AC-AC converter

Abstract

To provide an AC-AC converter that is smaller and has higher density.SOLUTION: An AC-AC converter includes rectifier circuit modules that are multiples of 3 that convert a three-phase AC input voltage supplied from a three-phase AC power supply to a DC voltage, and the same number of inverter circuit modules as the rectifier circuit modules that convert the DC voltage to the three-phase AC output voltage. Each of the three input terminals of each of the rectifier circuit modules is connected to an output terminal of each phase of the three-phase AC power supply and the input terminal of the rectifier circuit module different from the rectifier circuit module through an inductor.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Three-phase motors are widely used in industrial equipment such as fans, pumps, FA equipment, etc. Motor drive systems for driving such three-phase motors generally include an AC-AC converter that is composed of a rectifier circuit that rectifies a three-phase AC voltage to generate a DC voltage (rectified voltage), a DC link in the subsequent stage, and an inverter circuit that generates a three-phase AC voltage from the DC link voltage. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] M. Guacci, D. Bortis, and JWKolar, “High-Eciency Weight-Optimized Fault-Tolerant Modular Multi-Cell Three-Phase GaN Inverter for Next Generation Aerospace Applications,” in Proc. of IEEE Energy Conversion Congress and Exposition(ECCE-USA), Portland, OR, USA, September 2018, pp. 1334-1341. [Non-Patent Document 2] JWKolar and T. Friedli “The Essence of Three-Phase PFC Rectifir Systems-Part I,” IEEE Transactions on Power Electronics, vol. 28, no. 1, 1, pp. 176-198, Jan. 2013. [Non-Patent Document 3] J. Wen and K. Smedley, “A New Multilevel Inverter-Hexagram Inverter for Medium Voltage Adjustable Speed ​​Drive Systems PartII.Three-phase Motor Drive,” in Proc. of the IEEE Power Electronics Specialists Conference (PESC), Orlando, FL, USA, June 2007, pp. 1571-1577. [Non-Patent Document 4] J. Wen and KMSmedley, “Synthesis of Multilevel Converters Based on Single-and / or Three-Phase Converter Building Blocks,” IEEE Transactions on Power Electronics, vol.23, no.3, pp.1247-1256, May 2008. Summary of the Invention [Problem to be solved by the invention]

[0004] In a motor drive system, it is required to reduce the size and density of the entire motor drive system in order to use low-voltage elements, reduce design man-hours, and standardize parts. As one technology to achieve this, a "modular motor drive system (MMD)" has been proposed in which the motor is configured as a modular motor with independent segments of three-phase windings, and the inverter circuit is modularized to drive each segment individually (see, for example, Non-Patent Document 1). However, in this type of MMD, although the inverter circuit is modularized, the rectifier circuit is not. In this case, a high-voltage semiconductor element is required for the rectifier circuit, making it difficult to reduce the size and density of the entire motor drive system.

[0005] As a method for modularizing a rectifier circuit with a three-phase bridge configuration, a six-switch boost rectifier circuit has been proposed (see, for example, Non-Patent Document 2). In this circuit, a filter inductor is used as the boost inductor. In this case, to realize the boost operation, the output voltage of the rectifier circuit (i.e., the sum of the DC link voltages of the inverter circuit) must be greater than the line-to-line peak voltage of the input voltage. For this reason, the rectifier circuit must be operated at a high voltage, and high-voltage elements are required. As a result, it becomes difficult to reduce the size and density of the entire motor drive system, and a dedicated design according to the input voltage is required, which increases the design and manufacturing costs.

[0006] Another method for modularizing a rectifier circuit is the Back to Back Hexagram Converter, which uses the same low-voltage element circuit for the rectifier circuit and the inverter circuit (see, for example, Non-Patent Document 3). However, this configuration requires an insulated open delta connection, which is disadvantageous in terms of miniaturization, density, and cost.

[0007] Yet another way to modularize the rectifier circuit is to use several interconnected three-phase AC-DC rectifier cells (see, for example, Non-Patent Document 4). This interconnection can reduce the withstand voltage of the rectifier cells, so the same cells can be used for the rectifier cells and the inverter. However, to drive a load using inverter cells connected in parallel to the input, an additional isolated DC-DC converter is required. This additional DC-DC converter is an obstacle to miniaturization and high density of the entire motor drive system.

[0008] As described above, conventional rectifier circuits have the problem that they cannot adequately reduce the size and density of motor drive systems. The present invention has been made in consideration of these problems, and its purpose is to reduce the size and density of motor drive systems. [Means for solving the problem]

[0009] In order to solve the above problems, an AC-AC converter according to an embodiment of the present invention includes rectifier circuit modules (a multiple of three) that convert a three-phase AC input voltage supplied from a three-phase AC power source into a DC voltage, and inverter circuit modules (the same number as the rectifier circuit modules) that convert the DC voltage into a three-phase AC output voltage. Each of the rectifier circuit modules has three input terminals that are connected to an output terminal of each phase of the three-phase AC power source and an input terminal of the rectifier circuit module other than the rectifier circuit module via an inductor.

[0010] The AC-AC converter of the embodiment may include a control unit that controls switching elements constituting the rectifier circuit module and the inverter circuit module so that the DC voltage is a constant DC voltage and the phases of a three-phase input current input from an AC power source and the three-phase AC voltage match.

[0011] The control unit may control switching elements constituting the rectifier circuit module and the inverter circuit module so as to absorb pulsations in three-phase AC power related to the three-phase AC input voltage and DC power related to the DC voltage using a load of an external motor.

[0012] The control unit may calculate a target capacitor power based on a difference between a DC link voltage of a DC link provided downstream of the rectifier circuit module and a target link voltage, calculate a target motor power by subtracting the target capacitor power from the target DC power, and control switching elements constituting the rectifier circuit module and the inverter circuit module so as to absorb voltage pulsation of the DC link using an external motor load based on the target capacitor power and the target motor power.

[0013] The DC link may include a capacitor that absorbs pulsations in the three-phase AC power for the three-phase AC voltage and in the DC power for the DC voltage.

[0014] The number of rectifier circuit modules may be three.

[0015] Each of the rectifier circuit modules may include an energy buffer circuit connected to one of the three input terminals for buffering the energy of the three-phase AC input power supplied from the three-phase AC power source to prevent excessive power from being input to the rectifier circuit module.

[0016] A low-pass filter may be provided in front of the rectifier circuit module.

[0017] The low pass filter may be an LC low pass filter.

[0018] Each of the inverter circuit modules may be modularized with two AC-AC conversion sub-modules.

[0019] The rectifier circuit module and the inverter circuit module may be configured in the same circuit.

[0020] In addition, any combination of the above components, or mutual substitution of the components or expressions of the present invention among methods, devices, programs, temporary or non-temporary storage media recording programs, systems, etc., are also valid aspects of the present invention. Effect of the Invention

[0021] According to the present invention, the motor drive system can be made smaller and more dense. [Brief description of the drawings]

[0022] [Figure 1] 1 is a functional block diagram of an AC-AC converter according to a first embodiment. [Diagram 2] FIG. 2 is a functional block diagram of an AC-AC converter according to a comparative example. [Diagram 3] 1A is a graph showing the time variation of a first three-phase AC voltage, and FIG. 1B is a phasor representation of the three-phase AC voltage of FIG. [Figure 4](a) is a phasor display of the first three-phase AC voltage when there are three rectifier circuit modules, (b) is a phasor display of the first three-phase AC voltage when there are six rectifier circuit modules, and (c) is a phasor display of the first three-phase AC voltage when there are nine rectifier circuit modules. [Diagram 5] FIG. 11 is a functional block diagram of an AC-AC converter according to a second embodiment. [Figure 6] FIG. 11 is a functional block diagram of a control unit in an AC-AC converter according to a third embodiment. [Figure 7] FIG. 13 is a functional block diagram of an AC-AC converter according to a fourth embodiment. [Figure 8] FIG. 13 is a functional block diagram of a rectifier circuit including an energy buffer circuit in an AC-AC converter according to a fifth embodiment. [Figure 9] FIG. 13 is a functional block diagram of a rectifier circuit in an AC-AC converter according to a sixth embodiment. [Figure 10] FIG. 13 is a functional block diagram of an AC-AC conversion sub-module in an AC-AC converter according to a seventh embodiment. [Figure 11] FIG. 2 is a diagram showing a circuit configuration of a rectifier circuit module in an AC-AC converter according to a plurality of embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will be described below with reference to the drawings based on preferred embodiments. The embodiments are illustrative and do not limit the invention. All features and combinations described in the embodiments are not necessarily essential to the invention. The same or equivalent components, members, and processes shown in each drawing are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the scale and shape of each part shown in each drawing are set for convenience to facilitate explanation, and are not to be interpreted as being limiting unless otherwise specified. In addition, when terms such as "first" and "second" are used in this specification or claims, unless otherwise specified, these terms do not represent any order or importance, but are only intended to distinguish one configuration from another. In addition, some of the members that are not important in explaining the embodiment in each drawing are omitted.

[0024] [First embodiment] 1 is a functional block diagram of an AC-AC converter 1 according to a first embodiment. The AC-AC converter 1 includes a rectifier circuit 100 and an inverter circuit 300. The rectifier circuit 100 generates a DC voltage from a three-phase AC input voltage (hereinafter referred to as a "first three-phase AC input voltage") from a three-phase AC power source such as a commercial power source. This DC voltage is output to the inverter circuit 300. The inverter circuit 300 converts the DC voltage output from the rectifier circuit 100 into a three-phase AC input voltage (hereinafter referred to as a "second three-phase AC voltage"). A three-phase motor is driven by the second three-phase AC output voltage.

[0025] The rectifier circuit 100 is modularized. That is, the rectifier circuit 100 includes a first rectifier circuit module 11, a second rectifier circuit module 12, a third rectifier circuit module 13, and inductors 20, 21, 22, 23, 24, and 25. As described later, each of the first, second, and third rectifier circuit modules 11, 12, and 13 is, for example, a three-phase bridge circuit configured with six switching elements, and includes three input terminals and two output terminals. The first, second, and third rectifier circuit modules 11, 12, and 13 are all connected to each other via inductors. That is, the first rectifier circuit module 11 is connected to the second rectifier circuit module 12 via the inductor 23, and is connected to the third rectifier circuit module 13 via the inductor 25. The second rectifier circuit module 12 is connected to the third rectifier circuit module 13 via an inductor 24, and is connected to the first rectifier circuit module 11 via an inductor 23. The third rectifier circuit module 13 is connected to the first rectifier circuit module 11 via an inductor 25, and is connected to the second rectifier circuit module 12 via an inductor 24. Hereinafter, such a connection configuration in which all elements and circuits are interconnected with all other elements and circuits will be referred to as a "mesh connection." That is, in this embodiment, the first, second and third rectifier circuit modules 11, 12 and 13 are mesh-connected via inductors.

[0026] One of the input terminals of the first rectifier circuit module 11 is connected to the output terminal of the U-phase of the three-phase AC power source via the inductor 20. The U-phase 500U of the three-phase power source is input to the first rectifier circuit module 11 via the inductor 20. The input voltage to the first rectifier circuit module 11 is v u , input current i u One of the input terminals of the second rectifier circuit module 12 is connected to the output terminal of the V phase of the three-phase AC power supply via the inductor 21. The V phase of the three-phase power supply, 500 V, is input to the second rectifier circuit module 12 via the inductor 21. The input voltage to the second rectifier circuit module 12 is v v , input current i vOne of the input terminals of the third rectifier circuit module 13 is connected to the output terminal of the W phase of the three-phase AC power supply via the inductor 22. 500 W of the W phase of the three-phase power supply is input to the third rectifier circuit module 13 via the inductor 22. The input voltage to the third rectifier circuit module 13 is v w , input current i w Let us assume that.

[0027] The first, second and third rectifier circuit modules 11, 12 and 13 are followed by DC links v dc1 , v dc2 , v dc3 is provided.

[0028] The first rectifier circuit module 11 is connected to an input voltage v u and the input current i u The second rectifier circuit module 12 removes power pulsations caused by the input voltage v and generates a first DC voltage. v and the input current i v The third rectifier circuit module 13 removes the power pulsation caused by the input voltage v and generates a second DC voltage. w and the input current is i w The first, second and third DC voltages are output to first, second and third DC links, respectively, which are external to the rectifier circuit 101. The voltages of the first, second and third DC links (DC link voltages) are respectively denoted as v dc1 , v dc2 and v dc3 The first, second and third rectifier circuit modules 11, 12 and 13 are mesh-connected via inductors, so that each DC link voltage v dc1 , v dc2 and v dc3 will be equal.

[0029] The first, second and third external DC-link voltages v dc1 , v dc2 and v dc3is input to the inverter circuit 300. The inverter circuit 300 is modularized and includes a first inverter circuit module 31, a second inverter circuit module 32, and a third inverter circuit module 33. The first, second, and third external DC link voltages v dc1 , v dc2 and v dc3 are input to the first, second and third inverter circuit modules 31, 32 and 33 of the inverter circuit 300, respectively. The first inverter circuit module 31 outputs a first DC link voltage v dc1 to 3-phase AC voltage v 11a , v 11b and v 11c The second inverter circuit module 32 generates a second DC link voltage v dc2 to 3-phase AC voltage v 12a , v 12b and v 12c The third inverter circuit module 33 converts and generates a third DC link voltage v dc3 to 3-phase AC voltage v 13a , v 13b and v 13c Generate.

[0030] 3-phase AC voltage v 11a , v 11b and v 11c is supplied to a first winding WS1 of the three-phase motor 600. The three-phase AC voltage v 12a , v 12b and v 12c is supplied to the second winding WS2 of the three-phase motor 600. The three-phase AC voltage v 13a , v 13b and v 13c is supplied to the third winding WS3 of the three-phase motor 600. In this manner, the three-phase motor 600 is driven by a three-phase output supplied to the first, second and third windings WS1, WS2 and WS3.

[0031] In the above-described embodiment, the number of rectifier circuit modules and the number of inverter circuit modules are both 3. However, this is not limited to this, and the numbers of rectifier circuit modules and inverter circuit modules may be any multiple of 3 as long as they are the same number.

[0032] [Comparative Example] FIG. 2 is a functional block diagram of an AC-AC converter 2 according to a comparative example. The AC-AC converter 2 was devised in the process of arriving at the present invention. The AC-AC converter 2 according to the comparative example includes a rectifier 120 instead of the first, second, and third rectifier circuit modules 11, 12, and 13 of the AC-AC converter 1 according to the embodiment. That is, the rectifier 120 of the comparative example is different from the embodiment in that it is not modularized but is configured with a single DC bus. Other configurations of the AC-AC converter 2 are the same as those of the AC-AC converter 1, so duplicated explanations will be omitted.

[0033] The rectifier 120 receives the U-phase 500U, V-phase 500V, and W-phase 500W of a three-phase power supply via inductors 20, 21, and 22, respectively. The rectifier 120 converts the input voltage v u and the input current i u Power pulsation caused by V phase 500V input voltage v v and the input current i v The power ripple caused by the W-phase 500W input voltage v w and the input current i w It eliminates power ripples caused by and generates a DC voltage.

[0034] As described above, the rectifier 120 is not modularized and is configured with one DC bus. In this case, since the input and output peak voltages are high, the circuit elements used in the rectifier 120 are required to have high voltage resistance. In contrast, the rectifier circuit 100 is modularized with three rectifier circuit modules 11, 12, and 13, so that the voltage resistance of each module can be reduced to 1 / 3 of the input and output peak voltages. Therefore, all modules including the inverter circuit can use low-voltage circuit elements. This makes it possible to reduce the size and density of the entire motor drive system. In this way, according to this embodiment, the motor drive system can be reduced in size and density.

[0035] The number of rectifier circuit modules is a multiple of 3. This point will be described below. FIG. 3(a) is a graph showing the change over time of the first three-phase AC voltage. As shown in the figure, the first three-phase AC voltage v RiA , v RiB , v RiC are out of phase with each other by 120 degrees. Figure 3(b) shows the phasor display of the three-phase AC voltages in Figure 3(a). The phasor display shows the change in the power frequency, f G Figure 3(b) shows the power supply period T G Then, t=T G Note that each side of the equilateral triangle in Figure 3(b) is a line voltage.

[0036] FIG. 4(a) is a phasor display of the first three-phase AC voltage when the first, second and third rectifier circuit modules 11, 12 and 13 are mesh-connected via inductors in the first embodiment. This graph is a combination of three equilateral triangles R1, R2 and R3. The sides representing the line voltages are aligned and symmetrical. FIG. 4(b) is a phasor display of the first three-phase AC voltage when six rectifier circuit modules are mesh-connected via inductors. This graph is a combination of six equilateral triangles R1, R2, R3, R4, R5 and R6. In this case, the sides representing the line voltages are aligned and symmetrical. FIG. 4(c) is a phasor display of the first three-phase AC voltage when nine rectifier circuit modules are mesh-connected via inductors. This graph is a combination of nine equilateral triangles: R1, R2, R3, R4, R5, R6, R7, R8, and R9. In this case, each side showing the line voltage is aligned in a straight line and symmetrically. By making the number of rectifier circuit modules a multiple of three in this way, each side of the phasor display showing the line voltage can be aligned in a straight line and symmetrically. This allows the input voltage phases to be kept smooth without any disturbance.

[0037] In particular, when driving a three-phase motor with a motor drive device using the rectifier circuit of the embodiment, by using a multiple of three rectifier circuit modules, it is possible to generate a drive voltage that is an integer multiple of the number of motor windings. This makes it possible to realize smooth motor drive. As the number of rectifier circuit modules is increased to 3, 6, 9, ..., the withstand voltage of each module becomes smaller, to 1 / 3, 1 / 6, 1 / 9, .... Therefore, circuit elements with lower withstand voltages can be used.

[0038] In particular, the number of rectifier circuit modules may be three. In this case, smooth motor drive can be achieved with a minimum number of rectifier circuit modules. This allows the number of parts to be reduced.

[0039] [Second embodiment] Fig. 5 is a functional block diagram of an AC-AC converter 3 according to a second embodiment. The AC-AC converter 3 includes a control unit 40 in addition to the configuration of the AC-AC converter 1 in Fig. 1. Other configurations of the AC-AC converter 3 are the same as those of the AC-AC converter 1, so duplicated explanations will be omitted.

[0040] The control unit 40 controls the switching elements constituting the rectifier circuit modules 11, 12, 13 and the inverter circuit modules 31, 32, 33 so that the DC voltage is constant and the phases of the three-phase input current input from the AC power source and the first three-phase AC voltage match. In Fig. 5, one control unit 40 collectively controls the switching elements constituting the rectifier circuit modules 11, 12, 13 and the inverter circuit modules 31, 32, 33. However, this is not limited to this, and for example, six control units may be provided, and each of them may individually control the switching elements constituting the rectifier circuit modules 11, 12, 13 and the inverter circuit modules 31, 32, 33.

[0041] In this way, the control unit 40 controls the switching elements constituting the rectifier circuit modules 11, 12, and 13 and the inverter circuit modules 31, 32, and 33, thereby making it possible to remove power pulsation generated by the DC voltages generated by the rectifier circuit modules 11, 12, and 13. This allows the rectifier circuit 100 to function as a PFC rectifier circuit, making it possible to achieve control of a power factor of 1.

[0042] [Third embodiment] In the third embodiment, the control unit 40 in Fig. 5 controls the switching elements constituting the rectifier circuit module and the inverter circuit module so as to eliminate pulsation of the three-phase AC power related to the first three-phase AC voltage and the DC power related to the DC voltage by using the load of an external motor. According to this embodiment, the power pulsation can be eliminated without using a large-capacity DC link capacitor.

[0043] The configuration and operation of the control unit 40 in the third embodiment will be described in detail below with reference to Fig. 6. Fig. 6 is a detailed functional block diagram of the control unit 40. The control unit 40 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 40 controls the switching elements constituting the rectifier circuit modules 11, 12, and 13 and the inverter circuit modules 31, 32, and 33 to adjust the generated DC voltage and three-phase AC voltage.

[0044] 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 40 includes 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 40 includes a low-pass filter 43b in front of the second input terminal 46c of the speed control unit 46.

[0045] The first input terminal 42b of the DC link voltage control unit 42 is connected to a target DC link voltage v DC * The second input terminal 42c receives the current DC link voltage v DC is input. The DC link voltage control unit 42 receives v DC * and v DC Difference Δv DC (not shown) based on the target capacitor power p C * is calculated and output from output terminal 42d.

[0046] The target capacitor power P C * is branched into two at a branch point v3, one of which is input to a low-pass filter 43a. C* Remove high frequency components from the target average capacitor power <P C > * The output from the low-pass filter 43a is <P C > * is branched into two at a branch point v4, one of which is the target average inverter output from the output terminal 46d of the speed control unit 46. <P INV > * The result is the target average rectified power <P PFC > * but, <P PFC > * = <P C > * + <P INV > * It is calculated as: <P PFC > * is input to the input terminal 44b of the rectifier circuit control unit 44. <P C > * The other is P branched at branch point v3. C * The input power pulsation p C,AC That is, the input power pulsation p C,AC is the target capacitor power P C * The input power ripple p C,AC is the target rectified power p PFC * is subtracted from the target motor power p M * is calculated (p M * =p PFC * -p C,AC ). The calculated p M * is input to the input terminal 48b of the inverter control unit 48.

[0047] In this way, the target motor power p M * is the target rectified power p PFC * Input power pulsation p C,ACThat is, the three-phase motor 600 has a DC link pulsation Δp DC The three-phase motor 600 compensates for this pulsation by the inertia of the load connected to the three-phase motor 600. As a result, the pulsation of the DC link is absorbed, and p M =p G That is, the motor power p M is the input power p G Matches.

[0048] The speed ω of the three-phase motor 600 is determined by the input power p G Due to the compensation of the input power p G Frequency f G twice the frequency, 2f G Therefore, the high frequency components of ω are 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 components from ω to generate the current average motor speed <ω>, which is input to the second input terminal 46c of the speed control unit 46. The first input terminal 46b of the speed control unit 46 receives the target average speed <ω> of the three-phase motor 600. * is input to the speed control section 46. * Based on the difference Δω (not shown) between and <ω>, the target average inverter output <P INV > * is calculated and output from output terminal 46d.

[0049] The rectifier circuit control unit 44 feeds forward the DC link voltage v DC The rectifier circuit 10 is controlled so as to keep the target average inverter output from the output terminal 46d of the speed control unit 46 constant. <P INV > * is the target average capacitor power output from the low-pass filter 43a <P C > * The result is the target average rectified power <P PFC > * but, <P PFC > * = <P C > * + <PINV > * It is calculated as: <P PFC > * is input to the input terminal 44b of the rectifier circuit control unit 44. The rectifier circuit control unit 44 <P PFC > * Based on the target input current i G * (not shown) is calculated, and the output duty ratio d B The output duty ratio d B is input to the rectifier circuit 100 via a pulse width modulator (not shown) to realize the desired control.

[0050] According to this embodiment, the control unit specifically configured as described above can eliminate power pulsation by using the motor load. This eliminates the need to use a large-capacity DC link capacitor, and enables the entire motor drive system to be made smaller, more dense, less expensive, and have a longer life.

[0051] [Fourth embodiment] 7 is a functional block diagram of an AC-AC converter 4 according to a fourth embodiment. The AC-AC converter 1 includes a rectifier circuit 101 and an inverter circuit 300. The rectifier circuit 101 includes DC links including capacitors C1, C2, and C3 in the rear stages of the rectifier circuit modules 11, 12, and 13, respectively, in comparison with the rectifier circuit 100 in FIG. 1. The capacitors C1, C2, and C3 remove pulsation in the power generated by the input three-phase AC voltage and in the DC power generated by the rectifier circuit modules 11, 12, and 13.

[0052] Typically, when the rectifier circuit 103 operates at several kW and several hundreds of V, the capacitance of these capacitors is on the order of mF. According to this embodiment, power ripple can be eliminated without providing a special control unit.

[0053] [Fifth embodiment] In the fifth embodiment, the AC-AC converter includes an energy buffer circuit. Figure 8 is a functional block diagram of a rectifier circuit including an energy buffer circuit 14. The energy buffer circuit 14 is connected to one of three input terminals of the rectifier circuit modules 11, 12, and 13. The energy buffer circuit 14 is a three-phase bridge circuit composed of, for example, six switching elements, similar to the rectifier circuit modules. The energy buffer circuit 14 buffers the energy of the three-phase AC input power supplied from the three-phase AC power source to prevent excessive power from being input to the rectifier circuit modules 11, 12, and 13. According to this embodiment, energy can be buffered before the input power is input to the rectifier circuit modules, thereby achieving smoother voltage control.

[0054] [Sixth embodiment] FIG. 9 is a functional block diagram of a rectifier circuit 102 in an AC-AC converter according to a sixth embodiment. In the rectifier circuit 102, first, second and third low-pass filters 71, 72 and 73 are provided in front of the first, second and third rectifier circuit modules 11, 12 and 13 of the rectifier circuit 100 in FIG. 1, respectively. The first low-pass filter 71 is a π-type filter composed of inductors L11, L12 and L13, and capacitors C11, C12, C13, C14 and C15. The second low-pass filter 72 is a π-type filter composed of inductors L21, L22 and L23, and capacitors C21, C22, C23, C24 and C25. The third low-pass filter 73 is a π-type filter composed of inductors L31, L32 and L33, and capacitors C31, C32, C33, C34 and C35. The other configuration of the rectifier circuit 102 is the same as that of the rectifier circuit 100, so a duplicated description will be omitted.

[0055] The first, second and third low-pass filters 71, 72 and 73 respectively remove high-frequency components from the input AC voltage to generate a noise-free input AC voltage. The first, second and third rectifier circuit modules 11, 12 and 13 generate a DC voltage from the noise-free input AC voltage. According to this embodiment, a DC voltage with less noise can be generated.

[0056] The low-pass filters 71, 72, and 73 shown in Fig. 9 are simple LC low-pass filters composed of inductors and capacitors. In this case, the low-pass filters 71, 72, and 73 can be easily realized at low cost. However, the present invention is not limited to this, and the low-pass filters may be realized by any other suitable method such as an operational amplifier. Furthermore, the LC low-pass filter in Fig. 6 is a π-type low-pass filter, but is not limited to this, and may be any other suitable type of LC low-pass filter such as an L-type or a T-type.

[0057] [Seventh embodiment] In the AC-AC converter according to the seventh embodiment, each of the inverter circuit modules is modularized together with two AC-AC conversion submodules. Fig. 10 is a functional block diagram of AC-AC conversion submodules 801 and 802 according to the seventh embodiment. The AC-AC conversion submodule 801 includes a rectifier circuit submodule PFC11 and an inverter submodule INV11. The AC-AC conversion submodule 802 includes a rectifier circuit submodule PFC12 and an inverter submodule INV12. The AC-AC conversion submodules 801 and 802 are each modularized together with the inverter circuit module 31 of Fig. 7.

[0058] The rectifier circuit submodules PFC11 and PFC12 are configured with the same circuit as the rectifier circuit module 11. The inverter submodules INV11 and INV12 are configured with the same circuit as the inverter circuit module 31. The AC-AC conversion submodules 801 and 802 each generate a three-phase AC voltage from the three-phase AC voltage generated by the inverter circuit module 31. The three-phase AC voltage generated by the AC-AC conversion submodules 801 and 802 is respectively coupled to the double winding WS of the motor. 11 and W.S. 12 are supplied to.

[0059] Inverter circuit modules 32 and 33 (see, for example, FIG. 7) are also modularized with two AC-AC conversion submodules having the same configuration as AC-AC conversion submodules 801 and 802, respectively. The operation of the AC-AC conversion submodules is similar to that of the AC-AC conversion submodules 801 and 802 described above.

[0060] According to this embodiment, a compact and high-density motor drive device for a motor having dual windings can be realized.

[0061] 11 shows an example of a circuit configuration of the rectifier circuit module 11 in each of the above-mentioned embodiments. The rectifier circuit module 11 is a three-phase bridge circuit configured with switching elements SW1, SW2, SW3, SW4, SW5, and SW6. However, the rectifier circuit module is not limited to this, and may be configured with any other suitable circuit such as a bridgeless circuit.

[0062] In one embodiment, all of the rectifier circuit modules and the inverter circuit modules are configured with the same circuit, which allows the circuit components to be standardized, thereby reducing design and manufacturing costs.

[0063] The above description is based on the embodiment of the present invention. This embodiment is an example, and various modifications and changes are possible within the scope of the claims of the present invention, and it is understood by those skilled in the art that such modifications and changes are also within the scope of the claims of the present invention. Therefore, the description and drawings in this specification should be treated as illustrative rather than restrictive.

[0064] The following describes the modified examples. In the drawings and description of the modified examples, the same or equivalent components and members as those in the embodiment are denoted by the same reference numerals. Descriptions that overlap with the embodiment will be omitted as appropriate, and the description will focus on the configurations that differ from the embodiment.

[0065] The rectifier circuit modules of the embodiment are mesh-connected via inductors. However, the rectifier circuit modules may be mesh-connected via diodes. In this case, a small, high-density rectifier circuit can be realized at a lower cost.

[0066] The modified example provides the same functions and effects as the embodiment.

[0067] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present invention. A new embodiment resulting from the combination has the combined effects of each of the combined embodiments and modifications. [Explanation of symbols]

[0068] 1, 2, 3, 4 AC-AC converter, 11 - a first rectifier circuit module; 12. A second rectifier circuit module; 13. the third rectifier circuit module; 20, 21, 22, 23, 24, 25: Inductors, 31 - first inverter circuit module; 32 - second inverter circuit module; 33 - a third inverter circuit module; 40...Control section, 100, 101, 102... rectifier circuit, 300··Inverter circuit, 600··3-phase motor, 801, 802··AC-AC conversion submodules.

Claims

1. a rectifier circuit module (a multiple of three) for converting a three-phase AC input voltage supplied from a three-phase AC power source into a DC voltage; a rectifier circuit module for converting the DC voltage into a three-phase AC output voltage, and a number of inverter circuit modules equal to the number of the rectifier circuit modules; each of the three input terminals of each of the rectifier circuit modules is connected to an output terminal of each phase of the three-phase AC power supply and an input terminal of a rectifier circuit module other than the rectifier circuit module via an inductor; Each of the rectifier circuit modules is connected to one of the three input terminals of the rectifier circuit module, and is provided with an energy buffer circuit for buffering the energy of the three-phase AC input power supplied from the three-phase AC power source to prevent excessive power from being input to the rectifier circuit module.

2. a rectifier circuit module (a multiple of three) for converting a three-phase AC input voltage supplied from a three-phase AC power source into a DC voltage; a rectifier circuit module for converting the DC voltage into a three-phase AC output voltage, and a number of inverter circuit modules equal to the number of the rectifier circuit modules; each of the three input terminals of each of the rectifier circuit modules is connected to an output terminal of each phase of the three-phase AC power supply and an input terminal of a rectifier circuit module other than the rectifier circuit module via an inductor; An AC-AC converter in which each of the inverter circuit modules is modularized with two AC-AC conversion sub-modules.

3. 3. The AC-AC converter according to claim 1, further comprising a control unit that controls switching elements constituting the rectifier circuit module and the inverter circuit module so that the DC voltage is a constant DC voltage and a phase of a three-phase input current input from an AC power source and the three-phase AC input voltage match.

4. 4. The AC-AC converter according to claim 3, wherein the control unit controls switching elements constituting the rectifier circuit module and the inverter circuit module so as to absorb pulsation of three-phase AC power related to the three-phase AC input voltage and DC power related to the DC voltage using a load of an external motor.

5. 5. The AC-AC converter according to claim 4, wherein the control unit calculates a target capacitor power based on a difference between a DC link voltage of a DC link provided downstream of the rectifier circuit module and a target link voltage, calculates a target motor power by subtracting the target capacitor power from the target DC power, and controls switching elements constituting the rectifier circuit module and the inverter circuit module so as to absorb voltage pulsation of the DC link by using an external motor load based on the target capacitor power and the target motor power.

6. The DC link includes a capacitor; 3. The AC-AC converter of claim 1, wherein the capacitor absorbs pulsations in three-phase AC power for the three-phase AC input voltage and DC power for the DC voltage.

7. 3. The AC-AC converter according to claim 1, wherein the number of the rectifier circuit modules is three.

8. 3. The AC-AC converter according to claim 1, further comprising a low-pass filter provided in a stage preceding the rectifier circuit module.

9. 9. The AC-AC converter according to claim 8, wherein the low-pass filter is an LC low-pass filter.

10. 3. The AC-AC converter according to claim 1, wherein the rectifier circuit module and the inverter circuit module are configured as a same circuit.

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