JP7789503B2 - Calculation program, calculation method, and three-phase AC motor system - Google Patents

Description

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

When controlling a three-phase AC motor, it is necessary to detect the current value of the AC current flowing through each phase of the drive inverter. By detecting the current value of the current flowing through each phase of the inverter, it is possible to estimate the motor's rotational position and control the motor's rotational speed.

When determining the current value of the current flowing through each phase of an inverter for motor control, a shunt resistor is typically installed in each phase. However, installing a shunt resistor in each phase of the inverter increases costs and size, and also raises the issue of heat generation in the shunt resistor due to the current.

Japanese Patent Application Laid-Open No. 2020-58230

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

To solve the above-mentioned problems and achieve the objectives, the calculation program disclosed herein causes a computer to execute the following steps: detecting a total current, which is the sum of the AC currents flowing through each of the three phases of a three-phase AC motor; and calculating each phase current, which is the AC current flowing through each of the three phases of the three-phase AC motor, based on the total current and the duty ratio of each phase.

To solve the above-mentioned problems and achieve the objectives, the calculation method disclosed herein includes the steps of detecting a total current, which is the sum of the AC currents flowing through each of the three phases of a three-phase AC motor, and calculating each phase current, which is the AC current flowing through each of the three phases of the three-phase AC motor, based on the total current and the duty ratio of each phase.

In order to solve the above-mentioned problems and achieve the objectives, the three-phase AC motor system disclosed herein comprises a three-phase AC motor that operates using 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 in accordance with the duty ratio of each phase; a resistor that detects a voltage corresponding to the total value of the AC current flowing through each of the inverter's phases; a current detection unit that detects a total current, which is the total value of the AC current flowing through each of the three phases of the three-phase AC motor, from the voltage detected by the resistor; and a calculation unit that calculates each phase current, which is the AC current flowing through each of the three phases of the three-phase AC motor, based on the total current and the phase duty ratio.

This disclosure provides a calculation program, calculation method, and three-phase AC motor system that can properly detect the current flowing through each phase of a three-phase AC motor even when there is only one shunt resistor.

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

Embodiments of the present disclosure are described in detail below with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below.

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

The three-phase AC motor 110 converts electrical energy into mechanical work. The three-phase AC motor 110 includes, for example, a stator and a rotor. The stator is the fixed part of the motor. The stator includes coils. The coils may be connected using either a delta connection or a Y connection. The rotor is the rotating part of the motor. The three-phase AC motor 110 generates a magnetic field by passing an AC current through the coils in the stator, and rotates the rotor through interaction with the magnetic force of the permanent magnets in the rotor. A rotating magnetic field can be easily obtained by using three-phase AC. In this way, the three-phase AC motor 110 may convert electrical energy into mechanical work.

The position detection unit 120 detects the 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 that combines a Hall element and an operational amplifier into a single element. The Hall element is a magnetically responsive thin-film solid formed from a semiconductor. When a current flows through the Hall element and a magnetic flux approaches perpendicular to the current, a Hall voltage is generated in the direction perpendicular to the current and magnetic flux due to the influence of the Lorentz force. As a result, the Hall sensor outputs this voltage. Note that the Hall voltage output from the Hall element is small, so it is amplified by an operational amplifier. The position detection unit 120 detects the rotor rotation angle θ from the Hall voltage.

The position detection unit 120 may detect the induced voltage generated in the coils of the three-phase AC motor 110 and calculate the rotor rotation angle by calculation. Since the induced voltage changes depending on the positional relationship between the coils and the permanent magnets, the rotor rotation angle can be calculated by detecting the induced voltage. Furthermore, 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 not be required.

The inverter 130 converts the DC current supplied from the power supply unit 140 into AC current and supplies it to the three-phase AC motor 110. The inverter 130 includes an inverter circuit that supplies AC current to each phase of the 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 includes wiring that connects the power supply unit 140 to the U phase of the three-phase AC motor 110 and is equipped with semiconductor switching elements, wiring that connects the power supply unit 140 to the V phase of the three-phase AC motor 110 and is equipped with semiconductor switching elements, and wiring that connects the power supply unit 140 to the W phase of the three-phase AC motor 110 and is equipped with semiconductor switching elements, all connected in parallel to the positive side of the power supply unit 140. The semiconductor switching elements may be, for example, bipolar transistors. The semiconductor switching elements may be gate turn-off thyristors (GTOs), insulated gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), silicon carbide metal-oxide-semiconductor field-effect transistors (SiC-MOSFETs), gallium nitride field-effect transistors (GaN-FETs), or power semiconductors using gallium oxide (Ga2O3). The inverter circuit has six semiconductor switching elements provided above and below each phase of a circuit divided into three phases. The inverter 130 supplies AC current to each phase of the three-phase AC motor 110 by periodically turning the semiconductor switching elements on and off, i.e., switching them, when a PWM (Pulse Width Modulation) signal is provided to the gates of the semiconductor switching elements from the drive circuit 170, which will be described later.

The power supply unit 140 is a power supply that supplies DC current to the inverter 130. The power supply unit 140 supplies DC current to the inverter 130. The inverter 130 converts the DC current supplied from the power supply unit 140 into AC current.

The resistor unit 150 detects a voltage Vdd corresponding to the total value of the AC current flowing through each phase of the inverter. The resistor unit 150 is provided at the point where the wiring connected from the power supply unit 140 to each phase of the three-phase AC motor 110 via the inverter 130 converges. That is, the resistor unit 150 is provided at the convergence point of the wiring connecting the power supply unit 140 to the U phase of the three-phase AC motor 110, the wiring connecting the power supply unit 140 to the V phase of the three-phase AC motor 110, and the wiring connecting the power supply unit 140 to the W phase of the three-phase AC motor 110. The resistor unit 150 may be, for example, a shunt resistor. A shunt resistor is a resistor placed in parallel with a circuit, a stabilizing circuit for that purpose, or a resistor for current detection.

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

The drive circuit 170 outputs a PWM signal to each gate of the six semiconductor switching elements (U+, V+, W+, U-, V-, W-) included in the inverter circuit in accordance with the PWM signal generated by the command unit 1813 of the control unit 181.

The control device 180 generates a control signal for controlling the three-phase AC motor. The configuration of the control device 180 will be described using Figure 2. Figure 2 is a diagram showing an example configuration of a control device for a three-phase AC motor system according to the present disclosure. As shown in Figure 2, the control device 180 includes a control unit 181 and a memory unit 182.

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

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

The acquisition unit 1811 acquires the rotor rotation angle θ detected by the position detection unit 120.

Calculation unit 1812 calculates the phase currents (Iu, Iv, Iw) from the total current Idd detected by current detection unit 160. A method for calculating the total current Idd when the stator coils of three-phase AC motor 110 are connected in a Y-connection will be described. The same calculation method can also be used when the connection method is a δ-connection. Figure 3 shows the time variation of each phase current of a three-phase AC motor. First, we will explain the case where Iu≧0, Iv≦0, and Iw≦0, which is the hatched area second from the left in Figure 3. When δY conversion is performed on a Y-connected coil, current flows in each phase as shown in Figure 4. Figure 4 is a schematic diagram showing δY conversion. In other words, the total current Idd flowing through 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, V, and W phases, respectively, are expressed as shown in the following equations (1), (2), and (3), where the phase duty ratios are dutyU, dutyV, and dutyW. The duty ratio is the ratio of the period during which voltage is applied to one cycle.

The current Iuv flowing from the U phase to the V phase, the current Iuw flowing from the U phase to the W phase, and the current Iwv flowing from the W phase to the V phase are expressed as shown in the following equations (4), (5), and (6), respectively.

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

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

The calculation unit 1812 calculates the phase currents (Iu, Iv, Iw) from the total current Idd and the phase duty ratios (dutyU, dutyV, dutyW) using equations (10) and (11). The calculation unit 1812 performs a predetermined calculation using the voltage Vdd (total current Idd) and a value based on the duty ratio as input values, thereby calculating the phase currents (Iu, Iv, Iw) as output values. By performing a correction calculation using the duty ratio, the phase currents can be appropriately calculated based on the voltage Vdd (total current Idd), even when the voltage Vdd (total current Idd) is detected when positive or negative current is flowing through all three phases. While the above example illustrates the case where Iu≧0, Iv≦0, and Iw≦0, the phase currents can also be calculated for the other five conditions shown in Figure 3 by simply changing the sign from the total current Idd and the phase duty ratios.

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

For example, when vector control is performed, when the command unit 1813 is given a rotational speed command Fin, it generates a torque current command Iqin based on the difference with the measured rotational speed Fout. After performing a three-phase to two-phase transformation on the phase currents (Iu, Iv, Iw) calculated by the calculation unit 1812, it performs a rotational coordinate transformation using the rotor rotation angle θ detected by the position detection unit 120 to calculate the torque current Iq and excitation current Id. A PI (Proportional-Integral) control calculation is performed on the difference between the torque current command Iqin and the torque current Iq to generate a voltage command Vq. A similar process is performed on the excitation current Id to generate a voltage command Vd. The generated voltage commands Vd and Vq are then subjected to a fixed coordinate transformation using the rotor rotation angle θ, followed by a space vector transformation to convert them into phase voltages Vu, Vv, and Vw. The duty ratios of each phase (dutyU, dutyV, dutyW) are determined from the phase voltages Vu, Vv, and Vw. A PWM signal is generated by comparing the level of each phase duty ratio (dutyU, dutyV, dutyW) with the carrier wave. A signal for the lower arm is generated by inverting the PWM signal. Once the PWM signal has been generated, the command unit 1813 outputs the PWM signal to the drive circuit 170.

The memory unit 182 is realized, for example, by a semiconductor memory element such as RAM or flash memory, or a storage device such as a hard disk, SSD (Solid State Drive), or optical disk. The memory unit 182 stores various programs for realizing the functions of the control unit 181.

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

As such, with 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, thereby reducing the amount of heat generated. Furthermore, reducing the amount of heat generated can contribute to the miniaturization and longer life of the three-phase AC motor system 100. Furthermore, by reducing the number of shunt resistors to one, the number of current measurements required can be reduced to one.

Second Embodiment
The three-phase AC motor system 100 according to the second embodiment is the same as the three-phase AC motor system 100 according to the first embodiment except for the processing of the calculation unit 1812, and the addition of stored contents to the storage unit 182. Therefore, of the configuration of the three-phase AC motor system 100 according to the second embodiment, explanations of the parts common to the three-phase AC motor system 100 according to the first embodiment will be omitted, and only the calculation unit 1812 and the storage unit 182 will be explained.

Based on the relationship between the rotor rotation angle and the phase duty ratios stored in the memory unit 182 (described below), the calculation unit 1812 calculates the phase duty ratios for each phase assuming that the rotor rotation angle has advanced by a predetermined angle. That is, if the phase currents are calculated using the phase duty ratios at the time the rotor rotation angle is measured, the rotor rotation angle will have changed by the time the calculation of the phase duty ratios is completed. Therefore, the phase duty ratios required for the next control are calculated using values obtained when the rotor rotation angle has advanced by a predetermined value. For example, the rotor rotation speed may be calculated from the rotor rotation angle, and the rotor rotation speed may be multiplied by the calculation time to calculate the rotor rotation angle corresponding to the phase duty ratios required for the next control. After calculating the phase duty ratios for each phase assuming that the rotor rotation angle has advanced by a predetermined angle, the calculation unit 1812 calculates the phase currents (Iu, Iv, Iw) based on the aforementioned equations (10) and (11). The calculation unit 1812 performs a predetermined calculation using the voltage Vdd (total current Idd) and the duty ratio of each phase as input values, thereby calculating the currents of each phase (Iu, Iv, Iw) as output values.

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

In this way, with the three-phase AC motor system 100 according to the second embodiment, the calculation of each phase current can be simplified because the phase current is calculated using the phase duty ratio derived from the relationship between the rotor rotation angle and the phase duty ratio. In other words, the calculation speed of each phase current can be increased. Therefore, even if a low-performance MPU is used for the control unit 181, calculation of each phase current is possible, thereby reducing costs.

Third Embodiment
The three-phase AC motor system 100 according to the third embodiment is the same as the three-phase AC motor system 100 according to the first embodiment except for the processing of the calculation unit 1812, and the addition of stored contents to the storage unit 182. Therefore, of the configuration of the three-phase AC motor system 100 according to the third embodiment, explanations of the parts common to the three-phase AC motor system 100 according to the first embodiment will be omitted, and only the calculation unit 1812 and the storage unit 182 will be explained.

Calculation unit 1812 calculates the phase duty ratio required for the next control based on the detected rotor rotation angle and power factor, and calculates the phase current from the total current based on the calculated phase duty ratio. In the above equations (9), (10), and (11), the phase duty ratio is a voltage ratio, so it is converted to a current value taking the power factor into account. If the rotor rotation angle is θ and the power factor is φ, the 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, the phase currents (Iu, Iv, Iw) can be calculated. The calculation unit 1812 obtains the power factor from the memory unit 182 (described later) and calculates the phase currents (Iu, Iv, Iw) from the total current Idd, rotor rotation angle θ, and power factor φ based on equations (12), (13), and (14). That is, the calculation unit 1812 calculates the phase duty ratios required for the next control based on the rotor rotation angle θ and power factor φ, and calculates the phase currents from the total current based on the calculated phase duty ratios. The calculation unit 1812 performs a predetermined calculation using the voltage Vdd (total current Idd), rotor rotation angle θ, and power factor φ as input values, thereby calculating the phase currents (Iu, Iv, Iw) as output values. Note that 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 calculating the phase currents (Iu, Iv, Iw) based on the rotor rotation angle θ and the power factor φ as in the third embodiment, it can be said that the phase currents (Iu, Iv, Iw) are calculated based on the phase duty ratio.

The memory unit 182 stores the power factor of the three-phase AC motor 110. The power factor may be a value measured during a shipping test and stored in the memory unit 182. Because the power factor varies due to processing errors and clearance variations, storing the value measured during the shipping test allows for accurate calculation of the phase currents (Iu, Iv, Iw) flowing through the three-phase AC motor 110. Note that the power factor does not necessarily have to be measured during the shipping test. For example, the power factor may be determined from the rotor rotation angle, current phase, and voltage phase by providing a dedicated measuring device in the three-phase AC motor system 100.

In this way, with the three-phase AC motor system 100 according to the third embodiment, the current for each phase can be calculated from the total current Idd based on the rotor rotation angle θ and the power factor φ measured during shipping testing. Because the power factor value measured during shipping testing is used for the power factor, the currents for each phase (Iu, Iv, Iw) can be calculated with high accuracy. In other words, even if there are processing errors or variations in clearance, the currents for each phase (Iu, Iv, Iw) can be calculated with high accuracy because the currents for each phase (Iu, Iv, Iw) are calculated using the power factor value measured during shipping testing.

[Composition and Effects]
The calculation program according to the present disclosure causes a computer to execute the steps of detecting a total current, which is the sum of the AC currents flowing through each of the three phases of the three-phase AC motor 110, and calculating each phase current, which is the AC current flowing through each of the three phases of the three-phase AC motor 110, based on the total current and the duty ratio of each phase.

This calculation program allows the current flowing through each phase of the three-phase AC motor 110 to be properly detected. Furthermore, because the current for each phase is calculated from the total current, which is the sum of the AC currents flowing through each of the three phases of the three-phase AC motor 110, the number of shunt resistors can be reduced to one, thereby reducing the amount of heat generated. Furthermore, reducing the amount of heat generated can contribute to the miniaturization and longer life of the three-phase AC motor system 100. Furthermore, by reducing the number of shunt resistors to one, the number of current measurements required 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 calculation step includes a step of reading the relationship between the rotor rotation angle and the duty ratio of each phase from the memory unit 182, a step of calculating the duty ratio of each phase from the detected rotor rotation angle based on the relationship when it is assumed that the rotor rotation angle has advanced by a predetermined angle, and a step of calculating the current of each phase from the total current based on the calculated duty ratio of each phase.

This calculation program can simplify the calculation of each phase current. In other words, it can increase the calculation speed of each phase current. Therefore, even if a low-performance MPU is used for the control unit 181, it is possible to calculate each phase current, thereby reducing costs.

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 calculation step includes a step of reading the power factor of the three-phase AC motor 110 from the memory unit 182, and a step of calculating the current of each phase from the duty ratio and total current based on the detected rotor rotation angle and the read power factor.

This calculation program allows for accurate detection of the current flowing through each phase of the three-phase AC motor 110. Because the power factor uses values measured during shipping testing, even if there are manufacturing errors or clearance variations, the power factor reflects these effects when calculating the current for each phase, allowing for accurate calculations.

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

This calculation method allows for the appropriate detection of the current flowing through each phase of the three-phase AC motor 110.

The three-phase AC motor system 100 according to the present disclosure comprises a three-phase AC motor 110 that operates on three-phase AC, an inverter 130 that supplies AC current to each of the three phases of the three-phase AC motor 110 by switching semiconductor switching elements according to a duty ratio, a resistor unit 150 that detects a voltage corresponding to the total value of the AC current flowing through each of the phases of the inverter 130, a current detection unit 160 that detects a total current, which is the total value of the AC current flowing through each of the three phases of the three-phase AC motor 110, from the voltage detected by the resistor unit 150, and a calculation unit 1812 that calculates each phase current, which is the AC current flowing through each of the three phases of the three-phase AC motor 110, based on the total current and the duty ratio of each phase.

With the three-phase AC motor system 100, the number of shunt resistors can be reduced to one, thereby reducing the amount of heat generated. Furthermore, reducing the amount of heat generated can contribute to the miniaturization and longer life of the three-phase AC motor system 100. Furthermore, by reducing the number of shunt resistors to one, the number of current measurements required can be reduced to one.

Although the embodiments of the present disclosure have been described above, the embodiments are not limited to the content of these embodiments. Furthermore, the aforementioned components include those that would be easily conceivable to a person skilled in the art, those that are substantially identical, and those that are within the scope of what is known as equivalents. Furthermore, the aforementioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the aforementioned embodiments.

REFERENCE SIGNS LIST 100 Three-phase AC motor system 110 Three-phase AC motor 120 Position detection unit 130 Inverter 140 Power supply unit 150 Resistor 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 (8)

detecting a total current, which is a sum of AC currents flowing through three phases of the three-phase AC motor;
and calculating each phase current, which is an AC current flowing through each of the three phases of the three-phase AC motor, based on the total current and each phase duty ratio ;
In the step of calculating each phase current,
Using a calculation formula set on the assumption that the total current is equal to the current flowing in the U phase, the current of each phase is calculated based on the total current detected when a positive or negative current flows in all three phases and the duty ratio of each phase.
A calculation program that causes a computer to execute the following. detecting a rotor rotation angle of the three-phase AC motor;
The calculating step
reading out the relationship between the rotor rotation angle and each phase duty ratio from a storage unit;
calculating, from the detected rotor rotation angle, a duty ratio for each phase when it is assumed that the rotor rotation angle has advanced by a predetermined angle based on the relationship;
and calculating a current of each phase from the total current based on the calculated duty ratio of each phase.
The calculation program according to claim 1. detecting a rotor rotation angle of the three-phase AC motor;
The calculating step
reading out the power factor of the three-phase AC motor from a storage unit;
and 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.
The calculation program according to claim 1. detecting a total current, which is a sum of AC currents flowing through three phases of the three-phase AC motor;
and calculating each phase current, which is an AC current flowing through each of the three phases of the three-phase AC motor, based on the total current and each phase duty ratio ;
In the step of calculating each phase current,
calculating the current of each phase based on the total current detected when a positive or negative current flows in all three phases and the duty ratio of each phase, using a calculation formula set on the assumption that the total current is equal to the current flowing in the U phase;
Calculation method. 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 in accordance with the duty ratio of each phase;
a resistor unit for detecting a voltage corresponding to a total value of AC currents flowing through each phase of the inverter;
a current detection unit that detects a total current, which is a sum of AC currents flowing through 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 an AC current flowing through each of the three phases of the three-phase AC motor, based on the total current and the phase duty ratio ;
The calculation unit calculates the current of each phase based on the total current detected at a timing when a positive or negative current flows in all three phases and the duty ratio of each phase, using a calculation formula set on the assumption that the total current is equal to the current flowing in the U phase.
Three- phase AC motor system. In the step of calculating the phase currents, when the phase currents of the U phase, V phase, and W phase are Iu, Iv, and Iw, and the phase duty ratios are dutyU, dutyV, and dutyW, respectively, the following equations are obtained:
When Iu≧0, Iv≦0, and Iw≦0, the phase currents Iv and Iw are calculated based on the following equations (10) and (11):
The calculation program according to claim 1. In the step of calculating the phase currents, when the phase currents of the U phase, V phase, and W phase are Iu, Iv, and Iw, and the phase duty ratios are dutyU, dutyV, and dutyW, respectively, the following equations are obtained:
When Iu≧0, Iv≦0, and Iw≦0, the phase currents Iv and Iw are calculated based on the following equations (10) and (11):
5. The calculation method according to claim 4. The calculation unit calculates the following equation, where the phase currents of the U phase, V phase, and W phase are Iu, Iv, and Iw, and the phase duty ratios are dutyU, dutyV, and dutyW, respectively:
When Iu≧0, Iv≦0, and Iw≦0, the phase currents Iv and Iw are calculated based on the following equations (10) and (11):
6. The three-phase AC motor system according to claim 5.