A Symmetrical Three-Level BOOST Converter and Its Short-Circuit Fault Diagnosis Method

Abstract

The present invention provides a symmetrical three-level BOOST converter and a short-circuit fault diagnosis method therefor, comprehensively considering two situations: when the symmetrical three-level BOOST converter has a relatively large voltage on the input side during the day, i.e., in the working state, or when the input side voltage is basically zero at night, i.e., in the standby state. Different diagnosis methods are adopted for different situations, and it can accurately diagnose the BOOST circuit corresponding to the ground short circuit before the bus capacitor overvoltage caused by the ground short circuit on the input side of the symmetrical three-level BOOST converter, so as to avoid the bus capacitor overvoltage and prevent greater hazards from occurring.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to a symmetrical three-level BOOST converter and a short-circuit fault diagnosis method therefor. Background Art

[0002] In recent years, in order to meet the increasing requirements for voltage levels and power levels of power electronics, multilevel converters have received increasing attention. At the same time, in order to simplify the circuit structure, those skilled in the art replace single-input converters with multi-input converters, which can realize the preferential utilization of energy and improve its flexibility.

[0003] However, for a symmetrical three-level BOOST topology with two or more inputs, it is easy to occur that the positive pole of one input is short-circuited with the negative pole of another input at the same time, thereby causing overvoltage of the half-bus and full-bus of the symmetrical three-level BOOST topology; therefore, it is necessary to timely diagnose which BOOST circuit is short-circuited to the ground and take avoidance measures to avoid causing too high bus voltage resulting in the bursting of electrolytic capacitors and triggering greater risks. Summary of the Invention

[0004] In view of this, embodiments of the present invention provide a symmetrical three-level BOOST converter and a short-circuit fault diagnosis method therefor, which can accurately diagnose the BOOST circuit corresponding to the short circuit to the ground before the bus capacitor is overvoltage caused by the short circuit to the ground on the input side of the converter, so as to avoid overvoltage of the bus capacitor and avoid causing greater harm.

[0005] To achieve the above object, embodiments of the present invention provide the following technical solutions:

[0006] The first aspect of the present invention provides a short-circuit fault diagnosis method for a symmetrical three-level BOOST converter. The symmetrical three-level BOOST converter includes at least two BOOST circuits whose outputs are connected in parallel to a DC bus. The short-circuit fault diagnosis method includes:

[0007] Determine the current state of the symmetrical three-level BOOST converter;

[0008] If the current state is the working state, directly determine at least two of the BOOST circuits in the input series short-circuit state according to the bus voltage of the DC bus monitored in real time and the detection parameters of each BOOST circuit;

[0009] If the current state is the standby state, after a starting voltage is established at the input end of the BOOST circuit, when the switch tube branches in other BOOST circuits are directly connected, each BOOST circuit is controlled to be open one by one, and according to the bus voltage monitored in real time and the detection parameters of the corresponding BOOST circuit, it is determined whether the corresponding BOOST circuit is in the input series short - circuit state.

[0010] Preferably, the input series short - circuit state is: a state in which one pole of its own input end is directly or indirectly connected in series with the other pole of the input end of another BOOST.

[0011] Preferably, directly determining at least two BOOST circuits in the input series short - circuit state according to the bus voltage of the DC bus monitored in real time and the detection parameters of each BOOST circuit includes:

[0012] Judging according to the detection parameters whether there are at least two BOOST circuits whose input voltages meet the mutation condition;

[0013] If so, further judging according to the detection parameters whether an impact current appears in the corresponding BOOST circuit;

[0014] If the judgment result is yes, then judge whether the bus voltage is abnormal;

[0015] If it is determined that the bus voltage is abnormal, then it is determined that the corresponding BOOST circuit is in the input series short - circuit state.

[0016] Preferably, judging according to the detection parameters whether there are at least two BOOST circuits whose input voltages meet the mutation condition includes:

[0017] Judging according to the input voltages of each BOOST circuit detected in real time whether there are at least two input voltages that step - jump to within a first preset range of half of the bus voltage;

[0018] If the judgment result is yes, then it is determined that the input voltage of the corresponding BOOST circuit meets the mutation condition.

[0019] Preferably, judging whether the bus voltage is abnormal includes:

[0020] Judging whether the bus voltage increases according to a preset rule, or whether the bus capacitor is over - voltage and fails;

[0021] If the judgment result is yes, then it is determined that the bus voltage is abnormal.

[0022] Preferably, judging whether the bus voltage increases according to a preset rule includes:

[0023] Determine whether the variation law of the bus voltage coincides with the variation law of the input voltage of the corresponding BOOST circuit;

[0024] If the judgment result is yes, it is determined that the bus voltage increases according to a preset law.

[0025] Preferably, when the switch tube branches in other BOOST circuits are directly connected, control each BOOST circuit to be open one by one, and determine whether the corresponding BOOST circuit is in the input series short - circuit state according to the real - time monitored bus voltage and the detection parameters of the corresponding BOOST circuit, including:

[0026] Compare the input voltage of each BOOST circuit with the bus voltage, and determine whether at least two BOOST circuits are in the input series short - circuit state;

[0027] If the judgment result is yes, when the switch tube branches in other BOOST circuits are directly connected, control each BOOST circuit to be open one by one, and sequentially judge whether the magnitude relationship between the input voltage of each BOOST circuit and the upper and lower half - bus voltages of the DC bus meets the preset conditions, so as to determine the BOOST circuits in the input series short - circuit state.

[0028] Preferably, comparing the input voltage of each BOOST circuit with the bus voltage to determine whether at least two BOOST circuits are in the input series short - circuit state includes:

[0029] Compare the magnitudes of the input voltages of each BOOST circuit, and determine the maximum value among the input voltages;

[0030] Judge whether the difference between the bus voltage minus the maximum value is greater than a preset voltage;

[0031] If the judgment result is yes, it is determined that at least two BOOST circuits are in the input series short - circuit state.

[0032] Preferably, the preset voltage is less than the minimum value among the input voltages of all the BOOST circuits.

[0033] Preferably, when the switch tube branches in other BOOST circuits are directly connected, control each BOOST circuit to be open one by one, and sequentially judge whether the magnitude relationship between the input voltage of each BOOST circuit and the upper and lower half - bus voltages of the DC bus meets the preset conditions, so as to determine the BOOST circuits in the input series short - circuit state, including:

[0034] By controlling the on / off states of the switching transistors in each BOOST circuit, only one of the BOOST circuits is controlled to be in an open state in sequence, and the switching transistor branches in the other BOOST circuits are in a direct connection state;

[0035] Detect the upper and lower half-bus voltages and the open-circuit voltage of the BOOST circuit in the open state;

[0036] If the upper half-bus voltage or the lower half-bus voltage gradually rises to within the second preset range of the open-circuit voltage, it is determined that the corresponding BOOST circuit in the open state is in an input series short-circuit state.

[0037] Preferably, by controlling the on / off states of the switching transistors in each BOOST circuit, only one of the BOOST circuits is controlled to be in an open state in sequence, and the switching transistor branches in the other BOOST circuits are in a direct connection state, including:

[0038] By controlling the on / off states of the switching transistors in each BOOST circuit, according to a preset order, only one of the BOOST circuits is controlled to be in an open state in sequence, and the switching transistor branches in the other BOOST circuits are in a direct connection state.

[0039] Preferably, the preset order is the order from high to low input voltage.

[0040] The second aspect of the present invention provides a symmetric three-level BOOST converter, including: a control unit, a detection unit, and at least two BOOST circuits; wherein:

[0041] The input ends of each BOOST circuit are respectively connected to a corresponding input source, and the voltage of each input source is greater than a preset value;

[0042] The output ends of each BOOST circuit are connected in parallel to the DC bus;

[0043] The control unit is respectively connected to the output end of the detection unit and the control ends of the switching transistors in each BOOST circuit, and is used to execute the short-circuit fault diagnosis method of the symmetric three-level BOOST converter as described in any one of the above.

[0044] Preferably, the control unit is a software control device or a hardware control circuit.

[0045] Preferably, the detection unit includes: a voltage detection unit and a current detection unit; wherein:

[0046] The voltage detection unit is used to detect the bus voltage of the DC bus and the input voltage of each BOOST circuit;

[0047] The current detection unit is used to detect the input current of each of the BOOST circuits.

[0048] Based on the short-circuit fault diagnosis method of the symmetric three-level BOOST converter provided in the embodiments of the present invention, the two cases where the symmetric three-level BOOST converter operates with a relatively large voltage on the input side during the day or with a basically zero voltage on the input side at night are comprehensively considered. Therefore, this diagnosis method first determines the current state of the three-level BOOST converter; if it is in the working state, that is, when there is a relatively large voltage on the input side, at least two BOOST circuits in the input series short-circuit state can be directly determined according to the real-time monitored bus voltage of the DC bus and the detection parameters of each BOOST circuit; if it is in the standby state, that is, when the input side voltage is basically zero, after a relatively small voltage is established on the input side, only one BOOST circuit is controlled to be open at a time, and the switch tube branches in other BOOST circuits are directly connected. Then, according to the real-time monitored bus voltage and the detection parameters of each BOOST circuit, it can be determined whether there is a BOOST circuit in the input series short-circuit state, and the BOOST circuit in the input series short-circuit state can be further locked. Therefore, the short-circuit fault diagnosis method of the symmetric three-level BOOST converter provided in the embodiments of the present invention can accurately diagnose the BOOST circuit corresponding to the ground short-circuit before the bus capacitor overvoltage caused by the ground short-circuit on the input side of the converter, so as to avoid the bus capacitor overvoltage and prevent greater hazards, which has great significance. Description of the Drawings

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0050] Figure 1 It is a flowchart of a short-circuit fault diagnosis method for a symmetric three-level BOOST converter provided by an embodiment of the present invention;

[0051] Figure 2 It is a schematic structural diagram of a symmetric three-level BOOST converter provided by an embodiment of the present invention with two BOOST circuits;

[0052] Figure 3 It is a current loop diagram when at least two BOOST circuits in the input series short-circuit state exist on the input side of a symmetric three-level BOOST converter provided by an embodiment of the present invention;

[0053] Figure 4Flow chart when the symmetric three-level BOOST converter in a short-circuit fault diagnosis method provided by an embodiment of the present invention is in a working state;

[0054] Figure 5 Flow chart when the symmetric three-level BOOST converter in a short-circuit fault diagnosis method provided by an embodiment of the present invention is in a standby state;

[0055] Figure 6a Charging current loop diagram when only one BOOST circuit is controlled to be open when the symmetric three-level BOOST converter provided by an embodiment of the present invention is in a to-be-operated state;

[0056] Figure 6b Another charging current loop diagram when only one BOOST circuit is controlled to be open when the symmetric three-level BOOST converter provided by an embodiment of the present invention is in a to-be-operated state;

[0057] Figure 7 Structure schematic diagram of a symmetric three-level BOOST converter provided by another embodiment of the present invention. Detailed implementation manners

[0058] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0059] In this application, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0060] In the prior art, the structure of a symmetric three-level BOOST converter with multiple inputs sharing a common rear-stage bus is widely used in the front-stage boost circuit of an inverter. However, when a short circuit occurs between the positive pole of one branch and the negative pole of another branch in different branches of the symmetric three-level BOOST, the input voltages of the BOOST circuits corresponding to the ground short circuit jointly charge the rear-stage bus capacitor. If it is not diagnosed which BOOST is shorted to the ground and corresponding avoidance measures are not taken, it is very easy to cause the bus voltage to be too high, resulting in the bursting of electrolytic capacitors and triggering greater risks. For this, the prior art has not proposed an effective solution to accurately diagnose the branch shorted to the ground.

[0061] Therefore, an embodiment of the present invention provides a short-circuit fault diagnosis method for a symmetric three-level BOOST converter, which can accurately diagnose the BOOST circuit corresponding to the ground short circuit before the bus capacitor overvoltage caused by a ground short circuit on the input side of the converter, so as to avoid the overvoltage of the bus capacitor and prevent greater hazards.

[0062] Among them, the symmetric three-level BOOST converter includes at least two BOOST circuits with outputs connected in parallel to the DC bus.

[0063] The flowchart of the short-circuit fault diagnosis method is as Figure 1 shown, and includes:

[0064] S101. Determine the current state of the symmetric three-level BOOST converter.

[0065] When the symmetric three-level BOOST converter is applied to different scenarios, the factors causing a ground short circuit on its input side are different, and the short-circuit characteristics shown are also different. Therefore, at the beginning of the diagnosis method, it is first necessary to determine the current state of the symmetric three-level BOOST converter. For example, when the symmetric three-level BOOST converter is working during the day or when the light intensity is relatively large, there is a relatively large voltage on the input side. At this time, it can be considered that its current state is the working state, and step S102 is executed; or, when the symmetric three-level BOOST converter is working at night or when the light intensity is relatively weak, the input voltage is very small or even basically zero. At this time, it indicates that its current state is the standby state, and step S103 is executed.

[0066] S102. Directly determine at least two BOOST circuits in the input series short-circuit state according to the real-time monitored bus voltage of the DC bus and the detection parameters of each BOOST circuit.

[0067] Among them, the detection parameters include: the input voltage and input current of each BOOST circuit, or the upper and lower half-bus voltages of the DC bus, etc.

[0068] Furthermore, it is worth noting that the short-circuit fault diagnosis method of the embodiment of the present invention is mainly aimed at the fault of multiple input short circuit to ground. Therefore, the above-mentioned at least two BOOST circuits are in the input series short circuit state, which means that at least one BOOST circuit is directly connected in series with the other input terminal of another BOOST through one pole of its own input terminal, or is indirectly connected in series through grounding or other means. For example, if there are two BOOST circuits (such as Figure 2 PVj+, PVj- and PVk+, PVk- are shown in the figure. The schematic diagram of its structure is shown in Figure 2 As shown, the two BOOST circuits are in an input series short-circuit state, that is, the positive electrode (PVj+ or PVk+) of the input end of one BOOST circuit is connected in series with the negative electrode (PVk- or PVj-) of the input end of the other BOOST circuit, or, at the same time (that is, PVj+ and PVk-, or PVk+ and PVj-) are grounded, forming an indirect series state.

[0069] When the symmetrical three-level BOOST converter is in operation, that is, when the input voltage is large, if any of the above-mentioned input series short circuits occurs, assuming that PVk+ and PVj- are connected in series, such as Figure 3 As shown; at this time, the two BOOST currents in the input series short circuit will form a series loop with the bus capacitor of the DC bus. The series loop is as follows Figure 3 As shown by the dashed arrow line in the middle; at the same time, due to the operating characteristics of the photovoltaic panel, the input voltage of the two BOOST circuits will suddenly drop, and a large inrush current will appear in the series circuit, while the input voltage of the other BOOST circuits that are not in the input series short-circuit state will quickly return from the operating voltage to its open-circuit voltage. Moreover, after the series short-circuit fault occurs, the input voltage of the BOOST circuit in the input series short-circuit state will gradually recover from half the bus voltage to the open-circuit voltage. During this recovery process, the input terminals of the two BOOST circuits are connected in series and charge the DC bus together, causing the upper and lower half bus voltages of the DC bus to rise together. Ultimately, the DC bus voltage will reach the sum of the input voltages of the two BOOST circuits with input series short-circuit, or until the capacitor fails due to overvoltage.

[0070] Therefore, when the symmetrical three-level BOOST converter is in operation, determining the BOOST circuit in the input series short-circuit state can be achieved by the following process, the flow chart of which is as follows: Figure 4 Shown, including:

[0071] S201 , judging whether the input voltages of at least two BOOST circuits satisfy a mutation condition according to detection parameters.

[0072] That is, according to the input voltages of each BOOST circuit detected in real time, it is determined whether there are at least two input voltages that step-jump to within a first preset range of the half-bus voltage. If the determination result is yes, it is determined that the input voltage of the corresponding BOOST circuit meets the mutation condition, and then step S202 is executed.

[0073] Generally, when input series short circuit occurs in two BOOST circuits, the parallel operation of the original two BOOST circuits to support the DC bus capacitor voltage suddenly changes to series operation to support the DC bus capacitor voltage, and its charging circuit is as shown by the dotted line with arrows in Figure 3 the figure. Therefore, according to the changes in the circuit topology and current loop before and after the input series short circuit occurs, as well as the characteristics of the photovoltaic panels and Kirchhoff's voltage law, it can be known that the input voltage of the BOOST circuit where the input series short circuit occurs will step-jump from its normal operating voltage to the half-bus voltage. However, in the actual situation, due to factors such as incomplete short circuit and different characteristics of the photovoltaic panels, as long as it is determined that there are at least two input voltages that step-jump to within the first preset range of the half-bus voltage, the first preset range can be determined by technicians according to the actual application situation, and it can be within a range greater than or less than the half-bus voltage by a certain value, and all are within the protection scope of the embodiments of the present invention.

[0074] S202: Further determine whether there is an inrush current in the corresponding BOOST circuit according to the detection parameters.

[0075] After determining the BOOST circuit corresponding to the input voltage that meets the mutation condition according to step S201, the input current of this BOOST circuit is further detected and judged. Since the number of inductors in the series loop is reduced to half of the original after the input series short circuit occurs, the inductance value is greatly reduced, and a large voltage difference appears across the inductor at the moment of short circuit, so a large inrush current will appear on the input side when the input series short circuit occurs. Among them, the magnitude of the inrush current corresponds to different values in different application scenarios, and no specific limitation is made here.

[0076] If it is determined that there is a large inrush current in the corresponding BOOST circuit, step S203 is executed.

[0077] S203: Determine whether the bus voltage is abnormal.

[0078] Within a preset time after an input series short circuit occurs in at least two BOOST circuits, the bus voltage will increase according to a preset law. Here, the preset time is related to specific application scenarios and is not limited herein. Specifically, the bus voltage will gradually increase as the input voltage of the corresponding BOOST circuit recovers from the voltage drop after the short circuit to the open-circuit voltage, and its variation law coincides with the variation law of the input voltage of the corresponding BOOST circuit, indicating that the bus voltage is abnormal. Or, if the bus capacitor experiences overvoltage failure, it also indicates that the bus voltage is abnormal, and step S204 needs to be executed.

[0079] S204. Determine that the corresponding BOOST circuit is in an input series short circuit state.

[0080] That is, when the symmetric three-level BOOST converter is in the working state, the input voltage steps to near half of the bus voltage, accompanied by at least two BOOST circuits corresponding to a large inrush current on the input side. And within a period of time, if its variation law coincides with the variation law of the input voltage of the corresponding BOOST circuit, it is determined that the corresponding at least two BOOST circuits are in an input series short circuit state.

[0081] It should be noted that Figure 4 The judgment process shown is only a preferred implementation method provided by the embodiments of the present invention, not limited thereto. For example, after determining that the input voltages of at least two BOOST circuits satisfy the mutation condition and the bus voltage is abnormal, it can be considered that the corresponding BOOST circuits are in an input series short circuit state.

[0082] S103. After a starting voltage is established at the input end of the BOOST circuit, with the switch tube branches in other BOOST circuits shorted, each BOOST circuit is controlled to be open one by one, and based on the real-time monitored bus voltage and the detection parameters of the corresponding BOOST circuit, it is determined whether the corresponding BOOST circuit is in an input series short circuit state.

[0083] It is worth noting that when the symmetric three-level BOOST converter is in the standby state, since there is no voltage on the input side, if an input series short circuit occurs, the above characteristics will not appear. However, as the light intensity increases and there is a certain voltage greater than a preset base value on the input side, that is, after there is a starting voltage that can meet the subsequent detection requirements, the BOOST circuits in the input series short circuit state can be determined according to the method of step S103.

[0084] Preferably, the determination process can be as shown in the flow Figure 5 and includes:

[0085] S301. Compare the magnitudes of the input voltages of each BOOST circuit with the bus voltage.

[0086] S302. Determine whether there are at least two BOOST circuits in an input series short - circuit state.

[0087] After determining that the symmetric three - level BOOST converter is in the standby state, the input voltages of each BOOST circuit, as well as the bus voltage of the DC bus and the upper and lower half - bus voltages, are detected in real - time. Then, it can be determined whether there are at least two BOOST circuits in an input series short - circuit state according to the following method:

[0088] First, compare the magnitudes of the input voltages of each BOOST circuit to determine the maximum value and the minimum value among the input voltages. Then, determine whether the difference between the bus voltage of the DC bus minus its maximum value is greater than a preset voltage. If the determination result is yes, it means that there are at least two BOOST circuits in an input series short - circuit state, and then step S302 is executed. It should be noted that the preset voltage can be set according to the actual application situation, as long as it is less than its minimum value, and all are within the protection scope of the embodiments of the present invention.

[0089] S303. When the switch - tube branches in other BOOST circuits are in a direct - connection state, control each BOOST circuit to be open - circuited one by one, and sequentially determine whether the magnitudes of the input voltage of each BOOST circuit and the upper and lower half - bus voltages of the DC bus meet the preset conditions, so as to determine the BOOST circuits in an input series short - circuit state.

[0090] After determining that there is an input series short - circuit fault, each BOOST circuit can be judged in sequence, so as to accurately know the working state of each BOOST circuit. Specifically, by controlling the on - off of each switch tube in the BOOST circuit, in accordance with a preset order, each BOOST circuit is controlled to be open - circuited one by one. For example, all BOOST circuits can be sorted according to the magnitudes of their input voltages from high to low, and then only one BOOST circuit is controlled to be in an open - circuit state in sequence from large to small, and the switch - tube branches in other BOOST circuits are in a direct - connection state. At the same time, the upper and lower half - bus voltages of the DC bus and the open - circuit voltage of the BOOST circuit in the open - circuit state are detected in real - time until all BOOST circuits are judged. Among them, the method of sorting the input voltages is only an example of the embodiments of the present invention, and other sorting methods, as long as they can complete the judgment of all BOOST circuits in sequence, are acceptable.

[0091] If the BOOST circuit in the open state is not in the input series short - circuit state, since the bus voltage is greater than the input voltage of the BOOST circuit, the bus voltage will drop from the initial value until it is near the input voltage, and then the DC bus will be supported by the input voltage. However, if the BOOST circuit in the open state is in the input series short - circuit state, the input voltage of the BOOST circuit will charge the upper or lower half - bus capacitor of the DC bus, thereby causing the half - bus voltage to increase to near the input voltage of the BOOST circuit.

[0092] Specifically, taking two - path BOOST circuits as an example, after an input short - circuit fault as shown in Figure 3 occurs, first control the BOOST circuit corresponding to PVj + and PVj - on the input side to be in the open state, then the switch - tube branch in the other BOOST circuit corresponding to PVk + and PVk - on the input side is directly connected, and the current loop is as shown in Figure 6a . Among them, the dotted line with an arrow is the charging current loop of the input side of PVj + and PVj -, and the solid line with an arrow is the current loop of the input side of PVk + and PVk -. It can be seen that the BOOST circuit with the directly - connected switch - tube branch does not charge the DC bus, and only the BOOST circuit in the open state charges the upper half - bus capacitor of the DC bus. It can be determined that the negative terminal of the input end of the BOOST circuit corresponding to PVj + and PVj - is short - circuited to the ground. Then, when the other BOOST circuit corresponding to PVk + and PVk - on the input side is in the open state, the charging loops of each BOOST circuit are as shown in Figure 6b . Its principle is similar to the above Figure 6a and will not be elaborated here.

[0093] Therefore, it is necessary to sequentially determine whether the magnitudes of the input voltages of each BOOST circuit and the upper and lower half - bus voltages of the DC bus satisfy the preset conditions, that is, to determine whether the upper half - bus voltage or the lower half - bus voltage gradually rises to within the second preset range of the open - circuit voltage. If so, it is determined that the corresponding BOOST circuit in the open state is in the input series short - circuit state. It should be noted that the second preset range is a range near the open - circuit voltage, that is, it can be less than the open - circuit voltage by a certain value or greater than the open - circuit voltage by a certain value, which is determined by the technical personnel according to the actual application situation.

[0094] It is worth noting that in order to reduce the judgment error, after a round of judgment on all BOOST circuits is completed through the process shown in Figure 5 , the same method (that is, Figure 5)Perform the second-round judgment again, and compare whether the judgment results of the two rounds are the same. If the results of the two rounds are different, still use the above method to perform the third-round judgment until the BOOST circuits corresponding to the input series short-circuit state are accurately determined. Moreover, in order to ensure that each BOOST circuit is detected, a counter can be set during each round of judgment. For example, after detecting one BOOST circuit, the counter is decremented by one until the counter reaches zero, and the judgment process ends to avoid omission.

[0095] Therefore, the short-circuit fault diagnosis method of the symmetric three-level BOOST converter provided by the embodiment of the present invention can accurately diagnose each BOOST circuit corresponding to the input series short-circuit fault whether the input-side voltage is normal or very small or even zero at the input side, and then make corresponding treatments before the bus capacitor overvoltage caused to avoid the bus capacitor overvoltage, so as to avoid causing greater harm, which is of great significance.

[0096] The embodiment of the present invention also provides a symmetric three-level BOOST converter, and its structural schematic diagram is as Figure 7 shown, including: a control unit 110, a detection unit 120, and at least two BOOST circuits 130; wherein:

[0097] The input ends of each BOOST circuit 130 are respectively connected to a corresponding input source (respectively shown as PVj +, PVj-, PVk +, and PVk- in Figure 7 ), the voltages of each input source are greater than a preset value. If at least two BOOST circuits are in the input series short-circuit state, it will pose an overvoltage danger to the subsequent bus; the output ends of each BOOST circuit 130 are connected in parallel to the DC bus (shown as Bus + and Bus- in Figure 7 ); the control unit 110 is respectively connected to the output end of the detection unit 120 and the control ends of each switch tube in each BOOST circuit 130, and is used to execute the short-circuit fault diagnosis method of the symmetric three-level BOOST converter provided by the above embodiment to timely realize the corresponding short-circuit fault diagnosis and avoid serious overvoltage of the subsequent bus.

[0098] Specifically, the control unit 110 can be a software control device or a hardware control circuit. For example, a single-chip microcomputer or the like is used to control the on and off of each switch tube in each BOOST circuit 130, which is not specifically limited as long as it can implement the short-circuit fault diagnosis method provided by the above embodiment. Moreover, the detection unit 120 includes a voltage detection unit (not shown) and a current detection unit (shown as ij and ik in Figure 7 ), wherein the voltage detection unit is used to detect the bus voltage of the DC bus and the input voltage of each BOOST circuit 130, and the current detection unit is used to detect the input current of each BOOST circuit.

[0099] Preferably, the symmetric three-level BOOST converter may also be provided with an alarm circuit (not shown), and its working state is controlled by the control unit 110. It is used to generate and output an alarm signal after determining which BOOST circuit has an input series short circuit, so as to notify the maintenance personnel to remove the fault and avoid the bus voltage increasing to the sum of the input voltages of the BOOST circuit in the input series short circuit state or overvoltage failure.

[0100] It should be noted that in the embodiments of the present invention, the symmetric three-level BOOST converter including two BOOST circuits is used for demonstration. The structure of multiple BOOST circuits can be inferred by analogy and will not be elaborated here.

[0101] The rest of the principles are the same as those of the above embodiments and will not be elaborated one by one here.

[0102] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiments, since they are basically similar to the method embodiments, the description is relatively simple. For the relevant parts, refer to the partial description of the method embodiments. The systems and system embodiments described above are only illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative work.

[0103] Those skilled in the art can further realize that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of the two. To clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described according to functions in the above description. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present invention.

[0104] Regarding the above description of the disclosed embodiments, the features described in each embodiment in this specification can be replaced or combined with each other, enabling those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A short - circuit fault diagnosis method for a symmetric three - level BOOST converter, characterized in that, The symmetric three-level BOOST converter includes at least two BOOST circuits whose outputs are connected in parallel to the DC bus. The short-circuit fault diagnosis method includes: Determine the current state of the symmetric three-level BOOST converter; If the current state is the working state, directly determine at least two of the BOOST circuits in the input series short-circuit state according to the bus voltage of the DC bus monitored in real time and the detection parameters of each BOOST circuit; the input series short-circuit state is: a state of being directly or indirectly connected in series through one pole of its own input terminal and the other pole of the input terminal of another BOOST circuit; If the current state is the standby state, after establishing a starting voltage at the input terminal of the BOOST circuit, when the switch tube branches in other BOOST circuits are directly connected, control each BOOST circuit to open one by one, and determine whether the corresponding BOOST circuit is in the input series short-circuit state according to the bus voltage monitored in real time and the detection parameters of the corresponding BOOST circuit.

2. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 1, characterized in that, The step of directly determining at least two of the BOOST circuits in the input series short-circuit state according to the bus voltage of the DC bus monitored in real time and the detection parameters of each BOOST circuit includes: Judge whether there are at least two BOOST circuits whose input voltages satisfy the mutation condition according to the detection parameters; If so, further judge whether the corresponding BOOST circuit has an impact current according to the detection parameters; If the judgment result is yes, judge whether the bus voltage is abnormal; If it is determined that the bus voltage is abnormal, determine that the corresponding BOOST circuit is in the input series short-circuit state.

3. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 2, wherein The step of judging whether there are at least two BOOST circuits whose input voltages satisfy the mutation condition according to the detection parameters includes: Judge whether there are at least two input voltages that step-jump to the first preset range of half the bus voltage according to the input voltages of each BOOST circuit detected in real time; If the judgment result is yes, determine that the input voltage of the corresponding BOOST circuit satisfies the mutation condition.

4. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 2, characterized in that, The step of judging whether the bus voltage is abnormal includes: Judge whether the bus voltage increases according to a preset rule, or whether the bus capacitor is overvoltage and fails; If the judgment result is yes, determine that the bus voltage is abnormal.

5. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 4, characterized in that The step of judging whether the bus voltage increases according to a preset rule includes: Judge whether the change rule of the bus voltage coincides with the change rule of the input voltage of the corresponding BOOST circuit; If the judgment result is yes, determine that the bus voltage increases according to a preset rule.

6. The short - circuit fault diagnosis method of the symmetric three - level BOOST converter according to claim 1, characterized in that, When the switch tube branches in other BOOST circuits are directly connected, control each BOOST circuit to open one by one, and determine whether the corresponding BOOST circuit is in the input series short-circuit state according to the bus voltage monitored in real time and the detection parameters of the corresponding BOOST circuit, including: Compare the input voltages of the BOOST circuits in each path with the bus voltage to determine whether there are at least two BOOST circuits in the input series short - circuit state; If the judgment result is yes, when the switch - tube branches in the other BOOST circuits are directly connected, control each BOOST circuit to be open one by one, and sequentially judge whether the magnitudes of the input voltages of the BOOST circuits and the upper and lower half - bus voltages of the DC bus meet the preset conditions, so as to determine the BOOST circuits in the input series short - circuit state.

7. The short - circuit fault diagnosis method of the symmetric three - level BOOST converter according to claim 6, characterized in that, Comparing the input voltages of the BOOST circuits in each path with the bus voltage to determine whether there are at least two BOOST circuits in the input series short - circuit state includes: Compare the magnitudes of the input voltages of the BOOST circuits in each path to determine the maximum value among the input voltages; Judge whether the difference between the bus voltage and the maximum value is greater than the preset voltage; If the judgment result is yes, it is determined that there are at least two BOOST circuits in the input series short - circuit state.

8. The short - circuit fault diagnosis method of the symmetric three - level BOOST converter according to claim 7, characterized in that, The preset voltage is less than the minimum value among the input voltages of all the BOOST circuits.

9. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 6, characterized in that, When the switch - tube branches in the other BOOST circuits are directly connected, control each BOOST circuit to be open one by one, and sequentially judge whether the magnitudes of the input voltages of the BOOST circuits and the upper and lower half - bus voltages of the DC bus meet the preset conditions, so as to determine the BOOST circuits in the input series short - circuit state, including: By controlling the on - off of each switch tube in each BOOST circuit, sequentially control only one BOOST circuit to be in the open state, and the switch - tube branches in the other BOOST circuits are in the directly - connected state; Detect the upper and lower half - bus voltages and the open - circuit voltage of the BOOST circuit in the open state; If the upper half - bus voltage or the lower half - bus voltage gradually rises to the second preset range of the open - circuit voltage, it is determined that the corresponding BOOST circuit in the open state is in the input series short - circuit state.

10. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 9, characterized in that By controlling the on - off of each switch tube in each BOOST circuit, sequentially control only one BOOST circuit to be in the open state, and the switch - tube branches in the other BOOST circuits are in the directly - connected state, including: By controlling the on - off of each switch tube in each BOOST circuit, in accordance with the preset order, sequentially control only one BOOST circuit to be in the open state, and the switch - tube branches in the other BOOST circuits are in the directly - connected state.

11. The short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to claim 10, characterized in that The preset order is the order from high to low of the input voltages.

12. A symmetric three-level BOOST converter, characterized in that, Includes: A control unit, a detection unit, and at least two BOOST circuits; where: The input ends of the BOOST circuits in each path are respectively connected to a corresponding input source, and the voltage of each input source is greater than the preset value; The output ends of the BOOST circuits are connected in parallel to the DC bus; The control unit is respectively connected to the output end of the detection unit and the control ends of each switching tube in each BOOST circuit, and is configured to execute the short-circuit fault diagnosis method of the symmetric three-level BOOST converter according to any one of claims 1-11.

13. The symmetric three-level BOOST converter according to claim 12, wherein The control unit is a software control device or a hardware control circuit.

14. The symmetric three-level BOOST converter according to claim 12, wherein, The detection unit includes: a voltage detection unit and a current detection unit; wherein: The voltage detection unit is configured to detect the bus voltage of the DC bus and the input voltage of each BOOST circuit; The current detection unit is configured to detect the input current of each BOOST circuit.

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