Inverter and self-checking method thereof

Abstract

The embodiment of the invention discloses an inverter and a self-checking method thereof, and the method comprises the steps: adjusting the duty ratio of a switching tube from a set state before grid connection of the inverter, thereby adjusting the flying voltage at two ends of a flying capacitor, and determining whether at least one switching tube works normally or not according to whether the flying voltage can be stabilized at a set voltage or not. According to the invention, whether the charging switch tube and the discharging switch tube work normally can be judged, so that hardware faults of the inverter can be found in time before grid connection of the inverter, fault expansion is avoided, and the safety and reliability of the inverter are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to an inverter and a self-test method thereof. Background Art

[0002] The flying capacitor three-level boost circuit is increasingly being used in inverters due to its advantages such as increasing the equivalent switching frequency, reducing the volume cost of the inductor, and reducing the complexity of the inverter insulation impedance detection circuit.

[0003] In the prior art, a photovoltaic power station is usually connected to the power grid through multiple string inverters, and each inverter in the multiple string inverters includes a flying capacitor three-level boost circuit. When performing a photovoltaic inverter self-test in the prior art, it is usually determined whether the flying capacitor three-level boost circuit in the multiple string inverters has successfully boosted the voltage by judging the relationship between the bus voltage of the bus connected to the flying capacitor three-level boost circuit and the AC peak value.

[0004] However, the above judgment method cannot timely detect whether there is an abnormality in a certain Luffy transcapacitor three-level boost circuit, resulting in the inverter being connected to the grid with hidden dangers, reducing the safety and reliability of the inverter. Summary of the invention

[0005] The present invention provides an inverter and a self-checking method thereof, which can timely detect the hardware abnormality of the inverter before grid connection, thereby improving the safety and reliability of the inverter.

[0006] According to one aspect of the present invention, an inverter self-test method is provided, wherein the inverter includes at least one flying capacitor three-level boost circuit, the flying capacitor three-level boost circuit includes a switch tube and a flying capacitor, the flying capacitor is electrically connected to the switch tube, and the output end of the flying capacitor three-level boost circuit is electrically connected to a bus; the inverter self-test method includes:

[0007] Before the inverter is connected to the grid, the duty cycle corresponding to the switch tube is adjusted from a set state, thereby adjusting the flying voltage across the flying capacitor; wherein, in the set state, the flying voltage is a first voltage, the voltage on the bus is a second voltage, and the first voltage is equal to half of the second voltage;

[0008] Determine whether at least one switch tube is operating normally according to whether the flying voltage can be stabilized at a set voltage;

[0009] The set voltage is greater than half of the second voltage, or the set voltage is less than half of the second voltage.

[0010] Optionally, the switch tube includes a charging switch tube and a discharging switch tube, the charging switch tube and the discharging switch tube are connected in series, and the flying capacitor is connected to a common connection end of the charging switch tube and the discharging switch tube;

[0011] Before the inverter is connected to the grid, the duty cycle corresponding to the switch tube is adjusted from a set state, thereby adjusting the flying voltage across the flying capacitor, including: before the inverter is connected to the grid, in a first time period, controlling the first duty cycle corresponding to the charging switch tube to be greater than the second duty cycle corresponding to the discharging switch tube; in a second time period, controlling the first duty cycle to be equal to the second duty cycle, and the second time period is after the first time period;

[0012] Determining whether the switch tube is working normally according to whether the flying voltage can be stabilized at the set voltage includes: determining whether the charging switch tube is working normally according to whether the flying voltage is stable at the first set voltage in the second time period; the first set voltage is greater than half of the second voltage.

[0013] Optionally, during the first time period, the first duty cycle corresponding to the charging switch tube is controlled to be greater than the second duty cycle corresponding to the discharging switch tube, including: during the first time period, the first duty cycle corresponding to the charging switch tube is controlled to increase from 0 with a first slope, and the second duty cycle of the discharging switch tube is controlled to increase from 0 with a second slope, and the first slope is greater than the second slope.

[0014] Optionally, before the inverter is connected to the grid, the duty cycle corresponding to the switch tube is adjusted from a set state to adjust the flying voltage across the flying capacitor, and further includes: in a third time period, controlling the first duty cycle corresponding to the charging switch tube to be less than the second duty cycle corresponding to the discharging switch tube; in a fourth time period, controlling the first duty cycle to be equal to the second duty cycle, and the fourth time period is after the third time period;

[0015] Determining whether the switch tube is working normally according to whether the flying voltage can be stabilized at the set voltage, further comprising: determining whether the discharge switch tube is working normally according to whether the flying voltage is stabilized at the second set voltage in the fourth time period; the second set voltage is less than half of the second voltage;

[0016] Wherein, the fourth time period is before the first time period, and the flying capacitor three-level boost circuit is in a setting state at the beginning of the third time period;

[0017] Or the second time period is before the third time period, and the flying capacitor three-level boost circuit is in a setting state at the beginning of the first time period.

[0018] Optionally, during the third time period, the first duty cycle corresponding to the charging switch tube is controlled to be smaller than the second duty cycle corresponding to the discharging switch tube, including: during the third time period, the first duty cycle corresponding to the charging switch tube is controlled to increase from 0 with a third slope, and the second duty cycle of the discharging switch tube is controlled to increase from 0 with a fourth slope, and the third slope is smaller than the fourth slope.

[0019] Optionally, during the first time period, the second time period, the third time period and the fourth time period, the first duty cycle and the second duty cycle are both less than a preset duty cycle threshold.

[0020] Optionally, an absolute value of a difference between the first duty cycle and the second duty cycle is less than or equal to half of a preset duty cycle threshold.

[0021] Optionally, the inverter self-test method further includes: performing a startup condition judgment of the inverter or a closed-loop boost process of a flying capacitor three-level boost circuit;

[0022] The power-on condition judgment is performed before adjusting the duty cycle corresponding to the switch tube from the set state to adjust the flying voltage at both ends of the flying capacitor, or after determining that the switch tube is working normally;

[0023] The power-on condition judgment of the inverter includes: determining whether the power-on condition of the inverter is met according to the photovoltaic output voltage and output power of the photovoltaic panel connected to the input end of the flying capacitor three-level boost circuit;

[0024] The closed-loop boost process is performed before adjusting the duty cycle corresponding to the switch tube from a set state to adjust the flying voltage across the flying capacitor, or the closed-loop boost process is performed after determining that the switch tube is working normally, including controlling the flying capacitor three-level boost circuit to perform closed-loop boost until the output voltage reaches a third voltage.

[0025] Optionally, the inverter self-test method also includes: if it is determined based on whether the flying voltage can be stabilized at the set voltage that each switch tube is operating normally and the power-on conditions are met, and after the closed-loop boost process, the inverter open-loop self-test and relay self-test are controlled; after the inverter open-loop self-test and relay self-test pass, the inverter is controlled to connect to the grid and operate.

[0026] According to another aspect of the present invention, an inverter is provided, comprising at least one flying capacitor three-level boost circuit, the flying capacitor three-level boost circuit comprising a switch tube and a flying capacitor, the flying capacitor being electrically connected to the switch tube; the inverter performs self-test based on the inverter self-test method of any embodiment of the present invention.

[0027] The inverter and self-test method of the embodiment of the present invention adjust the flying voltage across the flying capacitor by adjusting the duty cycle of the switch tube from a set state before the inverter is connected to the grid, and determine whether at least one switch tube is working normally based on whether the flying voltage can be stabilized at the set voltage. It can be determined whether the charging switch tube and the discharging switch tube are working normally, and then the hardware fault of the inverter can be discovered in time before the inverter is connected to the grid, avoiding the expansion of the fault and improving the safety and reliability of the inverter.

[0028] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 is a structural schematic diagram of a flying capacitor three-level boost circuit;

[0031] Figure 2 is a flow chart of an inverter self-test method provided by an embodiment of the present invention;

[0032] Figure 3 is a flow chart of another inverter self-test method provided by an embodiment of the present invention;

[0033] Figure 4 is a graph of a first duty cycle and a second duty cycle;

[0034] Figure 5 It is a graph of the flying capacitor voltage;

[0035] Figure 6 is another graph of the first duty cycle and the second duty cycle;

[0036] Figure 7 is another graph of the flying capacitor voltage;

[0037] Figure 8 is a flow chart of another inverter self-test method provided by an embodiment of the present invention;

[0038] Fig. 9 is a flow chart of another inverter self-test method provided by an embodiment of the present invention;

[0039] Fig.10 This is a flow chart of another inverter self-test method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0042] An embodiment of the present invention provides an inverter self-test method, wherein the inverter includes at least one flying capacitor three-level boost circuit. Figure 1 This is a schematic diagram of the flying capacitor three-level boost circuit. Figure 1 The flying capacitor three-level boost circuit includes a switch tube and a flying capacitor Cfly, the flying capacitor Cfly is electrically connected to the switch tube, and the output end of the flying capacitor three-level boost circuit is electrically connected to the bus. In some optional embodiments, the inverter includes at least two flying capacitor three-level boost circuits. Figure 1 The case where the inverter includes two flying capacitor three-level boost circuits is exemplified. The photovoltaic output voltages input to the corresponding flying capacitor three-level boost circuits by the photovoltaic panels connected to the input ends of different flying capacitor three-level boost circuits may be the same or different. The output end of the flying capacitor three-level boost circuit may be connected in parallel to the bus. Specifically, the flying capacitor three-level boost circuit may include a charging switch tube VT12 and a discharging switch tube VT11. When the charging switch tube VT12 is turned on and the discharging switch tube VT11 is turned off, the flying capacitor Cfly can be charged. When the discharging switch tube VT11 is turned on and the charging switch tube VT12 is turned off, the flying capacitor Cfly can be discharged. Figure 2 is a flowchart of an inverter self-test method provided by an embodiment of the present invention, referring to Figure 2 , the inverter self-test method includes:

[0043] S110, before the inverter is connected to the grid, the duty cycle of the switch tube is adjusted from a set state, thereby adjusting the flying voltage across the flying capacitor.

[0044] Among them, in the set state, the flying voltage is a first voltage, the voltage on the bus is a second voltage, and the first voltage is equal to half of the second voltage.

[0045] Specifically, the driving of the charging switch tube VT12 and the discharging switch tube VT11 is a PWM pulse (Vge1 and Vge2 respectively) with a phase shift of 180° between the carriers. By adjusting the pulse length, the flying voltage of the flying capacitor Cfly is adjusted to be equal to half of the bus voltage. Figure 1 The flying capacitor three-level boost circuit also includes a first diode D12, a second diode D13, a third diode D11 and a fourth diode D14, wherein the anode of the first diode D12 is respectively connected to the collector of the discharge switch tube VT11 and the inductor L11, the cathode of the first diode D12 is connected to the anode of the second diode D13, and the cathode of the second diode D13 is connected to the first output terminal OUT1 of the flying capacitor three-level boost circuit; the emitter of the discharge switch tube VT11 is connected to the collector of the charging switch tube VT12, and the emitter of the charging switch tube VT12 is connected to the second output terminal OUT2 of the flying capacitor three-level boost circuit, and the voltage between the first output terminal OUT1 and the second output terminal OUT2 is the output voltage of the flying capacitor three-level boost circuit. A first output capacitor Cout+ and a second output capacitor Cout- are connected in series between the first output terminal OUT1 and the second output terminal OUT2. A fourth diode D14 is connected between the common connection terminal of the first output capacitor Cout+ and the second output capacitor Cout- and the common connection terminal of the discharge switch tube VT11 and the charging switch tube VT12. The cathode of the fourth diode D14 is electrically connected to the anode of the third diode D11. The cathode of the third diode D11 is connected to the common connection terminal of the first diode D12 and the second diode D13. One end of the flying capacitor Cfly is connected to the common connection terminal of the discharge switch tube VT11 and the charging switch tube VT12, and the other end of the flying capacitor Cfly is connected to the common connection terminal of the first diode D12 and the second diode D13. The input end of the flying capacitor three-level boost circuit can be connected to a photovoltaic panel, that is, the input voltage Vin of the flying capacitor three-level boost circuit is equal to the photovoltaic output voltage of the photovoltaic panel. The charging path of the flying capacitor Cfly is from the positive input terminal through the inductor L11 and the first diode D12, the flying capacitor Cfly and the charging switch tube VT12 to the negative input terminal. The discharging path of the flying capacitor Cfly is through the positive input terminal, the inductor L11, the discharging switch tube VT11, the flying capacitor Cfly, the second diode D13, the first output capacitor Cout+ and the second output capacitor Cout- back to the negative input terminal.

[0046] Due to the presence of the third diode D11 and the fourth diode D14, the flying capacitor three-level boost circuit can be in a set state when it is just powered on, that is, the voltage of the flying capacitor Cfly is equal to half of the output voltage of the flying capacitor three-level boost circuit. Figure 1As shown, the discharge switch tube VT11 and the charging switch tube VT12 use the same specification of wafer, and their allowable voltage stress requirements are consistent. During the operation of the flying capacitor three-level boost circuit, the fourth diode D14 is used to charge the flying capacitor Cfly when the discharge switch tube VT11 and the charging switch tube VT12 are not working (for example, when the flying capacitor three-level boost circuit is just powered on); the third diode D11 is used for regenerative energy charging, that is, when the bus voltage is higher than the output voltage of the flying capacitor three-level boost circuit, the flying capacitor Cfly is charged (this working condition of the inverter will hardly occur. If the flying voltage Vcly is greater than the voltage on the second output capacitor Cout-, the grid energy will be reversed, and this situation is not allowed in the inverter connected to the power generation equipment).

[0047] During operation, the discharge switch tube VT11, the first diode D12 and other internal tubes are subjected to a voltage stress platform V ds1 Should be:

[0048] V ds1 =V cfly ;

[0049] That is, the inner tube is subjected to the voltage stress platform V ds1 is the flying voltage V cfly .

[0050] During operation, the voltage stress platform borne by the charging switch tube VT12, the second diode D13 and other external tubes should be:

[0051] V ds2 =V bus -V cfly ;

[0052] That is, the outer tube is subjected to the voltage stress platform V ds2 is the bus voltage V bus Subtract the flying voltage V cfly .

[0053] In order to ensure that the discharge switch tube VT11 and the charging switch tube VT12 have sufficient voltage stress and sufficient margin when the circuit is working stably, this requires:

[0054] V ds1 =V ds2 ;

[0055] Thus, That is, the flying voltage V cfly is the bus voltage V bus half.

[0056] When the flying capacitor Cfly is subsequently controlled to charge and / or discharge, the setting state can be achieved by adjusting the duty cycle of the driving signal of the discharge switch tube VT11 and / or the duty cycle of the driving signal of the charging switch tube VT12, that is, the voltage of the flying capacitor Cfly is equal to half of the output voltage of the flying capacitor three-level boost circuit. In this step, the flying voltage across the flying capacitor Cfly is adjusted by adjusting the duty cycle of the switch tube from the setting state of the flying capacitor three-level boost circuit. When the switch tube in the flying capacitor three-level boost circuit works normally, the flying voltage will change. Because in the setting state, the first voltage across the flying capacitor Cfly is equal to half of the second voltage output by the flying capacitor three-level boost circuit, and accordingly, after the flying voltage changes, the flying voltage is no longer equal to half of the second voltage.

[0057] S120, obtaining a flying voltage.

[0058] Specifically, after adjusting the duty cycle corresponding to the charging switch tube and / or the discharging switch tube, under the condition that the charging switch tube and the discharging switch tube work normally, the flying voltage across the flying capacitor changes. In this step, the flying voltage across the flying capacitor can be obtained in real time or periodically.

[0059] S130, determining whether at least one switch tube works normally according to whether the flying voltage can be stabilized at the set voltage.

[0060] The set voltage is greater than half of the second voltage, or the set voltage is less than half of the second voltage. The set voltage is greater than 0 and less than the second voltage.

[0061] Specifically, through the analysis of failure cases on the production line and on-site, the flying capacitor three-level boost circuit usually has the following typical failure modes during application:

[0062] (1) The driving circuit of the discharge switch tube is damaged, and there is only a low level (short circuit of the optocoupler or the driving circuit) or the gate of the discharge switch tube is short-circuited (such as short circuit of the internal binding line), causing the discharge switch tube to be in an open circuit state.

[0063] (2) The driving circuit of the discharge switch tube is damaged, only a high level is present (the driving optocoupler is damaged) or the collector and emitter of the discharge switch tube are short-circuited (such as wafer short-circuit damage), causing the discharge switch tube to be in a short-circuit state.

[0064] (3) The driving circuit of the charging switch tube is damaged, and only a low level is generated or the gate of the charging switch tube is short-circuited (such as an internal binding line short-circuited), causing the charging switch tube to be in an open circuit state.

[0065] (4) The driving circuit of the charging switch tube and the discharging switch tube is damaged, only a high level is present or the collector and emitter of the charging switch tube are short-circuited (such as wafer short-circuit damage), causing the charging switch tube to be in a short-circuit state.

[0066] (5) The driving power supply is damaged, causing both the charging switch tube and the discharging switch tube to be in an open circuit state.

[0067] (6) The internal wafers of the charging switch tube and the discharging switch tube are damaged. Both the charging switch tube and the discharging switch tube are in a short-circuit state.

[0068] Combining the above failure modes, the main effect is whether the two key components in the flying capacitor three-level boost circuit, the charging switch tube and the discharging switch tube, can work normally. The charging switch tube and the discharging switch tube have two failure modes, namely open circuit or short circuit. Therefore, as long as it can be judged whether the charging switch tube and the discharging switch tube are working normally before the inverter is connected to the grid, it can be basically judged whether the circuit has hardware abnormalities. In the flying capacitor three-level boost circuit, the discharging switch tube discharges the flying capacitor when it is turned on, and the charging switch tube charges the flying capacitor when it is turned on. By using the charging and discharging characteristics of the discharging switch tube and the charging switch tube on the flying capacitor, it can be judged whether the discharging switch tube and the charging switch tube are abnormal, and then the hardware defects of the inverter boost circuit itself can be found before the grid is connected to avoid the expansion of the fault.

[0069] In this step, whether the charging switch tube and / or the discharging switch tube works normally can be determined based on whether the flying voltage can be stabilized at the set voltage. Optionally, when the set voltage is greater than half of the second voltage, if the flying voltage can be stabilized at the set voltage, it means that the flying voltage gradually increases from the first voltage to the set voltage, and the charging switch tube can be normally turned on and charged; in addition, since the flying voltage does not increase all the time and can be stabilized at the set voltage, it means that the charging switch tube can be normally turned off, that is, it means that the charging switch tube can work normally. If the flying voltage cannot be stabilized at the set voltage, it means that there is an abnormality in the charging switch tube. Optionally, when the set voltage is less than half of the second voltage, if the flying voltage can be stabilized at the set voltage, it means that the flying voltage gradually decreases from the first voltage to the set voltage, and the discharging switch tube can be normally turned on and discharged; in addition, since the flying voltage does not decrease all the time and can be stabilized at the set voltage, it means that the discharging switch tube can be normally turned off, that is, it means that the discharging switch tube can work normally. If the flying voltage cannot be stabilized at the set voltage, it means that there is an abnormality in the discharging switch tube. The inverter self-checking method of this embodiment can perform self-checking on each flying capacitor three-level boost circuit in the inverter, and timely determine whether the switch tube in each flying capacitor three-level boost circuit is abnormal.

[0070] The inverter self-test method of this embodiment adjusts the flying voltage across the flying capacitor by adjusting the duty cycle of the switch tube from a set state before the inverter is connected to the grid, and determines whether at least one switch tube is operating normally based on whether the flying voltage can be stabilized at the set voltage. It can determine whether the charging switch tube and the discharging switch tube are operating normally, and then timely discover the hardware fault of the inverter before the inverter is connected to the grid, avoid the expansion of the fault, and improve the safety and reliability of the inverter.

[0071] As described above, the switch tube includes a charging switch tube and a discharging switch tube, the charging switch tube and the discharging switch tube are connected in series, and the flying capacitor is connected to the common connection end of the charging switch tube and the discharging switch tube.

[0072] Figure 3 is a flowchart of another inverter self-test method provided by an embodiment of the present invention, referring to Figure 3 Optionally, the inverter self-test method includes:

[0073] S210. Before the inverter is connected to the grid, in a first time period, control a first duty cycle corresponding to the charging switch tube to be greater than a second duty cycle corresponding to the discharging switch tube.

[0074] In the first time period, the first duty cycle corresponding to the charging switch tube is controlled to be greater than the second duty cycle corresponding to the discharging switch tube, so that the flying capacitor is charged and the voltage of the flying capacitor increases. In this embodiment, the first duty cycle corresponding to the charging switch tube and the second duty cycle corresponding to the discharging switch tube are controlled to control the flying voltage of the flying capacitor, and an open-loop control method or a closed-loop control method can be used. Figure 4 is a graph of the first duty cycle and the second duty cycle, Figure 5 It is a graph of the flying capacitor voltage, refer to Figure 4 and Figure 5 Optionally, S210 includes: in the first time period t1, controlling the first duty cycle D12 corresponding to the charging switch tube to increase from 0 with a first slope, and controlling the second duty cycle D11 of the discharging switch tube to increase from 0 with a second slope, wherein the first slope is greater than the second slope. In this way, at any time in the first time period t1, the first duty cycle D12 corresponding to the charging switch tube is greater than the second duty cycle D11 corresponding to the discharging switch tube, so that the flying capacitor is charged when the charging switch tube is normal.

[0075] S220. In a second time period, control the first duty cycle to be equal to the second duty cycle, and the second time period is after the first time period.

[0076] Combination Figure 4 and Figure 5, wherein, when the flying voltage Vfly of the flying capacitor is controlled by an open-loop control method, the first duty cycle D12 and the second duty cycle D11 can be equal to each other. When a closed-loop control method is adopted, the first duty cycle D12 and the second duty cycle D11 can be controlled so that the first duty cycle D12 is equal to the second duty cycle D11 in the second period t2.

[0077] S230, determining whether the charging switch tube is operating normally according to whether the flying voltage is stable at the first set voltage during the second period.

[0078] The first set voltage is greater than half of the second voltage (i.e. Figure 5 Vbus / 2).

[0079] As described above, if the charging switch tube works normally, the flying voltage of the flying capacitor can be stable in the second time period, and because the flying capacitor is charged in the first time period, the flying voltage of the flying capacitor will be higher than the first voltage in the set state, that is, greater than half of the second voltage on the bus. Therefore, in this step, by determining whether the flying voltage can be stabilized at a first set voltage greater than half of the second voltage in the second time period, it can be determined whether the charging switch tube works normally. In some optional embodiments, the first set voltage can be set equal to the sum of half of the second voltage and the reference voltage, wherein the voltage value of the reference voltage can be set smaller, for example, the reference voltage value is less than or equal to 2% of the second voltage. Specifically, if the flying voltage can be stabilized at the first set voltage in the second time period, it can be determined that the charging switch tube can work normally; if the flying voltage cannot be stabilized at the first set voltage in the second time period, it means that the charging switch tube may be short-circuited or open-circuited, indicating that the charging switch tube cannot work normally.

[0080] S240. In a third time period, control the first duty cycle corresponding to the charging switch tube to be smaller than the second duty cycle corresponding to the discharging switch tube.

[0081] In the third time period, the first duty cycle corresponding to the charging switch tube is controlled to be smaller than the second duty cycle corresponding to the discharging switch tube, so that the flying capacitor is discharged and the voltage of the flying capacitor is reduced. In this embodiment, the first duty cycle corresponding to the charging switch tube and the second duty cycle corresponding to the discharging switch tube are controlled to control the flying voltage of the flying capacitor, and an open-loop control method or a closed-loop control method can be used. Figure 6 is another graph of the first duty cycle and the second duty cycle, Figure 7 is another graph of the flying capacitor voltage, see Figure 6 and Figure 7Optionally, S240 includes controlling the first duty cycle D12 corresponding to the charging switch tube to increase from 0 with a third slope, and controlling the second duty cycle D11 of the discharging switch tube to increase from 0 with a fourth slope in the third time period t3, wherein the third slope is smaller than the fourth slope. In this way, at any time in the third time period t3, the first duty cycle D12 corresponding to the charging switch tube is smaller than the second duty cycle D11 corresponding to the discharging switch tube, so that the flying capacitor is discharged when the discharging switch tube is normal.

[0082] S250. In a fourth time period, control the first duty cycle to be equal to the second duty cycle, and the fourth time period is after the third time period.

[0083] Combination Figure 6 and Figure 7 , wherein, when the flying voltage Vfly of the flying capacitor is controlled by an open-loop control method, the first duty cycle D12 and the second duty cycle D11 can be equal to each other. When a closed-loop control method is adopted, the first duty cycle D12 and the second duty cycle D11 can be controlled so that the first duty cycle D12 is equal to the second duty cycle D11 in the fourth time period t4.

[0084] S260, determining whether the discharge switch tube operates normally according to whether the flying voltage is stable at the second set voltage during the fourth time period.

[0085] The second set voltage is less than half of the second voltage (ie Figure 7 Vbus / 2).

[0086] As described above, if the discharge switch tube works normally, the flying voltage of the flying capacitor can be stable in the fourth time period, and because the flying capacitor is discharged in the third time period, the flying voltage of the flying capacitor will be lower than the first voltage in the set state, that is, less than half of the second voltage on the bus. Therefore, in this step, by determining whether the flying voltage can be stabilized at a second set voltage less than half of the second voltage in the second time period, it can be determined whether the discharge switch tube works normally. In some optional embodiments, the second set voltage can be set equal to the difference between half of the second voltage and the reference voltage. Specifically, if the flying voltage can be stabilized at the second set voltage in the fourth time period, it can be determined that the discharge switch tube can work normally; if the flying voltage cannot be stabilized at the second set voltage in the fourth time period, it means that the discharge switch tube may be short-circuited or open-circuited, indicating that the discharge switch tube cannot work normally.

[0087] like Figure 3As shown, in some optional embodiments of the present invention, the self-test of the charging switch tube (including S210-S230) can be performed before the self-test of the discharging switch tube (including S240-S260), and the corresponding second period is before the third period, and the flying capacitor three-level boost circuit is in a set state at the beginning of the first period. In this case, the self-test of the charging switch tube starts from the set state, and then the self-test of the discharging switch tube is performed.

[0088] In another optional embodiment of the present invention, the self-test of the charging switch tube (including S210-S230) can be performed after the self-test of the discharging switch tube (including S240-S260), and the corresponding fourth period is before the first period, and the flying capacitor three-level boost circuit is in a set state at the beginning of the third period. In this case, the discharging switch tube is self-tested from the set state, and then the charging switch tube is self-tested.

[0089] Combination Figure 4 and Figure 6 Optionally, during the first time period, the second time period, the third time period and the fourth time period, the first duty cycle and the second duty cycle are both less than a preset duty cycle threshold Dmin, so that the voltage fluctuation on the bus is within a preset range.

[0090] Among them, the preset duty cycle threshold can be set according to the allowed variation of the voltage on the bus. Optionally, the preset duty cycle threshold is less than or equal to 5%. Since the size of the first duty cycle and the second duty cycle will affect the output voltage of the flying capacitor three-level boost circuit, thereby affecting the bus voltage on the bus. In this embodiment, the first duty cycle and the second duty cycle are set to be less than the preset duty cycle threshold in the first time period, the second time period, the third time period and the fourth time period, so that the fluctuation of the bus voltage can be reduced.

[0091] In some optional embodiments of the present invention, the absolute value of the difference between the first duty cycle and the second duty cycle is less than or equal to half of the preset duty cycle threshold value. In this way, the influence of the adjustment of the first duty cycle and the second duty cycle on the bus voltage is further reduced, and the fluctuation of the bus voltage is further reduced.

[0092] Figure 8 is a flow chart of another inverter self-test method provided by an embodiment of the present invention. Fig. 9 is a flow chart of another inverter self-test method provided by an embodiment of the present invention. Fig.10 is a flowchart of another inverter self-test method provided by an embodiment of the present invention, referring to Figure 8-Figure 10Optionally, the inverter self-test method further includes: performing a startup condition judgment of the inverter or a closed-loop boost process of a flying capacitor three-level boost circuit. In some optional embodiments of the present invention, the inverter self-test method may include performing a startup condition judgment of the inverter and a closed-loop boost process of a flying capacitor three-level boost circuit.

[0093] refer to Figure 8-Figure 10 Optionally, the power-on condition judgment is performed before adjusting the duty cycle corresponding to the switch tube from the set state to adjust the flying voltage across the flying capacitor, or after determining that the switch tube (including the charging switch tube and the discharging switch tube) is working normally. The closed-loop boost process is performed before adjusting the duty cycle corresponding to the switch tube from the set state to adjust the flying voltage across the flying capacitor, or after determining that the switch tube (including the charging switch tube and the discharging switch tube) is working normally; the closed-loop boost process is performed after the power-on condition judgment.

[0094] The power-on condition judgment of the inverter includes: determining whether the power-on condition of the inverter is met according to the photovoltaic output voltage and output power of the photovoltaic panel connected to the input end of the flying capacitor three-level boost circuit. Optionally, when the photovoltaic output voltage of the photovoltaic panel reaches a set voltage threshold and the output power reaches a set output power threshold, it is determined that the power-on condition of the inverter is met.

[0095] The closed-loop boost process includes: controlling the flying capacitor three-level boost circuit to perform closed-loop boosting until the output voltage reaches a third voltage. The third voltage can be set according to the requirements of the inverter circuit to which the bus of the flying capacitor three-level boost circuit is connected, so as to ensure that the bus voltage can meet the requirements of the inverter circuit for the input voltage and ensure the power quality after grid connection. The closed-loop boost process can be achieved by controlling the duty cycle of the charging switch tube and the discharging switch tube.

[0096] Optionally, if it is determined that each switch tube is operating normally and the power-on conditions are met based on whether the flying voltage can be stabilized at the set voltage, and after the closed-loop boost process, the inverter open-loop self-test and relay self-test are controlled. After the inverter open-loop self-test and relay self-test pass, the inverter is controlled to connect to the grid and operate.

[0097] Specifically, the inverter includes an inverter circuit and a relay in addition to the flying capacitor three-level boost circuit. In this embodiment, after determining that each flying capacitor three-level boost circuit has no faults, before controlling the inverter to be connected to the grid, the inverter open-loop self-test and relay self-test are also performed to timely detect faults in other structures in the inverter, further avoid fault expansion, and ensure the safety and reliability of the inverter.

[0098] in, Figure 8It shows the situation that the power-on judgment condition and the closed-loop boost process are performed before the charging switch tube self-test (including S210-S230 in the above embodiment) and the discharging switch tube self-test (including S240-S260 in the above embodiment). Fig. 9 It is shown that the power-on judgment condition is performed before the charging switch tube self-test (including S210-S230 in the above embodiment) and the discharging switch tube self-test (including S240-S260 in the above embodiment), and the closed-loop boost process is performed after the charging switch tube self-test (including S210-S230 in the above embodiment) and the discharging switch tube self-test (including S240-S260 in the above embodiment). Fig.10 It shows the situation that the power-on judgment condition and the closed-loop boost process are both performed after the charging switch tube self-test (including S210-S230 in the above embodiment) and the discharging switch tube self-test (including S240-S260 in the above embodiment).

[0099] refer to Figure 8 , the inverter self-test method includes:

[0100] Initially, the inverter is in standby state.

[0101] S310, judging whether the power-on condition is met, that is, judging the power-on condition.

[0102] If yes, execute S320; if no, return to the standby state.

[0103] S320, performing a closed-loop boosting process of the flying capacitor three-level boosting circuit.

[0104] S330, determine whether the charging switch tube self-test passes.

[0105] If yes, execute S340; if no, execute S350.

[0106] S340, determine whether the discharge switch tube self-test has passed.

[0107] If yes, execute S360; if no, execute S350.

[0108] S350, control the Luffy transcapacitor three-level boost circuit and the corresponding maximum power point tracking controller to be in a standby state, and warn of a fault.

[0109] S360, controlling the inverter to perform open-loop self-test and relay self-test, and determining whether the inverter open-loop self-test and relay self-test are successful.

[0110] If yes, execute S370; if no, execute S380.

[0111] S370, control the inverter to connect to the grid.

[0112] S380: Determine that the inverter is in a fault state and issue a warning.

[0113] refer to Fig. 9 , the inverter self-test method includes:

[0114] Initially, the inverter is in standby state.

[0115] S410, judging whether the power-on condition is met, that is, judging the power-on condition.

[0116] If yes, execute S420; if no, return to the standby state.

[0117] S420, determine whether the charging switch tube self-test passes.

[0118] If yes, execute S430; if no, execute S440.

[0119] S430, determine whether the discharge switch tube self-test has passed.

[0120] If yes, execute S450; if no, execute S440.

[0121] S440, control the Luffy transcapacitor three-level boost circuit and the corresponding maximum power point tracking controller to be in a standby state, and warn of a fault.

[0122] S450, performing a closed-loop boosting process of the flying capacitor three-level boosting circuit.

[0123] S460, controlling the inverter to perform open-loop self-test and relay self-test, and determining whether the inverter open-loop self-test and relay self-test are successful.

[0124] If yes, execute S470; if no, execute S480.

[0125] S470, control the inverter to connect to the grid.

[0126] S480: Determine that the inverter is in a fault state and issue a warning.

[0127] refer to Fig.10 , the inverter self-test method includes:

[0128] Initially, the inverter is in standby state.

[0129] S510: Determine whether the charging switch tube self-test has passed.

[0130] If yes, execute 520; if no, execute S530.

[0131] S520, determine whether the discharge switch tube self-test has passed.

[0132] If yes, execute S540; if no, execute S530.

[0133] S530, control the Luffy transcapacitor three-level boost circuit and the corresponding maximum power point tracking controller to be in a standby state, and warn of a fault.

[0134] S540: Determine whether the power-on condition is met, that is, perform power-on condition determination.

[0135] If yes, execute S550; if no, return to the standby state.

[0136] S550 , performing a closed-loop boosting process of the flying capacitor three-level boosting circuit.

[0137] S560: Control the inverter open-loop self-test and the relay self-test, and determine whether the inverter open-loop self-test and the relay self-test are successful.

[0138] If yes, execute S570; if no, execute S580.

[0139] S570, control the inverter to connect to the grid.

[0140] S580: Determine that the inverter is in a fault state and issue a warning.

[0141] An embodiment of the present invention further provides an inverter, which includes at least one flying capacitor three-level boost circuit, the flying capacitor three-level boost circuit includes a switching tube and a flying capacitor, and the flying capacitor is electrically connected to the switching tube; the inverter performs self-test based on the inverter self-test method of any of the above embodiments of the present invention, and has the beneficial effects of the inverter self-test method of any of the above embodiments of the present invention, which will not be repeated here.

[0142] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0143] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A self-test method for an inverter, It is characterized in that The inverter comprises at least one flying capacitor three-level boost circuit, the flying capacitor three-level boost circuit comprises a switch tube and a flying capacitor, the flying capacitor is electrically connected to the switch tube, and the output end of the flying capacitor three-level boost circuit is electrically connected to the bus; The inverter self-test method comprises: Before the inverter is connected to the grid, the duty cycle corresponding to the switch tube is adjusted from a set state, thereby adjusting the flying voltage across the flying capacitor; wherein, in the set state, the flying voltage is a first voltage, the voltage on the bus is a second voltage, and the first voltage is equal to half of the second voltage; Determining whether at least one of the switch tubes is operating normally according to whether the flying voltage can be stabilized at a set voltage; The set voltage is greater than half of the second voltage, or the set voltage is less than half of the second voltage.

2. The inverter self-test method according to claim 1, It is characterized in that The switch tube comprises a charging switch tube and a discharging switch tube, the charging switch tube and the discharging switch tube are connected in series, and the flying capacitor is connected to the common connection end of the charging switch tube and the discharging switch tube; Before the inverter is connected to the grid, the duty cycle corresponding to the switch tube is adjusted from the set state, so as to adjust the flying voltage across the flying capacitor, including: before the inverter is connected to the grid, in a first time period, controlling the first duty cycle corresponding to the charging switch tube to be greater than the second duty cycle corresponding to the discharging switch tube; in a second time period, controlling the first duty cycle to be equal to the second duty cycle, and the second time period is after the first time period; Determining whether the switch tube is working normally according to whether the flying voltage can be stabilized at a set voltage includes: determining whether the charging switch tube is working normally according to whether the flying voltage is stabilized at a first set voltage during the second time period; the first set voltage is greater than half of the second voltage.

3. The inverter self-test method according to claim 2, It is characterized in that The controlling of the first duty cycle corresponding to the charging switch tube to be greater than the second duty cycle corresponding to the discharging switch tube during the first time period includes: controlling the first duty cycle corresponding to the charging switch tube to increase from 0 with a first slope during the first time period, and controlling the second duty cycle of the discharging switch tube to increase from 0 with a second slope, wherein the first slope is greater than the second slope.

4. The inverter self-test method according to claim 2, It is characterized in that Before the inverter is connected to the grid, the duty cycle corresponding to the switch tube is adjusted from the set state to adjust the flying voltage across the flying capacitor, and further includes: in a third time period, controlling the first duty cycle corresponding to the charging switch tube to be smaller than the second duty cycle corresponding to the discharging switch tube; in a fourth time period, controlling the first duty cycle to be equal to the second duty cycle, and the fourth time period is after the third time period; The step of determining whether the switch tube is operating normally according to whether the flying voltage can be stabilized at a set voltage further includes: determining whether the discharge switch tube is operating normally according to whether the flying voltage is stabilized at a second set voltage in the fourth time period; the second set voltage is less than half of the second voltage; The fourth time period is before the first time period, and the flying capacitor three-level boost circuit is in the set state at the start time of the third time period; Or the second time period is before the third time period, and at the start time of the first time period, the flying capacitor three-level boost circuit is in the set state.

5. The inverter self-test method according to claim 4, It is characterized in that The controlling, during the third time period, of the first duty cycle corresponding to the charging switch tube to be smaller than the second duty cycle corresponding to the discharging switch tube comprises: during the third time period, controlling the first duty cycle corresponding to the charging switch tube to increase from 0 with a third slope, and controlling the second duty cycle of the discharging switch tube to increase from 0 with a fourth slope, wherein the third slope is smaller than the fourth slope.

6. The inverter self-test method according to claim 4, It is characterized in that In the first time period, the second time period, the third time period and the fourth time period, the first duty cycle and the second duty cycle are both less than a preset duty cycle threshold.

7. The inverter self-test method according to claim 6, It is characterized in that An absolute value of a difference between the first duty cycle and the second duty cycle is less than or equal to half of the preset duty cycle threshold.

8. The inverter self-test method according to claim 1, It is characterized in that Also includes: Performing startup condition judgment of the inverter or a closed-loop boost process of the flying capacitor three-level boost circuit; The power-on condition judgment is performed before adjusting the duty cycle corresponding to the switch tube from the set state, thereby adjusting the flying voltage across the flying capacitor, or after determining that the switch tube is operating normally; The determining of the startup condition of the inverter includes: determining whether the startup condition of the inverter is met according to the photovoltaic output voltage and output power of the photovoltaic panel connected to the input end of the flying capacitor three-level boost circuit; The closed-loop boost process is performed before adjusting the duty cycle corresponding to the switch tube from a set state to adjust the flying voltage across the flying capacitor, or after determining that the switch tube is operating normally; the closed-loop boost process includes controlling the flying capacitor three-level boost circuit to perform closed-loop boost until the output voltage reaches a third voltage.

9. The inverter self-test method according to claim 8, It is characterized in that Also includes: If it is determined that each of the switching tubes is operating normally and the power-on conditions are met based on whether the flying voltage can be stabilized at the set voltage, and after the closed-loop boost process, the inverter open-loop self-test and relay self-test are controlled to be performed. After the inverter open-loop self-test and relay self-test pass, the inverter is controlled to be connected to the grid for operation.

10. An inverter, It is characterized in that The invention comprises at least one flying capacitor three-level boost circuit, wherein the flying capacitor three-level boost circuit comprises a switch tube and a flying capacitor, and the flying capacitor is electrically connected to the switch tube; and the inverter performs self-test based on the inverter self-test method according to any one of claims 1 to 9.

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