JP2023019760A - Calculation program, calculation method, and three-phase AC motor system - Google Patents

Abstract

To provide a calculation program, a calculation method, and a three-phase AC motor system capable of properly detecting a current flowing in each phase of a three-phase AC motor even if there is only one shunt resistor.SOLUTION: The calculation program causes a computer to perform the steps of detecting the total current, which is the sum of AC currents flowing in each of three phases of a three-phase AC motor 110 and calculating each phase current, which is an AC current flowing in each of the three phases of the three-phase AC motor 110 on the basis of the total current and a duty ratio of each phase.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a calculation program, a calculation method, and a three-phase AC motor system.

In controlling a three-phase AC motor, it is necessary to detect the current value of the AC current flowing through each phase of the driving inverter. By detecting the current value of the current flowing through each phase of the inverter, the rotational position of the motor can be estimated and the rotational speed of the motor can be controlled.

When obtaining a current value of a current flowing through each phase of an inverter for motor control, each phase is provided with a shunt resistor. However, when a shunt resistor is provided for each phase of the inverter, there are problems such as an increase in cost, an increase in size, and heat generated by the shunt resistor due to current.

Japanese Patent Application Laid-Open No. 2020-58230

In view of the above problems, an object of the present disclosure is to provide a calculation program, a calculation method, and a three-phase AC motor system that can appropriately detect the current flowing through each phase of the inverter even if there is only one shunt resistor.

In order to solve the above-described problems and achieve an object, a calculation program according to the present disclosure includes steps of detecting a total current that is a total value of alternating currents flowing in each of the three phases of a three-phase alternating current motor; and calculating each phase current, which is alternating current flowing in each of the three phases of the three-phase alternating current motor, based on the current and each phase duty ratio.

In order to solve the above-described problems and achieve the object, a calculation method according to the present disclosure includes steps of detecting a total current, which is a total value of alternating currents flowing in each of the three phases of a three-phase AC motor; and calculating each phase current, which is alternating current flowing in each of the three phases of the three-phase alternating current motor, based on the current and each phase duty ratio.

In order to solve the above-described problems and achieve the object, a three-phase AC motor system according to the present disclosure provides a three-phase AC motor that operates with a three-phase AC, and a semiconductor switching element that switches according to the duty ratio of each phase. an inverter for supplying an alternating current to each of the three phases of the three-phase alternating current motor by causing the a current detection unit for detecting a total current, which is the total value of alternating currents flowing in each of the three phases of the three-phase AC motor, from the voltage detected by the resistance unit; and based on the total current and the duty ratio of each phase, and a calculation unit for calculating each phase current, which is an alternating current flowing in each of the three phases of the three-phase alternating current motor.

According to the present disclosure, it is possible to provide a calculation program, a calculation method, and a three-phase AC motor system that can appropriately detect the current flowing through each phase of the three-phase AC motor even if there is only one shunt resistor.

FIG. 1 is a diagram showing a configuration example of a three-phase AC motor system according to the present disclosure. FIG. 2 is a diagram showing a configuration example of a control device for a three-phase AC motor system according to the present disclosure. FIG. 3 is a diagram showing temporal changes in each phase current of a three-phase AC motor. FIG. 4 is a schematic diagram schematically showing the δY conversion. FIG. 5 is a diagram showing a flowchart of a method for calculating each phase current of a three-phase AC motor.

Embodiments of the present disclosure will be described in detail below based on the drawings. It should be noted that the present disclosure is not limited by the embodiments described below.

[First embodiment]
FIG. 1 is a diagram showing a configuration example of a three-phase AC motor system according to the present disclosure. As shown in FIG. 1, a three-phase AC motor system 100 according to the present disclosure includes a three-phase AC motor 110, a position detection section 120, an inverter 130, a power supply section 140, a resistance section 150, and a current detection section 160. , a drive circuit 170 , and a control device 180 .

Three-phase AC motor 110 converts electrical energy into mechanical work. The three-phase AC motor 110 has, for example, a stator and a rotor. The stator is the stator or stationary part of the motor. The stator includes coils. Either δ connection or Y connection may be used as the coil connection method. The rotor is the rotor or rotating part of the motor. The three-phase AC motor 110 generates a magnetic field by passing an alternating current through the coils of the stator, and rotates the rotor by interacting with the magnetic force of the permanent magnets of the rotor. A rotating magnetic field can be easily obtained by using a three-phase alternating current. In this manner, three-phase AC motor 110 may convert electrical energy into mechanical work.

A position detector 120 detects a rotor rotation angle θ of the three-phase AC motor 110 . The position detection unit 120 may be, for example, a Hall sensor. A Hall sensor is an integrated circuit in which a Hall element and an operational amplifier are combined as one element. A Hall element is a magnetically responsive thin film solid made of semiconductors. When a magnetic flux approaches perpendicularly to the current while a current is flowing through the Hall element, a Hall voltage is generated in the direction perpendicular to the current and the magnetic flux due to the influence of the Lorentz force. Therefore, the Hall sensor outputs this voltage. Since the output of the Hall voltage of the Hall element is small, it is amplified by an operational amplifier. A position detector 120 detects the rotor rotation angle θ from the Hall voltage.

The position detector 120 may detect the induced voltage generated in the coils of the three-phase AC motor 110 and calculate the rotor rotation angle. Since the induced voltage changes depending on the positional relationship between the coil and the permanent magnet, the rotor rotation angle can be calculated by detecting the induced voltage. Further, the rotor rotation angle is not limited to the above method, and may be obtained by any method. For example, the rotor rotation angle may be calculated by any calculation. In this case, a sensor such as the position detection unit 120 may be unnecessary.

Inverter 130 converts the DC current supplied from power supply unit 140 into AC current and supplies the AC current to three-phase AC motor 110 . Inverter 130 includes an inverter circuit that supplies AC current to each phase of three-phase AC motor 110 . The inverter circuit includes semiconductor switching elements provided for each phase. That is, the inverter circuit of the inverter 130 connects the power supply unit 140 and the U phase of the three-phase AC motor 110 to the wiring provided with the semiconductor switching element, and connects the power supply unit 140 to the V phase of the three-phase AC motor 110. A wiring provided with a semiconductor switching element and a wiring provided with a semiconductor switching element connecting power supply section 140 and the W phase of three-phase AC motor 110 are connected in parallel to the positive side of power supply section 140. It is The semiconductor switching element may be, for example, a bipolar transistor. In addition, the semiconductor switching element includes a gate turn-off thyristor (GTO), an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET). effect transistor), silicon carbide metal oxide semiconductor field effect transistor (SiC-MOSFET), gallium nitride field effect transistor (GaN-FET), power semiconductor using gallium oxide (Ga2O3), and the like. In the inverter circuit, six semiconductor switching elements are provided above and below each phase of a circuit divided into three phases. Inverter 130 is provided with a PWM (Pulse Width Modulation) signal from drive circuit 170, which will be described later, to the gate of the semiconductor switching element to periodically turn ON/OFF the semiconductor switching element, that is, switch the semiconductor switching element. AC current is supplied to each phase of the three-phase AC motor 110 .

Power supply unit 140 is a power supply that supplies direct current to inverter 130 . Power supply unit 140 supplies direct current to inverter 130 . Inverter 130 converts the direct current supplied from power supply unit 140 into alternating current.

Resistor unit 150 detects voltage Vdd corresponding to the total value of alternating currents flowing through each phase of the inverter. Resistor section 150 is provided at a location where respective wirings connected to respective phases of three-phase AC motor 110 from power supply section 140 via inverter 130 join. That is, resistor section 150 includes wiring that connects power supply section 140 and the U phase of three-phase AC motor 110, wiring that connects power supply section 140 and the V phase of three-phase AC motor 110, A wiring that connects the W phase of the phase AC motor 110 is provided in the merged wiring. The resistor section 150 may be, for example, a shunt resistor. A shunt resistor is a resistor to be put in parallel with a circuit, a stabilization circuit for that purpose, and a resistor for current detection.

Current detection unit 160 calculates total current Idd in which currents flowing in respective phases of three-phase AC motor 110 are merged from voltage Vdd detected by resistance unit 150 . For example, the current detection section 160 amplifies the voltage Vdd detected by the resistance section 150 with a differential amplifier circuit and inputs the output to the sample hold circuit. The sample-and-hold circuit samples the input analog signal at a predetermined timing and sends it to the A/D conversion circuit. The A/D conversion circuit converts an input analog signal into a digital signal. The current detection unit 160 calculates the total current Idd using the resistance value R of the resistance unit 150 from the digital signal.

The drive circuit 170 outputs PWM Output a signal.

Controller 180 generates control signals for controlling the three-phase AC motor. The configuration of the control device 180 will be described with reference to FIG. FIG. 2 is a diagram showing a configuration example of a control device for a three-phase AC motor system according to the present disclosure. As shown in FIG. 2 , the control device 180 includes a control section 181 and a storage section 182 .

The control unit 181 is realized by executing various programs stored in the storage unit 182 using a RAM (Random Access Memory) as a work area by a CPU (Central Processing Unit), an MPU (Micro Processing Unit), or the like. . Further, the control unit 181 may be implemented by an analog circuit using an integrated circuit such as an ASIC (Application Specific Circuit) or an FPGA (Field Programmable Gate Array), or an operational amplifier.

As shown in FIG. 2 , the control section 181 includes an acquisition section 1811 , a calculation section 1812 and a command section 1813 .

Acquisition unit 1811 acquires rotor rotation angle θ detected by position detection unit 120 .

A calculator 1812 calculates each phase current (Iu, Iv, Iw) from the total current Idd detected by the current detector 160 . A method of calculating the total current Idd when the winding method of the stator coils of the three-phase AC motor 110 is Y-connection will be described. The same calculation method can be used when the connection method is δ connection. FIG. 3 is a diagram showing temporal changes in each phase current of a three-phase AC motor. First, the case where Iu≧0, Iv≦0, and Iw≦0, which is the second hatched portion from the left in FIG. 3, will be described. When the δY transformation is performed on the Y-connected coil, a current flows through each phase as shown in FIG. FIG. 4 is a schematic diagram schematically showing the δY conversion. That is, the total current Idd flowing through the three-phase AC motor 110 becomes equal to the phase current Iu flowing through the U phase. Here, the phase voltages Vu, Vv, and Vw applied to the U-phase, V-phase, and W-phase, respectively, are given by the following equations (1), (2), and (3), where dutyU, dutyV, and dutyW are the duty ratios of the respective phases. ). Note that the duty ratio is the ratio of the period during which the voltage is applied to one cycle.

A current Iuv flowing from the U phase to the V phase, a current Iuw flowing from the U phase to the W phase, and a current Iwv flowing from the W phase to the V phase are represented by the following equations (4), (5), and (6), respectively. expressed.

From Iuv+Iuw=Iu, Iuv+Iwv=Iv, and Iuw-Iwv=Iw, the following equations (7), (8), and (9) can be derived.

Eliminating Vdd/Z from the equations (7), (8) and (9), the following equations (10) and (11) can be derived.

Calculation unit 1812 calculates each phase current (Iu, Iv, Iw) from the total current Idd and each phase duty ratio (dutyU, dutyV, dutyW) using equations (10) and (11). Calculation unit 1812 calculates each phase current (Iu, Iv, Iw) as an output value by executing a predetermined calculation using voltage Vdd (total current Idd) and a value based on the duty ratio as input values. I can say. By executing a correction operation using the duty ratio, the voltage Vdd (total current Idd ), each phase current can be calculated appropriately. In the above, the case of Iu≧0, Iv≦0, and Iw≦0 was taken as an example, but in the other five conditions shown in FIG. It is possible to calculate each phase current only by

Command unit 1813 generates a PWM signal for each phase of inverter 130 based on each phase current calculated by calculation unit 1812 . That is, command unit 1813 calculates the duty ratio of each phase and generates a PWM signal to each phase of inverter 130 based on the duty ratio of each phase.

For example, in the case of performing vector control, command unit 1813 generates torque current command Iqin based on the difference from measured rotational speed Fout when rotational speed command Fin is given. After performing three-phase to two-phase conversion from each phase current (Iu, Iv, Iw) calculated by the calculation unit 1812, by performing rotation coordinate conversion using the rotor rotation angle θ detected by the position detection unit 120, the torque Calculate the current Iq and the excitation current Id. A PI (Proportional-Integral) control operation is performed on the difference between the torque current command Iqin and the torque current Iq to generate a voltage command Vq. The excitation current Id is similarly processed to generate the voltage command Vd. The generated voltage commands Vd and Vq are converted into phase voltages Vu, Vv and Vw by performing fixed coordinate transformation using the rotor rotation angle θ and then space vector transformation. Each phase duty ratio (dutyU, dutyV, dutyW) is determined from each phase voltage Vu, Vv, Vw. A PWM signal is generated by comparing the duty ratio (dutyU, dutyV, dutyW) of each phase and the level of the carrier wave. By inverting the PWM signal, a signal on the lower arm side is generated. After generating the PWM signal, command unit 1813 outputs the PWM signal to drive circuit 170 .

The storage unit 182 is implemented by, for example, a semiconductor memory device such as a RAM or flash memory, or a storage device such as a hard disk, a solid state drive (SSD), or an optical disc. Various programs for realizing the functions of the control unit 181 are stored in the storage unit 182 .

[Flow of calculation method for each phase current of three-phase AC motor]
Next, a method for calculating each phase current of the three-phase AC motor according to the present disclosure will be described using FIG. FIG. 5 is a diagram showing a flowchart of a method for calculating each phase current of a three-phase AC motor. The three-phase AC motor system 100 detects each phase current flowing through the three-phase AC motor 110 (step S101). The three-phase AC motor system 100 calculates each phase current based on the total current and each phase duty ratio (step S102).

As described above, according to the three-phase AC motor system 100 according to the first embodiment, the number of shunt resistors for current detection can be reduced to one, so the amount of heat generated can be reduced. Also, by reducing the amount of heat generated, it is possible to contribute to miniaturization and extension of the life of the three-phase AC motor system 100 . Also, by setting the number of shunt resistors to one, the number of times of current measurement can be reduced to one.

[Second embodiment]
The three-phase AC motor system 100 according to the second embodiment differs from the configuration of the three-phase AC motor system 100 according to the first embodiment in the processing of the calculation unit 1812, and the storage content is added to the storage unit 182. Other than that, they are the same. Therefore, of the configuration of the three-phase AC motor system 100 according to the second embodiment, the description of the parts common to the three-phase AC motor system 100 according to the first embodiment will be omitted, and the calculation unit 1812 and the storage unit 182 will be omitted. will be explained.

Based on the relationship between the rotor rotation angle and the duty ratio of each phase stored in the storage unit 182, which will be described later, the calculation unit 1812 calculates the duty ratio of each phase when it is assumed that the rotor rotation angle advances by a predetermined angle. to calculate That is, when each phase current is calculated using the duty ratio of each phase at the time when the rotor rotation angle is measured, the rotor rotation angle has changed when the calculation of each phase duty ratio is completed. The required duty ratio of each phase is calculated by using a value obtained by advancing the rotor rotation angle by a predetermined value. For example, the rotor rotation angle corresponding to each phase duty ratio required for the next control may be calculated by obtaining the rotor rotation speed from the rotor rotation angle and multiplying the rotor rotation speed by the calculation time. After calculating the duty ratio of each phase assuming that the rotor rotation angle advances by a predetermined angle, calculation unit 1812 calculates each phase current (Iu, Iv, Iw) is calculated. It can be said that the calculation unit 1812 calculates each phase current (Iu, Iv, Iw) as an output value by executing a predetermined calculation using the voltage Vdd (total current Idd) and the duty ratio of each phase as input values. .

Storage unit 182 stores the relationship between the rotor rotation angle and the duty ratio of each phase. That is, the storage unit 182 stores the phase duty ratios (dutyU, dutyV, dutyW) corresponding to the rotor rotation angle θ of the three-phase AC motor 110 as a table.

Thus, according to the three-phase AC motor system 100 according to the second embodiment, each phase current is calculated using each phase duty ratio derived using the relationship between the rotor rotation angle and each phase duty ratio. , the calculation of each phase current can be simplified. That is, the calculation speed of each phase current can be increased. Therefore, even if an MPU with low performance is used for the control unit 181, it is possible to calculate the current of each phase, so that the cost can be reduced.

[Third embodiment]
The three-phase AC motor system 100 according to the third embodiment differs from the configuration of the three-phase AC motor system 100 according to the first embodiment in the processing of the calculation unit 1812, and the storage content is added to the storage unit 182. Other than that, they are the same. Therefore, of the configuration of the three-phase AC motor system 100 according to the third embodiment, the description of the parts common to the three-phase AC motor system 100 according to the first embodiment is omitted, and the calculation unit 1812 and the storage unit 182 are omitted. will be explained.

Calculation unit 1812 calculates each phase duty ratio required for the next control based on the detected rotor rotation angle and power factor, and calculates each phase current from the total current based on the calculated each phase duty ratio. do. In the above equations (9), (10), and (11), each phase duty ratio is a voltage ratio, so it is converted into a current value in consideration of the power factor. Assuming that the rotor rotation angle is θ and the power factor is φ, phase currents Iu, Iv, and Iw are expressed as shown in the following equations (12), (13), and (14), respectively.

That is, if the total current Idd, rotor rotation angle θ, and power factor φ are known, each phase current (Iu, Iv, Iw) can be obtained. Calculation unit 1812 acquires the power factor from storage unit 182, which will be described later, and calculates each phase current based on equations (12), (13), and (14) from total current Idd, rotor rotation angle θ, and power factor φ. Calculate (Iu, Iv, Iw). That is, calculation unit 1812 calculates each phase duty ratio required for the next control based on rotor rotation angle θ and power factor φ, and calculates each phase current from the total current based on the calculated each phase duty ratio. to calculate Calculation unit 1812 performs a predetermined calculation using voltage Vdd (total current Idd), rotor rotation angle θ, and power factor φ as input values, and outputs each phase current (Iu, Iv, Iw) as an output value. It can be said that it is calculated as Equations (12), (13), and (14) express the duty ratio of each phase using the rotor rotation angle θ and the power factor φ. Therefore, even when each phase current (Iu, Iv, Iw) is calculated based on the rotor rotation angle θ and the power factor φ as in the third embodiment, each phase current (Iu, Iw) is calculated based on each phase duty ratio. Iv, Iw) can be said to be calculated.

Storage unit 182 stores the power factor of three-phase AC motor 110 . As for the power factor, a value measured during a shipping test may be stored in the storage unit 182 . Since the power factor changes due to machining errors and variations in clearance, by storing the values measured during the shipping test, each phase current (Iu, Iv, Iw) flowing through the three-phase AC motor 110 can be accurately calculated. can be calculated well. Note that the measurement of the power factor is not limited to being performed at the shipping test. For example, the three-phase AC motor system 100 may be provided with a dedicated measuring instrument to obtain the rotor rotation angle, the current phase, and the voltage phase.

Thus, according to the three-phase AC motor system 100 according to the third embodiment, each phase current is calculated from the total current Idd based on the rotor rotation angle θ and the power factor φ measured during the shipping test. be able to. Since the power factor uses the value measured in the shipping test, each phase current (Iu, Iv, Iw) can be calculated with high accuracy. That is, even if there are machining errors or variations in clearance, each phase current (Iu, Iv, Iw) is calculated using the power factor value measured during the shipping test. (Iu, Iv, Iw) can be calculated with high accuracy.

[Structure and effect]
The calculation program according to the present disclosure comprises a step of detecting a total current that is the total value of alternating currents flowing in each of the three phases of the three-phase AC motor 110, and based on the total current and the duty ratio of each phase, the three-phase AC motor and calculating each phase current, which is the alternating current flowing in each of the three phases 110 .

According to the calculation program with this configuration, the current flowing through each phase of the three-phase AC motor 110 can be detected appropriately. In addition, since each phase current is calculated from the total current, which is the sum of the alternating currents flowing in each of the three phases of the three-phase AC motor 110, the number of shunt resistors can be reduced to one, which reduces the amount of heat generated. can be made Also, by reducing the amount of heat generated, it is possible to contribute to miniaturization and extension of the life of the three-phase AC motor system 100 . Also, by setting the number of shunt resistors to one, the number of times of current measurement can be reduced to one.

The calculation program according to the present disclosure further includes a step of detecting the rotor rotation angle of the three-phase AC motor 110, and the calculating step includes reading from the storage unit 182 the relationship between the rotor rotation angle and the duty ratio of each phase; From the detected rotor rotation angle, a step of calculating the duty ratio of each phase when it is assumed that the rotor rotation angle advances by a predetermined angle based on the relationship; and calculating each phase current.

According to the calculation program with this configuration, the calculation of each phase current can be simplified. That is, the calculation speed of each phase current can be increased. Therefore, even if an MPU with low performance is used for the control unit 181, it is possible to calculate the current of each phase, so that the cost can be reduced.

The calculation program according to the present disclosure further includes a step of detecting the rotor rotation angle of the three-phase AC motor 110, and the calculating step includes reading the power factor of the three-phase AC motor 110 from the storage unit 182; calculating each phase current from the duty ratio and the total current based on the rotor rotation angle and the read power factor.

According to the calculation program with this configuration, the current flowing in each phase of the three-phase AC motor 110 can be detected with high accuracy. Since the power factor uses the value measured during the shipping test, even if there are machining errors or variations in clearance, each phase current is calculated using the power factor that reflects the effect. It can be calculated with high accuracy.

The calculation method according to the present disclosure includes steps of detecting a total current, which is the total value of alternating currents flowing in each of the three phases of the three-phase AC motor 110, and based on the total current and the duty ratio of each phase, the three-phase AC motor and calculating each phase current, which is the alternating current flowing in each of the three phases of 110 .

According to the calculation method with this configuration, the current flowing through each phase of the three-phase AC motor 110 can be detected appropriately.

A three-phase AC motor system 100 according to the present disclosure includes a three-phase AC motor 110 that operates with a three-phase AC, and a semiconductor switching element that performs switching operations according to a duty ratio to each of the three phases of the three-phase AC motor 110. An inverter 130 that supplies an alternating current, one resistor unit 150 that detects a voltage corresponding to the total value of alternating currents flowing in each phase of the inverter 130, and the three-phase AC motor 110 based on the voltage detected by the resistor unit 150. A current detection unit 160 that detects the total current that is the total value of the alternating currents flowing in each of the three phases, and the alternating current that flows in each of the three phases of the three-phase alternating current motor 110 based on the total current and the duty ratio of each phase and a calculation unit 1812 for calculating each phase current.

According to the three-phase AC motor system 100, since the number of shunt resistors can be reduced to one, the amount of heat generated can be reduced. Also, by reducing the amount of heat generated, it is possible to contribute to miniaturization and extension of the life of the three-phase AC motor system 100 . Also, by setting the number of shunt resistors to one, the number of times of current measurement can be reduced to one.

Although the embodiments of the present disclosure have been described above, the embodiments are not limited by the contents of the embodiments. In addition, the components described above include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the components described above can be combined as appropriate. Furthermore, various omissions, replacements, or modifications of components can be made without departing from the gist of the above-described embodiments.

100 three-phase AC motor system 110 three-phase AC motor 120 position detection unit 130 inverter 140 power supply unit 150 resistance unit 160 current detection unit 170 drive circuit 180 control device 181 control unit 1811 acquisition unit 1812 calculation unit 1813 command unit 182 storage unit

Claims (5)

a step of detecting a total current, which is the total value of alternating currents flowing in each of the three phases of the three-phase alternating current motor;
calculating each phase current, which is an alternating current flowing in each of the three phases of the three-phase alternating current motor, based on the total current and each phase duty ratio;
A calculation program that causes a computer to execute further comprising detecting a rotor rotation angle of the three-phase AC motor;
The calculating step includes:
a step of reading the relationship between the rotor rotation angle and the duty ratio of each phase from a storage unit;
calculating, from the detected rotor rotation angle, a duty ratio of each phase when it is assumed that the rotor rotation angle advances by a predetermined angle based on the relationship;
calculating each phase current from the total current based on the calculated duty ratio for each phase;
A computer program according to claim 1. further comprising detecting a rotor rotation angle of the three-phase AC motor;
The calculating step includes:
a step of reading the power factor of the three-phase AC motor from a storage unit;
calculating each phase current from the phase duty ratio and the total current based on the detected rotor rotation angle and the read power factor;
A computer program according to claim 1. a step of detecting a total current, which is the total value of alternating currents flowing in each of the three phases of the three-phase alternating current motor;
calculating each phase current, which is an alternating current flowing in each of the three phases of the three-phase alternating current motor, based on the total current and each phase duty ratio;
calculation method, including a three-phase AC motor operated by three-phase AC;
an inverter that supplies AC current to each of the three phases of the three-phase AC motor by switching semiconductor switching elements according to the duty ratio of each phase;
one resistor unit for detecting a voltage corresponding to the total value of alternating currents flowing in each phase of the inverter;
a current detection unit that detects a total current, which is a total value of alternating currents flowing in each of the three phases of the three-phase AC motor, from the voltage detected by the resistance unit;
a calculation unit that calculates each phase current, which is alternating current flowing in each of the three phases of the three-phase alternating current motor, based on the total current and the duty ratio of each phase;
A three-phase AC motor system comprising:

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