Motor current detection method, motor control device, motor device, exhaust fan, and blower

Abstract

To obtain a motor current detection method, a motor control device, a motor device, an exhaust fan, and a blower with which it is possible to detect the current value in each phase of a two-phase motor by a compact composition.SOLUTION: A shunt resistor 51 is connected to an electric wire connected to the source terminals of three switching elements 32a, 32b, 32c on the lower arm side. A motor control device 50 includes a motor current detection unit and an inverter control unit as functional blocks. A motor current detection unit 50a calculates the respective current values of a first winding 41a and a second winding 41b on the basis of the current flowing in the shunt resistor 51 and the switching timing of a plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a motor current detection method, a motor control device, a motor device, a ventilation fan, and a blower fan.

Background Art

[0002] In recent years, due to the increasing interest in energy conservation and comfort, products equipped with a constant air volume operation function, a low air volume long-time continuous operation function corresponding to 24 hours, etc. are preferred. In order to have these functions, it is necessary to make the air volume variable. As a method of making the air volume variable, a method of arbitrarily controlling the motor voltage and frequency using an inverter circuit has become mainstream.

[0003] In addition, as the motor, a DC motor with a permanent magnet mounted on the rotor is being adopted because of its high efficiency. For the control of a DC motor, detection of the magnetic pole position of the rotor is required. In recent technologies, a sensorless method of estimating the magnetic pole position from electrical information has become mainstream. In order to estimate the magnetic pole position, it is necessary to accurately measure the current flowing through the stator winding of the motor.

[0004] In a conventional motor drive control device, a shunt resistor is connected to each of the three switching elements on the lower arm side in the inverter circuit. The current detection unit converts the current flowing through the three shunt resistors into a voltage and outputs it to the sensorless control unit (see, for example, Patent Document 1).

[0005] In addition, as the motor, the stator of a capacitor-start AC motor may be diverted, and a two-phase DC brushless motor with a plurality of magnets mounted on the rotor may be used.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the conventional motor drive control device as described above, in order to suppress losses, resistors with relatively small resistance values are used as each shunt resistor. For this reason, an analog amplifier circuit is used to increase the value of the voltage drop calculated by multiplying the current value and the resistance value. However, in the conventional motor drive control device, since shunt resistors are connected to each of the three switching elements on the lower arm side, the number of the analog amplifier circuit and its peripheral components increases, and the occupied area of the analog amplifier circuit and its peripheral components on the circuit board increases.

[0008] The present disclosure has been made to solve the above problems, and an object thereof is to obtain a motor current detection method, a motor control device, a motor device, a ventilation fan, and a blower that can detect the current value of each phase in a two-phase motor with a compact configuration.

Means for Solving the Problems

[0009] The motor current detection method according to the present disclosure calculates the current value of each of the two-phase stator windings in a two-phase motor connected to an inverter circuit based on the current flowing through a resistor connected to a location where a plurality of switching elements in the inverter circuit are commonly connected, and the switching timing of the plurality of switching elements. The motor control device according to the present disclosure includes a motor current detection unit that calculates the current value of each of the two-phase stator windings in a two-phase motor connected to an inverter circuit based on the current flowing through a resistor connected to a location where a plurality of switching elements in the inverter circuit are commonly connected, and the switching timing of the plurality of switching elements, and an inverter control unit that controls the plurality of switching elements based on the calculation result by the motor current detection unit. The motor device according to the present disclosure includes a two-phase motor having two-phase stator windings, an inverter circuit having a plurality of switching elements and connected to the two-phase motor, a motor control device for controlling the plurality of switching elements, and a resistor connected to a location where the plurality of switching elements in the inverter circuit are commonly connected. The motor control device calculates the current value of each of the two-phase stator windings based on the current flowing through the resistor and the switching timing of the plurality of switching elements.

Effect of the Invention

[0010] According to the present disclosure, the current value of each phase in a two-phase motor can be detected with a compact configuration.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 10

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Figure 12

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments will be described with reference to the drawings. Embodiment 1. FIG. 1 is a circuit diagram showing a motor device according to Embodiment 1. In the figure, the motor device 60 according to Embodiment 1 includes a rectifier circuit 20, an inverter circuit 30, a two-phase motor 40, a motor control device 50, a shunt resistor 51, and an amplifier 52.

[0013] The rectifier circuit 20 is connected to the power supply 10. The power supply 10 is a single-phase commercial power supply. The rectifier circuit 20 has a first rectifier diode 21, a second rectifier diode 22, a third rectifier diode 23, and a fourth rectifier diode 24. The first rectifier diode 21, the second rectifier diode 22, the third rectifier diode 23, and the fourth rectifier diode 24 constitute a bridge circuit.

[0014] In the rectifier circuit 20, a smoothing capacitor 25 is connected to the output of the bridge circuit. An electrolytic capacitor is used as the smoothing capacitor 25.

[0015] The inverter circuit 30 is connected to the subsequent stage of the rectifier circuit 20. The inverter circuit 30 controls the rotational speed of the two-phase motor 40.

[0016] The inverter circuit 30 has a plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c. The plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c includes three switching elements 31a, 31b, 31c on the upper arm side and three switching elements 32a, 32b, 32c on the lower arm side.

[0017] As the three switching elements 31a, 31b, and 31c on the upper arm side, a first upper arm switching element 31a, a second upper arm switching element 31b, and a third upper arm switching element 31c are used.

[0018] As the three switching elements 32a, 32b, and 32c on the lower arm side, a first lower arm switching element 32a, a second lower arm switching element 32b, and a third lower arm switching element 32c are used.

[0019] For each of the plurality of switching elements 31a, 31b, 31c, 32a, 32b, and 32c, for example, a field effect transistor (FET) is used.

[0020] The two-phase motor 40 has a first winding 41a and a second winding 41b as two-phase stator windings.

[0021] The motor control device 50 controls the inverter circuit 30. That is, the motor control device 50 controls the on / off of the plurality of switching elements 31a, 31b, 31c, 32a, 32b, and 32c in the inverter circuit 30. Thereby, the motor control device 50 adjusts the AC voltage applied to the two-phase motor 40 and manages the operating state of the product in which the two-phase motor 40 is mounted.

[0022] Also, the motor control device 50 controls the inverter circuit 30 by sensorless control. In sensorless control, in order to estimate the magnetic pole position in the two-phase motor 40, the current values of the first winding 41a and the second winding 41b are detected. As the motor control device 50, for example, a microcomputer is used.

[0023] The shunt resistor 51 is connected to a location where a plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c in the inverter circuit 30 are commonly connected. Specifically, one end of the shunt resistor 51 is connected to a wire to which the source terminals of the three switching elements 32a, 32b, 32c on the lower arm side are connected. The other end of the shunt resistor 51 is grounded.

[0024] The amplifier 52 is connected between both ends of the shunt resistor 51 and the motor control device 50. As the amplifier 52, an operational amplifier is used.

[0025] FIG. 2 is a block diagram showing the motor control device 50 of FIG. 1. The motor control device 50 has, as functional blocks, a motor current detection unit 50a and an inverter control unit 50b.

[0026] The motor current detection unit 50a calculates the current values of the first winding 41a and the second winding 41b based on the current flowing through the shunt resistor 51 and the switching timings of the plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c. That is, in the motor current detection method of Embodiment 1, the current values of the first winding 41a and the second winding 41b are calculated based on the current flowing through the shunt resistor 51 and the switching timings.

[0027] Specifically, the motor current detection unit 50a measures the voltage drop due to the current flowing through the shunt resistor 51 in accordance with the switching timings, thereby calculating the current values of the first winding 41a and the second winding 41b.

[0028] The inverter control unit 50b controls the plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c based on the calculation result by the motor current detection unit 50a.

[0029] Here, a sinusoidal AC voltage with a 90-degree phase shift from each other is applied to the first winding 41a and the second winding 41b. For this reason, as shown in FIG. 3, a voltage that can be represented by voltage vectors with a 90-degree shift for each of the three phases is output from the inverter circuit 30.

[0030] The U-phase voltage and the V-phase voltage are voltages with a 180-degree phase shift from each other, and a W-phase voltage that lags and leads each by 90 degrees is output. As a result, the voltage applied to the two-phase motor 40, that is, the line voltage between the U phase and the W phase and the line voltage between the V phase and the W phase become two-phase AC voltages with a 90-degree phase difference from each other.

[0031] FIG. 4 is an explanatory diagram showing the modulation waveforms of the three-phase output voltages in the inverter circuit 30 of FIG. 1. The modulation waveforms of the three-phase output voltages can be divided into periods from T1 to T6 according to the magnitude relationship among the U-phase voltage, the V-phase voltage, and the W-phase voltage.

[0032] Specifically, the magnitude relationship of the modulated voltage of each phase in each period is as follows. Period T1: W-phase modulated voltage > U-phase modulated voltage > V-phase modulated voltage Period T2: U-phase modulated voltage > W-phase modulated voltage > V-phase modulated voltage Period T3: U-phase modulated voltage > V-phase modulated voltage > W-phase modulated voltage Period T4: V-phase modulated voltage > U-phase modulated voltage > W-phase modulated voltage Period T5: V-phase modulated voltage > W-phase modulated voltage > U-phase modulated voltage Period T6: W-phase modulated voltage > V-phase modulated voltage > U-phase modulated voltage

[0033] Since the current of all phases flows through the shunt resistor 51, it is necessary to separate the current of each phase in order to calculate the current value of each of the first winding 41a and the second winding 41b. In addition, the control of the two-phase motor 40 is performed by sine wave PWM control based on triangular wave comparison.

[0034] FIG. 5 is a diagram showing the relationship between a modulation wave and a triangular carrier in PWM control. FIG. 6 is an explanatory diagram showing the relationship between the modulation wave signal in period T1 of FIG. 4 and the drive signals for the plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c.

[0035] FIGS. 7 to 9 are explanatory diagrams showing the current flowing through the shunt resistor 51 when operating as shown in FIG. 6.

[0036] The switching timings of the plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c are obvious from the drive signals of the plurality of switching elements 31a, 31b, 31c, 32a, 32b, 32c. Therefore, if the current flowing through the shunt resistor 51 is measured at each switching timing, it can be converted into the respective current values of the first winding 41a and the second winding 41b.

[0037] Assuming that the current flowing from the U-phase terminal to the W-phase terminal has the positive polarity of Iu and the current flowing from the V-phase terminal to the W-phase terminal has the positive polarity of Iv, for example, in period t1 within period T1, the current value -Iv is calculated from the voltage drop across the shunt resistor 51. Also, in period t2 within period T1, the value of -(Iu + Iv) is calculated in the same manner.

[0038] Then, by subtracting the current value -Iv detected in period t1 from the current value -(Iu + Iv) detected in period t2, the value of -Iu can be obtained, so that the respective current values of Iu and Iv can be calculated from these two detected values.

[0039] Similarly, for other periods, current values other than the current detected by the shunt resistor 51 can be obtained by calculation.

[0040] During period t1, since the output of the V phase becomes Lo, only the current of the V phase flows through the shunt resistor 51. The U-phase current does not flow through the shunt resistor 51 because the U-phase coil is short-circuited through the transistor of the W phase. In this case, in terms of time, current is detected only during the times of t1 and t2 within one carrier cycle. During the time of t1, the V-phase current -Iv is detected, and during the time of t2, -(Iu + Iv) is detected respectively. t1: -Iv t2: -(Iu + Iv)

[0041] At this time, the value of Iu cannot be directly detected as the current flowing through the shunt resistor 51, but the value of -(Iu + Iv) is detected during the time of t2. Therefore, the value of Iu can be obtained by subtracting the previously detected value of -Iv from the value of -(Iu + Iv).

[0042] Normally, since the value of the voltage drop across the shunt resistor 51 is small, the signal amplified by the amplifier 52 is taken into the AD conversion port of the motor control device 50. Then, the AD-converted digital data is used for control. Therefore, it is easy to store or add and subtract the detected current values.

[0043] That is, by measuring the current flowing through the shunt resistor 51 during the times of period t1 and period t2, the current values Iu and Iv can be easily calculated.

[0044] Regarding periods T2 to T6, similarly, based on the relationship between the detected voltage across the shunt resistor 51 and the current values Iu and Iv, and based on the detected voltage and the output phase of the inverter, the respective current values of the first winding 41a and the second winding 41b can be obtained through calculation.

[0045] Period T2 t1: -Iv t2: Iu Period T3 t1: (Iu + Iv) t2: Iu Period T4 t1: (Iu + Iv) t2: Iv Period T5 t1: -Iu t2: Iv Period T6 t1: -Iu t2: -(Iu + Iv)

[0046] Note that during period t0, since the three switching elements 31a, 31b, and 31c on the upper arm side are turned on, the first winding 41a and the second winding 41b are all short - circuited, and the motor current does not flow out of the inverter circuit 30.

[0047] Also, during period t3, since the three switching elements 32a, 32b, and 32c on the lower arm side are turned on, the first winding 41a and the second winding 41b are all short - circuited, and the motor current does not flow out of the inverter circuit 30.

[0048] Therefore, no current flows through the shunt resistor 51, and the voltage Vrs across both ends of the shunt resistor 51 becomes 0. That is, periods t0 and t3 are periods in which the motor current cannot be detected.

[0049] According to such a motor current detection method, motor control device 50, and motor device 60, without connecting shunt resistors to each phase, the current values of the first winding 41a and the second winding 41b can be detected using one shunt resistor 51. For this reason, only one amplifier 52 is required, and with a compact configuration, the current values of each phase in the two - phase motor 40 can be detected.

[0050] FIG. 10 is a cross - sectional view schematically showing a ventilation fan using the motor device 60 of Embodiment 1. The ventilation fan includes a motor device 60, a housing 61, and a fan 62. The housing 61 is generally installed on the ceiling of a room to be ventilated. The motor device 60 and the fan 62 are provided in the housing 61. The motor device 60 rotates the fan 62.

[0051] In such a ventilation fan, since the motor device 60 of the first embodiment is used, the circuit board of the motor device 60 can be miniaturized, and the entire ventilation fan can be miniaturized. Also, the number of components can be reduced to achieve cost reduction.

[0052] Note that the device in FIG. 10 is a ventilation fan for ventilating the indoor air, but it may also be a blower that blows air to the air supply target. Also in this case, the circuit board of the motor device 60 can be miniaturized, the entire blower can be miniaturized, and the number of components can be reduced to achieve cost reduction.

[0053] Also, in FIG. 1, only one shunt resistor 51 is shown, but depending on the rated value and size of the resistor, a plurality of small resistors may be connected in series or in parallel and used, and it can be made substantially equivalent to one shunt resistor 51.

[0054] Also, each function of the motor control device 50 of the first embodiment is realized by a processing circuit. FIG. 11 is a configuration diagram showing a first example of a processing circuit that realizes each function of the motor control device 50 of the first embodiment. The processing circuit 100 of the first example is dedicated hardware.

[0055] Also, the processing circuit 100 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. Also, each function of the motor control device 50 may be realized by individual processing circuits 100, or each function may be realized collectively by the processing circuit 100.

[0056] Also, FIG. 12 is a configuration diagram showing a second example of a processing circuit that realizes each function of the motor control device 50 of the first embodiment. The processing circuit 200 of the second example includes a processor 201 and a memory 202.

[0057] As the processor 201, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a microprocessor, a microcontroller, or a DSP (Digital Signal Processor) is used.

[0058] In the processing circuit 200, each function of the motor control device 50 is realized by software, firmware, or a combination of software and firmware. The software and firmware are described as a program and stored in the memory 202. The processor 201 realizes each function by reading and executing the program stored in the memory 202.

[0059] The program stored in the memory 202 can also be said to cause the computer to execute the procedures or methods of the above-described respective parts. Here, the memory 202 is, for example, a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable Read Only Memory), or an EEPROM (Electrically Erasable and Programmable Read Only Memory). Also, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD, etc. also correspond to the memory 202.

[0060] Note that, regarding the functions of the above-described respective parts, some may be realized by dedicated hardware and some may be realized by software or firmware.

[0061] In this way, the processing circuit can realize the functions of the above-described respective parts by hardware, software, firmware, or a combination thereof.

Description of Reference Numerals

[0062] 30 Inverter circuit, 31a First upper arm switching element, 31b Second upper arm switching element, 31c Third upper arm switching element, 32a First lower arm switching element, 32b Second lower arm switching element, 32c Third lower arm switching element, 40 Two-phase motor, 41a First winding (stator winding), 41b Second winding (stator winding), 50 Motor control device, 50a Motor current detection unit, 50b Inverter control unit, 51 Shunt resistor, 60 Motor device.

Claims

1. A motor current detection method for calculating the current values of the two-phase stator windings in a two-phase motor connected to an inverter circuit based on the current flowing through a resistor connected to a location where a plurality of switching elements in the inverter circuit are commonly connected and the switching timing of the plurality of switching elements.

2. A motor current detection unit for calculating the current values of the two-phase stator windings in a two-phase motor connected to an inverter circuit based on the current flowing through a resistor connected to a location where a plurality of switching elements in the inverter circuit are commonly connected and the switching timing of the plurality of switching elements, and an inverter control unit for controlling the plurality of switching elements based on the calculation result by the motor current detection unit A motor control device comprising the same.

3. A two-phase motor having two-phase stator windings, an inverter circuit having a plurality of switching elements and connected to the two-phase motor, a motor control device for controlling the plurality of switching elements, and a resistor connected to a location where the plurality of switching elements in the inverter circuit are commonly connected A motor device comprising the same, wherein the motor control device calculates the current values of the two-phase stator windings based on the current flowing through the resistor and the switching timing of the plurality of switching elements.

4. The resistor is a shunt resistor connected to three switching elements on the lower arm side among the plurality of switching elements, and the motor control device calculates the current values of the two-phase stator windings by measuring the voltage drop due to the current flowing through the shunt resistor in accordance with the switching timing of the plurality of switching elements. The motor device according to Claim 3.

5. An air conditioner comprising the motor device according to Claim 3 or Claim 4.

6. A blower comprising the motor device according to Claim 3 or Claim 4.

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