Load driving system and load driving method

Abstract

To provide a technique that can prevent loads connected to an inverter from being affected by surge voltages that occur after the inverter stops operating.SOLUTION: A load drive system includes: an inverter; multiple loads with different rated voltages connected in parallel to the inverter; a first circuit breaker provided between the inverter and the multiple loads, and connecting one load to be operated out of the multiple loads; multiple arresters with different limiting voltages connected in parallel to the inverter; multiple second circuit breakers provided between the inverter and each of the multiple arresters; and a control device. The control device closes the first circuit breaker corresponding to the one load to be operated out of the multiple loads before the inverter starts operating, and closes the second circuit breakers that enable the arresters with the limiting voltages set to meet protection conditions for the one load out of the multiple arresters.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a system for driving a load using an inverter. [Background technology]

[0002] Patent Document 1 discloses a different voltage motor drive system that can drive motors (loads) with different rated voltages using a single voltage-type inverter (hereinafter simply referred to as the inverter). With this technology, when switching the load connected to the inverter, the tap connected to the power grid is switched to a tap that matches the rated voltage of the load. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-115155 Summary of the Invention [Problem to be solved by the invention]

[0004] After the inverter is shut down, a surge voltage occurs whose magnitude depends on the inverter's rated voltage and the energy stored in the inductive component of the load connected to the inverter. If this voltage is equal to or greater than a predetermined voltage, it is possible that a surge voltage higher than the load's surge tolerance voltage will be applied to the load. This could result in a breakdown of the load. Generally, the load's surge tolerance voltage is determined by the load's rated voltage.

[0005] An object of the present disclosure is to provide a technique that can prevent a load connected to an inverter from being affected by a surge voltage that occurs after the inverter stops operating. [Means for solving the problem]

[0006] A first aspect of the present disclosure relates to a load drive system. The load drive system includes a power conversion device, a plurality of loads with different rated voltages connected in parallel to the power conversion device, and a first switch provided between the power conversion device and the plurality of loads, connecting one of the plurality of loads to be operated. The power conversion device includes an inverter, a plurality of arresters with different clamping voltages connected in parallel to the inverter, and a plurality of second switches provided between the inverter and each of the plurality of arresters. The load drive system further includes a control device connected to the first switch, the plurality of second switches, and the inverter. Before starting operation of the inverter, the control device closes the first switch and closes the second switch, which activates one of the plurality of arresters with a clamping voltage set to satisfy protection conditions for the load.

[0007] A second aspect of the present disclosure relates to a load drive system. The load drive system includes a power conversion device, multiple loads with different rated voltages connected in parallel to the power conversion device, and a first switch provided between the power conversion device and the multiple loads to connect one of the multiple loads to be operated. The power conversion device includes an inverter, a series arrester connected in parallel to the inverter and having multiple arresters connected in series, a third switch provided between the inverter and the series arrester, and multiple fourth switches provided between terminals of the multiple arresters excluding some of the arresters. The load drive system also includes a control device connected to the first switch, the third switch, the multiple fourth switches, and the inverter. Before starting operation of the inverter, the control device closes the first switch and the third switch and closes the fourth switch to activate at least one arrester of the multiple arresters that meets protection conditions for one of the loads. [Effects of the Invention]

[0008] According to the present disclosure, the surge voltage generated after the inverter operation is stopped is limited to a voltage lower than the surge allowable voltage of the load. As a result, even if a surge voltage higher than the surge allowable voltage of the load occurs, a voltage lower than the surge allowable voltage of the load is applied to the load. Therefore, it is possible to avoid a failure of the load. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a block diagram showing an example of the configuration of a load driving system according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing a specific example of the load driving system according to the first embodiment. [Figure 3] FIG. 2 is an explanatory diagram showing a specific example of the load driving system according to the first embodiment. [Figure 4] FIG. 2 is an explanatory diagram showing a specific example of the load driving system according to the first embodiment. [Figure 5] FIG. 2 is an explanatory diagram showing a specific example of the load driving system according to the first embodiment. [Figure 6] FIG. 10 is a block diagram showing an example of the configuration of a load driving system according to a second embodiment. [Figure 7] FIG. 10 is an explanatory diagram showing a specific example of a load driving system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A load driving system and a load driving method according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. Elements common to the various drawings will be designated by the same reference numerals, and duplicated descriptions will be omitted.

[0011] 1. First Embodiment 1-1.Configuration example Fig. 1 is a block diagram showing an example of the configuration of a load driving system 1 according to embodiment 1. The load driving system 1 includes a power conversion device 2, a plurality of three-phase AC loads 6, a first switch 5, a three-phase AC power supply 3, a power switch 4, and a control device 20. Note that the control device 20 may be provided outside the power conversion device 2 as shown in Fig. 1, or all or part of the functions of the control device 20 may be provided inside the power conversion device 2.

[0012] The power conversion device 2 is a device that converts power supplied from an AC power source 3 into power of an arbitrary AC voltage and outputs it. The input side of the power conversion device 2 is a three-phase AC, and is connected to the AC power source 3 via a power switch 4. The output side of the power conversion device 2 is a three-phase AC, and is connected to a plurality of loads 6 via a plurality of first switches 5.

[0013] A plurality of loads 6 are connected to the power conversion device 2. Specifically, each of the plurality of loads 6 (load 6A, load 6B, load 6C) is connected to a respective one of a plurality of wirings branched at position a of a first power line 13 connected to the output side of the power conversion device 2. In other words, each of the plurality of loads 6 (load 6A, load 6B, load 6C) is in a parallel relationship. The loads 6A, load 6B, and load 6C have different rated voltages. Examples of the loads 6A, load 6B, and load 6C include AC motors.

[0014] Here, the magnitude relationship among the rated voltage V6A of the load 6A, the rated voltage V6B of the load 6B, and the rated voltage V6C of the load 6C is expressed, for example, by the following formula (1): Here, the rated voltages V6A, V6B, and V6C are line voltages.

[0015]

number

[0016] Moreover, the rated voltages V6B and V6C are expressed by, for example, the following formulas (2) and (3), respectively.

[0017]

number

[0018] In addition, the phase voltage surge tolerance V of the 6A load s 6A, load 6B phase voltage surge allowable voltage V s 6B, the surge allowable voltage V of the phase voltage of the load 6C s The magnitude relationship of 6C is expressed by the following formula (4).

[0019]

number

[0020] Here, let us consider a case where the load 6 is a three-phase load. In this case, the operating peak voltage V of the phase voltage of the load 6A is OP 6A, the operating peak voltage V of the phase voltage of the load 6B OP 6B, the operating peak voltage V of the phase voltage of the load 6C OP 6C are expressed by the following equations (5), (6), and (7), respectively.

[0021]

number

[0022] Furthermore, the surge tolerance voltage V s 6A and operating peak voltage V OP The relationship of 6A is expressed by the following formula (8), and the surge allowable voltage V s 6B and operating peak voltage V OP The relationship between 6B is expressed by the following formula (9), and the surge allowable voltage V s 6C and operating peak voltage V OP The 6C relationship is expressed by the following equation (10).

[0023]

number

[0024] The plurality of first switches 5 are provided between the power conversion device 2 and the plurality of loads 6. Specifically, the plurality of first switches 5 include a first switch 5A, a first switch 5B, and a first switch 5C, and the plurality of loads 6 include a load 6A, a load 6B, and a load 6C. The first switch 5A is provided on the input side of the load 6A, the first switch 5B is provided on the input side of the load 6B, and the first switch 5C is provided on the input side of the load 6C. The first switch 5A is a switch that opens or closes a circuit between the power conversion device 2 and the load 6A, the first switch 5B is a switch that opens or closes a circuit between the power conversion device 2 and the load 6B, and the first switch 5C is a switch that opens or closes a circuit between the power conversion device 2 and the load 6C.

[0025] The target load 6 connected to the power conversion device 2 is one load 6 that is the target of operation among the multiple loads 6. In other words, not all of the multiple loads 6 are operated at the same time. Therefore, among the multiple first switches 5, the first switch 5 corresponding to the target load 6 is closed, and the first switches 5 corresponding to the loads 6 other than the target load 6 are kept open. This makes it possible to connect only the target load 6 among the multiple loads 6 to the inverter 10. Therefore, the first switch 5 may be configured as a single switch having a switchable structure so that only the target load 6 among the multiple loads 6 can be connected. Note that the switching between open and closed of the multiple first switches 5 is controlled, for example, by a first switch control signal 21A from the control device 20, which will be described later.

[0026] The power conversion device 2 includes an inverter 10, a plurality of arresters 12, and a plurality of second switches 11. The inverter 10 converts a voltage input from an AC power source 3 into AC of a desired voltage and frequency. Specifically, the inverter 10 is a modular multilevel converter (MMC) configured by connecting the outputs of a plurality of cell inverters 23 in series. AC power supplied from the AC power source 3 is input to the primary side of a transformer (not shown) via a power switch 4. The secondary side of the transformer has a plurality of secondary windings insulated from one another, and each secondary winding is connected to the input side of each cell inverter 23. The AC power input to the cell inverter 23 is converted to DC power by a rectifier (not shown). The DC power converted by the rectifier is then smoothed by a capacitor (not shown) in the cell inverter 23. The DC power smoothed by the capacitor is then converted back to AC voltage by an inverter unit (not shown) in the cell inverter 23. The inverter section is configured by, for example, connecting a bridge of a combination of a self-extinguishing semiconductor and a diode (freewheeling diode) connected in anti-parallel.

[0027] Consider a case where the load 6 is a three-phase AC motor. In this case, the three-phase output inverter 10 is composed of, for example, three series cell inverters, each of which has four cell inverters 23 connected in series. Specifically, as shown in FIG. 1, the three-phase output inverter 10 is composed of three parts: a first series cell inverter in which four cell inverters 23, 23RA, 23RB, 23RC, and 23RD, are connected in series to form the first phase; a second series cell inverter in which four cell inverters 23, 23SA, 23SB, 23SC, and 23SD, are connected in series to form the second phase; and a third cell inverter in which four cell inverters 23, 23TA, 23TB, 23TC, and 23TD, are connected in series to form the third phase.

[0028] 1, the three-phase output inverter 10 has a first series cell inverter, a second series cell inverter, and a third series cell inverter connected in a Y connection. Specifically, one output terminal of the cell inverter 23RA is connected to the neutral point of the inverter 10, the other output terminal of the cell inverter 23RA is connected to one output terminal of the cell inverter 23RB, the other output terminal of the cell inverter 23RB is connected to one output terminal of the cell inverter 23RC, the other output terminal of the cell inverter 23RC is connected to one output terminal of the cell inverter 23RD, and the other output terminal of the cell inverter 23RD becomes the first phase (R phase) output of the inverter 10 and is connected to the first switch 5 and the second switch 11.

[0029] In addition, one end of the output of the cell inverter 23SA is connected to the neutral point of the inverter 10, the other end of the output of the cell inverter 23SA is connected to one end of the output of the cell inverter 23SB, the other end of the output of the cell inverter 23SB is connected to one end of the output of the cell inverter 23SC, the other end of the output of the cell inverter 23SC is connected to one end of the output of the cell inverter 23SD, and the other end of the output of the cell inverter 23SD becomes the second phase (S phase) output of the inverter 10 and is connected to the first switch 5 and the second switch 11.

[0030] One output terminal of the cell inverter 23TA is connected to the neutral point of the inverter 10, the other output terminal of the cell inverter 23TA is connected to one output terminal of the cell inverter 23TB, the other output terminal of the cell inverter 23TB is connected to one output terminal of the cell inverter 23TC, the other output terminal of the cell inverter 23TC is connected to one output terminal of the cell inverter 23TD, and the other output terminal of the cell inverter 23TD becomes the third phase (T phase) output of the inverter 10 and is connected to the first switch 5 and the second switch 11. The neutral point of the inverter 10 is grounded.

[0031] As shown in Fig. 1 , the output of inverter 10 branches at position b on first power line 13 into first power line 13 and second power line 14 connected in parallel to first power line 13. The branched first power line 13 is connected to load 6 via first switch 5. On the other hand, second power line 14 has one end connected to first power line 13 and the other end grounded via multiple second switches 11 and multiple arresters 12.

[0032] The multiple arresters 12 are connected to the inverter 10. Specifically, each of the multiple arresters 12 (arrester 12A, arrester 12B, arrester 12C) is connected to each of the multiple wirings branched at positions c and d of the second power line 14. That is, each of the multiple arresters 12 (arrester 12A, arrester 12B, arrester 12C) is in a parallel relationship. The arrester 12 is a device that absorbs (grounds) a surge voltage 15 that occurs after the inverter 10 stops operating. A limiting voltage is set to the arrester 12. Each of the multiple arresters 12 (arrester 12A, arrester 12B, arrester 12C) has a different limiting voltage V12. Zinc oxide elements are exemplified as the arresters 12A, arrester 12B, and arrester 12C. Each of the arresters 12A, arrester 12B, and arrester 12C is configured with three phases.

[0033] The plurality of second switches 11 are provided between the inverter 10 and the plurality of arresters 12. The plurality of second switches 11 include a second switch 11A, a second switch 11B, and a second switch 11C, and the plurality of arresters 12 include an arrester 12A, an arrester 12B, and an arrester 12C. The second switch 11A is a switch that connects or disconnects between the inverter 10 and the arrester 12A, the second switch 11B is a switch that connects or disconnects between the inverter 10 and the arrester 12B, and the second switch 11C is a switch that connects or disconnects between the inverter 10 and the arrester 12C. Circuit breakers are exemplified as the second switch 11A, the second switch 11B, and the second switch 11C.

[0034] The target arrester 12 connected to the inverter 10 is one arrester 12 that is made active among the multiple arresters 12. In other words, not all of the multiple arresters 12 are connected at the same time. Therefore, among the multiple arresters 12, the second switch 11 corresponding to the target arrester 12 is closed, and the second switches 11 corresponding to the arresters 12 other than the target arrester 12 are kept open. This makes it possible to connect only the target arrester 12 among the multiple arresters 12 to the output of the inverter 10. Note that the switching between opening and closing of the multiple second switches 11 is controlled, for example, by a control device 20, which will be described later.

[0035] The control device 20 is a computer that controls the load driving system 1. The control device 20 includes a processor (not shown) and a memory (not shown) that stores a control program (a control program according to this embodiment) executed by the processor. The control program is executed by the processor, whereby the functions described below are realized in the control device 20.

[0036] The control device 20 is connected to each of the first switches 5A, 5B, and 5C and each of the second switches 11A, 11B, and 11C. The control device 20 controls the on / off switching of each of the first switches 5A, 5B, and 5C using a first switch control signal 21A. The control device 20 also controls the on / off switching of each of the second switches 11A, 11B, and 11C using a second switch control signal 21B. This allows the inverter 10 to connect or disconnect multiple loads 6. It also allows the inverter 10 to connect or disconnect multiple arresters 12. Therefore, a surge voltage 15 generated after the inverter 10 stops operating is grounded via the target arrester 12. This prevents the target load 6 from failing.

[0037] The control device 20 is also connected to the inverter 10. The control device 20 commands the inverter 10 to start and stop operation (gate block) of the inverter 10 using an inverter control signal 21D. The control device 20 is further connected to a power switch 4. Before starting operation of the inverter 10, the control device 20 switches the power switch 4 to close using a power switch control signal 21C, and after stopping operation of the inverter 10, switches the power switch 4 to open using the power switch control signal 21C.

[0038] 1-2.Specific examples 1-2-1. Example of inverter (MMC) output voltage In the MMC inverter 10, each cell inverter 23 outputs a positive voltage, zero voltage, or negative voltage, thereby outputting a target AC voltage. Furthermore, by using PWM (Pulse Width Modulation) as the output method for each cell inverter 23, it is possible to output an intermediate voltage between the DC voltage of the cell inverter 23 and zero voltage as the average value of the cycle of the PWM carrier frequency. Specific examples of voltages output from the inverter 10 are described below.

[0039] FIG. 2 shows an example of the output waveform of the first phase of the power conversion device 2 when the power conversion device 2 is connected to a load 6C. Specifically, the horizontal axis of the waveform shown in FIG. 2 represents the time axis, and the vertical axis represents the phase voltage. The sinusoidal waveform shown by the solid line represents the output voltage waveform 100 of the inverter 10. The output voltage waveform 100 of the inverter 10 is a waveform that is schematically represented by moving averaging the output voltage waveform of the power conversion device 2 with a period of the carrier frequency of the cell inverter 23. Meanwhile, the rectangular waveform shown by the dashed line represents a waveform that is a schematic representation of the envelope of the output voltage waveform 100 of the inverter 10.

[0040] Here, we will explain the output voltage waveforms of the cell inverter 23RA, the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD in each section from time t1 to time ts1. First, in the section from time t1 to time t2, the cell inverter 23RA, the cell inverter 23RB, and the cell inverter 23RC each output a positive voltage, and the cell inverter 23RD outputs a positive value of the PWM waveform.

[0041] In the period from time t2 to time t3, the cell inverter 23RA and the cell inverter 23RB each output a positive voltage, the cell inverter 23RC outputs a positive value of the PWM waveform, and the cell inverter 23RD outputs zero voltage.

[0042] In the period from time t3 to time t4, the cell inverter 23RA outputs a positive voltage, the cell inverter 23RB outputs a positive value of the PWM waveform, and the cell inverter 23RC and the cell inverter 23RD each output a zero voltage.

[0043] In the period from time t4 to time t5, the cell inverter 23RA outputs a positive value of the PWM waveform, and the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD each output a zero voltage.

[0044] In the period from time t5 to time t6, the cell inverter 23RA outputs a negative value of the PWM waveform, and the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD each output a zero voltage.

[0045] In the period from time t6 to time t7, the cell inverter 23RA outputs a negative voltage, the cell inverter 23RB outputs a negative value of the PWM waveform, and the cell inverter 23RC and the cell inverter 23RD each output a zero voltage.

[0046] In the period from time t7 to time t8, the cell inverter 23RA and the cell inverter 23RB output negative voltages, the cell inverter 23RC outputs a negative voltage with a PWM waveform, and the cell inverter 23RD outputs zero voltage.

[0047] In the period from time t8 to time t9, the cell inverter 23RA, the cell inverter 23RB, and the cell inverter 23RC each output a negative voltage, and the cell inverter 23RD outputs a negative voltage with a PWM waveform.

[0048] In the period from time t9 to time t10, the cell inverter 23RA and the cell inverter 23RB each output a negative voltage, the cell inverter 23RC outputs a negative voltage with a PWM waveform, and the cell inverter 23RD outputs zero voltage.

[0049] In the period from time t10 to time ts1, the cell inverter 23RA outputs a negative voltage, the cell inverter 23RB outputs a negative voltage with a PWM waveform, and the cell inverter 23RC and the cell inverter 23RD each output a zero voltage.

[0050] In the example shown in FIG. 2, at time ts1, the cell inverter 23RA, the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD are each in a stopped state (gate blocked).

[0051] In this way, by controlling the output voltage of each cell inverter 23, the power conversion device 2 can output a sinusoidal AC voltage waveform as shown by the solid line in Fig. 2. Note that the absolute value of the peak value in the positive direction of the sinusoidal AC voltage waveform in the section from time t1 to time t2 is the operating peak voltage V OP 6C. The absolute value of the negative peak value of the sinusoidal AC voltage waveform in the section from time t8 to time t9 is equal to the operating peak voltage V OP It can be made equal to 6C.

[0052] 3 shows an example of the output waveform of the first phase of the power conversion device 2 when the power conversion device 2 is connected to a load 6A. Specifically, the horizontal axis of the waveform shown in FIG. 3 represents the time axis, and the vertical axis represents the phase voltage. The sinusoidal waveform shown by the solid line is the output voltage waveform 200 of the inverter 10. Furthermore, the rectangular waveform shown by the dashed line is a waveform that schematically represents the envelope of the output voltage waveform 200 of the inverter 10.

[0053] Here, we will explain the output voltage waveforms of the cell inverter 23RA, cell inverter 23RB, cell inverter 23RC, and cell inverter 23RD in each section from time t11 to time ts11. First, in the section from time t11 to time t12, the cell inverter 23RA outputs a positive voltage, the cell inverter 23RB outputs a positive value of the PWM waveform, and the cell inverter 23RC and cell inverter 23RD each output zero voltage.

[0054] In the period from time t12 to time t13, the cell inverter 23RA outputs a positive value of the PWM waveform, and the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD each output a zero voltage.

[0055] In the period from time t13 to time t14, the cell inverter 23RA outputs a negative value of the PWM waveform, and the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD each output a zero voltage.

[0056] In the period from time t14 to time t15, the cell inverter 23RA outputs a negative voltage, the cell inverter 23RB outputs a negative value of the PWM waveform, and the cell inverter 23RC and the cell inverter 23RD each output a zero voltage.

[0057] In the period from time t15 to time ts11, the cell inverter 23RA outputs a negative value of the PWM waveform, and the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD each output a zero voltage.

[0058] Then, at time ts11, the cell inverter 23RA, the cell inverter 23RB, the cell inverter 23RC, and the cell inverter 23RD are each put into a stopped state (gate blocked).

[0059] In this way, by controlling the output voltage of each cell inverter 23, the power conversion device 2 can output a sinusoidal AC voltage waveform as shown by the solid line in Fig. 3. Note that the absolute value of the peak value in the positive direction of the sinusoidal AC voltage waveform in the section from time t11 to time t12 is the operating peak voltage V OP 6A. The absolute value of the negative peak value of the sinusoidal AC voltage waveform in the section from time t14 to time t15 is equal to the operating peak voltage V OP It can be equal to 6A.

[0060] As described above, by applying the MMC inverter 10, the number of cell inverters 23 that output zero voltage is adjusted, and the cell inverters 23 are operated by PWM. This makes it possible to output voltages according to the rated voltages of the loads 6A, 6B, and 6C connected to the inverter 10 without changing the internal circuit of the inverter 10.

[0061] 1-2-2. Setting example of limit voltage of target arrester An example of setting the clamping voltage of the target arrester 12 will be described in detail with reference to Fig. 2 and Fig. 3. First, an example of setting the clamping voltage of the target arrester 12 shown in Fig. 2 will be described. Fig. 2 shows the state of the output voltage waveform 100 of the inverter 10 when a load 6C is connected to the power conversion device 2 and the power conversion device 2 is brought to an emergency stop at time ts1.

[0062] The power conversion device 2 typically shuts down after gradually reducing its output current. That is, the power conversion device 2 shuts down by reducing the current supplied to the load 6 at an effective value level, thereby bringing the output current close to zero. However, when shutting down the power conversion device 2 due to the detection of an abnormality, the inverter 10 is shut down while the current supplied to the load 6 is relatively large. In this case, the DC capacitors of the cell inverters 23 constituting the inverter 10 are charged by the energy stored in the inductive component of the load 6, and the DC voltage of the cell inverters 23 increases. When the freewheel diodes are conducting, the DC capacitors of the cell inverters 23 are connected in series, and the terminal voltage of the inverter 10 may become large due to the increase in the DC voltage of each cell inverter 23.

[0063] In this case, a surge voltage 15 may occur after the inverter 10 stops operating due to an emergency shutdown of the power conversion device 2. In the example shown in Fig. 2, the output voltage waveform 100 of the inverter 10 includes a surge voltage 15 that occurs for a predetermined time after the inverter 10 stops operating at time ts1. The predetermined time is, for example, about several milliseconds.

[0064] Therefore, in the load drive system 1 according to the first embodiment, the arrester 12 is set so that the surge voltage 15 generated when the operation of the inverter 10 is stopped is equal to or lower than the surge allowable voltage of the load 6. Specifically, when the target load is the load 6C, the first switch 5C is closed, and the arrester 12C is set as the target arrester. In this case, the second switch 11C is closed, and therefore, as shown in FIG. 2, the surge voltage 15 is limited to the limit voltage V12C of the arrester 12C at time ts2 after time ts1. In addition, the surge voltage 15 is limited to the limit voltage V12C of the arrester 12C at time ts2 after time ts1. s This limits the voltage applied to the load 6C to a value lower than the surge allowable voltage, thereby preventing damage to the load 6C.

[0065] Next, a description will be given of an example of setting the limit voltage of the target arrester 12 shown in Fig. 3. Fig. 3 shows the state of the output voltage waveform 200 of the inverter 10 when a load 6A is connected to the power conversion device 2 and the power conversion device 2 is brought to an emergency stop at time ts11.

[0066] 3, similar to the above-described FIG. 2, a surge voltage 25 occurs after the inverter 10 stops operating due to an emergency shutdown of the power conversion device 2. Specifically, the output voltage waveform 200 of the inverter 10 includes a surge voltage 25 that occurs for a predetermined time after the inverter 10 stops operating at time ts11. The predetermined time is, for example, about several milliseconds.

[0067] Here, consider a case where the operation of the inverter 10 is stopped in a state where an arrester 12 other than the arrester 12 corresponding to the load 6 connected to the inverter 10 is connected to the inverter 10. For example, in a state where the load 6A is connected to the inverter 10 and the arrester 12C is connected to the inverter 10, if the operation of the inverter 10 is stopped at time ts12 shown in FIG. 3, it is assumed that the surge voltage 25 changes as follows. Specifically, the surge voltage 25 reaches the limit voltage V12C of the arrester 12C at time ts13 after time ts12. In this case, the surge voltage 25 reaches the surge allowable voltage V12C of the load 6A. s If it is higher than 6A, it may cause damage to the load 6A.

[0068] Therefore, in the load drive system 1 according to the first embodiment, the arrester 12 is set so that the surge voltage 25 generated when the operation of the inverter 10 is stopped is equal to or lower than the surge allowable voltage of the load 6. Specifically, when the target load is the load 6A, the first switch 5A is closed and the arrester 12A is set as the target arrester. In this case, since the second switch 11A is closed, the surge voltage 25 is limited to the limit voltage V12A of the arrester 12A at time ts12 after time ts11, as shown in FIG. 3 . In addition, the surge voltage 25 is limited to the limit voltage V12A of the arrester 12A at time ts12 after time ts11. sThe voltage applied to the load 6A is suppressed to a value lower than the surge allowable voltage, thereby preventing damage to the load 6A.

[0069] Furthermore, when a load 6B is connected to the inverter 10, the first switch 5B is closed and the arrester 12B is set as the target arrester. In this case, the second switch 11B is closed, so that the surge voltage (not shown) generated when the operation of the inverter 10 is stopped is limited to the limit voltage V12B of the arrester 12B, as in the above-described FIGS. 2 and 3, and the surge allowable voltage V s As a result, the voltage applied to the load 6B is lower than the surge allowable voltage, thereby preventing damage to the load 6B.

[0070] In addition, the limiting voltage V12A of the arrester 12A and the surge allowable voltage V s 6A and operating peak voltage V OP The relationship between the limit voltage V12B of the arrester 12B and the surge allowable voltage V s 6B and the operating peak voltage V OP The relationship between the arrester 12C and the surge voltage V12 is expressed by the following equation (12). s 6C and the operating peak voltage V OP The relationship between the voltages V and V is expressed by the following equation (13). OP The arrester 12B is selected so that there is no problem even if 6 A is applied, and the arrester 12B periodically operates at an operating peak voltage V OP The arrester 12C is selected so that there is no problem even if the voltage V 6B is applied, and the arrester 12C periodically detects the operating peak voltage V OP It is selected so that there is no problem even if 6C is applied.

[0071]

number

[0072] That is, the limiting voltage V12 of the arrester 12 is the operating peak voltage V of the phase voltage of the load 6 connected to the inverter 10. OP 6, and the limiting voltage V12 of the arrester 12 is higher than the surge allowable voltage V s The control device 20 controls the opening / closing of the second switch 11 so that the voltage Vcc is lower than 6. The control of the opening / closing of the second switch 11 will be described in detail later.

[0073] As described above, in the load drive system 1 according to the embodiment, as a protection condition for protecting the target load 6 from the surge voltage 15 or the surge voltage 25, the limiting voltage V12 of the target arrester 12 is set to a predetermined voltage range so as to limit the surge voltage 15 or the surge voltage 25, etc., to a predetermined voltage range. Then, the target arrester 12 to which the limiting voltage V12 is set is connected to the output side of the inverter 10. The predetermined voltage range is set by setting the limiting voltage V12 to the operating peak voltage V of the target load 6. op 6 and the surge allowable voltage V of the target load 6 s 6 of the target load 6. This limits the surge voltage 15 or surge voltage 25, etc. that occurs after the inverter 10 stops operating, to a predetermined voltage range. This makes it possible to prevent thermal runaway of the target arrester 12 while the inverter 10 is operating. This allows the load drive system 1 to operate stably. Furthermore, the target arrester 12 limits the surge allowable voltage V of the target load 6 to a predetermined voltage range so that the surge voltage 15 or surge voltage 25, etc. that is higher than the rated voltage of the target load 6 does not occur after the inverter 10 stops operating. s Therefore, the surge voltage of the load 6 is controlled to a surge voltage 15 or a surge voltage 25 which is lower than the surge voltage of the load 6. Therefore, it is possible to avoid a failure of the load 6.

[0074] 1-2-3. Example of operation of the first and second switches FIG. 4 is an explanatory diagram showing a specific example of the load driving system 1 according to the first embodiment. Specifically, FIG. 4 shows an example of switching between open and closed states of the first switch 5 for connecting the target load 6 to the inverter 10, and an example of switching between open and closed states of the second switch 11 for connecting the target arrester 12 to the inverter 10. Note that the switching between open and closed states of the first switch 5 and the second switch 11 is not performed during operation of the inverter 10, but is performed before the inverter 10 starts operating. Also, the initial states of the first switch 5 and the second switch 11 are all open. Based on this, details of the example of switching between open and closed states of the first switch 5 and the second switch 11 will be described later. Note that in FIG. 4, the open states of the first switch 5 and the second switch 11 are represented by OFF, and the closed states of the first switch 5 and the second switch 11 are represented by ON.

[0075] First, a detailed description will be given of an example of switching the first switch 5 to open / close for connecting the target load 6 to the inverter 10. Specifically, as shown in case (A) of FIG. 4, when the target load 6 is load 6A, the control device 20 closes the first switch 5A and keeps both the first switch 5B and the first switch 5C open. Also, as shown in case (B) of FIG. 4, when the target load 6 is load 6B, the control device 20 closes the first switch 5B and keeps both the first switch 5A and the first switch 5C open. Furthermore, as shown in case (C) of FIG. 4, when the target load 6 is load 6C, the control device 20 closes the first switch 5C and keeps both the first switch 5A and the first switch 5B open. This makes it possible to connect only the target load 6 of the multiple loads 6 to the inverter 10.

[0076] Next, a detailed description will be given of an example of switching the second switch 11 open / closed to connect the target arrester 12 to the inverter 10. Specifically, as shown in case (A) of Fig. 4, when the target load 6 is load 6A and the target arrester 12 is arrester 12A, the control device 20 closes the second switch 11A and keeps both the second switch 11B and the second switch 11C open. Also, as shown in case (B) of Fig. 4, when the target load 6 is load 6B and the target arrester 12 is arrester 12B, the control device 20 closes the second switch 11B and keeps both the second switch 11A and the second switch 11C open. 4, when the target load 6 is the load 6C and the target arrester 12 is the arrester 12C, the control device 20 closes the second switch 11C and keeps both the second switch 11A and the second switch 11B open. This makes it possible to connect only the target arrester 12 of the multiple arresters 12 to the inverter 10.

[0077] 1-3. Processing example FIG. 5 is a flowchart showing an example of processing by the control device 20 in the load driving system 1 according to the first embodiment.

[0078] In step S100, the control device 20 opens the power switch 4, the first switch 5, and all of the plurality of second switches 11. Thereafter, the process proceeds to step S110.

[0079] In step S110, the control device 20 closes the power switch 4. After that, the process proceeds to step S120.

[0080] In step S120, the control device 20 selects the target load 6 in response to a command from a higher-level device (not shown) or manually. Then, the control device 20 closes both the first switch 5 corresponding to the selected target load 6 and the second switch 11 corresponding to the selected target arrester 12. Thereafter, the process proceeds to step S130.

[0081] In step S130, the control device 20 determines whether or not there is a command from a higher-level device (not shown) or a manual operation to operate the inverter 10. If it is determined that there is a command to operate the inverter 10 (step S130; Yes), the process proceeds to step S140. Otherwise (step S130; No), the process returns to step S130.

[0082] In step S140, the control device 20 issues an instruction to the inverter 10 to start operation of the inverter 10. Thereafter, the process proceeds to step S150.

[0083] In step S150, the control device 20 determines whether or not there is a command from a higher-level device (not shown) or a manual operation to stop the inverter 10. If it is determined that there is a command to stop the inverter 10 (step S150; Yes), the process proceeds to step S160. Otherwise (step S150; No), the process returns to step S150.

[0084] In step S160, the control device 20 issues an instruction to the inverter 10 to stop the operation of the inverter 10. Thereafter, the process proceeds to step S170.

[0085] In step S170, the control device 20 switches both the first switch 5 corresponding to the target load 6 and the second switch 11 corresponding to the target arrester 12 from closed to open. After that, the processing proceeds to step S180.

[0086] In step S180, the control device 20 opens the power switch 4.

[0087] As described above, the load driving system 1 according to the first embodiment has a plurality of second switches 11 that connect between a plurality of arresters 12 with different clamping voltages V12 and the output of the inverter 10, thereby making it possible to easily change the connection of the arrester 12, among the plurality of arresters 12, that corresponds to the rated voltage of the target load 6 connected to the output of the power conversion device 2 to the output of the inverter 10. This makes it possible to easily protect the load 6 against surge voltage 15 or surge voltage 25, etc. that occurs after the inverter 10 stops operating, even if the rated voltage of the target load 6 connected to the power conversion device 2 is changed.

[0088] More specifically, the surge voltage 15 or surge voltage 25 generated after the inverter 10 stops operating exceeds the surge allowable voltage V s Therefore, the surge tolerance voltage of load 6 is limited to a voltage lower than V s Even if a surge voltage higher than 6 occurs, the surge tolerance voltage V of load 6 s A voltage lower than that of load 6 is applied to load 6. Therefore, it is possible to avoid failure of load 6.

[0089] 2. Second Embodiment 2-1. Overview FIG. 6 is a block diagram showing a configuration example of a load driving system 1A according to the second embodiment. The load driving system 1A includes a power conversion device 2A, a plurality of loads 6, a first switch 5, an AC power supply 3, a power switch 4, and a control device 20A. As shown in FIG. 6, the control device 20A may be provided outside the power conversion device 2A, or all or part of the functions of the control device 20A may be provided inside the power conversion device 2A. Furthermore, the plurality of loads 6, the first switch 5, the AC power supply 3, and the power switch 4 have the same configuration as those in the first embodiment described above, and therefore a description of these configurations will be omitted. Here, the differences from the first embodiment will be mainly described.

[0090] The power conversion device 2A includes an inverter 10, a plurality of arresters 112, a third switch 510, and a plurality of fourth switches 51. The output of the inverter 10 is connected to one end of the third switch 510 via the second power line 14. The other end of the third switch 510 is connected to a series arrester 113 in which a plurality of arresters 112 are connected in series with respect to a branch point e. In the example shown in FIG. 6 , the series arresters 113 are connected in series in the order of arrester 112C, arrester 112B, and arrester 112A from the third switch 510 side. The third switch 510 is provided between the output of the inverter 10 and the series arrester 113, and is a switch that connects or disconnects the inverter 10 and the series arrester 113. The opening / closing of the third switch 510 is controlled, for example, by a control device 20A described later.

[0091] The other end of the third switch 510 is connected to a series fourth switch 52 in which a plurality of fourth switches 51 are connected in series with respect to the branch point e. In the example shown in Fig. 6, the series fourth switches 52 are connected in series in the order of the fourth switch 51C and the fourth switch 51B from the third switch 510 side.

[0092] Furthermore, as shown in Fig. 6, the arrester 112B is connected in parallel with the fourth switch 51B. Also, as shown in Fig. 6, the arrester 112C is connected in parallel with the fourth switch 51C. That is, the plurality of fourth switches 51 are provided between the terminals of the arresters 112 (arrester 112B and arrester 112C shown in Fig. 6) excluding the arrester 112 having one end grounded (arrester 112A shown in Fig. 6) among the plurality of arresters 112. Therefore, the number of fourth switches 51 is configured to be fewer than the number of arresters 112 connected in series. In the example shown in Fig. 6, the number of series of the plurality of arresters 112 is configured to be three, and the number of fourth switches 51 is configured to be two.

[0093] The multiple fourth switches 51 are switches that short-circuit or open the terminals of the arrester 112. For example, as shown in FIG. 6, when the fourth switch 51B is closed, the terminals of the arrester 112B are short-circuited. When the fourth switch 51C is closed, the terminals of the arrester 112C are short-circuited. In other words, the multiple fourth switches 51 are switched between open and closed so as to enable at least one arrester 112 that satisfies the protection condition for the target load 6 among the multiple arresters 112. The protection condition is the same as that in the first embodiment described above. The switching between open and closed of the multiple fourth switches 51 is controlled, for example, by a control device 20A described later.

[0094] The control device 20A is connected to the first switch 5, the power switch 4, the inverter 10, the third switch 510, and the fourth switches 51B and 51C. As in the first embodiment described above, the control device 20A controls the opening / closing of the first switch 5 using a first switch control signal 21A, controls the opening / closing of the power switch 4 using a power switch control signal 21C, and issues commands to the inverter 10 to start and stop operation (gate block) of the inverter 10 using an inverter control signal 21D. The control device 20A also controls the opening / closing of the third switch 510 using a third switch control signal 21E, and controls the opening / closing of each of the fourth switches 51B and 51C using a fourth switch control signal 21F. This makes it possible to connect or disconnect the inverter 10 to or from a plurality of loads 6. It is also possible to connect or disconnect the inverter 10 and the series arrester 113. Furthermore, it is possible to short or open the terminals of each of the arresters 112, except for the arrester 112 whose one end is grounded, among the plurality of arresters 112. Therefore, the surge voltage 15 or surge voltage 25, etc., generated after the inverter 10 stops operating is grounded via the target arrester 112. This makes it possible to avoid failure of the target load 6.

[0095] 2-2.Specific examples 2-2-1. Setting example of limit voltage of target arrester The limiting voltage V112A of the arrester 112A and the surge allowable voltage V s 6A and operating peak voltage V OP The relationship between the limit voltage V112B of the arrester 112B and the surge allowable voltage V s 6B and the operating peak voltage V OP The relationship between the limit voltage V112 of the arrester 112C and the surge allowable voltage V s 6C and the operating peak voltage V OP The 6C relationship is expressed by the following equation (16).

[0096]

number

[0097] That is, the limiting voltage V112 of the arrester 112 is the operating peak voltage V of the phase voltage of the load 6 connected to the inverter 10. OP 6, and the limiting voltage V112 of the arrester 112 is higher than the surge allowable voltage V of the phase voltage of the load 6 connected to the inverter 10. s The control device 20A controls the opening / closing of the plurality of fourth switches 51 so that the operating peak voltage V is lower than V.6. The control of the opening / closing of the plurality of fourth switches 51 will be described in detail later. OP The series circuit of the arrester 112A and the arrester 112B is selected so that there is no problem even if a current of 6 A is applied, and the operating peak voltage V OP 6B is applied, the series circuit of the arrester 112A, the arrester 112B, and the arrester 112C is periodically applied with the operating peak voltage V OP It is selected so that there is no problem even if 6C is applied.

[0098] 2-2-2. Example of operation of the first, third, and fourth switches Fig. 7 is an explanatory diagram showing a specific example of the load driving system 1A according to embodiment 2. Specifically, Fig. 7 shows an example of switching between open and closed states of the first switch 5 for connecting the target load 6 to the inverter 10, and an example of switching between open and closed states of the third switch 510 and the fourth switch 51 for connecting the target arrester 112 to the inverter 10. Note that Fig. 7 indicates that the first switch 5, the third switch 510, and the fourth switch 51 are open by OFF, and that the first switch 5, the third switch 510, and the fourth switch 51 are closed by ON.

[0099] The first switch 5, the third switch 510, and the fourth switch 51 are switched open / closed before the inverter 10 starts operating, not while the inverter 10 is operating. The initial states of the first switch 5, the third switch 510, and the fourth switch 51 are open. Based on this, an example of switching open / closed of the first switch 5, the third switch 510, and the fourth switch 51 will be described in detail later. Note that an example of switching open / closed of the first switch 5 for connecting the target load 6 to the inverter 10 is the same as that in FIG. 4 described above, and therefore will not be described here.

[0100] First, a detailed description will be given of an example of switching between opening and closing the third switch 510. As shown in Fig. 7, in all of case (A1), case (B1), and case (C1), the control device 20A closes the third switch 510.

[0101] Next, an example of switching the fourth switch 51 between open and closed will be described in detail. Since the fourth switch 51 is connected in parallel with the arrester 112, the fourth switch 51 connected in parallel with the arrester 112 selected as the target arrester is opened, and the fourth switch 51 connected in parallel with the arrester 112 not selected as the target arrester is closed. As shown in case (A1) of FIG. 7, consider the case where the target load 6 is a load 6A. In this case, the total limiting voltage V113 of the series arrester 113 is V op 6A <V113<V s6A. Therefore, according to the above-mentioned formula (14), the arrester 112B and the arrester 112C are short-circuited so that only the arrester 112A is effective in the series arrester 113. Therefore, the control device 20A closes both the fourth switch 51B and the fourth switch 51C.

[0102] Also, consider the case where the target load 6 is the load 6B, as shown in case (B1) of FIG. 7. In this case, the total clamping voltage V113 of the series arrester 113 is V op 6B <V113<V s 6B. Therefore, according to the above-described formula (15), the arrester 112C is short-circuited so that the arrester 112A and the arrester 112B of the series arrester 113 are effective. Therefore, the control device 20A closes the fourth switch 51C while keeping the fourth switch 51B open.

[0103] Also, consider the case where the target load 6 is a load 6C, as shown in case (C1) of FIG. 7. In this case, the total clamping voltage V113 of the series arrester 113 is V op 6C <V113<V s 6C must be satisfied. Therefore, according to the above-described formula (16), the arrester 112A, the arrester 112B, and the arrester 112C of the series arrester 113 are all enabled. Therefore, the control device 20A keeps both the fourth switch 51B and the fourth switch 51C open.

[0104] 2-2-3. Processing example In the flowchart showing an example of processing by the control device 20A in the load driving system 1A according to the second embodiment, in FIG. 5, the control device 20 is replaced with the control device 20A, and the explanations of steps S120 and S170 are replaced with the following contents.

[0105] Specifically, in step S120, the control device 20A closes the third switch 510 and selects the target load 6 in response to a command from a higher-level device (not shown) or by manual operation. Furthermore, the control device 20A closes both the first switch 5 corresponding to the selected target load 6 and the fourth switch 51 corresponding to the target arrester 112 to be placed in a short-circuit state. Thereafter, the process proceeds to step S130.

[0106] In step S170, the control device 20A switches from closed to open all of the first switch 5, the third switch 510 corresponding to the target load 6, and the fourth switch 51 corresponding to the arrester 112 not selected as the target arrester. Then, the processing proceeds to step S180.

[0107] 6, the arrester 112A, which does not have the fourth switch 51 provided between its terminals, is arranged on the ground side. However, this is not limited to this. For example, the arrester 112A may be arranged on the third switch 510 side, or may be arranged between the arrester 112C and the arrester 112B. In other words, as long as the fourth switch 51C is connected so as to be able to short-circuit the terminals of the arrester 112C, and the fourth switch 51B is connected so as to be able to short-circuit the terminals of the arrester 112B, the order in which the arrester 112A, the arrester 112B, and the arrester 112C are connected in series does not matter.

[0108] As described above, the load driving system 1A according to the second embodiment includes the series arrester 113 in which multiple arresters 112 with different clamping voltages are connected in series and connected in parallel to the inverter 10, and multiple fourth switches 51 capable of short-circuiting the terminals of each of the multiple arresters 112 except for the arrester 112 whose one end is grounded. This makes it possible to easily change the total clamping voltage V113 of the series arresters 113 so that the clamping voltage of the target arrester 112 corresponding to the rated voltage of the target load 6 connected to the output of the power conversion device 2A is equal to or less than the surge allowable voltage of the target load 6. As a result, even if the rated voltage of the load 6 connected to the power conversion device 2A is changed, it is possible to easily protect the load 6 against surge voltage 15 or surge voltage 25 that occurs after the inverter 10 stops operating.

[0109] 3. Other embodiments As described above, the surge voltage 15, surge voltage 25, etc. that occurs after the inverter 10 is stopped is generated for a predetermined time. In other words, the surge voltage 15, surge voltage 25, etc. does not occur after the predetermined time has elapsed. Therefore, the load driving system 1B according to other embodiments may be configured to open the first switch 5 corresponding to the target load 6 and open the second switch 11 or the third switch 510 corresponding to the target arrester 112 after the predetermined time has elapsed since the inverter 10 was stopped. This makes it possible to safely stop the load driving system 1B while avoiding a failure of the target load 6.

[0110] The first switch 5 may be manually switched to connect the load 6. In this case, the specification information of the load 6 (rated voltage, allowable surge voltage V s 6) is input to the control device 20 or the control device 20A, the opening / closing of the second switch 11 or the fourth switch 51 is automatically set.

[0111] Furthermore, the control device 20 and the control device 20A do not have to be a single device. For example, the control device 20 and the control device 20A may be distributed across multiple devices, and various functions may be processed in a distributed manner. Furthermore, some or all of the multiple devices may be a cloud system on a network. [Explanation of symbols]

[0112] 1, 1A, 1B...load drive system, 2...power conversion device, 3...AC power supply, 4...power switch, 5, 5A, 5B, 5C...first switch, 6, 6A, 6B, 6C...load, 10...inverter, 11, 11A, 11B, 11C...second switch, 12, 12A, 12B, 12C, 112, 112A, 112B, 112C...arrester, 113...series arrester, 13...first power line, 14...second power line, 15, 25...surge voltage, 20, 20A...control device, 21A...first switch control signal, 21B...second switch control signal, 21C...power switch control signal, 21D...inverter control signal, 21E...third switch control signal, 21F...fourth switch control signal 510...Third switch, 51...Fourth switch, 52...Series fourth switch, 100, 200...Output voltage waveform of inverter 10

Claims

1. a power conversion device; a plurality of loads having different rated voltages connected in parallel to the power conversion device; a first switch provided between the power conversion device and the plurality of loads, the first switch connecting one of the plurality of loads to be operated; Equipped with The power conversion device is An inverter; a plurality of arresters having different clamping voltages connected in parallel to the inverter; a plurality of second switches provided between the inverter and each of the plurality of arresters; Including, a control device connected to the first switch, the plurality of second switches, and the inverter; Before the inverter starts operating, the control device The apparatus is configured to close the first switch and close a second switch that enables an arrester among the plurality of arresters, the arrester having a limit voltage set to satisfy a protection condition for the one load. A load driving system comprising:

2. a power conversion device; a plurality of loads having different rated voltages connected in parallel to the power conversion device; a first switch provided between the power conversion device and the plurality of loads, the first switch connecting one of the plurality of loads to be operated; Equipped with The power conversion device is An inverter; a series arrester connected in parallel to the inverter and including a plurality of arresters connected in series; a third switch provided between the inverter and the series arrester; a plurality of fourth switches provided between terminals of the arresters excluding some of the arresters among the plurality of arresters; Including, a control device connected to the first switch, the third switch, the plurality of fourth switches, and the inverter; Before the inverter starts operating, the control device The first switch and the third switch are closed, and a fourth switch that activates at least one arrester that satisfies a protection condition for the one load among the plurality of arresters is closed. A load driving system comprising:

3. 3. The load driving system according to claim 1 or 2, The protection condition is a voltage range in which the limit voltage of the arrester corresponding to the one load is higher than the operating peak voltage of the one load and lower than the surge allowable voltage of the one load. A load driving system comprising:

4. 2. The load driving system according to claim 1, The control device is further configured to open both the first switch and the second switch corresponding to the one load after a predetermined time has elapsed since the operation of the inverter was stopped. A load driving system comprising:

5. 3. The load driving system according to claim 1 or 2, the first switch is provided between the power conversion device and each of the plurality of loads, The control device is configured to close only the first switch corresponding to the one load. A load driving system comprising:

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