JP6710786B2 - Control system, moving body and control method - Google Patents

Description

The present invention relates to a control system, a moving body, and a control method.
The present application claims priority based on Japanese Patent Application No. 2017-023374 filed on February 10, 2017, the content of which is incorporated herein by reference.

2. Description of the Related Art In recent years, a technique of electrifying a driving method of a moving body has been known (for example, see Patent Document 1). Such a moving body is provided with a power storage unit, and it is necessary to efficiently obtain power from the electric power stored in the power storage unit. Patent Document 1 discloses an electric circuit in which a plurality of power storage units are connected in series. By forming a power source in which a plurality of storage batteries are connected in series, it is possible to obtain a voltage higher than that of a single storage battery, where the power supply voltage is the total value of the voltages of the storage batteries.

As an example of a storage battery, there is a storage battery including a storage battery main body and a protection switch (switch) that switches a connection state between the storage battery main body and a terminal of the storage battery. The rating of the storage battery protection switch is determined based on the voltage of the storage battery body. For example, the allowable voltage in the open state of the protection switch is determined to be a voltage higher than the voltage of the storage battery main body.

Japanese Patent Laid-Open No. 2012-34515

However, when a plurality of storage batteries having such a protection switch are connected in series to form a power supply, the power supply voltage of the power supply exceeds the allowable voltage of the protection switch of each storage battery forming the power supply. There are cases.
An aspect of the present invention is to provide a control system, a moving body, and a control method capable of further increasing the reliability of a switch in a closed circuit in which a power source, a switch, and a load are connected in series. To do.

A control system according to one aspect of the present invention includes a power supply, a first switch, and a closed circuit that electrically connects a load in series; a power storage unit that is connected in parallel to the load; A protection unit for suppressing a voltage applied to the first switch from being in an overvoltage state in which the voltage applied to the first switch exceeds an allowable voltage of the first switch; and the protection unit is in an open state of the first switch. In this case, the operating state of the load is adjusted to prevent the first switch from entering the overvoltage state.

In the control system, the load includes a drive unit that drives an electric motor, and the protection unit shuts off power supply from the drive unit to the electric motor when the first switch is in the open state. It may be possible to suppress the first switch from entering the overvoltage state by controlling the above.

In the control system, the protection unit may detect an open state of the first switch based on a voltage of the power storage unit and suppress the first switch from being in the overvoltage state.

The control system includes a second switch connected in series to the power source, the first switch, and the load in the closed circuit, and the protection unit has the first switch in the open state. In this case, the first switch may be prevented from being in the overvoltage state by opening the second switch.

In the above control system, when the first switch is in the open state, the protection unit opens the second switch by limiting the power consumption of the load, thereby opening the first switch. May be prevented from entering the overvoltage state.

In the control system, the power source may include a plurality of batteries connected in series, and the second switch may be provided in the closed circuit including the plurality of batteries.

In the control system, the allowable voltage of the first switch in the open state may be smaller than the voltage value of the power supply.

A mobile body according to another aspect of the present invention is a closed circuit that electrically connects a power source, a first switch, and a load in series; a power storage unit that is connected in parallel to the load; A switch that prevents the voltage applied to the first switch from becoming an overvoltage state in which the voltage applied to the first switch exceeds the allowable voltage of the first switch; When the open state is achieved, the operating state of the load is adjusted to prevent the first switch from entering the overvoltage state.

A control method according to yet another aspect of the present invention includes a closed circuit that electrically connects a power supply, a first switch, and a load in series; and a power storage unit that is connected in parallel to the load. The control method according to claim 1, wherein when the first switch is in an open state, the operating state of the load is adjusted so that the state of the first switch is the voltage applied to the first switch. It includes suppressing an overvoltage state that exceeds the allowable voltage of the first switch.

According to the above configuration, the control system includes a power supply, a first switch, a closed circuit that electrically connects a load in series, a power storage unit that is connected in parallel to the load, and a state of the first switch. A protection unit that suppresses a voltage applied to the first switch from being in an overvoltage state in which the voltage exceeds the allowable voltage of the first switch; and the protection unit opens the first switch. When the load becomes low, the operating state of the load is adjusted to prevent the first switch from entering the overvoltage state. This makes it possible to provide a control system, a moving body, and a control method in which the protection unit can suppress the overvoltage state of the first switch and further improve the reliability of the first switch.

It is a figure which shows an example of a saddle type electric vehicle to which the electric circuit of 1st Embodiment is applied. FIG. 3 is a block diagram showing a schematic configuration of a control system for controlling traveling of the electric motorcycle of the present embodiment. It is a figure for demonstrating operation|movement when the process for avoiding the influence of the unexpected event of embodiment is implemented. It is a flow chart of processing for avoiding the influence of a sudden event of an embodiment.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are viewed in the direction of the reference numerals, and the left, right, front, and rear directions mean the directions viewed from the driver.

FIG. 1 is a diagram showing an example of a saddle-ride type electric vehicle to which the electric circuit of the embodiment is applied. FIG. 1 shows an example of a scooter-type saddle-ride type electric vehicle having a low floor (hereinafter referred to as “electric motorcycle”). The electric motorcycle 1 shown in FIG. 1 is an example of a moving body. The body frame F of the electric motorcycle 1 supports the front fork 11 so as to be steerable. A front wheel WF is pivotally supported on the lower end of the front fork 11. A steering handle 16 is connected to an upper portion of the front fork 11.

The front end of the swing arm 17 is swingably supported on the rear portion of the vehicle body frame F.
An electric motor 135 (electric motor) is provided at the rear end of the swing arm 17. The rear wheel WR is rotationally driven by the power output from the electric motor 135.

A pair of left and right seat frames 15 are provided so as to be connected to the rear portion of the vehicle body frame F. The passenger seat 21 is supported by the seat frame 15. A body cover 22 made of synthetic resin is attached to the body frame F to cover the body frame F.

FIG. 1 shows an arrangement example of some electric components. For example, a battery storage portion 120C made of synthetic resin is provided below the passenger seat 21 and between the pair of left and right seat frames 15. The battery 120 is detachably stored in the battery storage portion 120C.

In the electric motorcycle 1, the electric motor 135 provided on the swing arm 17 is driven by the PDU (Power Driver Unit) 130 by the electric power supplied from the battery 120 via the electric circuit 110, and the electric motor 135 is driven. The vehicle travels by transmitting the rotational power at that time to the rear wheels WR. For example, the battery 120 of the embodiment is divided into a plurality of battery units such as the batteries 121 and 122. The traveling of the electric motorcycle 1 is controlled by, for example, an ECU (Electric Control Unit) 140 or the like arranged in a proper place inside the vehicle body cover 22 or the like. The charger 150 converts electric power supplied from the outside and charges the battery 120 via the electric circuit 110. The charger 150 may be detachable from the electric motorcycle 1.

FIG. 2 is a block diagram showing a schematic configuration of a control system for controlling traveling of the electric motorcycle 1 of the present embodiment.

The control system 10 includes an electric circuit 110 (closed circuit), a battery 120, a PDU 130 (load), an ECU 140 (protection unit), and a charger 150.
The electric circuit 110 electrically connects the battery 120 (power source and first switch), the contactor 115 (first contactor), and the PDU 130 in series.

The PDU 130 includes an inverter 131, a capacitor 133 (power storage unit), and a voltage detection unit 134. The inverter 131 converts the DC power supplied from the battery 120 into, for example, three-phase AC power under the control of the ECU 140. The capacitor 133 reduces voltage fluctuation due to mechanical load fluctuation of the electric motor 135 and smoothes the voltage. The voltage detection unit 134 detects the voltage on the power supply side of the PDU 130. The electric motor 135 is, for example, a three-phase AC motor.

The battery 120 includes, for example, batteries 121 and 122. The batteries 121 and 122 are examples of a plurality of power storage units. Battery 120 generates a predetermined voltage (for example, its nominal voltage is 48V) by connecting a plurality of single batteries such as a lithium ion battery, a nickel hydrogen battery, and a lead battery in series.

Electric power from the batteries 121 and 122 is supplied to the PDU 130 that drives the electric motor 135 via the electric circuit 110. For example, the inverter 131 of the PDU 130 converts DC into three-phase AC and supplies the electric motor 135. It

For example, the output voltage of the batteries 121 and 122 is stepped down to a low voltage (for example, 12V) by a DC-DC converter (not shown) and supplied to control system components such as the ECU 140. For example, the output voltage of the battery 121 may be allowed to normally change from an upper limit voltage that is 125% of the nominal voltage of the battery 121 to a lower limit voltage that is 90% of the nominal voltage of the battery 121. For example, the output voltage of the battery 122 may be allowed to fluctuate normally from an upper limit voltage that is 125% of the nominal voltage of the battery 122 to a lower limit voltage that is 90% of the nominal voltage of the battery 122.

In addition, a part of the low-voltage power stepped down by the DC-DC converter is supplied to the control battery 125 (not shown) and general electric components such as a lighting device (not shown).

The batteries 121 and 122 can be charged by, for example, a charger 150 connected to a power supply of AC 100V.

The battery 121 of the embodiment includes a battery main body 1211, a BMU (Battery Managing Unit) 1212, a switch 1213, a high potential side terminal 121P (first pole terminal), and a low potential side terminal 121N (second pole terminal). Equipped with. Similarly, the battery 122 includes a battery body 1221, a BMU 1222, and a switch 1223. In the following description, the BMU 1212 and the BMU 1222 may be collectively referred to simply as the BMU. The BMU of each battery monitors the charging/discharging status of the batteries 121, 122, the amount of stored electricity, the temperature, and the like. Information on the monitored batteries 121 and 122 is shared with the ECU 140. The BMU limits the charging/discharging of the battery main body 1211 or the like by controlling the switch 1213 or the like according to a control command from the ECU 140 described later or the above monitoring result. Details of the switch 1213 will be described later. The BMU 1212 communicates with the ECU 140 via a connector (not shown). The BMU 1212 is supplied with control power via its connector.
The battery 122 is similar to the battery 121. The switches 1213 and 1223 may be semiconductor devices such as FETs.

Information about an output request from the throttle (accelerator) sensor 180 is input to the ECU 140. The ECU 140 controls the contactor 115, the battery 120, the PDU 130, and the like based on the input output request information. For example, the ECU 140 can control charging and discharging of the battery 120 by controlling the battery 120. The ECU 140 controls the contactor 115 to switch the supply of electric power to the battery 120 and the discharge from the battery 120. The ECU 140 controls driving of the electric motor 135 by controlling electric power supplied from the PDU 130 to the electric motor 135. In the block diagram shown in FIG. 2, the charger 150 is also included in the control system 10 that controls the traveling of the electric motorcycle 1. However, the charger 150 is configured to be detachable from the electric motorcycle 1. Good. In this case, the charger 150 may be provided outside the electric motorcycle 1. A general method may be selected as the charging method by the charger 150.

The contactor 115 (second switch) is provided between the low potential side terminal 121N of the battery 121 and the high potential side terminal 122P of the battery 122. The contactor 115 connects and disconnects the low potential side terminal 121N of the battery 121 and the high potential side terminal 122P of the battery 122. The contactor 115 connects the batteries 120 in series in a conductive state. The contactor 115 disconnects the series connection of the battery 120 in the cutoff state. The period in which the contactor 115 is in the cutoff state includes at least the period in which the charger 150 supplies power to the battery 120.

The allowable voltage of the contactor 115 when the contactor 115 is in the open state is set sufficiently higher than the voltage of the battery 120, and is at least higher than the upper limit value (maximum voltage value) of the fluctuation range of the voltage of the battery 120. It shall be large.

[Example of connection configuration of drive system of electric circuit]
The battery 120 of the drive system of the electric circuit 110, the contactor 115, and the PDU 130 are electrically connected in series by the electric circuit 110. As described above, the battery 120 includes the battery 121 and the battery 122, and the battery 121 and the battery 122 can be connected in series. A battery main body 1211 and a switch 1213 are built in the battery 121. The battery 122 has a battery body 1221 and a switch 1223 built therein.

The set of the battery body 1211 and the battery body 1221 is an example of a power supply. The switch 1213 or the switch 1223 is an example of a first switch. The PDU 130 is an example of a load. The electric circuit 110 electrically connects the battery 120, the contactor 115, and the PDU 130 in series. That is, the electric circuit 110 electrically connects the battery main body 1211 and the battery main body 1221, the switch 1213 or the switch 1223, the contactor 115, and the PDU 130 in series. The capacitor 133 and the voltage detection unit 134 are connected in parallel to the power supply line of the PDU 130.

[Operation of electric circuit]
The ECU 140 acquires the state of the battery 120 from the BMU of the battery 120. The ECU 140 acquires the power supply side voltage of the PDU 130 from the voltage detection unit 134 of the PDU 130. The ECU 140 detects a user operation from the throttle sensor 180 and the like. For example, the ECU 140 controls the contactor 115 and the PDU 130 based on the collected information.

For example, the ECU 140 uses the external charger 150 or the like to perform a process for charging the battery 120 with the electric power of the charger 150. Further, ECU 140 performs a process of precharging capacitor 133 by detecting the user's operation and supplying electric power to PDU 130 to drive electric motorcycle 1 in response to the user's request. In addition, the ECU 140 implements a process for driving the electric two-wheeled vehicle 1 by driving the PDU 130 according to the user's operation. These treatments may be performed according to general procedures.

The ECU 140 of the embodiment further executes “processing for a sudden event that occurs while the electric motorcycle 1 is in operation”.
The sudden event in the present embodiment refers to an operation performed to protect the configuration, an operation performed to maintain a safe state, and the like while the electric motor 135 is being driven by the drive unit 130. This is an event that has resulted in a result different from the result of the processing requested by the user as a result of the execution of each functional part of.

A more specific example will be described.
For example, the switch 1213 or the switch 1223 of the battery 120 is not controlled to the cutoff state by the process of the ECU 140 during the above control, but is controlled by the process of the BMU in the battery 120 or the like. That is, an event in which the switch 1213 or the switch 1223 is in the cutoff state during the above control is included in the unexpected event.

[Effect of unexpected event]
While the power is being supplied to the PDU 130, if the above-mentioned sudden event occurs and either the switch 1213 or the switch 1223 is turned off, the power supply from the battery 120 to the PDU 130 is stopped.

On the other hand, the ECU 140 continues to supply the control signal for driving the electric motor 135 to the PDU 130 while the state in which the occurrence of the sudden event cannot be detected continues. Since no electric power is supplied from the battery 120, the PDU 130 continues to drive the electric motor 135 by consuming the electric power stored in the capacitor, but when the amount of stored electricity in the capacitor is exhausted, the electric motor 135 cannot be driven. (First effect).

In the case of the embodiment, the allowable voltage of the switch 1213 or the switch 1223 of the battery 120 is smaller than the power supply voltage of the battery 120. When the above-mentioned sudden event occurs, the voltage applied to the switch 1213 switch 1223 may exceed the allowable voltage of the switch 1213, or the voltage applied to the switch 1223 may exceed the allowable voltage of the switch 1223 ( Second effect). This second effect may cause a situation in which the electric motorcycle 1 cannot travel. The second effect needs to be avoided so that such a situation does not occur.

[Avoiding the effects of unexpected events]
The electric circuit 10 according to the embodiment avoids the above influence by performing the following processing. The details will be described below.

FIG. 3 is a diagram for explaining the operation when the processing for avoiding the influence of the unexpected event of the embodiment is performed. This figure shows the change in the voltage Vin(V) of the capacitor 133 after the occurrence of the sudden event.

FIG. 4 is a flowchart of a process for avoiding the influence of the unexpected event according to the embodiment.
First, at time t1, an unexpected event occurs in which the switch 1213 or the switch 1223 of the battery 120 is cut off (SA0). As a result, the voltage of the capacitor 133 begins to drop, but the driving of the electric motor 135 continues (SA1).

Next, it is determined whether or not the voltage of the capacitor 133 has dropped below a predetermined threshold value TH (SA2). When the voltage of the capacitor 133 is not lower than the threshold value TH, the ECU 140 returns the process to SA1.

Next, when the voltage of the capacitor 133 is lower than the threshold value TH, the ECU 140 controls the PDU 130 to stop supplying current to the electric motor 135 (SA3). That is, at time t3, all the FETs included in the PDU 130 as semiconductor switches are turned off. As a result, the electric current flowing in the direction of supplying electric power to the electric motor 135 on the electric circuit 110 is cut off at two points.

Next, after a lapse of a predetermined time from the time t3, the ECU 140 puts the contactor 115 into the cutoff state (SA4). As a result, at time t5, the electric circuit 110 is cut off at at least two places, and the voltage applied to the switch 1213 or the switch 1223 disappears, thereby avoiding the occurrence of the second effect.

The description of the above processing will be supplemented.
When the voltage of the capacitor 133 is consumed by the load (electric motor 135), the voltage of the battery 120 is maintained as it is, and only the voltage of the capacitor 133 drops. Therefore, the potential difference between the voltage of the battery 120 and the voltage of the capacitor 133 is applied to the switch (the switch 1213 or the switch 1223) cut off due to the unexpected event. If this voltage exceeds the allowable voltage of the switch, the switch may be destroyed.

On the other hand, an embodiment is conceivable in which, in addition to the above-mentioned switch, another switch (switch) is arranged in the closed circuit of the electric circuit 10 and this switch is quickly cut off when an unexpected event occurs (implementation). Example 1). When the method of Example 1 is implemented by a mechanical switch (switch), the time required to disconnect the circuit is expected to take about 100 milliseconds.

Instead of the mechanical switch (switch) of the first embodiment described above, a countermeasure realized by an electric switch can be considered (second embodiment). In this case, there is no time delay depending on the mechanical element and the time required for disconnecting the circuit can be shortened, which is preferable from the viewpoint of shortening the response time. By using the electric switch, for example, even when the charge of the capacitor 133 is consumed in about 10 milliseconds, a process for suppressing the consumption can be performed in the process.

However, when a mechanical switch as a main switch is provided in the electric circuit 110, it is necessary to additionally provide an electric switch. Therefore, in this embodiment, the control of the PDU 130 is combined in order to secure the responsiveness without adding an electric switch.

The PDU 130 includes an inverter 131 for driving the electric motor 135, that is, a semiconductor switch. The PDU 130 uses this semiconductor switch to cut off the current of the electric circuit 110 when a predetermined condition is satisfied.

According to the embodiment, the control system includes a closed circuit that electrically connects the main body of the battery 120, a switch (first switch) in the battery 120, and the PDU 130 in series, and a capacitor connected in parallel to the PDU 130. 133 and an ECU 140 (protection unit) that suppresses the state of the first switch from becoming an overvoltage state in which the voltage applied to the first switch exceeds the allowable voltage of the first switch. The EUC 140 adjusts the operating state of the PDU 130 and limits the power consumption when the first switch is in the open state, thereby suppressing the first switch from being in the overvoltage state, and thus the first switch described above. The reliability of the switch can be further increased.

The overvoltage state of the first switch is a state in which the voltage applied to the first switch exceeds the allowable voltage of the first switch. The allowable voltage of the first switch is the maximum allowable terminal voltage in the open state. The open state of the first switch includes the state after the transition from the conductive state in which the electric circuit 10 is energized to the open state.

The overvoltage state described above is included in a state in which the voltage of the capacitor 133 has dropped below a desired voltage (power supply voltage). More specifically, the above-mentioned overvoltage state is included in a state in which the voltage of the capacitor 133 has dropped to a voltage equal to or lower than the independent voltage of the battery 121 or the battery 122.

The load of the capacitor 133 includes the electric motor 135 and the PDU 130 (driving unit) that drives the electric motor 135. The ECU 140 may prevent the first switch from becoming an overvoltage state by controlling the PDU 130 to cut off the power supply to the electric motor 135 when the first switch is opened.

Further, the ECU 140 may suppress the first switch from being in the overvoltage state by detecting the open state of the first switch based on the voltage of the capacitor 133.

Further, the control system 10 includes, in the electric circuit 110, a main body of the battery 120, a switch (first switch) in the battery 120, and a contactor 115 (second switch) connected in series to the PDU 130. The ECU 140 may prevent the first switch from being in an overvoltage state by opening the contactor 115 when the first switch is in an open state.

Further, when the first switch is in the open state, the ECU 140 may limit the power consumption of the PDU 130 and then open the contactor 115 to prevent the first switch from becoming an overvoltage state. Good.

Further, the battery 120 includes a plurality of battery bodies connected in series as a power source.
The contactor 115 is provided in the electric circuit 110 including a plurality of battery main bodies, and may open the electric circuit 110 under the control of the ECU 140 to prevent the first switch from becoming an overvoltage state.

Further, the allowable voltage of the first switch in the open state may be smaller than the voltage value of the power supply.

The ECU 140 according to the embodiment includes a computer system. The ECU 140 records the program for realizing the above-described processing in a computer-readable recording medium, causes the computer system to read the program recorded in the recording medium, and executes the program to perform the various processing described above. You can go. The “computer system” may include an OS and hardware such as peripheral devices. The "computer-readable recording medium" means a writable nonvolatile memory such as a flexible disk, a magneto-optical disk, a ROM, a flash memory, a portable medium such as a CD-ROM, a hard disk built in a computer system, or the like. Storage device.

Further, the "computer-readable recording medium" means a volatile memory (for example, a DRAM (Dynamic) in a computer system serving as a server or a client when a program is transmitted through a network such as the Internet or a communication line such as a telephone line. Random Access Memory)) which holds the program for a certain period of time. Further, the program may be transmitted from a computer system that stores the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium having a function of transmitting information such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Further, the program may be a program for realizing a part of the functions described above. Further, it may be a so-called difference file (difference program) that can realize the above-mentioned functions in combination with a program already recorded in the computer system.

Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to these embodiments and various modifications and substitutions may be made without departing from the scope of the present invention. it can.

1... Electric motorcycle (moving body)
10... Control system 110... Electric circuit (closed circuit)
115... Contactor (second switch)
120, 121, 122... Battery 120C... Battery storage 130... PDU (load)
133... Capacitor (power storage unit)
135...Electric motor 140...ECU (protection unit)
150... Charger 1211, 1221... Battery main body (power source)
1212, 1222...BMU
1213, 1223... Switch (first switch).

Claims (8)

A closed circuit that electrically connects the power supply, the first switch, and the load in series;
A power storage unit connected in parallel to the load;
A protection unit that prevents the state of the first switch from becoming an overvoltage state in which the voltage applied to the first switch exceeds the allowable voltage of the first switch;
A second switch connected in series with the power source, the first switch, and the load in the closed circuit;
Equipped with
The protection unit prevents the first switch from being in the overvoltage state by adjusting an operating state of the load when the first switch is in an open state,
The protection unit prevents the first switch from being in the overvoltage state by opening the second switch when the first switch is in the opening state,
Control system. The load includes a drive unit that drives an electric motor,
When the first switch is in the open state, the protection unit controls the drive unit to cut off power supply to the electric motor, thereby preventing the first switch from being in the overvoltage state. Suppress,
The control system according to claim 1. The protection unit detects an open state of the first switch based on a voltage of the power storage unit and suppresses the first switch from being in the overvoltage state;
The control system according to claim 1 or 2. When the first switch is in the open state, the protection unit opens the second switch after limiting the power consumption of the load, so that the first switch is brought into the overvoltage state. To suppress
The control system according to claim 1. The power source includes a plurality of batteries connected in series,
The second switch is provided in the closed circuit including the plurality of batteries,
The control system according to claim 1 or claim 5. The allowable voltage of the first switch in the open state is smaller than the voltage value of the power supply,
The control system according to any one of claims 1 to 3, claim 5, and claim 6. A closed circuit that electrically connects the power supply, the first switch, and the load in series;
A power storage unit connected in parallel to the load;
A protection unit that prevents the state of the first switch from becoming an overvoltage state in which the voltage applied to the first switch exceeds the allowable voltage of the first switch;
A second switch connected in series with the power source, the first switch, and the load in the closed circuit;
Equipped with
The protection unit prevents the first switch from being in the overvoltage state by adjusting an operating state of the load when the first switch is in an open state,
The protection unit prevents the first switch from being in the overvoltage state by opening the second switch when the first switch is in the opening state,
Moving body. A closed circuit that electrically connects a power supply, a first switch, and a load in series; a power storage unit that is connected in parallel to the load; and a power supply, the first switch, and the load in the closed circuit. A second switch connected in series;
When the first switch is in the open state, the operating state of the load is adjusted so that the state of the first switch is such that the voltage applied to the first switch is the allowable voltage of the first switch. To suppress exceeding overvoltage condition,
Suppressing the first switch from entering the overvoltage state by opening the second switch when the first switch is in the open state.
Control method.

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