Circulating current reduction circuit for inverters for modular motors and its operation method

Abstract

The present invention discloses a technique for reducing circulating current in a modular inverter circuit that drives a motor by connecting multiple inverter modules in parallel. The invention includes a master control unit that outputs a pulse-width modulated signal to a master inverter unit and synchronizes it with the pulse-width modulated signal supplied to the slave inverter unit via CAN communication, and a slave control unit that outputs a pulse-width modulated signal to the slave inverter unit and synchronizes it with the pulse-width modulated signal supplied to the master inverter unit via CAN communication.

Description

[Technical Field]

[0001] The present invention relates to a technology for reducing circulating current in a modular inverter circuit that drives a motor by connecting multiple inverter modules in parallel, and more particularly to a circulating current reduction circuit for a modular motor inverter that can reduce circulating current inside the inverter by using an internal communication cycle and a circulating current reduction technique, and an operating method thereof. [Background technology]

[0002] FIG. 1 is a circuit diagram of a conventional inverter for a modular motor, which includes a master inverter unit 11 and a slave inverter unit 21 connected in parallel to a motor M.

[0003] The master inverter unit 11 includes MOS transistors MM1, MM2, MM3, MM4, and MM5, MM6 connected in series. The MOS transistors MM1, MM2 are switched by pulse-width modulation signals PWM supplied to their gates, respectively, and supply a phase current U to the motor M via a common connection point. The MOS transistors MM3, MM4 are switched by pulse-width modulation signals PWM supplied to their gates, respectively, and supply a phase current V to the motor M via a common connection point. The MOS transistors MM5, MM6 are switched by pulse-width modulation signals PWM supplied to their gates, respectively, and supply a phase current W to the motor M via a common connection point.

[0004] The slave inverter unit (21) has MOS transistors (SM1, SM2); (SM3, SM4); (SM5, SM6) of the same configuration as the master inverter unit (11), and supplies U-, V-, and W-phase currents to the motor (M) via their respective common connection points.

[0005] Incidentally, a circulating current flows in such modular motor inverter circuits (11, 21). For example, as shown in FIG. 1, a U-phase current supplied to the motor (M) from the common connection point of the MOS transistors (MM1, MM2) in the master inverter unit (11) is fed back to the input terminal via the MOS transistors (SM1, SM2) of the slave inverter unit 21, generating a circulating current.

[0006] However, conventional inverter circuits for modular motors do not adequately reduce circulating current, which causes stress on power semiconductors and adversely affects current control performance, making it difficult to share the load.

[0007] Conventional techniques for reducing circulating current in inverter circuits for modular motors have been proposed, including isolating each inverter from the load end using a transformer and adding a high-impedance inductor. However, these techniques have the disadvantage of increasing the volume and cost of the system.

[0008] Another conventional technique is to synchronize the PWM phase angles of the inverters using a PWM synchronization signal, but this technique has the problem of noise entering the PWM synchronization signal and distorting the synchronization. Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to provide a circulating current reduction circuit for a modular motor inverter, which allows the number of inverters to be selectively used according to the required capacity in a modular inverter circuit configured with multiple inverter modules connected in parallel, and which solves the synchronization of pulse width modulation signals via CAN (Controller Area Network) communication and a zero-phase component PI (Proportional Integral) controller, thereby reducing the circulating current that occurs when inverter modules are connected in parallel, and a method for operating the same. [Means for solving the problem]

[0010] To achieve the above object, the present invention provides a circulating current reduction circuit for a modular motor inverter, comprising: a master inverter including a master inverter unit having MOS transistors that perform switching operations in response to pulse-width modulation signals supplied to gates and that supplies a three-phase drive current to a motor; one or more slave inverters including slave inverter units having the same configuration as the master inverter unit and connected in parallel to the master inverter; a master control unit that outputs the pulse-width modulation signal to the master inverter unit and synchronizes it with the pulse-width modulation signal supplied to the slave inverter unit via CAN communication; and a slave control unit that outputs a pulse-width modulation signal to the slave inverter unit and synchronizes it with the pulse-width modulation signal supplied to the master inverter unit via CAN communication.

[0011] The master inverter further includes a master input voltage sensing unit that senses a DC voltage supplied to the master inverter unit and outputs a voltage sensing signal accordingly; and a master phase current sensing unit that senses a three-phase current supplied from the master inverter unit to the motor and outputs a current sensing signal accordingly.

[0012] The slave inverter may further include a slave input voltage sensing unit that senses a DC voltage supplied to the slave inverter and outputs a voltage sensing signal accordingly; and a slave phase current sensing unit that senses three-phase currents supplied from the slave inverter to the motor and outputs a current sensing signal accordingly.

[0013] The master control unit is characterized by including: a master pulse-width modulation signal output unit that outputs pulse-width modulation signals to the gates of the MOS transistors of the master inverter unit in order to switch and drive the transistors; a master CAN communication unit that performs CAN communication with the slave control unit; and a master DSP that performs CAN communication with the slave control unit via the master CAN communication unit and synchronizes the pulse-width modulation signal supplied to the master inverter unit with the pulse-width modulation signal supplied to the slave inverter by an interrupt for each period (each period).

[0014] In addition, the master DSP compensates for the duty ratio using a circulating current controller when the duty ratio values ​​of the pulse width modulation signal supplied to the master inverter unit and the pulse width modulation signal supplied to the slave inverter do not match.

[0015] The slave control unit is characterized by including: a slave pulse-width modulation signal output unit that outputs pulse-width modulation signals to the gates of the MOS transistors of the slave inverter unit in order to switch and drive the transistors; a slave CAN communication unit that performs CAN communication with the master control unit; and a slave DSP that performs CAN communication with the master control unit via the slave CAN communication unit and synchronizes the pulse-width modulation signal supplied to the slave inverter by periodic interrupts with the pulse-width modulation signal supplied to the master inverter unit.

[0016] Furthermore, when CAN communication reception with the master DSP is completed and a CAN reception interrupt occurs, the slave DSP calculates the current pulse width modulation signal carrier using a formula, and if the calculation result does not satisfy the synchronization condition, it increases or decreases the frequency of the pulse width modulation signal supplied to the slave inverter unit to perform synchronization and respond to the CAN transmission of the master DSP.

[0017] In addition, when the master inverter and the slave inverter perform CAN communication and synchronize the pulse width modulation signal period, the carrier frequency of the pulse width modulation signal supplied to the slave inverter unit is varied to match the interrupt period of the CAN communication.

[0018] To achieve the above object, a method for operating a circulating current reduction circuit for an inverter for a modular motor according to the present invention includes: a master inverter configuration step of configuring a master inverter including a master inverter unit having MOS transistors that perform switching operations in response to pulse-width modulation signals supplied to gates, and that supplies a three-phase driving current to the motor; a slave inverter configuration step of configuring one or more slave inverters including slave inverter units having the same configuration as the master inverter unit and connected in parallel to the master inverter; a master pulse-width modulation signal synchronization step of outputting the pulse-width modulation signal to the master inverter unit and synchronizing it with the pulse-width modulation signal supplied to the slave inverter unit via CAN communication; and a slave pulse-width modulation signal synchronization step of outputting a pulse-width modulation signal to the slave inverter unit and synchronizing it with the pulse-width modulation signal supplied to the master inverter unit via CAN communication. [Effects of the Invention]

[0019] The circulating current reduction circuit for a modular motor inverter and its operating method according to the present invention have the following advantages.

[0020] First, in a modular inverter circuit that consists of multiple inverter modules connected in parallel, the number of inverters can be selectively used depending on the required capacity, and by solving the synchronization of pulse width modulation signals via CAN communication and a zero-phase sequence PI controller, it is possible to reduce the circulating current that occurs when inverter modules are connected in parallel.

[0021] Second, the internal CAN communication can be used to synchronize pulse width modulated signals, which reduces costs compared to the prior art.

[0022] Third, when synchronizing a pulse width modulation signal, by synchronizing through frequency adjustment, synchronization can be achieved without being particularly affected by noise contamination. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a circuit diagram of a prior art inverter for a modular motor. [Figure 2] FIG. 1 is a block diagram of a circulating current reduction circuit for a modular motor inverter according to an embodiment of the present invention. [Figure 3] 10(a) and 10(b) are waveform diagrams of pulse width modulation signals synchronized with each other. [Figure 4] 10 is an exemplary diagram of address values ​​for transmission and reception between a master DSP and a slave DSP. FIG. [Figure 5] 10 is a table showing the timing of receiving information of a slave DSP when the master DSP is in a transmission mode. [Figure 6] FIG. 10 is an exemplary diagram showing the reception state of the master DSP when the slave DSP responds. [Figure 7] 10 is a table showing reception by a master DSP and responses by a slave DSP. [Figure 8] 10(a) and 10(b) are waveform diagrams showing an example of occurrence of time errors due to data length during reception. [Figure 9] 10 is a CAN communication flowchart of the master DSP. [Figure 10] 10 is a flowchart of a pulse width modulation signal synchronization process of a slave DSP. [Figure 11] FIG. 2 is a detailed block diagram of a master DSP and a slave DSP. [Figure 12] 10A and 10B are exemplary waveform diagrams showing the duty ratio compensated by the circulating current controller; [Figure 13]10A and 10B are waveform diagrams of various parts when two slave inverters are connected in parallel to one master inverter and operated. [Figure 14] 3 is a flowchart illustrating a method for operating a circulating current reduction circuit for a modular motor inverter according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, when assigning reference numerals to components in each drawing, it should be noted that the same reference numerals are used for the same components even if they are displayed in different drawings. Furthermore, when describing the present invention, detailed descriptions of related known structures or functions will be omitted if they are obvious to those skilled in the art or are deemed to obscure the gist of the present invention.

[0025] FIG. 2 is a block diagram of a circulating current reduction circuit for a modular motor inverter according to an embodiment of the present invention; FIGS. 3(a) and 3(b) are pulse width modulation signal synchronization waveform diagrams; FIG. 4 is an example diagram of address values ​​for transmission and reception between a master DSP and a slave DSP; FIG. 5 is a table showing the timing of reception information of a slave DSP when the master DSP is in a transmission mode; FIG. 6 is an example diagram showing the reception state of the master DSP when the slave DSP responds; FIG. 7 is a table showing reception of the master DSP and response of the slave DSP; and FIG. 8(a) is a table showing reception of the master DSP and response of the slave DSP. ), (b) are waveform diagrams showing an example of a time error occurring due to data length during reception, FIG. 9 is a CAN communication flowchart of the master DSP, FIG. 10 is a flowchart of the pulse width modulation signal synchronization process of the slave DSP, FIG. 11 is a detailed block diagram of the master DSP and the slave DSP, FIGS. 12(a) and (b) are example waveform diagrams showing that the duty ratio is compensated by the circulating current controller, and FIG. 13 is a diagram showing the waveforms of each part when two slave inverters are connected in parallel to one master inverter and operated.

[0026] Referring to FIG. 2, the circulating current reduction circuit (1000) for a modular motor inverter includes a master inverter (100), a slave inverter (200), a master control unit (300) and a slave control unit (400).

[0027] Hereinafter, the operation of the circulating current reducing circuit for a modular motor inverter according to an embodiment of the present invention configured as above will be described with reference to FIGS.

[0028] The master inverter 100 includes a master inverter unit 110, a master input voltage sensing unit 120, a master phase current sensing unit 130, and a position sensing unit 140. The master inverter 100 may be configured as a module.

[0029] The master inverter unit 110 includes series-connected MOS transistors MM1, MM2, MM3, MM4, and MM5, MM6. The MOS transistors MM1, MM2 are switched by pulse-width modulation signals (PWM) supplied to their gates, respectively, and supply a phase current U to the motor M via a common connection point. The MOS transistors MM3, MM4 are switched by pulse-width modulation signals (PWM) supplied to their gates, respectively, and supply a phase current V to the motor M via a common connection point. The MOS transistors MM5, MM6 are switched by pulse-width modulation signals (PWM) supplied to their gates, respectively, and supply a phase current W to the motor M via a common connection point.

[0030] The master input voltage detector 120 detects the DC voltage VDC that supplies the DC voltage to the master inverter 110 and outputs a voltage detection signal accordingly.

[0031] The master phase current sensing unit 130 senses the currents of the U, V, and W phases supplied from the master inverter unit 110 to the motor M, and outputs a current sensing signal accordingly.

[0032] The position sensor 140 senses the rotational position of the motor shaft and generates position sensing information accordingly.

[0033] The slave inverter 200 includes a slave inverter unit 210, a slave input voltage sensing unit 220, and a slave phase current sensing unit 230. The slave inverter 200 may be configured as a module.

[0034] The slave inverter unit (210) comprises MOS transistors (SM1, SM2); (SM3, SM4); (SM5, SM6) of the same configuration as the master inverter unit (110), and is switched by the pulse width modulation signal PWM as described above, supplying U, V, and W phase currents to the motor (M) through their respective common connection points.

[0035] The slave input voltage detector 220 detects the DC voltage supplied to the slave inverter 210 and outputs a voltage detection signal accordingly.

[0036] The slave phase current sensing unit 230 senses the currents of the U, V, and W phases supplied from the slave inverter unit 210 to the motor M, and outputs a current sensing signal accordingly.

[0037] The master control unit (300) includes a master pulse width modulation signal output unit (310), a master CAN (Controller Area Network) communication unit (320), and a master DSP (Master Digital Signal Processor) (330).

[0038] The master pulse width modulation signal output unit (310) outputs pulse width modulation signals (PWM) to the gates of the MOS transistors (MM1, MM2); (MM3, MM4); and (MM5, MM6) of the master inverter unit (110) in order to switch and drive the transistors.

[0039] The master CAN communication unit (320) performs CAN communication with the slave CAN communication unit (420) for synchronization of pulse width modulation signals (PWM) between the master inverter unit (110) and the slave inverter unit (210).

[0040] The master DSP (330) controls the generation of the pulse width modulation signal of the master pulse width modulation signal output unit (310) based on the voltage sensing signal of the master input voltage sensing unit (120), the current sensing signal of the master phase current sensing unit (130), and the position sensing information of the position sensing unit (140).

[0041] The master DSP (330) performs CAN communication with the slave DSP (430) via the master CAN communication unit (320) and performs PWM synchronization using periodic interrupts, which will be described in detail below.

[0042] The slave control unit (400) includes a slave pulse width modulation signal output unit (410), a slave CAN (Controller Area Network) communication unit (420), and a slave DSP (Master Digital Signal Processor) (430).

[0043] The slave pulse width modulation signal output unit (410) outputs pulse width modulation signals (PWM) to the gates of the MOS transistors (SM1, SM2); (SM3, SM4); and (SM5, SM6) of the slave inverter unit (210) in order to switch and drive the transistors.

[0044] The slave CAN communication unit (420) performs CAN communication with the master CAN communication unit (320) for synchronization of the pulse width modulation signal PWM between the master inverter unit (110) and the slave inverter unit (210).

[0045] The slave DSP (430) controls the generation of the pulse width modulation signal of the slave pulse width modulation signal output unit (410) based on the voltage sensing signal of the slave input voltage sensing unit (220), the current sensing signal of the slave phase current sensing unit (230), and the position sensing information of the position sensing unit (140).

[0046] The slave DSP (430) performs CAN communication with the master DSP (330) via the slave CAN communication unit (420) and performs PWM synchronization using periodic interrupts, which will be described in detail below.

[0047] Inverter modules can be configured and operated in parallel. For example, as shown in FIG. 2, a master inverter (100) and a slave inverter (200) can be configured and operated in parallel for one motor (M). In this case, the master DSP (330) and the slave DSP (430) synchronize the PWM cycles through CAN communication via the master CAN communication unit (320) and the slave CAN communication unit (420) to reduce circulating currents occurring between the master inverter unit (110) and the slave inverter unit (210). In this case, circulating currents due to errors are compensated for by the zero-phase-sequence controllers at each slave end.

[0048] When the master DSP (330) and the slave DSP (430) perform CAN communication via the master CAN communication unit (320) and the slave CAN communication unit (420) and synchronize the PWM period, the synchronization is realized by varying the PWM carrier frequency of the slave to match the interrupt period of the CAN communication, as shown in Figures 3(a) and 3(b).

[0049] It should be noted that, since CAN communication uses mailbox IDs, when multiple inverter modules are configured in parallel, the receiving IDs must be configured to have the same address value. FIG. 4 illustrates an example of this. That is, FIG. 4 illustrates an example in which, when N slave inverters are configured in parallel with one master inverter 100 and N slave DSPs 430A-430N are configured in parallel with one master DSP 330, the receiving IDs of the slave DSPs 430A-430N have the same address value. Here, the first slave DSP 430A refers to the slave DSP 430.

[0050] The table in Figure 5 shows the timing of receiving information for the slave DSPs 430A-430I when the master DSP 330 is in transmit mode. That is, when the master DSP 330 is in transmit mode, the slave DSPs 430A-430I receive and respond in sequence at the assigned interval. The slave DSPs 430A-430I can receive information when other slave DSPs are receiving and responding.

[0051] 6 shows an example of reception by the master DSP 330 when the slave DSPs 430A-430N respond in parallel, as in the example described above, in which N slave DSPs 430A-430N are connected to one master DSP 330. That is, the slave DSPs 430A-430N respond sequentially at a preset interval, and the master DSP 330 receives the responses from the slave DSPs 430A-430N.

[0052] FIG. 7 is a table showing that, as in FIG. 6, the slave DSPs 430A-430N respond in sequence at a preset cycle, and the master DSP 330 receives the responses of the slave DSPs 430A-430N.

[0053] As described above, when the master DSP (330) and slave DSP (430) perform CAN communication, an error occurs in the PWM synchronization time at the completion of the transmission interrupt and the completion of the reception interrupt, so compensation processing is performed for that time. Figures 8(a) and 8(b) show an example of a time error that occurs due to the data length during reception.

[0054] As shown in Figure 9, when a PWM interrupt occurs, the master DSP (330) sends a command voltage (V * dq )

[0055] Referring to FIG. 10, when a PWM interrupt occurs in the receiving mode, the slave DSP (430) drives the speed controller (431) and the current controller (433).

[0056] In this state, when the CAN communication reception is completed and a CAN reception interrupt occurs, the slave DSP (430) calculates the current PWM carrier using the following formula:

[0057] Formula Bound Limit Value ≦Communication speed (bit rate) - (current PWM carrier counter) ≦Bound Limit Value

[0058] When the calculation result of the PWM carrier does not satisfy the synchronization condition, the slave DSP (430) increases or decreases the PWM frequency to perform PWM synchronization and responds to the CAN transmission of the master DSP (330).

[0059] Referring to FIG. 11, the master DSP 330 corresponds to a master PCS (Power Conditioning System), and controls the command current value (id) of the motor M calculated through the speed PI controller. * ) is used to control the slave command current and the motor (M). In order to control the current command to the same value between the master DSP (330) and the slave DSP (430), the command current value of the master DSP (330) is sent to the slave DSP (430) via CAN communication, and the slave DSP (430) drives the motor (M) using the received command current. The command current of the master DSP (330) and the slave DSP (430) is calculated as a command phase voltage of the motor (M) through a current PI controller, and the calculated phase voltage is calculated as a PWM duty and used to drive the motor (M).

[0060] In the CAN communication between the master DSP (330) and the slave DSP (430), the control values ​​are not processed in the same PWM period as shown in Figure 8, so the command current values ​​are not synchronized. This can cause a difference of more than one period.

[0061] Therefore, not only PWM synchronization using CAN communication but also a duty ratio compensation value is required, and in this embodiment, the duty ratio is compensated using a circulating current controller (435).

[0062] If the duty ratios are not the same, a high circulating current (a phenomenon in which a grid current flows) occurs between the master inverter unit 110 and the slave inverter unit 210 by the amount of the error.

[0063] Therefore, since the grid current is calculated as 0 according to the KCL law, the circulating current controller 435 serves to compensate the slave duty ratio so that the grid current can become 0 when a circulating current occurs.

[0064] 12(a) and 12(b) are diagrams showing an example in which the duty ratio is compensated by the circulating current controller 435. Here, the value of the compensated duty ratio is "Io."

[0065] FIG. 13 is a diagram showing waveforms at various points when two slave inverters are connected in parallel to one master inverter.

[0066] FIG. 14 is a flowchart showing a method of operating the circulating current reducing circuit of the inverter for a modular motor according to the present invention.

[0067] Referring to FIG. 14, the method for operating the circulating current reduction circuit for a modular motor inverter according to the present invention includes a master inverter configuration step (S100), a slave inverter configuration step (S200), a master pulse width modulation signal synchronization step (S300), and a slave pulse width modulation signal synchronization step (S400).

[0068] In the master inverter configuration step (S100), a master inverter (100) is configured, which includes MOS transistors (MM1, MM2); (MM3, MM4); (MM5, MM6) that perform switching operations in response to pulse width modulation signals supplied to their gates, and includes a master inverter section (110) that supplies a three-phase driving current to a motor (M).

[0069] In the slave inverter configuration step (S200), one or more slave inverters (200) are configured, each including a slave inverter unit (210) having the same configuration as the master inverter unit (110) and connected in parallel to the master inverter (100).

[0070] In the master pulse width modulation signal synchronization step (S300), the master control unit (300) outputs the pulse width modulation signal to the master inverter (100) and operates to synchronize it with the pulse width modulation signal supplied to the slave inverter unit (210) via CAN communication.

[0071] In the slave pulse width modulation signal synchronization step (S400), the slave control unit (400) outputs a pulse width modulation signal to the slave inverter unit (210) and operates to synchronize it with the pulse width modulation signal supplied to the master inverter unit (110) via CAN communication.

[0072] Although the present invention has been described and illustrated in connection with preferred embodiments for illustrating the technical concept of the present invention, it will be readily understood by those skilled in the art that the present invention is not limited to the exact configuration and operation thus illustrated and described, and that numerous changes and modifications can be made to the present invention without departing from the scope of the technical concept. Therefore, all such appropriate changes, modifications, and equivalents should be considered to fall within the scope of the present invention. [Explanation of symbols]

[0073] 100: Master inverter 110: Master inverter section 120: Master input voltage sensor 130: Master phase current sensor 140: Position sensing unit 200: Slave inverter 210: Slave inverter unit 220: Slave input voltage sensing unit 230: Slave phase current sensing unit 300: Master control unit 310: Master pulse width modulation signal output unit 320: Master CAN communication unit 330: Master DSP 400: Slave control unit 410: Slave pulse width modulation signal output unit 420: Slave CAN communication unit 430: Slave DSP 1000: Circulating current reduction circuit

Claims

1. a master inverter including a master inverter unit having a MOS transistor that performs a switching operation in response to a pulse width modulation signal supplied to a gate thereof and that supplies a three-phase drive current to the motor; one or more slave inverters including a slave inverter unit having the same configuration as the master inverter unit and connected in parallel to the master inverter; a master control unit that outputs the pulse width modulation signal to the master inverter unit and synchronizes it with a pulse width modulation signal supplied to the slave inverter unit via CAN communication; A circulating current reduction circuit for a modular motor inverter, comprising: a slave control unit that outputs a pulse width modulation signal to the slave inverter unit and synchronizes it with the pulse width modulation signal supplied to the master inverter unit via CAN communication.

2. The master inverter is a master input voltage detection unit that detects a DC voltage supplied to the master inverter unit and outputs a voltage detection signal according to the detected DC voltage; 2. The circulating current reduction circuit of claim 1, further comprising: a master phase current detection unit that detects three-phase currents supplied from the master inverter unit to the motor and outputs a current detection signal based on the detected currents.

3. The slave inverter a slave input voltage detection unit that detects a DC voltage supplied to the slave inverter unit and outputs a voltage detection signal according to the detected DC voltage; 2. The circulating current reduction circuit of claim 1, further comprising: a slave phase current detection unit that detects three-phase currents supplied from the slave inverter unit to the motor and outputs a current detection signal based on the detected currents.

4. The master control unit a master pulse width modulation signal output unit that outputs pulse width modulation signals to gates of the MOS transistors of the master inverter unit in order to switch and drive the transistors; a master CAN communication unit that performs CAN communication with the slave control unit; 2. The circulating current reduction circuit for a modular motor inverter according to claim 1, further comprising: a master DSP that performs CAN communication with the slave control unit via the master CAN communication unit and synchronizes the pulse width modulation signal supplied to the master inverter unit with the pulse width modulation signal supplied to the slave inverter by a periodic interrupt.

5. The master DSP 5. The circulating current reduction circuit for a modular motor inverter according to claim 4, wherein when a duty ratio value between a pulse width modulation signal supplied to a master inverter unit and a pulse width modulation signal supplied to the slave inverter unit does not match, the duty ratio is compensated for using a circulating current controller.

6. The slave control unit a slave pulse width modulation signal output unit that outputs pulse width modulation signals to gates of the MOS transistors of the slave inverter unit in order to switch and drive the transistors; a slave CAN communication unit that performs CAN communication with the master control unit; 2. The circulating current reduction circuit for a modular motor inverter according to claim 1, further comprising: a slave DSP that performs CAN communication with the master control unit via the slave CAN communication unit and synchronizes a pulse width modulation signal supplied to the slave inverter by a periodic interrupt with a pulse width modulation signal supplied to the master inverter unit.

7. The slave DSP 7. The circuit for reducing circulating current in an inverter for a modular motor according to claim 6, wherein when CAN communication reception with the master DSP is completed and a CAN reception interrupt occurs, a current pulse width modulation signal carrier is calculated using a formula, and when the calculation result does not satisfy a synchronization condition, the frequency of the pulse width modulation signal supplied to the slave inverter unit is increased or decreased to perform synchronization and respond to the CAN transmission from the master DSP.

8. 2. The circulating current reduction circuit for a modular motor inverter according to claim 1, wherein when the master inverter and the slave inverter perform CAN communication and synchronize the pulse width modulation signal period, a carrier frequency of the pulse width modulation signal supplied to the slave inverter unit is varied to match the CAN communication interrupt period.

9. a master inverter configuring step of configuring a master inverter including a master inverter unit having a MOS transistor that performs a switching operation in response to a pulse width modulation signal supplied to a gate thereof and that supplies a three-phase driving current to the motor; a slave inverter configuring step of configuring one or more slave inverters, each slave inverter having the same configuration as the master inverter and connected in parallel to the master inverter; a master pulse width modulation signal synchronizing step of outputting the pulse width modulation signal to the master inverter unit and synchronizing the pulse width modulation signal with the pulse width modulation signal supplied to the slave inverter unit via CAN communication; a slave pulse width modulation signal synchronization step of outputting a pulse width modulation signal to the slave inverter unit and synchronizing the slave pulse width modulation signal with the pulse width modulation signal supplied to the master inverter unit via CAN communication.

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