KR20220067873A - Inverter system and electric motor driving system - Google Patents

Abstract

The present invention is to provide an inverter system distributing regenerative power at no load to all power cells connected in series and a motor driving system. An embodiment of the present invention provides an inverter system and a motor driving system, wherein the inverter system comprises: a primary winding receiving input power; a transformer having a plurality of secondary windings magnetically coupled with the primary winding and outputting power transformed according to a winding ratio; a plurality of power cells which invert the power transformed by the transformer through a switching operation and to which output ends outputting the inverted power are serially connected for each phase; a power cell control unit controlling a phase shift pulse width modulation (PWM) switching operation of the power cell selected among the plurality of power cells; and a main control unit selecting the power cell, which performs a switching operation, among the plurality of power cells to transfer information on the selected power cell to the power cell control unit, and changing phase shift amounts of the plurality of power cells among one another according to a preset cycle. The present invention can suppress direct current voltage of partial power cells from increasing.

Description

Inverter system and motor drive system {INVERTER SYSTEM AND ELECTRIC MOTOR DRIVING SYSTEM}

The present invention relates to an inverter system and a motor driving system operating in a phase shift PWM (Phase Shift Pulse Width Modulation) method.

In general, a multi-level inverter system may be mainly used as a driving system for driving an electric motor.

In such a multi-level inverter system, a phase shift PWM method is mainly used.

In the phase shift PWM method described above, power is equally distributed between power cells, and if the heat generation of the power cells is the same, the primary side AC harmonics of the multi-winding transformer can be reduced. There is a problem in that some power cell DC voltages rise due to the regenerative power flowing from the motor to the inverter by transitioning to this negative, which is the output of the inverter during the motor no-load test run or after the user's motor load coupling is disconnected. There is a problem in that the voltage reduction must be separately set.

Republic of Korea Patent Publication No. 10-2015-0005822

According to an embodiment of the present invention, there is provided an inverter system and a motor driving system for distributing regenerative power during no load to all power cells connected in series.

In order to solve the problems of the present invention described above, an inverter system according to an embodiment of the present invention includes a primary winding that receives input power, and a plurality of magnetically coupled primary windings to output power transformed according to a turns ratio, respectively. A transformer having a secondary winding, a plurality of power cells inverting power transformed by the transformer through a switching operation, and each output terminal outputting the inverted power is connected in series for each phase, the plurality of power A power cell control unit that controls a phase shift pulse width modulation (PWM) switching operation of a selected power cell among cells, selects a power cell performing a switching operation among the plurality of power cells and transmits the selected power cell information to the power cell control unit and a main controller configured to change the phase shift amounts of the plurality of power cells from each other according to a preset period.

A motor driving system according to an embodiment of the present invention is a transformer having a primary winding that receives input power, and a plurality of secondary windings that are magnetically coupled with the primary winding to output power transformed according to a turns ratio, respectively, through a switching operation A plurality of power cells outputting driving power for driving an electric motor by inverting the electric power transformed by the transformer, each output terminal being serially connected for each phase according to electrical characteristics required for driving the electric motor, the plurality of A power cell control unit that controls a phase shift pulse width modulation (PWM) switching operation of a selected power cell among power cells, a power cell that performs a switching operation among the plurality of power cells is selected and the selected power cell information is transmitted to the power cell control unit and a main controller configured to change the phase shift amounts of the plurality of power cells from each other according to a preset period.

According to an embodiment of the present invention, regenerative power is equally distributed to each power cell under a no-load driving condition, thereby suppressing an increase in the DC voltage of some power cells.

1 is a schematic circuit diagram of an inverter system according to an embodiment of the present invention.
FIG. 2 is a schematic circuit diagram of a power cell employed in an inverter system according to an embodiment of the present invention shown in FIG. 1 .
3 is a schematic block diagram of a power cell control unit and a main control unit applied to an inverter system according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating a schematic configuration of a power cell controller or a controller of the power cell control unit and the main control unit shown in FIG. 3 .
5 is a schematic circuit diagram of an electric motor driving system according to an embodiment of the present invention.
6 is a diagram illustrating a switching operation of a plurality of power cells of an inverter system according to an embodiment of the present invention.
7 is a graph illustrating a switching operation of an inverter system according to an embodiment of the present invention.
8A is a graph showing the operation of a general phase shift PWM inverter system, and FIG. 8B is a graph showing the operation of the phase shift PWM inverter system according to the present invention.
9 is a diagram illustrating a difference in electrical results between a general phase shift PWM inverter system and a phase shift PWM inverter system according to the present invention.

Hereinafter, preferred embodiments will be described in detail so that those of ordinary skill in the art can easily practice the present invention with reference to the accompanying drawings.

1 is a schematic circuit diagram of an inverter system according to an embodiment of the present invention.

Referring to FIG. 1 , an inverter system 100 according to an embodiment of the present invention includes a transformer 110 , a power cell group 120 having a plurality of power cells, a power cell control unit 130 , and a main control unit 140 . may include

The transformer 110 may include a primary winding 111 receiving input power, and a plurality of secondary windings 112 magnetically coupled to the primary winding 111 to transform the input power according to a turns ratio.

The transformer 110 may be composed of various types of transformers, for example, the primary winding 111 may be composed of a Y-connected structure, and although not shown, may also be composed of a delta-connected structure, and other It can be composed of various wiring structures of

Also, for example, the plurality of secondary windings 112 may be configured in a Y connection structure, or may be configured in a delta connection structure or various connection structures.

The power cell group 120 may include a plurality of power cells, and each of the plurality of power cells receives independent DC power from each of the plurality of secondary windings 112 of the transformer 110, Each of them can be switched to output power.

The outputs of each of the plurality of power cells may be connected in series with corresponding phases.

For example, the power cells 121-1, 121-2, and 121-n may respectively output power of phase A among three phases, and the power cells 122-1, 122-2, and 122-n may respectively output power of phase B among three phases. , and the power cells 123-1, 123-2, and 123-n may respectively output the power of the C phase among the three phases.

In addition, as shown, the output terminals of the power cells 121-1, 121-2, 121-n of the A-phase power cell group 121 that output the A-phase power can be connected in series, and the B-phase power cell that outputs the B-phase power The output terminals of the power cells 122-1, 122-2, 122-n of the group 122 may be connected in series, and the power cells 123-1, 123-2, 123-n of the C-phase power cell group 123 outputting C-phase power. The output terminals of the may be connected in series. Accordingly, each of the three-phase power levels may be multi-level.

When a multi-level is configured as three levels, the power cell may be configured in three stages (where n may be 3), and in the case of a multi-level of three or more levels, a power cell may be provided for each phase by the number of corresponding levels. have.

FIG. 2 is a schematic circuit diagram of a power cell employed in an inverter system according to an embodiment of the present invention shown in FIG. 1 .

Referring to FIG. 2 , each power cell employed in the inverter system shown in FIG. 1 may include a rectifying unit rect, a smoothing unit Ca, and a switching unit SW.

The rectifying unit rect may rectify the three-phase power R, S, and T transformed from the transformer 110 , and the smoothing unit Ca may include at least one capacitor to smooth the rectified power. A plurality of capacitors of the smoothing part Ca may be connected in series in consideration of the allowable voltage.

The switching unit SW may include first to fourth insulated gate bipolar transistors (IGBTs) Q1, Q2, Q3, and Q4, and transmits DC power smoothed by the smoothing unit Ca. By controlling the voltage phase difference of each level by switching, it is possible to reduce the voltage change per time (dv/dt) of the output power.

As shown, the first and second insulated gate bipolar transistors Q1 and Q2 may be connected in series to each other and may be connected in parallel to the output terminal of the smoothing part Ca. The third and fourth insulated gate bipolar transistors Q3 and Q4 may be connected in series with each other and may be connected in parallel to the first and second insulated gate bipolar transistors Q1 and Q2.

Power of each phase may be output at a connection point of the first and second insulated gate bipolar transistors Q1 and Q2 and a connection point of the third and fourth insulated gate bipolar transistors Q3 and Q4.

Referring back to FIG. 1 together with FIG. 2 , the power cell control unit 130 may control the switching of the switching unit SW by transmitting a power command to each power cell according to the control from the main control unit 140 . In this case, the phase shift amount may be reflected in the power command.

The main control unit 140 may transmit output information to the power cell control unit 130 so that the power cells operate sequentially for each phase.

3 is a schematic block diagram of a power cell control unit and a main control unit applied to an inverter system according to an embodiment of the present invention.

Referring to FIG. 3 together with FIG. 1 , the power cell controller 130 may include an A-phase power cell controller group 131 , a B-phase power cell controller group 132 , and a C-phase power cell controller group 133 . can

The phase A power cell controller group 131 may include first to Nth phase A power cell controllers 131-1,131-2, and 131-n, and the first to Nth phase A power cell controllers 131-1,131-2,131-n n) may correspond to each of the first to Nth phase A power cells 121-1, 121-2, and 121-n one-to-one to control power switching of the corresponding power cell.

In addition, the phase B power cell controller group 132 may include first to N-th phase B power cell controllers 132-1, 132-2, and 132-n, and the first to N-th phase B power cell controllers 132-1 and 132-n. 2,132-n) may correspond one-to-one to each of the first to Nth phase B power cells 122-1, 122-2, and 122-n to control power switching of the corresponding power cell.

Similarly, the C-phase power cell controller group 133 may include first to N-th phase C power cell controllers 133-1, 133-2, and 133-n, and the first to N-th C-phase power cell controllers 133-1 and 133-n. 2,133-n) may correspond one-to-one to each of the first to Nth phase C power cells 123-1, 123-2, and 123-n to control power switching of the corresponding power cell.

1st to Nth phase A power cell controllers 131-1,131-2,131-n, 1st to Nth phase B power cell controllers 132-1,132-2,132-n, and 1st to Nth phase C power cell controller 133- 1,133-2,133-n) each has a unique ID, and the main control unit 140 transmits the ID of the corresponding power cell controller together with output information for controlling the switching of the corresponding power cell to the power cell control unit 130 . , the power cell to be operated can be selected. Selection of a power cell to be operated may be performed for each phase.

For example, the main controller 140 controls the first phase A power cell 121 to the N-th phase A power cell 121-n in the case of phase A, and the first phase B power cell 122-1 to the phase B power cell 122-1 in the case of phase B. It can be controlled through each power cell controller to sequentially operate from the N-th phase B power cell 122-n, from the first C-phase power cell 123-1 to the N-th phase power cell 123-n in the case of C-phase. can In this case, the main controller 140 may change the operation order of the power cell during no-load operation. That is, the phase shift amounts of the plurality of power cells of the corresponding phase may be changed from each other.

The main control unit 140 may include a communication unit 141 , a state determination unit 142 , and a controller 143 .

The communication unit 141 may communicate with each power cell controller in a controller area network (CAN) method. The communication unit 141 transmits to each power cell controller the ID of the power cell controller responsible for the power cell to be selected and the power command for instructing the output power of the power cell, and the power state of the power cell in charge from each power cell controller. can be delivered.

The state determination unit 142 receives the power state of each power cell from the communication unit 141 and transmits the result of the determination on the corresponding power cell to the controller 143, and the controller 143 transmits the power command accordingly. may be transmitted to the communication unit 141 . In addition, the controller 143 may transmit the ID of the power cell controller in charge of the corresponding power cell to the communication unit 141 so that the power cell performs a switching operation in order for each phase.

FIG. 4 is a diagram illustrating a schematic configuration of a power cell controller or a controller of the power cell control unit and the main control unit shown in FIG. 3 .

Referring to FIG. 4 together with FIG. 3, FIG. 4 is a diagram illustrating an exemplary configuration in which an embodiment of a power cell control unit and a main control unit or a power cell controller or controller thereof may be implemented, wherein the device 1100 is a personal computer; A distributed computing environment including server computers, handheld or laptop devices, mobile devices (mobile phones, PDAs, media players, etc.), multiprocessor systems, consumer electronics, minicomputers, mainframe computers, any of the aforementioned systems or devices. etc., but are not limited thereto.

The device 1100 may include at least one processing unit 1110 and a memory 1120 . Here, the processing unit 1110 may include, for example, a central processing unit (CPU), a graphic processing unit (GPU), a microprocessor, an Application Specific Integrated Circuit (ASIC), Field Programmable Gate Arrays (FPGA), etc. and may have a plurality of cores. The memory 1120 may be a volatile memory (eg, RAM, etc.), a non-volatile memory (eg, ROM, flash memory, etc.), or a combination thereof.

Also, the device 1100 may include an additional storage 1130 . Storage 1130 includes, but is not limited to, magnetic storage, optical storage, and the like. The storage 1130 may store computer readable instructions for implementing one or more embodiments disclosed herein, and other computer readable instructions for implementing an operating system, an application program, and the like. Computer readable instructions stored in storage 1130 may be loaded into memory 1120 for execution by processing unit 1110 .

In addition, device 1100 may include input device(s) 1140 and output device(s) 1150 . Here, the input device(s) 1140 may include, for example, a keyboard, mouse, pen, voice input device, touch input device, infrared camera, video input device, or any other input device, or the like. Further, the output device(s) 1150 may include, for example, one or more displays, speakers, printers, or any other output device, or the like. Also, the device 1100 may use an input device or an output device included in another device as the input device(s) 1140 or the output device(s) 1150 .

In addition, the device 1100 may include communication connection(s) 1160 that enable communication with other devices. Here, communication connection(s) 1160 may be a modem, network interface card (NIC), integrated network interface, radio frequency transmitter/receiver, infrared port, USB connection, or other interface for connecting device 1100 to another device. may include Also, the communication connection(s) 1160 may include a wired connection or a wireless connection.

Each component of the device 1100 described above may be connected by various interconnections such as a bus (eg, peripheral component interconnection (PCI), USB, firmware (IEEE 1394), optical bus structure, etc.) , may be interconnected by communication.

As used herein, terms such as "power cell controller", "main controller", "power cell controller", "controller", etc. generally refer to a computer-related entity that is hardware, a combination of hardware and software, software, or software in execution. it refers to For example, a component can be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and/or a computer. For example, both an application running on a controller and a controller may be a component. One or more components may reside within a process and/or thread of execution, and a component may be localized on one computer or distributed between two or more computers.

5 is a schematic circuit diagram of an electric motor driving system according to an embodiment of the present invention.

Referring to FIG. 5 , the inverter system 100 according to the embodiment of the present invention shown in FIG. 1 may be an electric motor driving system 200 .

The electric motor driving system 200 shown in FIG. 5 has a transformer 210 having a primary winding 211 and a plurality of secondary windings 212 and a power having a plurality of power cells, similar to the inverter system 100 of FIG. 1 . It may include a cell group 220 , a power cell controller 230 , and a main controller 240 .

Output terminals of the power cells 221-1, 221-2, 221-n of the A-phase power cell group 221 that output the A-phase power may be connected in series, and the power of the B-phase power cell group 222 that outputs the B-phase power The output terminals of the cells 222-1, 222-2, 222-n may be connected in series, and the output terminals of the power cells 223-1, 223-2, 223-n of the C-phase power cell group 223 outputting the C-phase power may be connected in series. and output the three-phase power to the motor M to drive the motor M.

For example, when a multi-level consists of three levels, a power cell may be configured in three stages (where n may be three), and in the case of a multi-level of three or more levels, a power cell for each phase by the number of corresponding levels This may be provided.

Detailed configurations and functions of the power cell control unit 230 and the main control unit 240 are the same as those in FIGS. 1, 3, and 4, and thus a detailed description thereof will be omitted.

6 is a diagram illustrating a switching operation of a plurality of power cells of an inverter system according to an embodiment of the present invention.

Referring to FIG. 6 together with FIGS. 1 and 3 , among a plurality of power cells of the inverter system 100 according to an embodiment of the present invention, for example, when four power cells of phase A are provided, four power cells may be switched in the phase shift PWM method through comparison between the reference signal V_ref having a preset reference frequency and the switching signals Vtri_1, Vtri_2, Vtri_3, and Vtri_4 of the four power cells.

The phase A power cell controller group 131 , the phase B power cell controller group 132 , and the phase C power cell controller group 133 of the power cell controller 130 may each have a reference signal as shown in Equation 1 .

(Formula 1)

Here, V _A ^* , V _B ^* , and V _C ^* may be reference signals of the A-phase power cell, the B-phase power cell, and the C-phase power cell, respectively.

The output voltages of the A-phase power cell, the B-phase power cell, and the C-phase power cell having the above-described reference signal may be as shown in Equation 2 below.

(Formula 2)

는 인접한 캐리어들(adjacent carriers) 간의 시간차이, T_S는 PWM 샘플링 시간, N은 직렬 연결된 해당 상의 파워셀의 개수를 나타낼 수 있으며, K는 파워셀의 번호이고, K번째 파워셀의 출력 전압은 사전에 설정된 기준 출력 전압에 대비하여

의 시간 딜레이를 가질 수 있다.Here, V _AK , V _BK , and V _CK are the output voltages of the A-phase power cell, B-phase power cell, and C-phase power cell, respectively,

is the time difference between adjacent carriers, T _S is the PWM sampling time, N may represent the number of power cells in the corresponding phase connected in series, K is the number of the power cell, and the output voltage of the K-th power cell is against a preset reference output voltage

can have a time delay of

The sum of the output voltages of the plurality of power cells in each phase may be expressed as Equation 3 below.

(Formula 3)

는 사전에 설정된 총 기준 출력 전압에 대비하여 인버터 시스템의 출력 전압의 시간 딜레이를 나타낼 수 있다.Here, V _A , V _B , and V _C are the sum of the output voltages of each of the plurality of power cells in phase A, the plurality of power cells in phase B and the plurality of power cells in phase C, respectively,

may represent a time delay of the output voltage of the inverter system with respect to the preset total reference output voltage.

7 is a graph illustrating a switching operation of an inverter system according to an embodiment of the present invention.

Referring to FIG. 7 along with the description of FIG. 6 , the output voltage with 6 power cells in each phase is shown. As shown, the output voltages of the first three power cells lead the inverter output voltage, and the output voltages of the last three power cells delay the output voltage of the inverter system.

When the inverter system drives the motor in the no-load state, the active power, that is, P = VIcosθ, is '0', so the phase difference between the inverter output voltage and the current is 90 degrees.

In this case, as shown, the output voltage of the power cells that lead the inverter output voltage, such as power cells A1 to A3, can lead the inverter output current by 90 degrees or more.

Accordingly, the active power of the power cells A1 to A3 becomes negative (-), and a DC link overvoltage occurs due to the regenerative power.

For this reason, it is possible to reduce the regenerative power by reducing the output voltage to avoid an inverter trip due to DC link overvoltage when the inverter system drives a motor in a no-load state. The operation of the above-described inverter system may be the same in the electric motor system shown in FIG. 5 .

8A is a graph showing the operation of a general phase shift PWM inverter system, and FIG. 8B is a graph showing the operation of the phase shift PWM inverter system according to the present invention.

Referring to FIG. 8A , in the case of a general phase shift PWM inverter system, for example, when five power cells operate, the phase shift PWM scheme can be switched in a fixed order in a fixed order. As regenerative power may be input to the , DC voltage may increase, and thus a normal operation may not be possible.

However, referring to FIG. 8B , in the phase-shifting PWM inverter system (or motor driving system) of the present invention, the power cells operate sequentially, but during no-load operation, the operation sequence is changed and the regenerative power is supplied to the DC voltage of the power cell. rise can be suppressed. For example, when the first to fifth power cells A1, A2, A3, A4, and A5 of phase A perform a switching operation, the main controller 140 controls the first power cell A1 - the second power cell A2. -The third power cell (A3) - the fourth power cell (A4) - the fifth power cell (A5) may be operated in the order of the phase shift PWM switching operation, in this case, the regenerative power to the first power cell (A1) during no-load operation may have the highest inflow. Accordingly. Synchronized with a preset period, that is, the frequency period of the switching reference signal, the second power cell A2 - the third power cell A3 - the fourth power cell A4 - the fifth power cell A5 - The amount of phase shift may be changed to perform switching operations in the order of the first power cell A1 . Meanwhile, in the no-load operation, the amount of regenerative power flowing in is the first power cell (A1) - the second power cell (A2) - the third power cell (A3) - the fourth power cell (A4) - the fifth power cell (A5) may be higher. Accordingly, during the no-load operation, the operation sequence is changed to change the operation sequence to the fifth power cell A5 - the fourth power cell A4 - the third power cell A3 - the second power cell A2 - the first power cell A1. ), the amount of phase shift can be changed from each other to operate sequentially. Thereafter, in the next cycle, the phase shift PWM switching is performed in the order of the first power cell A1 - the second power cell A2 - the third power cell A3 - the fourth power cell A4 - the fifth power cell A5. operation, and the changed order may be repeated in synchronization with a preset period, that is, the frequency period of the switching reference signal. This may also be the same as the phase shift PWM switching operation of the B-phase and C-phase power cells.

9 is a diagram illustrating a difference in electrical results between a general phase shift PWM inverter system and a phase shift PWM inverter system according to the present invention.

Referring to FIG. 9 , in contrast to the general phase shift PWM inverter system shown on the left, the level shift PWM inverter system (or motor driving system) of the present invention on the right has the power load of the power cell distributed during no-load operation. you can see

As described above, according to the present invention, the regenerative power is equally distributed to each power cell under the no-load driving condition, thereby suppressing the increase in the DC voltage of some power cells.

The present invention described above is not limited by the above-described embodiments and the accompanying drawings, but is limited by the claims described below, and the configuration of the present invention may vary within the scope without departing from the technical spirit of the present invention. Those of ordinary skill in the art to which the present invention pertains can easily recognize that the present invention can be changed and modified.

100: inverter system
110,210: Transformers
111,211: primary winding
112,212: a plurality of secondary windings
120,220: a plurality of power cell groups
130,230: power cell control unit
140,240: main control unit
141: communication department
142: state determination unit
143: controller
200: electric motor drive system

Claims (14)

a transformer having a primary winding receiving input power and a plurality of secondary windings magnetically coupled to the primary winding to respectively output power transformed according to a turns ratio;
a plurality of power cells inverting the power transformed by the transformer through a switching operation, and each output terminal outputting the inverted power is connected in series for each phase;
a power cell controller for controlling a phase shift pulse width modulation (PWM) switching operation of the selected power cell among the plurality of power cells; and
A main control unit that selects a power cell performing a switching operation among the plurality of power cells, transmits selected power cell information to the power cell control unit, and changes the phase shift amounts of the plurality of power cells with each other according to a preset period
Inverter system comprising a.
According to claim 1,
The main control unit is an inverter system for sequentially selecting the power cells connected to each phase from among the plurality of power cells.
3. The method of claim 2,
The main control unit changes the selection order of the power cells connected to each phase among the plurality of power cells according to the preset period.
4. The method of claim 3,
The main control unit is an inverter system for changing the selection order in synchronization with the reference frequency of the power cells connected to each phase among the plurality of power cells.
According to claim 1,
Each of the plurality of power cells is
a rectifier for rectifying the power transformed by the transformer;
a smoothing unit for smoothing the power rectified by the rectifying unit; and
A switching unit for switching the power smoothed by the smoothing unit
Inverter system comprising a.
According to claim 1,
The power cell control unit
A plurality of power cell controllers for controlling each of the plurality of power cells,
Each of the plurality of power cell controllers has a preset ID,
An inverter system in which a power cell controller having a corresponding ID according to selection of the main controller controls switching of the corresponding power cell.
7. The method of claim 6,
The main control unit is
a communication unit communicating with each of the plurality of power cell controllers in a CAN (Controller Area Network) method;
a state determination unit configured to determine the power state of the plurality of power cells based on the information received through the communication unit; and
A controller that selects and controls an ID of a power cell controller of a power cell to operate among the plurality of power cell controllers according to a determination result of the state determination unit
Inverter system comprising a.
a transformer having a primary winding receiving input power and a plurality of secondary windings magnetically coupled to the primary winding to respectively output power transformed according to a turns ratio;
A plurality of power cells that output driving power for driving an electric motor by inverting the power transformed by the transformer through a switching operation, and each output terminal is connected in series for each phase according to electrical characteristics required for driving the motor. ;
a power cell controller for controlling a phase shift pulse width modulation (PWM) switching operation of the selected power cell among the plurality of power cells; and
A main control unit that selects a power cell performing a switching operation among the plurality of power cells, transmits selected power cell information to the power cell control unit, and changes the phase shift amounts of the plurality of power cells with each other according to a preset period
A motor drive system comprising a.
9. The method of claim 8,
The main control unit sequentially selects the power cells connected to each phase from among the plurality of power cells.
10. The method of claim 9,
The main control unit changes the selection order of the power cells connected to each phase among the plurality of power cells according to the preset period.
11. The method of claim 10,
The main control unit is synchronized with a reference frequency of the power cells connected to each phase among the plurality of power cells to change the selection order.
9. The method of claim 8,
Each of the plurality of power cells is
a rectifier for rectifying the power transformed by the transformer;
a smoothing unit for smoothing the power rectified by the rectifying unit; and
A switching unit for switching the power smoothed by the smoothing unit
A motor drive system comprising a.
9. The method of claim 8,
The power cell control unit
A plurality of power cell controllers for controlling each of the plurality of power cells,
Each of the plurality of power cell controllers has a preset ID,
A power cell controller having a corresponding ID according to selection of the main controller controls switching of the corresponding power cell.
14. The method of claim 13,
The main control unit is
a communication unit communicating with each of the plurality of power cell controllers in a CAN (Controller Area Network) method;
a state determination unit configured to determine the power state of the plurality of power cells based on the information received through the communication unit; and
A controller that selects and controls an ID of a power cell controller of a power cell to operate among the plurality of power cell controllers according to a determination result of the state determination unit
A motor drive system comprising a.

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