Improved power grid support control method and system adapting to unbalanced power grid voltage

Abstract

The invention belongs to the technical field of power electronic systems, and discloses an improved power grid support control method and system adaptive to unbalanced power grid voltage, positive and negative sequence voltages # imgabs0 # and # imgabs1 # and equivalent impedance # imgabs2 # of a power grid are measured, and a relational expression between the positive and negative sequence voltages of a PCC point and positive and negative sequence components of given power of an outer ring is deduced under a synchronous rotating coordinate system; giving active and reactive power negative-sequence component reference values, and calculating an adjustable range of a reactive power positive-sequence component # imgabs3 # according to national standard requirements of grid-connected voltage deviation of the photovoltaic inverter; establishing a relational expression between an index value mu representing the distance from the three-phase voltage to the nominal voltage and a reactive power positive-sequence component, and calculating a reactive power positive-sequence component reference value # imgabs4 # and a PCC point positive-sequence voltage reference value # imgabs5 # when the index value is minimum; a positive sequence voltage-reactive power control parameter is set by using reference values # imgabs6 # and # imgabs7 #, and an index value is kept near a minimum value by using adaptive additional control.

Description

Technical Field

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

[0002] Photovoltaic power is massively connected to the grid. However, with the increase in the installed capacity of photovoltaic power, its output defects have brought new challenges to the grid. Therefore, photovoltaic grid-connected converters are required to have the ability to actively support the grid voltage and support the voltage at the photovoltaic grid connection point by flexibly adjusting the output power of the converter. However, due to the use of unbalanced loads and the occurrence of unbalanced faults, the grid voltage presents an unbalanced state, and the existing voltage support strategies cannot effectively achieve the support control of unbalanced three-phase voltages.

[0003] Currently, many grid standards require that distributed grid-connected power generation systems remain grid-connected and provide dynamic reactive power support under voltage dips within a certain range, and a voltage-reactive power control method is proposed, requiring that the reference value of the reactive power output should be given according to the change in the positive-sequence voltage or the average value of the three-phase voltage (RMS) at the grid connection point. When the grid voltage is balanced, the positive-sequence voltage or the average value of the three-phase voltage (RMS) at the grid connection point can effectively characterize the change in the three-phase voltage, and the voltage-reactive power control method can be used to suppress the over-limit voltage and boost the voltage dip. However, for unbalanced grid voltages, due to the presence of negative-sequence voltages, the original control voltage cannot fully characterize the change in each phase voltage, resulting in a situation where the voltage of a certain phase exceeds the limit range and the unbalance degree of the grid connection point voltage deteriorates. And under traditional grid-following current control, due to the presence of negative-sequence reactive current, when using reactive power to suppress over-voltage, it may cause a change in the negative-sequence voltage, further deteriorating the unbalance degree of the grid connection point voltage.

[0004] Regarding the voltage support problem under unbalanced grid voltages, some literature has proposed to distribute the positive-sequence active current and reactive current according to the line impedance ratio, thereby effectively supporting the lowest phase voltage. This method can effectively support the minimum phase voltage when an asymmetric fault occurs in the grid, but it ignores the change in the voltages of the other two phases and does not consider reducing the negative-sequence voltage. Therefore, some literature suppresses the negative-sequence voltage on the premise of taking the boost of the positive-sequence voltage as the primary goal, which can not only effectively support the voltage at the PCC point but also reduce the unbalance degree of the grid voltage. However, the above methods mainly consider the voltage dip problem caused by asymmetric faults in the grid and ignore the voltage over-limit problem caused by the access of large-capacity photovoltaic power under unbalanced load scenarios. Therefore, a flexible voltage support strategy is needed to effectively support the three-phase voltages under different unbalanced grid voltage scenarios.

[0005] Through the above analysis, the problems and defects existing in the prior art are as follows: The prior art ignores the voltage over-limit problem caused by the access of large-capacity photovoltaic power in the unbalanced load scenario. 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 adapted to unbalanced grid voltages, aiming to achieve optimal support for the three-phase voltages 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 voltages includes:

[0008] 1) Measuring the positive and negative sequence voltages of the grid and the equivalent impedance , and deriving 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 the synchronous rotating coordinate system;

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

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

[0011] 4) Use the reference values and to set the positive sequence voltage-reactive power control parameters, and use the 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] Wherein, and Indicates the positive and negative sequence voltages at the PCC point. The subscripts "d" and "q" represent the dq-axis components respectively. 、 Indicates the positive and negative sequence voltages of the power grid. 、 Indicates the equivalent resistance and reactance of the power grid. 、 Indicates the reference value of the positive sequence component of the given active / reactive power. 、 Indicates the reference value of the negative sequence component of the given active / reactive power, m 01 、n 01 、m 02 、n 02 Indicates intermediate variables.

[0020] Furthermore, the selection of the reference value of the positive sequence component of reactive power should satisfy the following three constraint conditions:

[0021] 1) The maximum response of the three-phase voltage should be less than or equal to the upper limit value of the voltage deviation standard, i.e.:

[0022]

[0023]

[0024] In the formula, Indicates the maximum phase voltage value, Indicates the upper limit value of the voltage deviation requirement in the PV grid connection technical standard;

[0025] 2) The minimum response of the three-phase voltage should be greater than or equal to the lower limit value of the voltage deviation standard, i.e.:

[0026]

[0027]

[0028] In the formula, Indicates the minimum phase voltage value, Indicates the lower limit value of the voltage deviation requirement in the PV grid connection technical standard;

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

[0030]

[0031] In the formula, S N Indicates the rated capacity of the PV grid connection inverter, and P indicates the active power generated by the PV grid connection inverter.

[0032] Furthermore, the index value μ representing the distance from the three-phase voltage to the nominal voltage is:

[0033]

[0034] Among them, 、 、 respectively represent the effective values of the three-phase voltages at the PCC point;

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

[0036]

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

[0038] Setting the voltage-reactive power control curve, according to the reference value of the positive-sequence component of the reactive power when the index value is the smallest 、the reference value of the positive-sequence voltage at the PCC point 、the remaining capacity of the photovoltaic grid-connected inverter and the voltage deviation limit specified by the photovoltaic grid-connection technical standard to determine the control curve parameters;

[0039] Adaptive additional control, according to the changes in the previous two index values, adjust the control voltage so as to make the index value approach the minimum value.

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

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

[0042]

[0043] Among them, 、 represent the limit values of the adjustable range of the positive-sequence component of the reactive power, represents the reference value of the positive-sequence component of the reactive power corresponding to the minimum index value, represents the effective value of the positive-sequence voltage at the PCC point when the index value is the smallest;

[0044] 2) If , then 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 set the control voltage ;

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

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

[0051] Another object of the present invention is to provide an improved power grid support control system for adapting to unbalanced grid voltages to implement the improved power grid support control method for adapting to unbalanced grid voltages, including:

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

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

[0054] Positive and negative sequence voltage / component relation derivation module, used to derive the relation 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 the synchronous rotating coordinate system;

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

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

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

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

[0059] Sequence voltage-reactive power control parameter setting module, used to set the positive sequence voltage-reactive power control parameters by using the reference values and ;

[0060] Adaptive additional control module, used to keep the index value near the minimum value by using adaptive additional control.

[0061] Another object of the present invention is to provide 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 the improved grid support control method for adapting to unbalanced grid voltage.

[0062] Another object of the present invention is to provide a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of the improved grid support control method for adapting to unbalanced grid voltage.

[0063] Another object of the present invention is to provide an information data processing terminal for implementing the improved grid support control system for adapting to unbalanced grid voltage.

[0064] Combined with the above technical solutions and solved technical problems, 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 by the present invention characterizes the change of three-phase voltage by the distance from the three-phase voltage to the nominal voltage, and uses the change trend of the index value to set the positive-sequence voltage-reactive power control parameters, taking into account the change of three-phase voltage, rather than only considering the change of positive-sequence voltage or a certain phase voltage.

[0066] (2) The control method proposed by the present invention is premised on the balance of three-phase currents, and then gives the adjustment range of the positive-sequence component of reactive power, and further realizes the effective support of three-phase voltage on the premise of ensuring that each phase voltage is within the range required by the voltage deviation standard.

[0067] (3) The control method proposed by the present invention has strong applicability and can effectively support three-phase voltage for voltage dips and voltage over-limit under unbalanced grid voltage conditions.

[0068] (4) The control method proposed by the present invention can adaptively adjust the control voltage according to parameter changes. When the degree of unbalanced grid voltage changes, it can re-control the index value near the new minimum value according to the change of the index value and the control voltage, and realize the effective support of three-phase point voltage.

[0069] Regarding 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 specifically described as follows:

[0070] The present invention provides an improved grid support control method and system for adapting 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 system always operates at the maximum power point. At this time, the positive sequence active power reference value is the product of the positive sequence component reference value of the active current and the DC-side voltage reference value output by 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 deduced. Considering that most current photovoltaic grid-connected converters do not control the negative sequence voltage, the present invention takes the balance of the converter output current as a premise. At this time, the negative sequence reference current is set to 0, which reduces the negative sequence power control loop and 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. Furthermore, according to the voltage deviation limit, the adjustment range of the positive sequence reactive power can be obtained, and then the three-phase voltages can be controlled within the limit range. In addition, by determining the positive sequence reactive power reference value corresponding to the minimum index value to determine the control curve, the overshoot and undershoot problems of the original voltage-reactive power 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 at the minimum value, making the three-phase voltages close to the nominal voltage.

[0071] Using the control method disclosed in the present invention, the optimal support of the three-phase voltages under different grid voltage imbalance conditions can be realized: measure the equivalent line impedance and the positive and negative sequence components of the grid voltage, calculate the adjustable range of the positive sequence reactive power according to the standard voltage deviation requirements for distributed power grid connection, and then set the positive sequence voltage-positive sequence reactive power control curve parameters in the photovoltaic converter. Through the above settings, the three-phase voltages can be kept within the limit range and the sum of the distances between the three-phase voltages and the nominal voltage can be minimized. This control method and the controller system can be widely applied to the scenarios where the grid voltage is unbalanced during the grid connection of new energy. Since only the equivalent line impedance and the grid voltage need to be monitored, the requirement for communication is greatly reduced. At the same time, the system can adaptively adjust the output of the reactive power according to the changes of the line impedance and the grid voltage, greatly simplifying the implementation and operation difficulties in engineering practice.

[0072] Currently, both domestic and foreign standards for distributed power grid connection require that distributed power sources have the voltage support function. However, 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 of the three-phase voltages simultaneously, resulting in a decline in control performance, which greatly limits its application in engineering. When using voltage-reactive power control, the adjustable range of reactive power usually depends on the remaining capacity of the converter. When the grid conditions change under this condition, existing research usually adjusts by changing the slope of the control curve, which not only affects the stability of the system but also ignores the scenario of grid voltage imbalance. The control method provided by the present invention fills this gap and provides a control basis for the voltage support problem under unbalanced grid voltages.

[0073] In current grid connection test standards at home and abroad, it is required that voltage support functions such as voltage - reactive power control should also be able to achieve good three - phase voltage support effects in unbalanced voltage scenarios. However, the existing voltage - reactive control curves are difficult to adapt to the complex and changing grid operating conditions. When the grid impedance characteristics change with the topology, the preset control parameters do not match the actual grid impedance, which will then cause over - compensation or under - compensation. The control method provided by the present invention overcomes the problem of mismatch between reactive power output and voltage support requirements, improves the flexibility and adaptability of voltage support control, and enables it to still ensure effective three - phase voltage support under various operating condition changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments of the present invention. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0075] Figure 1 is the flowchart of the improved grid support control method for adapting to unbalanced grid voltage provided by the embodiment of the present invention;

[0076] Figure 2 is the schematic structural diagram of the photovoltaic grid - connection control system when the grid voltage is unbalanced provided by the embodiment of the present invention;

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

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

[0079] Figure 5 is the flowchart of parameter setting for the voltage - reactive control curve provided by the embodiment of the present invention;

[0080] Figure 6 is the flowchart of the additional adaptive control method provided by the embodiment of the present invention;

[0081] Figure 7 is the structural diagram of the improved grid support control system for adapting to unbalanced grid voltage provided by the embodiment of the present invention; Figure 8 is the comparison diagram of the voltage - reactive control and the improved voltage support control effects under different voltage unbalance scenarios 1 provided by the embodiment of the present invention;

[0082] Figure 9 It is a comparison diagram of 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 It is an improved voltage support control effect diagram under continuous change of voltage imbalance conditions provided by an embodiment of the present invention. Detailed implementation manners

[0083] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used 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 adapted to unbalanced grid voltages, which will be described in detail below with reference to the accompanying drawings.

[0085] In order to enable those skilled in the art to fully understand how the present invention is specifically implemented, this part is an explanatory embodiment that expands and explains the technical solution of the claims.

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

[0087] 1) Measure the positive and negative sequence voltages , and the equivalent impedance of the power grid, and deduce 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 in the synchronous rotating coordinate system;

[0088] 2) Given the reference values of the negative sequence components of the active and reactive powers, calculate the adjustable range of the positive sequence component of the reactive power according to the national standard requirements for the grid connection voltage deviation of the photovoltaic inverter;

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

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

[0091] According to Figure 2 the equivalent circuit of photovoltaic grid connection shown, the electrical relationships between the voltage and current at the PCC point, the grid voltage and the grid equivalent impedance can be obtained:

[0092]

[0093] Among them, V represents the voltage at the PCC point, i represents the current at the PCC point, V g represents the equivalent voltage of the power grid, and R g , L g represent the equivalent impedance of the power grid.

[0094] When the power grid voltage is unbalanced, the power grid voltage can be decomposed into positive-sequence, negative-sequence, and zero-sequence components. Since the main research object here is the three-phase three-wire system and there is no zero-sequence component loop, the influence of the zero-sequence component is ignored. Furthermore, as shown in Figure (a) and Figure (b) in Figure 3 , the vector relation expressions between the positive-sequence and negative-sequence components can be obtained:

[0095]

[0096]

[0097] Among them, , represent the positive-sequence and negative-sequence components of the voltage at the PCC point, , represent the positive-sequence and negative-sequence components of the current at the PCC point, , represent the positive-sequence and negative-sequence components of the power grid voltage. Furthermore, the mathematical model of the grid-connected converter in the two-phase synchronous rotating dq coordinate system can be obtained. By making the real and imaginary parts of both sides of the equation equal, the following can be obtained:

[0098]

[0099]

[0100]

[0101]

[0102] Among them, the subscripts "d" and "q" are the d-axis and q-axis components respectively.

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

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] Among them, represents the DC component of the instantaneous active power, represents the DC component of the instantaneous reactive power, , represents the double-frequency fluctuation component of the instantaneous active power, , represents the double-frequency fluctuation component of the instantaneous active power.

[0111] The active DC component is split into a positive-sequence component and a negative-sequence component , and the reactive DC component is split into a positive-sequence component and a negative-sequence component .

[0112]

[0113]

[0114] Substitute the expressions of the dq-axis components of the PCC point current into the above formula and simplify to obtain the expressions of the dq-axis components of the positive and negative sequence voltages at the PCC point:

[0115]

[0116]

[0117]

[0118]

[0119] Among them:

[0120]

[0121]

[0122]

[0123]

[0124] Furthermore, the relationship between the positive and negative sequence components of the PCC point voltage and the positive and negative sequence components of the 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] Wherein, 、 represent the maximum and minimum voltage amplitudes at the PCC point, 、 represent the phases of the positive and negative sequence voltage components at the PCC point, represents the phase difference between the positive and negative sequence components at the PCC point. When the maximum phase voltage is the largest, , that is ; when the minimum phase voltage is the smallest, , that is . The GB / T 33593 Technical Requirements for Grid Connection of Distributed Generation distributed in China in 2017 stipulates that the voltage deviation should satisfy , so the three-phase voltages at the PCC point should satisfy:

[0134]

[0135]

[0136] In order to ensure the balance of three-phase currents, let the negative sequence components of active and reactive powers be 0. At this time, the negative sequence voltage at the PCC point is a fixed value, that is:

[0137]

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

[0139]

[0140] When the grid voltage is unbalanced, neither the positive sequence voltage nor the average value of the three-phase voltage (RMS) can characterize the change of the three-phase voltage. In order to achieve the optimal support for the three-phase voltage, here it is proposed to use the distance from the three-phase voltage to the nominal voltage as an index to characterize 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, the relational expression between the index value and the positive-sequence voltage and phase angle difference at the PCC point can be obtained. To neglect the influence of the phase angle difference, further consider using the square of each phase voltage to replace the change of each phase voltage, and then the relational expression between the index value and the positive-sequence voltage at the PCC point can be obtained:

[0143]

[0144] When the negative-sequence voltage remains 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 makes the index value minimum, and at this time, the optimal control of the three-phase voltage can be realized. When determining the positive-sequence voltage at the minimum of the index value After that, according to the relationship between the positive-sequence voltage and the positive-sequence component of the reactive power, the negative-sequence component of the reactive power corresponding to the minimum of the index value can be obtained .

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

[0146] First, it is necessary to determine the reactive power control range of the control curve:

[0147]

[0148]

[0149] Furthermore, given the control curve parameters, the setting process is as Figure 5 shown. If , the control curve is set as follows:

[0150]

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

[0152]

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

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

[0155] 2) If and , then set the control voltage ;

[0156] 3) If and , then set the control voltage ;

[0157] 4) If and , then set the control voltage .

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

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

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

[0161] Positive and negative sequence voltage / component relation derivation module, used to derive the relation 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 the synchronous rotating coordinate system;

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

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

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

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

[0166] Sequence voltage - reactive power control parameter setting module, used to set the positive sequence voltage - reactive power control parameters by using the reference values and ;

[0167] Adaptive additional control module, used to keep the index value near the minimum value by using 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 adapted 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 for implementing an improved grid support control system adapted to unbalanced grid voltage.

[0171] The present invention provides two invention embodiments: First, under unbalanced grid voltage, the improved voltage support control method disclosed in the present invention is compared with the simulation results of 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 condition changes is continuously verified to verify its practicability.

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

[0173] In the second embodiment, first, the improved voltage support control method proposed by the present invention is used for simulation under the grid voltage unbalance condition provided in Scenario 1. After 2.5 s, it is changed to the voltage unbalance condition in Scenario 2. The simulation result is as Figure 10 shown. It can be seen that when the grid voltage unbalance condition changes, the control method proposed in this paper can still ensure that the index value is controlled to the minimum and the positive-sequence voltage is adjusted to near the nominal voltage, proving the effectiveness of the adaptive module of the control method disclosed in the present invention.

[0174] Table 1 Grid-connected system parameters of photovoltaic converters

[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 part can be implemented using dedicated logic; the software part can be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or dedicated designed hardware. Those of ordinary skill in the art can understand that the above devices and methods can be implemented using computer-executable instructions and / or included in processor control code, for example, such code is provided on a carrier medium such as a disk, CD, or DVD-ROM, a programmable memory such as read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The devices and their modules of the present invention can be implemented by hardware circuits of programmable hardware devices such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or 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 hardware circuits and software such as firmware.

[0179] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope 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 voltage 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 the 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 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 for adapting 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 given power in the outer loop is: ； ； ； ； ； ； in, , Represents the positive and negative sequence voltages at the PCC point, and the subscripts "d" and "q" represent 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 for adapting to unbalanced grid voltage according to claim 1, 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: ； ； In the formula, Indicates the maximum phase voltage value. Indicates the upper limit of the voltage deviation requirement of the photovoltaic grid-connected technology standard; 2) The minimum three-phase voltage should be greater than or equal to the upper limit of the voltage deviation standard, that is: ； ； In the formula, Indicates the minimum phase voltage value. Indicates the lower limit of the voltage deviation requirement of the photovoltaic grid-connected technology standard; 3) The sum of the positive and negative sequence reference values ​​of reactive power should be less than or equal to the remaining capacity of the photovoltaic inverter, that is: ； In the formula, 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 for adapting to unbalanced grid voltage according to claim 1, 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 the 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 reactive power positive sequence component reference value 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 indicator values, the control voltage Make adjustments so that the indicator value approaches the minimum value.

6. The improved grid support control method for adapting 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, It 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 for adapting 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 voltage of the PCC point and the positive and negative sequence components of the given power of the outer ring 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 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 ; The 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 adapted to unbalanced grid voltage as described in 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 as claimed in claim 8.

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