Drive device and refrigeration cycle device

Abstract

In the present invention, a drive device (100) comprises: a boost converter (3); an inverter (4); a connection switching device (20) that alternatingly switches the windings of an electric motor (1) between a Y connection and a ∆ connection; and a control unit (30) that controls the boost converter (3), the inverter (4), and the connection switching device (20). The control unit (30) performs zero current control that switches the winding connection in a state where the current of the electric motor (1) has been set to zero, and, in a state where the ∆ connection has been selected by the connection switching device (20), switches to the Y connection when the speed of the electric motor (1) before the zero current control period has not exceeded the speed upper limit.

Description

[Technical field]

[0001] The present disclosure relates to a drive device that drives an electric motor and a refrigeration cycle device. [Background technology]

[0002] Conventionally, a driving device is known that includes a connection switching device that switches the stator winding (hereinafter simply referred to as "winding") of an electric motor between a plurality of different connection states, and that is capable of switching the connection of the winding while the electric motor is rotating. For example, the following Patent Document 1 discloses a technique in which, when a first connection is selected and the electric motor is in a first state, when switching from the first connection to a second connection, the second connection is selected after the electric motor has transitioned to the second state. The first state is a state in which the output voltage of a DC power supply circuit is a first voltage value, and the rotation speed of the electric motor is a first speed value. The second state is a state in which the output voltage of a DC power supply circuit is higher than the first voltage value, the rotation speed of the electric motor is higher than the first speed value, and the current flowing through the electric motor is equal to or lower than a predetermined threshold value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Re-tabled issue 2020 / 021681 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the above-mentioned conventional technology, it is possible to avoid the increase in size of the equipment and obtain a highly reliable driving device. On the other hand, the above-mentioned conventional technology does not take into consideration the magnitude of the load when the motor connection is switched, i.e., the load state when the connection is switched. For example, if the load is large when the connection is switched, the voltage of the motor exceeds the voltage of the internal circuit of the driving device after the connection is switched, and the regenerative current generated may cause the internal circuit of the driving device to become overvoltage. In order to prevent the failure of the driving device and extend the life of the driving device, it is desirable to suppress the overvoltage that may occur in the internal circuit of the driving device.

[0005] The present disclosure has been made in consideration of the above, and has an object to provide a drive device that can suppress overvoltage that may occur in an internal circuit of the drive device, regardless of the load state at the time of wiring switching. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a drive device according to the present disclosure includes a boost converter, an inverter, a connection switching device, and a control unit. The boost converter receives an AC voltage output from an AC power source and outputs a DC voltage with a variable voltage value. The inverter converts a bus voltage output from the boost converter into an AC voltage with a variable voltage and frequency and applies the AC voltage to an electric motor. The connection switching device switches the winding of the electric motor between a first connection and a second connection. The control unit controls the boost converter, the inverter, and the connection switching device. The control unit performs zero current control to switch the winding connection with the electric motor current set to zero. Furthermore, when the second connection is selected by the connection switching device, the control unit switches the electric motor to the first connection if the rotation speed of the electric motor before the zero current control period does not exceed an upper limit value of the rotation speed. Effect of the Invention

[0007] The drive device according to the present disclosure has the advantage of being able to suppress overvoltage that may occur in the internal circuitry of the drive device, regardless of the load state at the time of switching the wiring. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing a configuration example of a drive device according to a first embodiment; [Diagram 2] FIG. 2 is a detailed diagram showing a connection state between the connection switching device and the electric motor shown in FIG. 1; [Diagram 3] FIG. 2 is a diagram showing a detailed configuration of a switch in the wiring switching device shown in FIG. 1; [Figure 4] FIG. 2 is a diagram showing two connection states that can be switched in the electric motor shown in FIG. 1; [Diagram 5] FIG. 1 is a diagram showing an example of a detailed configuration of a control unit according to the first embodiment; [Figure 6] 1 is a first time chart for explaining a control sequence in the connection switching control according to the first embodiment; [Figure 7] 2 is a second time chart for explaining a control sequence in the connection switching control according to the first embodiment; [Figure 8] A flowchart showing an example of a process flow for implementing the control sequence of FIG. 7. [Figure 9] FIG. 1 is a block diagram showing an example of a hardware configuration for implementing the functions of a control unit according to a first embodiment; [Figure 10] FIG. 11 is a block diagram showing another example of a hardware configuration for implementing the functions of the control unit according to the first embodiment; [Figure 11] FIG. 1 shows a configuration example of a refrigeration cycle device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A drive device and a refrigeration cycle device according to embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0010] Embodiment 1 1 is a diagram showing an example of the configuration of a drive device 100 according to a first embodiment. The drive device 100 is connected to an AC power source 2, and drives an electric motor 1 using power from the AC power source 2. An apparatus 5 is connected to the electric motor 1. The drive device 100 has a boost converter 3, an inverter 4, a connection switching device 20, and a control unit 30. The control unit 30 controls the boost converter 3, the inverter 4, and the connection switching device 20.

[0011] The boost converter 3 receives the AC voltage output from the AC power supply 2, and outputs a DC voltage whose voltage value is variable. Hereinafter, this DC voltage will be referred to as a "bus voltage."

[0012] The inverter 4 converts the bus voltage output from the boost converter 3 into an AC voltage whose voltage and frequency are variable, and applies the AC voltage to the motor 1. The control unit 30 controls the operation of the inverter 4 based on the current output by the inverter 4.

[0013] An example of the motor 1 is a three-phase motor as shown in the figure. In this paper, a three-phase synchronous motor is assumed. The ends of the windings in the motor 1 are drawn out to the outside of the motor 1. The windings can be a star connection (hereinafter, appropriately referred to as a "Y connection") which is a first connection, or a delta connection (hereinafter, appropriately referred to as a "Δ connection") which is a second connection. In each of the Y connection and the Δ connection, switching to the other connection is performed by a connection switching device 20. The connection switching device 20 has switches 21, 22, and 23 for switching the connection of the windings of the motor 1. The selection of whether the motor 1 is driven in the Y connection or the Δ connection is controlled by a control unit 30.

[0014] Fig. 2 is a diagram showing in detail a connection state between the connection switching device 20 and the electric motor 1 shown in Fig. 1. Fig. 3 is a diagram showing a detailed configuration of the switches 21, 22, and 23 of the connection switching device 20 shown in Fig. 1.

[0015] 2, first ends 41a, 42a, 43a of the windings 41, 42, 43 of the three phases consisting of U-phase, V-phase, and W-phase of the electric motor 1 are connected to external terminals 41c, 42c, 43c, respectively. Second ends 41b, 42b, 43b of the windings 41, 42, 43 of the U-phase, V-phase, and W-phase are connected to external terminals 41d, 42d, 43d, respectively. The external terminals 41c, 42c, 43c, 41d, 42d, 43d are terminals that can be connected to the outside of the electric motor 1. The external terminals 41c, 42c, 43c are connected to the output lines 61, 62, 63 of the U-phase, V-phase, and W-phase of the inverter 4.

[0016] As described above, the connection switching device 20 has the switches 21, 22, and 23. The switches 21, 22, and 23 are connected to the windings 41, 42, and 43, respectively. The switches 21, 22, and 23 switch the paths of the currents flowing through the windings 41, 42, and 43, respectively. The switches 21, 22, and 23 are electromagnetic contactors whose contacts are electromagnetically opened and closed. Such electromagnetic contactors include those called relays and contactors. The switches 21, 22, and 23 are configured, for example, as shown in FIG. 3. In FIG. 3, the switches 21, 22, and 23 are configured so that the contacts of the switches 21, 22, and 23 are in different connection states when a current is flowing through the excitation coils 211, 221, and 231 and when a current is not flowing through the excitation coils 211, 221, and 231.

[0017] In FIG. 3, the excitation coils 211, 221, and 231 are connected to receive the switching power supply voltage V20 via a semiconductor switch 204. The opening and closing of the semiconductor switch 204 is controlled by a connection selection signal Sc output from the control unit 30. For example, when the connection selection signal Sc has a first value, the semiconductor switch 204 is turned off, and when the connection selection signal Sc has a second value, the semiconductor switch 204 is turned on. The first value is, for example, a logical value of "Low," and the second value is, for example, a logical value of "High." These may be inversely related. Note that, when the connection selection signal Sc is output from a circuit having a sufficient current capacity, the current due to the connection selection signal Sc may be configured to flow directly from the circuit to the excitation coils 211, 221, and 231. In that case, the semiconductor switch 204 is not necessary.

[0018] The semiconductor switch 204 is generally formed using a semiconductor element made of a silicon-based material, but is not limited to this. The semiconductor switch 204 may be formed using a semiconductor element made of a wide band gap semiconductor. By using a switching element made of a wide band gap semiconductor, a device with lower loss can be configured.

[0019] 2, the common contact 21c of the switch 21 is connected to an external terminal 41d via a lead wire 71, the normally closed contact 21b is connected to the neutral node 24, and the normally open contact 21a is connected to a V-phase output line 62 of the inverter 4. The common contact 22c of the switch 22 is connected to an external terminal 42d via a lead wire 72, the normally closed contact 22b is connected to the neutral node 24, and the normally open contact 22a is connected to a W-phase output line 63 of the inverter 4. The common contact 23c of the switch 23 is connected to an external terminal 43d via a lead wire 73, the normally closed contact 23b is connected to the neutral node 24, and the normally open contact 23a is connected to a U-phase output line 61 of the inverter 4.

[0020] In Fig. 3, when no current flows through the excitation coils 211, 221, 231, the switches 21, 22, 23 are switched to the normally closed contact side as shown in the figure, i.e., the common contacts 21c, 22c, 23c are connected to the normally closed contacts 21b, 22b, 23b. In this state, the motor 1 is in a Y-connection state. When current flows through the excitation coils 211, 221, 231, the switches 21, 22, 23 are switched to the normally open contact side as opposed to the state shown in the figure, i.e., the common contacts 21c, 22c, 23c are connected to the normally open contacts 21a, 22a, 23a. In this state, the motor 1 is in a Δ-connection state.

[0021] As explained above, when the connection selection signal Sc has a first value, for example, Low, the motor 1 is in a Y-connection state. When the connection selection signal Sc has a second value, for example, High, the motor 1 is in a Δ-connection state. Hereinafter, the control for switching the windings of the motor 1 between the Y-connection and the Δ-connection will be referred to as "connection switching control" as appropriate.

[0022] Next, the advantages of switching the connection state of the electric motor 1 to either the Y connection or the Δ connection will be described with reference to Fig. 4. Fig. 4 is a diagram showing two connection states that can be switched in the electric motor 1 shown in Fig. 1.

[0023] Figure 4(a) shows the connection state when the three windings are connected in a Y-connection, and Figure 4(b) shows the connection state when the three windings are connected in a Δ-connection. The line voltage in the Y-connection is V Y , the current flowing in is I Y The line voltage in the Δ connection is V Δ , the current flowing in is I Δ Assume that the voltages applied to the windings of each phase are equal. In this case, the voltage V Y and voltage V Δ The relationship between them is expressed by the following equation (1).

[0024]

number

[0025] In addition, the current I Y and current I Δ The relationship between them is expressed by the following equation (2).

[0026]

number

[0027] Voltage V when wired in Y Y and current I Y and the voltage V when connected in delta Δ and current I Δ When these have the relationship of the above formulas (1) and (2), the power supplied to the motor 1 in the Y connection and the Δ connection are equal. In other words, when the power supplied to the motor 1 is equal, the Δ connection requires a larger current to drive it and conversely requires a lower voltage to drive it.

[0028] If the motor 1 is a synchronous motor, as the rotation speed increases, that is, as the load increases, the back electromotive force increases and the voltage required for driving the motor increases. As described above, this back electromotive force is greater in the Y connection than in the Δ connection.

[0029] When the motor 1 is a permanent magnet motor, it is possible to reduce the magnetic force of the permanent magnet or the number of turns of the winding in order to suppress the back electromotive force at higher speeds, but doing so would increase the current required to obtain the same output torque, which would increase the current flowing through the motor 1 and inverter 4, reducing the efficiency of the device.

[0030] Therefore, it is possible to switch the connection depending on the rotation speed. For example, in high-load areas where high-speed operation is required, the connection state is set to Δ connection. This makes it possible to reduce the voltage required for drive to 1 / √3 compared to Y connection. This eliminates the need to reduce the number of turns of the windings, and suppresses the decrease in efficiency.

[0031] On the other hand, in the low load region where operation at low speed is possible, the connection state is Y connection. This makes it possible to reduce the current value required for driving to 1 / √3 compared to the Δ connection. Also, since high speed operation is not required in the Y connection state, it becomes possible to design the windings in the Y connection state so that they are suitable for driving at low speed. This makes it possible to reduce the current value compared to when the Y connection is used over the entire speed range. This makes it possible to reduce losses in the inverter 4 and increase the efficiency of the device.

[0032] From the above, by switching the connections of the electric motor 1 according to the load conditions, it is possible to improve the efficiency at low loads while also increasing the output at high loads.

[0033] The control unit 30 controls the boost converter 3 to change the bus voltage output from the boost converter 3. The control unit 30 also controls the inverter 4 to change the frequency and voltage value of the voltage applied to the motor 1. Furthermore, the control unit 30 controls the connection switching device 20 to switch the connection state of the motor 1 between Y connection and Δ connection.

[0034] In this paper, the Y connection is an example of the first connection, and the Δ connection is an example of the second connection. As long as the relationship in formula (1) above holds between the voltages between the terminals of the first and second connections, and the relationship in formula (2) above holds between the currents flowing through the windings, connections other than the Y connection and Δ connection may be used.

[0035] Fig. 5 is a diagram showing an example of the detailed configuration of the control unit 30 according to embodiment 1. As shown in Fig. 5, the control unit 30 can be configured to include an operation command unit 31, a bus voltage control unit 32, and an inverter control unit 33.

[0036] 5 also shows a voltage detection unit 6 and current detection units 7 and 8. The voltage detection unit 6 detects the bus voltage Vdc output by the boost converter 3, and outputs the detected value to a bus voltage control unit 32. The current detection unit 7 detects the bus current Idc flowing between the boost converter 3 and the inverter 4, and outputs the detected value to an inverter control unit 33. The current detection unit 8 detects the motor current Im flowing through the motor 1, and outputs the detected value to an operation command unit 31.

[0037] The operation command unit 31 determines the bus voltage command value Vdc * and the frequency command value ω * The zero selection signal Sz and the above-mentioned connection selection signal Sc are calculated. * is output to the bus voltage control unit 32, and the frequency command value ω * The zero selection signal Sz is output to the inverter control unit 33. Information on the motor current Im is referred to by the operation command unit 31 whenever necessary.

[0038] As described above, when the Y connection is selected, the connection selection signal Sc is controlled to a first value (e.g., Low), and when the Δ connection is selected, the connection selection signal Sc is controlled to a second value (e.g., High).

[0039] The zero selection signal Sz is normally controlled to a first value (eg, Low), and is controlled to a second value (eg, High) during a period of zero current control, which will be described later.

[0040] The operation command unit 31 determines, for example, whether the windings of the electric motor 1 are to be Y-connected or Δ-connected, and determines the target rotation speed, and generates a connection selection signal Sc and a frequency command value ω based on this determination. * are output to the connection switching device 20 and the inverter control unit 33, respectively.

[0041] Here, consider a case where the device 5 connected to the motor 1 is, for example, an air conditioner. In the air conditioner, the control unit 30 determines to use a Δ connection when the difference between the room temperature and the set temperature is large, and sets the connection selection signal Sc to a second value. Also, the operation command unit 31 sets the target rotation speed to a relatively high value, and after startup, sets a frequency command value ω that gradually increases the frequency to the frequency corresponding to the set target rotation speed. * When the frequency corresponding to the target rotation speed is reached, the operation command unit 31 maintains that state until the room temperature approaches the set temperature, and when the room temperature approaches the set temperature, sets the connection selection signal Sc to a first value and switches to a Y connection. Thereafter, the operation command unit 31 performs control to maintain the room temperature close to the set temperature. Note that these controls include adjusting the frequency, stopping the motor 1, restarting it, and the like.

[0042] In addition, the operation command unit 31 changes the value of the connection selection signal Sc in order to switch from one of the Y connection and the Δ connection to the other, and also changes the frequency command value ω * and temporarily changing the value of the zero selection signal Sz.

[0043] For example, when switching the connection state, the operation command unit 31 changes the bus voltage command value Vdc * and frequency command value ω * is temporarily set to a larger value. Then, the bus voltage command value Vdc * and frequency command value ω * is set to a larger value, the zero selection signal Sz is temporarily changed from a first value (e.g., Low) to a second value (e.g., High). Then, during the period in which the zero selection signal Sz is at the second value, the connection selection signal Sc is switched from the second value to the first value, or from the first value to the second value.

[0044] The bus voltage control unit 32 determines the bus voltage command value Vdc * Based on the detected value of the bus voltage Vdc and the drive signal Xn, the boost converter 3 generates the drive signal Xn and outputs it to the boost converter 3. The boost converter 3 controls the bus voltage Vdc to be equal to or higher than the bus voltage command value Vdc in accordance with the drive signal Xn. *A switching element (not shown) in the boost converter 3 is operated so that the output voltage Vout coincides with the reference voltage Vout.

[0045] The inverter control unit 33 generates a pulse width modulation (PWM) signal Sm based on the detected values ​​of the bus voltage Vdc and the bus current Idc, and outputs the signal Sm to the inverter 4. The inverter 4 drives the motor 1 by maintaining or changing the frequency and voltage value of the output voltage in accordance with the PWM signal Sm.

[0046] Next, a description will be given of the operation of the driving device 100 when the connection switching device 20 is operated while the electric motor 1 is in operation. This operation includes zero current control, which is a characteristic control in the first embodiment. The zero current control is a control for switching the winding connections while the current of the electric motor 1 is set to zero.

[0047] As described above, when the connection state of the motor 1 is switched between the two, the switches 21, 22, and 23 of the connection switching device 20 are operated. In this operation, the switches 21, 22, and 23 switch the connection of the common contacts 21c, 22c, and 23c between the normally closed contacts 21b, 22b, and 23b and the normally open contacts 21a, 22a, and 23a. If this switching operation is performed while the motor 1 is in operation, that is, while power is being supplied from the inverter 4 to the motor 1, an arc discharge may occur between the contacts of the switches 21, 22, and 23, which may cause a failure such as contact welding.

[0048] In order to avoid such a failure, it is conceivable to stop the power supply from the inverter 4 to the motor 1 before operating the connection switching device 20, and to perform the switching in a state where the rotation speed of the motor 1 is zero.

[0049] However, if the rotation speed of the motor 1 is set to zero, the torque required for restarting increases, and the current at start-up may increase or restarting may become impossible. For example, if the device 5 driven by the motor 1 is an air conditioner, the torque required for restarting increases immediately after the rotation speed is set to zero in order to drive the compressor, since the state of the refrigerant is not stable. It is also possible to restart the motor 1 after a period of time has passed since the rotation speed of the motor 1 was set to zero, which is sufficient for the state of the refrigerant to be sufficiently stabilized. In that case, the compressor will no longer be able to pressurize the refrigerant, and the cooling capacity and heating capacity will decrease, which may result in a large deviation from the desired room temperature.

[0050] Therefore, the current flowing through the connection switching device 20 is controlled to be zero, and the connection switching device 20 is made to perform switching operation in this state. This control is called zero current control. By using the zero current control, it is possible to prevent arc discharge from occurring between the contacts of the switches 21, 22, and 23 when switching the connection state. Furthermore, by using the zero current control, it is no longer necessary to take the trouble of setting the rotation speed of the motor 1 to zero every time the connection state is switched.

[0051] In order to make the current flowing through the connection switching device 20 zero, the current flowing through the motor 1 is detected and the switching operation of the inverter 4 is controlled to make the current zero. Alternatively, the current is cut off by stopping the switching operation of the inverter 4. This can also be achieved by using both of these methods in combination.

[0052] However, when implementing the above-mentioned zero current control, the following points must be noted. First, when switching the winding connections of the motor 1, it is necessary to maintain a zero current state for a certain amount of time. During the zero current control period, the output torque of the motor 1 is zero, and the rotation speed decreases in proportion to the magnitude of the load torque applied to the motor 1. Also, the longer the period of zero current control and the greater the load torque, the greater the decrease in the rotation speed. Furthermore, if zero current control is started at a low speed, the rotation speed may decrease to near zero, causing the motor 1 to step out.

[0053] Regarding the decrease in the rotation speed of the electric motor 1, in order to prevent the rotation speed from dropping to near zero, it is conceivable to simply increase the rotation speed of the electric motor 1 and perform zero current control in that state.

[0054] However, as the rotation speed of the motor 1 increases, the back electromotive force generated in the motor 1 increases, and a voltage equal to or greater than the back electromotive force must be output from the inverter 4. On the other hand, the voltage that can be output from the inverter 4 is restricted by the bus voltage, which is the output voltage of the boost converter 3. The region where the output voltage from the inverter 4 exceeds the upper limit limited by the bus voltage and becomes saturated is called the "overmodulation region."

[0055] In order to suppress the back electromotive force of the motor 1 in the overmodulation region, it is necessary to perform the well-known flux-weakening control, which reduces the magnetic flux generated by the motor 1, which is the source of the back electromotive force. On the other hand, in the flux-weakening control, it is necessary to pass a negative d-axis current. Therefore, the flux-weakening control and the zero current control cannot be achieved at the same time. In addition, when the switching operation of the inverter 4 is stopped, the voltage of the motor 1 increases due to the back electromotive force, and when the voltage of the motor 1 exceeds the bus voltage, a regenerative current is generated from the motor 1 to the inverter 4, and the inverter 4 enters an overvoltage state.

[0056] Therefore, in the first embodiment, before performing zero current control, boost control is performed to increase the bus voltage by the boost converter 3. This boost control makes the bus voltage higher than the voltage of the motor 1 due to the back electromotive force. In this state, zero current control is then performed to switch the connections. Once the connection switching is complete, the bus voltage is returned to its original state. These controls make it possible to switch the connections smoothly even in the high load region.

[0057] Fig. 6 is a first time chart for explaining a control sequence in the connection switching control of the first embodiment. In Fig. 6, switching from Y connection to Δ connection is assumed. In order to avoid complicating the explanation, Fig. 6 does not show a control sequence for avoiding a transition to the overmodulation region. The control sequence for avoiding a transition to the overmodulation region will be explained with reference to Figs. 7 and 8 described later.

[0058] FIG. 6(a) shows the current flowing through the connection switching device 20. FIG. 6(b) shows the change in the zero selection signal Sz. FIG. 6(c) shows the change in the connection selection signal Sc. FIG. 6(d) shows the bus voltage command value Vdc * The change in the frequency command value ω * The changes in are shown.

[0059] As shown in Fig. 6, before switching the connection, the bus voltage command value Vdc * and frequency command value ω * is temporarily increased, zero current control is performed while the current is being increased, and the wiring is switched while the zero current control is being performed. This will be described in more detail below.

[0060] First, before the switching process starts, the bus voltage command value Vdc * is the first voltage value Vdc * (0), and the frequency command value ω * is the first frequency value ω * Assume that motor 1 is driven in state (0).

[0061] After the switching process starts, in the period from time ta1 to time ta2, the bus voltage command value Vdc * The first voltage value Vdc * A second voltage value Vdc that is greater than (0) * (1) (FIG. 6(d)). This causes the boost converter 3 to increase the bus voltage Vdc.

[0062] At time ta2, when the rise of the bus voltage Vdc is completed, the frequency command value ω * The first frequency value ω * A second frequency value ω greater than (0) * (1) (Figure 6(e)). This increases the frequency ω.

[0063] Then, in the period from time tc to time te, the value of the zero selection signal Sz is set to High (FIG. 6(b)), thereby performing zero current control by selecting zero as the current command value (FIG. 6(a)). Also, at time td during the zero current control period, the value of the connection selection signal Sc is changed from Low to High (FIG. 6(c)), thereby switching the contacts of the connection switching device 20.

[0064] When the switching of the contacts of the connection switching device 20 is completed, the frequency command value ω * The original value of the first frequency ω * (0) (Fig. 6(e)). Then, when the rotation speed decreases, the bus voltage command value Vdc * The original value of the first voltage value Vdc * Return to (0) (Figure 6(d)).

[0065] In the above explanation, the bus voltage command value Vdc * There is no delay in the bus voltage Vdc relative to the frequency command value ω * It is assumed that there is no delay in the frequency ω relative to the bus voltage Vdc. If it is necessary to take into consideration the delay in operation, the connection switching device 20 may be switched during the period in which the bus voltage Vdc and the frequency ω are at their larger values. During the zero current control period, the motor 1 generates no torque, and the speed of the motor 1 decreases in proportion to the magnitude of the load torque applied to the motor 1. For this reason, in anticipation of this speed decrease, the frequency command value ω at time te is set to * to the second frequency value ω * (1) Set the frequency to a value lower than the frequency command value ω * is the first frequency value ω* It is also possible that the first frequency value ω * (0) The frequency command value ω * Gives.

[0066] 6, it is assumed that the connection is switched from the Y connection to the Δ connection, but the connection can also be switched from the Δ connection to the Y connection in a similar sequence. However, when switching from the Δ connection to the Y connection, the connection selection signal Sc in FIG. 6(c) switches from High to Low, not from Low to High.

[0067] Note that the sequence in Fig. 6 is just an example, and sequences other than those in Fig. 6 may also be used. However, when performing zero current control in the high speed rotation range, it is necessary to increase the bus voltage Vdc to increase the voltage that can be output from the inverter 4 before driving the motor 1.

[0068] Next, the bus voltage command value Vdc for the boost converter 3 during the zero current control is * The set values ​​of the motor 1 will be described. Any type of motor may be used as the motor 1, but a permanent magnet synchronous motor will be taken as an example for description here.

[0069] First, the voltage equations on the dq coordinate axes of a permanent magnet synchronous motor are expressed by the following equations (3) and (4).

[0070]

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[0071] In the above equations (3) and (4), Vd and Vq represent the dq-axis components of the armature voltage, and id and iq represent the dq-axis components of the armature current. Ld and Lq represent the dq-axis inductances, and Ra represents the armature winding resistance. Φa represents the armature flux linkage, and p represents the differential operator. ω is the rotation speed expressed in electrical angle.

[0072] Here, in the above equations (3) and (4), id = iq = 0 due to the previously described zero current control. Also, as previously described, the zero current control continues from time tc to time te, so p·id = p·iq = 0. Therefore, the following equation (5) holds from the above equation (4).

[0073]

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[0074] Furthermore, as described above, when performing zero current control, it is necessary to boost the bus voltage Vdc. The condition of the bus voltage Vdc can be expressed by the following equation (6) based on the above equation (5).

[0075]

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[0076] The value of the armature flux linkage Φa varies depending on the connection state, but it is necessary to use the larger of the values ​​before and after the connection switching. For example, the value of the armature flux linkage Φa in the Y connection is √3 times the value of the armature flux linkage Φa in the Δ connection. Here, for example, when switching from the Δ connection to the Y connection, it is considered that the bus voltage Vdc is set using the value of the Δ connection as the armature flux linkage Φa in the above formula (6). After setting in this way, if the speed reduction of the motor 1 during the zero current control period is small, it is assumed that the armature voltage due to the back electromotive force of the motor 1 will be larger than the set value of the bus voltage Vdc. Therefore, immediately after switching from the Δ connection to the Y connection, the armature voltage due to the back electromotive force of the motor 1 will exceed the voltage that can be output from the inverter 4, and an overvoltage may occur in the inverter 4.

[0077] For this reason, when the connection state of the motor 1 is switched between the Y connection and the Δ connection, the value of the armature interlinkage magnetic flux Φa in the Y connection is used. In addition, in order to suppress overvoltage, the frequency command value ω * In addition, in order to suppress overvoltage, an upper limit is set on the rotation speed when the connection of the motor 1 is switched based on the bus voltage Vdc.

[0078] Next, the connection switching control considering the load state at the time of connection switching will be described with reference to Figs. 7 and 8. Fig. 7 is a second time chart for explaining the control sequence in the connection switching control of the first embodiment. Fig. 8 is a flowchart showing an example of a process flow for implementing the control sequence of Fig. 7. The connection switching control considering the load state here is a control for switching the connection state of the motor 1 without entering the overmodulation region when switching the connection state. As described above, flux weakening control and zero current control in the overmodulation region cannot be achieved at the same time. By using the control sequence of Fig. 7 and the flowchart of Fig. 8, it becomes possible to switch the connection state of the motor 1 without entering the overmodulation region.

[0079] FIG. 7 shows the switching operation from the Δ connection to the Y connection. Specifically, FIG. 7(a) shows the change in the rotation speed of the motor 1. FIG. 7(b) shows the change in the armature voltage together with the bus voltage Vdc. FIG. 7(c) shows the change in the connection selection signal Sc. FIG. 7(d) shows the change in the bus voltage command value Vdc. * The changes in are shown.

[0080] First, as a preparation for the connection switching, the bus voltage command value Vdc * The maximum bus voltage command value Vdc_ max * and the bus voltage Vdc is increased (Figure 7(d)).

[0081] After the boost of the bus voltage Vdc is completed, the control unit 30 judges whether or not the voltage is in the overmodulation region (FIG. 8: step S500). If the voltage is in the overmodulation region at this point, it is necessary to perform flux-weakening control, and the current of the motor 1 cannot be controlled to zero. Furthermore, when the switching operation of the inverter 4 is stopped, a regenerative current is generated from the motor 1 side to the inverter 4, resulting in an overvoltage state.

[0082] Therefore, if the frequency is in the overmodulation region (FIG. 8: step S500, No), the control unit 30 sets the frequency command value ω * (FIG. 8: step S501). * The armature voltage of the motor 1 is reduced by lowering the armature voltage, and then it is determined again whether the motor has entered the overmodulation region (FIG. 8: step S500).

[0083] If it is determined that the motor is not in the overmodulation region (FIG. 8: step S500, Yes), the control unit 30 acquires information on the rotation speed and the load torque of the motor 1 before the zero current control period (FIG. 8: step S502). The information on the load torque is, for example, the rotation speed and the frequency command value ω * The frequency command value ω * Specifically, the load torque Tload of the electric motor 1 can be calculated using the following equation (7).

[0084]

number

[0085] In the above formula (7), Pn represents the number of pole pairs of the electric motor 1.

[0086] The control unit 30 calculates the rotation speed drop amount during the zero current control period (FIG. 8: step S503). The rotation speed drop amount is the amount of rotation speed drop during the zero current control period, and can be obtained from the calculated value of the load torque Tload before the zero current control period. The control unit 30 determines whether the rotation speed before the zero current control period exceeds the upper limit of the rotation speed (FIG. 8: step S504).

[0087] The amount of rotational speed drop caused by the load torque Tload during the zero current control period is represented as Δω. Note that in this paper, the rotational speed is also sometimes represented by the symbol ω.

[0088] In addition, the upper limit of the rotation speed taking into account the rotation speed drop amount Δω is set as β Tmax The upper limit of this rotation speed is β Tmax is expressed by the following equation (8).

[0089]

number

[0090] In the above formula (8), Vdc _max represents the maximum value of the output voltage of the boost converter 3, i.e., the maximum value of the bus voltage Vdc, and Φy represents the armature flux linkage in the Y-connection. The rotation speed drop amount Δω depends on the load torque Tload. Therefore, the upper limit value β of the rotation speed Tmax will vary depending on the load conditions of the motor 1.

[0091] During the zero current control period, the strictest condition occurs when no load torque is applied to the motor 1. The condition in this case can be expressed by the following equation (9).

[0092]

number

[0093] In the above formula (9), β max is the upper limit of the rotation speed when the rotation speed drop amount Δω is not taken into consideration.

[0094] When the rotation speed before the zero current control period exceeds the upper limit of the rotation speed (FIG. 8: step S504, No), the control unit 30 adjusts the frequency command value ω * (FIG. 8: step S505), and again acquires information on the rotation speed and the load torque Tload before the zero current control period (FIG. 8: step S502). Then, the control unit 30 calculates the amount of decrease in the rotation speed during the zero current control period (FIG. 8: step S503), and again performs the determination process of step S504.

[0095] On the other hand, if the rotation speed before the zero current control period does not exceed the upper limit of the rotation speed (FIG. 8: Step S504, Yes), the control unit 30 performs wiring switching (FIG. 8: Step S506).

[0096] As described above, the processes of steps S502 to S505 are repeated until the judgment process of step S504 becomes "Yes". By these processes, as shown in Fig. 7(a), the rotation speed immediately before and after the zero current control period and during the zero current control period does not exceed the upper limit of the rotation speed. This makes it possible to avoid entering the overmodulation region when the wiring connection is switched.

[0097] As described above, the rotation speed drop amount Δω depends on the load torque Tload. Therefore, if a table of the rotation speed drop amount Δω corresponding to the load torque Tload is stored in the control unit 30, the upper limit value β of the rotation speed can be easily calculated. Tmax This makes it easier to calculate.

[0098] By performing connection switching according to the above sequence, it is possible to perform connection switching with the current at zero without entering the overmodulation region when switching the connection.

[0099] In the process flow of FIG. 8, the upper limit value β Tmaxis set as a constraint. On the other hand, if the connection state is switched when the rotation speed is low, the rotation speed will decrease during the zero current control period, and the rotation speed may drop to near zero, causing the motor 1 to step out. Also, if the rotation speed of the motor 1 drops to near zero, it may be necessary to restart the motor 1. For this reason, there is also a constraint on the lower limit of the rotation speed.

[0100] Therefore, in the first embodiment, β shown in the following formula (10) min is set as the lower limit of the rotation speed.

[0101]

number

[0102] In the above formula (10), T mmax represents the maximum load torque, and J m represents the inertia around the rotating shaft of the motor 1, and T0 [sec] represents the length of the zero current control period, i.e., the zero current control time. min The minimum guaranteed rotation speed ω min It is preferable to add a margin as shown in the following equation (11).

[0103]

number

[0104] In addition, in the control sequence of Fig. 7, the bus voltage command value Vdc * The maximum bus voltage command value Vdc_ max * Instead, the bus voltage command value Vdc is set to * A sequence may be inserted to gradually increase the boost amount of the boost converter 3 so that the lower limit value β of the rotation speed becomes a value corresponding to the rotation speed. minThe minimum guaranteed rotation speed ω min It is preferable to add a margin as shown in the above formula (11). The upper limit value β of the above formula (9) max is the lower limit value β of the above equation (11). min The boost amount of the boost converter 3 is increased so that the output voltage does not fall below the upper limit value β max is the lower limit value β of the above equation (11). min If the rotation speed does not exceed the maximum rotation speed, the connection can be switched in a sequence to lower the rotation speed.

[0105] In this way, the upper limit value β of the rotation speed obtained by the armature interlinkage magnetic flux Φy in the Y-connection and the load torque Tload of the motor 1 is Tmax and the lower limit of the rotation speed β min Based on this, the frequency command value ω * (1) is set (see FIG. 6(e)). However, during the zero current control period, the rotation speed drop amount Δω due to the maximum load torque Tmmax is set to the upper limit value β Tmax and the lower limit of the rotation speed β min In the example shown in FIG. 8(a), the rotation speed drop amount Δω due to the maximum load torque Tmmax is greater than the upper limit value β of the rotation speed. Tmax and the lower limit of the rotation speed β min This is an example where the difference is within the range of .

[0106] As described above, by using the connection switching control according to the first embodiment, it is possible to reliably perform the zero current control required for suppressing arcs between the contacts of the switches 21, 22, and 23 when switching the connection of the electric motor 1. Furthermore, by using the connection switching control according to the first embodiment, it is possible to reliably suppress overvoltage that may occur in the internal circuit of the drive device 100, regardless of the load state at the time of switching the connection.

[0107] The above-mentioned functions of the control unit 30 can be realized by the hardware configuration shown in Fig. 9 or Fig. 10. Fig. 9 is a block diagram showing an example of a hardware configuration for realizing the functions of the control unit 30 according to the first embodiment. Fig. 10 is a block diagram showing another example of a hardware configuration for realizing the functions of the control unit 30 according to the first embodiment.

[0108] When realizing some or all of the functions of the control unit 30 in embodiment 1, the configuration can include a processor 300 that performs calculations, a memory 302 in which programs read by the processor 300 are stored, and an interface 304 that inputs and outputs signals, as shown in FIG. 9.

[0109] The processor 300 is an example of a calculation means called a calculation device, a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The memory 302 can be an example of a non-volatile or volatile semiconductor memory such as a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an EPROM (Erasable Programmable ROM), or an EEPROM (registered trademark) (Electrically EPROM), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, or a DVD (Digital Versatile Disc).

[0110] The memory 302 stores a program for executing the functions of the control unit 30 according to the first embodiment. The processor 300 receives and transmits necessary information via the interface 304, executes the program stored in the memory 302, and refers to the table stored in the memory 302, thereby performing the above-mentioned processing. The calculation results by the processor 300 can be stored in the memory 302.

[0111] In addition, when implementing part of the functions of the control unit 30 according to the first embodiment, a processing circuit 305 shown in Fig. 10 can be used. The processing circuit 305 corresponds to a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination of these. Information to be input to the processing circuit 305 and information to be output from the processing circuit 305 can be obtained via an interface 304.

[0112] It should be noted that some of the processes in the control unit 30 may be performed by the processing circuit 305 , and the processes that are not performed by the processing circuit 305 may be performed by the processor 300 and the memory 302 .

[0113] As described above, the drive device according to the first embodiment includes a boost converter, an inverter, a connection switching device that switches the windings of the motor between the first connection and the second connection, and a control unit that controls the boost converter, the inverter, and the connection switching device. The control unit performs zero current control to switch the winding connections with the current of the motor set to zero. In addition, in a state in which the second connection is selected by the connection switching device, if the rotation speed of the motor before the zero current control period does not exceed the upper limit of the rotation speed, the control unit switches to the first connection. This makes it possible to switch the winding connections even while the motor is rotating. In addition, it is possible to suppress overvoltage that may occur in the internal circuit of the drive device regardless of the load state at the time of connection switching.

[0114] Furthermore, in the drive device according to the first embodiment, when the first connection is selected by the connection switching device and the state transitions from a first state in which the bus voltage is a first voltage value and the rotation speed of the motor is a first speed value to a second state in which the bus voltage is higher than the first voltage value and the current flowing through the motor is equal to or lower than a predetermined threshold, the control unit switches from the first connection to the second connection. This makes it possible to avoid an increase in size of the device and obtain a highly reliable drive device.

[0115] Embodiment 2 Fig. 11 is a diagram showing a configuration example of a refrigeration cycle apparatus 900 according to the second embodiment. The refrigeration cycle apparatus 900 according to the second embodiment includes the drive device 100 described in the first embodiment. The refrigeration cycle apparatus 900 according to the second embodiment can be applied to products including a refrigeration cycle, such as air conditioners, refrigerators, freezers, and heat pump water heaters. In Fig. 11, components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment.

[0116] The refrigeration cycle device 900 includes a compressor 901 incorporating the electric motor 1 in embodiment 1, a four-way valve 902, an indoor heat exchanger 906, an expansion valve 908, and an outdoor heat exchanger 910, which are attached via refrigerant piping 912.

[0117] Inside the compressor 901, a compression mechanism 904 that compresses the refrigerant, and an electric motor 1 that operates the compression mechanism 904 are provided.

[0118] The refrigeration cycle apparatus 900 can perform heating operation or cooling operation by switching the four-way valve 902. The compression mechanism 904 is driven by the electric motor 1 which is variably controlled in speed.

[0119] During heating operation, as indicated by the solid arrow, the refrigerant is pressurized by the compression mechanism 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 returns to the compression mechanism 904.

[0120] During cooling operation, as indicated by the dashed arrow, the refrigerant is pressurized by the compression mechanism 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 compression mechanism 904.

[0121] During heating operation, the indoor heat exchanger 906 acts as a condenser to release heat, and the outdoor heat exchanger 910 acts as an evaporator to absorb heat. During cooling operation, the outdoor heat exchanger 910 acts as a condenser to release heat, and the indoor heat exchanger 906 acts as an evaporator to absorb heat. The expansion valve 908 reduces the pressure of the refrigerant to expand it.

[0122] The refrigeration cycle apparatus 900 according to the second embodiment is equipped with the drive device 100 according to the first embodiment, and therefore can enjoy the effects obtained in the first embodiment.

[0123] It should be noted that the configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0124] REFERENCE SIGNS LIST 1 electric motor, 2 AC power source, 3 boost converter, 4 inverter, 5 equipment, 6 voltage detection unit, 7, 8 current detection unit, 20 connection switching device, 21, 22, 23 switch, 21a, 22a, 23a normally open contact, 21b, 22b, 23b normally closed contact, 21c, 22c, 23c common contact, 24 neutral node, 30 control unit, 31 operation command unit, 32 bus voltage control unit, 33 inverter control unit, 41, 42, 43 winding, 41a, 42a, 43a first end, 41b, 42b, 43b second end, 41c, 42c, 43c, 41d, 42d, 43d external terminal, 61, 62, 63 output line, 71, 72, 73 lead wire, 100 drive unit, 204 Semiconductor switch, 211, 221, 231 exciting coil, 300 processor, 302 memory, 304 interface, 305 processing circuit, 900 refrigeration cycle device, 901 compressor, 902 four-way valve, 904 compression mechanism, 906 indoor heat exchanger, 908 expansion valve, 910 outdoor heat exchanger, 912 refrigerant piping.

Claims

1. a boost converter that receives an AC voltage output from an AC power supply and outputs a DC voltage having a variable voltage value; an inverter that converts the bus voltage output from the boost converter into an AC voltage having a variable voltage and a variable frequency and applies the AC voltage to an electric motor; a connection switching device that switches the windings of the motor between a first connection and a second connection; a control unit that controls the boost converter, the inverter, and the connection switching device; Equipped with the control unit performs zero current control to switch the connections of the windings while keeping the current of the motor at zero, When the rotation speed of the motor before the zero current control period does not exceed an upper limit value of the rotation speed in a state in which the second connection is selected by the connection switching device, switching to the first connection is performed. Drive unit.

2. The winding connections are switched while an upper limit is set for the bus voltage. The drive device according to claim 1 .

3. The control unit switches from the first connection to the second connection when, in a state in which the first connection is selected by the connection switching device, a transition is made from a first state in which the bus voltage is a first voltage value and the rotation speed of the motor is a first speed value to a second state in which the bus voltage is higher than the first voltage value and the current flowing through the motor is equal to or lower than a predetermined threshold value. The drive device according to claim 1 .

4. The first connection is a star connection and the second connection is a delta connection. The drive device according to claim 3.

5. A detection unit is provided for detecting a motor current flowing through the motor, The control unit estimates a rotation speed and also estimates a load torque applied to the motor based on a detected value of the motor current. The drive device according to claim 3.

6. the motor is a permanent magnet motor, The maximum value of the bus voltage when switching is Vdc_ ｍａｘ year, The rotation speed of the motor when the switching is performed is denoted by ω, When the armature interlinkage magnetic flux of the permanent magnet motor when the switching is performed is denoted by Φy, Before the transition to the second state, the following formula (1) is satisfied: The drive device according to claim 5. [0010]

7. the motor is a permanent magnet motor, The maximum value of the bus voltage when switching is Vdc_ ｍａｘ year, The rotation speed of the motor when the switching is performed is denoted by ω, The armature flux linkage of the permanent magnet motor when the switching is performed is defined as Φy, The rotation speed drop amount when switching is set to Δ ω When Before the transition to the second state, the following formula (2) is satisfied: The drive device according to claim 5. [0025]

8. The minimum guaranteed operating speed when switching is ω ｍｉｎ year, The inertia around the rotating shaft of the motor when the switching is performed is J ｍ year, The maximum load torque when the switching is performed is T ｍｍａｘ year, The zero current control period when the switching is performed is defined as T ０ When Before the transition to the second state, the following formula (3) is satisfied:

7. The drive device according to claim 6. [0030]

9. The bus voltage is Vdc, The maximum value of the bus voltage when switching is Vdc_ ｍａｘ year, The rotation speed of the motor when the switching is performed is denoted by ω, The armature flux linkage of the permanent magnet motor when the switching is performed is defined as Φy, The rotation speed drop amount when switching is set to Δ ω When When the rotation speed ω in the first state does not satisfy the following formula (4), the boost converter boosts the bus voltage Vdc, The bus voltage Vdc is the maximum value Vdc of the bus voltage ＿ｍａｘ If the following formula (4) is not satisfied even if the pressure is increased to the value, the rotation speed is reduced.

7. The drive device according to claim 6. [0045]

10. The rotation speed drop amount is calculated based on the load torque before the zero current control period. The drive device according to claim 7.

11. A refrigeration cycle apparatus comprising the drive device according to any one of claims 1 to 10.

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