An island detection method based on signal cooperative injection

Abstract

A method for detecting an island based on coordinated signal injection belongs to the technical field of active island detection. It is characterized by comprising the following steps: step a, whether the timer interrupt is triggered; step b, measuring the signal; step c, whether the flag bit based on the synchronous injection of the satellite timing signal is set; step d, executing the synchronous injection based on the satellite timing signal; step e, current tracking control; step f, PWM modulation output; step g, timer reset; step h, whether the flag bit based on the synchronous injection of the system voltage is set; step i, executing the synchronous injection based on the system voltage; step j, electrical quantity disturbance judgment; step k, whether the satellite timing signal is reliable; step l, system voltage and current data processing; step m, RLC calculation; step n, island judgment. In this method for detecting an island based on coordinated signal injection, the problems of narrow application scenarios, low measurement accuracy, single criterion, poor reliability, etc. existing in the current method are solved.

Description

Technical Field

[0001] The invention discloses an island detection method based on signal cooperative injection, belonging to the technical field of active island detection. Background Art

[0002] With the continuous development of social economy, people's demand for energy is increasing, and distributed generation (DG) plays an increasingly important role in the power system. The connection of distributed power sources to the grid helps to improve the quality of power, reduce line losses, ease the transmission and distribution capacity, and improve the stability of the power system. At the same time, we should also see that the access of distributed power sources will inevitably bring a series of problems to the operation of the power grid, one of which is the protection of distributed generation.

[0003] When the DG with partial load is disconnected from the power system, it is possible that the DG will continue to supply power to the isolated power system, and the isolated system formed is an island. In general, based on the safety of equipment and operators and the power quality in the island system, DG should be avoided from operating in an island state. Therefore, it is of great practical significance to study the island detection method and protection measures to minimize the harm caused by the island. According to the current research situation at home and abroad, the island detection method can be divided into three categories: passive detection method, active detection method and communication-based anti-island strategy. The passive detection method identifies the island operation state by detecting the change of the system electrical quantity. The detection method is simple and easy to implement, but the detection blind area is large and it is easy to be disturbed by the system and cause false operation. The active detection method injects a certain disturbance and detects the change of the corresponding electrical quantity to determine whether it is in an island operation state. This method has a small detection blind area, but it will affect the power quality and there is a problem of injection signal synchronization. The communication-based anti-islanding strategy determines the islanding operation status by directly transmitting the circuit breaker status through an independent communication channel. Its detection performance is not affected by the type of distributed power supply and the measurement of electrical quantities, but its reliability is poor and the construction cost is high. The active detection method based on impedance measurement detects the output impedance of the inverter output or the grid connection point by injecting harmonics. It can identify the islanding operation status under the condition of fundamental power balance and will not cause obvious voltage and frequency disturbances. It has broad application prospects.

[0004] Combination Fig.15The figure shows a schematic diagram of a single island detection system based on the impedance measurement method. The installation point of the signal injection device in the figure is generally located at the access point of the distributed power supply device, or integrated inside the distributed power supply device. The device will use the change in the system operating state as a starting criterion to inject a voltage or current signal of a specific frequency into the system, and collect the corresponding current or voltage signal generated on the system impedance. Then, the system impedance is calculated based on the injected and collected signals, and the system is judged whether it is in a grid-connected operation state or an island operation state based on the calculated system impedance. When the upstream circuit breaker is disconnected due to a fault or other factors, the device detects the island operation state based on the impedance change, executes the island protection action, causes the distributed power supply to exit operation, and completes the island protection.

[0005] Fig.16 This is the equivalent circuit of a single island detection system based on the impedance measurement method. This equivalent circuit only discusses the influence of the injected signal. Therefore, according to the superposition theorem, the effect of the power frequency signal in the system is ignored. s The output impedance of the power grid when the system is connected to the grid; Z Load is the load impedance; assuming that the injection device is a current source, its injection signal A voltage signal is generated across the system impedance

[0006] When connected to the grid (upstream circuit breaker closed), the system output impedance Z can be obtained m for:

[0007] When the upstream circuit breaker is disconnected, the system output impedance Z can be obtained m for:

[0008] Due to the inherent characteristics of the system Z s < <Z Load , so when connected to the grid Z m ≈Z s , the impedance criterion Z can be set in the formula c , when Z m <Z c When Z m >Z c It is judged as island operation state.

[0009] From the above, it can be seen that in a system with a single detection device, the island detection method based on impedance measurement can well complete the detection of the island operation status. Fig.17 In the system shown in the figure containing multiple island detection devices, there is a problem of injection signal dilution, which causes the island judgment criterion to fail.

[0010] Fig.18is the equivalent circuit of the multi-injection device system. According to the superposition theorem, the influence of distributed power supply and grid voltage is ignored. All loads in the system are equivalent to the total load Z Load , Z s is the grid impedance. Assuming that the injection signals of the two injection devices have the same frequency and amplitude, the system impedance measured at the access point of each injection device is: When connected to the grid, the system impedance Z measured at the access point of the two injection devices is m1 , Z m2 They are:

[0011]

[0012] When the upstream circuit breaker is open, the system impedance Z measured at the access point of the two injection devices m1 , Z m2 They are:

[0013]

[0014] In the actual operation of the system, each injection device lacks effective synchronization means to achieve injection signal synchronization, so there is a problem of synchronization signal dilution, which leads to impedance measurement failure. The specific reasons are as follows:

[0015] Since the injected signal is not synchronized, the injected signal and The phase relationship can be arbitrary, considering the following two extreme cases:

[0016] (1) and When the phases of are the same, we can

[0017] System impedance when connected to the grid: Z m1 =Z m2 =2Z s / / Z Load , system impedance when the circuit breaker is disconnected: Z m1 =Z m2 =2Z Load

[0018] (2) and When the phases of are opposite,

[0019] System impedance when connected to the grid: Z m1 =Z m2 =0, system impedance when circuit breaker is disconnected: Z m1 =Z m2 =0

[0020] It can be seen that without synchronization means, the signal injection of multiple devices will lead to signal dilution and the system impedance measurement cannot be accurately completed.

[0021] In the active detection method based on impedance detection, if there are multiple injection sources in the system, there is a problem of disturbance injection synchronization. If this problem is not properly solved, it may cause obvious detection errors and harmonic circulation, resulting in detection failure. Existing literature proposes the following solutions:

[0022] (1) Lv Weilong et al., Research on anti-islanding technology of distribution network based on active and passive detection. Electrical Applications, 2018.37(06). The master-slave control proposed in this paper requires injection of the master inverter but not the slave inverter. However, when the master inverter fails, it is necessary to rely on communication technology to realize the new master inverter configuration. The implementation method is complex and has poor reliability.

[0023] (2) Wang Linfu et al., Research on Anti-Islanding Protection Strategy for Distributed Photovoltaic Power Generation System. Electrical Engineering, 2019(10). This paper mentions the use of droop control to achieve synchronous injection of harmonic signals, but the deviation of line parameters between injection points will cause obvious injection signal deviation, reduce the detection accuracy of this method, and cause misjudgment.

[0024] (3) Some literature has proposed to directly inject different frequency signals at integer multiples of the fundamental wave phase when injecting harmonic waves. However, this method is sensitive to the fundamental wave phase and also has the problem of low detection accuracy. In addition, there is interference between different injection frequencies.

[0025] In the prior art, the following problems are still common: (1) Narrow application scenarios. At present, most island detection methods based on impedance measurement only consider the island protection of distributed power sources, and rarely involve the island protection of the common connection point as the boundary between the power grid and user assets. When the power grid is disconnected, if the common connection point can achieve island protection and the distributed power sources remain in operation, it will help improve the power supply reliability. (2) Poor measurement accuracy. The injection signal synchronization based on droop control draws on the droop control principle of the industrial frequency signal during power distribution, but there is a problem that the synchronization effect is greatly affected by the line parameters, and the synchronization accuracy cannot be guaranteed. (3) Poor data accuracy: The current impedance measurement method only considers the injection of a single signal and the impedance judgment at the corresponding frequency, and cannot eliminate the influence of signal dilution on the impedance measurement accuracy when multiple machines inject signals at the same time. Summary of the invention

[0026] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a signal injection method synchronized by satellite timing signals to solve the problem of multi-machine signal dilution, improve the impedance measurement accuracy, and thus improve the island detection accuracy. At the same time, considering the reliability problem of the satellite timing signal itself, a signal injection method for bus voltage synchronization is further proposed, which can also effectively solve the problem of multi-machine signal injection dilution and an island detection method based on signal collaborative injection.

[0027] The technical solution adopted by the present invention to solve the technical problem is: the island detection method based on signal cooperative injection is characterized by comprising the following steps:

[0028] Step a, determine whether the timer interrupt is triggered, if the timer interrupt occurs, execute step b, if the timer interrupt does not occur, execute step l;

[0029] Step b, measuring the voltage and current signals of the system, and recording and storing the measured signals;

[0030] Step c, determining whether the flag bit based on the synchronous injection of the satellite timing signal is set, if it is set, executing step d, if it is not set, executing step h;

[0031] Step d, execute the satellite timing signal synchronization injection subroutine, use the satellite timing signal as a reference, generate a dual-frequency current injection signal instruction i with a coded pulse ref , the injection signal is composed of a pulse sequence and a four-cycle dual-frequency sinusoidal signal, and any one of the three phases ABC is selected as the injection phase;

[0032] Step e, current tracking control generates a modulation signal according to the injection signal instruction;

[0033] Step f, PWM control generates a pulse modulation signal that finally drives the inverter according to the modulation signal;

[0034] Step g, the timer is reset and restarted;

[0035] Step h, determining whether the flag bit based on system voltage synchronous injection is set, if the flag bit based on system voltage synchronous injection is set, executing step i, if the flag bit based on system voltage synchronous injection is not set, executing step j;

[0036] Step i, execute the system voltage based synchronous injection subroutine, that is, use the system voltage as the synchronization reference to generate a pulse modulated sinusoidal current injection instruction i with a coded pulse ref , and return to execute step e;

[0037] Step j, judging whether the voltage amplitude and frequency exceed the set threshold value according to the sampled data in step b, if they exceed the set threshold value, executing step k, otherwise returning to executing step g;

[0038] Step k, judging whether the satellite timing signal is reliable and stable. If the satellite timing signal is reliable, it indicates that the flag position based on the synchronous injection of the satellite timing signal is in place, and the process returns to step e. If the satellite timing signal is unreliable, it indicates that the flag position based on the synchronous injection of the system voltage is in place, and the process returns to step e.

[0039] Step 1, extracting the voltage and current phasors in the same frequency band as the injected signal and the coded pulses in the corresponding signal from the voltage and current recorded in step b;

[0040] Step m, calculating the system parameters: resistance R, inductance L and capacitance C according to the voltage and current phasors obtained in step l and the signal strength information obtained from the coded pulse;

[0041] Step n, judging whether it is in an island operation state according to the system parameters calculated in step m, if it is in an island operation state, performing an island protection action, if it is not in an island operation state, returning to execute step a.

[0042] Preferably, the satellite timing signal synchronization injection subroutine comprises the following steps:

[0043] Step d-1, determine whether to capture the 1PPS pulse signal, if the rising edge of the 1PPS timing signal is captured, execute step d-2, if not, execute step d-4;

[0044] Step d-2, injection point timing t s Accumulation;

[0045] Step d-3, determine the accumulated time t s Is it greater than or equal to 2π? If the accumulated time is greater than or equal to 2π, execute step d-4; if the accumulated time is less than 2π, return to step d-1;

[0046] Step d-4, injection point generation, cumulative time t s reset to zero;

[0047] Step d-5, determining whether the injected signal has completed the generation of four-cycle sinusoidal signals, if the injected signal has completed the generation of four-cycle sinusoidal signals, executing step d-10, if the injected signal has not completed the generation of four-cycle sinusoidal signals, executing step d-6;

[0048] Step d-6, calculating the phase angles θ1 and θ2 of the injected signals with frequencies f1 and f2 respectively;

[0049] Step d-7, determining whether the phase angles θ1 and θ2 of the injected signals of the frequencies f1 and f2 are greater than or equal to 2π, if the phase angles θ1 and θ2 are greater than or equal to 2π, executing step d-8, if the phase angles θ1 and θ2 are less than 2π, executing step d-11;

[0050] Step d-8, the phase angles θ1 and θ2 of the injected signals of frequencies f1 and f2 are set to zero;

[0051] Step d-9, generate current injection instruction: i ref =i 1ref +i 2ref , where i 1ref =I1sinθ1,i 2ref =I2sinθ2, and exit the satellite timing signal synchronization injection subroutine;

[0052] Step d-10, determining whether the delay time satisfies nΔt, if the delay time does not satisfy nΔt, executing step d-12, if the delay time satisfies nΔt, executing step d-11;

[0053] Step d-11, when the delay time satisfies nΔt, the current injection instruction i ref =P(t), P(t) is a single positive and negative alternating pulse signal, and execute step d-12;

[0054] Step d-12, if the delay time does not satisfy nΔt, the current injection instruction is set to zero: i ref =0.

[0055] Preferably, the injection point timing t s The cumulative calculation formula for the accumulation is:

[0056] t s (k) = t s (k-1)+Δt2πf t ,

[0057] Among them, t s (k) is the current accumulated time, t s (k-1) is the accumulated time of the previous fixed time period, Δt2πf t is the timing increment.

[0058] Preferably, the phase angle calculation formula of the injection signal with frequency f1 is:

[0059] θ1(k)=θ1(k-1)+Δt2πf1

[0060] Among them, θ1(k) is the current phase angle cumulative value, θ1(k-1) is the phase angle cumulative value of the previous sampling cycle, and Δt2πf1 is the phase angle increment since this week;

[0061] The phase angle calculation formula for the injected signal with frequency f2 is:

[0062] θ2(k)=θ2(k-1)+Δt2πf2

[0063] Among them, θ2(k) is the current phase angle cumulative value, θ2(k-1) is the phase angle cumulative value of the previous sampling cycle, and Δt / (2πf2) is the phase angle increment since this week.

[0064] Preferably, in step i, the system voltage synchronous injection subroutine comprises the following steps:

[0065] Step i-1, determine whether to capture the voltage rising edge signal, if the voltage rising edge is captured, execute step i-2, if the voltage rising edge is not captured, continue to execute this step;

[0066] Step i-2, if the value S(k-1) of the pulse function s(t) in the previous sampling period is equal to the pulse intensity S0: S(k-1) = S0, then S(k) = 0; if the value S(k-1) of the pulse function s(t) in the previous sampling period is zero: S(k-1) = 0, then the pulse intensity S0 is the value S(k) of the pulse function s(t) in this period: S(k) = S0;

[0067] Step i-3, determining whether the generation of four cycles of the sinusoidal injection signal is completed, if the generation of four cycles of the sinusoidal injection signal is completed, executing step i-5, if the generation of four cycles of the sinusoidal injection signal is not completed, executing step i-4;

[0068] Step i-4, whether the value S(k) of the pulse function s(t) in this cycle is 0: S(k)==0. If S(k)==0 is satisfied, execute step i-6, otherwise execute step i-7;

[0069] Step i-5, determine whether the delay time satisfies nΔt, if the delay time does not satisfy nΔt, execute step i-7, if the delay time satisfies nΔt, execute step i-8;

[0070] Step i-6, generate current injection instruction, let i ref =S0i(k), and end;

[0071] Step i-7, set the current injection instruction to zero, i.e. ref =0, and end;

[0072] Step i-8, the current injection instruction is generated as a positive and negative alternating pulse signal, i.e. ref =P(t), P(t) is a single positive and negative alternating pulse signal, and ends.

[0073] Preferably, in step m, the calculation step of the system parameters is:

[0074] Step m-1, solve the system impedance at frequencies f1 and f2

[0075] Step m-2, assuming Z1 = R + jX1, Z2 = R + jX2, then the system resistance is R and the capacitance is inductance Among them, ω1=2πf1, ω2=2πf2.

[0076] Preferably, in step n, the island operation status determination step is:

[0077] Step n-1, assume that the system voltage collected during the current timing period is u o (k), the output current is i o (k), the system voltage before Δt1 is u o (k-Δt1 / Δt k ), the output current is i o (k-Δt1 / Δt k ), where Δt k is the timer period;

[0078] Solve for the disturbance signal u s (k) = u o (k)-u o (k-Δt1 / Δt k ),i s (k) = i o (k)-i o (k-Δt1 / Δt k );

[0079] Step n-2, record a complete disturbance signal u s , which includes a disturbance signal and a coded pulse signal;

[0080] Step n-3, according to the disturbance signal u s The coded pulse in obtains the current injected signal strength k n , and calculate u through the DFT algorithm s andi s Voltage phasors at frequencies f1 and f2 and current phasor

[0081] Step n-4, according to the current system impedance parameters R, L, C obtained in step i, when the system RLC parameters are within the set threshold, i.e. R min <R<R max , L min <L<L max , Cmin <C<C max It is judged as an island operation state.

[0082] Compared with the prior art, the present invention has the following beneficial effects:

[0083] In this island detection method based on coordinated signal injection, the signal injection method synchronized with the satellite timing signal solves the problem of multi-machine signal dilution, improves the impedance measurement accuracy, and thus improves the island detection accuracy. Taking into account the reliability of the satellite timing signal itself, a bus voltage synchronized signal injection method is further proposed, which can also effectively solve the dilution problem of multi-machine signal injection.

[0084] In this island detection method based on signal collaborative injection, the proposed island detection method can achieve flexible coverage of island protection from distributed power sources to public connection points through flexible combination of devices and detection methods, while taking into account cost control, so it has a wide range of application scenarios.

[0085] In the island detection method based on signal cooperative injection, the proposed island detection method uses the timing signal as a synchronization means to achieve the synchronization of the injected signal, avoid the signal dilution problem formed between multiple injection island detection devices, and improve the island detection accuracy. At the same time, multi-signal injection and the multi-impedance criterion coordinated therewith can further avoid the accuracy of island detection, so the detection accuracy is high.

[0086] The injection signal for impedance detection is directly generated by utilizing the external communication channel, and the implementation method is simple and can be easily integrated into the existing control strategy of distributed power supply.

[0087] The island detection method uses a signal injection method based on voltage synchronization as a backup signal injection method, avoiding the problem of injection signal loss caused by timing signal loss, and thus has higher reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 This is a flow chart of the island detection method based on signal cooperative injection.

[0089] Figure 2 This is a schematic diagram for generating synchronous injection current signals based on WeChat.

[0090] Figure 3 This is a flow chart of the subroutine for synchronous injection based on satellite timing signals.

[0091] Figure 4 Schematic diagram for injection signal generation based on system voltage synchronization.

[0092] Figure 5 This is a flow chart of the subroutine for synchronous injection based on system voltage.

[0093] Figure 6 This is the voltage detection waveform.

[0094] Figure 7 Schematic diagram of the integrated signal injection and impedance measurement device module.

[0095] Figure 8 Schematic diagram of the independent impedance measurement device module with a common connection point.

[0096] Fig. 9 This is a schematic diagram of the hardware circuit for island protection at the distributed power supply of the integrated signal injection and impedance measurement device.

[0097] Fig.10 This is a schematic diagram of the hardware circuit for island protection at the common connection point of the integrated signal injection and impedance measurement device.

[0098] Fig.11 Schematic diagram of the circuit for independent impedance measurement device with common connection point.

[0099] Fig.12 This is a flowchart of the island protection software flow at the distributed power supply of the integrated signal injection and impedance measurement device.

[0100] Fig.13 This is a flowchart of the island protection software at the common connection point of the integrated signal injection and impedance measurement device.

[0101] Fig.14 This is a schematic diagram of the software flow of the circuit of the common connection point independent impedance measurement device.

[0102] Fig.15 Schematic diagram of the impedance measurement method in the prior art.

[0103] Fig.16 for Fig.15 Schematic diagram of equivalent circuit.

[0104] Fig.17 It is a schematic diagram of a multi-injection device in the prior art.

[0105] Fig.18 for Fig.17 Schematic diagram of equivalent circuit. DETAILED DESCRIPTION

[0106] Figures 1 to 14 The best embodiment of the present invention is shown below in conjunction with the attached Figures 1 to 14 The present invention is further described.

[0107] like Figure 1 As shown, an island detection method based on signal cooperative injection includes the following steps:

[0108] Step 1001, start, start executing the island detection method based on signal cooperative injection;

[0109] Step 1002, determine whether the timer interrupt is triggered;

[0110] Determine whether the timer interrupt is triggered. If the timer interrupt occurs, execute step 1003; if the timer interrupt does not occur, execute step 1013.

[0111] Step 1003, measuring system voltage and current signals;

[0112] Measure the voltage and current signals of the system, and record and store the measured signals.

[0113] Step 1004: Whether the "synchronous injection based on satellite timing signal" flag is set;

[0114] Determine whether the flag bit of "synchronous injection based on satellite timing signal" is set, if it is set, execute step 1005, if it is not set, execute step 1009;

[0115] Step 1005, execute the subroutine of "synchronous injection based on satellite timing signal". That is, use the satellite timing signal as a reference to generate a dual-frequency current injection signal instruction i with coded pulses. ref ;

[0116] The injection signal is a four-cycle dual-frequency sinusoidal signal containing a pulse sequence, which is injected into the system at a specified time to achieve island detection. When multiple devices are injected at the same time, the phases of the injection signals are consistent. For a three-phase inverter, any phase of the three phases ABC can be selected as the injection phase. The injection signal generation process is as follows: Figure 2 shown.

[0117] The controller first needs to use the rising edge of the 1PPS second pulse signal as a reference to generate a frequency of f t injection point; when the device receives the instruction to generate the injection signal, it starts to synchronously generate equal sinusoidal signals with frequencies f1 and f2 at the first subsequent injection point, and each frequency signal has 4 cycles, and then adds a ± pulse signal with a delay of n*Δt to the tail of the sinusoidal signal with frequency f1 to identify the signal of this device. It should be emphasized that if there are multiple injection devices in this island area, the number n of each device must be continuous and unique, and n should not be too large to cause the pulse signal to be delayed to the next signal injection point, resulting in signal overlap.

[0118] like Figure 3 As shown in the figure, the specific steps of the "Synchronous injection based on satellite timing signal" subroutine are as follows:

[0119] Step 1005-1, start;

[0120] Wait for the main program's timing interrupt to be triggered and enter the "satellite timing synchronization signal injection" subroutine.

[0121] Step 1005-2, whether to capture pulse signal;

[0122] Determine whether to capture the 1PPS pulse signal. If the rising edge of the 1PPS timing signal is captured, execute step 1005-3; if not, execute step 1005-5;

[0123] Step 1005-3, the injection point timing is accumulated;

[0124] Injection point timing t s Accumulation, the accumulation calculation formula is:

[0125] t s (k) = t s (k-1)+Δt2πf t ,

[0126] Among them, t s (k) is the current accumulated time, t s (k-1) is the accumulated time of the previous fixed time period, Δt2πf t is the timing increment.

[0127] Step 1005-4, whether the accumulated time is greater than or equal to 2π;

[0128] Determine whether the accumulated time is greater than or equal to 2π, if the accumulated time is greater than or equal to 2π, execute step 1005-5, if the accumulated time is less than 2π, return to step 1005-1;

[0129] Step 1005-5, accumulating time instruction;

[0130] Injection point generation, cumulative time t s Reset to zero.

[0131] Step 1005-6, whether the four-cycle sine signal is completed;

[0132] Determine whether the generation of the four-cycle sinusoidal injection signal is completed. If the generation of the four-cycle sinusoidal injection signal is completed, execute step 1005-11; if the generation of the four-cycle sinusoidal injection signal is not completed, execute step 1005-7;

[0133] Step 1005-7, respectively calculating the phase angles θ1 and θ2 of the injected signals with frequencies f1 and f2;

[0134] Calculate the phase angle of the injected signal with frequency f1:

[0135] θ1(k)=θ1(k-1)+Δt2πf1

[0136] Among them, θ1(k) is the current phase angle cumulative value, θ1(k-1) is the phase angle cumulative value of the previous sampling cycle, and Δt / (2πf1) is the phase angle increment since this week.

[0137] Calculate the phase angle of the injected signal with frequency f2:

[0138] θ2(k)=θ2(k-1)+Δt2πf2

[0139] Among them, θ2(k) is the current phase angle cumulative value, θ2(k-1) is the phase angle cumulative value of the previous sampling cycle, and Δt2πf2 is the phase angle increment since this week.

[0140] Step 1005-8, determining whether the phase angles θ1 and θ2 of the injected signals of the frequencies f1 and f2 are greater than or equal to 2π;

[0141] Determine whether the phase angles θ1 and θ2 of the injected signals of the frequencies f1 and f2 are greater than or equal to 2π. If the phase angles θ1 and θ2 are greater than or equal to 2π, execute step 1005-9. If the phase angles θ1 and θ2 are less than 2π, execute step 1005-12.

[0142] Step 1005-9, the phase angles θ1 and θ2 of the injection signals of frequencies f1 and f2 are set to zero.

[0143] Step 1005-10, generating a current injection instruction;

[0144] Generate current injection instructions:

[0145] i ref =i 1ref +i 2ref

[0146] Among them, i 1ref =I1sinθ1,i 2ref =I2sinθ2, and execute step 1005-14.

[0147] Step 1005-11, determine whether the delay time satisfies nΔt;

[0148] Determine whether the delay time satisfies nΔt. If the delay time does not satisfy nΔt, execute step 1005-13. If the delay time satisfies nΔt, execute step 1005-12.

[0149] Step 1005-12, the current injection instruction is set to a positive and negative alternating pulse signal;

[0150] If the delay time satisfies nΔt, then let i ref=P(t), P(t) is a single positive and negative alternating pulse signal, and execute step 1005-14.

[0151] Step 1005-13, if the delay time does not satisfy nΔt, the current injection instruction is set to zero: i ref =0.

[0152] Step 1005-14, end, exit the "satellite timing synchronization signal injection based on" subroutine.

[0153] Step 1006, current tracking control;

[0154] The current tracking control generates a modulation signal according to the injection signal command.

[0155] Step 1007, PWM modulation output;

[0156] PWM control generates a pulse modulation signal that ultimately drives the inverter based on the modulation signal.

[0157] Step 1008, the timer is reset;

[0158] The timer is reset and restarted.

[0159] Step 1009, judging "synchronous injection based on system voltage";

[0160] Determine whether the flag bit of "based on system voltage synchronous injection" is set. If the flag bit of "based on system voltage synchronous injection" is set, execute step 1010; if the flag bit of "based on system voltage synchronous injection" is not set, execute step 1011.

[0161] Step 1010, executing the subroutine of "synchronous injection based on system voltage".

[0162] Execute the "system voltage based synchronous injection" subroutine, that is, use the system voltage as the synchronization reference to generate a 25Hz pulse modulated sinusoidal current injection instruction i with coded pulses ref , and returns to execute step 1006.

[0163] When the satellite timing signal is unreliable, the system voltage can be used as a backup synchronization method to achieve island detection. Considering the characteristics of system voltage changes, the synchronization method and signal injection method must be adjusted accordingly. This method first uses the rising zero-crossing point of the system voltage as a reference to generate a 25Hz pulse function s(t). If the island detection method is applied to a photovoltaic inverter, then the power frequency current instruction that the photovoltaic inverter needs to inject into the system is i(t), and the generated injection signal is i ref=s(t)i(t); If the island detection method is applied to non-photovoltaic inverters, the photovoltaic inverter principle can be used to generate a power frequency current signal i(t) similar to the photovoltaic inverter, and further generate an injection signal i ref =s(t)i(t). After generating four periodic signals, the injection signal is similar to the satellite timing synchronization signal injection method. A coding pulse needs to be added at the end of the signal, such as Figure 4 shown.

[0164] It should be noted that ref It is composed of a pulse signal modulating an industrial frequency sinusoidal current signal. According to spectrum analysis, it contains 25Hz and 75Hz harmonic signals, achieving an effect similar to satellite timing synchronization injection. For the convenience of the following introduction, f1 can be considered as a 25Hz signal and f2 as a 75Hz signal.

[0165] like Figure 5 As shown in the figure, the subroutine of "system voltage synchronous injection" includes the following steps:

[0166] Step 1010-1, start; wait for the timing interrupt of the main program to be triggered and enter the "system voltage based synchronous injection" subroutine;

[0167] Step 1010 - 2 , determining whether a voltage rising edge signal is captured, if a voltage rising edge is captured, executing step 1010 - 2 , if not, returning to executing step 1010 - 1 .

[0168] Step 1010-3, determining the pulse intensity of the pulse function;

[0169] If the value S(k-1) of the pulse function s(t) in the previous sampling period is equal to the pulse intensity S0: S(k-1) = S0, then S(k) = 0; if the value S(k-1) of the pulse function s(t) in the previous sampling period is zero: S(k-1) = 0, then the pulse intensity S0 is the value S(k) of the pulse function s(t) in this period: S(k) = S0.

[0170] Step 1010-4, whether the four-cycle sine signal is completed;

[0171] Determine whether the generation of four cycles of the sinusoidal injection signal is completed. If the generation of four cycles of the sinusoidal injection signal is completed, execute step 1010-6; if the generation of four cycles of the sinusoidal injection signal is not completed, execute step 1010-5.

[0172] Step 1010-5, determining whether the pulse function value is 0;

[0173] Whether the value S(k) of the pulse function s(t) in this period is 0: S(k)==0. If S(k)==0, execute step 1010-7; otherwise, execute step 1010-8.

[0174] Step 1010-6, determining whether the delay time satisfies nΔt;

[0175] Determine whether the delay time satisfies nΔt. If the delay time does not satisfy nΔt, execute step 1010-8. If the delay time satisfies nΔt, execute step 1010-9.

[0176] Step 1010-7, assign a value to the current injection instruction, and let i ref =S0i(k), and execute step 1010-10.

[0177] Step 1010-8, the current injection instruction is zero, that is, i ref =0, and execute step 1010-10.

[0178] Step 1010-9, the current injection instruction is set to a positive and negative alternating pulse signal, i.e. ref =P(t), P(t) is a single positive and negative alternating pulse signal, and execute step 1010-10.

[0179] Step 1010 - 10, end, exit the “system voltage based synchronous injection” subroutine.

[0180] Step 1011, determining whether the electrical quantity disturbance is greater than or equal to a threshold;

[0181] According to the sampled data in step 1003, the voltage amplitude and the frequency of the electrical quantities are analyzed to see whether they exceed the set threshold. If they exceed the set threshold, step 1012 is executed, otherwise, the execution returns to step 1008.

[0182] Step 1012, determining whether the satellite timing signal is reliable;

[0183] Determine whether the satellite timing signal is reliable and stable. If the satellite timing signal is reliable, it indicates that the flag position of "synchronous injection based on satellite timing signal" is in position, and return to step 1006. If the satellite timing signal is unreliable, it indicates that the flag position of "synchronous injection based on system voltage" is in position, and return to step 1006.

[0184] When judging whether the satellite timing signal is reliable, it can be achieved in the following way: set the interruption period to Δt, 1s is approximately hΔt, that is, h = 1 / Δt. Detection method: judge whether the pulse interval t of the 600 consecutive satellite timing signals received in the past satisfies (h-1)Δt≤t≤(h+1)Δt. If so, it means that the satellite timing signal is reliable; otherwise, it is unreliable.

[0185] Step 1013, system voltage and current data processing;

[0186] The voltage and current phasors in the same frequency band as the injected signal and the coded pulses in the corresponding signal are extracted from the voltage and current recorded in step 1003 .

[0187] Voltage and current signal processing refers to extracting the injected detection signal from the voltage and current information measured by the device through the mutation method. Then, the voltage phasor of the injected frequency and the signal strength information represented by the coded pulse are extracted from the voltage disturbance signal through algorithms such as DFT. n , extract the voltage vector and current phasor at the injection frequencies f1 and f2 from the current disturbance signal. It should be noted that since the device in the three-phase system may inject the island detection signal from any direction, the voltage signal and current signal of each phase must be collected during signal detection and island judgment. Since the three phases ABC are completely symmetrical, the signal processing process of any phase is introduced below. Figure 6 This is the processing process of voltage disturbance signal.

[0188] Step 1014, system RLC calculation;

[0189] The resistance, inductance and capacitance (RLC) parameters of the system are calculated based on the voltage and current phasors obtained in step 1013 and the signal strength information obtained from the coded pulse.

[0190] The impedance information of the system at each frequency can be obtained based on the voltage and current phasors of the dual-band, and the signal strength k can be obtained by combining the number of coded pulses. n , and then accurately obtain the R, L, and C parameters of the system under the RLC series model. The specific solution method is:

[0191] Step 1014-1, solve the system impedance at frequencies f1 and f2

[0192] Step 1014-2, assuming Z1 = R + jX1, Z2 = R + jX2, then the system resistance is R and the capacitance is inductance

[0193] Where ω1=2πf1, ω2=2πf2. R, L, C are the current system impedance parameters, which can be used as the basis for subsequent islanding judgment.

[0194] Step 1015, determining whether it is in an island operation state;

[0195] Determine whether it is in the island operation state. If it is in the island operation state, execute step 1016. If it is not in the island operation state, return to execute step 1001.

[0196] The specific process of island judgment is as follows:

[0197] Step 1015-1, assuming that the system voltage collected in the current timing period is u o (k), the output current is i o (k), the system voltage before Δt1 is u o (k-Δt1 / Δt k ), the output current is i o (k-Δt1 / Δt k ), where Δt k is the timer period.

[0198] Solve for the disturbance signal u s (k) = u o (k)-u o (k-Δt1 / Δt k ),i s (k) = i o (k)-i o (k-Δt1 / Δt k ).

[0199] Step 1015-2, record a complete disturbance signal u s , which contains disturbance signal and coded pulse signal, such as Figure 6 As shown, the same record i s .

[0200] Step 1015-3, according to the disturbance signal u s The coded pulse in obtains the current injected signal strength k n , and calculate u through the DFT algorithm s andi s Voltage phasors at frequencies f1 and f2 and current phasor

[0201] Step 1015-4, according to the current system impedance parameters R, L, C obtained in step 1014, when the RLC parameters of the system are within the set threshold, that is, R min <R<R max , L min <L<L max , C min <C<C max It is judged as an island operation state.

[0202] Step 1016, island protection action;

[0203] The island protection is activated, the circuit breaker trips, and the device stops operating.

[0204] As an island protection solution at distributed power sources or public connection points, considering the diversity of actual on-site needs, its specific implementation method will be different in different application scenarios. The following is an introduction to island protection solutions in several typical scenarios.

[0205] The core of the active island detection method based on impedance measurement consists of two modules: signal injection and impedance measurement. When the two functional modules are combined into a single integrated application, it can be inherited in the existing distributed power supply as part of the control to achieve the island protection of the distributed power supply, or it can be installed as an independent device at the common connection point to complete the island protection of the common connection point. Figure 7 The two installation points 1 and 2 are shown in the figure. Alternatively, the island detection device can be installed only at the common connection point, and the signal injection can be completed by the local distributed power supply. The two cooperate with each other to realize the protection of the common connection point, such as Figure 8 shown.

[0206] As can be seen from the above, since the island detection method based on signal cooperative injection includes two links: signal injection and island detection, its specific hardware configuration will be different in different application scenarios, and the hardware configuration specifically includes:

[0207] (1) When signal injection and island detection are integrated into a single device, the existing mainstream inverter configuration scheme can be used whether it is used as a distributed power supply island protection or to achieve island protection of the common connection point, such as Figures 9-10 As shown. The controller needs to collect the inductor current i of the inverter circuit labc , output current i oabc And output voltage u oabc , and gives the corresponding switch tube PWM drive signal, as well as the circuit breaker drive signal for island protection. The difference is that the distributed power supply island protection drives the grid-connected switch, and the common connection point protection drives the circuit breaker at the common connection point.

[0208] (2) If the island detection is completed only at the common connection point, the controller only needs to measure the voltage u inside the circuit breaker oabc and current i oabc , and give the driving signal of the circuit breaker, such as Fig.11 shown.

[0209] The software configuration specifically includes:

[0210] The functions of the island protection at the distributed power source and the common connection point are similar when the signal is injected. The only difference is that the island protection of the distributed power source needs to superimpose the injection signal for island detection on its original power frequency control command. Figures 12-13For an island protection device that only implements island detection at the common connection point, its control function only needs to complete island detection and implement island protection action based on the voltage and current signals measured at the access point. Fig.14 shown.

[0211] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. An island detection method based on signal cooperative injection, characterized in that: The steps include: Step a, determine whether the timer interrupt is triggered, if the timer interrupt occurs, execute step b, if the timer interrupt does not occur, execute step l; Step b, measuring the voltage and current signals of the system, and recording and storing the measured signals; Step c, determining whether the flag bit based on the synchronous injection of the satellite timing signal is set, if it is set, executing step d, if it is not set, executing step h; Step d, execute the satellite timing signal synchronization injection subroutine, use the satellite timing signal as a reference, generate a dual-frequency current injection signal instruction i with a coded pulse ref , the injection signal is composed of a pulse sequence and a four-cycle dual-frequency sinusoidal signal, and any one of the three phases ABC is selected as the injection phase; Step e, current tracking control generates a modulation signal according to the injection signal instruction; Step f, PWM control generates a pulse modulation signal that finally drives the inverter according to the modulation signal; Step g, the timer is reset and restarted; Step h, determining whether the flag bit based on system voltage synchronous injection is set, if the flag bit based on system voltage synchronous injection is set, executing step i, if the flag bit based on system voltage synchronous injection is not set, executing step j; Step i, execute the system voltage based synchronous injection subroutine, that is, use the system voltage as the synchronization reference to generate a pulse modulated sinusoidal current injection instruction i with a coded pulse ref , and return to execute step e; Step j, judging whether the voltage amplitude and frequency exceed the set threshold value according to the sampled data in step b, if they exceed the set threshold value, executing step k, otherwise returning to executing step g; Step k, judging whether the satellite timing signal is reliable and stable. If the satellite timing signal is reliable, it indicates that the flag position based on the synchronous injection of the satellite timing signal is in place, and the process returns to step e. If the satellite timing signal is unreliable, it indicates that the flag position based on the synchronous injection of the system voltage is in place, and the process returns to step e. Step 1, extracting the voltage and current phasors in the same frequency band as the injected signal and the coded pulses in the corresponding signal from the voltage and current recorded in step b; Step m, calculating the system parameters: resistance R, inductance L and capacitance C according to the voltage and current phasors obtained in step l and the signal strength information obtained from the coded pulse; Step n, judging whether the system is in an island operation state according to the system parameters calculated in step m, if it is in an island operation state, performing an island protection action, if it is not in an island operation state, returning to step a; In step m, the calculation steps of system parameters are: Step m-1, solve the system impedance at frequencies f1 and f2 Step m-2, assuming Z1 = R + jX1, Z2 = R + jX2, then the system resistance is R and the capacitance is inductance Where ω1=2πf1,ω2=2πf2; In step n, the island operation status determination step is: Step n-1, assume that the system voltage collected during the current timing period is u o (k), the output current is i o (k), the system voltage before Δt1 is u o (k-Δt1 / Δt k ), the output current is i o (k-Δt1 / Δt k ), where Δt k is the timer period; Solve for the disturbance signal u s (k) = u o (k)-u o (k-Δt1 / Δt k ),i s (k) = i o (k)-i o (k-Δt1 / Δt k ); Step n-2, record a complete disturbance signal u s , which includes a disturbance signal and a coded pulse signal; Step n-3, according to the disturbance signal u s The coded pulse in obtains the current injected signal strength k n , and calculate u through the DFT algorithm s andi s Voltage phasors at frequencies f1 and f2 and current phasor Step n-4, according to the current system impedance parameters R, L, C obtained in step i, when the system RLC parameters are within the set threshold, i.e. R min <R<R max , L min <L<L max , C min <C<C max It is judged as an island operation state.

2. The island detection method based on signal cooperative injection according to claim 1, characterized in that: In step d, the satellite timing signal synchronization injection subroutine comprises the following steps: Step d-1, determine whether to capture the 1PPS pulse signal, if the rising edge of the 1PPS timing signal is captured, execute step d-2, if not, execute step d-4; Step d-2, injection point timing t s Accumulation; Step d-3, determine the accumulated time t s Is it greater than or equal to 2π? If the accumulated time is greater than or equal to 2π, execute step d-4; if the accumulated time is less than 2π, return to step d-1; Step d-4, injection point generation, cumulative time t s reset to zero; Step d-5, determining whether the injected signal has completed the generation of four-cycle sinusoidal signals, if the injected signal has completed the generation of four-cycle sinusoidal signals, executing step d-10, if the injected signal has not completed the generation of four-cycle sinusoidal signals, executing step d-6; Step d-6, calculating the phase angles θ1 and θ2 of the injected signals with frequencies f1 and f2 respectively; Step d-7, determining whether the phase angles θ1 and θ2 of the injected signals of the frequencies f1 and f2 are greater than or equal to 2π, if the phase angles θ1 and θ2 are greater than or equal to 2π, executing step d-8, if the phase angles θ1 and θ2 are less than 2π, executing step d-11; Step d-8, the phase angles θ1 and θ2 of the injected signals of frequencies f1 and f2 are set to zero; Step d-9, generate current injection instruction: i ref =i 1ref +i 2ref , where i 1ref =I1sinθ1,i 2ref =I2sinθ2, and exit the satellite timing signal synchronization injection subroutine; Step d-10, determining whether the delay time satisfies nΔt, if the delay time does not satisfy nΔt, executing step d-12, if the delay time satisfies nΔt, executing step d-11; Step d-11, when the delay time satisfies nΔt, the current injection instruction i ref =P(t), P(t) is a single positive and negative alternating pulse signal, and execute step d-12; Step d-12, if the delay time does not satisfy nΔt, the current injection instruction is set to zero: i ref =0.

3. The island detection method based on signal cooperative injection according to claim 2 is characterized in that: In step d-2, the injection point timing t s The cumulative calculation formula for the accumulation is: t s (k)=t s (k-1)+Δt2πf t , Among them, t s (k) is the current accumulated time, t s (k-1) is the accumulated time of the previous fixed time period, Δt2πf t is the timing increment.

4. The island detection method based on signal cooperative injection according to claim 2 is characterized in that: In step d-6, the phase angle calculation formula of the injection signal with frequency f1 is: θ1(k)=θ1(k-1)+Δt2πf1 Among them, θ1(k) is the current phase angle cumulative value, θ1(k-1) is the phase angle cumulative value of the previous sampling cycle, and Δt2πf1 is the phase angle increment since this week; The phase angle calculation formula for the injected signal with frequency f2 is: θ2(k)=θ2(k-1)+Δt2πf2 Among them, θ2(k) is the current phase angle cumulative value, θ2(k-1) is the phase angle cumulative value of the previous sampling cycle, and Δt / (2πf2) is the phase angle increment since this week.

5. The island detection method based on signal cooperative injection according to claim 1, characterized in that: In step i, the system voltage synchronous injection subroutine comprises the following steps: Step i-1, determine whether to capture the voltage rising edge signal, if the voltage rising edge is captured, execute step i-2, if the voltage rising edge is not captured, continue to execute this step; Step i-2, if the value S(k-1) of the pulse function s(t) in the previous sampling period is equal to the pulse intensity S0: S(k-1) = S0, then S(k) = 0; if the value S(k-1) of the pulse function s(t) in the previous sampling period is zero: S(k-1) = 0, then the pulse intensity S0 is the value S(k) of the pulse function s(t) in this period: S(k) = S0; Step i-3, determining whether the generation of four cycles of the sinusoidal injection signal is completed, if the generation of four cycles of the sinusoidal injection signal is completed, executing step i-5, if the generation of four cycles of the sinusoidal injection signal is not completed, executing step i-4; Step i-4, whether the value S(k) of the pulse function s(t) in this cycle is 0: S(k)==0. If S(k)==0 is satisfied, execute step i-6, otherwise execute step i-7; Step i-5, determine whether the delay time satisfies nΔt, if the delay time does not satisfy nΔt, execute step i-7, if the delay time satisfies nΔt, execute step i-8; Step i-6, generate current injection instruction, let i ref =S0i(k), and end; Step i-7, set the current injection instruction to zero, i.e. ref =0, and end; Step i-8, the current injection instruction is generated as a positive and negative alternating pulse signal, i.e. ref =P(t), P(t) is a single positive and negative alternating pulse signal, and ends.

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