JP7638448B2 - Power conversion device, refrigeration cycle device using the same, and leakage inductance calculation method - Google Patents

Description

The present disclosure relates to a power conversion device that converts supplied power into power suitable for an electric motor driven by a three-phase AC voltage, a refrigeration cycle device using the same, and a method for calculating leakage inductance.

Conventionally, there is known a power conversion device that converts commercial AC power into an arbitrary frequency and an arbitrary voltage using a rectifier circuit and an inverter circuit, and supplies the converted power to a load such as an electric motor (see, for example, Patent Document 1). In addition, three-phase electric motors driven by AC voltage generally have delta and Y connections, but a delta-connected electric motor requires a lower voltage to drive than a Y-connected electric motor. Therefore, taking advantage of the fact that the power required to drive the motor differs depending on the connection state, electric motors that can be switched between Y and delta connections to improve drive efficiency are used mainly in large-capacity fields.

Japanese Patent Application Publication No. 11-69897

However, in motors that can switch connection states, leakage current caused by leakage inductance can become a problem when the motor is in a delta connection. In order to understand the characteristics of the leakage current and take measures to prevent it, it is necessary to know the value of the leakage inductance, but because leakage inductance is small compared to the effective inductance, it is difficult to accurately measure the leakage inductance of a delta-connected motor.

The present disclosure has been made in consideration of the problems in the above-mentioned conventional technology, and aims to provide a power conversion device capable of accurately measuring the leakage inductance of a delta-connected electric motor, a refrigeration cycle device using the same, and a leakage inductance calculation method.

The power conversion device disclosed herein comprises a voltage application means for converting a DC voltage into an AC voltage and supplying the converted AC voltage to a three-phase electric motor, a current detection means for detecting a current flowing through the electric motor, and a control device for controlling the voltage application means, and the control device calculates the leakage inductance in the electric motor based on the current detected by the current detection means when the connection state of the electric motor is a V-shaped measurement delta connection in which one connection part of the delta connection has been removed.

The refrigeration cycle device of the present disclosure is equipped with the above-mentioned power conversion device.

The leakage inductance calculation method disclosed herein is a leakage inductance calculation method for calculating the leakage inductance of a three-phase electric motor, which calculates the leakage inductance in the electric motor based on the current flowing through the electric motor to which an AC voltage is applied, in a state in which the windings of the electric motor are connected to a V-shaped measurement delta connection in which one connection part of the delta connection has been removed.

According to the present disclosure, the connection state of the motor is a measurement delta connection, and the current flowing through the motor is detected in the measurement delta connection state. The leakage inductance is then calculated based on the detected current, so that the leakage inductance of a delta-connected motor can be accurately measured.

1 is a circuit diagram showing an example of a configuration of a power conversion device according to a first embodiment; FIG. 2 is a hardware configuration diagram showing an example of the configuration of the control device of FIG. 1 . 1. FIG. 4 is a hardware configuration diagram showing another example of the configuration of the control device of FIG. FIG. 11 is a circuit diagram when the motor is in an operational Δ connection state. FIG. 11 is a circuit diagram when the connection state of the motor is a measurement Δ connection. 5 is a flowchart showing an example of a flow of a leakage inductance measurement process according to the first embodiment. 5 is a schematic diagram for explaining a state of a switching element of a voltage application means in a first connection state. FIG. FIG. 4 is a circuit diagram for explaining a current flow in a first connection state. 10 is a schematic diagram for explaining a state of a switching element of a voltage application means in a second connection state. FIG. FIG. 11 is a circuit diagram for explaining a current flow in a second connection state. 13 is a schematic diagram for explaining a state of a switching element of a voltage application means in a third connection state. FIG. FIG. 11 is a circuit diagram for explaining a current flow in a third connection state. FIG. 11 is a configuration diagram showing an example of the configuration of an air conditioning device according to a second embodiment.

The following describes embodiments of the present disclosure with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications are possible without departing from the spirit of the present disclosure. In addition, in each drawing, the same reference numerals are used to denote the same or equivalent parts, and this is common throughout the entire specification. Furthermore, the highs and lows of voltage and current are not determined in relation to absolute values, but are determined relatively in the state and operation of the device, etc.

Embodiment 1.
Hereinafter, a description will be given of the power conversion device according to the present embodiment 1. The power conversion device according to the present embodiment 1 converts supplied power into power suitable for driving an electric motor that can be switched between a Y connection and a Δ connection.

[Configuration of power conversion device 100]
Fig. 1 is a circuit diagram showing an example of the configuration of a power conversion device according to the present embodiment 1. As shown in Fig. 1, the power conversion device 100 includes a voltage application means 1, a current detection means 2, a connection switching device 3, and a control device 4. In addition, a DC voltage source 200 and an electric motor 300, which is a load, are connected to the power conversion device 100.

DC voltage source 200 supplies DC voltage _Vdc to voltage application means 1 of power conversion device 100. An output end of DC voltage source 200 is connected to a positive side busbar 5 and a negative side busbar 6 which are busbars of power conversion device 100. Positive side busbar 5 is a busbar on the high potential side, and negative side busbar 6 is a busbar on the low potential side. Motor 300 is a three-phase motor having U-phase, V-phase and W-phase stator windings, which is driven by AC voltage converted by power conversion device 100.

The voltage application means 1 is connected to a positive bus 5 and a negative bus 6 which are output terminals of the DC voltage source 200. The voltage application means 1 converts the DC voltage _Vdc supplied from the DC voltage source 200 into an AC voltage. The voltage application means 1 is connected to the electric motor 300 and supplies the converted AC voltage to the electric motor 300.

The voltage application means 1 is, for example, a three-phase voltage-type inverter, and is composed of a full-bridge circuit equipped with six switching elements 11 to 16. Specifically, in the voltage application means 1, two switching elements are connected in series to form a series body. Then, three such series bodies are connected in parallel to form a full-bridge circuit. In addition, a freewheeling diode is connected in inverse parallel to each of the switching elements 11 to 16.

The voltage application means 1 outputs a pulsed AC voltage, which is a PWM (Pulse Width Modulation) voltage, by controlling these switching elements 11 to 16 with a voltage command supplied from the control device 4. The switching elements 11 to 16 perform on and off operations independently of each other based on the voltage command, which is a switching signal supplied from the control device 4.

The current detection means 2 detects the current output from the voltage application means 1 and supplied to the electric motor 300, and outputs the value of the detected current as current information. In this embodiment 1, the current detection means 2 is configured by providing a shunt resistor on the negative bus 6 of the voltage application means 1. Note that the current detection means 2 is not limited to a shunt resistor, and for example, a current sensor using an instrument current transformer called a CT (Current Transformer) may be used.

The connection switching device 3 has switches 31 to 33 provided according to the number of phases of the electric motor 300. The connection switching device 3 switches the connection state of each phase of the electric motor 300 to Y connection or Δ connection by performing a switching operation of the switches 31 to 33 based on a switching command from the control device 4. The switches 31 to 33 may be configured, for example, as mechanical relays or semiconductor switches.

The control device 4 controls the entire power conversion device 100 based on commands from the outside or information from various detection means and sensors provided in the power conversion device 100. In addition, in this embodiment 1, the control device 4 performs a leakage inductance measurement process to measure the value of the leakage inductance in the electric motor 300. Details of the leakage inductance measurement process will be described later.

The control device 4 includes a voltage control unit 41, a switching control unit 42, and a measurement unit 43. The control device 4 is configured such that various functions are realized by executing software on a calculation device such as a microcomputer, or is configured with hardware such as a circuit device that realizes various functions.

The voltage control unit 41 generates a voltage command for controlling the switching elements 11 to 16 of the voltage application means 1 based on an operation command such as a speed command or a torque command input from the outside. The voltage control unit 41 then outputs the generated voltage command to the voltage application means 1.

At this time, the control device 4 generates a voltage command using various control methods so that an appropriate AC voltage is supplied from the voltage application means 1 to the electric motor 300. For example, constant V/f control, vector control, direct torque control, etc. are used as control methods. Constant V/f control is a control method that outputs a voltage proportional to the operating frequency of the electric motor 300. Vector control is a control method that controls the current flowing through the electric motor 300 using a rotating coordinate system. Direct torque control is a control method that controls the magnetic flux and torque of the electric motor 300.

The switching control unit 42 generates a switching command for switching the switches 31 to 33 of the connection switching device 3. The switching control unit 42 then outputs the generated switching command to the connection switching device 3.

During the leakage inductance measurement process, the measurement unit 43 calculates the leakage inductance based on the current information supplied from the current detection means 2. Details of the method for calculating the leakage inductance will be described later.

Figure 2 is a hardware configuration diagram showing an example of the configuration of the control device in Figure 1. When the various functions of the control device 4 are executed by hardware, the control device 4 in Figure 1 is configured by a processing circuit 51 as shown in Figure 2. Each function of the voltage control unit 41, switching control unit 42 and measurement unit 43 in Figure 1 is realized by the processing circuit 51.

When each function is executed by hardware, the processing circuit 51 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 of these. The functions of each of the voltage control unit 41, the switching control unit 42, and the measurement unit 43 may be realized by the processing circuit 51, or the functions of each unit may be realized by a single processing circuit 51.

Figure 3 is a hardware configuration diagram showing another example of the configuration of the control device of Figure 1. When the various functions of the control device 4 are executed by software, the control device 4 of Figure 1 is configured with a processor 52 and a memory 53 as shown in Figure 3. The functions of the voltage control unit 41, the switching control unit 42 and the measurement unit 43 are realized by the processor 52 and the memory 53.

When each function is performed by software, the functions of the voltage control unit 41, the switching control unit 42 and the measurement unit 43 are realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 53. The processor 52 realizes the function of each unit by reading and executing the programs stored in the memory 53.

As the memory 53, 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 and Programmable ROM), and an EEPROM (Electrically Erasable and Programmable ROM) is used. In addition, as the memory 53, for example, a removable recording medium such as a magnetic disk, a flexible disk, an optical disk, a CD (Compact Disc), an MD (Mini Disc), and a DVD (Digital Versatile Disc) may be used.

[Connection state of the electric motor 300]
Here, we will explain the connection state of the electric motor 300. When the connection state of the electric motor 300 is a Y connection state, the line voltage is " _VY " and the current flowing into the stator winding is " _IY ". Furthermore, when the connection state of the electric motor 300 is a Δ connection state, the line voltage is " _VΔ " and the current flowing into the stator winding is " _IΔ ".

Assuming that the voltages applied to the stator windings of each phase are equal to each other, the relationship shown in formula (1) holds between the voltage _VY and the voltage _VΔ , and the relationship shown in formula (2) holds between the currents _IY and _IΔ .
_VΔ = _VY /√3...(1)
I _Δ =√3×I _Y ...(2)

When the voltage VY and current _IY in the Y-connection state and the voltage _VΔ and current _IΔ in _the Δ-connection state have the relationship shown in formula (1) and formula (2), the power supplied to the motor 300 in the Y-connection state and the Δ-connection state are equal to each other. In other words, when the powers supplied to the motor 300 are equal to each other, the current flowing into the stator winding is larger in the Δ-connection state than in the Y-connection state, and the voltage required to drive the motor 300 is lower.

For this reason, when driving the electric motor 300, it is possible to select the connection state according to the load conditions. For example, at low load, the electric motor 300 operates at low speed in a Y connection state, and at high load, the electric motor 300 operates at high speed in a Δ connection state. This makes it possible to improve efficiency at low loads and increase output at high loads.

However, as explained in the Background section, since leakage inductance is small compared to effective inductance, it is difficult to accurately measure leakage inductance in a motor in a delta connection state. Therefore, in order to accurately measure the leakage inductance of a delta-connected motor, the power conversion device 100 according to the first embodiment performs leakage inductance measurement processing by treating the connection state of the motor 300 as a special delta connection.

Figure 4 is a circuit diagram when the motor is connected in an operating Δ connection. Figure 5 is a circuit diagram when the motor is connected in a measurement Δ connection. Note that in Figures 4 and 5, the connection switching device 3 and the control device 4 are omitted from the illustration so that the connection state can be easily understood.

The operating delta connection is a normal delta connection, and as shown in Figure 4, the stator windings between each phase are completely delta connected. In this case, one end of the stator winding between the U- and V-phases is connected between switching elements 11 and 12 of the voltage application means 1, and the other end is connected between switching elements 13 and 14. Also, one end of the stator winding between the V- and W-phases is connected between switching elements 13 and 14 of the voltage application means 1, and the other end is connected between switching elements 15 and 16. Furthermore, one end of the stator winding between the W- and U-phases is connected between switching elements 15 and 16 of the voltage application means 1, and the other end is connected between switching elements 11 and 12.

In contrast, the measurement delta connection is an incomplete delta connection in which one end of one of the stator windings between each phase is removed, as shown in Figure 5. In other words, the measurement delta connection is a so-called V-shaped connection in which one connection part of the delta connection is removed. In the example shown in Figure 5, one end of the stator winding between the W-U phases is removed, and a V-shape is formed by the stator windings between the U-V phases and the V-W phases. Specifically, one end of the stator winding between the U-V phases is connected between switching elements 11 and 12 of the voltage application means 1, and the other end is connected between switching elements 13 and 14. In addition, one end of the stator winding between the V-W phases is connected between switching elements 13 and 14 of the voltage application means 1, and the other end is connected between switching elements 15 and 16. On the other hand, one end of the stator winding between the W- and U-phases is connected between the switching elements 15 and 16 of the voltage application means 1, but the other end is not connected anywhere and is in a disconnected state.

When such a measurement delta connection is used as the connection state of the motor 300, the switching elements 11 to 16 of the voltage application means 1 in the power conversion device 100 are controlled to apply a voltage between specific phases of the motor 300. Then, by measuring the current that flows when a voltage is applied between specific phases, the inductance value at that time can be derived.

[Leakage inductance measurement process]
In the first embodiment, when the leakage inductance measurement process is performed, the connection state of the electric motor 300 is switched from the operation Δ connection in Fig. 4 to the measurement Δ connection in Fig. 5. Then, with the connection state of the electric motor 300 set to the measurement Δ connection, the connection state between the power conversion device 100 and the electric motor 300 is switched, and the leakage inductance measurement process is performed.

Figure 6 is a flowchart showing an example of the flow of the leakage inductance measurement process according to the present embodiment 1. The leakage inductance measurement process according to the present embodiment 1 is performed in a state where the electric motor 300 is stopped in order to prevent the influence of the speed electromotive force generated by the operation of the electric motor 300.

First, in step S1, the connection state of the electric motor 300 is switched to the measurement delta connection. In this case, the switching control unit 42 of the control device 4 outputs a switching command to the connection switching device 3 to switch the switches 31 to 33 so that the connection state of the electric motor 300 becomes the measurement delta connection shown in FIG. 5.

Next, in step S2, the connection between the power conversion device 100 and the electric motor 300 is set to a first connection state. The first connection state is a connection state for allowing current to flow through the stator windings between the U and V phases.

Figure 7 is a schematic diagram for explaining the state of the switching elements of the voltage application means in the first connection state. Figure 7 shows the setting states of the switching elements 11 to 16 of the voltage application means 1 for bringing the connection between the power conversion device 100 and the electric motor 300 into the first connection state in response to a voltage command from the voltage control unit 41.

Fig. 8 is a circuit diagram for explaining the flow of current in the first connection state. In Fig. 8, the thick lines in the circuit diagram indicate the current paths in the first connection state when the switching elements 11 to 16 are set as shown in Fig. 7. The arrows in the circuit diagram indicate the current _I1 flowing through the current paths.

7, the voltage control unit 41 outputs a voltage command to the voltage application means 1 to turn on the switching elements 11 and 14 and turn off the switching elements 12, 13, 15 and 16, thereby switching the switching elements 11 to 16. As a result, a pulsed voltage is applied between the UV phases of the electric motor 300, and a current _I1 flows.

The current detection means 2 detects the negative DC bus current _I1 , which is a current between the U and V phases that flows in the negative bus 6 as a result of the application of a pulsed voltage. Then, when the negative DC bus current _I1 is detected, the voltage control unit 41 outputs a voltage command to the voltage application means 1 to turn off all the switching elements 11 to 16, and makes the current flowing in the current detection means 2 sufficiently small.

In step S3 of Figure 6, the connection between the power conversion device 100 and the electric motor 300 is set to a second connection state. The second connection state is a connection state for allowing current to flow through the stator winding between the V-W phases.

Figure 9 is a schematic diagram for explaining the state of the switching elements of the voltage application means in the second connection state. Figure 9 shows the setting states of the switching elements 11 to 16 of the voltage application means 1 for bringing the connection between the power conversion device 100 and the electric motor 300 into the second connection state in response to a voltage command from the voltage control unit 41.

Fig. 10 is a circuit diagram for explaining the flow of current in the second connection state. In Fig. 10, the thick lines in the circuit diagram indicate the current paths in the second connection state when the switching elements 11 to 16 are set as shown in Fig. 9. The arrows in the circuit diagram indicate the current _I2 flowing through the current paths.

9, the voltage control unit 41 outputs a voltage command to the voltage application means 1 to turn on the switching elements 13 and 16 and turn off the switching elements 11, 12, 14 and 15, thereby switching the switching elements 11 to 16. As a result, a pulsed voltage is applied between the V-W phase of the motor 300, and a current _I2 flows.

The current detection means 2 detects the negative DC bus current _I2 , which is a current between the V-W phase and flows in the negative bus 6 as a result of the application of a pulsed voltage. Then, when the negative DC bus current _I2 is detected, the voltage control unit 41 outputs a voltage command to the voltage application means 1 to turn off all the switching elements 11 to 16, and makes the current flowing in the current detection means 2 sufficiently small.

In step S4 of FIG. 6, the connection between the power conversion device 100 and the electric motor 300 is set to the third connection state. The third connection state is a connection state for allowing current to flow through the stator winding between the W- and U-phases. Here, in the measurement delta connection, the stator winding between the W- and U-phases is in a disconnected state. Therefore, in the third connection state, current flows through the stator winding between the V- and W-phases and the stator winding between the U- and V-phases.

Figure 11 is a schematic diagram for explaining the state of the switching elements of the voltage application means in the third connection state. Figure 11 shows the setting states of the switching elements 11 to 16 of the voltage application means 1 for bringing the connection between the power conversion device 100 and the electric motor 300 into the third connection state in response to a voltage command from the voltage control unit 41.

Fig. 12 is a circuit diagram for explaining the flow of current in the third connection state. In Fig. 12, the thick lines in the circuit diagram indicate the current paths in the third connection state when the switching elements 11 to 16 are set as shown in Fig. 11. The arrows in the circuit diagram indicate the current _I3 flowing through the current paths.

11, the voltage control unit 41 outputs a voltage command to the voltage application means 1 to turn on the switching elements 12 and 15 and turn off the switching elements 11, 13, 14 and 16, thereby switching the switching elements 11 to 16. As a result, a pulsed voltage is applied between the W-U phases of the motor 300, and a current _I3 flows.

The current detection means 2 detects the negative DC bus current _I3 , which is a current between the W-U phases that flows in the negative bus 6 as a result of the application of a pulsed voltage. Then, when the negative DC bus current _I3 is detected, the voltage control unit 41 outputs a voltage command to the voltage application means 1 to turn off all the switching elements 11 to 16, and makes the current flowing in the current detection means 2 sufficiently small.

6, the measuring unit 43 calculates the leakage inductance based on the DC voltage _Vdc supplied from the DC voltage source 200 and the negative DC bus currents _I1 to _I3 detected by the current detection means 2. Generally, when a voltage V is input in a step to an RL load consisting of a resistance R and an inductance L, the response of the current I rises with a slope of "voltage V/inductance L". Therefore, the inductance L can be calculated from "V/I".

In the first embodiment, in the first connection state of step S2, a current _I1 flows only through the stator winding between the U and V phases of the electric motor 300. Therefore, the inductance _L1 of the current path at this time is expressed as in equation (3). In equation (3), "L _a " represents the average value of the effective inductance per phase of the electric motor 300. Furthermore, "l _a " represents the leakage inductance per phase.
L ₁ =I ₁ /V _dc =L _a +l _a ...(3)

In the second connection state in step S3, a current flows only through the stator winding between the V- and W-phases in the electric motor 300. Therefore, the inductance _L2 of the current path at this time is expressed as in equation (4).
L ₂ =I ₂ /V _dc =L _a +l _a ...(4)

On the other hand, in the third connection state of step S4, current flows through both the U-V phase and V-W phase stator windings of the electric motor 300. Furthermore, mutual induction acts in the respective stator windings in a direction that weakens the magnetic flux of each other. Therefore, the inductance _L3 of the current path at this time is expressed as in equation (5). In equation (5), "M" represents the mutual inductance between the phases, and the relationship is "M = L _a /2."
L ₃ = (L _a + l _a −M)×2
=(L _a +l _a -L _a /2)×2
=L _a +2l _a ...(5)

Therefore, the leakage inductance _la is calculated based on the equation (6) by using the currents I1 and _I3 acquired in steps S2 and _S4 and the DC voltage _Vdc , and by using the equations (3) and (5). Note that the leakage inductance _la may be calculated by using _I2 instead of _I1 .
l _a = L ₃ - _{L 1} = V _dc / (I ₃ - _{I 1} ) ... (6)

Finally, in step S6 of FIG. 6, the wiring state of the electric motor 300 is switched to the operational Δ wiring state shown in FIG. 4. Then, the series of processes ends.

Thus, in the leakage inductance measurement process, the connection state of the motor 300 is set as a measurement Δ connection, and the leakage inductance is calculated based on the current _I1 flowing between the U-V phases or the current _I2 flowing between the V-W _phases , and the current I3 flowing between the W-U phases. At this time, when calculating the current _I3 , attention is paid to the mutual induction effect, so that it is possible to accurately calculate a leakage inductance that is small compared to the effective inductance. The calculated leakage inductance can be used, for example, when designing the next or subsequent motors.

The calculated leakage inductance may also change depending on the usage time of the electric motor 300. Therefore, the changing leakage inductance can be used to detect abnormalities such as the life span or failure of the electric motor 300 or the power conversion device 100. In this case, the control device 4 of the power conversion device 100 presets a threshold value for the leakage inductance, and determines that an abnormality has occurred in the electric motor 300 or the power conversion device 100 when the calculated leakage inductance exceeds the threshold value.

As described above, in the power conversion device 100 according to the first embodiment, the connection state of the three-phase motor 300, which can be switched between a Y connection and a Δ connection, is a V-shaped measurement Δ connection in which one connection part of the Δ connection is removed. Then, the leakage inductance in the motor 300 is calculated based on the current flowing through the motor 300 in the measurement Δ connection state. This allows the leakage inductance in the motor 300 to be accurately calculated.

Furthermore, since the leakage inductance can be accurately calculated in this manner, it is possible to predict failure of the motor 300, for example, by obtaining the leakage inductance periodically.

Embodiment 2.
Next, a description will be given of a second embodiment of the present invention. In the second embodiment of the present invention, an example in which the power conversion device 100 described in the first embodiment is applied to an air conditioner will be described.

[Configuration of the air conditioning device 500]
Fig. 13 is a configuration diagram showing an example of the configuration of an air conditioner according to Embodiment 2. An air conditioner 500 in Fig. 13 performs cooling operation and heating operation by using a heat pump system.

As shown in Figure 13, the air conditioning device 500 is composed of an outdoor unit 500A equipped with a compressor 501, a refrigerant flow switching device 502, an outdoor heat exchanger 503, and an expansion valve 504, and an indoor unit 500B equipped with an indoor heat exchanger 505. In the air conditioning device 500, the compressor 501, the refrigerant flow switching device 502, the outdoor heat exchanger 503, the expansion valve 504, and the indoor heat exchanger 505 are sequentially connected by refrigerant piping to form a refrigerant circuit in which the refrigerant circulates through the refrigerant piping.

Of these, the compressor 501 has a compression element 501a that compresses the refrigerant, and a motor M as an electric motor 300 that is connected to the compression element 501a and is supplied with power by the power conversion device 100. The power conversion device 100 is a device according to the above-mentioned embodiment 1, and receives power from a DC voltage source 200 that is a power source, and supplies the converted power to the motor M to rotate the motor M.

The refrigerant flow switching device 502 is, for example, a four-way valve, and switches between cooling and heating operations by switching the direction of refrigerant flow. The outdoor heat exchanger 503 exchanges heat between the refrigerant and the outside air. The outdoor heat exchanger 503 functions as a condenser during cooling operation and as an evaporator during heating operation. The expansion valve 504 expands the refrigerant. The indoor heat exchanger 505 exchanges heat between the refrigerant and the indoor air in the space to be air-conditioned. The indoor heat exchanger 505 functions as an evaporator during cooling operation and as a condenser during heating operation.

[Operation of the air conditioning device 500]
Next, the operation of the air-conditioning apparatus 500 according to the second embodiment will be described with reference to Fig. 13. Here, the cooling operation will be described as an example. When performing the cooling operation, the refrigerant flow path switching device 502 switches the flow path in advance so that the refrigerant discharged from the compressor 501 flows toward the outdoor heat exchanger 503, and the refrigerant flowing out from the indoor heat exchanger 505 flows toward the compressor 501. At this time, the outdoor heat exchanger 503 functions as a condenser, and the indoor heat exchanger 505 functions as an evaporator.

When the motor M of the compressor 501 is driven by the power conversion device 100, the compression element 501a of the compressor 501 connected to the motor M compresses the low-temperature, low-pressure refrigerant, and the compressor 501 discharges a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor 501 flows through the refrigerant flow switching device 502 into the outdoor heat exchanger 503, which functions as a condenser.

The high-temperature, high-pressure gas refrigerant that flows into the outdoor heat exchanger 503 condenses while exchanging heat with the outside air and releasing heat, becoming a high-pressure liquid refrigerant that flows out of the outdoor heat exchanger 503. The high-pressure liquid refrigerant that flows out of the outdoor heat exchanger 503 is expanded and decompressed by the expansion valve 504, becoming a low-temperature, low-pressure, gas-liquid two-phase refrigerant that flows into the indoor heat exchanger 505, which functions as an evaporator.

The low-temperature, low-pressure, two-phase gas-liquid refrigerant that flows into the indoor heat exchanger 505 exchanges heat with the air in the space to be air-conditioned, absorbing heat and evaporating, thereby cooling the indoor air, and flows out of the indoor heat exchanger 505 as a low-temperature, low-pressure gas refrigerant. The low-temperature, low-pressure gas refrigerant that flows out of the indoor heat exchanger 505 is sucked into the compressor 501 via the refrigerant flow switching device 502 and compressed again. The above-mentioned operations are then repeated.

13 shows an example in which the power conversion device 100 according to embodiment 1 is applied to the compressor 501 of the air conditioning device 500, but the present invention is not limited to this and may be applied, for example, to a power source for driving a fan (not shown) that blows air to the outdoor heat exchanger 503. The power conversion device 100 may also be applied, for example, to a heat pump device using the compressor 501, a refrigeration device, and other refrigeration cycle devices in general.

As described above, in the air conditioning device 500 according to the second embodiment, the compressor 501 provided in the refrigerant circuit is driven by power supplied from the power conversion device 100. The power conversion device 100 measures the leakage inductance when the motor M, which is the electric motor 300 of the compressor 501, is stopped, so that the leakage inductance in the Δ-connected electric motor 300 can be accurately measured, as in the first embodiment.

Although the first and second embodiments have been described above, the present disclosure is not limited to the first and second embodiments described above, and various modifications and applications are possible within the scope of the present disclosure. In the first embodiment, a case has been described in which the DC voltage source 200 is connected to the power conversion device 100 and the DC voltage _Vdc is supplied, but this is not limited to this example. For example, a commercial AC power supply that is a three-phase AC power supply may be connected to the power conversion device 100.

In this case, however, a rectifier circuit and a smoothing capacitor are provided in power conversion device 100 in the upstream of voltage application means 1. As a result, the AC voltage supplied from the AC power supply is rectified by the rectifier circuit, and the rectified DC voltage is smoothed by the smoothing capacitor. Then, a DC voltage equivalent to the DC voltage _Vdc output from DC voltage source 200 is supplied from the smoothing capacitor to voltage application means 1 in the downstream stage.

In addition, in the first embodiment, a case has been described in which one of the two ends of the stator winding between the W-U phases is in a disconnected state in the measurement delta connection, but this is not limited to this example. For example, in the measurement delta connection, one of the two ends of the stator winding between the U-V phases may be in a disconnected state, or one of the two ends of the stator winding between the V-W phases may be in a disconnected state.

Furthermore, the power conversion device 100 has been described as controlling the driving of one electric motor 300 as a load with one voltage application means 1, but this is not limited to this example. For example, the power conversion device 100 may control the driving of multiple loads (electric motors) with one voltage application means 1.

1 Voltage application means, 2 Current detection means, 3 Connection switching device, 4 Control device, 5 Positive busbar, 6 Negative busbar, 11, 12, 13, 14, 15, 16 Switching element, 31, 32, 33 Switch, 41 Voltage control unit, 42 Switching control unit, 43 Measurement unit, 51 Processing circuit, 52 Processor, 53 Memory, 100 Power conversion device, 200 DC voltage source, 300 Electric motor, 500 Air conditioning device, 500A Outdoor unit, 500B Indoor unit, 501 Compressor, 501a Compression element, 502 Refrigerant flow switching device, 503 Outdoor heat exchanger, 504 Expansion valve, 505 Indoor heat exchanger.

Claims (7)

a voltage application means for converting a DC voltage into an AC voltage and supplying the converted AC voltage to a three-phase motor;
A current detection means for detecting a current flowing through the electric motor;
A control device for controlling the voltage application means,
The control device includes:
A power conversion device that calculates the leakage inductance in the motor based on the current detected by the current detection means when the wiring state of the motor is a V-shaped measurement Δ connection in which one connection part of the Δ connection is removed. The voltage application means is
It is composed of multiple switching elements,
The control device includes:
sequentially controlling the switching elements so that the motor in the measurement delta connection state is in a first connection state in which a current flows between first phases, a second connection state in which a current flows between second phases, and a third connection state in which a current flows between third phases;
2. The power conversion device according to claim 1, wherein the leakage inductance is calculated based on a first current or a second current which is a current flowing through the motor in the first connection state or the second connection state, respectively, and a third current which is a current flowing through the motor in the third connection state. The control device includes:
3. The power conversion device according to claim 2, wherein the leakage inductance is calculated by subtracting the first inductance of the motor in the first connection state or the second inductance of the motor in the second connection state from the third inductance of the motor in the third connection state. The voltage application means is
4. The power conversion device according to claim 2, wherein the power conversion device is formed by connecting three series bodies, each of which has two of the switching elements connected in series, in parallel. When the motor is a three-phase motor capable of switching a winding connection state between a Y connection and a Δ connection, a connection switching device is further provided for switching the connection state of the motor,
The control device includes:
The power conversion device according to any one of claims 1 to 3 , wherein the connection switching device is controlled so that a connection state of the motor is switched from the Δ connection to the measurement Δ connection when the leakage inductance is calculated. A refrigeration cycle device comprising the power conversion device according to any one of claims 1 to 3 . A leakage inductance calculation method for calculating a leakage inductance of a three-phase electric motor, comprising the steps of:
A leakage inductance calculation method for calculating leakage inductance in a motor based on the current flowing through the motor to which an AC voltage is applied, when the windings of the motor are connected in a V-shaped measurement delta connection in which one connection part of the delta connection is removed.

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