AC-AC converter

Abstract

The present invention provides a fault-tolerant miniaturized and high-density motor drive system. The AC-AC converter includes a three-times number of single-phase rectifier circuit modules, the same number of inverter circuit modules as the single-phase rectifier circuit modules, and a control unit. The single-phase rectifier circuit modules are connected to each other using a delta connection or a star connection, and the single-phase rectifier circuit modules convert the single-phase AC voltage of each phase of the three-phase AC input voltage supplied from a three-phase AC power supply into a DC voltage. The inverter circuit modules convert the DC voltage into a three-phase AC output voltage. The control unit controls the switching elements constituting the single-phase rectifier circuit modules and the inverter circuit modules so that when a fault occurs in any one of the single-phase rectifier circuit modules, the power of the three-phase AC power supply is evenly distributed to the remaining single-phase rectifier circuit modules.

Description

Technical Field

[0001] The present invention relates to an AC-AC converter. Background Art

[0002] Three-phase motors are widely used in industrial equipment such as fans, pumps, and FA equipment. A motor drive system for driving such a three-phase motor generally includes an AC-AC converter, which is composed of a rectifier circuit that rectifies a three-phase AC voltage to generate a DC voltage (rectified voltage), a DC link at the subsequent stage of the rectifier circuit, and an inverter circuit that generates a three-phase AC voltage based on the DC link voltage.

[0003] Prior Art Documents

[0004] Non-Patent Documents

[0005] Non-Patent Document 1: M. Guacci, D. Bortis, and J. W. Kolar, “High-Eciency Weight-Optimized Fault-Tolerant Modular Multi-Cell Three-Phase GaN Inverter for NextGeneration Aerospace Applications,” in Proc. of IEEE Energy Conversion Congressand Exposition (ECCE-USA), Portland, OR, USA, Sept. 2018, pp. 1334-1341. Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In a motor drive system, for the purposes of being able to use components with low withstand voltage, being able to reduce design man-hours, and being able to share components, etc., it is required to miniaturize and densify the entire system. As one of the technologies for achieving this, there has been proposed a “modular motor drive system (MMD: Modular Motor Drive)” in which the inverter circuit is modularized to use a modular motor that is independent for each segment of the three-phase winding to form a motor and each segment is driven by each module (for example, refer to Non-Patent Document 1). However, in this type of MMD, although the inverter circuit is modularized, the rectifier circuit is not modularized. In this case, since high withstand voltage semiconductor components are required in the rectifier circuit, it is difficult to miniaturize and densify the entire motor drive system. Also, in this MMD, fault tolerance of the rectifier circuit is not considered, and there is a problem that the motor cannot be driven when a fault occurs in the rectifier circuit.

[0008] Thus, in conventional rectifier circuits, there are problems such as the inability to sufficiently miniaturize and densify the motor drive system, and there is also a problem that fault tolerance cannot be achieved when the rectifier circuit fails. The present invention has been completed in view of such problems, and an object thereof is to realize a fault-tolerant motor drive system.

[0009] Solution to the problem

[0010] To solve the above problems, an AC-AC converter according to an aspect of the present invention includes: a multiple of three single-phase rectifier circuit modules that convert the AC voltage of each phase of a three-phase AC input voltage supplied from a three-phase AC power supply into a DC voltage, and each of the multiple of three single-phase rectifier circuit modules is connected to each other using a delta connection or a star connection; an inverter circuit module having the same number as the single-phase rectifier circuit module that converts the DC voltage into a three-phase AC output voltage; and a control unit that controls switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that when any one of the multiple of three single-phase rectifier circuit modules fails, the remaining single-phase rectifier circuit modules and the inverter circuit module connected to the single-phase rectifier circuit module equally output three-phase AC output power.

[0011] Alternatively, the AC-AC converter according to the embodiment may further include a switching unit that switches the single-phase rectifier circuit module between a delta connection and a star connection.

[0012] Let the ratio of the power supply voltage of the three-phase power supply to the maximum value of the DC link voltage be R. Alternatively, at this time, when R is less than a specified value, the switching unit switches the single-phase rectifier circuit module to a delta connection, and when R is greater than or equal to the specified value, the switching unit switches the single-phase rectifier circuit module to a star connection.

[0013] Alternatively, the value of R is within the range of.

[0014] Alternatively, the value of R is

[0015] Alternatively, the control unit controls switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the DC voltage is fixed and the phase of the three-phase input current input from the three-phase AC power supply coincides with the phase of the three-phase AC input voltage.

[0016] Alternatively, the control unit calculates the target capacitor power based on the difference between the DC link voltage of the DC link provided at the subsequent stage of the single-phase rectifier circuit module and the target link voltage, calculates the target motor power for outputting power to an external motor by subtracting the target capacitor power from the target DC power, and controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module based on the target capacitor power and the target motor power, so that the load using the external motor absorbs the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage.

[0017] Alternatively, the DC link includes a capacitor. In this case, the capacitor can also be used to absorb the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage.

[0018] Alternatively, the control unit controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the input power from the three-phase AC power source is evenly distributed to all the single-phase rectifier circuit modules.

[0019] Alternatively, the control unit controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the input power from the three-phase AC power source is distributed to the single-phase rectifier circuit modules at different ratios.

[0020] Alternatively, the control unit calculates the power supply voltage of each phase of the three-phase AC power source, and controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the amount of power distributed to the single-phase rectifier circuit module corresponding to the phase with a higher power supply voltage is greater than the amount of power distributed to the single-phase rectifier circuit module corresponding to the phase with a lower power supply voltage.

[0021] In addition, any combination of the above structural elements, or a mode obtained by mutually replacing the structural elements and forms of the present invention among methods, devices, programs, temporary or non-temporary storage media recording programs, systems, etc. is also effective as a mode of the present invention.

[0022] Effects of the Invention

[0023] According to the present invention, a fault-tolerant, miniaturized, and high-density motor drive system can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a functional block diagram of the delta-connected AC-AC converter according to the first embodiment.

[0025] Figure 2 is a functional block diagram of the star-connected AC-AC converter according to the first embodiment.

[0026] Figure 3 is a diagram showing the state when a failure occurs in one of the single-phase rectifier circuit modules in the Figure 1 AC-AC converter.

[0027] Figure 4 is a diagram showing the state when a failure occurs in one of the single-phase rectifier circuit modules in the Figure 2 AC-AC converter.

[0028] Figure 5 is a functional block diagram of the AC-AC converter in the case of the delta connection according to the second embodiment.

[0029] Figure 6 is a functional block diagram of the AC-AC converter in the case of the star connection according to the second embodiment.

[0030] Figure 7 is a graph of the rectifier circuit input voltage, modulation rate, and rectifier circuit input current with respect to the power supply voltage.

[0031] Figure 8 is a functional block diagram of the control unit in the AC-AC converter according to the fourth embodiment. Detailed Embodiment

[0032] Hereinafter, the present invention will be described based on preferred embodiments with reference to the attached Figure 1 drawings. The embodiments do not limit the invention but are examples. All features described in the embodiments and their combinations are not necessarily essential features of the invention. The same or equivalent structural elements, components, and processes shown in the respective drawings are denoted by the same reference numerals, and repeated descriptions are appropriately omitted. In addition, the scales and shapes of the respective parts shown in the drawings are appropriately set for easy explanation and are not to be construed as being limited unless otherwise specifically mentioned. Further, when terms such as "first" and "second" are used in this specification or claims, unless otherwise specifically mentioned, these terms do not indicate any order or importance and are only used to distinguish one structure from another. In addition, in each drawing, a part of the components that are not important for explaining the embodiments is omitted.

[0033] [First Embodiment]

[0034] Figure 1 and Figure 2This is a functional block diagram of the AC-AC converter 1 according to the first embodiment. The AC-AC converter 1 includes single-phase rectifier circuit modules 11, 12, 13, inverter circuit modules 21, 22, 23, and control units 31, 32, 33. That is, the rectifier circuit of the AC-AC converter 1 is modularized by the single-phase rectifier circuit modules 11, 12, 13. In addition, the inverter circuit of the AC-AC converter 1 is modularized by the inverter circuit modules 21, 22, 23. The single-phase rectifier circuit modules 11, 12, 13 are, for example, single-phase bridge circuits formed using switching elements, and each has 2 input terminals and 2 output terminals. The inverter circuit modules 21, 22, 23 are, for example, three-phase bridge circuits formed using switching elements, and each has 2 input terminals and 3 output terminals. In this way, in the AC-AC converter 1, both the rectifier circuit and the inverter circuit are modularized, so that the entire motor drive system can be configured in a small size and with high density.

[0035] The single-phase rectifier circuit module 11 is connected to the output terminal ACU of the U-phase of a three-phase AC power supply such as a commercial power supply, and is used to convert the single-phase AC voltage v of the U-phase supplied from the output terminal ACU U into a DC voltage. The single-phase rectifier circuit module 12 is connected to the output terminal ACV of the V-phase of the above-mentioned three-phase AC power supply, and is used to convert the single-phase AC voltage v of the V-phase supplied from the output terminal ACV V into a DC voltage. The single-phase rectifier circuit module 13 is connected to the output terminal ACW of the W-phase of the above-mentioned three-phase AC power supply, and is used to convert the single-phase AC voltage v of the W-phase supplied from the output terminal ACW W into a DC voltage. The single-phase rectifier circuit modules 11, 12, 13 are connected to each other using a delta connection ( Figure 1 ) or a star connection ( Figure 2 ). The delta connection (also called the Δ connection) and the star connection (also called the Y connection) are wiring methods widely known in the field of three-phase AC circuits. That is, the delta connection is a method of connecting each of the U-phase, V-phase, and W-phase in the direction of the applied phase voltage and forming a closed circuit. In the delta connection, the line-to-line voltage is equal to the phase voltage, and the line current is equal to the phase current times. The star connection is a method of connecting each of the U-phase, V-phase, and W-phase to the neutral point N at one end of them. In the star connection, the line-to-line voltage is equal to the phase voltage times, and the line current is equal to the phase current.

[0036] DC links v dc1 , v dc2 , v dc3 are respectively provided at the subsequent stages of the single-phase rectifier circuit modules 11, 12, 13 (refer to Figure 5 and Figure 6 ).

[0037] The inverter circuit module 21 converts the DC voltage v converted by the single-phase rectifier circuit module 11 dc1 into a three-phase AC output voltage v 11a , v 11b , v 11c . The inverter circuit module 22 converts the DC voltage v converted by the single-phase rectifier circuit module 12 dc2 into a three-phase AC output voltage v 12a , v 12b , v 12c . The inverter circuit module 21 converts the DC voltage v converted by the single-phase rectifier circuit module 13 dc3 into a three-phase AC output voltage v 13a , v 13b , v 13c . The three-phase AC output voltages v 11a , v 11b , v 11c are supplied to the first winding WS1 of the three-phase motor. The three-phase AC output voltages v 12a , v 12b , v 12c are supplied to the second winding WS2 of the three-phase motor. The three-phase AC output voltages v 13a , v 13b , v 13c are supplied to the third winding WS3 of the three-phase motor. In this way, the three-phase motor is driven by the three-phase outputs supplied to the first winding WS1, the second winding WS2, and the third winding WS3.

[0038] The control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23 so that when a failure occurs in any one of the single-phase rectifier circuit modules 11, 12, and 13, the remaining single-phase rectifier circuit modules and the inverter circuit modules output three-phase AC output power equally.

[0039] Figure 3 shows in Figure 1A diagram showing the state when a fault occurs in one of the single-phase rectifier circuit modules in the AC-AC converter, i.e., the single-phase rectifier circuit module 13. It is assumed that before the single-phase rectifier circuit module 13 fails, the single-phase rectifier circuit modules 11, 12, and 13 respectively output 1 / 3 of the three-phase AC output power equally. If the single-phase rectifier circuit module 13 fails, the control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23 so that the remaining single-phase rectifier circuit module 11 and the inverter circuit module 21, the single-phase rectifier circuit module 12 and the inverter circuit module 22 output 1 / 2 of the three-phase AC output power equally. At this time, the third winding WS3 of the motor does not operate, but since the output to the remaining windings WS1 and WS2 increases from 1 / 3 to 1 / 2, the total output of the motor does not change. As Figure 3 shown, since the single-phase rectifier circuit modules 11, 12, and 13 are connected to each other using a delta connection, even if a fault occurs in the single-phase rectifier circuit module 13, a three-phase AC output power is output without the influence of this fault spreading to the remaining single-phase rectifier circuit modules 11 and 12, and the motor can be driven continuously in a fault-tolerant manner.

[0040] Figure 4 A diagram showing the state when a fault occurs in one of the single-phase rectifier circuit modules in the Figure 2 AC-AC converter, i.e., the single-phase rectifier circuit module 13. It is assumed that before the single-phase rectifier circuit module 13 fails, the single-phase rectifier circuit modules 11, 12, and 13 respectively output 1 / 3 of the three-phase AC output power equally. If the single-phase rectifier circuit module 13 fails, the control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23 so that the remaining single-phase rectifier circuit module 11 and the inverter circuit module 21, the single-phase rectifier circuit module 12 and the inverter circuit module 22 output 1 / 2 of the three-phase AC output power equally. At this time, the third winding WS3 of the motor does not operate, but since the output to the remaining windings WS1 and WS2 increases from 1 / 3 to 1 / 2, the total output of the motor does not change. As Figure 4As shown, since the single-phase rectifier circuit modules 11, 12, and 13 are connected to each other using a star connection, even if a failure occurs in the single-phase rectifier circuit module 13, three-phase AC output power is output without the influence of this failure reaching the remaining single-phase rectifier circuit modules 11 and 12, and the motor can be continuously driven in a fault-tolerant manner.

[0041] As described above, according to this embodiment, a fault-tolerant, miniaturized, and high-density motor drive system can be realized.

[0042] In the above embodiment, the number of single-phase rectifier circuit modules and the number of inverter circuit modules are both three. However, this is not limited thereto. Regarding the number of rectifier circuit modules and inverter circuit modules, as long as the two are the same number, it can also be any multiple of three. For example, the following cases: when there are six (3 × 2) rectifier circuit modules and inverter circuit modules, two sets of delta connections or star connections can be formed; when there are nine (3 × 3) rectifier circuit modules and inverter circuit modules, three sets of delta connections or star connections can be formed.

[0043] In the above embodiment, three control units 31, 32, and 33 are provided, which independently control the single-phase rectifier circuit module 11 and the inverter circuit module 21, the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the single-phase rectifier circuit module 13 and the inverter circuit module 23, respectively. However, this is not limited thereto. For example, it can also be that one control unit comprehensively controls the single-phase rectifier circuit modules 11, 12, 13 and the inverter circuit modules 21, 22, 23.

[0044] [Second Embodiment]

[0045] Figure 5 and Figure 6 are functional block diagrams of the AC-AC converter 2 according to the second embodiment. The AC-AC converter 2 adds a switching unit 50 to the structure of the Figure 1 and Figure 2 AC-AC converter 1. Other structures of the AC-AC converter 2 are the same as those of the AC-AC converter 1, so repeated descriptions are omitted.

[0046] The switching unit 50 switches the single-phase rectifier circuit modules 11, 12, and 13 between a delta connection and a star connection. The switching unit 50 can be, for example, an automatic switch or a manual switch. Figure 5 Shows the AC-AC converter 2 when it is switched to a delta connection by the switching unit 50. Figure 6 Shows the AC-AC converter 2 when it is switched to a star connection by the switching unit 50.

[0047] According to this embodiment, the connection method of the single-phase rectifier circuit module can be freely switched between the delta connection and the star connection according to the magnitude and application of the input voltage.

[0048] [Third Embodiment]

[0049] Figure 7 The upper part of is the rectifier input voltage v in the case of delta connection and star connection R with respect to the power supply voltage v G The curve graph. Among them, the power supply voltage on the horizontal axis uses the ratio v dc,max with respect to the maximum value v G of the DC link voltage dc,max to represent (the same below). Figure 7 The middle part of is the modulation ratio M R in the case of delta connection and star connection G with respect to the power supply voltage v R The curve graph. Here, the modulation ratio M R is defined as the ratio of the rectifier input peak voltage v dc to the DC link voltage v

[0050] That is, R M R = v dc / v

[0051] Figure 7 The lower part of is the rectifier input current i R in the case of delta connection and star connection G with respect to the power supply voltage v

[0052] In the case of delta connection, the rectifier input voltage is equal to the line-to-line voltage. Therefore, the rectifier input voltage v R,D is G times the power supply voltage v (below, let the subscript on the right D represent delta connection and Y represent star connection). That is,

[0053]

[0054] Therefore, the modulation ratio M R,D in the case of delta connection is:

[0055]

[0056] In the case of star connection, the rectifier input voltage is equal to the line-to-line voltage. Therefore,

[0057] v R,Y = v G

[0058] Modulation rate M R,Y is as follows:

[0059] M R,Y = v G / v dc .

[0060] As Figure 7 shown, in terms of obtaining a high rectifier input voltage when the power supply voltage is low, using the delta connection is more advantageous than using the star connection. On the other hand, when the power supply voltage is high, the rectifier input voltage becomes too high, so using the star connection is more advantageous than using the delta connection. In particular, if the power supply voltage v G is the maximum value v dc,max of the DC link voltage or more and the delta connection is used, then the maximum DC link voltage v dc,max needs to be designed to be more than

[0061] times the maximum power supply voltage, and high-voltage withstand components need to be used. G According to the above, in the third embodiment, when the ratio of the power supply voltage v dc,max to the maximum value v

[0062] of the DC link voltage of the DC link provided at the subsequent stage of the single-phase rectifier circuit module is set as R, when R is less than the specified value, the switching unit 50 switches the single-phase rectifier circuit modules 11, 12, 13 to the delta connection, and when R is equal to or more than the specified value, the switching unit 50 switches the single-phase rectifier circuit modules 11, 12, 13 to the star connection.

[0063] According to this embodiment, it is possible to accurately switch the connection method of the single-phase rectifier circuit module between the delta connection and the star connection according to the magnitude of the power supply voltage. In particular, the value of R can also be within the range of

[0064] . Thus, a margin of ±5% can be provided, and an accurate R can be selected. In particular, the value of R can also be

[0065] [Fourth Embodiment]

[0066] In the fourth embodiment, the control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23 so that the DC voltage is fixed and the phase of the three-phase input current input from the three-phase AC power supply coincides with the phase of the three-phase AC input voltage.

[0067] In this way, the control unit 31 controls the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the single-phase rectifier circuit module 13 and the inverter circuit module 23, whereby it is possible to absorb the pulsation of the power generated by the DC voltages generated by the single-phase rectifier circuit modules 11, 12, and 13. That is, according to the present embodiment, the rectifier circuit 100 can be made into a PFC rectifier circuit, and thus it is possible to achieve a power factor = 1 control.

[0068] [Fifth Embodiment]

[0069] In the fifth embodiment, the control units 31, 32, and 33 calculate the target capacitor power based on the difference between the DC link voltage and the target link voltage, calculate the target motor power by subtracting the target capacitor power from the target DC power, and control the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23 based on the target capacitor power and the target motor power so as to absorb the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage. According to this embodiment, it is possible to absorb the power pulsation without using a large-capacity DC link capacitor.

[0070] Next, use Figure 8 to describe in detail the structure and operation of the control units 31, 32, and 33 in the fifth embodiment. Figure 8 is a detailed functional block diagram of the control unit 31 ( Figure 8 showing the control unit 31 to represent the control units 31, 32, and 33, and the same applies to the control units 32 and 33). The control unit 31 includes a DC link voltage control unit 42, a rectifier circuit control unit 44, a speed control unit 46, and an inverter control unit 48. The control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21 to adjust the generated DC voltage and three-phase AC voltage.

[0071] The DC link voltage control unit 42 includes a first input terminal 42b, a second input terminal 42c, and an output terminal 42d. The rectifier circuit control unit 44 includes an input terminal 44b and an output terminal 44c. The speed control unit 46 includes a first input terminal 46b, a second input terminal 46c, and an output terminal 46d. The inverter control unit 48 includes an input terminal 48b, a first output terminal 48c, a second output terminal 48d, and a third output terminal 48e. The control unit 31 sets a low-pass filter 43a between the output terminal 42d of the DC link voltage control unit 42 and the input terminal 44b of the rectifier circuit control unit 44. The control unit 31 sets a low-pass filter 43b in the front stage of the second input terminal 46c of the speed control unit 46.

[0072] The target DC link voltage v is input to the first input terminal 42b of the DC link voltage control unit 42. DC *. Input the current DC link voltage v to the second input terminal 42c DC The DC link voltage control unit 42 is based on v DC * and v DC The difference Δv DC (not shown), to find the target capacitor power P C *, and outputs it from the output terminal 42d.

[0073] The target capacitor power P outputted from the output terminal 42d of the DC link voltage control unit 42 C * At the branch point v3, it is branched into two, one of which is input to the low-pass filter 43a. The low-pass filter 43a is from P C * Absorbs high frequency components to generate target average capacitor power <P C >*, and output it. The output from the low-pass filter 43a <P C >*Branched into two at branch point v4, one of which is the target average inverter output output from output terminal 46d of speed control unit 46. <P INV >* Add. As a result, the target average rectified power <P PFC >* is evaluated as <P PFC >*= <P C >*+ <P INV >*. Calculated <P PFC >* is input to the input terminal 44b of the rectifier circuit control unit 44. C * minus the one branched at branch point v4 <P C >* another one to generate input power pulsation P C,AC That is, the input power pulsation P C,AC is the target capacitor power P C * is obtained by extracting only the pulsating part. From the target rectified power pPFC Subtract the input power ripple P from it C,AC to calculate the target motor power p M *(p M * = p PFC * - P C,AC ). The calculated p* M is input to the input terminal 48b of the inverter control unit 48.

[0074] In this way, the target motor power p* M input to the inverter control unit 48 is obtained by subtracting the input power ripple P from the target rectifier power p* PFC . That is, the ripple Δp of the DC link is input to the three-phase motor 600 C,AC . The three-phase motor 600 compensates for this ripple using the inertia of the load connected to the three-phase motor 600. As a result, the ripple of the DC link is absorbed, and p DC = p M holds. That is, the motor power p G is consistent with the input power p M . G

[0075] Due to the compensation of the input power p G by the three-phase motor 600, the speed ω of the three-phase motor 600 pulsates at twice the frequency 2f G of the frequency f G of the input power p G . Therefore, the high-frequency component of ω is removed using a low-pass filter as follows. The current motor speed ω is input to the low-pass filter 43b. The low-pass filter 43b removes the high-frequency component from ω to generate the current average motor speed <ω>, and inputs it to the second input terminal 46c of the speed control unit 46. The target average speed <ω>* of the three-phase motor 600 is input to the first input terminal 46b of the speed control unit 46. The speed control unit 46 calculates the target average inverter output <P INV >* based on the difference Δω (not shown) between <ω>* and <ω>, and outputs it from the output terminal 46d.

[0076] The rectifier circuit control unit 44 controls the rectifier circuit 10 in a feed-forward manner to keep the DC link voltage v DC fixed. The target average inverter output <P INV >* output from the output terminal 46d of the speed control unit 46 is added to the target average capacitor power <P C >* output from the low-pass filter 43a. As a result, the target average rectifier power <P PFC >* is calculated as <P PFC >* = <P C >* + <PINV >*。The calculated <P PFC >* is input to the input terminal 44b of the rectifier circuit control unit 44. Based on the input <P PFC >*, the rectifier circuit control unit 44 calculates the target input current i G >*(not shown), obtains the output duty ratio d based on the inductor current difference B >, and outputs it from the output terminal 44c. The output duty ratio d B > is input to the rectifier circuit 100 via a pulse width modulator (not shown) to achieve the desired control.

[0077] According to this embodiment, the control units 31, 32, and 33 configured as described above can be used to absorb power pulsations using the load of the motor. Thus, without using a large-capacity DC link capacitor, it is possible to further miniaturize, increase the density, reduce the cost, and extend the lifespan of the entire motor drive system.

[0078] [Sixth Embodiment]

[0079] In the sixth embodiment, DC links v dc1 、v dc2 、v dc3 provided respectively at the subsequent stages of the single-phase rectifier circuit modules 11, 12, and 13 each have a capacitor. These capacitors are used to absorb the pulsations of the three-phase AC power related to the three-phase AC input voltage and the pulsations of the DC power related to the DC voltage.

[0080] In a typical example, when the rectifier circuit 103 operates at several kW and several hundred V, the capacitance of these capacitors is in the mF range.

[0081] According to this embodiment, it is possible to absorb power pulsations without providing a special control unit.

[0082] [Seventh Embodiment]

[0083] In the seventh embodiment, the control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23 so that the input power from the three-phase AC power supply is evenly distributed to all the single-phase rectifier circuit modules 11, 12, and 13. That is, the single-phase rectifier circuit modules 11, 12, and 13 respectively output 1 / 3 of the three-phase AC output power evenly to the inverter circuit modules 21, 22, and 23. In this case, since the same amount of power is evenly supplied to the windings WS1, WS2, and WS3 of the three-phase motor, the motor is driven smoothly.

[0084] According to this embodiment, stable motor drive can be achieved.

[0085] [Eighth Embodiment]

[0086] In the eighth embodiment, the control unit 31 controls the switching elements constituting the single-phase rectifier circuit module 11 and the inverter circuit module 21, and the control unit 32 controls the switching elements constituting the single-phase rectifier circuit module 12 and the inverter circuit module 22, and the control unit 33 controls the switching elements constituting the single-phase rectifier circuit module 13 and the inverter circuit module 23, so that the input power from the three-phase AC power supply is distributed to the single-phase rectifier circuit modules 11, 12, and 13 at different ratios. For example, the control units 31, 32, and 33 may also calculate the motor drive efficiency of each phase to obtain the power distribution that can drive the motor most efficiently. As a result, for example, the following cases may occur: 50%, 30%, and 20% of the input power are respectively distributed to the single-phase rectifier circuit modules 11, 12, and 13, or 50%, 50%, and 0% (in this case, equally distributed to the modules of the U phase and the V phase, and the module of the W phase stops).

[0087] According to this embodiment, efficient motor drive can be achieved.

[0088] [Ninth Embodiment]

[0089] In the ninth embodiment, the control units 31, 32, and 33 calculate the power supply voltage of each phase of the three-phase AC power supply, and control the switching elements constituting the single-phase rectifier circuit module 11 and the above-mentioned inverter circuit module 21, the single-phase rectifier circuit module 12 and the above-mentioned inverter circuit module 22, and the single-phase rectifier circuit module 13 and the above-mentioned inverter circuit module 23, so that the amount of power distributed to the single-phase rectifier circuit module corresponding to the phase with a higher power supply voltage is larger than the amount of power distributed to the single-phase rectifier circuit module corresponding to the phase with a lower power supply voltage. This compensates for the imbalance by supplying more power to the load corresponding to the phase with a higher power supply voltage when there is an imbalance between the phases of the power supply voltage. Thus, even when there is an imbalance between the phases of the power supply voltage, the motor can be driven with optimal efficiency.

[0090] According to this embodiment, efficient motor drive can be achieved.

[0091] The above is an explanation based on the embodiments of the present invention. These embodiments are examples, and those skilled in the art understand that various deformations and changes can be made within the scope of the claims of the present invention. In addition, those skilled in the art understand that such deformation examples and changes are also within the scope of the claims of the present invention. Therefore, the descriptions and drawings in this specification should not be regarded as restrictive, but should be regarded as illustrative.

[0092] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present invention. The new embodiment produced by the combination has the effects of the respective embodiments and modifications being combined.

[0093] Description of Reference Numerals

[0094] 1, 2: AC-AC converter; 11, 12, 13: single-phase rectifier circuit module; 21, 22, 23: inverter circuit module; 31, 32, 33: control unit; 50: control unit.

Claims

1. An AC-AC converter, comprising: A number of single-phase rectifier circuit modules that is a multiple of 3, each of the single-phase rectifier circuit modules converting the AC voltage of each phase of a three-phase AC input voltage supplied from a three-phase AC power supply into a DC voltage, and the single-phase rectifier circuit modules of the number that is a multiple of 3 being connected to each other using a delta connection or a star connection; An inverter circuit module having the same number as the single-phase rectifier circuit module, the inverter circuit module converting the DC voltage into a three-phase AC output voltage; and A control unit that controls switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that when a failure occurs in any one of the single-phase rectifier circuit modules of the number that is a multiple of 3, the remaining single-phase rectifier circuit modules and the inverter circuit module connected to the single-phase rectifier circuit module output three-phase AC output power equally.

2. The AC-AC converter according to claim 1, wherein It further comprises a switching unit that switches the single-phase rectifier circuit module between the delta connection and the star connection.

3. The AC-AC converter according to claim 2, wherein When the ratio of the power supply voltage of the three-phase AC power supply to the maximum value of the DC link voltage of a DC link that is a DC coupling stage provided at the subsequent stage of the single-phase rectifier circuit module is set as R, When R is less than a specified value, the switching unit switches the single-phase rectifier circuit module to a delta connection, and when R is greater than or equal to the specified value, the switching unit switches the single-phase rectifier circuit module to a star connection.

4. The AC-AC converter according to claim 3, wherein The value of R lies within the range of.

5. The AC-AC converter according to claim 4, wherein The value of R is 6. The AC-AC converter according to any one of claims 1 to 5, wherein The control unit controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the DC voltage is fixed and the phase of the three-phase input current input from the three-phase AC power supply is made to coincide with the phase of the three-phase AC input voltage.

7. The AC-AC converter according to claim 6, wherein The control unit calculates a target capacitor power based on the difference between the DC link voltage and a target link voltage, calculates a target motor power for outputting power to an external motor by subtracting the target capacitor power from the target DC power, and controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module based on the target capacitor power and the target motor power so as to absorb the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage using the load of an external motor.

8. The AC-AC converter according to claim 7, wherein The DC link includes a capacitor, The capacitor is used to absorb the pulsation of the three-phase AC power related to the three-phase AC input voltage and the pulsation of the DC power related to the DC voltage.

9. The AC-AC converter according to any one of claims 1 to 5, wherein the control unit controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the input power from the three-phase AC power supply is equally distributed to all of the single-phase rectifier circuit modules.

10. The AC-AC converter according to any one of claims 1 to 5, wherein the control unit controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the input power from the three-phase AC power supply is distributed to the single-phase rectifier circuit modules at different ratios.

11. The AC-AC converter according to any one of claims 1 to 5, wherein the control unit calculates the power supply voltage of each phase of the three-phase AC power supply, and controls the switching elements constituting the single-phase rectifier circuit module and the inverter circuit module so that the amount of power distributed to the single-phase rectifier circuit module corresponding to the phase with a higher power supply voltage is greater than the amount of power distributed to the single-phase rectifier circuit module corresponding to the phase with a lower power supply voltage.

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