、 Represents the positive and negative sequence voltages at the PCC point, with the subscripts “d” and “q” representing the d and q axis components, respectively. 、 Indicates the positive and negative sequence voltage of the power grid, 、 represents the equivalent resistance and reactance of the power grid, 、 Indicates the given active / reactive power positive sequence component reference value, 、 Indicates the reference value of the negative sequence component of the given active / reactive power, m 01 、n 01 、m 02 、n 02 Represents an intermediate variable.

[0020] Furthermore, the selection of the reference value of the reactive power positive sequence component should meet the following three constraints:

[0021] 1) The maximum three-phase voltage should be less than or equal to the upper limit of the voltage deviation standard, that is:

[0022]

[0023]

[0024] Where, Indicates the maximum phase voltage value. Indicates the upper limit of voltage deviation requirement of photovoltaic grid-connected technical standards;

[0025] 2) The minimum three-phase voltage should be greater than or equal to the upper limit of the voltage deviation standard, that is:

[0026]

[0027]

[0028] Where, Indicates the minimum phase voltage value. Indicates the lower limit of voltage deviation requirement of photovoltaic grid-connected technical standards;

[0029] 3) The sum of the reactive power positive and negative sequence reference values should be less than or equal to the remaining capacity of the photovoltaic inverter, that is:

[0030]

[0031] Where S N It represents the rated capacity of the photovoltaic grid-connected inverter, and P represents the active power generated by the photovoltaic grid-connected inverter.

[0032] Furthermore, the index value μ that characterizes the distance between the three-phase voltage and the nominal voltage is:

[0033]

[0034] in, 、 、 Respectively represent the effective values of the three-phase voltages at PCC points;

[0035] The relationship between the index value μ and the reactive power positive sequence component is:

[0036]

[0037] Furthermore, the positive sequence voltage-reactive power control strategy includes:

[0038] Voltage-reactive power control curve setting, based on the reference value of reactive power positive sequence component when the index value is minimum , PCC point positive sequence voltage reference value , the remaining capacity of the photovoltaic grid-connected inverter and the voltage deviation limit specified in the photovoltaic grid-connected technical standards to determine the control curve parameters;

[0039] Adaptive additional control, according to the changes of the previous two index values, the control voltage Make adjustments so that the indicator value approaches the minimum value.

[0040] Furthermore, the voltage-reactive power control curve is set as follows:

[0041] 1) If , the control curve is set as follows:

[0042]

[0043] in, 、 Indicates the adjustable range limit of reactive power positive sequence component, Indicates the reference value of reactive power positive sequence component corresponding to the minimum index value, Indicates the effective value of the positive sequence voltage at the PCC point when the index value is minimum;

[0044] 2) If , the control curve is set as follows:

[0045]

[0046] Furthermore, the adaptive additional control method is as follows:

[0047] 1) If 、 , then let the control voltage ;

[0048] 2) If 、 , then let the control voltage ;

[0049] 3) If 、 , then let the control voltage ;

[0050] 4) If 、 , then let the control voltage .

[0051] Another object of the present invention is to provide an improved grid support control system adapted to unbalanced grid voltages that implements the improved grid support control method adapted to unbalanced grid voltages, comprising:

[0052] Positive and negative sequence voltage measurement module, used to measure the positive and negative sequence voltage of the power grid 、 ;

[0053] Equivalent impedance measurement module, used to measure equivalent impedance ;

[0054] The positive and negative sequence voltage / component relationship derivation module is used to derive the relationship between the positive and negative sequence voltages at the PCC point and the positive and negative sequence components of the outer loop given power in a synchronous rotating coordinate system;

[0055] Negative sequence component reference value setting module, used to set the reference value of the negative sequence component of active and reactive power;

[0056] Reactive power positive sequence component adjustment range calculation module, used to calculate the reactive power positive sequence component according to the national standard requirements of photovoltaic inverter grid-connected voltage deviation Adjustable range;

[0057] Reactive power positive sequence component reference value calculation module, used to calculate the reactive power positive sequence component reference value when the index value is minimum ;

[0058] PCC point positive sequence voltage reference value calculation module is used to calculate the PCC point positive sequence voltage reference value when the index value is minimum ;

[0059] Sequence voltage-reactive power control parameter setting module, used to use reference value and Set positive sequence voltage-reactive power control parameters;

[0060] The adaptive additional control module is used to maintain the index value near the minimum value by using the adaptive additional control.

[0061] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the improved grid support control method that adapts to unbalanced grid voltage.

[0062] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to perform the steps of the improved grid support control method adapted to unbalanced grid voltage.

[0063] Another object of the present invention is to provide an information data processing terminal, which is used to implement the improved power grid support control system that adapts to unbalanced power grid voltage.

[0064] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0065] (1) The control method proposed in the present invention characterizes the change of the three-phase voltage by the distance between the three-phase voltage and the nominal voltage, and uses the change trend of the index value to set the positive-sequence voltage-reactive power control parameter, taking into account the change of the three-phase voltage instead of only considering the change of the positive-sequence voltage or a certain phase voltage.

[0066] (2) The control method proposed in the present invention is based on the premise of three-phase current balance, and further provides the adjustment range of the reactive power positive sequence component, and further realizes the effective support of the three-phase voltage on the premise of ensuring that the voltage of each phase is within the voltage deviation standard requirement range.

[0067] (3) The control method proposed in the present invention has strong applicability and can effectively support the three-phase voltage for voltage drops and voltage over-limits under the condition of unbalanced grid voltage.

[0068] (4) The control method proposed in the present invention can adaptively adjust the control voltage according to parameter changes. When the degree of grid voltage imbalance changes, the index value can be re-controlled to be near the new minimum value based on the changes in the index value and the control voltage, thereby achieving effective support for the three-phase point voltage.

[0069] Taking the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0070] The present invention provides an improved grid support control method and system adapted to unbalanced grid voltage. When the grid voltage is in an unbalanced state, the equivalent line resistance is measured by injecting non-characteristic harmonics. and inductance , and then measure the positive and negative sequence voltages of the equivalent power grid. Through MPPT control, the photovoltaic power generation always operates at the maximum power point. At this time, the positive sequence active power reference value is the product of the reference value of the positive sequence component of the active current and the reference value of the DC side voltage output by the MPPT. According to the above known conditions, the mathematical relationship between the positive sequence voltage and the positive sequence reactive power at the PCC point can be derived. Considering that most of the current photovoltaic grid-connected converters do not control the negative sequence voltage, the present invention is based on the premise of converter output current balance. At this time, the negative sequence reference current is set to 0, which reduces the negative sequence power control loop and reduces the complexity of the control method. At this time, the negative sequence voltage at the PCC point is equal to the negative sequence voltage of the power grid. Then, according to the voltage deviation limit, the adjustment range of the positive sequence reactive power can be obtained, and then the three-phase voltage can be controlled within the limit range. In addition, by determining the size of the positive sequence reactive power reference value corresponding to the minimum index value to determine the control curve, the over-regulation and under-regulation problems of the original voltage-reactive control method can be eliminated. Since the control method proposed in the present invention adds an adaptive control module, when the voltage imbalance condition changes, the index value can still be controlled to the minimum value, so that the three-phase voltage is close to the nominal voltage.

[0071] The control method disclosed in the present invention can achieve optimized support for three-phase voltage under different grid voltage imbalance conditions: measuring the equivalent line impedance and the positive and negative sequence components of the grid voltage, calculating the adjustable range of positive sequence reactive power based on the standard voltage deviation requirements for distributed power grid connection, and then setting the positive sequence voltage-positive sequence reactive power control curve parameters in the photovoltaic converter. Through the above settings, the three-phase voltage can be kept within the limit and the sum of the distances between the three-phase voltage and the nominal voltage can be minimized. This control method and controller system can be widely used in scenarios where grid voltage imbalance occurs when new energy is connected to the grid. Since only the equivalent line impedance and grid voltage need to be monitored, the communication requirements are greatly reduced. At the same time, the system can adaptively adjust the output of reactive power according to changes in line impedance and grid voltage, greatly simplifying the difficulty of implementation and operation in engineering practice.

[0072] At present, the distributed power grid connection standards at home and abroad all require distributed power sources to have a voltage support function, but this function is based on a three-phase balanced power grid. When the grid voltage is unbalanced, the voltage-reactive power control cannot take into account the changes in the three-phase voltage at the same time, resulting in a decrease in control performance, which greatly limits its application in engineering. When using voltage-reactive power control, the reactive power adjustment range usually depends on the remaining capacity of the converter. When the grid conditions change under this condition, existing research usually adopts the method of changing the slope of the control curve to adjust, which not only affects the stability of the system, but also ignores the scenario of unbalanced grid voltage. The control method provided by the present invention fills this gap and provides a control basis for the voltage support problem under unbalanced grid voltage.

[0073] Current domestic and international grid-connection test standards require voltage support functions such as voltage-reactive power control. These functions should also provide good three-phase voltage support in unbalanced voltage scenarios. However, existing voltage-reactive power control curves struggle to adapt to complex and changing grid conditions. When grid impedance characteristics change with topology, mismatches between preset control parameters and the actual grid impedance can lead to overcompensation or undercompensation. The control method provided by the present invention overcomes this mismatch between reactive power output and voltage support requirements, improving the flexibility and adaptability of voltage support control and ensuring effective three-phase voltage support under a variety of operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0075] Figure 1 This is a flow chart of an improved grid support control method adapted to unbalanced grid voltage provided by an embodiment of the present invention;

[0076] Figure 2 This is a schematic diagram of the structure of a photovoltaic grid-connected control system when the grid voltage is unbalanced, provided by an embodiment of the present invention;

[0077] Figure 3 Schematic diagram of photovoltaic grid connection when the grid voltage is unbalanced, provided by an embodiment of the present invention; wherein (a) is a positive sequence equivalent circuit of photovoltaic grid connection when the grid voltage is unbalanced, and (b) is a negative sequence equivalent circuit of photovoltaic grid connection when the grid voltage is unbalanced;

[0078] Figure 4 This is a block diagram of an improved voltage support control method provided by an embodiment of the present invention;

[0079] Figure 5 This is a flow chart of voltage-reactive power control curve parameter setting provided by an embodiment of the present invention;

[0080] Figure 6 is a flow chart of an additional adaptive control method provided by an embodiment of the present invention;

[0081] Figure 7 This is a structural diagram of an improved grid support control system adapted to unbalanced grid voltage provided by an embodiment of the present invention; Figure 8 This is a comparison diagram of the voltage-reactive power control and improved voltage support control effects under different voltage imbalance scenarios 1 provided by an embodiment of the present invention;

[0082] Figure 9 This is a comparison diagram of the voltage-reactive power control and improved voltage support control effects under different voltage imbalance scenarios 2 provided by an embodiment of the present invention; Figure 10 This is a diagram showing the effect of improved voltage support control under continuously changing voltage imbalance conditions provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0083] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0084] In view of the problems existing in the prior art, the present invention provides an improved grid support control method and system that adapts to unbalanced grid voltage. The present invention is described in detail below with reference to the accompanying drawings.

[0085] In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an explanatory embodiment that expands on the technical solutions of the claims.

[0086] like Figure 1 As shown, the negative sequence current control method for multiple wind farms applicable to flexible direct current grid connection includes the following steps:

[0087] 1) Measure the positive and negative sequence voltages of the power grid 、 and equivalent impedance , derive the relationship between the positive and negative sequence voltages at the PCC point and the reference values of the positive and negative sequence components of the given power in the outer loop in the synchronous rotating coordinate system;

[0088] 2) Given the reference values of the negative sequence components of active and reactive power, calculate the positive sequence component of reactive power according to the national standard requirements for the grid-connected voltage deviation of photovoltaic inverters. Adjustable range;

[0089] 3) Establish the relationship between the index value μ representing the distance from the three-phase voltage to the nominal voltage and the reactive power positive sequence component, and calculate the reference value of the reactive power positive sequence component when the index value is minimum And PCC point positive sequence voltage reference value ;

[0090] 4) Using reference values and Set the positive sequence voltage-reactive power control parameters and use adaptive additional control to keep the index value near the minimum value.

[0091] according to Figure 2 The PV grid-connected equivalent circuit shown in the figure can be used to obtain the electrical relationship between the voltage and current at the PCC point and the grid voltage and grid equivalent impedance:

[0092]

[0093] Where V represents the voltage at PCC point, i represents the current at PCC point, V g Indicates the equivalent voltage of the power grid, R g 、L g Represents the equivalent impedance of the power grid.

[0094] When the grid voltage is unbalanced, it can be decomposed into positive sequence, negative sequence and zero sequence components. Since the main research object here is the three-wire three-phase system, there is no zero sequence component circuit, so the influence of the zero sequence component is ignored. Figure 3 As shown in Figures (a) and (b) in the figure, the vector relationship between the positive sequence and negative sequence components can be obtained:

[0095]

[0096]

[0097] in, 、 Represents the positive and negative sequence components of the PCC point voltage, 、 Indicates the positive and negative sequence components of the PCC point current, 、 represents the positive and negative sequence components of the grid voltage. The mathematical model of the grid-connected converter in the two-phase synchronous rotating dq coordinate system is then obtained. The real and imaginary parts on both sides of the equation are equal, and we can obtain:

[0098]

[0099]

[0100]

[0101]

[0102] The subscripts “d” and “q” represent the d-axis and q-axis components, respectively.

[0103] Under unbalanced grid voltage, according to the instantaneous power theory, the active and reactive power on the grid side of the grid-connected inverter are expressed as:

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] in, represents the instantaneous active power DC component, represents the instantaneous reactive power DC component, 、 Represents the double frequency fluctuation component of instantaneous active power, 、 Represents the double frequency fluctuation component of instantaneous active power.

[0111] The active DC component Split into positive sequence components and negative sequence components , the reactive DC component Split into positive sequence components and negative sequence components .

[0112]

[0113]

[0114] Substituting the dq-axis component expressions of the PCC point current into the above formula and simplifying it, we can obtain the dq-axis component expressions of the positive and negative sequence voltages at the PCC point:

[0115]

[0116]

[0117]

[0118]

[0119] in:

[0120]

[0121]

[0122]

[0123]

[0124] Then, the relationship between the positive and negative sequence components of the PCC voltage and the positive and negative sequence components of active and reactive power can be obtained:

[0125]

[0126]

[0127] When the grid voltage is unbalanced, the voltage amplitude at the PCC point can be expressed as:

[0128]

[0129]

[0130]

[0131]

[0132]

[0133] in, 、 Indicates the maximum and minimum voltage amplitudes at the PCC point, 、 Indicates the phase of the positive and negative sequence voltage components at the PCC point, Indicates the phase difference between the positive and negative sequence components of the PCC point. When the maximum phase voltage is the largest, ,Right now ; When the minimum phase voltage is the smallest, ,Right now In 2017, my country's GB / T33593 distributed power grid connection technical requirements stipulated that the voltage deviation should meet , so the three-phase voltage at PCC point should satisfy:

[0134]

[0135]

[0136] In order to ensure the balance of three-phase current, the negative sequence components of active and reactive power are set to 0. At this time, the negative sequence voltage at the PCC point is a constant value, that is:

[0137]

[0138] At this time, the photovoltaic converter is kept operating at the maximum power point, and the value range of the reactive power positive sequence component can be obtained according to the above voltage constraints:

[0139]

[0140] When the grid voltage is unbalanced, neither the positive sequence voltage nor the average value of the three-phase voltage (RMS) can represent the change of the three-phase voltage. In order to achieve optimal support for the three-phase voltage, it is proposed to use the distance between the three-phase voltage and the nominal voltage as an indicator to represent the change of the three-phase voltage, that is:

[0141]

[0142] After substituting the three-phase voltage expression composed of positive and negative sequence voltages and phase difference into the equation, we can obtain the relationship between the index value and the positive sequence voltage and phase angle difference at the PCC point. In order to ignore the influence of the phase angle difference, we further consider using the square of each phase voltage to replace the phase voltage change, and then we can obtain the expression of the index value and the positive sequence voltage at the PCC point:

[0143]

[0144] When the negative sequence voltage is kept constant, the index value is a quadratic function composed of the square of the positive sequence voltage. Therefore, there is a certain positive sequence voltage that minimizes the index value, and at this time, the optimal control of the three-phase voltage can be achieved. Finally, according to the relationship between the positive sequence voltage and the reactive power positive sequence component, the reactive power negative sequence component corresponding to the minimum index value can be obtained. .

[0145] according to 、 , the range of possible values of the reactive power positive sequence component and the remaining capacity of the converter The voltage-reactive power control curve can be determined as follows:

[0146] First, we need to determine the reactive power control range of the control curve:

[0147]

[0148]

[0149] Then, given the control curve parameters, the process is set as Figure 5 As shown, if , the control curve is set as follows:

[0150]

[0151] like , the control curve is set as follows:

[0152]

[0153] Since the unbalanced state of the grid voltage will change and there is a certain error in the setting of the control curve, an adaptive additional control method is further proposed. The control process is as follows: Figure 6 As shown, the main control methods are as follows:

[0154] 1) If 、 , then let the control voltage ;

[0155] 2) If 、 , then let the control voltage ;

[0156] 3) If 、 , then let the control voltage ;

[0157] 4) If 、 , then let the control voltage .

[0158] like Figure 7 As shown, an improved grid support control system adapted to unbalanced grid voltage provided by an embodiment of the present invention includes:

[0159] Positive and negative sequence voltage measurement module, used to measure the positive and negative sequence voltage of the power grid 、 ;

[0160] Equivalent impedance measurement module, used to measure equivalent impedance ;

[0161] The positive and negative sequence voltage / component relationship derivation module is used to derive the relationship between the positive and negative sequence voltages at the PCC point and the positive and negative sequence components of the outer loop given power in a synchronous rotating coordinate system;

[0162] Negative sequence component reference value setting module, used to set the reference value of the negative sequence component of active and reactive power;

[0163] Reactive power positive sequence component adjustment range calculation module, used to calculate the reactive power positive sequence component according to the national standard requirements of photovoltaic inverter grid-connected voltage deviation Adjustable range;

[0164] Reactive power positive sequence component reference value calculation module, used to calculate the reactive power positive sequence component reference value when the index value is minimum ;

[0165] PCC point positive sequence voltage reference value calculation module is used to calculate the PCC point positive sequence voltage reference value when the index value is minimum ;

[0166] Sequence voltage-reactive power control parameter setting module, used to use reference value and Set positive sequence voltage-reactive power control parameters;

[0167] The adaptive additional control module is used to maintain the index value near the minimum value by using the adaptive additional control.

[0168] An application embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of an improved grid support control method that adapts to unbalanced grid voltage.

[0169] An application embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of an improved grid support control method adapted to unbalanced grid voltage.

[0170] An application embodiment of the present invention provides an information data processing terminal, which is used to implement an improved power grid support control system that adapts to unbalanced power grid voltage.

[0171] The present invention provides two embodiments of the invention: first, under unbalanced grid voltage, the simulation results of the improved voltage support control method disclosed in the present invention are compared with the existing voltage-reactive power control to verify the effectiveness and advantages of the proposed control method; second, the control effect of the proposed improved voltage support control method when the grid voltage unbalance conditions change is further verified to verify its practicality.

[0172] In the first embodiment, the system parameters are shown in Table 1. Simulations are performed under different grid voltage imbalance conditions. The grid voltage settings are shown in Table 2. Voltage-reactive power control is used at 1.5s, and improved voltage support control is used after 2.5s. The simulation results under the two scenarios are shown in Figure 2. Figure 8 and Figure 9 As shown, in both scenarios, it can be seen that compared with the existing voltage-reactive power control method, the improved method proposed in the present invention can reduce the distance between the three-phase voltage and the nominal voltage, make the three-phase voltage as close to the nominal voltage as possible, and can adjust the positive sequence voltage to the nominal voltage, which proves the effectiveness of the improved voltage support control method disclosed in the present invention.

[0173] In the second embodiment, the improved voltage support control method proposed in the present invention is first used to simulate the grid voltage unbalanced condition provided by scenario 1, and then the voltage unbalanced condition in scenario 2 is changed after 2.5 seconds. The simulation results are as follows: Figure 10 As shown, it can be seen that when the grid voltage imbalance condition changes, the control method proposed in this article can still ensure that the index value is controlled to the minimum and the positive sequence voltage is adjusted to near the nominal voltage, which proves the effectiveness of the adaptive module of the control method disclosed in the present invention.

[0174] Table 1 Parameters of the photovoltaic converter grid-connected system

[0175]

[0176] Table 2 Grid voltage unbalance condition settings

[0177]

[0178] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware portion can be implemented using dedicated logic; the software portion can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. Those skilled in the art will appreciate that the above-mentioned devices and methods can be implemented using computer-executable instructions and / or contained in processor control code, for example, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, or can be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0179] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. An improved grid support control method adapted to unbalanced grid voltage, characterized in that: include: 1) Measure the positive and negative sequence voltages of the power grid 、 and equivalent impedance , derive the relationship between the positive and negative sequence voltages at the PCC point and the positive and negative sequence components of the given power in the outer loop in a synchronous rotating coordinate system; 2) Given the reference values of the negative sequence components of active and reactive power, calculate the positive sequence component of reactive power according to the national standard requirements for the grid-connected voltage deviation of photovoltaic inverters. Adjustable range; 3) Establish the relationship between the index value μ representing the distance from the three-phase voltage to the nominal voltage and the reactive power positive sequence component, and calculate the reference value of the reactive power positive sequence component when the index value is minimum And PCC point positive sequence voltage reference value ; 4) Using reference values and Set the positive sequence voltage-reactive power control parameters and use adaptive additional control to keep the index value near the minimum value.

2. The improved grid support control method adapted to unbalanced grid voltage according to claim 1, characterized in that: The relationship between the positive and negative sequence voltages at the PCC point and the reference values of the positive and negative sequence components of the outer loop given power is: ； ； ； ； ； ； Among them, V + 、 Represents the positive and negative sequence voltages at the PCC point, with the subscripts "d" and "q" representing the d and q axis components, respectively. 、 Indicates the positive and negative sequence voltage of the power grid, 、 represents the equivalent resistance and reactance of the power grid, 、 Indicates the given active / reactive power positive sequence component reference value, 、 Indicates the reference value of the negative sequence component of the given active / reactive power.

3. The improved grid support control method adapted to unbalanced grid voltage according to claim 2, characterized in that: The selection of the reference value of the reactive power positive sequence component should meet the following three constraints: 1) The maximum three-phase voltage should be less than or equal to the upper limit of the voltage deviation standard, that is: ； ； Where, Indicates the maximum phase voltage value. Indicates the upper limit of voltage deviation requirement of photovoltaic grid-connected technical standards; 2) The minimum three-phase voltage should be greater than or equal to the lower limit of the voltage deviation standard, that is: ； ； Where, Indicates the minimum phase voltage value. Indicates the lower limit of voltage deviation requirement of photovoltaic grid-connected technical standards; 3) The sum of the reactive power positive and negative sequence reference values should be less than or equal to the remaining capacity of the photovoltaic inverter, that is: ； Where S N It represents the rated capacity of the photovoltaic grid-connected inverter, and P represents the active power generated by the photovoltaic grid-connected inverter.

4. The improved grid support control method adapted to unbalanced grid voltage according to claim 2, characterized in that: The index value μ that characterizes the distance between the three-phase voltage and the nominal voltage is: ； in, 、 、 Respectively represent the effective values of the three-phase voltages at PCC point; The relationship between the index value μ and the reactive power positive sequence component is: 。 5. The improved grid support control method adapted to unbalanced grid voltage according to claim 1, characterized in that: Positive sequence voltage-reactive power control strategy includes: Voltage-reactive power control curve setting, based on the reference value of reactive power positive sequence component when the index value is minimum , PCC point positive sequence voltage reference value , the remaining capacity of the photovoltaic grid-connected inverter and the voltage deviation limit specified in the photovoltaic grid-connected technical standards to determine the control curve parameters; Adaptive additional control, according to the changes of the previous two index values, the control voltage Make adjustments so that the indicator value approaches the minimum value.

6. The improved grid support control method adapted to unbalanced grid voltage according to claim 5, characterized in that: The voltage-reactive power control curve is set as follows: 1) If , the control curve is set as follows: ； in, 、 Indicates the adjustable range limit of reactive power positive sequence component, Indicates the reference value of reactive power positive sequence component corresponding to the minimum index value, Indicates the effective value of the positive sequence voltage at the PCC point when the index value is minimum; 2) If , the control curve is set as follows: 。 7. The improved grid support control method adapted to unbalanced grid voltage according to claim 5, characterized in that: The adaptive additional control method is as follows: 1) If 、 , then let the control voltage ; 2) If 、 , then let the control voltage ; 3) If 、 , then let the control voltage ; 4) If 、 , then let the control voltage .

8. An improved grid support control system adapted to unbalanced grid voltage that implements the improved grid support control method adapted to unbalanced grid voltage as claimed in any one of claims 1 to 7, characterized in that: include: Positive and negative sequence voltage measurement module, used to measure the positive and negative sequence voltage of the power grid 、 ; Equivalent impedance measurement module, used to measure equivalent impedance ; The positive and negative sequence voltage / component relationship derivation module is used to derive the relationship between the positive and negative sequence voltages at the PCC point and the positive and negative sequence components of the outer loop given power in a synchronous rotating coordinate system; Negative sequence component reference value setting module, used to set the reference value of the negative sequence component of active and reactive power; Reactive power positive sequence component adjustment range calculation module, used to calculate the reactive power positive sequence component according to the national standard requirements of photovoltaic inverter grid-connected voltage deviation Adjustable range; Reactive power positive sequence component reference value calculation module, used to calculate the reactive power positive sequence component reference value when the index value is minimum ; PCC point positive sequence voltage reference value calculation module is used to calculate the PCC point positive sequence voltage reference value when the index value is minimum ; Sequence voltage-reactive power control parameter setting module, used to use reference value and Set positive sequence voltage-reactive power control parameters; The adaptive additional control module is used to maintain the index value near the minimum value by using the adaptive additional control.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the improved grid support control method for adapting to unbalanced grid voltage according to any one of claims 1 to 7.

10. An information data processing terminal, used for implementing the improved grid support control system adapted to unbalanced grid voltage according to claim 8.

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