CN117767229A - Protection method for bus capacitor voltage faults and inverter - Google Patents

Abstract

The application provides a protection method for bus capacitor voltage faults, which comprises the following steps: and responding to the voltage failure of at least one of the n bus capacitors, and opening the output switch, opening the photovoltaic input switch, and starting the bus discharging module. The application also provides an inverter. Therefore, the protection method for the voltage faults of the bus capacitor and the inverter can prevent the bus capacitor from faults caused by overhigh pressure bearing, so that the fault rate of the inverter is reduced, and the working stability of the inverter is improved.

Description

Protection method for bus capacitor voltage faults and inverter

Technical Field

The application relates to the technical field of energy storage, in particular to a protection method for a bus capacitor voltage fault and an inverter.

Background

Along with the development of new energy technology, the inverter is widely applied, wherein, two ends of a direct current bus in the inverter are generally connected with a plurality of bus capacitors in series, if any one of the bus capacitors connected in series fails, the voltage of the bus capacitor is uneven, the capacitor has overvoltage risk, and if the capacitor bears overvoltage for a long time, the capacitor can explode. When the bus capacitor breaks down, if the power transmission is stopped by direct shutdown, the voltage of the photovoltaic module can be directly raised to the open-circuit voltage, the bus voltage can be further raised, and the risk of overvoltage explosion of the bus capacitor is increased.

Disclosure of Invention

In view of the above problems, the present application provides a protection method for a voltage fault of a bus capacitor and an inverter, which can prevent explosion of the bus capacitor due to over-high bearing pressure, thereby reducing the fault rate of the inverter and improving the working stability of the inverter.

In a first aspect, the present application provides a protection method for a bus capacitor voltage fault, applied to an inverter, where the inverter includes a bus discharging module, an output switch, an inverter power conversion circuit, n bus capacitors, one or more photovoltaic input switches and one or more photovoltaic power conversion circuits, the one or more photovoltaic power conversion circuits are correspondingly connected to one or more photovoltaic modules through the one or more input switches, each photovoltaic power conversion circuit is connected to a dc bus, the n bus capacitors are sequentially connected in series between two ends of the dc bus, the inverter power conversion circuit is connected to the dc bus and is connected to a power grid and/or a load through the output switch, and the bus discharging module is used to reduce a bus voltage of the dc bus, and the method includes: and responding to the voltage failure of at least one of the n bus capacitors, and opening the output switch, opening the photovoltaic input switch, and starting the bus discharging module.

With reference to the first aspect, in one possible implementation manner, the protection method for the bus capacitor voltage fault further includes: responding to the voltage failure of at least one of the n bus capacitors and the conduction of an output switch, and executing a corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold; the photovoltaic maximum voltage is the maximum value of output voltages of one or more photovoltaic modules, and the first voltage threshold is proportional to the bus voltage.

With reference to the first aspect, in one possible implementation manner, according to a comparison result of the photovoltaic maximum voltage and the first voltage threshold, a corresponding control method is performed, including: in response to the photovoltaic maximum voltage being less than the first voltage threshold, the output switch is disconnected from the one or more photovoltaic input switches and the bus discharge module is started.

With reference to the first aspect, in one possible implementation manner, according to a comparison result of the photovoltaic maximum voltage and the first voltage threshold, a corresponding control method is performed, including: and in response to the photovoltaic maximum voltage being greater than or equal to a first voltage threshold, and the presence of a bus capacitor having a voltage greater than a second voltage threshold in the n bus capacitors, disconnecting the output switch from the one or more photovoltaic input switches and starting the bus discharge module.

With reference to the first aspect, in one possible implementation manner, according to a comparison result of the photovoltaic maximum voltage and the first voltage threshold, a corresponding control method is performed, including: and in response to the fact that the maximum photovoltaic voltage is greater than or equal to a first voltage threshold and the voltages of the n busbar capacitors are smaller than or equal to a second voltage threshold, one or more photovoltaic input switches are disconnected firstly, then the output switch is disconnected, and the busbar discharging module is started.

With reference to the first aspect, in one possible implementation manner, the inverter further includes one or more battery input switches and one or more battery power conversion circuits, where the one or more battery power conversion circuits are correspondingly connected to the one or more batteries through the one or more battery input switches, and each battery power conversion circuit is connected to the dc bus, and the method further includes: responding to voltage faults of at least one bus capacitor in the n bus capacitors, switching off an output switch, switching off a battery input switch, and starting a bus discharging module; responding to the voltage failure of at least one of the n bus capacitors and the output switch is conducted, and executing a corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold value and the comparison result of the battery maximum voltage and the third voltage threshold value;

the photovoltaic maximum voltage is the maximum value of the output voltage of one or more photovoltaic modules, the battery maximum voltage is the maximum value of the output voltage of one or more batteries, and the first voltage threshold and the third voltage threshold are both in direct proportion to the bus voltage.

With reference to the first aspect, in one possible implementation manner, according to a comparison result of the photovoltaic maximum voltage and the first voltage threshold and a comparison result of the battery maximum voltage and the third voltage threshold, a corresponding control method is performed, including: in response to the photovoltaic maximum voltage being less than the first voltage threshold and the battery maximum voltage being less than the third voltage threshold, the output switch, the one or more photovoltaic input switches, and the one or more battery input switches are opened, and the bus discharge module is started.

With reference to the first aspect, in one possible implementation manner, according to a comparison result of the photovoltaic maximum voltage and the first voltage threshold and a comparison result of the battery maximum voltage and the third voltage threshold, a corresponding control method is performed, including: in response to the photovoltaic maximum voltage being greater than or equal to a first voltage threshold, and the n bus capacitances having a voltage greater than a second voltage threshold, disconnecting the output switch, the one or more photovoltaic input switches, and the one or more battery input switches, and starting the bus discharge module; or in response to the maximum voltage of the battery being greater than or equal to the third voltage threshold, and there being a bus capacitor of the n bus capacitors having a voltage greater than the second voltage threshold, opening the output switch, the one or more photovoltaic input switches, and the one or more battery input switches, and starting the bus discharge module.

With reference to the first aspect, in one possible implementation manner, according to a comparison result of the photovoltaic maximum voltage and the first voltage threshold and a comparison result of the battery maximum voltage and the third voltage threshold, a corresponding control method is performed, including: responding to the fact that the maximum voltage of the photovoltaic is larger than or equal to a first voltage threshold value, the voltages of the n busbar capacitors are smaller than or equal to a second voltage threshold value, firstly disconnecting one or more photovoltaic input switches and one or more battery input switches, then disconnecting an output switch, and starting a busbar discharging module; or in response to the maximum voltage of the battery being greater than or equal to a third voltage threshold and the voltages of the n bus capacitors being less than or equal to a second voltage threshold, disconnecting one or more photovoltaic input switches and one or more battery input switches, disconnecting the output switch, and starting the bus discharging module.

With reference to the first aspect, in one possible implementation manner, the inverter further includes a discharge switch, the discharge switch is connected between the bus discharge module and the dc bus, and starts the bus discharge module, including: the discharge switch is turned on.

With reference to the first aspect, in one possible implementation manner, the bus capacitor voltage fault includes: the absolute value of the difference between the voltage of the bus capacitor and the fault threshold is larger than a preset voltage threshold; wherein the fault threshold is the bus voltage divided by n.

In a second aspect, the present application provides an inverter comprising a control circuit for performing the method of protecting against a bus capacitor voltage fault as provided in any one of the possible implementations of the first aspect.

Drawings

Fig. 1 is a schematic diagram of an energy storage device provided in the present application.

Fig. 2 is a schematic diagram of an inverter provided in the present application.

Fig. 3 is another schematic diagram of the inverter provided herein.

Fig. 4 is a schematic diagram of an inverter provided herein.

Fig. 5 is a schematic diagram of a neutral point of a bus capacitor provided in the present application.

Fig. 6 is another schematic view of a neutral point of a bus capacitor provided herein.

Fig. 7 is a further schematic diagram of the neutral point of the bus capacitor provided herein.

Fig. 8 is a flowchart of a protection method for a bus capacitor voltage fault provided in the present application.

Fig. 9 is another flowchart of a protection method for a bus capacitor voltage fault provided in the present application.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly described below with reference to the drawings in the embodiments of the present application.

It is understood that the connection relationships described in this application refer to direct or indirect connections. For example, the connection between a and B may be a direct connection between a and B or an indirect connection between a and B via one or more other electrical components. For example, a may be directly connected to C, and C may be directly connected to B, so that a connection between a and B is achieved through C. It is also understood that "a-connection B" as described herein may be a direct connection between a and B, or an indirect connection between a and B via one or more other electrical components.

In the description of the present application, "/" means "or" unless otherwise indicated, for example, a/B may mean a or B. "and/or" herein is merely an association relationship describing an association object, and means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone.

In the description of the present application, the words "first", "second", etc. are used merely to distinguish different objects, and are not limited in number and order of execution, and the words "first", "second", etc. are not necessarily different. Furthermore, the terms "comprising," "including," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion.

Along with the development of new energy technology, the inverter is widely applied, wherein, two ends of a direct current bus in the inverter are generally connected with a plurality of bus capacitors in series, if any one of the bus capacitors connected in series fails, the voltage of the bus capacitor is uneven, the capacitor has overvoltage risk, and if the capacitor bears overvoltage for a long time, the capacitor can explode. When the bus capacitor breaks down, if the power transmission is stopped by direct shutdown, the voltage of the photovoltaic module can be directly raised to the open-circuit voltage, the bus voltage can be further raised, and the risk of overvoltage explosion of the bus capacitor is increased.

Therefore, the protection method for the voltage faults of the bus capacitor and the inverter can prevent explosion of the bus capacitor due to overhigh pressure bearing, so that the fault rate of the inverter is reduced, and the working stability of the inverter is improved.

Specifically, referring to fig. 1, fig. 1 is a schematic diagram of an energy storage device 10 provided in the present application. Energy storage device 10 the energy storage device 10 comprises a power supply 11 and an inverter 12. The power supply 11 is connected to an inverter 12. The power supply 11 is configured to output a voltage, and the voltage is converted by the inverter 12 and then output to an external device. The external device may output the charging voltage, convert the voltage by the inverter 12, and then charge the power supply 11.

The inverter 12 may be a bidirectional inverter circuit, and the external device may be an ac load, other energy storage devices, a battery device, a power grid, or the like. For example, when the inverter 12 is connected to an ac load, the inverter 12 may output electric power supplied from the power source 11 to the ac load to supply ac power to the ac load. For another example, when the inverter 12 is connected to another energy storage device, the inverter 12 may provide the electric energy output by the power source 11 to the other energy storage device, or output the electric energy stored by the other energy storage device to the power source 11, so as to realize the transfer of the electric energy between the different energy storage devices. For another example, when the inverter 12 is connected to the power grid, the inverter 12 may output the power supplied from the power grid to the power source 11 to charge the power source 11, or convert the power output from the power source 11 into ac power and then incorporate the ac power into the power grid.

Referring to fig. 2, fig. 2 is a schematic diagram of an inverter 12 provided in the present application. The inverter 12 includes an inverter circuit 12a and a control circuit 12b, and the inverter circuit 12a includes a first conversion circuit 121, a second conversion circuit 122, an input switch K1, an input switch K2, a discharge switch K3, a bus discharge module 123, n bus capacitors C1, … …, cn, an inverter power conversion circuit 124, an output switch K4, and an output switch K5.

The input switch K1 is connected between the photovoltaic module 11a and the first conversion circuit 121, and the first conversion circuit 121 is connected to one end of the dc bus. The input switch K1 is used to turn on or off the voltage transfer between the photovoltaic module 11a and the first conversion circuit 121. The first conversion circuit 121 is used for performing voltage conversion on the output voltage of the photovoltaic module 11a.

The input switch K2 is connected between the battery 11b and the second conversion circuit 122. The second conversion circuit 122 is connected to one end of the dc bus. The input switch K2 is used to turn on or off the voltage transfer between the battery 11b and the second conversion circuit 122. The second conversion circuit 122 is configured to convert the output voltage of the battery 11b into a voltage or convert other voltages to charge the battery 11b. Here, the other voltage may be an output voltage provided by other energy storage devices, batteries, etc. That is, the second conversion circuit 122 may be a bidirectional power conversion circuit, and may convert the output voltage of the battery 11b and output the converted output voltage to one end of the dc bus, or may convert the bus voltage on the dc bus and charge the battery 11b.

The first conversion circuit 121 is a photovoltaic power conversion circuit, and the second conversion circuit 122 is a battery power conversion circuit. The input switch K1 is a photovoltaic input switch, and the input switch K2 is a battery input switch.

In some embodiments, as shown in fig. 3, the inverter 12 may also include a greater number of input switches K1, and not include the second conversion circuit 122 and the input switches K2. As shown in fig. 4, the inverter 12 may further include a greater number of input switches K1 and a greater number of input switches K2 to respectively connect the plurality of photovoltaic modules 11a and the plurality of storage batteries 11b.

It is understood that the photovoltaic module 11a and the storage battery 11b belong to one implementation manner of the power supply 11, and the type of the power supply 11 is not limited in this application.

The discharging switch K3 is connected between one end of the dc bus and the bus discharging module 123, and the bus discharging module 123 is connected to the other end of the dc bus. The discharging switch K3 is used to turn on or off the electrical connection between the bus discharging module 123 and the dc bus. When the discharging switch K3 is turned on, the bus discharging module 123 is connected to the dc bus, and the bus discharging module 123 is in a working state. That is, when the discharge switch K3 is closed and turned on, the bus bar discharge module 123 is started. When the discharging switch K3 is turned off, the connection between the bus discharging module 123 and the dc bus is disconnected, and at this time, the bus discharging module 123 stops operating. The bus discharging module 123 is configured to reduce the bus voltage, and specifically, the bus discharging module 123 may include a plurality of resistors, capacitors, inductors, or a combination thereof, so as to release the bus voltage, so that when the bus voltage is high, the bus voltage can be reduced by rapidly consuming or storing the electric energy of the converted dc bus.

In some embodiments, the bus discharge module 123 may also be configured to store the bus voltage, such that when the bus voltage is low, the bus voltage may be raised by discharging the stored electrical energy.

The n busbar capacitors C1, … …, cn are connected in series between two ends of the dc busbar, an input end of the inverter power conversion circuit 124 is connected to the dc busbar, and an output end of the inverter power conversion circuit 124 is connected to the output switch K4 and the output switch K5. The inverter power conversion circuit 124 converts the dc bus voltage into an ac voltage, and outputs the ac voltage to an external device, such as a power grid, an ac load, or the like, through the output switches K4 and K5.

The control circuit 12b is connected to the input switch K1, the input switch K2, the discharge switch K3, the output switch K4, and the output switch K5, and is used for controlling the on or off of the switches. Specifically, the control circuit 12b detects the voltage of each bus capacitor, and determines whether or not each bus capacitor voltage has failed. And when the absolute value of the difference between the voltage on one of the bus capacitors and the fault threshold is detected to be larger than the preset voltage threshold, determining that the voltage of the bus capacitor is faulty. Otherwise, continuing to detect until any bus capacitor voltage fault is determined. The fault threshold is a number n of dividing the bus voltage by the bus capacitance, and the preset voltage threshold can be a value according to actual needs, for example, 0.1V. The voltage of each bus capacitor can be measured through a voltage sensor, and the sampled current can be converted into the sampled voltage through a sampling resistor for measurement.

In some embodiments, the reasons for the voltage failure of the bus capacitor may include that the bus capacitor itself fails, that circuit elements such as a resistor and an inductor connected to the bus capacitor fail, that a power switch tube in the inverter circuit 12a fails, and the like, and the reasons for the voltage failure of the bus capacitor are not limited in this application.

The control circuit 12b is also configured to determine an operating state of the inverter 12 in response to a voltage failure of at least one of the n bus capacitances. The operating states of the inverter 12 include a stopped output state and a non-stopped output state. Determining the operating state of the inverter 12 can be achieved by detecting the on states of the output switch K4 and the output switch K5. For example, when the output switch K4 is disconnected from the output switch K5, the electrical connection between the external device and the inverter power conversion circuit 124 is disconnected, and the inverter 12 is in a stopped output state, whereas when the output switch K4 is turned on with the output switch K5, the output voltage of the inverter power conversion circuit 124 is normally transmitted to the external device, and the inverter 12 is in an un-stopped output state.

The control circuit 12b is further configured to open the input switch K1, the input switch K2, and start the bus discharge module 123 in response to at least one of the n bus capacitances having a voltage failure and the inverter 12 being in a stopped output state. Specifically, when the inverter 12 is in the stopped output state, the control circuit 12b may disconnect the input switch K1 from the input switch K2, disconnect the electrical connection between the inverter 12 and the photovoltaic module 11a, and disconnect the electrical connection between the inverter 12 and the battery 11b, thereby realizing the disconnection of the power supply of the power source 11 to the inverter 12, to prevent the bus voltage from continuing to rise. The control circuit 12b simultaneously activates the bus bar discharge module 123 such that the bus bar voltage drops, thereby reducing the risk of a bus bar capacitor explosion causing the inverter 12 to fail.

The control circuit 12b is further configured to further obtain a comparison result of the photovoltaic maximum voltage and the first voltage threshold, or obtain a comparison result of the battery maximum voltage and the third voltage threshold when the inverter 12 is in the non-stop output state, and execute a corresponding control method. Specifically, taking the embodiment shown in fig. 3 as an example, the inverter 12 includes m input switches K1, and the m input switches K1 are respectively connected to the m photovoltaic modules 11a correspondingly.

In the present embodiment, the control circuit 12b turns off the m input switches K1 and K2 and starts the bus discharging module 123 in response to at least one bus capacitor voltage failure of the n bus capacitors and the inverter 12 being in the stop output state.

The control circuit 12b is further configured to further obtain a comparison result between the photovoltaic maximum voltage and the first voltage threshold when the inverter 12 is in the non-stop output state, and execute a corresponding control method. The photovoltaic maximum voltage is the maximum value of the output voltages of the m photovoltaic modules 11a, and the first voltage threshold is proportional to the bus voltage. Specifically, the relationship between the first voltage threshold V1 and the bus voltage VBUS satisfies the formula (1):

where Vm is the maximum power point operating voltage of the photovoltaic module 11a corresponding to the maximum output voltage, and Voc is the open circuit voltage of the photovoltaic module 11a corresponding to the maximum output voltage.The value of (2) can be determined according to the characteristics of the photovoltaic module 11a and the actual application scenario, for example, 0.8.

When the control circuit 12b detects that the photovoltaic maximum voltage is smaller than the first voltage threshold, m input switches K1 are turned off, the output switch K4 and the output switch K5 are turned off, and the discharge switch K3 is turned on.

When the control circuit 12b detects that the photovoltaic maximum voltage is greater than or equal to the first voltage threshold, it is further determined whether there is a bus capacitor having a voltage greater than the second voltage threshold V2 among the n bus capacitors.

It will be appreciated that, after determining that the photovoltaic maximum voltage is less than the first voltage threshold V1, the control circuit 12b characterizes that if shutdown is performed at this time, the output voltage of the photovoltaic module 11a with the largest output voltage is raised to the open circuit voltage, and the bus voltage is not further raised, so that the bus capacitance is not affected more seriously, and the shutdown can be performed immediately to turn off the input and output switches. After determining that the maximum photovoltaic voltage is greater than or equal to the first voltage threshold, it is indicated that if the shutdown is performed at this time, the output voltage of the photovoltaic module 11a with the maximum output voltage will rise to the open circuit voltage, the bus voltage may be further raised, and the specific bearing condition of each bus capacitor is still not determined, so that the shutdown cannot be performed immediately. At this time, by detecting the voltage of each bus capacitor, if the voltage of any one of the n bus capacitors is greater than the second voltage threshold V2, the probability of exceeding the withstand voltage value of the bus capacitor in a short time is higher, otherwise, that is, the voltage of all the n bus capacitors is less than or equal to the second voltage threshold V2, and the probability of exceeding the withstand voltage value of the bus capacitor in a short time is lower.

Accordingly, when the control circuit 12b detects that a bus capacitor with a voltage greater than the second voltage threshold V2 exists in the n bus capacitors, the m input switches K1, K4 and K5 are turned off, and the bus discharging module 123 is started. When the control circuit 12b detects that the voltages of the n bus capacitors are smaller than or equal to the second voltage threshold V2, the input switch K1 and the input switch K2 are turned off, the output switch K4 and the output switch K5 are turned off, and the bus discharging module 123 is started.

It can be understood that when the maximum photovoltaic voltage is greater than or equal to the first voltage threshold and the voltage of any one of the n bus capacitors is greater than the second voltage threshold V2, the bus capacitor is highly likely to explode due to the voltage exceeding the withstand voltage value in a short time, and the input end and the output end of the inverter 12 should be cut off at the first time to prevent the fault from diffusing to the external load or the power grid of the photovoltaic module 11a at the input end and the output end. Meanwhile, the bus discharging module 123 is started, so that the bus voltage is reduced, the risk of explosion of more bus capacitors due to voltage exceeding a withstand voltage value is reduced, and the severity of faults is reduced.

And when the voltage of all the n bus capacitors is smaller than or equal to the second voltage threshold V2, the voltage of other bus capacitors which are not faulty at the moment cannot rise to exceed the withstand voltage value in a short time. At this time, the normal operation state of the inverter 12 can be maintained, and the m input switches K1 are turned off first, and then the output switch K4 and the output switch K5 are turned off, and then the bus discharging module 123 is started, so that the bus voltage drops, and the risk of explosion of the bus capacitor due to the voltage exceeding the withstand voltage value is further reduced.

Taking the embodiment shown in fig. 4 as an example, the inverter 12 includes m input switches K1 and p input switches K2, where the m input switches K1 are respectively connected to the m photovoltaic modules 11a correspondingly, and the p input switches K2 are respectively connected to the p storage batteries 11b correspondingly.

Unlike the embodiment shown in fig. 3, the control circuit 12b needs to obtain not only the comparison result of the photovoltaic maximum voltage with the first voltage threshold value, but also the comparison result of the battery maximum voltage with the third voltage threshold value. The maximum battery voltage is the maximum value of the output voltages of the p secondary batteries 11b, and the third voltage threshold is proportional to the bus voltage. Specifically, the relationship between the third voltage threshold V3 and the bus voltage VBUS satisfies the formula (2):

where Vo is the full-load voltage of the battery 11b corresponding to the maximum output voltage, and Vb is the no-load voltage of the battery 11b corresponding to the maximum output voltage.The value of (2) may be determined according to the characteristics of the battery 11b and the actual application scenario, for example, 0.9.

When the control circuit 12b detects that the photovoltaic maximum voltage is smaller than the first voltage threshold and the battery maximum voltage is smaller than the third voltage threshold, the direct shutdown is performed, m input switches K1 and p input switches K2 are disconnected, the output switches K4 and K5 are disconnected, and the discharge switch K3 is turned on. Otherwise, further judging whether the bus capacitors with the voltage larger than the second voltage threshold V2 exist in the n bus capacitors. The subsequent control strategy is similar to that of fig. 3, and in fig. 3, the control method for turning off m input switches K1 is shown in fig. 4, that is, turning off m input switches K1 and p input switches K2, and the rest is the same, and will not be described herein.

Therefore, the control circuit 12b provided by the application can judge whether the bus capacitor fails according to the voltage condition of each bus capacitor, so that different control strategies are further executed under the condition that the bus capacitor fails, the probability of explosion of each bus capacitor in a short time is more accurately judged, the fault diffusion of the inverter 12 after the bus capacitor is exploded is effectively reduced, and the loss and bad experience sense of customers caused by the fault are reduced.

Please refer to fig. 5 to fig. 7, which are two other schematic diagrams of the inverter 12 provided in the present application. A neutral point N can be arranged among the N bus capacitors, for example, the neutral point N is arranged on the bus capacitor C _(n/2) And C _(n/2)+1 Between them. As shown in fig. 5, the neutral point N may be connected to the first conversion circuit 121, the second conversion circuit 122. As shown in fig. 6, the neutral point N may also be connected to an inverter power conversion circuit 124. As shown in fig. 7, the neutral point N may also be connected to both the first conversion circuit 121, the second conversion circuit 122, and the inverter power conversion circuit 124.

Referring to fig. 8, fig. 8 is a flowchart of a protection method for a bus capacitor voltage fault provided in the present application. The protection method for the bus capacitor voltage fault provided by the application can be executed by the control circuit 12b, and the protection method for the bus capacitor voltage fault comprises the following steps:

step S1, detecting the voltage of each bus capacitor, and judging whether each bus capacitor voltage fails.

In the application, by detecting the voltage of each bus capacitor, when the absolute value of the difference between the voltage on any bus capacitor and the fault threshold is detected to be larger than the preset voltage threshold, the voltage fault of the bus capacitor is determined, wherein the fault threshold is the bus voltage divided by n. Otherwise, continuing to detect until the voltage on any bus capacitor meets the fault condition. For example, the preset voltage threshold may be set to 20V. The voltage of each bus capacitor can be measured through a voltage sensor, and the sampled current can be converted into the sampled voltage through a sampling resistor for measurement.

Step S2 determines whether the inverter 12 stops outputting.

In this application, to determine a corresponding control policy according to the operating state of the inverter 12, the operating state of the inverter 12 may be determined when at least one bus capacitor is detected to be faulty. The determination of the operating state of the inverter 12 can be achieved by detecting the on states of the output switch K4 and the output switch K5. For example, when the output switch K4 is disconnected from the output switch K5, the electrical connection between the output terminal of the inverter 12 and the inverter power conversion circuit 124 is disconnected, and the inverter 12 is in a stopped output state, whereas when the output switch K4 is turned on with the output switch K5, the output voltage of the inverter power conversion circuit 124 is normally transmitted to the output terminal, and the inverter 12 is in an un-stopped output state. Step S3 is performed when the inverter 12 is in the stopped output state, and step S4 is performed when the inverter 12 is in the non-stopped output state.

Step S3, the photovoltaic input switch K1 is turned off, and the bus discharging module 123 is started.

In this application, when the inverter 12 is in the output-stopped state, the control circuit 12b may disconnect the input switch K1, so that the electrical connection between the inverter 12 and the photovoltaic module 11a is disconnected, and the power supply of the power supply 11 to the inverter 12 is disconnected, thereby preventing the bus voltage from continuously rising. In addition, the control circuit 12b also activates the bus bar discharging module 123 such that the bus bar voltage drops, thereby reducing the risk of the bus bar capacitor explosion causing the inverter 12 to malfunction.

Step S4, determining whether the photovoltaic maximum voltage is less than a first voltage threshold.

In the present application, when the inverter 12 is in the non-stop output state, the control circuit 12b further compares the photovoltaic maximum voltage with the first voltage threshold, specifically, when it is detected that the photovoltaic maximum voltage is smaller than the first voltage threshold, step S6 is performed, otherwise, step S5 is performed.

Step S5, judging whether the bus capacitor with the voltage larger than a second voltage threshold V2 exists in the n bus capacitors.

In the present application, when it is detected that there is a bus capacitor with a voltage greater than the second voltage threshold V2 in the n bus capacitors, step S6 is executed, otherwise, step S7 is executed.

Step S6, the photovoltaic input switch K1, the output switch K4 and the output switch K5 are disconnected, and the bus discharging module 123 is started.

In step S7, the input switch K1 is turned off, the output switch K4 and the output switch K5 are turned off, and the bus discharging module 123 is started.

In this application, when the control circuit 12b detects that there is a bus capacitor having a voltage greater than the second voltage threshold V2 among the n bus capacitors, the input switch K1, the output switch K4, and the output switch K5 are turned off, and the bus discharging module 123 is started. When the control circuit 12b detects that the voltages of the n bus capacitors are less than or equal to the second voltage threshold V2, the input switch K1 is turned off, the output switch K4 and the output switch K5 are turned off, and the bus discharging module 123 is started.

Referring to fig. 9, fig. 9 is another flowchart of a protection method for a bus capacitor voltage fault provided in the present application. The difference from the protection method of the bus capacitor voltage fault shown in fig. 8 is that in this embodiment, the battery input switch K2 is turned off together when the photovoltaic input switch K1 is turned off. And step S4 is to determine whether the maximum photovoltaic voltage is less than the first voltage threshold V1 and the maximum battery voltage is less than the third voltage threshold V3, if yes, step S6 is executed, otherwise step S5 is executed.

Therefore, the protection method for the bus capacitor voltage faults can judge the fault condition of each bus capacitor by monitoring the voltage and the total bus voltage of each bus capacitor in real time, and under the condition of the bus capacitor voltage faults, the sequence of the disconnection of the input switch K1, the input switch K2, the discharge switch K3, the output switch K4 and the output switch K5 is controlled so as to achieve the purpose of preventing the bus capacitor from explosion, prevent the fault from influencing expansion and reduce the loss and bad experience feeling of customers caused by the faults.

It will be appreciated by persons skilled in the art that the above embodiments have been provided for the purpose of illustration only and not as a definition of the limits of the present application, and that appropriate modifications and variations of the above embodiments are within the scope of the invention as claimed.

Claims (12)

1. The utility model provides a protection method of bus capacitor voltage trouble, is applied to the dc-to-ac converter, characterized in that, the dc-to-ac converter includes bus discharging module, output switch, contravariant power conversion circuit, n bus capacitor, one or more photovoltaic input switch and one or more photovoltaic power conversion circuit, one or more photovoltaic power conversion circuit corresponds one or more photovoltaic module through one or more input switch connection, every photovoltaic power conversion circuit all connects the direct current bus, n bus capacitor connects in series in proper order between the both ends of direct current bus, contravariant power conversion circuit connects the direct current bus to connect electric wire netting and/or load through output switch, bus discharging module is used for reducing the bus voltage of direct current bus, the method includes:

and responding to the voltage fault of at least one bus capacitor in the n bus capacitors, and opening the output switch, opening the photovoltaic input switch, and starting the bus discharging module.

2. The method of protecting against a bus capacitor voltage fault of claim 1, further comprising:

responding to the voltage fault of at least one of the n bus capacitors and the output switch is conducted, and executing a corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold value;

wherein the photovoltaic maximum voltage is a maximum value of output voltages of the one or more photovoltaic modules, and the first voltage threshold is proportional to the bus voltage.

3. The method for protecting against a bus capacitor voltage fault according to claim 2, wherein said performing a corresponding control method based on a comparison of said photovoltaic maximum voltage with a first voltage threshold comprises:

and in response to the photovoltaic maximum voltage being less than the first voltage threshold, opening the output switch and the one or more photovoltaic input switches and starting the bus discharge module.

4. The method for protecting against a bus capacitor voltage fault according to claim 2, wherein said performing a corresponding control method based on a comparison of said photovoltaic maximum voltage with a first voltage threshold comprises:

and in response to the photovoltaic maximum voltage being greater than or equal to the first voltage threshold, and the n bus capacitances having a voltage greater than a second voltage threshold, disconnecting the output switch from the one or more photovoltaic input switches and starting the bus discharge module.

5. The method for protecting against a bus capacitor voltage fault according to claim 2, wherein the corresponding control method is performed according to a comparison result of the photovoltaic maximum voltage and a first voltage threshold, comprising:

and in response to the photovoltaic maximum voltage being greater than or equal to the first voltage threshold and the voltages of the n busbar capacitors being less than or equal to the second voltage threshold, switching off the one or more photovoltaic input switches first, switching off the output switch, and starting the busbar discharge module.

6. The method of claim 1, wherein the inverter further comprises one or more battery input switches and one or more battery power conversion circuits, the one or more battery power conversion circuits being correspondingly connected to one or more batteries through the one or more battery input switches, each of the battery power conversion circuits being connected to a dc bus, the method further comprising:

responding to the voltage fault of at least one bus capacitor in the n bus capacitors, and the output switch is disconnected, disconnecting the battery input switch and starting the bus discharging module;

responding to the voltage failure of at least one bus capacitor in the n bus capacitors and the output switch is conducted, and executing a corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold value and the comparison result of the battery maximum voltage and the third voltage threshold value;

the photovoltaic maximum voltage is the maximum value of the output voltage of the one or more photovoltaic modules, the battery maximum voltage is the maximum value of the output voltage of the one or more batteries, and the first voltage threshold and the third voltage threshold are both in direct proportion to the bus voltage.

7. The method according to claim 6, wherein the performing the corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold and the comparison result of the battery maximum voltage and the third voltage threshold comprises:

in response to the photovoltaic maximum voltage being less than the first voltage threshold and the battery maximum voltage being less than the third voltage threshold, the output switch, the one or more photovoltaic input switches, and the one or more battery input switches are opened and the bus discharge module is started.

8. The method according to claim 6, wherein the performing the corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold and the comparison result of the battery maximum voltage and the third voltage threshold comprises:

in response to the photovoltaic maximum voltage being greater than or equal to the first voltage threshold, and there being a bus capacitor of the n bus capacitors having a voltage greater than a second voltage threshold, opening the output switch, the one or more photovoltaic input switches, and the one or more battery input switches, and starting the bus discharge module; or alternatively

And in response to the maximum voltage of the battery being greater than or equal to the third voltage threshold, and the n bus capacitances having a voltage greater than a second voltage threshold, disconnecting the output switch, the one or more photovoltaic input switches, and the one or more battery input switches, and starting the bus discharge module.

9. The method according to claim 6, wherein the performing the corresponding control method according to the comparison result of the photovoltaic maximum voltage and the first voltage threshold and the comparison result of the battery maximum voltage and the third voltage threshold comprises:

responding to the fact that the photovoltaic maximum voltage is greater than or equal to the first voltage threshold value, and the voltages of the n busbar capacitors are smaller than or equal to the second voltage threshold value, firstly disconnecting the one or more photovoltaic input switches and the one or more battery input switches, then disconnecting the output switch, and starting the busbar discharging module; or alternatively

And in response to the maximum voltage of the battery being greater than or equal to the third voltage threshold and the voltages of the n busbar capacitors being less than or equal to the second voltage threshold, disconnecting the one or more photovoltaic input switches and the one or more battery input switches, disconnecting the output switch, and starting the busbar discharge module.

10. The method of claim 1, wherein the inverter further comprises a discharge switch connected between the bus discharge module and the dc bus, the activating the bus discharge module comprising: and turning on the discharge switch.

11. The protection method for a bus capacitor voltage fault as claimed in any one of claims 1 to 10, wherein the bus capacitor voltage fault comprises:

the absolute value of the difference between the voltage of the bus capacitor and the fault threshold is larger than a preset voltage threshold;

wherein the fault threshold is the bus voltage divided by n.

12. An inverter, characterized in that the inverter comprises a control circuit for performing the protection method of a bus capacitor voltage fault as claimed in any one of claims 1 to 11.