JP7515574B2 - Motor drive device, refrigeration cycle device, air conditioner, water heater, and refrigerator - Google Patents

Description

The present disclosure relates to an electric motor drive device, a refrigeration cycle device equipped with the same, and an air conditioner, a water heater, and a refrigerator equipped with the refrigeration cycle device.

There has been proposed an electric motor drive device that switches the connection state of the windings of the electric motor using a switch (e.g., a mechanical relay) of a connection switching device without stopping the rotation of the electric motor (see, for example, Patent Document 1). This electric motor drive device switches the switch during a period in which the output voltage of the inverter is controlled so as to bring the effective value of the AC current (i.e., the motor current) flowing through the windings of the electric motor closer to zero.

International Publication No. 2019/087243 (see, for example, Figs. 4 and 6)

However, in the above-mentioned conventional motor drive device, in order to make the effective value of the AC current flowing through the windings nearly zero, it is necessary to make the output voltage of the inverter nearly equal to the back electromotive force generated by the motor. In other words, the inverter continues to supply current during the switching operation of the switch. For example, if a mechanical relay is used as the switch, an arc discharge may occur between the contacts in the relay, forming a short circuit that does not pass through the motor windings, causing a short circuit current to flow, which may cause the switch or inverter to fail.

The present disclosure aims to provide an electric motor drive device and an apparatus equipped with the same that are less susceptible to failures caused by performing the switching operation of a switch that switches the connection state of the windings of an electric motor without stopping the rotation of the electric motor.

An electric motor drive device according to the present disclosure comprises a connection switching device having a plurality of switches and switching a connection state of a winding of an electric motor by performing a switching operation of the plurality of switches, an inverter that applies an AC voltage to the winding via the plurality of switches and to which a back electromotive force is applied from the winding of the electric motor during a rotating operation via the plurality of switches, and a control device that controls the rotation operation of the electric motor by controlling the inverter and causes the connection switching device to switch the connection state, and when switching the connection state during a rotating operation of the electric motor, the connection switching device sequentially performs the switching operations of all of the plurality of switches at different timings and with a time interval between each of the switching operations of the plurality of switches, and the control The device causes the connection switching device to execute switching operations of the multiple switches within a current control period in which a first effective value of the AC current flowing through the winding is closer to zero than a second effective value of the AC current flowing through the winding before the switching operations of the multiple switches, and within the current control period in which the rotation speed of the motor is not zero , each of the multiple switches has an electromagnetic contactor including an excitation coil, the switching operation of the multiple switches is performed by switching between conductivity and non-conduction between contacts of the electromagnetic contactor, the time interval when the excitation coil is switched from a non-excitation state to an excitation state is 5 ms or more, and the time interval when the excitation coil is switched from an excitation state to a non-excitation state is 2 ms or more .

According to the present disclosure, failures of the motor drive device caused by performing the switching operation of a switch that switches the connection state of the motor windings without stopping the rotation of the motor are less likely to occur, and the life of the motor drive device can be extended.

1 is a schematic diagram illustrating a configuration example of an air conditioner (including a refrigeration cycle device) according to an embodiment. 1 is a schematic diagram showing a configuration example of a water heater (including a refrigeration cycle device) according to an embodiment; 1 is a schematic diagram illustrating a configuration example of a refrigerator (including a refrigeration cycle device) according to an embodiment. 1 is a diagram showing a configuration of an electric motor drive device according to a first embodiment; FIG. 4 is a diagram showing another configuration of the electric motor drive device according to the first embodiment. FIG. 5 is a diagram showing a configuration of the inverter shown in FIG. 4 . 5 is a circuit diagram showing in detail an example of the configuration of the windings and connection switching device of the motor of FIG. 4. 5 is a circuit diagram showing in detail an example of the configuration of the connection switching device of FIG. 4. 4A and 4B are diagrams conceptually showing windings in different connection states of a motor; FIG. 2 is a functional block diagram showing an example of a control device used in the first embodiment. 11 is a diagram illustrating an example of the configuration of a voltage command calculation unit in FIG. 10 . FIG. 11 is a circuit diagram showing a path of a short-circuit current that may occur in the comparative example. 6A and 6B are diagrams illustrating an example of a signal of a switch when a connection is switched. 13A and 13B are diagrams illustrating a connection state when a plurality of switches are switched sequentially with a time lag. 11A to 11C are diagrams showing the connection state when a plurality of switches are switched sequentially with a time lag. 4 shows an example of current waveforms before and after connection switching. FIG. 11 is a circuit diagram showing a winding of an electric motor and a connection switching device in a second embodiment. 18 is a circuit diagram showing a configuration example in which a MOS transistor is used as a switch in the connection switching device of FIG. 17. FIG. 20 illustrates, in tabular form, examples of on and off states of MOS transistors of the switch of FIG. 18. FIG. 11 is a circuit diagram showing a winding of an electric motor and a connection switching device in a third embodiment.

Below, with reference to the drawings, an electric motor drive device according to an embodiment, a refrigeration cycle device that is a refrigeration cycle application device equipped with the same, and an air conditioner, a water heater, and a refrigerator equipped with the refrigeration cycle device will be described. Note that the embodiments shown below are merely examples, and the electric motor drive device and each device equipped with the same can be modified in various ways. Note that in the following description, components with the same reference numerals have the same or similar functions.

Figure 1 is a schematic diagram showing an example of the configuration of an air conditioner (including a refrigeration cycle device 900) according to an embodiment. As shown in Figure 1, the refrigeration cycle device 900 can perform heating or cooling operation by switching the four-way valve 902.

During heating operation, as shown by the solid arrows, the refrigerant is pressurized by the compressor 904 and sent out, passes through the four-way valve 902, the indoor heat exchanger 906, the expansion valve 908, the outdoor heat exchanger 910, and the four-way valve 902, and returns to the compressor 904. During cooling operation, as shown by the dashed arrows, the refrigerant is pressurized by the compressor 904 and sent out, passes through the four-way valve 902, the outdoor heat exchanger 910, the expansion valve 908, the indoor heat exchanger 906, and the four-way valve 902, and returns to the compressor 904.

During heating operation, the heat exchanger 906 acts as a condenser to release heat (i.e., to heat the room), and the heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the heat exchanger 910 acts as a condenser to release heat, and the heat exchanger 906 acts as an evaporator to absorb heat (i.e., to cool the room). The compressor 904 is driven by an electric motor 7 that is variably speed controlled by the electric motor drive device 200.

2 is a schematic diagram showing an example of the configuration of a heat pump water heater (including a refrigeration cycle device 900a) according to an embodiment. As shown in FIG. 2, in the refrigeration cycle device 900a, the heat exchanger 906 acts as a condenser to release heat (i.e., to heat water), and the heat exchanger 910 acts as an evaporator to absorb heat. The compressor 904 is driven by an electric motor 7 that is variably speed controlled by an electric motor drive device 200.

Figure 3 is a schematic diagram showing an example of the configuration of a refrigerator (including a refrigeration cycle device 900b) according to an embodiment. As shown in Figure 3, in the refrigeration cycle device 900b, the heat exchanger 910 acts as a condenser to release heat, and the heat exchanger 906 acts as an evaporator to absorb heat (i.e., to cool the inside of the refrigerator). The compressor 904 is driven by an electric motor 7 that is variably speed controlled by the electric motor drive device 200.

<<1>>Embodiment 1.
<<1-1>> Overview of the First Embodiment Fig. 4 is a diagram showing a configuration example of the electric motor drive device 200 according to the first embodiment, together with the electric motor 7 and the AC power supply 1. Fig. 5 is a diagram showing another configuration example of the electric motor drive device 200. The electric motor drive device 200 is a circuit for driving the electric motor 7. As shown in Fig. 4, the electric motor drive device 200 includes an inverter 30, a connection switching device 60, and a control device 100. The electric motor drive device 200 may also include an AC power supply input terminal, a reactor 2, a rectifier circuit 3, a capacitor 10, a control power supply generation circuit 50, a bus current detection unit 40, and an electric quantity detection unit 70.

The connection switching device 60 has switches 61, 62, and 63 as multiple switch circuits. The connection switching device 60 switches the connection state (i.e., the wiring state) of the windings 71, 72, and 73 of the motor 7 by performing the switching operation of the switches 61, 62, and 63 during the rotation operation of the motor 7, i.e., without stopping the rotation of the motor 7. The inverter 30 applies an AC voltage to the windings 71, 72, and 73 via the switches 61, 62, and 63, and applies a back electromotive voltage from the windings 71, 72, and 73 of the motor 7 during the rotation operation via the switches 61, 62, and 63.

The control device 100 controls the rotation operation of the electric motor 7 by controlling the inverter 30. The control device 100 also causes the connection switching device 60 to switch the connection state of the windings. In the first embodiment, the control device 100 causes the switches 61, 62, and 63 to perform switching operations during a current control period Pc (shown in FIG. 16, described later) during which the value of the AC current flowing through the windings 71, 72, and 73 is brought close to zero. The current control period Pc is also called the "zero current control period."

In this application, the connection state of the windings includes both the connection state of the windings (e.g., Y connection and Δ connection) and the number of turns of the windings. The switching of the number of turns of the windings will be described in embodiment 3. If the switches 61, 62, and 63 are configured with mechanical relays, the current control period Pc can be set to several hundred milliseconds or less. If the switches 61, 62, and 63 are configured with semiconductor switches, the current control period Pc can be set to several milliseconds or less. If the motor 7 is used as a compressor for a refrigeration cycle device such as an air conditioner, a heat pump water heater, or a refrigerator, the current control period Pc can be set within a range of several milliseconds to 1 second.

<<1-2>> Configuration of the First Embodiment The control device 100 is configured, for example, by a microcomputer (microcomputer) having a memory as a storage device that stores control information as a software program and a CPU (Central Processing Unit) as an information processing device that executes the program, or a DSP (Digital Signal Processor). The control device 100 may also be configured by dedicated hardware (for example, a processing circuit). The following describes the case where the control device 100 is configured by a microcomputer.

An AC voltage is applied to the electric motor drive device 200 from an external AC power source 1 via an AC power input terminal. The applied voltage has, for example, an effective amplitude of 100 V or 200 V, and a frequency of 50 Hz or 60 Hz.

The rectifier circuit 3 receives AC voltage from the AC power source 1 via the AC power source input terminal and the reactor 2, and rectifies it to generate DC voltage. The rectifier circuit 3 is a full-wave rectifier circuit formed by connecting rectifier elements such as diodes in a bridge configuration.

Capacitor 10 smoothes the DC voltage generated by rectifier circuit 3 and outputs a DC voltage (V20 shown in Figure 6).

Figure 6 is a diagram showing the configuration of the inverter 30 in Figure 4. As shown in Figure 6, the inverter 30 has an inverter main circuit 310 and a drive circuit 350. The input terminal of the inverter main circuit 310 is connected to the electrode of the capacitor 10. The line connecting the output of the rectifier circuit 3, the electrode of the capacitor 10, and the input terminal of the inverter main circuit 310 is called the DC bus.

The inverter 30 is controlled by the control device 100, and the switching elements 311 to 316 of the six arms of the inverter main circuit 310 are turned on and off. Through this on and off operation, the inverter 30 generates a three-phase AC current with variable frequency and voltage, and supplies this three-phase AC current to the electric motor 7. Rectifier elements 321 to 326 for return current are connected in parallel to the switching elements 311 to 316, respectively.

The motor 7 is a three-phase permanent magnet synchronous motor, with the ends of the stator winding (also simply called "winding") pulled out to the outside of the motor 7, and capable of switching to either a star connection (Y connection) or a delta connection (Δ connection). This switching is performed by a connection switching device 60. Note that when the Y connection is referred to as the first connection, the Δ connection is the second connection, and when the Δ connection is referred to as the first connection, the Y connection is the second connection. Also, there may be three or more types of winding connection states.

7 is a circuit diagram showing in detail an example of the configuration of the windings 71, 72, 73 of the motor 7 and the connection switching device 60. As shown in FIG. 7, the first ends 71a, 72a, 73a of the windings 71, 72, 73 of the three phases consisting of the U phase, V phase, and W phase of the motor 7 are connected to the external terminals 71c, 72c, 73c, respectively. The second ends 71b, 72b, 73b of the windings 71, 72, 73 of the U phase, V phase, and W phase of the motor 7 are connected to the external terminals 71d, 72d, 73d, respectively. In this way, the motor 7 is connected to the connection switching device 60. In addition, the output lines 331, 332, 333 of the U phase, V phase, and W phase of the inverter 30 are connected to the external terminals 71c, 72c, 73c.

In the illustrated example, the connection switching device 60 is composed of switches 61, 62, and 63. Electromagnetic contactors that electromagnetically open and close contacts are used as the switches 61, 62, and 63. Such electromagnetic contactors include those called relays, contactors, etc.

Figure 8 is a circuit diagram showing in detail an example of the configuration of the connection switching device 60 in Figure 4. The switches 61, 62, and 63 of the connection switching device 60 are configured, for example, as shown in Figure 8. When current is flowing through the excitation coils 611, 621, and 631, the connection state is different from when current is not flowing. The excitation coils 611, 621, and 631 are connected to receive a switching power supply voltage V60 via semiconductor switches 604, 605, and 606. In the example shown in Figures 4 and 8, the opening and closing of the semiconductor switches 604, 605, and 606 is controlled by switching control signals S61, S62, and S63 output from the control device 100. 5 and 8, the opening and closing of the semiconductor switches 604, 605, and 606 is controlled by Sc_1, which is a switching control signal Sc output from the control device 100, Sc_2, which is a signal obtained by delaying the signal Sc, and Sc_3, which is a signal obtained by further delaying the signal Sc. When a sufficient current supply from the microcomputer included in the control device 100 is ensured, the microcomputer may directly supply current to the exciting coils 611, 621, and 631.

The common contact 61c of the switch 61 is connected to an external terminal 71d via a lead wire 61e. The normally closed contact 61b is connected to a neutral node 64, and the normally open contact 61a is connected to the V-phase output line 332 of the inverter 30.

The common contact 62c of the switch 62 is connected to an external terminal 72d via a lead wire 62e. The normally closed contact 62b is connected to a neutral node 64, and the normally open contact 62a is connected to the W-phase output line 333 of the inverter 30.

The common contact 63c of the switch 63 is connected to an external terminal 73d via a lead wire 63e. The normally closed contact 63b is connected to a neutral node 64, and the normally open contact 63a is connected to a U-phase output line 331 of the inverter 30.

When no current flows through the excitation coils 611, 621, and 631, the switches 61, 62, and 63 are switched to the normally closed contact side as shown in Figure 8, that is, the common contacts 61c, 62c, and 63c are connected to the normally closed contacts 61b, 62b, and 63b (i.e., conductive state), and are not connected to the normally open contacts 61a, 62a, and 63a (i.e., non-conductive state). In this state, the motor 7 is in a Y-connection state.

When current flows through the excitation coils 611, 621, and 631, the switches 61, 62, and 63 are switched to the normally open contact side, in other words, the common contacts 61c, 62c, and 63c are connected to the normally open contacts 61a, 62a, and 63a, and are not connected to the normally closed contacts 61b, 62b, and 63b (i.e., non-conductive). In this state, the motor 7 is in a delta connection state.

Here, the advantages of using a motor 7 that can be switched to either Y-connection or Δ-connection will be explained with reference to Figures 9(a) and (b). Figure 9(a) conceptually shows the winding connection state when the motor is Y-connected, and Figure 9(b) conceptually shows the winding connection state when the motor is Δ-connected.

If the line voltage in Y connection is _VY , the current flowing into the winding is _IY , the line voltage in Δ connection is _VΔ , the current flowing into the winding is _IΔ , and the voltages applied to the windings of each phase are equal, then the relationships in the following equations (1) and (2) hold.
V _Δ = V _Y / √3 (1)
I _Δ = √3 × I _Y (2)

When the voltage _VY and current _IY in the Y connection and the voltage _VΔ and current _IΔ in the Δ connection have the relationship shown in formulas (1) and (2), the power supplied to the motor in the Y connection and the Δ connection are equal. In other words, when the power supplied to the motor is equal, the Δ connection has a larger current and requires a lower voltage to drive.

Taking advantage of the above properties, it is possible to select the wiring state depending on the load conditions. For example, it is possible to operate at low speed with Y connection at low load, and at high speed with Delta connection at high load. In this way, it is possible to improve efficiency at low load and increase output at high load.

This point will be described in more detail below, taking the example of a motor that drives the compressor of an air conditioner. To meet the demand for energy saving, synchronous motors with permanent magnets in the rotor are widely used as the motor 7 for driving the compressor of an air conditioner. Furthermore, in recent air conditioners, when there is a large difference between the room temperature and the set temperature, the room temperature is quickly brought closer to the set temperature by high-speed operation, which rotates the motor 7 at high speed, and when the room temperature is close to the set temperature, the room temperature is maintained by low-speed operation, which rotates the motor 7 at low speed. When controlled in this way, the time spent in low-speed operation accounts for a large proportion of the total operating time.

When using a synchronous motor, as the rotation speed increases, the back electromotive force increases, and the voltage required to drive it increases. As mentioned above, this back electromotive force is higher in the Y connection than in the Delta connection.

In order to suppress the back electromotive force at high speeds, it is possible to reduce the magnetic force of the permanent magnets or the number of turns of the windings. However, doing so would increase the current required to obtain the same output torque, which would increase the current flowing through the motor 7 and inverter 30, reducing efficiency.

It is therefore possible to switch the connection state depending on the rotation speed. For example, when high-speed operation is required, the delta connection state is used. By doing this, the voltage required for driving can be reduced to 1/√3 (compared to the voltage required for a Y connection). This means there is no need to reduce the number of turns in the windings, nor is there any need to use flux-weakening control.

On the other hand, at low speeds, the Y-connection allows the current value to be reduced to 1/√3 compared to the Delta connection. Furthermore, it is possible to design the windings in the Y-connection state to be suitable for low-speed driving, making it possible to reduce the current value compared to when the Y-connection is used across the entire speed range. As a result, the losses in the inverter 30 can be reduced, and efficiency can be increased.

As explained above, it is meaningful to switch the wiring state depending on the load conditions, and the connection switching device 60 is provided to enable such switching.

4 and 5 detects the bus current, i.e., the DC current Idc input to the inverter 30. The bus current detection unit 40 includes a shunt resistor inserted in the DC bus, and supplies an analog signal indicating the detection result to the control device 100. This analog signal (i.e., the detection signal) is converted to a digital signal by an A/D (Analog to Digital) conversion unit (not shown) in the control device 100 and used for processing inside the control device 100.

As described above, the control device 100 controls the switching of the connection state by the connection switching device 60 and also controls the operation of the inverter 30. To control the inverter 30, the control device 100 generates PWM (Pulse Width Modulation) signals Sm1 to Sm6 and supplies them to the inverter 30.

6, the inverter 30 includes a drive circuit 350 in addition to the inverter main circuit 310, which generates drive signals Sr1 to Sr6 based on the PWM signals Sm1 to Sm6. The drive circuit 350 controls the on/off of the switching elements 311 to 316 using the drive signals Sr1 to Sr6, so that a variable frequency, variable voltage three-phase AC voltage is applied to the electric motor 7.

While the PWM signals Sm1 to Sm6 have a logic circuit signal level magnitude (0 to 5 V), the drive signals Sr1 to Sr6 are signals with a voltage level required to control the switching elements 311 to 316, for example, a magnitude ranging from +15 V to -15 V. Also, while the PWM signals Sm1 to Sm6 have the ground potential of the control device 100 as a reference potential, the drive signals Sr1 to Sr6 have the potential of the emitter terminal, which is the negative terminal of the corresponding switching element, as a reference potential.

Figure 10 is a functional block diagram showing an example of the control device 100 of Figure 4. As shown in Figure 10, the control device 100 has an operation control unit 102 and an inverter control unit 110.

The operation control unit 102 outputs an instruction signal based on a command signal Qe provided by the electricity quantity detection unit 70. The electricity quantity detection unit 70 receives a command signal based on the electrical quantity of an electrical signal indicating room temperature (e.g., the temperature of the space to be air-conditioned) detected by a temperature sensor not shown, as well as a command signal indicating instruction information from an operation unit not shown (e.g., a remote control), and controls the operation of each part of the air conditioner. Instructions from the operation unit include information indicating the set temperature, selection of an operation mode, and instructions to start and stop operation.

The operation control unit 102, for example, determines whether the windings of the motor 7 are Y-connected or Δ-connected, determines the target rotation speed, and outputs a switching control signal Sc and a frequency command value ω ^* based on this determination. For example, when there is a large difference between the room temperature and the set temperature, the operation control unit 102 determines to use the Δ-connection, sets the target rotation speed to a relatively high value, and outputs a frequency command value ω ^* that gradually increases the frequency after startup to a frequency corresponding to the target rotation speed.

When the frequency reaches the frequency corresponding to the target rotation speed, the operation control unit 102 maintains that state until the room temperature approaches the set temperature, and when the room temperature approaches the set temperature, it temporarily stops the motor, switches to Y connection, and outputs a frequency command value ω ^* that gradually increases to a frequency corresponding to a relatively low target rotation speed. After the frequency reaches the frequency corresponding to the target rotation speed, the operation control unit 102 performs control to maintain the room temperature close to the set temperature. This control includes adjusting the frequency, stopping the motor, restarting it, and the like.

As shown in FIG. 10, the inverter control unit 110 has a current restoration unit 111, a three-phase to two-phase conversion unit 112, a frequency compensation unit 113, a primary frequency calculation unit 114, a voltage command calculation unit 115, a two-phase to three-phase conversion unit 116, a PWM generation unit 117, an electrical angle phase calculation unit 118, and an excitation current command control unit 119.

The current restoration unit 111 restores the phase currents _{iu, iv, iw flowing through the motor 7 based on the value of the DC current Idc detected by the bus current detection unit 40 (shown in FIGS. 4 and 5 ). The current restoration unit 111 restores the phase currents iu , iv , iw} by sampling _the DC current _Idc detected by the bus _current detection unit 40 at a timing determined based on the PWM signal provided from the PWM generation unit 117.

The three-phase to two-phase conversion unit 112 converts the current values _iu , _iv , and _iw restored by the current restoration unit 111 into current values of the γ-δ axes represented by the excitation current component (also referred to as the "γ-axis current") _iγ and the torque current component (also referred to as the "δ-axis current") _iδ , using an electrical angle phase θ generated by an electrical angle phase calculation unit 118 described below.

The excitation current command control unit 119 determines, based on the torque current component (δ-axis current) _iδ , an optimum excitation current command value _iγ ^* that provides the most efficient driving of the motor 7. Note that, although the excitation current command value _iγ ^* is determined based on the torque current component _iδ in Fig. 9, the same effect can be obtained by determining the excitation current command value iγ ^* based on the excitation current component _iγ and the frequency command value _ω ^* .

The excitation current command control unit 119 outputs an excitation current command value i γ * based on the torque current component i _δ (or the excitation current component i _γ , the frequency command value ω ^* ) such that the output torque is equal to or greater than a predetermined value (or is maximum), i.e., the current value is equal to or less than a predetermined value (or is minimum), at a current phase angle _βm (not shown ⁾ .

Fig. 11 is a diagram showing an example of the voltage command calculation unit 115 of Fig. 10. As shown in Fig. 11, the voltage command calculation unit 115 operates to output voltage command values V γ *, V δ * based on the γ-axis current i _γ and the δ-axis current i _δ obtained from the three-phase to two-phase conversion unit 112, the frequency command value ω ^* , and the excitation current command value i _γ ^* obtained from ^the excitation current command ^control _{unit 119} .

The controller 1152 is, for example, a proportional-integral (PI) controller, and outputs a δ-axis current command value i _δ ^* such that the frequency estimation value ωest coincides with the frequency command value ω* based on the difference (ω ^* -ωest) between the frequency command value ω ^* and the frequency estimation value ^ωest generated by the frequency estimation unit 1151.

The frequency estimator 1151 estimates the frequency of the electric motor 7 based on the γ-axis current i _γ and the δ-axis current i _δ and the voltage command values V _γ ^* , V _δ ^* to generate a frequency estimate value ωest.

A switching unit 1155 selects the value of the specified δ-axis current value i _δ ^** from either the specified δ-axis current value i _δ ^* or 0, and a controller 1156 such as a PI controller outputs a specified δ-axis voltage value V _δ ^* such that the specified δ-axis current i _δ matches the specified δ-axis current value i _δ ^** .

A switching unit 1153 selects the value of the specified γ-axis current value i _δ ^** from either the specified γ-axis current value i _γ ^* or 0, and a controller 1154 such as a PI controller outputs a specified γ-axis voltage value V _γ ^* such that the specified γ-axis current i _γ matches the specified γ-axis current value i _γ ^** .

A two-phase to three-phase conversion section 116 shown in FIG. 10 converts the γ-axis voltage command value V _γ ^* and the δ-axis voltage command value V _δ ^* (voltage command values in a two-phase coordinate system) obtained by the voltage command calculation section 115 into output voltage command values (three-phase voltage command values) V _u ^* , V _v ^* , V _w ^* in a three-phase coordinate system using the electrical angle phase θ obtained by the electrical angle phase calculation section 118, and outputs the converted output voltage command values.

The PWM generating unit 117 generates and outputs PWM signals Sm1 to Sm6 based on the three-phase voltage command values _Vu ^* , _Vv ^* , and _Vw ^* obtained from the two-phase to three-phase conversion unit .

The stop signal St provided from the operation control unit 102 is given, for example, to the PWM generation unit 117, and upon receiving the stop signal St, the PWM generation unit 117 immediately stops outputting the PWM signals Sm1 to Sm6.

10 illustrates a configuration in which the phase currents _iu , _iv , and _iw are restored from the DC current Idc on the input side of the inverter 30, but a configuration in which current detectors are provided on the output lines 331, 332, and 333 of the inverter 30 and the phase currents are detected by the current detectors may be used in place of the current restored by the current restoration unit 111.

Furthermore, when a three-phase permanent magnet synchronous motor is used as the motor 7, when an excessive current flows through the motor 7, irreversible demagnetization of the permanent magnet occurs, and the magnetic force decreases. When such a state occurs, the current required to output the same torque increases, causing a problem of worsening losses. Therefore, by inputting the phase currents _iu , _iv , and _iw or the direct current Idc to the control device 100, when an excessive current flows through the motor 7, the PWM signals Sm1 to Sm6 are stopped to stop the current supply to the motor 7, thereby making it possible to prevent irreversible demagnetization. In addition, by providing an LPF (Low Pass Filter) that removes noise from the phase currents _iu , _iv , and _iw or the direct current Idc, it is possible to prevent Sm1 to Sm6 from being erroneously stopped due to noise, and it is possible to further improve reliability.

Here, when the motor 7 can be switched between Y-connection and Δ-connection, the current values at which irreversible demagnetization occurs in the Y-connection and Δ-connection (I _Y and I _Δ in FIG. 9 ) differ by approximately √3 times, and this current value is √3 times higher in the Δ-connection than in the Y-connection. Therefore, if a protection level (i.e., an overcurrent protection level) for preventing irreversible demagnetization from occurring is set according to the Y-connection, the protection of I _Δ will be activated early, making it difficult to expand the operating range. Therefore, by switching the protection level according to the Y-connection and Δ-connection in the control device 100 (i.e., making the protection level in the Δ-connection higher than the protection level in the Y-connection), it becomes possible to reliably protect the motor 7 from irreversible demagnetization in each winding, and it becomes possible to obtain an electric motor drive device with improved reliability.

The protection level can be set by setting the magnetic force of the motor 7 in its initial state to 100%, and then setting the current value within a range that does not affect performance in the event of irreversible demagnetization (for example, the current value at which the magnetic force drops to 97%). However, there is no problem with changing the set current value of the protection level depending on the equipment used.

<<1-3>> Operation of First Embodiment Hereinafter, an operation of the motor drive device 200 when the switches 61, 62, 63 of the connection switching device 60 are switched while the motor 7 is in operation (i.e., during rotation) will be described.

First, the problems of the prior art, that is, the operation of a comparative example of an electric motor drive device not having the features of the present embodiment, will be briefly described with reference to Figures 4, 7, 8, and 12. Figure 12 is a circuit diagram showing the path of a short-circuit current that can occur in the electric motor drive device 200a of the comparative example. When the electric motor is in operation, that is, when current flows through the switches 61, 62, and 63 constituting the connection switching device 60, if the switching control signals S61, S62, and S63 are sent as synchronized signals without shifting to switch the wiring, the contacts to which the common contacts 61c, 62c, and 63c are connected are simultaneously switched to the normally closed contacts 61b, 62b, and 63b or the normally open contacts 61a, 62a, and 63a. If the power supply from the inverter 30 to the electric motor 7 continues and the rotation speed Nm of the electric motor 7 is not zero when the switching occurs, an arc discharge may occur between the contacts of the switches 61, 62, and 63. That is, in the comparative example, since the switches 61, 62, and 63 attempt to switch at the same timing, in at least two of the three switches 61, 62, and 63, an arc short circuit occurs between the ab contacts (i.e., between 61a and 61b, between 62a and 62b, and between 63a and 63b), which may cause a short circuit through a short circuit path not passing through the windings 71, 72, and 73 of the motor 7 as shown in Fig. 12, causing a short circuit current to flow and causing a failure such as welding of the contacts of the switches 61, 62, and 63 or destruction of the semiconductor elements constituting the inverter 30. The path indicated by the thick dashed arrow in Fig. 12 is an example of a short circuit path not passing through the windings 71, 72, and 73 of the motor 7.

Therefore, in the electric motor drive device 200 of the first embodiment, in order to avoid a failure caused by a short-circuit current in a short-circuit path that does not pass through the windings 71, 72, and 73 of the electric motor 7, the control device 100 shown in FIG. 4 outputs switching control signals S61, S62, and S63 of the switches 61, 62, and 63 with shifted timing, respectively. Alternatively, by preparing filters LPF_1 and LPF_2 with different time constants for the one-phase signal shown in FIG. 5, it is possible to shift the switching timing of the switches 61, 62, and 63 and perform switching without generating a short-circuit current during energization. In other words, when switching the connection state during the rotation operation of the electric motor 7, the control device 100 of the electric motor drive device 200 of the first embodiment controls the connection switching device 60 so that the connection switching device 60 sequentially performs the switching operation of each of the multiple switches 61, 62, and 63 with a time interval.

It is desirable that the time intervals t1, t2 of the switching operation of each of the multiple switches 61, 62, 63 be 50 ms or less. It is also desirable that the time intervals t1, t2 be 2 ms or more. It is also desirable that the switches 61, 62, 63 have mechanical relays, and that the time interval when the excitation coil of the relay is switched from a non-excited state to an excited state is 5 ms or more, and the time interval when the excitation coil is switched from an excited state to a non-excited state is 2 ms or more.

13(a) and (b) are diagrams showing an example of the on/off operation of semiconductor switches 604, 605, and 606 that provide drive signals to the excitation coils of switches 61, 62, and 63 when switching connections. Fig. 13(a) shows the switching operation of semiconductor switches 604, 605, and 606 from off to on when switching from Y connection to Δ connection. Fig. 13(b) shows the switching operation of semiconductor switches 604, 605, and 606 from on to off when switching from Δ connection to Y connection. Note that the following explanation will be given assuming that the timing of the switching operation of semiconductor switches 604, 605, and 606 is the same as the timing of the switching operation of the mechanical relays of switches 61, 62, and 63.

As shown in Fig. 13(a), the time interval t1 for shifting the switching timing of the switches 61, 62, and 63 is the time from when a signal (switching control signal S61 or Sc_1 in Fig. 4 or Fig. 5) is sent to turn on the semiconductor switch (for example, the semiconductor switch 604 in Fig. 8) until a current flows through the excitation coil (for example, the excitation coil 611 in Fig. 8) and the connection destination of the common contact 61c of the switch (for example, the switch 61 in Fig. 8) is switched from the normally closed contact 61b to the normally open contact 61a (this time is a value taking individual variations into consideration). In this way, when switching from Y connection to Δ connection, the signal provided by the semiconductor switch 605 is turned on after the time interval t1 has elapsed since the signal provided by the semiconductor switch 604 was turned on, and after another time interval t1 has elapsed since that point, the signal provided by the semiconductor switch 606 is turned on.

As shown in Fig. 13(b), the time interval t2 for shifting the switching timing of the switches 61, 62, and 63 is the time from when a signal (switching control signal S61 or Sc_1 in Fig. 4) is sent to turn on the semiconductor switch (e.g., the semiconductor switch 604 in Fig. 8) until the current stops flowing through the excitation coil (e.g., the excitation coil 611 in Fig. 8) and the connection destination of the common contact 61c of the switch (e.g., the switch 61 in Fig. 8) switches from the normally open contact 61a to the normally closed contact 61b (this time is a value that takes individual variations into consideration). In this way, when switching from a Δ connection to a Y connection, the signal provided by the semiconductor switch 605 turns off after the time interval t2 has elapsed since the signal provided by the semiconductor switch 604 turned off, and after another time interval t2 has elapsed from that point, the signal provided by the semiconductor switch 606 turns off.

As described above, by performing the switching operations of the switches 61, 62, and 63 one by one in sequence with a time interval, it is possible to reliably prevent the occurrence of a state in which an arc short circuit occurs in the switches simultaneously in two phases. Therefore, it is possible to prevent the occurrence of a short circuit current as shown by the thick arrow in Figure 12. Note that the suitable range of the time intervals t1 and t2, which is considered based on the operating time of the mechanical relay, is, for example, 2 ms to 50 ms.

14(a) and (b) are diagrams showing the connection state when multiple switches 61, 62, and 63 are switched sequentially with a time lag. FIG. 14(a) shows the case where switch 61 is in the Δ connection state and switches 62 and 63 are in the Y connection state. FIG. 14(b) shows the case where switches 61 and 62 are in the Δ connection state and switch 63 is in the Y connection state. These states occur in the middle of switching the connection state of windings 71, 72, and 73 from Δ connection to Y connection or from Y connection to Δ connection by switches 61, 62, and 63. As shown in FIG. 14(a) and (b), in the first embodiment, when switching the connection state of windings 71, 72, and 73, each of switches 61, 62, and 63 is switched sequentially with a time interval, so that a short-circuit path that does not pass through the windings as shown in FIG. 12 is not formed.

15(a) to (c) are diagrams showing other examples of the connection state when multiple switches 61, 62, and 63 are switched sequentially with a time lag. FIG. 15(a) shows a case where all of the switches 61, 62, and 63 are in a Y-connection state, an arc discharge (shown by double lines) occurs between the normally closed and normally open terminals of the switch 61, and the switch 61 is in a three-point short-circuit state (i.e., the three terminals are in a state of mutual conduction). FIG. 15(b) shows a case where the switch 61 is in a Y-connection state, the switches 62 and 63 are in a Δ-connection state, an arc discharge (shown by double lines) occurs between the normally closed and normally open terminals of the switch 61, and the switch 61 is in a three-point short-circuit state (i.e., the three terminals are in a state of mutual conduction). FIG. 15(c) shows a case where switches 61 and 63 are in a Y-connection state, switch 62 is in a Δ-connection state, an arc discharge (indicated by a double line) occurs between the normally closed terminal and the normally open terminal of switch 61, and switch 61 is in a three-point short-circuit state (i.e., the three terminals are mutually conductive).

As shown in Figures 14(a) and (b), in embodiment 1, when switching the connection state of windings 71, 72, and 73, each of switches 61, 62, and 63 is switched in sequence with a time interval between them, so that a short-circuit path that does not pass through any of windings 71, 72, and 73 as shown in Figure 12 is not formed.

In addition, as shown in Figures 15(a) to (c), in embodiment 1, when switching the connection state of windings 71, 72, and 73, each of switches 61, 62, and 63 is switched in sequence with a time interval between them. Therefore, even if an arc discharge occurs in one of switches 61, 62, and 63, as shown in Figure 12, a short-circuit path is not formed that does not pass through any of windings 71, 72, and 73.

14(a) and (b) and 15(a) to (c), in the first embodiment, the switching operations of the switches 61, 62, and 63 are shifted in time, so that the occurrence of a short circuit path shown in FIG. 12, which is formed by the simultaneous occurrence of a short circuit in two switches, is avoided. Therefore, in the first embodiment, it is possible to avoid the occurrence of a failure of the switches 61, 62, and 63 or the inverter 30 due to a short circuit current.

In addition, for example, in order to avoid such a failure, a method of switching the relay with the rotation speed Nm of the motor 7 set to zero and no current being applied can be considered. However, if the rotation speed Nm of the motor 7 is set to zero, when restarting the motor 7, the load on the motor 7, for example, in the case of the compressor 904 (Figure 1), increases the torque required for restarting because the refrigerant state is not stable, and the current at start-up increases, and in the worst case, restarting may not be possible. Therefore, it is necessary to restart the motor 7 after a period of time has passed without operating the motor 7 until the refrigerant state is sufficiently stable. Therefore, the compressor 904 will no longer be able to pressurize the refrigerant, which may lead to an increase or decrease in room temperature due to a decrease in cooling or heating capacity, and the room temperature may not be kept constant.

Therefore, in the electric motor 7 of the first embodiment, it is desirable to control the value (effective value) of the current flowing through the windings of the electric motor 7 or the connection switching device 60 during the rotational operation (operation) of the electric motor 7 so as to approach zero (current control period Pc), and in this state, operate the multiple switches of the connection switching device 60 one by one at time intervals, thereby completing the switching without generating arc discharge and excessive current between the contacts of the switches 61, 62, and 63. Note that the current control period Pc, which controls the value (effective value) of the current flowing through the windings of the electric motor 7 or the connection switching device 60 so as to approach zero, is a period during which the first effective value of the AC current flowing through the windings is closer to zero than the second effective value of the AC current flowing through the windings before the switching operation of the multiple switches.

The current control period Pc is a period during which the inverter applies an AC voltage to the motor so as to cancel the back electromotive force generated by the rotation of the motor 7. In this way, the value (effective value) of the current flowing through the windings of the motor 7 can be brought close to zero without making the rotation speed Nm of the motor 7 zero, i.e., without stopping the rotation. In this state, by switching the multiple relays one by one at time intervals, it is possible to switch the connection state of the windings 71, 72, and 73 in a more reliable state without causing a short circuit current to flow. Therefore, in the case of an air conditioner, since it is not necessary to stop the rotation of the motor 7 when switching the connection state, there is no need to wait until the refrigerant stabilizes due to the stop of the rotation, and it is possible to suppress the rise or fall of the room temperature.

11 , the voltage command calculation unit 115 operates the switching unit 1155 to select 0 for the specified δ-axis current value i _δ ^** , thereby outputting a specified δ-axis voltage value V _δ ^* such that the δ-axis current i _δ matches the specified δ-axis current value i _δ ^* , i.e., the specified δ-axis current value i δ ** matches 0. Furthermore, the voltage command calculation unit 115 operates the switching unit 1153 to select 0 for the specified γ-axis current value i _γ ^** , thereby outputting a specified γ-axis voltage value V _γ ^* such that the γ-axis current i _γ matches the specified γ- ^axis current value i _γ ^* , i.e., the specified γ-axis current value _{i γ} ^** matches 0.

1-4 Effect of the First Embodiment By the above operation, the current flowing through the windings 71, 72, and 73 of the motor 7, i.e., the value (effective value) of the current flowing through the switches 61, 62, and 63, can be controlled to approach zero (preferably to zero) (referred to as "zero current control") as shown in the current control period Pc in FIG. 16. Therefore, the switches 61, 62, and 63 can be switched in a state where no current flows through them, and no large short-circuit current flows between the contacts of the switches 61, 62, and 63. Therefore, when mechanical relays are used as the switches 61, 62, and 63, it is possible to prevent contact welding and realize a highly reliable motor drive device. Note that "control to zero" does not mean that the value (effective value) of the current flowing through the switches 61, 62, and 63 is exactly zero, but means that it is close to zero so that it can be considered to be substantially zero.

However, since the value of the current flowing through the switches 61, 62, and 63 cannot be made exactly zero, a weak current flows through the windings 71, 72, and 73 of the motor 7. When the switches 61, 62, and 63 are switched in this state, assuming that the switches 61, 62, and 63 are connected as shown in FIG. 7, for example, if the normally closed contact 61b and the common contact 61c are connected and the normally closed contact 61b and the common contact 61c are opened in this state, an arc discharge due to the current may occur. The arc discharge in this case is minor, but if the normally open contact 61a is touched in a state where an arc discharge has occurred, the normally open contact 61a, the normally closed contact 61b, and the common contact 61c are connected with low impedance. In the zero current control, a voltage is supplied by the inverter 30 to cancel out the induced voltage of the motor 7. In this state, if two or more states occur in which the normally open contacts 61a, 62a, 63a, the normally closed contacts 61b, 62b, 63b, and the common contacts 61c, 62c, 63c are connected with low impedance, a short circuit current will occur, and as shown in Figure 12, there is a risk that an excessive current will flow through the switches 61, 62, 63.

Therefore, the control device 100 of the first embodiment controls the value of the current (e.g., effective value) flowing through the motor 7 or the connection switching device 60 to approach zero (preferably to approximately 0) when the motor 7 is rotating at high speed, and after confirming that the current has sufficiently reached zero, controls the switching operations of the multiple switches 61, 62, and 63 of the connection switching device 60 to be performed one by one with a time interval. In this way, it is possible to prevent failures such as contact welding that occur when a mechanical relay is used for the connection switching device 60, and a highly reliable motor drive device can be obtained.

In other words, even if the connection switching device 60 of the electric motor driving device 200 of embodiment 1 is constructed using inexpensive parts, it is possible to reduce the failure rate and extend the life of the device, thereby reducing product costs.

In addition, the winding connection state is switched during the current control period when the rotational operation of the motor 7 is not stopped. Therefore, there is no need to temporarily suspend the rotational operation of the motor and then restart the motor 7 in order to switch the winding connection state.

Note that, since the current values at which irreversible demagnetization occurs are different between the Y-connection and the Δ-connection, by switching the protection level at the timing of switching between the Y-connection and the Δ-connection, it is possible to provide protection corresponding to each winding. However, when a mechanical relay is used, a time delay occurs between when the current flows through the excitation coils 611, 621, and 631 and when the switches 61, 62, and 63 switch to the normally open contacts 61a, 62a, and 63ba or the normally closed contacts 61b, 62b, and 63b. Therefore, for example, when switching from the Y-connection to the Δ-connection, the protection level is switched to the Δ-connection, but the motor 7 is assumed to remain in the Y-connection state because it is in the process of switching to the Δ-connection. In that case, if an excessive current flows by mistake, there is a possibility that irreversible demagnetization of the motor 7 will occur.

Therefore, by setting the protection level to the lower protection level of the Y connection during the period from the start of control to make the current zero when the connections are switched until the connections are switched, it is possible to protect against irreversible demagnetization regardless of whether the connection is in the Y or Δ state when the connections are switched. Furthermore, because control is performed to make the current zero when the connections are switched, there is no effect on the operation of the motor 7.

As for the protection level, as explained above, the magnetic force in the initial state of the motor 7 is set to 100%, and a current value (for example, a current value at which the magnetic force drops to 97%) within a range that does not affect performance when irreversible demagnetization occurs can be set, and further, by setting the current value in the Δ connection to a value that is √3 times that of the Y connection, it is possible to reliably protect against irreversible demagnetization regardless of the connection state. However, when protection is performed by detecting the current value flowing through the windings without detecting I _Δ in FIG. 9(b), it is desirable to set the current value of I _Δ ÷ √3 (equivalent to the current value of the protection level in the Y connection) as the protection level. The set current value of the protection level may be changed depending on the equipment used.

<<1-5>> Modification of the First Embodiment Diodes and the like are generally used as the rectifying elements of the rectifier circuit 3. However, the configuration of the rectifier circuit 3 is not limited to the example of FIG. 4. For example, instead of the rectifying elements of the rectifier circuit 3, transistor elements (semiconductor switches) such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect-Transistors) may be used and rectified by turning them on in accordance with the polarity of the voltage (input AC voltage) supplied from the AC power source 1.

The switching elements 311 to 316 of the inverter main circuit 310 may be, but are not limited to, IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs. Any elements capable of switching may be used for the switching elements 311 to 316. When using MOSFETs as the switching elements 311 to 316, it is not necessary to connect the freewheeling rectifier elements 321 to 326 shown in FIG. 6 in parallel, since MOSFETs have parasitic diodes due to their structure.

The materials constituting the rectifying elements and switching elements 311 to 316 can be made not only of silicon (Si), but also of wide band gap semiconductors such as silicon carbide (SiC), gallium nitride (GaN), and diamond, thereby making it possible to further reduce losses.

<<2>>Embodiment 2.
The electric motor drive device of the second embodiment differs from the electric motor drive device 200 of the first embodiment in that a connection switching device 260 is used instead of the connection switching device 60. In the configuration of Fig. 4, the switches 61, 62, and 63 of the connection switching device 60 are made up of selection switches. In the second embodiment, each switch of the connection switching device 260 is made up of a combination of a normally closed switch and a normally open switch, that is, a combination of on-off type switches.

17 is a circuit diagram showing windings 71, 72, 73 of motor 7 and connection switching device 260 in embodiment 2. In connection switching device 260, switch 61 is configured with a combination of normally closed switch 615 and normally open switch 616, switch 62 is configured with a combination of normally closed switch 625 and normally open switch 626, and switch 63 is configured with a combination of normally closed switch 635 and normally open switch 636.

17, when the normally closed switches 615, 625, and 635 are closed (i.e., turned on) and the normally open switches 616, 626, and 636 are open (i.e., turned off), the windings 71, 72, and 73 of the motor 7 are in a Y-connected state. Conversely to the illustrated state, when the normally closed switches 615, 625, and 635 are open (i.e., turned off) and the normally open switches 616, 626, and 636 are closed (i.e., turned on), the motor is in a Δ-connected state.

As shown in Figure 17, when each switch is configured by a combination of normally closed switches 615, 625, 635 and normally open switches 616, 626, 636, an electromagnetic contactor can be used as each switch. Electromagnetic contactors are suitable because they have small conduction loss when on.

As shown in FIG. 18, each switch may be configured using a semiconductor switch. FIG. 18 is a circuit diagram showing an example of a configuration in which MOS transistors are used for switch 61 (62, 63) of connection switching device 260. One of switches 61, 62, and 63 is shown in FIG. 18. Switches 61, 62, and 63 have the same configuration and operate in the same way. FIG. 19 is a diagram showing, in tabular form, examples of the on and off states of the MOS transistors of the switch in FIG. 18.

As shown in FIG. 18, the switch 61 (62, 63) includes a MOS transistor 616a (626a, 636a) and a diode 616c (626c, 636c) connected in series between the lead wire 61e (62e, 63e) and the output line 332 (333, 331), and a MOS transistor 616b (626b, 636b) and a diode 616d (626d, 636d) connected in series between the lead wire 61e (62e, 63e) and the output line 332 (333, 331).

In addition, the switch 61 (62, 63) includes a MOS transistor 615a (625a, 635a) and a diode 615c (625c, 635c) connected in series between the lead wire 61e (62e, 63e) and the neutral node 64, and a MOS transistor 615b (625b, 635b) and a diode 615d (625d, 635d) connected in series between the lead wire 61e (62e, 63e) and the neutral node 64.

Each MOS transistor 616a (626a, 636a), 616b (626b, 636b), 615a (625a, 635a), and 615b (625b, 635b) has a parasitic diode whose anode is connected to the diode and whose cathode is connected to a lead wire (or neutral node or output line).

As shown in FIG. 19, by inputting a control signal to the control terminal, MOS transistors 616a, 626a, 636a are turned on, MOS transistors 616b, 626b, 636b are turned on, MOS transistors 615a, 625a, 635a are turned off, and MOS transistors 615b, 625b, 635b are turned off, thereby making it possible to make windings 71, 72, 73 into a delta connection.

Also, as shown in FIG. 19, windings 71, 72, 73 can be Y-connected by turning off MOS transistors 616a, 626a, 636a, turning off MOS transistors 616b, 626b, 636b, turning on MOS transistors 615a, 625a, 635a, and turning on MOS transistors 615b, 625b, 635b.

In addition, it is preferable that the MOS transistor as the semiconductor switch is composed of a wide band gap (WBG) semiconductor. The WBG semiconductor is a semiconductor containing, for example, silicon carbide (SiC), gallium nitride (GaN), gallium oxide ( _Ga2O3 ), and diamond as constituent materials. When composed of a _WBG semiconductor, the on-resistance is small, the loss is low, the element generates little heat, and the switching operation can be performed quickly.

Even when semiconductor switches are used, there is a possibility that, for example, MOS transistors 616a and 615a may erroneously turn on or off simultaneously due to the influence of noise, etc., and this may result in erroneous turning on or off not only in the MOS transistors 616a and 615a phase but also in at least two phases of MOS transistors 616a and 615a and MOS transistors 616b and 615b simultaneously, creating a short circuit path that does not go through the motor windings, and resulting in a failure.

Therefore, in the connection switching device 260 made of semiconductors, by shifting the timing of the switching operation of the switch as shown in Figures 4 and 5, it is possible to prevent the occurrence of short-circuit current that does not pass through the windings, and a highly reliable motor drive device can be obtained.

In other words, even if the connection switching device 260 of the electric motor drive device of embodiment 2 is constructed using inexpensive parts, it is possible to reduce the failure rate and extend the life of the device, thereby reducing product costs.

Other than the above, the electric motor driving device of embodiment 2 is the same as the electric motor driving device 200 of embodiment 1.

<3>Embodiment 3.
In the first and second embodiments, a motor drive device 200 is described which is connected to a motor 7 in which the windings 71, 72, 73 can be switched between Y-connection and Δ-connection. In the third embodiment, a motor drive device is described which is connected to a motor 7a in which the number of turns of each of the windings 71, 72, 73 can be switched. Fig. 20 shows a configuration in which the windings 71, 72, 73 of each phase in a Y-connected motor 7a are composed of two winding parts 711 and 712, two winding parts 721 and 722, and two winding parts 731 and 732, and both ends of each of the winding parts can be connected to the outside of the motor 7a, and the connection state is switched by a connection switching device 360. Note that each of the windings 71, 72, 73 of each phase may have three or more winding parts.

In the third embodiment, the windings 71, 72, and 73 of each phase have two winding portions. In this case, both ends of each of the two winding portions constituting the windings 71, 72, and 73 of each phase are connectable to the outside of the motor 7a, and the connection state of the windings 71, 72, and 73 (the number of turns of the winding in the third embodiment) is switched by the connection switching device 360. The connection switching device 360 can also be applied to a motor in which the winding portions can be switched between a parallel connection and a series connection.

In FIG. 20, the U-phase winding 71 is composed of two winding portions 711 and 712, the V-phase winding 72 is composed of two winding portions 721 and 722, and the W-phase winding 73 is composed of two winding portions 731 and 732.

The first ends of the windings 711, 721, and 731 are connected to the output lines 331, 332, and 333 of the inverter 30 via external terminals 71c, 72c, and 73c, respectively. The second ends of the windings 711, 721, and 731 are connected to the common contacts of the changeover switches 617, 627, and 627, respectively, via external terminals 71g, 72g, and 73g.

First ends of winding portions 712, 722, and 732 are connected to the common contacts of changeover switches 618, 628, and 638 via external terminals 71h, 72h, and 73h, respectively. Second ends of winding portions 712, 722, and 732 are connected to neutral node 64 via external terminals 71d, 72d, and 73d, respectively.

The normally closed contacts of the changeover switches 617, 627, and 637 are connected to the normally closed contacts of the changeover switches 618, 628, and 638, respectively. The normally open contacts of the changeover switches 617, 627, and 637 are connected to the neutral node 64. The normally open contacts of the changeover switches 618, 628, and 638 are connected to the output lines 331, 332, and 333 of the inverter 30.

The connection switching device 360 is composed of changeover switches 617, 627, 637, 618, 628, and 638.

Even when such a connection switching device 360 is used, the mechanical relay or semiconductor switch can be protected by performing the switching operation of the switch of the connection switching device 360 during the current control period Pc, as in the case of the first and second embodiments. Also, as in the case of the first and second embodiments, by performing the switching operation of each of the multiple switches of the connection switching device 360 sequentially with a time interval, it becomes difficult for the motor drive device to malfunction due to the switching operation of the switch that switches the connection state of the windings of the motor 7a being performed without stopping the rotation of the motor.

In the configuration shown in FIG. 20, when the change-over switches 617, 627, 637, 618, 628, and 638 are switched to the normally closed contact side as shown, the electric motor 7a is in a series connection state, and when the change-over switches 617, 627, 637, 618, 628, and 638 are switched to the normally open contact side opposite to that shown, the electric motor 7a is in a parallel connection state.

In addition, in the third embodiment, as described in the second embodiment, a combination of a normally closed switch and a normally open switch can be used instead of a changeover switch. Also, the normally closed switch and the normally open switch can be semiconductor switches.

The above describes the case where a Y-connected motor 7a is switched between a series connection state and a parallel connection state, but a configuration similar to that of the connection switching device 360 can also be applied when switching between a series connection state and a parallel connection state in a motor drive device for a Δ-connected motor.

The motor drive device of this embodiment can also be applied to a motor drive device for an electric motor having a configuration in which a center tap is provided on the windings in a Y-connection or Δ-connection state and a part of the windings is short-circuited by a switching means to change the voltage required for driving. In short, the configuration of embodiment 3 can be applied to an electric motor in which the connection state of the windings can be switched and the back electromotive voltage can be switched by switching the connection state.

Other than the above, the electric motor drive device of embodiment 3 is the same as the electric motor drive device of embodiment 1 or 2.

Note that the configurations shown in the above embodiments 1 to 3 are merely examples and may be combined with other known technologies.

REFRIGERATION CYCLE DEVICE 900, 900a, 900b REFRIGERATION CYCLE DEVICE 902 FOUR-WAY VALVE 904 COMPRESSOR 906 HEAT EXCHANGER 908 EXPANSION VALVE 910 HEAT EXCHANGER

Claims (9)

a connection switching device having a plurality of switches and switching a connection state of a winding of a motor by performing a switching operation of the plurality of switches;
an inverter that applies an AC voltage to the windings via the plurality of switches and receives a back electromotive voltage from the windings of the electric motor during rotation via the plurality of switches;
a control device that controls the inverter to control a rotation operation of the motor and causes the connection switching device to switch the connection state;
having
when switching the connection state during a rotation operation of the motor, the connection switching device sequentially performs switching operations of all of the plurality of switches at different timings and with a time interval between each of the plurality of switches;
the control device causes the connection switching device to execute a switching operation of the plurality of switches during a current control period during which a first effective value of the AC current flowing through the winding is closer to zero than a second effective value of the AC current flowing through the winding before a switching operation of the plurality of switches and during which a rotation speed of the motor is not zero ;
Each of the plurality of switches has an electromagnetic contactor including an excitation coil;
The switching operation of the plurality of switches is performed by switching between electrical continuity and non-conduction between contacts of the electromagnetic contactors,
The time interval when switching the excitation coil from a non-excitation state to an excitation state is 5 ms or more,
The time interval when the excitation coil is switched from an excited state to a non-excited state is 2 ms or more.
Electric motor drive unit. 2. The electric motor drive device according to claim 1, wherein the time interval is within a range of 2 ms to 50 ms. A detection unit that detects a current supplied to the inverter is further provided.
The electric motor drive device according to claim 1 or 2, wherein the control device controls the inverter based on the current detected by the detection unit. The electric motor drive device according to claim 1 , wherein the switching of the connection state is switching between a Y connection and a Δ connection. The electric motor drive device according to claim 1 , wherein the switching of the connection state is a switching of the number of turns of the winding. A refrigeration cycle device comprising the motor drive device according to any one of claims 1 to 5 . An air conditioner comprising the refrigeration cycle device according to claim 6 . A water heater comprising the refrigeration cycle device according to claim 6 . A refrigerator comprising the refrigeration cycle device according to claim 6 .

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