Method and system for suppressing abrupt change leakage current in grid-connected stage

Abstract

The invention discloses a suppression method and system for abrupt-change leakage current in a grid-connected stage, the suppression method is applied to a Heric and H4 inversion topology system, and the suppression method comprises the following steps: collecting a ground voltage, a bus voltage and a power grid voltage of an inverter system; constructing a safety voltage threshold range according to the collected ground voltage and bus voltage; and closing the grid-connected relay when the power grid voltage falls into the safe time zone corresponding to the safe voltage threshold range. The suppression system is used for implementing the suppression method. The system has the advantages that the hardware structure of the system circuit does not need to be changed, the abrupt change leakage current can be completely eliminated by controlling the pull-in time of the grid-connected relay only by utilizing the characteristics of the circuit, the working stability of the inverter system is enhanced, and the reliability of the inverter system is improved. Damage of Y capacitor large voltage generated along with the abrupt change current to other parts of the system is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of renewable energy power generation, and in particular to a method for suppressing sudden leakage current during a grid-connected phase. Background Art

[0002] The inverter system generally includes a power generation unit, a DC / DC unit, and a DC / AC unit. The inverter system can be connected to the grid through the AC side of the DC / AC unit. In order to achieve on-grid and off-grid control of the inverter system, a relay is often connected between the DC / AC unit and the grid to achieve on-grid and off-grid control of the inverter system.

[0003] When the inverter system is connected to the grid, in order to ensure the working safety of the inverter system, it is often necessary to perform a self-check on the relay first, and the inverter system can be connected to the grid only after ensuring that the relays are working normally. However, during the self-check process of the relay, the leakage current of the inverter system may increase suddenly, which in turn triggers the leakage current protector to trip, which may easily cause the inverter system to fail to connect to the grid and go offline. Summary of the invention

[0004] One of the objectives of the present application is to provide a method for suppressing sudden leakage current during the grid-connection phase, which can solve at least one of the defects in the above-mentioned background technology.

[0005] In order to achieve at least one of the above-mentioned purposes, the technical solution adopted in the present application is: a method for suppressing sudden leakage current in the grid-connected stage, applied to Heric and H4 inverter topology systems, including the following steps: collecting the ground voltage, bus voltage and grid voltage of the inverter system; constructing a safe voltage threshold range based on the collected ground voltage and bus voltage; and closing the grid-connected relay within the safe time zone corresponding to the grid voltage falling into the safe voltage threshold range.

[0006] Preferably, the lower limit of the safety voltage threshold range is the ground voltage, and the upper limit of the safety voltage threshold range is the sum of the ground voltage and the bus voltage.

[0007] Preferably, the grid-connected relay's pickup delay time is ΔT; the grid voltage intersects the safety time period corresponding to the upper and lower limits of the safety voltage threshold range by ΔT to obtain a safety time zone.

[0008] Preferably, there are multiple continuous safety time zones corresponding to the grid voltage falling into the safety voltage threshold range; the grid-connected relay is suitable for being attracted in the closest safety time zone that meets the attraction time requirement from the current moment.

[0009] Preferably, if the current moment is within the most recent safety time period, the determination of the most recent safety time zone that meets the pull-in time requirement includes the following process: calculating the time interval between the current moment and the end point of the most recent safety time period; if the calculated time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; if the calculated time interval is less than or equal to ΔT, continue to calculate the time interval between the current moment and the end point of the most recent safety time period; if the calculated time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; otherwise, the safety time zone corresponding to the most recent safety time period does not meet the pull-in time requirement, and at this time, the next safety time zone is used as the most recent safety time zone that meets the pull-in time requirement.

[0010] Preferably, if the current moment is outside the nearest safe time period, the judgment of the nearest safe time zone that meets the pull-in time requirement includes the following process: calculating a first time interval between the current moment and the starting point of the nearest safe time period; if the calculated first time interval is greater than ΔT, the safe time zone corresponding to the nearest safe time period meets the pull-in time requirement; if the calculated first time interval is less than or equal to ΔT, continue to calculate the second time interval between the current moment and the end point of the nearest safe time period; if the calculated second time interval is greater than ΔT, the safe time zone corresponding to the nearest safe time period meets the pull-in time requirement; otherwise, the safe time zone corresponding to the nearest safe time period does not meet the pull-in time requirement, and the next safe time zone is used as the nearest safe time zone that meets the pull-in time requirement.

[0011] Preferably, if the duration of the safety time zone does not meet the closing time requirement of the grid-connected relay, the bus voltage is raised to increase the upper limit of the safety voltage threshold range, thereby increasing the duration of the safety time zone to meet the closing time requirement; after the grid-connected relay is closed, the grid voltage is reduced and reset.

[0012] Preferably, the bus voltage is raised to a value greater than the peak value of the grid voltage.

[0013] Preferably, the bus voltage is boosted by a BOOST voltage-boosting circuit.

[0014] A system for suppressing sudden leakage current in the grid-connected stage, used for implementing the above-mentioned method for suppressing sudden leakage current in the grid-connected stage, comprises a collection unit, a calculation unit and a control unit; the collection unit is used for collecting the ground voltage, bus voltage and grid voltage of the inverter system; the calculation unit calculates the safe voltage threshold range according to the voltage data obtained by the collection unit, and constructs a safe time zone in which the grid voltage falls into the safe voltage threshold range; the control unit is suitable for sending a pull-in control signal to a grid-connected relay, so that the grid-connected relay completes pull-in within the safe time zone.

[0015] Compared with the prior art, the beneficial effects of this application are: The present application does not require changing the hardware structure of the system circuit, but only utilizes the characteristics of the circuit itself. By controlling the closing timing of the grid-connected relay, the sudden leakage current can be completely eliminated, thereby enhancing the working stability of the inverter system and reducing the damage to other components of the system caused by the large voltage of the Y capacitor generated by the sudden current. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the architecture of the existing Heric type inverter topology system.

[0017] Figure 2 It is a schematic diagram of the architecture of the existing H4 inverter topology system.

[0018] Figure 3 Schematic diagram of leakage current equivalent circuit of Heric type inverter topology system and H4 type inverter topology system.

[0019] Figure 4 Schematic diagram of grid voltage waveform.

[0020] Figure 5 Schematic diagram of the leakage current loop formed by the equivalent circuit when the grid voltage is 0-T / 4.

[0021] Figure 6 Schematic diagram of the leakage current loop formed by the equivalent circuit when the grid voltage is T / 2-3T / 4.

[0022] Figure 7 To conduct simulation model Figure 1 and Figure 2 Schematic diagram of waveforms obtained by simulating the inverter system shown.

[0023] Figure 8 It is a partial enlarged schematic diagram of the oscillating current waveform of the Y capacitor.

[0024] Fig. 9 Schematic diagram of the sudden leakage current waveform of the inverter system.

[0025] Fig.10 This is a schematic diagram of the time domain response waveform of the leakage current when the positive and negative poles of the inverter system diode are short-circuited.

[0026] Fig.11 This is a partially enlarged schematic diagram of the leakage current time domain response waveform when the positive and negative poles of the inverter system diode are short-circuited.

[0027] Fig.12 Schematic diagram of the work flow of the inhibition method in this application.

[0028] Fig.13A schematic diagram of the safe time zone division of the grid-connected relay in this application.

[0029] Fig.14 This is a control logic diagram for the grid-connected relay energization in this application.

[0030] Fig.15 This is a schematic diagram of the safe time zone division after the bus voltage is raised for this application.

[0031] Fig.16 Schematic diagram of the work flow of the inhibition system in this application.

[0032] In the figure: a collection unit 100, a calculation unit 200, and a control unit 300. DETAILED DESCRIPTION

[0033] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that in the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0034] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of the present application.

[0035] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0036] In this application, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be connected, detachably connected, or integrated; it can be mechanically connected or electrically connected; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0038] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0039] It should be known that a sudden change in leakage current is likely to occur during the grid-connected process of the Heric and H4 inverter topology systems. To facilitate the understanding of the technical solution of the present application, the specific reasons for the sudden change in leakage current generated by the Heric and H4 inverter topology systems during the grid-connected process are analyzed below.

[0040] like Figure 1 and Figure 2 As shown, they are typical architecture schematic diagrams of the existing Heric type inverter topology system and the H4 type inverter topology system. The specific structure and working principle of the architecture are well known to those skilled in the art, so they will not be elaborated here in detail.

[0041] Depend on Figure 1 and Figure 2It can be seen that when the inverter system has not yet started the inverter operation, the Heric inverter topology system and the H4 inverter topology system only differ in the two IGBT switches S5 and S6. Taking photovoltaic power generation as an example, if the voltage output by the solar cell PV is lower than the voltage required for grid connection, the bus voltage needs to be raised to a certain value through the BOOST boost circuit, and then the BOOST boost circuit stops working; but regardless of whether the BOOST circuit is working or not, in the leakage current analysis loop, assuming that the output voltage of the PV cell is constant or changes very little, the Y capacitor C on the PV cell side PV+ The Y capacitor C on the bus side DC+ It can be equivalent to a capacitor C on the bus side after the two capacitors are connected in parallel POS , we can set C POS = C PV+ +C DC+ The specific proof process is a well-known technology to those skilled in the art, so it will not be elaborated in detail here.

[0042] In addition, the Heric inverter topology did not work during the relay self-test stage and the grid-connected stage, and the switches S1~S6 did not operate; the two freewheeling IGBT switches S5 and S6 were connected in series at the reverse ends, and due to the presence of anti-parallel diodes, current was not allowed to pass through them, that is, in the leakage current loop analysis, the Heric inverter topology is consistent with the H4 inverter topology leakage current loop.

[0043] In general, in the power system, the N line of the grid is connected to the earth, that is, the voltage between the N line and the earth is V N =0V and the voltage change rate is 0; due to the bus voltage v bus Greater than the peak value of the grid voltage v gmax , then in the case where there is no huge leakage current through the Y capacitor into the ground, the Y capacitor C NEG The voltage v neg <0V, v neg ≤V N (ie 0V) ≤v dc+ ; where v dc+ It indicates the voltage between the positive busbar and the ground, which causes the anti-parallel diodes of the switch tubes S1~S4 to be reverse biased. When the grid-connected relays T3 and T4 are both energized and turned on, the N line cannot form a leakage current loop with the DC side. Therefore, the Heric type and H4 type inverter topology systems can construct the same leakage current equivalent loop. The specific loop structure is as follows: Figure 3 Based on Figure 3 The leakage current equivalent circuit is shown, and the specific generation process of the leakage current will be described in detail below.

[0044] like Figure 4 As shown, it is the grid voltage v g Schematic diagram of the waveform structure; Figure 4 It can be seen that the grid voltage v g The waveform is sinusoidal and periodic. bus Greater than the peak value of the grid voltage v gmax When the inverter system is connected to the grid, the grid-connected relays T1 and T2 will always be in a closed state. The leakage current generation process can be analyzed specifically according to the waveform change of the grid voltage. The waveform change process of the grid voltage can be divided into four processes, which will be described in detail below.

[0045] Process 1: Figure 4 As shown, in the 0~T / 4 period of the grid voltage, there are 0 <v g <v gmax , and the change in grid voltage dv g / dt≥0. When the grid voltage rises to v g >v pos When the diode D1 is turned on, the conduction state of the leakage current equivalent circuit is as follows: Figure 5 As shown. Among them, v pos Represents the equivalent capacitance C POS The voltage, and v pos =v bus +v neg .

[0046] After diode D1 is turned on, the equivalent capacitance C POS Charge to make its voltage v pos As the grid voltage increases, until v pos =v gmax , then the equivalent capacitance C POS The current i p =C POS ×dv pos / dt. Bus voltage v bus Approximately constant, then from the KVL equation, we know that the capacitance C NEG Charge to make its voltage v neg Increase, and due to the busbar voltage stabilizing capacitor C BUS (usually hundreds to thousands of microfarads, related to the inverter power) much larger than the capacitor C POS With capacitor C NEG , so according to the capacitor series formula, C BUS With C NEG The equivalent series capacitance is approximately C NEG , then we can get the capacitance C NEG The current i n =C NEG ×dv pos / dt; then there is i p / i n =C POS / CNEG .exist Figure 5 In the leakage current equivalent circuit shown in the figure, the circuit current i L According to the KCL equation, we can get: i L = i p +i n =( C POS + C NEG )×dv pos / dt.

[0047] Since the damping resistance in the current loop is very small, there is almost only the parasitic resistance of the inductor copper wire and the PCB copper, which is about hundreds of milliohms. The ratio of the inductance value of the inductor L1 to the total capacitance of the Y capacitor is large, which is prone to series oscillation. At the same time, the grid voltage is constantly rising during this period, so the capacitor C BUS With capacitor C POS The voltage waveform is an upward curve accompanied by slight oscillation. Since the capacitor current is proportional to the derivative of the capacitor voltage (leading voltage), the capacitor voltage oscillation will also cause the current i p with i n Violent shock.

[0048] Process 2: Figure 4 As shown, after completing process 1, there is v pos =v gmax , v neg =v pos -v bus = v gmax -v bus <0. Then in the T / 4~T / 2 period of the grid voltage, there is 0 <v g <v gmax , and the rate of change of the grid voltage dv g / dt≤0. When the grid voltage exceeds the peak time point (t>T / 4), the grid voltage begins to decrease. At this time, v g >0,v pos =v gmax , v neg <0. Due to v pos >v g And v neg <v g , so diodes D1 and D3 are cut off, and the leakage current loop cannot be formed. Then the loop current i L =0, capacitor C POS With capacitor C NEG The voltage will remain constant.

[0049] Process 3: Figure 4 As shown, within the T / 2~3T / 4 period of the grid voltage, there are 0 <v g <vgmax , and the rate of change of the grid voltage dv g / dt≤0; grid voltage v g Less than 0 and keeps decreasing. In the initial short period of time, because v pos =v gmax >0>v g >v neg , so diodes D1 and D3 remain cut off, that is, no leakage current loop is generated. At this time, capacitor C POS With capacitor C NEG The voltage remains unchanged. But when the grid voltage drops to v g <v neg When the diode D3 is turned on, the corresponding leakage current loop is as follows: Figure 6 shown.

[0050] Depend on Figure 6 It can be seen that when the diode D3 is turned on, the capacitor C NEG Discharge to make its voltage v neg As the grid voltage decreases until v neg =-v gmax , then i n =C NEG ×dv neg / dt. Bus voltage v bus Approximately constant, then from the KVL equation, we know that the capacitance C POS Discharge to make its voltage v pos Reduced, and due to the busbar voltage stabilizing capacitor C BUS (usually hundreds to thousands of microfarads, related to the inverter power) much larger than the capacitor C POS With capacitor C NEG , so according to the capacitor series formula, C BUS With C POS The equivalent series capacitance is approximately C POS , then we can get i p =C POS ×dv neg / dt; then there is i p / i n =C POS / C NEG According to the KCL equation: i L =-(i p +i n )=-(C POS + C NEG )×dv neg / dt.

[0051] Similar to process 1, in process 3, since the damping resistance in the current loop is very small and the grid voltage is continuously decreasing during this period, the capacitor C BUS With C POS The voltage waveform is a downward curve accompanied by slight oscillation. Since the capacitor current is proportional to the derivative of the capacitor voltage, the capacitor voltage oscillation will also cause the current i p with i n Violent shock.

[0052] Process 4: Figure 4 As shown, within the 3T / 4~T period of the grid voltage, there is -v gmax <v g <0, and the grid voltage change rate dv g / dt≥0. When the grid voltage exceeds the negative peak time point (t>3T / 4), the grid voltage begins to increase. At this time, v g <0, v neg =-v gmax , v pos >0. Since v pos >v g And v neg <v g , so diodes D1 and D3 are cut off, and the leakage current loop cannot be formed. Then the loop current i L =0, capacitor C POS With capacitor C NEG The voltage will remain constant.

[0053] Through the analysis of the above four processes, it can be seen that when the grid-connected relays T1 and T2 are always closed, the magnitude of the leakage current is proportional to the sum of all Y capacitors on the DC side. In order to understand the formation of the leakage current more clearly, the waveform structure of the leakage current can also be obtained through software simulation.

[0054] For example, a simulation model can be built in MATLAB / SIMULINK software, and the parameters of each component can be determined in the simulation software: C POS =C NEG =20nF (total capacitance is 40nF), inductor L1 is 450uH, bus voltage is 400V, Y capacitor C POS The initial voltage v pos =150V. Through software simulation, the simulation waveforms of process one to process four can be obtained. Figure 7 As shown in the figure, the peak leakage current is about 7mA. By partially amplifying the waveform of the loop current, we can get the following: Figure 8 The waveform is shown as a partial enlarged schematic diagram. Figure 8 It can be seen that the waveform of the Y capacitor current in the circuit is in a continuous oscillation state.

[0055] However, in the actual working process, the grid-connected relays T1 and T2 are not always energized, but have multiple stages of energization and disconnection. If the timing of energizing the grid-connected relays T1 and T2 is not selected correctly, it will lead to huge leakage current, thus causing the leakage protector to falsely report disconnection. Fig. 9 As shown, when the grid relays T1 and T2 are attracted at t=T+T / 4, the grid voltage v g Greater than v pos , so the diode D1 is turned on, the Y capacitor is charged, and a leakage current spike appears. Under the same component parameters, if the grid-connected relay is not properly selected, the leakage current peak can reach more than 1.5A. Compared with the 7mA peak leakage current generated when the grid-connected relay is always closed, the inappropriate grid-connected relay is more likely to cause the leakage protector to falsely report disconnection, which has a huge impact on the grid-connected stage. At the same time, due to the half-cycle LC oscillation of the Y capacitor and the inductor L1, the voltage v pos The value is much larger than the grid voltage, and the peak value can reach 500V. Such a large voltage will seriously threaten the safe working performance of the Y capacitor.

[0056] For ease of understanding, the following will describe the generation process of the sudden current through specific parameters. para The LCR series circuit consists of a parasitic resistance R para Basically, it is only a few hundred milliohms. The energization of the grid-connected relays T1 and T2 is equivalent to inputting a step voltage signal into the LCR series circuit. According to the LCR oscillation critical damping formula, the minimum resistance R that can prevent the Y capacitor voltage from oscillating is CRI for: .

[0057] Since the resistor R para Much smaller than R CRI , so the voltage of the Y capacitor will oscillate, making the voltage across the Y capacitor much larger than the input step voltage (i.e. v g ). If the positive and negative electrodes of the diode are short-circuited, the leakage current through the Y capacitor and the inductor L1 will continue to oscillate. In the mathematical tool Mathcad, the time domain function expression of the leakage current can be solved relatively easily through the relevant knowledge of Laplace. The time domain waveform of the leakage current is as follows Fig.10 As shown, it can be seen that when the positive and negative poles of the diode are short-circuited, the leakage current value will oscillate back and forth between the positive and negative regions.

[0058] However, due to the presence of diodes D1 and D3, the leakage current can only flow in one direction, and its value can only be limited to above 0A or below 0A, resulting in the Y capacitor voltage being unable to release the current after oscillating for half a cycle (similar to quickly going from process one to process two or from process three to process four). Fig.11 As shown, the circuit oscillates only half a cycle, causing a very large leakage current spike to appear at the moment of closing. The leakage current spike may cause the leakage protector to trip or the inverter to fail to connect to the grid.

[0059] Based on the above analysis process, one aspect of the present application provides a method for suppressing sudden leakage current during the grid-connected phase, which is applied to Heric and H4 inverter topology systems. Figure 1 As shown, one of the preferred embodiments includes the following steps: collecting the ground voltage, bus voltage and grid voltage of the inverter system; constructing a safe voltage threshold range based on the collected ground voltage and bus voltage; and closing the grid-connected relay within the safe time zone corresponding to the grid voltage falling into the safe voltage threshold range.

[0060] It is understandable that the premise of leakage current mutation is that the leakage current loop can be formed; from the above analysis process, it can be seen that when the grid voltage rises to v g >v pos When the diode D1 is turned on, a leakage current loop can be formed, or when the grid voltage drops to v g <v neg When the diode D3 is turned on, a leakage current loop can also be formed. Then, those skilled in the art should know that if the leakage current loop cannot be formed, the leakage current mutation will not occur. Therefore, the idea of ​​the technical solution of the present application to achieve leakage current mutation suppression is to cut off the formation of the leakage current loop; that is, the closing timing of the grid-connected relays T1 and T2 is selected in the time period that can make the diodes D1 and D3 both in reverse bias, so that it can be ensured that the leakage current loop cannot be formed and the corresponding leakage current mutation will not occur.

[0061] Compared with the traditional method of suppressing leakage current mutation, the present application does not need to change the hardware structure of the system circuit, but only utilizes the characteristics of the circuit itself. By controlling the closing timing of the grid-connected relay, the sudden leakage current can be completely eliminated, thereby enhancing the working stability of the inverter system and reducing the damage to other components of the system caused by the large voltage of the Y capacitor generated by the sudden current.

[0062] It should be known that there are many range limits for the safe time zone that can be used for the grid-connected relays to be simultaneously attracted. However, from the above analysis process, it can be seen that the voltage range corresponding to the safe time zone needs to be within the voltage v neg and v pos between; Fig.13 As shown, the lower limit of the safe voltage threshold range is the ground voltage v neg The upper limit of the safety voltage threshold range is the sum of the ground voltage and the bus voltage v pos .

[0063] In this embodiment, during the actual grid-connected relay energization process, there will be a delay ΔT between the issuance of the grid-connected relay energization signal and the complete energization success of the grid-connected relay. This is related to the model of the grid-connected relay, the power supply voltage, etc., but the energization delay of each model can basically be actually measured. Therefore, when setting the safe time zone, it is necessary to consider the energization delay time ΔT of the grid-connected relay; that is, by advancing the safe time period corresponding to the upper and lower limits of the safe voltage threshold range where the grid voltage intersects, by ΔT, the actual required safe time zone can be obtained. That is, the safe time period and the safe time are equal in duration, but the safe time zone is advanced by ΔT relative to the safe time period. The grid-connected relay only needs to be closed within the safe time zone to ensure that the moment of complete energization is within the safe time period.

[0064] For ease of understanding, a specific example is described in detail below. Fig.13 As shown, the grid voltage and voltage v neg and v pos The time nodes corresponding to the intersection points are t 01 ,t 02 ,t 03 and t 04 Among them, t 01 and t 02 A safe time period can be formed between 03 and t 04 When the inverter system is connected to the grid, it is only necessary to include the time point when the grid-connected relay is fully energized at t 01 and t 02 Between or t 03 and t 04 Then, for the timing of the grid-connected relay, it is only necessary to change the time node t 01 ,t 02 ,t 03 and t 04 All of them are advanced by a ΔT time, and then the time nodes t1, t2, t3 and t4 can be obtained; among them, a safe time zone can be formed between t1 and t2, and a safe time zone can be formed between t3 and t4; then the grid-connected relay starts to be attracted between t1 and t2 or between t3 and t4, and the time node when the grid-connected relay stops achieving full attraction must be at t 01 and t 02 Between or t 03 and t 04 between.

[0065] In this embodiment, Fig.13As shown, there are multiple continuous safety time zones corresponding to the grid voltage falling into the safety voltage threshold range, and the grid-connected relay can be closed in any safety time zone to achieve complete suppression of leakage current mutation. However, in order to improve the self-test efficiency of the grid-connected relay, the grid-connected relay is preferably closed in the nearest safety time zone that meets the closing time requirements at the current moment.

[0066] In this embodiment, the judgment of the nearest safe time zone that meets the pull-in time requirement at the current moment for the grid-connected relay is related to the current moment's location. Based on the different locations at the current moment, the judgment process for the nearest safe time zone that meets the pull-in time requirement is different. For ease of understanding, a detailed description will be given below.

[0067] Position 1: If the current time is outside the nearest safe time period, the judgment of the nearest safe time zone that meets the pull-in time requirements includes the following process: Calculate the current time t p The starting point of the most recent safe time period t s If the calculated first time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement. If the calculated first time interval is less than or equal to ΔT, continue to calculate the time interval between the current time and the end point of the most recent safety time period t k if the calculated second time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; otherwise, the safety time zone corresponding to the most recent safety time period does not meet the pull-in time requirement, and the next safety time zone is used as the most recent safety time zone that meets the pull-in time requirement.

[0068] Position 2: If the current time is within the nearest safe time period, the judgment of the nearest safe time zone that meets the pull-in time requirements includes the following process: Calculate the current time t p The end point of the nearest safe time period t k time interval; if the calculated time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; if the calculated time interval is less than or equal to ΔT, the safety time zone corresponding to the most recent safety time period does not meet the pull-in time requirement, and the next safety time zone is used as the most recent safety time zone that meets the pull-in time requirement.

[0069] For ease of understanding, the specific pickup process of the grid-connected relay will be described in detail below. Fig.14 As shown, first the voltage to ground v neg , bus voltage v bus And the grid voltage v g The safe voltage threshold range [v neg , v neg+v bus ], and then according to the grid voltage v g The intersection with the safe voltage threshold range divides the entire safe time period.

[0070] Then determine whether it is necessary to simultaneously close the grid-connected relays T1 and T2. If the grid-connected relays T1 and T2 are closed successively, a grid-connected relay closing signal is directly sent to the grid-connected relays T1 and T2. If the grid-connected relays T1 and T2 need to be closed at the same time, calculate the current time t p The distance to the starting point of the nearest safe time period t s and the end point t k time interval.

[0071] If the current time t p and the starting point of the safety time period t s The interval is greater than the grid-connected relay's pick-up delay time ΔT, that is, t s -t p >ΔT, indicating the current time t p If it is outside the nearest safe time period, it can be delayed by at least t s -t p After -ΔT time, a grid-connected relay pickup signal is sent to grid-connected relays T1 and T2.

[0072] If the current time t p and the starting point of the safety time period t s The interval is less than or equal to the grid-connected relay's pick-up delay time ΔT, that is, t s -t p ≤ΔT; there are two situations at this time, which are described in detail below.

[0073] The first case: t s -t p ≥0, indicating that the current time t p It is still outside the nearest safe time period. At this time, it is necessary to determine whether the duration of the safe time period can meet the pickup delay time requirement of the grid-connected relay. p and the end point of the safety time period t k The interval is calculated and judged whether it is greater than the pick-up delay time ΔT of the grid-connected relay. If t k -t p > ΔT, then immediately or with a delay of at most t k -t p -ΔT time to send the grid-connected relay pickup signal to the grid-connected relays T1 and T2. If t k -t p >ΔT, then find the starting point t of the next safe time period sAnd calculate again whether the interval between the starting point and the current time meets the pull-in delay time ΔT requirement of the grid-connected relay. Generally speaking, the interval of the next safe time period can meet the pull-in delay time ΔT requirement of the grid-connected relay, so it only needs to delay at least t s -t p After -ΔT time, a grid-connected relay pickup signal is sent to grid-connected relays T1 and T2.

[0074] The second case: s -t p <0, indicating that the current time t p It is in the nearest safety time period. At this time, it is necessary to determine whether the remaining duration of the safety time period can meet the pick-up delay time requirement of the grid-connected relay. p and the end point of the safety time period t k The interval is calculated and judged whether it is greater than the pick-up delay time ΔT of the grid-connected relay. If t k -t p > ΔT, then immediately or with a delay of at most t k -t p -ΔT time to send the grid-connected relay pickup signal to the grid-connected relays T1 and T2. If t k -t p >ΔT, then find the starting point t of the next safe time period s And calculate whether the interval between the starting point and the current time meets the pull-in delay time ΔT requirement of the grid-connected relay. Generally speaking, the interval of the next safe time period can meet the pull-in delay time ΔT requirement of the grid-connected relay, so it only needs to delay at least t s -t p After -ΔT time, a grid-connected relay pickup signal is sent to grid-connected relays T1 and T2.

[0075] In this embodiment, if the frequency of the grid voltage is too high, the duration of the safety time zone may be shortened to a level that does not meet the requirements for the grid-connected relay's energizing time, that is, the duration of the grid-connected relay from receiving the energizing signal to fully energizing may need to span multiple safety time zones; since the selection of the energizing timing of the grid-connected relay requires the calculation of the time interval for each energized safety zone, this will increase the overall calculation amount of the inverter system, thereby reducing the response speed and affecting the energizing accuracy of the grid-connected relay. Therefore, when the duration of the safety time zone does not meet the requirements for the energizing time of the grid-connected relay, the bus voltage can be raised to increase the upper limit of the safety voltage threshold range, thereby increasing the duration of the safety time zone to meet the energizing time requirements; after the grid-connected relay is energized, the grid voltage is stepped down and reset.

[0076] It can be understood that, from the above content, the upper limit of the safe voltage threshold range is the sum of the ground voltage and the bus voltage. Therefore, raising the bus voltage can increase the upper limit of the safe voltage threshold range, thereby moving the intersection of the grid voltage and the upper limit of the safe voltage range upward, and the duration of the corresponding safe time zone will gradually increase. The degree of increase in the duration of the safe time zone can be selected according to actual needs; in order to further facilitate the simultaneous energization of the grid-connected relays T1 and T2, such as Fig.15 As shown, this embodiment preferably raises the bus voltage to a peak value greater than the grid voltage.

[0077] It should be known that there are multiple ways to raise the bus voltage. Considering that the converter of the inverter system often adopts a BOOST boost circuit, the bus voltage can be raised by the BOOST boost circuit.

[0078] Another aspect of the present application provides a system for suppressing sudden leakage current during the grid-connection phase, which is used to implement the above-mentioned method for suppressing sudden leakage current during the grid-connection phase, such as Fig.16 As shown, one preferred embodiment includes a collection unit 100, a calculation unit 200 and a control unit 300; the collection unit 100 is used to collect the ground voltage, bus voltage and grid voltage of the inverter system; the calculation unit 200 calculates the safe voltage threshold range according to the voltage data obtained by the collection unit 100, and constructs a safe time zone in which the grid voltage falls into the safe voltage threshold range; the control unit 300 can send a pull-in control signal to the grid-connected relay so that the grid-connected relay completes the pull-in within the safe time zone.

[0079] It should be known that the specific structures and working principles of the acquisition unit 100, the calculation unit 200 and the control unit 300 are well-known technologies to those skilled in the art, so they will not be elaborated in detail here. The common acquisition unit 100 can use a voltage sensor, and the ground voltage, bus voltage and grid voltage can be collected by corresponding voltage sensors respectively. The calculation unit 200 and the control unit 300 can be independently set or integrated, such as an MCU chip and a DSP chip.

[0080] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. A method for suppressing sudden leakage current during the grid-connected phase, applied to Heric and H4 inverter topology systems, characterized in that: The steps include: Collect the ground voltage, bus voltage and grid voltage of the inverter system; construct a safe voltage threshold range based on the collected ground voltage and bus voltage; and close the grid-connected relay in the safe time zone corresponding to the safe voltage threshold range when the grid voltage falls into the safe time zone; The lower limit of the safety voltage threshold range is the ground voltage, and the upper limit of the safety voltage threshold range is the sum of the ground voltage and the bus voltage; The grid-connected relay's pickup delay time is ΔT; the safety time period corresponding to the intersection of the grid voltage at the upper and lower limits of the safety voltage threshold range is advanced by ΔT to obtain the safety time zone.

2. The method for suppressing sudden leakage current during the grid connection phase according to claim 1, characterized in that: There are multiple continuous safety time zones corresponding to the grid voltage falling into the safety voltage threshold range; the grid-connected relay is suitable for being attracted in the nearest safety time zone that meets the attraction time requirement at the current moment.

3. The method for suppressing sudden leakage current during the grid connection phase according to claim 2, characterized in that: If the current time is within the nearest safe time period, the determination of the nearest safe time zone that meets the pull-in time requirements includes the following process: Calculate the time interval between the current time and the end point of the nearest safe time period; If the calculated time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; If the calculated time interval is less than or equal to ΔT, the safety time zone corresponding to the most recent safety time period does not meet the pull-in time requirement, and the next safety time zone is used as the most recent safety time zone that meets the pull-in time requirement.

4. The method for suppressing sudden leakage current during the grid connection phase according to claim 2, characterized in that: If the current time is outside the nearest safe time period, the determination of the nearest safe time zone that meets the pull-in time requirements includes the following process: Calculate the first time interval between the current time and the starting point of the nearest safe time period; If the calculated first time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; If the calculated first time interval is less than or equal to ΔT, continue to calculate the second time interval between the current time and the end point of the nearest safety time period; If the calculated second time interval is greater than ΔT, the safety time zone corresponding to the most recent safety time period meets the pull-in time requirement; Otherwise, the safety time zone corresponding to the nearest safety time period does not meet the pull-in time requirement, and the next safety time zone is used as the nearest safety time zone that meets the pull-in time requirement.

5. The method for suppressing sudden leakage current during the grid connection phase according to any one of claims 1 to 4, characterized in that: If the duration of the safety time zone does not meet the closing time requirement of the grid-connected relay, the bus voltage is raised to increase the upper limit of the safety voltage threshold range, thereby increasing the duration of the safety time zone to meet the closing time requirement; after the grid-connected relay is closed, the grid voltage is reduced and reset.

6. The method for suppressing sudden leakage current during the grid connection phase according to claim 5, characterized in that: The bus voltage rises to a peak value greater than the grid voltage.

7. The method for suppressing sudden leakage current during the grid connection phase according to claim 5, characterized in that: The bus voltage is boosted by the BOOST circuit.

8. A system for suppressing sudden leakage current during the grid-connection phase, used for implementing the method for suppressing sudden leakage current during the grid-connection phase according to any one of claims 1 to 7, characterized in that: include: Acquisition unit; The acquisition unit is used to collect the ground voltage, bus voltage and grid voltage of the inverter system; Computational unit; The calculation unit calculates the safe voltage threshold range according to the voltage data acquired by the acquisition unit, and constructs a safe time zone in which the grid voltage falls within the safe voltage threshold range; as well as Control unit; the control unit is suitable for sending a pull-in control signal to the grid-connected relay so that the grid-connected relay completes the pull-in within the safe time zone.

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