Virtual synchronous machine island detection method and device based on impedance and phase deviation detection

Abstract

The invention discloses a virtual synchronous machine island detection method and device based on impedance and phase deviation detection. The method comprises the following steps: measuring power grid impedance near a specified high-order switching frequency of a virtual synchronous machine under a no-load condition; calculating the value range of the load impedance of the virtual synchronous machine in the blind area; according to the measured power grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the value range of the load impedance of the virtual synchronous machine in the blind area, calculating the value range of the impedance of the PCC point under the condition of the virtual synchronous machine island and the grid-connected condition of the island detection based on the phase deviation under the blind area condition; constructing island judgment logic of impedance detection; constructing decision fusion logic of phase detection and impedance detection; and executing the constructed decision fusion logic of phase detection and impedance detection, and outputting an island detection result. According to the method, non-blind area island detection is realized under the condition that disturbance is not brought, and the sensitivity of island detection of the virtual synchronous machine system is improved.

Description

Technical Field

[0001] The present invention belongs to the field of virtual synchronous machine control, and in particular relates to a virtual synchronous machine island detection method and device based on impedance and phase offset detection. Background Art

[0002] A virtual synchronous machine is a power electronic device that simulates the characteristics of a traditional synchronous generator. It plays a key role in distributed power sources, especially in improving the stability and reliability of power systems. With the popularization of distributed energy, the island effect has become an important safety issue. The island effect refers to the situation where when a distributed generation system is accidentally disconnected from the main power grid, the distributed power source continues to supply power, forming an independently operated small power grid (island).

[0003] In order to detect and prevent the occurrence of islanding, a variety of detection methods have been proposed, which are mainly divided into two categories: active and passive. In VSG systems, passive islanding detection methods have received particular attention, mainly because of the following reasons:

[0004] (1) Stability and power quality: Passive methods do not affect power quality and are beneficial for maintaining grid stability.

[0005] (2) Sensitivity and reliability: Modern passive methods have achieved significant improvements in detection sensitivity and reliability, especially when combined with advanced signal processing and data analysis techniques.

[0006] (3) Difficulty of implementation: The passive method is relatively simple to implement and does not require additional disturbance signal injection equipment.

[0007] Passive island detection based on phase shift is a commonly used passive island detection method. However, its threshold setting will cause the following problems during detection:

[0008] (1) If the threshold is too large, a large phase offset is required to output an island signal. That is, when the difference between the load and the command value is small to a certain extent, the phase offset will be too small and a detection blind spot will appear.

[0009] (2) If the threshold is too small, when the virtual synchronous machine system fluctuates during grid connection, such as grid fluctuations or load switching, it will also cause phase shift, so island detection malfunction may occur.

[0010] The real-time grid impedance estimation technology based on the inherent switching characteristics can calculate the PCC point impedance value at the inherent high-frequency harmonic frequency caused by the inherent switching characteristics of the virtual synchronous machine by processing the PCC point voltage and current signals without injecting harmonic disturbances. However, if the passive island detection based on impedance detection is directly designed according to this impedance value, the following problems will also occur:

[0011] (1) When there are different load conditions and grid impedance conditions, the change characteristics of the PCC point impedance are different, which makes it difficult to design the logic of impedance detection and may even cause the island detection to malfunction or refuse to operate.

[0012] (2) The inherent high-frequency harmonics of the voltage and current at the PCC point of the virtual synchronous machine are a necessary condition for this detection method. Generally, their content is relatively small. Therefore, the impedance value directly measured by this method sometimes lacks accuracy. When directly applied to the island detection method based on impedance detection, it may also cause the island detection to malfunction or refuse to operate. Summary of the invention

[0013] The object of the present invention is to provide a method and device for detecting virtual synchronous machine islanding based on impedance and phase offset detection, so as to solve the above-mentioned problem.

[0014] The present invention is implemented according to the following technical solutions:

[0015] In a first aspect, the present invention provides a method for detecting an island of a virtual synchronous machine based on impedance and phase offset detection, the method comprising:

[0016] The real-time grid impedance estimation technology using inherent switching characteristics is used to measure the grid impedance near the specified high-order switching frequency of the virtual synchronous machine under no-load conditions;

[0017] Based on the blind zone condition of phase-shifted island detection, the range of the load impedance of the virtual synchronous machine in the blind zone is calculated;

[0018] According to the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the value range of the load impedance of the virtual synchronous machine in the blind zone, the impedance value range near the specified high-order switching frequency of the PCC point under the blind zone conditions of the virtual synchronous machine islanding and grid-connected conditions of the phase-shift-based islanding detection is calculated;

[0019] According to the PCC point, the impedance value range near the high-order switching frequency is specified, and the island judgment logic of impedance detection is constructed;

[0020] According to the island judgment logic of impedance detection, the decision fusion logic of phase detection and impedance detection is constructed;

[0021] By measuring the phase offset value of the virtual synchronous machine and the impedance value of the PCC point near the specified high-order switching frequency, the constructed decision fusion logic of phase detection and impedance detection is executed to output the island detection result.

[0022] In one implementation, the grid impedance measured near the specified high-order switching frequency of the virtual synchronous machine under no-load condition is expressed as:

[0023] Zgs =R g +jω s L g

[0024] Among them, Z gs is the grid impedance, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance.

[0025] In one implementation, the blind area condition of the phase offset-based island detection is approximately expressed as:

[0026]

[0027] Among them, Δθ is the actual phase offset value, ΔP is the actual power offset value, Δt is the phase offset detection setting integration time, k f is the sum of the equivalent frequency droop coefficients of the virtual synchronous machine speed regulator and the main body, Δθ th is the phase shift threshold.

[0028] In one implementation, the calculating of the value range of the load impedance of the virtual synchronous machine in the blind area includes:

[0029] The load impedance corresponding to the blind area is expressed as Z load , specifically:

[0030] When ΔP>0,

[0031]

[0032] When ΔP<0,

[0033]

[0034] The value range of the virtual synchronous machine load impedance in the blind area is:

[0035]

[0036] Among them, U n is the rated voltage of the power grid, P ref is the active power instruction;

[0037] Substitute the specific parameters into the value range of the virtual synchronous machine load impedance in the blind area, calculate the specific parameter range and express it as:

[0038] Z load =R load ∈(R min ,R max )

[0039] Among them, R load is the load resistance corresponding to the blind area, R min ,R max They are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area respectively.

[0040] In one embodiment, the virtual synchronous machine PCC point specifies the grid impedance Z near the high-order switching frequency. pccs , the expression is:

[0041] Z pccs =R pcc +jω s L pcc

[0042] The PCC point in the case of a virtual synchronous machine island specifies the impedance near the high-order switching frequency, and the expression is:

[0043] Z pccs =Z load =R load ;

[0044] The PCC point specifies the impedance near the high-order switching frequency when the virtual synchronous machine is connected to the grid. The expression is:

[0045]

[0046] Among them, R pcc Z pccs The resistance component, L pcc Z pccs The inductance component, R load is the load resistance corresponding to the blind area, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance.

[0047] In one implementation, the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the value range of the load impedance of the virtual synchronous machine in the blind area are substituted into the impedance expression near the specified high-order switching frequency of the PCC point in the case of virtual synchronous machine islanding and grid connection, and the following can be obtained:

[0048] The impedance value range near the high-order switching frequency of the PCC point specified under the blind zone condition of the virtual synchronous machine islanding case based on phase offset islanding detection is expressed as:

[0049]

[0050] The impedance value range near the PCC point of the virtual synchronous machine grid-connected under the blind zone condition of phase-shift island detection is expressed as:

[0051]

[0052] Among them, R load is the load resistance corresponding to the blind area, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance, R min ,R max are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area, R 并网min , R 并网max The minimum and maximum values ​​of the impedance resistance components near the high-order switching frequency are respectively specified for the PCC point under the condition of virtual synchronous machine grid connection under blind zone conditions.

[0053] L 并网min , L 并网max The minimum and maximum values ​​of the impedance and inductance components near the high-order switching frequency are respectively specified for the PCC point when the virtual synchronous machine is connected to the grid under blind zone conditions.

[0054] In one implementation, the impedance value range near the high-order switching frequency is specified according to the PCC point, and the island determination logic of impedance detection is constructed as follows:

[0055] Measure the impedance of the grid connection point near the s-th switching frequency of the virtual synchronous machine and set k 阻抗检测 and M 阻抗检测 The initial value of is 0;

[0056] When R is detected pcc ∈(R min ,R max )and When k 阻抗检测 The count is increased by 1; otherwise, k 阻抗检测 The count is reset, and M 阻抗检测 =0;

[0057] When k 阻抗检测 When the cumulative value is greater than or equal to 100, set M 阻抗检测 =1; otherwise, continue to detect;

[0058] Among them, R pcc Z pccs The resistance component, L pcc Z pccs The inductance component, R load is the load resistance corresponding to the blind area, ω s is the angular frequency corresponding to the specified switching frequency s times; R min ,R max are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area, R 并网min , R并网max are the minimum and maximum values ​​of the impedance and resistance components near the high-order switching frequency specified by the PCC point under the condition of virtual synchronous machine grid connection under blind zone conditions, L 并网min , L 并网max The minimum and maximum values ​​of the impedance and inductance components near the high-order switching frequency are respectively specified for the PCC point when the virtual synchronous machine is connected to the grid under blind zone conditions.

[0059] In one implementation, the decision fusion logic for phase detection and impedance detection is constructed based on the island judgment logic for impedance detection as follows:

[0060] Measure the impedance of the grid connection point near the s-th switching frequency of the virtual synchronous machine;

[0061] when When M=M 相位检测 ;

[0062] When R pcc ∈(0.8R min ,1.2R max ), there are two cases:

[0063] (1) When R pcc ∈(R min ,R max ), M=M 阻抗检测 ;

[0064] (2) When M=M 相位检测 |M 阻抗检测 .

[0065] Among them, R pcc Z pccs The resistance component, R min ,R max They are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area respectively.

[0066] In a second aspect, the present invention provides a virtual synchronous machine island detection device based on impedance and phase offset detection, the device comprising:

[0067] A grid impedance calculation module near a specified high-order switching frequency is used to measure the grid impedance near a specified high-order switching frequency of a virtual synchronous machine under no-load conditions by using a real-time grid impedance estimation technique based on inherent switching characteristics;

[0068] A load impedance value range calculation module is used to calculate the load impedance value range of the virtual synchronous machine in the blind zone based on the blind zone condition of the island detection of the phase offset;

[0069] The PCC point impedance value range calculation module is used to calculate the impedance value range near the PCC point specified high-order switching frequency under the blind zone conditions of the virtual synchronous machine islanding and grid-connected conditions under the phase offset-based islanding detection according to the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the virtual synchronous machine load impedance value range in the blind zone;

[0070] The island judgment logic module of impedance detection is used to specify the impedance value range near the high-order switching frequency at the PCC point and build the island judgment logic of impedance detection;

[0071] A decision fusion logic module is used to construct a decision fusion logic of phase detection and impedance detection according to the constructed island judgment logic of impedance detection;

[0072] The island detection result output module is used to measure the phase offset value of the virtual synchronous machine and the impedance value of the PCC point near the specified high-order switching frequency, execute the constructed decision fusion logic of phase detection and impedance detection, and output the island detection result.

[0073] In a third aspect, the present invention provides a virtual synchronous machine system, including the above-mentioned virtual synchronous machine island detection device based on impedance and phase offset detection.

[0074] Beneficial effects of the present invention:

[0075] The present invention discloses a method and device for detecting an island of a virtual synchronous machine based on impedance and phase shift detection, which solves the risk of possible refusal to operate or erroneous operation caused by problems such as threshold setting or detection accuracy in a single passive island detection method based on phase shift detection or a passive island detection method based on impedance detection. For the phase detection part, since there is impedance detection as a supplementary detection of its blind area, the difficulty of setting its own threshold is reduced. For the impedance detection part, it is only responsible for the impedance conditions near the blind area of ​​the phase detection, so the difficulty of setting its detection logic is reduced and the high demand for detection accuracy is reduced. The present invention realizes the passive island detection of the virtual synchronous machine without blind areas without external interference, with high sensitivity and fast detection speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the accompanying drawings described below are only some embodiments. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0077] Figure 1 Schematic diagram of the overall structure of the virtual synchronous machine system;

[0078] Figure 2 A flow chart of a virtual synchronous machine island detection method based on impedance and phase offset detection provided in one embodiment of the present invention;

[0079] Figure 3 A logic flow chart of an impedance detection part provided in one embodiment of the present invention;

[0080] Figure 4 A decision fusion logic flow chart of phase detection and impedance detection provided in one embodiment of the present invention;

[0081] Figure 5 A voltage and current simulation waveform diagram of a virtual synchronous machine PCC point provided in one embodiment of the present invention;

[0082] Figure 6 A simulation diagram of the PCC point resistance measurement value at 198 switching frequencies provided in one embodiment of the present invention;

[0083] Figure 7 A simulation diagram of the reactance measurement value of the PCC point at 198 switching frequencies provided in one embodiment of the present invention;

[0084] Figure 8 The diagram is a simulated waveform diagram of an island signal output by a phase detection part, an impedance detection part and a virtual synchronous machine island detection method based on impedance and phase offset detection provided in one embodiment of the present invention.

[0085] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0086] The present invention will be further described below in conjunction with the accompanying drawings.

[0087] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0088] In one embodiment of the present invention, a virtual synchronous machine island detection method based on impedance and phase offset detection is proposed. Figure 1 and 2 , the method comprises the following steps:

[0089] Step S100: using the real-time grid impedance estimation technology based on inherent switching characteristics, the grid impedance near the specified high-order switching frequency of the virtual synchronous machine is measured under no-load conditions.

[0090] The real-time grid impedance estimation technology based on inherent switching characteristics is an impedance identification technology based on the switching characteristics of the inverter, using the characteristics of the rich specified high-order harmonics in the voltage and current at the grid connection point and the low high-order harmonic content of the actual power grid.

[0091] According to the real-time grid impedance estimation technology based on inherent switching characteristics, the grid impedance near the switching frequency of the virtual synchronous machine at a specified high order (usually 198 or 202) can be measured under no-load impedance and expressed as:

[0092] Z gs =R g +jω s L g

[0093] Among them, Z gs is the grid impedance, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance.

[0094] Step S200: Based on the blind zone condition of phase-shifted island detection, the load impedance value range of the virtual synchronous machine in the blind zone is calculated.

[0095] It is known that conventional passive island detection based on phase shift has a blind spot when the difference between the active load and the command value is too small so that the phase shift is less than the phase detection threshold.

[0096] Furthermore, the blind zone condition of island detection based on phase shift after reaching steady state is approximately expressed as:

[0097]

[0098] Among them, Δθ is the actual phase offset value, ΔP is the actual power offset value, Δt is the phase offset detection setting integration time, k f is the sum of the equivalent frequency droop coefficients of the virtual synchronous machine speed regulator and the main body, Δθ th is the phase shift threshold.

[0099] The load impedance corresponding to the blind area is expressed as Z load , specifically:

[0100] When ΔP>0

[0101]

[0102] When ΔP<0

[0103]

[0104] It can be deduced that the load impedance value range of the blind area is:

[0105]

[0106] Among them, U n is the rated voltage of the power grid, P ref is the active power instruction;

[0107] Substituting the specific parameters into the derived load impedance value range of the blind zone, the specific parameter range is calculated and expressed as:

[0108] Z load =R load ∈(R min ,R max ).

[0109] Among them, R load is the load resistance corresponding to the blind area, R min ,R max They are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area respectively.

[0110] Step S300: Calculate the PCC point impedance value range of the virtual synchronous machine islanding and grid-connected conditions under the blind zone conditions of phase-shift-based islanding detection according to the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the virtual synchronous machine load impedance value range in the blind zone.

[0111] The impedance of the PCC point at the specified high switching frequency of the virtual synchronous machine can be expressed as:

[0112] Z pccs =R pcc +jω s L pcc

[0113] The PCC point in the case of a virtual synchronous machine island specifies the impedance near the high-order switching frequency, and the expression is:

[0114] Z pccs =Z load =R load ;

[0115] The PCC point specifies the impedance near the high-order switching frequency when the virtual synchronous machine is connected to the grid. The expression is:

[0116]

[0117] Among them, R pcc Zpccs The resistance component, L pcc Z pccs The inductance component, R load is the load resistance corresponding to the blind area, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance.

[0118] Substituting the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the value range of the virtual synchronous machine load impedance in the blind area into the impedance expression near the specified high-order switching frequency of the PCC point in the case of virtual synchronous machine islanding and grid connection, we can get:

[0119] The impedance value range near the high-order switching frequency of the PCC point specified under the blind zone condition of the virtual synchronous machine islanding case based on phase offset islanding detection is expressed as:

[0120]

[0121] The impedance value range near the PCC point of the virtual synchronous machine grid-connected under the blind zone condition of phase-shift island detection is expressed as:

[0122]

[0123] Among them, R load is the load resistance corresponding to the blind area, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance, R min ,R max are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area, R 并网min , R 并网max The minimum and maximum values ​​of the impedance resistance components near the high-order switching frequency are respectively specified for the PCC point under the condition of virtual synchronous machine grid connection under blind zone conditions.

[0124] L 并网min , L 并网max The minimum and maximum values ​​of the impedance and inductance components near the high-order switching frequency are respectively specified for the PCC point when the virtual synchronous machine is connected to the grid under blind zone conditions.

[0125] Step S400: constructing the island determination logic of impedance detection according to the impedance value range of the PCC point.

[0126] According to ω s The high-frequency characteristics of the virtual synchronous machine and the load and grid impedance value law generally have obvious ω in the blind area. s Lg >R load >R g , that is, R 并网min Slightly smaller than R min , R 并网max Slightly smaller than R max ,ω s L pcc Less than ω s L g .

[0127] Combined with Figure 3 , set the impedance detection part logic as follows: measure the impedance of the grid connection point near the virtual synchronous machine s switching frequency, set k 阻抗检测 and M 阻抗检测 The initial value of is 0;

[0128] When R is detected pcc ∈(R min ,R max )and When k 阻抗检测 The count is increased by 1; otherwise, k 阻抗检测 The count is reset, and M 阻抗检测 =0;

[0129] When k 阻抗检测 When the cumulative value is greater than or equal to 100, set M 阻抗检测 =1; otherwise, continue to detect;

[0130] Among them, R pcc Z pccs The resistance component, L pcc Z pccs The inductance component, R load is the load resistance corresponding to the blind area, ω s is the angular frequency corresponding to the specified switching frequency s times; R min ,R max are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area, R 并网min , R 并网max are the minimum and maximum values ​​of the impedance and resistance components near the high-order switching frequency specified by the PCC point under the condition of virtual synchronous machine grid connection under blind zone conditions, L 并网min , L 并网max The minimum and maximum values ​​of the impedance and inductance components near the high-order switching frequency are respectively specified for the PCC point when the virtual synchronous machine is connected to the grid under blind zone conditions.

[0131] Step S500: constructing a decision fusion logic for phase detection and impedance detection according to the constructed island judgment logic for impedance detection.

[0132] Impedance detection works in conjunction with phase detection. Figure 4, the decision fusion logic of phase detection and impedance detection is constructed as follows:

[0133] Measure the impedance of the grid connection point near the s-th switching frequency of the virtual synchronous machine;

[0134] when When M=M 相位检测 ;

[0135] When R pcc ∈(0.8R min ,1.2R max ), there are two cases:

[0136] (1) When R pcc ∈(R min ,R max ), M=M 阻抗检测 ;

[0137] (2) When M=M 相位检测 |M 阻抗检测 .

[0138] Among them, R pcc Z pccs The resistance component, R min ,R max They are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area respectively.

[0139] Step S600: By measuring the phase offset value of the virtual synchronous machine and the impedance value of the PCC point near the specified high-order switching frequency, the constructed decision fusion logic of phase detection and impedance detection is executed to output the island detection result.

[0140] Measure the virtual synchronous machine phase offset value and the PCC point impedance value near the specified high-order switching frequency to obtain the specific Δθ and Z pccs The value is substituted into the constructed decision fusion logic of phase detection and impedance detection, and the island detection result is output.

[0141] The present invention is verified by building a virtual synchronous machine system island detection simulation in the Matlab / Simulink platform, and the relevant parameters are shown in Table 1.

[0142] Table 1

[0143]

[0144] The virtual synchronous machine system initially operates in a grid-connected state. At 1.5 s, the grid-connected switch is disconnected. According to the above derivation and calculation, this will occur in the blind area of ​​island detection based on phase offset.

[0145] Based on Matlab / Simulink simulation, we can get the following Figure 5 , 6 , 7 and 8. Figure 5 It shows that the virtual synchronous machine system can operate stably whether it is grid-connected or islanded; Figure 6 It shows that the resistance value of the PCC point can be accurately measured at 198 switching frequencies, and the measured value is consistent with the calculated value in both isolated island and grid-connected conditions; Figure 7 It shows that the reactance value of PCC point at 198 switching frequencies can be accurately measured, and its measured value is consistent with the calculated value in both isolated island and grid-connected conditions; Figure 8 It shows that under this parameter setting, after the grid-connected switch of the virtual synchronous machine is disconnected at 1.5s, the phase detection part does not output an island signal and is in a detection blind area. The impedance detection part outputs an island signal at 1.603s. According to the constructed decision fusion logic of phase detection and impedance detection, it is determined that the virtual synchronous machine island detection method and device based on impedance and phase offset detection sends an island signal at 1.603s.

[0146] The following is an embodiment of the virtual synchronous machine island detection device based on impedance and phase offset detection of the present invention, which can be used to execute the embodiment of the virtual synchronous machine island detection method based on impedance and phase offset detection of the present invention. For details not disclosed in the embodiment of the virtual synchronous machine island detection device based on impedance and phase offset detection of the present invention, please refer to the embodiment of the virtual synchronous machine island detection method based on impedance and phase offset detection of the present invention.

[0147] An exemplary embodiment of the present invention provides a virtual synchronous machine island detection device based on impedance and phase offset detection, the device comprising:

[0148] A grid impedance calculation module near a specified high-order switching frequency is used to measure the grid impedance near a specified high-order switching frequency of a virtual synchronous machine under no-load conditions by using a real-time grid impedance estimation technique based on inherent switching characteristics;

[0149] A load impedance value range calculation module is used to calculate the load impedance value range of the virtual synchronous machine in the blind zone based on the blind zone condition of the island detection of the phase offset;

[0150] The PCC point impedance value range calculation module is used to calculate the impedance value range near the PCC point specified high-order switching frequency under the blind zone conditions of the virtual synchronous machine islanding and grid-connected conditions under the phase offset-based islanding detection according to the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the virtual synchronous machine load impedance value range in the blind zone;

[0151] The island judgment logic module of impedance detection is used to specify the impedance value range near the high-order switching frequency at the PCC point and build the island judgment logic of impedance detection;

[0152] A decision fusion logic module is used to construct a decision fusion logic of phase detection and impedance detection according to the constructed island judgment logic of impedance detection;

[0153] The island detection result output module is used to measure the phase offset value of the virtual synchronous machine and the impedance value of the PCC point near the specified high-order switching frequency, execute the constructed decision fusion logic of phase detection and impedance detection, and output the island detection result.

[0154] It should be noted that the virtual synchronous machine island detection device based on impedance and phase offset detection provided in the above embodiment only uses the division of the above functional modules as an example when executing the virtual synchronous machine island detection method based on impedance and phase offset detection. In actual applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. In addition, the virtual synchronous machine island detection device based on impedance and phase offset detection provided in the above embodiment and the embodiment of the virtual synchronous machine island detection method based on impedance and phase offset detection belong to the same concept. The embodiment and implementation process thereof are detailed in the embodiment of the virtual synchronous machine island detection method based on impedance and phase offset detection, which will not be repeated here.

[0155] In one embodiment, a virtual synchronous machine system is proposed. The virtual synchronous machine system includes the above-mentioned virtual synchronous machine island detection device based on impedance and phase offset detection.

[0156] The description of the virtual synchronous machine islanding detection device based on impedance and phase offset detection refers to the above embodiment, which will not be repeated here.

[0157] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0158] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any slight modification, equivalent substitution and improvement made to the above embodiment based on the technical essence of the present invention should be included in the protection scope of the technical solution of the present invention.

Claims

1. A virtual synchronous machine island detection method based on impedance and phase offset detection, characterized in that: The method comprises: The real-time grid impedance estimation technology using inherent switching characteristics is used to measure the grid impedance near the specified high-order switching frequency of the virtual synchronous machine under no-load conditions; Based on the blind zone condition of phase-shifted island detection, the range of the load impedance of the virtual synchronous machine in the blind zone is calculated; According to the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the value range of the load impedance of the virtual synchronous machine in the blind zone, the impedance value range near the specified high-order switching frequency of the PCC point under the blind zone conditions of the virtual synchronous machine islanding and grid-connected conditions of the phase-shift-based islanding detection is calculated; According to the PCC point, the impedance value range near the high-order switching frequency is specified, and the island judgment logic of impedance detection is constructed; According to the island judgment logic of impedance detection, the decision fusion logic of phase detection and impedance detection is constructed; By measuring the phase offset value of the virtual synchronous machine and the impedance value of the PCC point near the specified high-order switching frequency, the constructed decision fusion logic of phase detection and impedance detection is executed to output the island detection result.

2. The method for detecting an island of a virtual synchronous machine based on impedance and phase offset detection according to claim 2, characterized in that: The grid impedance measured near the specified high-order switching frequency of the virtual synchronous machine under no-load condition is expressed as: FROM gs =R g +jω s L g Among them, Z gs is the grid impedance, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance.

3. The method for detecting virtual synchronous machine islanding based on impedance and phase offset detection according to claim 1, characterized in that: The blind area condition of the island detection based on phase offset is approximately expressed as: Among them, Δθ is the actual phase offset value, ΔP is the actual power offset value, Δt is the phase offset detection setting integration time, k f is the sum of the equivalent frequency droop coefficients of the virtual synchronous machine speed regulator and the main body, Δθ th is the phase shift threshold.

4. The method for detecting an island of a virtual synchronous machine based on impedance and phase shift detection according to claim 3, characterized in that: The calculating of the value range of the load impedance of the virtual synchronous machine in the blind area includes: The load impedance corresponding to the blind area is expressed as Z load , specifically: When ΔP>0, When ΔP<0, The value range of the virtual synchronous machine load impedance in the blind area is: Among them, U n is the rated voltage of the power grid, P ref is the active power instruction; Substitute the specific parameters into the value range of the virtual synchronous machine load impedance in the blind area, calculate the specific parameter range and express it as: Z load =R load ∈(R min ,R max ) Among them, R load is the load resistance corresponding to the blind area, R min ,R max They are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area respectively.

5. The method for detecting virtual synchronous machine islanding based on impedance and phase offset detection according to claim 1, characterized in that: The grid impedance Z near the virtual synchronous machine PCC point specifies the high-order switching frequency pccs , the expression is: FROM pccs =R pcc +jω s L pcc The PCC point in the case of a virtual synchronous machine island specifies the impedance near the high-order switching frequency, and the expression is: Z pccs =Z load =R load ; The PCC point specifies the impedance near the high-order switching frequency when the virtual synchronous machine is connected to the grid. The expression is: Among them, R pcc Z pccs The resistance component, L pcc Z pccs The inductance component, R load is the load resistance corresponding to the blind area, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance.

6. The method for detecting virtual synchronous machine islanding based on impedance and phase offset detection according to claim 5, characterized in that: Substituting the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the value range of the virtual synchronous machine load impedance in the blind area into the impedance expression near the specified high-order switching frequency of the PCC point in the case of virtual synchronous machine islanding and grid connection, we can get: The impedance value range near the high-order switching frequency of the PCC point specified under the blind zone condition of the virtual synchronous machine islanding case based on phase offset islanding detection is expressed as: The impedance value range near the PCC point of the virtual synchronous machine grid-connected under the blind zone condition of phase-shift island detection is expressed as: Among them, R load is the load resistance corresponding to the blind area, R g is the grid resistance, ω s The angular frequency corresponding to the specified switching frequency is L g is the grid inductance, R min ,R max are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area, R 并网min , R 并网max are the minimum and maximum values ​​of the impedance and resistance components near the high-order switching frequency specified by the PCC point under the condition of virtual synchronous machine grid connection under blind zone conditions, L 并网min , L 并网max The minimum and maximum values ​​of the impedance and inductance components near the high-order switching frequency are respectively specified for the PCC point when the virtual synchronous machine is connected to the grid under blind zone conditions.

7. The method for detecting virtual synchronous machine islanding based on impedance and phase offset detection according to claim 1, characterized in that: The impedance value range near the high-order switching frequency is specified according to the PCC point, and the island judgment logic of impedance detection is constructed as follows: Measure the impedance of the grid connection point near the s-th switching frequency of the virtual synchronous machine and set k 阻抗检测 and M 阻抗检测 The initial value of is 0; When R is detected pcc ∈(R min ,R max )and When k 阻抗检测 The count is increased by 1; otherwise, k 阻抗检测 The count is reset, and M 阻抗检测 =0; When k 阻抗检测 When the cumulative value is greater than or equal to 100, set M 阻抗检测 =1; otherwise, continue to detect; Among them, R pcc Z pccs The resistance component, L pcc Z pccs The inductance component, R load is the load resistance corresponding to the blind area, ω s is the angular frequency corresponding to the specified switching frequency s times; R min ,R max are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area, R 并网min , R 并网max are the minimum and maximum values ​​of the impedance and resistance components near the high-order switching frequency specified by the PCC point under the condition of virtual synchronous machine grid connection under blind zone conditions, L 并网min , L 并网max The minimum and maximum values ​​of the impedance and inductance components near the high-order switching frequency are respectively specified for the PCC point when the virtual synchronous machine is connected to the grid under blind zone conditions.

8. The method for detecting virtual synchronous machine islanding based on impedance and phase offset detection according to claim 1, characterized in that: According to the island judgment logic of the impedance detection, the decision fusion logic of the phase detection and impedance detection is constructed as follows: Measure the impedance of the grid connection point near the s-th switching frequency of the virtual synchronous machine; when When M=M 相位检测 ; When R pcc ∈(0.8R min ,1.2R max ), there are two cases: (1) When R pcc ∈(R min ,R max ), M=M 阻抗检测 ; (2) When M=M 相位检测 |M 阻抗检测 . Among them, R pcc Z pccs The resistance component, R min ,R max They are the minimum and maximum values ​​of the virtual synchronous machine load resistance in the blind area respectively.

9. A virtual synchronous machine island detection device based on impedance and phase offset detection, characterized in that: The device comprises: A grid impedance calculation module near a specified high-order switching frequency is used to measure the grid impedance near a specified high-order switching frequency of a virtual synchronous machine under no-load conditions by using a real-time grid impedance estimation technique based on inherent switching characteristics; A load impedance value range calculation module is used to calculate the load impedance value range of the virtual synchronous machine in the blind zone based on the blind zone condition of the island detection of the phase offset; The PCC point impedance value range calculation module is used to calculate the impedance value range near the PCC point specified high-order switching frequency under the blind zone conditions of the virtual synchronous machine islanding and grid-connected conditions under the phase offset-based islanding detection according to the measured grid impedance near the specified high-order switching frequency of the virtual synchronous machine and the virtual synchronous machine load impedance value range in the blind zone; The island judgment logic module of impedance detection is used to specify the impedance value range near the high-order switching frequency at the PCC point and build the island judgment logic of impedance detection; A decision fusion logic module is used to construct a decision fusion logic of phase detection and impedance detection according to the constructed island judgment logic of impedance detection; The island detection result output module is used to measure the phase offset value of the virtual synchronous machine and the impedance value of the PCC point near the specified high-order switching frequency, execute the constructed decision fusion logic of phase detection and impedance detection, and output the island detection result.

10. A virtual synchronous machine system, characterized in that: It includes the virtual synchronous machine island detection device based on impedance and phase offset detection as described in claim 9.

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