Power conversion system

Abstract

To provide a power conversion system capable of suppressing an overvoltage of a DC voltage.SOLUTION: A power conversion system includes a power conversion device, a capacitive element, an overvoltage protection part, and a switching control part. The power conversion device converts a DC power supplied through a circuit switch and a DC circuit. The capacitive element is provided in parallel with the DC circuit. The overvoltage protection part is provided so as to be in parallel with the capacitive element under control. The switching control part closes the circuit switch to start energization in a state in which the overvoltage protection part is connected to the DC circuit to be enabled, and disables the overvoltage protection part after the energization is started.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a power conversion system. [Background technology]

[0002] When a static AC power converter has a DC circuit with a certain capacitance, an overvoltage may occur in the DC circuit when DC power is supplied to the AC power converter. Suppressing the overvoltage of the DC voltage has been desired for some time. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 60-55289 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a power conversion system capable of suppressing an overvoltage of a DC voltage. [Means for solving the problem]

[0005] According to an embodiment, a power conversion system includes a power conversion device, a capacitive element, an overvoltage protection unit, and a switching control unit. The power conversion device converts DC power supplied via a circuit switch and a DC circuit. The capacitive element is arranged in parallel with the DC circuit. The overvoltage protection unit is arranged in parallel with the capacitive element through control. The switching control unit connects the overvoltage protection unit to the DC circuit to enable it, closes the circuit switch, and starts current flow, and then disables the overvoltage protection unit after current flow has started. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a schematic configuration diagram of a power conversion system according to an embodiment; [Figure 2] 5A and 5B are diagrams for explaining a DC voltage waveform according to the embodiment; [Figure 3] FIG. 10 is a diagram for explaining a DC voltage waveform of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, a power conversion system according to an embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions are denoted by the same reference numerals. Duplicate descriptions of those components may be omitted. Electrical connection may simply be referred to as "connected."

[0008] (Embodiment) A power conversion system 1 according to an embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of a power conversion system 1 according to an embodiment.

[0009] The power conversion system 1 includes, for example, a transformer 11, a DC power supply 12, a power conversion device 13, a capacitive element 14, an overvoltage suppression circuit 15, a circuit switch (breaker) 16, and a control unit 20.

[0010] The DC power supply 12 is, for example, a rectifier or a converter. A DC circuit DCL is connected to the output of the DC power supply 12. The DC power supply 12 of the embodiment converts AC power supplied via a transformer 11 into DC power and outputs the DC power to the DC circuit DCL. The DC circuit DCL is provided with a circuit breaker 16. The circuit breaker 16 opens the DC circuit DCL connecting the DC power supply 12 and the power conversion device 13, for example, by control. The DC power supply 12 may be a battery (secondary battery, fuel cell), a DC power supply device, or the like that supplies DC power to the DC circuit DCL.

[0011] The power conversion device 13 converts and outputs DC power supplied via the circuit switch 16 and the DC circuit DCL. An inverter is an example of the power conversion device 13. In this case, the power conversion device 13 supplies AC power converted from DC power to the AC motor M through control. The circuit switch 16 is, for example, a breaker that opens the DC circuit DCL that connects the DC power supply 12 and the power conversion device 13 under control. The capacitive element 14 is connected to the DC circuit DCL. More specifically, the capacitive element 14 is provided in the DC circuit DCL between the circuit switch 16 and the power conversion device 13.

[0012] The overvoltage suppression circuit 15 is provided in parallel with the input of the power conversion device 13 and the capacitive element 14. The overvoltage suppression circuit 15 suppresses the application of an overvoltage to the input of the power conversion device 13.

[0013] For example, the overvoltage suppression circuit 15 includes a DC voltmeter (VDC) 151, a switching control unit (gate condition) 152, a driver circuit 153, and an overvoltage protection unit 154.

[0014] The DC voltmeter 151 detects the voltage of the DC circuit DCL, that is, the input voltage of the power conversion device 13 .

[0015] The switching control unit 152 generates a control signal for controlling the semiconductor switch 154S1 of the overvoltage protection unit 154 based on the detection result of the DC voltmeter 151, a signal (auxiliary contact signal) indicating the state of the circuit switch 16, and a signal from the control unit 20. Using the control signal, the switching control unit 152 connects the overvoltage protection unit 154 to the DC circuit DCL to enable it, closes the circuit switch 16 to start the flow of current, and disables the overvoltage protection unit 154 after the flow of current has started.

[0016] Driver circuit 153 generates a signal for driving semiconductor switch 154S1 based on the control signal generated by switching control section 152, and supplies the signal to semiconductor switch 154S1. Semiconductor switch 154S1 switches ON / OFF upon receiving the signal from driver circuit 153.

[0017] The overvoltage protection unit 154 is configured to be connected in parallel with the capacitive element 14 by control. For example, the overvoltage protection unit 154 includes a snubber circuit 154SN and a semiconductor switch 154S1. One end of the snubber circuit 154SN is connected to the positive electrode of the DC circuit DCL. The snubber circuit 154SN is configured to suppress an overvoltage occurring in the DC circuit DCL. The snubber circuit 154SN is enabled to suppress the overvoltage when a semiconductor switch 154S1 (described later) is in the ON state. The snubber circuit 154SN will be described in detail later.

[0018] The semiconductor switch 154S1 is connected in series to the snubber circuit 154SN. For example, the semiconductor switch 154S1 is an NPN transistor, which is a type of bipolar semiconductor switch element. The emitter of the semiconductor switch 154S1 is connected to the negative electrode of the DC circuit DCL. The collector of the semiconductor switch 154S1 is connected to the other end of the snubber circuit 154SN. Note that the semiconductor switch 154S1 is separate from the multiple power conversion switches that make up the power conversion device 13.

[0019] The snubber circuit 154SN and the semiconductor switch 154S1 connected in series in this manner are connected in parallel to the capacitive element 14.

[0020] A detailed example of the snubber circuit 154SN is shown. The snubber circuit 154SN includes an RC series circuit 154RC and a discharge resistor 154R2. The RC series circuit 154RC includes a resistor 154R1 and a capacitor 154C1 and forms an "RC type snubber circuit." The discharge resistor 154R2 is a resistor for discharging the capacitive element 14. The discharge resistor 154R2 is connected to the negative electrode of the DC circuit DCL via the semiconductor switch 154S1, similar to the RC series circuit 154RC. The constants of the components of the snubber circuit 154SN may be appropriately determined to values ​​that suppress the overvoltage of the DC circuit DCL.

[0021] The control unit 20 controls the power conversion device 13 . The control unit 20 includes an inverter control unit (INV control unit) 21 and an operating state management unit 22. The inverter control unit 21 detects the operating state of the power conversion device 13 and controls the power conversion device 13 in accordance with instructions from a higher-level device. The operating state management unit 22 acquires information generated in accordance with the control of the inverter control unit 21 and generates a signal indicating whether the power conversion device 13 is operating or not.

[0022] <<Processing related to switching control>> The process relating to the switching control will be described with reference to FIGS.

[0023] The switching control unit 152 controls the conduction of the snubber circuit 154SN by controlling the semiconductor switch 154S1. When the DC circuit DCL is not supplied with power, the switching control unit 152 turns on the semiconductor switch 154S1 to connect the snubber circuit 154SN to the DC circuit DCL and waits for the DC circuit DCL to start supplying power. The state in which the DC circuit DCL is not supplied with power means that there is no power supply from the DC power source 12 and power conversion by the power conversion device 13 is stopped.

[0024] The switching control unit 152 opens the circuit switch 16 to disconnect the power conversion device 13 from the DC power supply 12 . With the semiconductor switch 154S1 in the ON state, the switching control unit 152 closes the circuit breaker 16 to start the supply of DC power.

[0025] Fig. 2 is a diagram for explaining the operation at the start of energization in the embodiment, and Fig. 3 is a diagram for explaining the operation at the start of energization in the comparative example. 2(a) shows the change in voltage of the DC circuit DCL over time, and FIG. 2(b) shows the state of the semiconductor switch 154S1 at each time. In the initial stage shown in FIG. 2, the semiconductor switch 154S1 is in the ON state, and the circuit breaker 16 is in the open state. As described above, since the semiconductor switch 154S1 is in the ON state, the overvoltage suppression function of the overvoltage suppression circuit 15 is enabled. At this stage, the voltage of the DC circuit DCL is 0 V. The DC power supply 12 is capable of supplying the rated voltage E to the DC circuit DCL.

[0026] At time t0, when the circuit breaker 16 is closed, the DC circuit DCL is charged by the rated voltage E output by the DC power supply 12, and the voltage rises. At this time, because the semiconductor switch 154S1 remains ON, the overvoltage suppression function of the overvoltage suppression circuit 15 suppresses the overvoltage of the DC circuit DCL. After the voltage fluctuation of the DC circuit DCL has settled, time t1 arrives. Time t1 occurs when a predetermined time has elapsed since the semiconductor switch 154S1 transitioned from the OFF state to the ON state.

[0027] For example, the switching control unit 152 detects that a predetermined time has passed since the circuit switch 16 was closed using a timer in the switching control unit 152, and thus detects that time t1 has arrived. At time t1, the switching control unit 152 switches the semiconductor switch 154S1 from the ON state to the OFF state, which causes small amplitude fluctuations in the DC voltage waveform as shown in Fig. 2(a), but the magnitude of these fluctuations is negligible.

[0028] In contrast to this, in the voltage waveform of the comparative example shown in FIG. 3, closing the circuit switch 16 at time t0 causes an overvoltage that oscillates across the rated voltage E output by the DC power supply 12. Comparing the waveform in FIG. 3 with the waveform in FIG. 2(a), there is a clear difference, and the effect of suppressing overvoltage according to this embodiment is recognized.

[0029] When the power conversion device 13 receives DC power as in this embodiment, a small-capacity capacitor (capacitive element 14) may be connected to the DC input of the power conversion device 13. When the circuit switch (breaker) 16 is turned on in the power conversion system 1 configured in this way, a relatively large current flows through the small-capacity capacitor depending on the rate of change (dV / dt) of the DC voltage after the turning on. This current may cause an excessive surge voltage to be applied between the DC voltages P and N. Depending on the impedance between the power source and the power conversion device 13, an excessive surge voltage (called a "breaker closing surge") may occur.

[0030] It is known that using a snubber circuit is a common method for suppressing surge voltages, but simply connecting a snubber circuit to a DC circuit all the time will result in constant losses, which will reduce efficiency. However, the circuit breaker closing surge occurs only at the moment when the circuit breaker 16 is closed. If a circuit breaker closing surge does not occur, there is no need to constantly protect against overvoltage.

[0031] Therefore, as in the overvoltage protection unit 154 of this embodiment, by combining the snubber circuit 154SN with a semiconductor switch 154S1 and electrically isolating the snubber circuit 154SN from the DC circuit DCL, the loss caused by the snubber circuit 154SN is eliminated, making it possible to suppress the resulting decrease in efficiency.

[0032] In other words, the semiconductor switch 154S1 is kept in the ON state when the power conversion device 13 is started up, and is made to function as a snubber circuit when the circuit breaker 16 is closed. Then, after the circuit switch 16 is closed, the DC voltage of the DC circuit DCL is identified. This causes the DC voltage to fall within a certain range and stabilize. In response to this, the semiconductor switch 154S1 can be turned off. By turning off the semiconductor switch 154S1, a voltage is constantly applied to the semiconductor switch 154S1, but no voltage is applied to the snubber circuit 154SN, thereby reducing loss due to the snubber circuit 154SN.

[0033] By opening the circuit switch 16, the supply of DC power to the power conversion device 13 is stopped, and the power conversion device 13 is brought into a stopped state. Therefore, it is advisable to open the circuit breaker 16 to stop the power conversion device 13, and then turn on the semiconductor switch 154S1.

[0034] According to the above embodiment, the power conversion system 1 includes a power conversion device 13, a capacitive element 14, an overvoltage protection unit 154, and a switching control unit 152. The power conversion device converts DC power supplied via a circuit switch and a DC circuit. The capacitive element is provided in the DC circuit. The overvoltage protection unit is provided so as to be connected in parallel with the capacitive element by control. The switching control unit connects the overvoltage protection unit to the DC circuit and enables it, closes the circuit switch, and starts current flow, and disables the overvoltage protection unit after current flow has started. This makes it possible to suppress overvoltage in the DC voltage.

[0035] The functions described herein and performed by components such as the control unit 20 may be implemented in circuitry or processing circuitry. The circuitry or processing circuitry may include general-purpose processors, application-specific processors, integrated circuits, application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), central processing units (CPUs), graphics processing units (GPUs), conventional circuits, and / or combinations thereof, programmed to perform the described functions. Processors that perform the above functions include transistors and other circuits and are considered circuitry or processing circuitry. The processor for performing the above functions may include or be a programmable processor that executes a program stored in a memory and / or a programmable device that can be reconfigured by data stored in a memory. In this specification, a circuit, unit, or means is hardware that is programmed to realize or performs the described functions, which may be any hardware disclosed herein or any hardware known to be programmed to realize or perform the described functions. If the hardware is a processor that is considered to be a type of circuitry, the circuitry, means, or unit is a combination of hardware and software used to configure the hardware and / or processor.

[0036] According to at least one embodiment described above, a power conversion system includes a power conversion device, a capacitive element, an overvoltage protection unit, and a switching control unit. The power conversion device converts DC power supplied via a circuit switch and a DC circuit. The capacitive element is arranged in parallel with the DC circuit. The overvoltage protection unit is arranged in parallel with the capacitive element by control. The switching control unit connects the overvoltage protection unit to the DC circuit and enables it, closes the circuit switch, and starts current flow, and disables the overvoltage protection unit after current flow has started. This makes it possible to suppress overvoltage in the DC voltage.

[0037] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. [Explanation of symbols]

[0038] 1 Power Conversion System 11. Transformer 12 DC power supply 13 Power conversion equipment 14 Capacitive Elements 15 Overvoltage suppression circuit 16 Circuit breaker 20 Control Unit 152 Switching control unit 154 Overvoltage protection unit

Claims

1. a power conversion device that converts DC power supplied via the circuit switch and the DC circuit; a capacitive element connected to the DC circuit; an overvoltage protection unit provided so as to be connected in parallel with the capacitive element by control; a switching control unit that closes the circuit switch to start energization while the overvoltage protection unit is connected to the DC circuit and enabled, and disables the overvoltage protection unit after energization has started; A power conversion system comprising:

2. The overvoltage protection unit A snubber circuit; a semiconductor switch connected in series with the snubber circuit; Including, a series circuit including the snubber circuit and the semiconductor switch forms an overvoltage protection unit, the overvoltage protection unit is connected in parallel with the capacitive element; The power conversion system of claim 1 .

3. The switching control unit controlling the semiconductor switch to control energization of the snubber circuit; The power conversion system of claim 2 .

4. The snubber circuit comprises: an RC series circuit including a resistor and a capacitor; a discharge resistor for discharging the capacitive element; The power conversion system of claim 2 .

5. The switching control unit The semiconductor switch is turned on while the DC circuit is not being powered, thereby connecting the snubber circuit to the DC circuit and waiting for the DC circuit to start supplying power. The power conversion system of claim 2 .

6. The state in which power is not being supplied to the DC circuit is a state in which power is not being supplied from a DC power source and power conversion by the power conversion device is stopped. The power conversion system of claim 1 .

7. The semiconductor switch is separate from a plurality of power conversion switches that configure the power conversion device. The power conversion system of claim 2 .

8. The circuit switch is Opening the DC circuit connecting the DC power supply and the power conversion device by control; The switching control unit Opening the circuit switch to disconnect the power conversion device from the DC power source; With the semiconductor switch in the ON state, the circuit breaker is closed to start supplying DC power. The power conversion system according to claim 5 .

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