A method for fault detection and control of an inverter system

Abstract

This invention discloses a fault detection and control method for an inverter system. The inverter system includes several boost modules connected between a photovoltaic module and an inverter module to boost the voltage output by the photovoltaic module. Each boost module has a first switching unit and a second switching unit. The first switching unit is connected between the positive bus and the midpoint of the bus in the inverter system, and the second switching unit is connected between the negative bus and the midpoint of the bus in the inverter system. The method monitors the voltage characteristic value ΔU at the midpoint of the bus in the inverter system. When the absolute value of the voltage characteristic value ΔU is greater than a threshold A, it is determined that a short circuit fault has occurred in either the first or second switching unit. By sequentially controlling the first and second switching units of a single boost module to conduct until the absolute value of the voltage characteristic value ΔU is less than the threshold A, the boost module with the short circuit fault can be located, thereby improving the efficiency of subsequent maintenance.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic energy storage technology, and in particular to a fault detection and control method for an inverter system. Background Technology

[0002] In inverter systems, boost modules are typically used to achieve maximum power point tracking of photovoltaic modules and provide a stable DC bus voltage for subsequent inverter modules. However, short-circuit faults may occur in the upper or lower bridge arm switching unit of the boost module during operation, thereby disrupting the DC bus voltage balance and causing severe voltage imbalance between the positive and negative sides of the bus.

[0003] When a short-circuit fault occurs in the upper or lower bridge arm switching unit of the boost module, the inverter system must be shut down immediately and can only be restarted after the damaged boost module is replaced. Therefore, quickly identifying and accurately locating the switching unit where the short-circuit fault has occurred is an important prerequisite for taking subsequent targeted maintenance measures and preventing the impact of the fault from spreading. Summary of the Invention

[0004] One objective of this invention is to provide a fault detection and control method for an inverter system, which can promptly detect and locate boost modules that have experienced short-circuit faults.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a fault detection and control method for an inverter system, wherein the inverter system includes a plurality of boost modules, the boost modules being connected between a photovoltaic module and an inverter module, and used to boost the voltage output by the photovoltaic module. Each boost module has a first switching unit and a second switching unit. The first switching unit is connected between the positive bus and the midpoint of the bus in the inverter system, and the second switching unit is connected between the negative bus and the midpoint of the bus in the inverter system. The method monitors the voltage characteristic value ΔU at the midpoint of the bus in the inverter system. When the absolute value of the voltage characteristic value ΔU is greater than a threshold A, it is determined that either the first switching unit or the second switching unit has a short-circuit fault. The method locates the boost module with the short-circuit fault by sequentially controlling the first and second switching units of a single boost module to conduct until the absolute value of the voltage characteristic value ΔU is less than the threshold A.

[0006] As a preferred embodiment, the inverter system further includes several MPPT modules, which are connected between the photovoltaic module and the boost module and are used to control the output voltage Upv of the photovoltaic module. The boost module that experiences a short-circuit fault is designated as the fault module. When the inverter system is connected to the grid, the MPPT modules are used to ensure that the output voltage Upv of the photovoltaic module corresponding to the fault module is half of the bus voltage Ubus under normal operating conditions of the inverter system.

[0007] As a preferred embodiment, when the inverter system is started, the first and second switching units of the faulty module are turned on to restore the bus voltage of the inverter system to balance.

[0008] As a preferred embodiment, the voltage characteristic value Wherein, Ubus is the bus voltage of the inverter system under normal operating conditions, and Umid is the positive half-bus voltage of the inverter system.

[0009] As a preferred embodiment, when the absolute value of the voltage characteristic value ΔU is greater than the threshold A and the voltage characteristic value ΔU is negative, it is determined that the first switching unit has a short circuit fault; when the absolute value of the voltage characteristic value ΔU is greater than the threshold A and the voltage characteristic value ΔU is positive, it is determined that the second switching unit has a short circuit fault.

[0010] As a preferred embodiment, the threshold A is 2% to 8% of the bus voltage Ubus under normal operating conditions of the inverter system.

[0011] As a preferred embodiment, the boost module that experiences a short-circuit fault is designated as the fault module; after locating the fault module, the inverter system records the fault module and issues a fault alarm.

[0012] As a preferred embodiment, the MPPT module controls the first and second switching units through a PWM signal to adjust the duty cycle D of the PWM signal so that the output voltage Upv of the photovoltaic module is half of the bus voltage Ubus under normal operating conditions of the inverter system, where Upv = Uout(1-D) and Uout is the output voltage of the boost module.

[0013] As a preferred embodiment, the MPPT module includes a main controller, an amplifier, a first PI controller, a second PI controller, and a PWM controller. The main controller is used to acquire the output voltage Upv and output current Ipv of the photovoltaic module and calculate the target voltage Uref. The input terminal of the amplifier is used to receive the target voltage Uref, the output voltage Upv of the photovoltaic module, and the actual bus voltage Udc processed by the second PI controller. One input terminal of the PWM controller is connected to the output terminal of the amplifier via the first PI controller, and the other input terminal of the PWM controller is used to receive a triangular carrier wave. The PWM controller is used to output a PWM signal to control the first switching unit and the second switching unit.

[0014] As a preferred embodiment, the inverter module of the inverter system has a three-level topology.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] By monitoring the voltage characteristic value ΔU at the midpoint of the bus and comparing the absolute value of ΔU with the threshold A, it is possible to promptly detect whether a short circuit fault has occurred in the first or second switching unit of the inverter system. By sequentially controlling the first and second switching units of a single boost module to conduct, the absolute value of the voltage characteristic value ΔU is less than the threshold A, thus locating the boost module with the short circuit fault, thereby improving the efficiency of subsequent maintenance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an inverter system in normal operating condition according to some embodiments of this application.

[0018] Figure 2 This is a schematic diagram of the switching unit of the MPPT module controlling the boost module according to some embodiments of this application.

[0019] Figure 3 This is a flowchart of a control method according to some embodiments of this application.

[0020] Figure 4 These are PV tracking curves of photovoltaic modules corresponding to normal boost modules according to some embodiments of this application.

[0021] Figure 5 This is a schematic diagram of an inverter system with a faulty module in operation according to some embodiments of this application.

[0022] Figure 6 These are PV tracking curves of photovoltaic modules corresponding to faulty modules according to some embodiments of this application.

[0023] Figure 7 This is a schematic diagram of a bus voltage imbalance during startup of an inverter system with a faulty module according to some embodiments of this application.

[0024] Figure 8 This is a schematic diagram of the bus voltage balance during startup of an inverter system with a faulty module according to some embodiments of this application. Detailed Implementation

[0025] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0026] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, 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 explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0028] To facilitate understanding of the following content, this application will describe it using an inverter system. The inverter system includes an inverter module, which is connected to multiple boost modules, each of which is connected to a photovoltaic module. The low-voltage DC power output from the photovoltaic module can be boosted by the boost modules to obtain high-voltage DC power, which is then converted by the inverter module into AC power suitable for supplying the power grid. For example, as... Figure 1 As shown, the inverter module is connected to boost module #1 and boost module #2. Boost module #1 is connected to photovoltaic module PV1, and boost module #2 is connected to photovoltaic module PV2. It is worth mentioning that the inverter module can also be connected to three or more boost modules and photovoltaic modules; this application does not impose specific limitations on this.

[0029] Specifically, the boost module includes inductor L a Inductor L b diode D a diode D b First switching unit S a Second switch unit S b The positive terminal of the photovoltaic module passes through inductor L in sequence. a and diode D a Connected to the positive bus of the inverter system; the negative terminal of the photovoltaic module passes through inductor L in sequence. b and diode D b The negative busbar connected to the inverter system; the first switching unit S a One end is connected to diode D a Connected to the positive busbar, the first switching unit S a The other end is connected to the midpoint of the bus between the positive half-bus capacitor C1 and the negative half-bus capacitor C2; the second switching unit S b One end is connected to diode D b Connected to the negative busbar, the second switching unit S b The other end is connected to the midpoint of the bus between the positive half-bus capacitor C1 and the negative half-bus capacitor C2. For example, as... Figure 1 As shown, boost module #1 includes inductor L a1 Inductor L b1 diode D a1 diode D b1First switching unit S a1 Second switch unit S b1 Boost module #2 includes inductor L a2 Inductor L b2 diode D a2 diode D b2 First switching unit S a2 Second switch unit S b2 .

[0030] It should be understandable that when the first switching unit S a Or the second switching unit S b When a short-circuit fault occurs, the output voltage Upv of the photovoltaic module will be directly applied to the bus midpoint, causing a bus voltage imbalance. In this case, the inverter system needs to be shut down immediately to prevent the impact of the fault from spreading.

[0031] Based on the above, in order to promptly detect and locate boost modules experiencing short-circuit faults, this invention provides a fault detection and control method for inverter systems, such as... Figures 1-8 As shown. Specifically, as mentioned above, the inverter system includes several boost modules, which are connected between the photovoltaic module and the inverter module to boost the voltage output from the photovoltaic module. Each boost module has a first switching unit S. a Second switch unit S b Among them, the first switching unit S a Connected between the positive bus and the midpoint of the inverter system, in other words, the first switching unit S a One end is connected to diode D a Connected to the positive busbar, the first switching unit S a The other end is connected to the midpoint of the bus between the positive half-bus capacitor C1 and the negative half-bus capacitor C2; the second switching unit S b Connected between the negative bus and the midpoint of the bus in the inverter system; in other words, the second switching unit S b One end is connected to diode D b Connected to the negative busbar, the second switching unit S b The other end is connected to the midpoint of the bus between the positive half bus capacitor C1 and the negative half bus capacitor C2.

[0032] Furthermore, the voltage characteristic value ΔU at the bus midpoint of the inverter system is monitored. When the absolute value of the voltage characteristic value ΔU is greater than the threshold A, it is determined that the first switching unit S has a voltage characteristic value ΔU. a Or the second switching unit S b A short circuit fault has occurred. This is understandable; under normal operating conditions of the inverter system, such as... Figure 1As shown, the bus voltage is denoted as Ubus, and the voltage at the bus midpoint fluctuates around Ubus / 2; in other words, the DC component of the voltage at the bus midpoint is 0V or close to 0V. When the first switching unit S... a Or the second switching unit S b When a short-circuit fault occurs, the DC voltage output by the photovoltaic module will be connected to the bus midpoint, causing the voltage at the bus midpoint to fluctuate around a new reference point that is either higher or lower than Ubus / 2; in other words, a DC component is superimposed on the voltage at the bus midpoint. Therefore, by detecting the voltage characteristic value ΔU at the bus midpoint, it is possible to promptly detect whether there is a first switching unit S in the inverter system. a Or the second switching unit S b A short circuit fault has occurred.

[0033] Furthermore, when the inverter system has a first switching unit S a Or the second switching unit S b When a short circuit fault occurs, the first switching unit S of each individual boost module is controlled sequentially. a Second switch unit S b The inverter is turned on until the absolute value of the voltage characteristic value ΔU is less than the threshold A, that is, the bus voltage of the inverter system is restored to balance, in order to locate the boost module that has a short-circuit fault. The boost module that has a short-circuit fault is denoted as the fault module.

[0034] It should be understandable that when the first switching unit S of the normal module... a Second switch unit S b When the circuit is turned on, since the DC voltage output by the photovoltaic module corresponding to the faulty module is still connected to the midpoint of the bus, the absolute value of the voltage characteristic value ΔU is still greater than A. When the first switching unit S of the faulty module... a Second switch unit S b When the circuit is turned on, the photovoltaic module corresponding to the faulty module is short-circuited, resulting in an output voltage of 0V. The bus voltage is then restored to balance, meaning the absolute value of the voltage characteristic value ΔU is less than the threshold value A. Therefore, by sequentially controlling the first switching unit S of each individual boost module... a Second switch unit S b The circuit was activated, allowing the faulty module to be located. It's worth noting that during the faulty module location process, the inverter system did not need to shut down and maintained a high power output.

[0035] In some embodiments, voltage characteristic value Where Ubus is the bus voltage under normal operating conditions of the inverter system, and Umid is the positive half-bus voltage of the inverter system. It should be understood that, as mentioned earlier, under normal operating conditions of the inverter system, the voltage at the midpoint of the bus fluctuates around Ubus / 2; in other words, the positive half-bus voltage Umid fluctuates around Ubus / 2, and at this time, the voltage characteristic value ΔU approaches 0V. When the first switching unit S... a Or the second switching unit S b When a short-circuit fault occurs, the voltage at the bus midpoint fluctuates around a new reference point that is either higher or lower than Ubus / 2; in other words, the positive half-bus voltage Umid fluctuates around a new reference point that is either higher or lower than Ubus / 2. At this time, the absolute value of the voltage characteristic value ΔU will be greater than 0. Therefore, by comparing the voltage characteristic value ΔU with the threshold A, it can be determined whether the first switching unit S is present. a Or the second switching unit S b A short circuit fault has occurred.

[0036] In at least one embodiment, the threshold A is 2% to 8% of the bus voltage Ubus under normal operating conditions of the inverter system. It should be understood that under normal operating conditions of the inverter system, the voltage at the bus midpoint fluctuates around Ubus / 2, therefore, the voltage characteristic value ΔU may momentarily be positive or negative. In this embodiment, setting the threshold A between 0.02Ubus and 0.08Ubus helps avoid false alarms triggered by normal fluctuations and enables timely detection of genuine bus voltage imbalances, thus achieving a good balance between reliability and sensitivity. In one specific embodiment, the threshold A is 5% of the bus voltage Ubus under normal operating conditions of the inverter system.

[0037] In some embodiments, when the absolute value of the voltage characteristic value ΔU is greater than the threshold A, and the voltage characteristic value ΔU is negative, it is determined that the first switching unit S exists. a A short circuit fault occurs; when the absolute value of the voltage characteristic value ΔU is greater than the threshold A, and the voltage characteristic value ΔU is positive, it is determined that there is a second switching unit S. b A short circuit fault occurs, which allows for more accurate location of the fault and further improves the efficiency of subsequent maintenance.

[0038] Taking an inverter module with a three-level topology, an open-circuit output voltage of 1000V for each photovoltaic module, and a maximum power point voltage of 850V for the MPPT module as an example. Under normal operating conditions of the inverter system, such as... Figure 1 and Figure 4As shown, the bus voltage Ubus is 1000V, the voltage at the bus midpoint is based on 500V, and there is a 150Hz AC fluctuation. The output voltage Upv of each photovoltaic module is 850V. When the first switching unit S... a During a short circuit, the positive terminal of the photovoltaic module is connected to the short-circuited first switching unit S. a Connecting to the midpoint of the busbar causes the voltage on the negative half of the busbar to rise, exceeding 500V, while the voltage on the positive half of the busbar, Umid, drops, falling below 500V. If the value is negative, ΔU is a negative number. Similarly, when the second switching unit S... b During a short circuit, the negative terminal of the photovoltaic module is connected to the short-circuited second switching unit S. b Connecting to the midpoint of the busbar causes the positive half-busbar voltage Umid to rise, exceeding 500V, while the negative half-busbar voltage drops, falling below 500V, and thus... It is a positive value, and ΔU is a positive number.

[0039] In some embodiments, such as Figure 2 As shown, the inverter system also includes several MPPT (Maximum Power Point Tracking) modules. The MPPT modules are connected between the photovoltaic (PV) modules and the boost module to control the output voltage Upv of the PV modules. When the inverter system is running in grid-connected mode, the MPPT modules ensure that the output voltage Upv of the PV module corresponding to the faulty module is half of the bus voltage Ubus under normal operating conditions of the inverter system. That is, Upv = Ubus / 2. Figure 5 and Figure 6 As shown; in this way, the positive half-bus voltage and the negative half-bus voltage can be made equal or nearly equal, thereby enabling the inverter system to maintain safe operation.

[0040] It should be understood that in related technologies, when the first switching unit S of the boost module... a Or the second switching unit S b When a short circuit fault occurs, the inverter system needs to be shut down immediately due to the severe imbalance of the bus voltage. It can only be restarted after the faulty module is replaced. This results in the inverter system being completely shut down from the time of the fault until the maintenance, causing a loss of power generation.

[0041] In this embodiment, the MPPT module makes the output voltage Upv of the photovoltaic module corresponding to the faulty module equal to Ubus / 2, thus preventing the photovoltaic module's positive terminal from being short-circuited via the first switching unit S. a The connection point is either the midpoint of the busbar or the negative terminal of the photovoltaic module via the short-circuited second switching unit S. bBy connecting to the bus midpoint, the voltage at the bus midpoint can be maintained at Ubus / 2. In other words, the bus voltage can be kept balanced, so that the inverter system can maintain safe operation and maintain a high power output before the faulty module is replaced.

[0042] It is understandable that during the grid-connected operation of the inverter system, if there is a first switching unit S... a Or the second switching unit S b In the event of a short-circuit fault, due to the large energy storage at the bus midpoint, the inverter system will not immediately reach a state of bus voltage imbalance. Furthermore, the first switching unit S of each boost module... a Second switch unit S b The high switching frequency allows for the location of faulty modules before bus voltage imbalance occurs. In at least one instance, each first switching unit S... a Second switch unit S b The switching frequency is 16kHz.

[0043] Furthermore, by using the MPPT module to make the output voltage Upv of the photovoltaic module corresponding to the faulty module equal to Ubus / 2, the faulty module can then rely solely on another normal second switching unit S. b Or the first switching unit S a Maintain operation so that the photovoltaic module corresponding to the faulty module can output power to the inverter module, and keep the voltage at the bus midpoint at Ubus / 2, so that the inverter system can maintain safe operation.

[0044] In some embodiments, after locating the faulty module, the inverter system records the fault and issues a fault alarm. It should be understood that although the aforementioned method enables the inverter system to maintain safe operation after a faulty module occurs, a short circuit still exists in the first switching unit S within the inverter system. a Or the second switching unit S b Therefore, it is necessary to issue a fault alarm to remind maintenance personnel to inspect and replace the faulty module as soon as possible, thereby improving the safety of the inverter system.

[0045] In some embodiments, when the inverter system is started, the first switching unit S of the faulty module is... a Second switch unit S b The inverter is switched on to restore the bus voltage balance of the inverter system. Specifically, for example... Figure 7 and Figure 8 As shown, after the inverter system enters the startup state and before grid connection, if there is a first switching unit S a Or the second switching unit S bIn the event of a short-circuit fault, due to the relatively small energy storage at the bus midpoint, the inverter system may reach a state of bus voltage imbalance. This can be addressed by switching the first switching unit S of the faulty module. a Second switch unit S b When the circuit is turned on, the bus voltage can be quickly restored to balance, meaning that the absolute value of the voltage characteristic value ΔU is less than the threshold value A, so that the inverter system can smoothly enter the grid-connected operation state.

[0046] Taking an inverter module with a three-level topology, and each photovoltaic module having an open-circuit output voltage of 1000V, and the MPPT module having a maximum power point voltage of 850V as an example. After the inverter system enters the startup state and before grid connection, such as... Figure 7 As shown, the first switching unit S of boost module #1 a1 Second switch unit S b1 Normally, the output voltage Upv of photovoltaic module PV1 is 1000V. The first switching unit S of boost module #2... a2 A short circuit fault occurred, affecting the second switching unit S of boost module #2. b2 Normally, the output voltage Upv of photovoltaic module PV2 is close to 1000V, for example, 950V. At this time, the DC voltage output by photovoltaic module PV2 will be connected to the midpoint of the bus, resulting in the positive half bus voltage being 50V and the negative half bus voltage being 950V, that is, the bus voltage is unbalanced.

[0047] Furthermore, such as Figure 8 As shown, by switching the first switching unit S of the boost module #2 a2 Second switch unit S b2 The circuit is turned on, allowing the photovoltaic module PV2 to be short-circuited, thus restoring the bus voltage of the inverter system to balance. Furthermore, as... Figure 5 and Figure 6 As stated above, when the inverter system enters the grid-connected operation state, the MPPT module reduces the output voltage Upv of the photovoltaic module PV2 corresponding to the faulty module to 500V, thereby enabling the inverter system to maintain safe operation and maintain a high power output.

[0048] It is understandable that if the first switching unit S occurs after the inverter system enters the startup state and before grid connection, a Or the second switching unit S b A short circuit can also be detected by locating the faulty module in the manner described above, namely by sequentially controlling the first switching unit S of a single boost module. a Second switch unit S b The circuit is turned on until the absolute value of the voltage characteristic value ΔU is less than the threshold A, in order to locate the boost module that has a short circuit fault, and at the same time, the bus voltage can be restored to balance.

[0049] It is worth mentioning that if a faulty module has been previously recorded, then when the inverter system is started, the first switching unit S of the faulty module can be switched off first. a Second switch unit S b Turning the inverter on helps prevent bus voltage imbalance and further improves the safety and stability of the inverter system.

[0050] In some embodiments, the MPPT module controls the first switching unit S via a PWM signal. a Second switch unit S b The duty cycle D of the PWM signal is adjusted so that the output voltage Upv of the photovoltaic module is half of the bus voltage Ubus under normal inverter system operation, where Upv = Uout(1-D), and Uout is the output voltage of the boost module. It should be understood that the output voltage Uout of the boost module is usually kept fixed; under normal inverter system operation, the output voltage Uout ≈ Ubus; therefore, by adjusting the duty cycle D, the output voltage Upv of the photovoltaic module can be adjusted.

[0051] Taking an inverter module with a three-level topology, and each photovoltaic module having an open-circuit output voltage of 1000V, and the MPPT module having a maximum power point voltage of 850V as an example. When the inverter system is operating normally, the bus voltage Ubus is 1000V, and the output voltage Uout of each boost module is also 1000V. At this time, the duty cycle D of the PWM signal output by each MPPT module is 0.15 to stabilize the output voltage Upv of each photovoltaic module at 850V. Figure 1 As shown. When the first switching unit S of boost module #2... a2 When a short circuit fault occurs, such as Figure 5 and Figure 6 As shown, the duty cycle of the PWM signal output by the MPPT module corresponding to boost module #2 is adjusted from 0.15 to 0.5, so that the output voltage Upv of photovoltaic module PV2 drops to 500V; while the duty cycle D of the PWM signal output by the MPPT module corresponding to normal boost module #1 remains at 0.15, so that the output voltage Upv of photovoltaic module PV1 is maintained at 850V, thus enabling the inverter system to maintain a high power output.

[0052] In one specific embodiment, such as Figure 2As shown, the MPPT module includes a main controller, an amplifier, a first PI controller, a second PI controller, and a PWM controller. The main controller acquires the output voltage Upv and output circuit Ipv of the photovoltaic module and calculates the target voltage Uref. The amplifier's input receives the target voltage Uref, the photovoltaic module's output voltage Upv, and the actual bus voltage Udc processed by the second PI controller, enabling dynamic correction of the target voltage Uref. One input of the PWM controller is connected to the amplifier's output via the first PI controller, and the other input receives a triangular carrier wave. The PWM controller outputs a PWM signal to control the first switching unit S. a Second switch unit S b .

[0053] It should be understood that the target voltage Uref of the MPPT module corresponding to a normal boost module is the maximum power point voltage, such as 850V as mentioned earlier, so that the photovoltaic module operates at the maximum power point to generate as much electrical energy as possible. However, the target voltage Uref of the MPPT module corresponding to a faulty module is half of the bus voltage Ubus under normal inverter system operation, i.e., Ubus / 2. This ensures that the positive and negative bus voltages are equal or nearly equal, allowing the inverter system to maintain a higher power output while ensuring safe operation.

[0054] In some embodiments, the inverter module of the inverter system has a three-level topology. The specific location of the bus midpoint of the three-level topology is well known to those skilled in the art and will not be described in detail here. In other embodiments, the inverter module of the inverter system has a two-level topology, and the ideal midpoint of the two capacitors connected in series between the positive and negative buses on the DC side of the inverter module is used as the virtual bus midpoint.

[0055] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection claimed by this invention is defined by the appended claims and their equivalents.

Claims

1. A method for fault detection and control of an inverter system, characterized by, The inverter system comprises several voltage-boosting modules connected between photovoltaic modules and inverter modules, for boosting the voltage output by the photovoltaic modules, the voltage-boosting modules having first switching units and second switching units, the first switching units being connected between positive busbars of the inverter system and busbar midpoints, and the second switching units being connected between negative busbars of the inverter system and the busbar midpoints; The voltage characteristic value ΔU of the busbar midpoint of the inverter system is monitored, and when the absolute value of the voltage characteristic value ΔU is greater than a threshold value A, it is determined that short-circuit failure has occurred in the first switching unit or the second switching unit; The first switching unit and the second switching unit of a single voltage-boosting module are sequentially controlled to be turned on until the absolute value of the voltage characteristic value ΔU is less than the threshold value A, so as to locate the voltage-boosting module in which short-circuit failure has occurred.

2. The fault detection and control method of an inverter system according to claim 1, characterized by, The inverter system further comprises several MPPT modules connected between the photovoltaic modules and the voltage-boosting modules, for controlling the output voltage Upv of the photovoltaic modules; The voltage-boosting module in which short-circuit failure has occurred is recorded as a failure module; when the inverter system is operating in grid-connected mode, the MPPT module is used to make the output voltage Upv of the photovoltaic module corresponding to the failure module half of the busbar voltage Ubus in the normal working state of the inverter system.

3. The fault detection and control method of an inverter system according to claim 2, characterized by, When the inverter system is started, the first switching unit and the second switching unit of the failure module are turned on, so as to restore the balance of the busbar voltage of the inverter system.

4. The fault detection and control method of an inverter system according to any one of claims 1 to 3, characterized in that, the voltage characteristic value wherein Ubus is the bus voltage in the normal operating state of the inverter system and Umid is the positive half bus voltage of the inverter system.

5. The fault detection and control method of an inverter system according to claim 4, characterized by, When the absolute value of the voltage characteristic value ΔU is greater than the threshold value A and the voltage characteristic value ΔU is negative, it is determined that short-circuit failure has occurred in the first switching unit; when the absolute value of the voltage characteristic value ΔU is greater than the threshold value A and the voltage characteristic value ΔU is positive, it is determined that short-circuit failure has occurred in the second switching unit.

6. The fault detection and control method of an inverter system according to claim 5, wherein The threshold value A is 2% to 8% of the busbar voltage Ubus in the normal working state of the inverter system.

7. The fault detection and control method of an inverter system according to any one of claims 1 to 3, characterized in that, The voltage-boosting module in which short-circuit failure has occurred is recorded as a failure module; after the inverter system locates the failure module, the failure module is recorded and a failure alarm is issued.

8. The fault detection and control method of an inverter system according to any one of claims 2-3, characterized in that, The MPPT module controls the first switching unit and the second switching unit through a PWM signal, adjusts the duty cycle D of the PWM signal, so as to make the output voltage Upv of the photovoltaic module half of the busbar voltage Ubus in the normal working state of the inverter system, wherein Upv=Uout(1-D), and Uout is the output voltage of the voltage-boosting module.

9. The fault detection and control method of an inverter system according to claim 8, characterized by, The MPPT module comprises a master controller, an amplifier, a first PI controller, a second PI controller and a PWM controller, the master controller is used for collecting output voltage Upv and output current Ipv of the photovoltaic module and calculating a target voltage Uref; an input end of the amplifier is used for receiving the target voltage Uref, the output voltage Upv of the photovoltaic module and receiving an actual bus voltage Udc processed via the second PI controller, one input end of the PWM controller is connected to an output end of the amplifier via the first PI controller, and the other input end of the PWM controller is used for receiving a triangular carrier, and the PWM controller is used for outputting a PWM signal to control the first switching unit and the second switching unit.

10. The fault detection and control method of an inverter system according to any one of claims 1 to 3, characterized in that, The inverter module of the inverter system is a three-level topology structure.

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