WO2020066028A1 - Motor drive device and air conditioner - Google Patents

Abstract

A motor drive device (100) is equipped with: a booster circuit (3) for boosting AC voltage that is output from an AC power supply (1); a capacitor (4) for smoothing DC voltage that is output from the booster circuit (3); an inverter circuit (18) for converting power accumulated in the capacitor (4) to AC power and supplying the AC power to a motor; and a connection switching unit (60) for switching, by means of a switching signal, the connection state of the motor (500) windings between a star connection and a delta connection. At a first rotational speed that is the rotational speed at a switching point where switching of the connection state of the windings between the star connection and the delta connection is performed, it is possible to boost the output voltage of the booster circuit (3) to a first voltage that is higher than the output voltage of the booster circuit (3) when the booster circuit (3) is not caused to perform boost operation.

Description

Motor drive device and air conditioner

The present invention relates to a motor driving device for driving a motor, and an air conditioner including the motor driving device.

Patent Literature 1 listed below discloses a technique for increasing the efficiency of an air conditioner, in which the connection of a stator winding (hereinafter simply referred to as “winding”) of a motor is switched between a star connection and a delta connection. A configuration of a motor driving device is disclosed. In this patent document, a technique is proposed in which a star connection is used in a low-speed rotation region and a delta connection is used in a high-speed rotation region to expand a high-speed rotation region and increase efficiency in a low-speed rotation region.

Japanese Patent No. 4619826

However, when the star connection and the delta connection are used at the same bus voltage, the number of windings of the winding is determined based on the motor applied voltage in the delta connection according to the requirement of the rotation speed in the high-speed rotation region. For this reason, there is room for improvement in the efficiency in the low-speed rotation region using the star connection.

The present invention has been made in view of the above, and an object of the present invention is to provide a motor drive device capable of further improving efficiency in a low-speed rotation range.

In order to solve the above-described problem and achieve the object, a motor driving device according to the present invention includes at least one switching element, and converts an AC voltage output from an AC power supply into a DC voltage by opening and closing the switching element. A booster circuit for converting and boosting is provided. Further, the motor driving device includes a capacitor for smoothing a DC voltage output from the booster circuit, and an inverter circuit for converting power stored in the capacitor into AC power and supplying the AC power to the motor. The motor has a plurality of windings, the windings are open at both ends, and by changing the connection destination at both ends, the winding connection state can be changed between the first connection state and the second connection state. Can be switched to The motor applied voltage in the first connection state is higher than the motor applied voltage in the second connection state under the same motor rotation speed. At the first rotation speed, which is the rotation speed at the switching point at which the connection state of the winding is switched between the first connection state and the second connection state, the output voltage of the booster circuit increases when the booster circuit is not operated. Can be boosted to a first voltage higher than the rectified voltage which is the output voltage of the rectifier.

According to the motor drive device of the present invention, there is an effect that the efficiency in the low-speed rotation range can be further improved.

1 is a circuit diagram showing a configuration of a motor drive device according to a first embodiment. FIG. 1 is a circuit diagram showing a detailed configuration of the inverter circuit shown in FIG. FIG. 2 is a circuit diagram showing a configuration of the inverter circuit shown in FIG. 1 which is different from FIG. FIG. 11 is a diagram for describing another example of the first and second connection states according to the first embodiment. FIG. 7 is a diagram for describing an operation mode of the motor drive device according to the first embodiment. FIG. 4 is a diagram showing one current path in the passive synchronous rectification mode in the booster circuit of the first embodiment. The figure which shows the current-loss characteristic in the general switching element typically FIG. 5 shows one of current paths in the simple switching mode in the booster circuit of the first embodiment. FIG. 7 is a diagram for explaining the relationship between the connection state and the efficiency in the connection switching motor according to the first embodiment. FIG. 7 is a diagram for describing initial matters when configuring the connection switching motor according to the first embodiment. FIG. 7 is a diagram for describing output voltage control in the booster circuit according to the first embodiment. FIG. 2 is a block diagram illustrating an example of a hardware configuration that implements the function of the control unit according to the first embodiment. FIG. 4 is a block diagram showing another example of a hardware configuration that embodies the function of the control unit according to the first embodiment. The figure which shows the example of a structure of the air conditioner which concerns on Embodiment 2. Time chart showing an example of the operation method of the air conditioner according to Embodiment 2.

Hereinafter, a motor drive device and an air conditioner according to an embodiment of the present invention will be described with reference to the accompanying drawings. The present invention is not limited by the embodiments described below. In the description below, the electrical connection is simply referred to as “connection”.

Embodiment 1 FIG.
FIG. 1 is a circuit diagram showing a configuration of the motor drive device 100 according to the first embodiment. FIG. 2 is a circuit diagram showing a detailed configuration of the inverter circuit shown in FIG.

The motor drive device 100 according to the first embodiment converts AC power supplied from a single-phase AC power supply 1 into DC power, as shown in FIG. In addition, the motor driving device 100 converts the converted DC power into AC power again, and supplies the converted AC power to the motor 500 as a load to drive the motor 500. An example of the motor 500 is a motor built in a blower, a compressor, or an air conditioner.

In FIG. 1, the motor driving device 100 includes a booster circuit 3, a capacitor 4, a control unit 10, an inverter circuit 18 including a current detector 18S, a connection switching unit 60, and a voltage serving as a first voltage detector. It includes a detector 5 and a voltage detector 7 as a second voltage detector.

The booster circuit 3 is a boost converter that converts an AC voltage output from the AC power supply 1 into a DC voltage and boosts the DC voltage by opening and closing a switching element described later. When converting the AC voltage into the DC voltage, the booster circuit 3 controls the voltage value of the converted DC voltage, that is, boosts the voltage value. Note that the AC voltage output from the AC power supply 1 is referred to as “power supply voltage” and is represented by “Vs”.

(4) The booster circuit 3 includes the reactor 2, a first leg 31, and a second leg 32. The first leg 31 and the second leg 32 are connected in parallel. In the first leg 31, a first upper arm element 311 and a first lower arm element 312 are connected in series. In the second leg 32, a second upper arm element 321 and a second lower arm element 322 are connected in series. One end of reactor 2 is connected to AC power supply 1. The other end of the reactor 2 is connected to a connection point 3 a between the first upper arm element 311 and the first lower arm element 312 in the first leg 31. A connection point 3 b between the second upper arm element 321 and the second lower arm element 322 is connected to the other end of the AC power supply 1. In the booster circuit 3, the connection points 3a and 3b constitute an AC terminal.

The first upper arm element 311 includes a switching element Q1 and a diode D1 connected in anti-parallel to the switching element Q1. First lower arm element 312 includes a switching element Q2 and a diode D2 connected in anti-parallel to switching element Q2. Second upper arm element 321 includes switching element Q3 and diode D3 connected in antiparallel to switching element Q3. Second lower arm element 322 includes a switching element Q4 and a diode D4 connected in anti-parallel to switching element Q4.

In FIG. 1, each of the switching elements Q1, Q2, Q3, and Q4 is exemplified by a metal oxide semiconductor field effect transistor (Metal Oxide Semiconductor Field Effect Transistor: MOSFET), but is not limited to a MOSFET. A MOSFET is a switching element capable of flowing current bidirectionally between a drain and a source. Any switching element can be used as long as current can flow bidirectionally between the first terminal corresponding to the drain and the second terminal corresponding to the source.

{In addition, antiparallel means that the first terminal corresponding to the drain of the MOSFET is connected to the cathode of the diode, and the second terminal corresponding to the source of the MOSFET is connected to the anode of the diode. Note that a parasitic diode included in the MOSFET itself may be used as the diode. Parasitic diodes are also called body diodes.

At least one of the switching elements Q1, Q2, Q3, and Q4 is not limited to a MOSFET formed of a silicon-based material, and is formed of a wide band gap semiconductor such as silicon carbide, gallium nitride, gallium oxide, or diamond. MOSFET may be used.

ワ イ ド Generally, wide band gap semiconductors have higher withstand voltage and heat resistance than silicon semiconductors. Therefore, by using a wide band gap semiconductor for at least one of the switching elements Q1, Q2, Q3, and Q4, the withstand voltage and the allowable current density of the switching element are increased, and the semiconductor module incorporating the switching element is reduced in size. Can be

Note that three of the switching elements Q1, Q2, Q3, and Q4 may use diodes instead of the switching elements. That is, at least one of the switching elements Q1, Q2, Q3, and Q4 may be a switching element. Even with such an alternative configuration, a boosting operation described later can be performed.

一端 One end of the capacitor 4 is connected to the DC bus 12a on the high potential side. The DC bus 12a is drawn out from a connection point 3c between the first upper arm element 311 on the first leg 31 and the second upper arm element 321 on the second leg 32. The other end of the capacitor 4 is connected to the low potential side DC bus 12b. The DC bus 12 b is drawn out from a connection point 3 d between a first lower arm element 312 on the first leg 31 and a second lower arm element 322 on the second leg 32. In the booster circuit 3, the connection points 3c and 3d constitute DC terminals. In the booster circuit 3, the side where the connection points 3c and 3d are located is referred to as "DC side".

(4) The output voltage of the booster circuit 3 is applied to both ends of the capacitor 4. Capacitor 4 is connected to DC buses 12a and 12b, and smoothes the output voltage of booster circuit 3. The voltage generated at the DC buses 12a and 12b is called "bus voltage" and is represented by "Vdc". An AC current flowing between the AC power supply 1 and the booster circuit 3 may be referred to as a “first current”.

(4) The voltage detector 5 detects the power supply voltage Vs and outputs a detected value of the power supply voltage Vs to the control unit 10.

The voltage detector 7 detects the bus voltage Vdc and outputs a detected value of the bus voltage Vdc to the control unit 10.

Next, the circuit configuration of the inverter circuit 18 will be described with reference to FIG. As shown in FIG. 2, the inverter circuit 18 includes a leg 18A in which an upper arm element 18UP and a lower arm element 18UN are connected in series, and a leg 18B in which an upper arm element 18VP and a lower arm element 18VN are connected in series. And a leg 18C in which the upper arm element 18WP and the lower arm element 18WN are connected in series. The legs 18A, 18B and 18C are connected in parallel with each other. A shunt resistor 18DS is inserted into the DC bus 12b. The shunt resistor 18DS is a component of the current detector 18S shown in FIG. Note that the upper arm elements 18UP, 18VP, 18WP and the lower arm elements 18UN, 18VN, 18WN may be referred to as “second switching elements”.

FIG. 2 illustrates a case where the upper arm elements 18UP, 18VP, 18WP and the lower arm elements 18UN, 18VN, 18WN are insulated gate bipolar transistors (Insulated Gate Bipolar Transistor: IGBT), but the present invention is not limited to this. A MOSFET may be used instead of the IGBT.

The upper arm element 18UP includes a transistor 18a and a diode 18b connected in anti-parallel to the transistor 18a. The other upper arm elements 18VP, 18WP and the lower arm elements 18UN, 18VN, 18WN have the same configuration. Anti-parallel means that the anode side of the diode is connected to the first terminal corresponding to the emitter of the IGBT and the cathode side of the diode is connected to the second terminal corresponding to the collector of the IGBT, as in the case of the booster circuit 3. means.

The shunt resistor 18DS detects a current flowing between the capacitor 4 and the inverter circuit 18. The detected value of the current flowing through the shunt resistor 18DS is sent to the control unit 10.

FIG. 2 shows a configuration including three legs in which the upper arm element and the lower arm element are connected in series, but is not limited to this configuration. The number of legs may be four or more.

When the transistors 18a of the upper arm elements 18UP, 18VP, 18WP and the lower arm elements 18UN, 18VN, 18WN are MOSFETs, at least one of the upper arm elements 18UP, 18VP, 18WP and the lower arm elements 18UN, 18VN, 18WN , A wide band gap semiconductor such as silicon carbide, gallium nitride, gallium oxide or diamond. If a MOSFET formed of a wide band gap semiconductor is used, the effects of withstand voltage and heat resistance can be enjoyed.

A connection point 26a between the upper arm element 18UP and the lower arm element 18UN is connected to a first phase (for example, U phase) of the motor 500 (not shown in FIG. 2), and a connection point between the upper arm element 18VP and the lower arm element 18VN. 26b is connected to a second phase (for example, V phase) of the motor 500, and a connection point 26c between the upper arm element 18WP and the lower arm element 18WN is connected to a third phase (for example, W phase) of the motor 500. In the inverter circuit 18, the connection points 26a, 26b, 26c form an AC terminal.

(4) Instead of the inverter circuit 18 shown in FIG. 2, an inverter circuit 18X shown in FIG. 3 may be used. FIG. 3 is a circuit diagram showing a configuration of the inverter circuit shown in FIG. 1 different from that of FIG.

In the inverter circuit 18X shown in FIG. 3, a lower arm shunt resistor 18US connected in series with the lower arm element 18UN is provided between the lower arm element 18UN and the DC bus 12b. Thus, the leg 18A includes the upper arm element 18UP, the lower arm element 18UN, and the lower arm shunt resistor 18US that are connected to each other in series.

も The same applies to other legs. Specifically, a lower arm shunt resistor 18VS connected in series to the lower arm element 18VN is provided between the lower arm element 18VN and the DC bus 12b. Thus, the leg 18B includes the upper arm element 18VP, the lower arm element 18VN, and the lower arm shunt resistor 18VS that are connected to each other in series. A lower arm shunt resistor 18WS connected in series with the lower arm element 18WN is provided between the lower arm element 18WN and the DC bus 12b. Thus, the leg 18CB is configured by the upper arm element 18WP, the lower arm element 18WN, and the lower arm shunt resistor 18WS that are connected to each other in series.

The lower arm shunt resistor 18US detects a current flowing in the lower arm of the U phase. The lower arm shunt resistor 18VS detects a current flowing through the V-phase lower arm. The lower arm shunt resistor 18WS detects a current flowing through the W-phase lower arm. The detected value of the current flowing through the lower arm shunt resistors 18US, 18VS, 18WS is sent to the control unit 10.

FIG. 2 shows a circuit configuration of a so-called one-shunt current detection system. The circuit of FIG. 2 is preferably used mainly for a motor for driving a compressor. FIG. 3 shows a circuit configuration of a so-called three-shunt current detection system. The circuit of FIG. 3 is preferably used mainly for a fan driving motor.

Next, the motor 500 according to the first embodiment will be described. Note that the rotation speed of the motor 500 is appropriately referred to as “motor rotation speed”. The voltage applied to the motor 500 by the inverter circuit 18 is referred to as “motor applied voltage” or simply “applied voltage”.

In FIG. 1, the motor 500 includes a U-phase winding 502U, a V-phase winding 502V, and a W-phase winding 502W. The U-phase winding 502U, the V-phase winding 502V, and the W-phase winding 502W are three windings provided in the motor 500.

両 端 Both ends of the U-phase winding 502U are open. The same applies to the V-phase winding 502V and the W-phase winding 502W. The connection switching unit 60 switches the connection state of the three windings included in the motor 500 between a first connection state and a second connection state. The second connection state is a state in which the motor applied voltage is lower than in the first connection state under the same motor rotation speed condition. Therefore, the motor applied voltage in the first connection state is higher than the motor applied voltage in the second connection state under the same motor rotation speed condition. In the case of the motor 500 of FIG. 1, the first connection state is a state of connection in a star connection, and the second connection state is a state of connection in a delta connection.

The connection switching unit 60 has a function of switching the connection state of the windings of the motor between the star connection and the delta connection by changing the connection destinations at both ends of each open winding. To realize this function, the connection switching unit 60 includes a U-phase switch 62U, a V-phase switch 62V, and a W-phase switch 62W. The U-phase switch 62U is a switching unit that switches the connection destination of the U-phase winding 502U. The V-phase switch 62V is a switching unit that switches the connection destination of the V-phase winding 502V. The W-phase switch 62W is a switching unit that switches the connection destination of the W-phase winding 502W.

The contacts of the U-phase switch 62U, the V-phase switch 62V, and the W-phase switch 62W are individually switched by switching signals CS1 to CS3 from the control unit 10.

(4) The current contact point of each phase switch is in a state of connecting each phase winding of the motor 500 to a star connection. That is, the default contact is a state where each phase winding of the motor 500 is connected to the star connection.

In FIG. 1, each phase switch is described as a c-contact switch, but is not limited to these examples. Each phase switch may be any switch that can be opened and closed in both directions. For example, each phase switch may be configured by combining an a contact switch or a b contact switch. Further, each phase switch may be a semiconductor switch.

Each phase switch preferably has a small conduction loss at the time of ON, and a mechanical switch such as a relay or a contactor can be used. Further, a switching element formed of a wide band gap semiconductor may be used instead of the mechanical switch. By using a switching element formed of a wide band gap semiconductor, it is possible to obtain the effects of low on-resistance, low loss, and low element heat generation.

Note that FIG. 1 illustrates a case where the first connection state is a star connection and the second connection state is a delta connection, but the present invention is not limited to this. For example, the two connection states shown in FIG. 4 may be switched. FIG. 4 is a diagram provided for describing another example of the first and second connection states according to the first embodiment.

FIG. 4 schematically shows a connection state of the motor 500 shown in FIG. 1 which is different from FIG. The upper part of FIG. 4 shows an example of series connection in which windings of each phase in a star connection are connected in series. The lower part of FIG. 4 shows an example of a parallel connection in which the respective phase windings in the star connection are connected in parallel.

(4) The impedance of the U-phase winding 33U1 in the series connection is larger than the impedance of the U-phase winding 33U2 in the parallel connection. Similarly, the impedance of the V-phase winding 33V1 in the serial connection is larger than the impedance of the V-phase winding 33V2 in the parallel connection, and the impedance of the W-phase winding 33W1 in the serial connection is larger than that of the W-phase winding 33W2 in the parallel connection. Larger than impedance. Therefore, if the phase current is the same, the induced voltage induced in each phase winding is greater in the series connection than in the parallel connection. Therefore, the series connection shown in the upper part of FIG. 4 is a connection state in which the motor applied voltage is higher than the parallel connection, and corresponds to the first connection state described above. Conversely, the parallel connection shown in the lower part of FIG. 4 is a connection state in which the motor applied voltage is lower than the serial connection, and corresponds to the above-described second connection state.

In FIG. 4, components corresponding to the connection switching unit 60 shown in FIG. 1 are not shown, but the first connection state can be obtained by appropriately combining a contact switch, b contact switch, or c contact switch. And the second connection state.

Returning to FIG. 1, the control unit 10 generates control signals S311 to S322 for controlling each switching element in the booster circuit 3 based on the detection values of the voltage detector 5 and the voltage detector 7. The control signal S311 is a control signal for controlling the switching element Q1, and the control signal S322 is a control signal for controlling the switching element Q4. Switching elements Q2 and Q3 are also controlled by a control signal from control unit 10. The control signals S311 to S322 generated by the control unit 10 are input to a gate drive circuit (not shown) in the booster circuit 3.

Further, the control unit 10 generates control signals S1 to S6 for controlling each switching element in the inverter circuit 18 based on each detection value of the voltage detector 5, the voltage detector 7, and the current detector 18S. . The control signal S1 is a control signal for controlling the upper arm element 18UP, and the control signal S6 is a control signal for controlling the lower arm element 18WN. The other upper arm elements 18VP, WP and the other lower arm elements 18UN, VN are also controlled by control signals from the control unit 10. The control signals S1 to S6 generated by the control unit 10 are input to a gate drive circuit (not shown) in the inverter circuit 18.

Next, the circuit operation of the main part of the motor drive device 100 according to the first embodiment will be described with reference to the drawings of FIGS.

FIG. 5 is a diagram provided for describing an operation mode of motor drive device 100 according to the first embodiment. FIG. 5 shows three operation modes: a passive synchronous rectification mode, a simple switching mode, and a pulse width modulation (Pulse Width Modulation: PWM) control mode. FIG. 6 is a diagram illustrating one of the current paths in the passive synchronous rectification mode in the booster circuit 3 of the first embodiment. FIG. 7 is a diagram schematically showing current-loss characteristics of a general switching element. FIG. 8 is a diagram illustrating one of the current paths in the simple switching mode in the booster circuit 3 of the first embodiment.

電源 The upper part of FIG. 5 shows the power supply voltage and the power supply current in the passive synchronous rectification mode. This operation mode is a mode in which synchronous rectification is performed without boosting. Non-boosting means that the power supply short-circuit operation is not performed. The power supply short-circuit operation will be described later. Synchronous rectification is a control method in which a switching element connected in anti-parallel to a diode is turned on in accordance with the timing at which a current flows through the diode.

FIG. 6 shows a charging path for the capacitor 4 when the power supply voltage is positive and synchronous rectification is performed. As shown in FIG. 6, it is assumed that the polarity of the power supply voltage is positive when the upper terminal of the AC power supply 1 has a positive potential. When the upper terminal of the AC power supply 1 has a negative potential, the polarity of the power supply voltage is assumed to be negative.

In FIG. 6, when the capacitor 4 is charged by the current supplied from the AC power supply 1, when the switching elements Q1 and Q4 are not turned on, the AC power supply 1, the reactor 2, the diode D1, the capacitor 4, the diode D4, and the AC power supply Current flows in the order of 1. The diode does not conduct unless a voltage corresponding to a voltage drop is applied in the direction in which current flows, that is, in the forward direction. Therefore, as shown in the upper part of FIG. 5, in the period of the positive half cycle T1 in which the power supply voltage is positive, the current flows in the period T2 shorter than the half cycle T1. In the passive synchronous rectification mode, in the period T2, the switching elements Q1 and Q4 are controlled to be ON according to the conduction timing of the diodes D1 and D4. Therefore, in the period T2, current flows in the order of the AC power supply 1, the reactor 2, the switching element Q1, the capacitor 4, the switching element Q4, and the AC power supply 1.

同 様 Similar operation is performed in the negative half cycle of the power supply voltage. However, in the period T3 in the negative half cycle of the power supply voltage, the switching elements Q2 and Q3 are controlled to be ON according to the conduction timing of the diodes D2 and D3.

FIG. 7 shows the loss characteristic of the diode and the loss characteristic when the switching element is turned on. As shown in FIG. 7, in a region A where the current is smaller than the current value I0, the loss of the diode is larger than the loss of the switching element. By utilizing this characteristic and using synchronous rectification for turning on a switching element connected in anti-parallel to the diode in accordance with the timing at which current flows through the diode, the motor drive device 100 can be operated with high efficiency.

(5) In the middle part of FIG. 5, the power supply voltage and the power supply current in the simple switching mode are shown. This operation mode is an operation mode in which the booster circuit 3 performs a boost operation by performing one or several short-circuit operations of the power supply during a half cycle of the power supply voltage. In the example of the middle part of FIG. 5, one power supply short-circuit operation is performed during a half cycle of the power supply voltage.

FIG. 8 shows a short-circuit path of the AC power supply 1 via the reactor 2 when the power supply voltage is positive and synchronous rectification is performed. As shown in FIG. 8, the switching elements Q1 and Q3 are turned on in the period T4. By doing so, current flows in the order of AC power supply 1, reactor 2, switching element Q1, switching element Q3, AC power supply 1, and electric energy is accumulated in reactor 2.

After the period T4, the operation is in the passive synchronous rectification mode shown in the upper part of FIG. Immediately after the period T4, the sum of the voltage of the AC power supply 1 and the voltage generated in the reactor 2 is applied to the booster circuit 3. Therefore, the diodes D1 and D4 of the booster circuit 3 conduct. Then, the switching elements Q1 and Q4 are turned on in accordance with the conduction timing of the diodes D1 and D4, and the power supply current flows.

In FIG. 8, the switching elements Q1 and Q3 are turned on, but the switching elements Q2 and Q4 may be turned on instead. In this case, current flows in the order of the AC power supply 1, the reactor 2, the switching element Q2, the switching element Q4, and the AC power supply 1.

で The same applies to the negative half cycle, and the passive synchronous rectification operation is performed after one or several power supply short-circuit operations. In the power supply short-circuit operation, the switching elements Q1 and Q3 may be turned on, or the switching elements Q2 and Q4 may be turned on.

(5) The lower part of FIG. 5 shows the power supply voltage and the power supply current in the PWM control mode. In this operation mode, a power supply short-circuit operation for storing electric energy in the reactor 2 and a charging operation for charging the capacitor 4 using the electric energy stored in the reactor 2 are alternately repeated. Switching between the power short-circuit operation and the charging operation is performed at a high frequency of several kHz to several tens kHz. Thereby, as shown in the lower part of FIG. 5, the power supply current is controlled to a sinusoidal current. Further, the boosting operation time is longer than in the simple switching mode shown in the middle part, and a boosted voltage higher than that in the simple switching mode can be obtained.

３The above three modes are switched according to operating conditions and load conditions. Thereby, the motor drive device 100 can be operated with high efficiency.

Next, boost control in the motor drive device 100 according to the first embodiment will be described with reference to FIG. 1 and FIGS. 9 to 11. In the following description, a motor having a structure capable of connection switching, such as the motor 500 shown in FIG. 1, is referred to as a “connection switching motor”, and the operation efficiency of the motor 500 is simply referred to as “efficiency”. Here, the “efficiency” is the ratio of the mechanical output of the motor 500 to the input power to the motor 500. In some drawings, the star connection is referred to as “Y connection” and the delta connection is referred to as “Δ connection”.

FIG. 9 is a diagram for explaining the relationship between the connection state and the efficiency in the connection switching motor according to the first embodiment. FIG. 10 is a diagram provided to explain matters to be considered when configuring the connection switching motor according to the first embodiment. FIG. 11 is a diagram provided for explanation of output voltage control in booster circuit 3 of the first embodiment.

FIG. 9 shows the relationship between the number of rotations of the motor 500 and the efficiency of the motor 500 when the connection state is the star connection and the delta connection. The horizontal axis shows the rotation speed of the motor 500, and the vertical axis shows the efficiency of the motor 500. As shown in FIG. 9, the efficiency of the motor 500 when the connection state is the star connection is better in the low speed region where the rotation speed is small, that is, in the light load region, than in the delta connection, but in the high speed region where the rotation speed is large. That is, it decreases in the high load region or the overload region.

On the other hand, the efficiency of the motor 500 when the connection state is the delta connection is inferior to the star connection in the low speed region where the rotation speed is low, but is improved in the high speed region where the rotation speed is high.

Therefore, the star connection is more efficient than the delta connection in the low speed region, and the delta connection is more efficient than the star connection in the high speed region. Therefore, the switching point shown in FIG. 9 exists, and if the connection state is switched at this switching point, efficient operation can be performed. Note that the switching speed at the switching point may be referred to as a “first speed”.

ア プ リ ケ ー シ ョ ン One of the applications of the motor drive device 100 is an air conditioner. One of the indexes related to energy saving in an air conditioner is an annual performance factor (APF). The efficiency at an intermediate load of the air conditioner greatly contributes to the APF. Note that the above-described low-speed region or light-load region may be considered to be substantially synonymous with the intermediate load referred to in APF.

FIG. 10 shows the relationship between the number of rotations of the motor 500 and the induced voltages of the two windings. The horizontal axis indicates the number of rotations of the motor 500, and the vertical axis indicates various voltages.

In FIG. 10, the induced voltage of the winding of the number A of turns is shown by a thick solid line in the winding of the number of turns A and the winding of the number of turns B, and the induced voltage of the winding of the number of turns B is large. Indicated by broken lines. The relationship between the number of turns A and the number of turns B is such that the number of turns B> the number of turns A, and the induced voltage of the winding of the number of turns B is higher than the induced voltage of the winding of the number of turns A. Further, if the induced voltage is increased by increasing the number of windings of the winding, the motor current can be reduced, so that the efficiency can be improved. Therefore, it can be understood that increasing the number of windings of the winding is effective for improving efficiency at an intermediate load.

However, when the induced voltage is increased by increasing the number of windings of the winding, the voltage may be insufficient in a low speed region or a light load region. In FIG. 10, the rectified voltage is the output voltage of the booster circuit 3 when the booster circuit 3 is not operated to boost the voltage, that is, when the booster circuit 3 is operated in the passive synchronous rectification mode. With respect to the rectified voltage shown in FIG. 10, the winding with the number of turns A does not become insufficient in voltage even at the rated rotation speed, but the winding with the number of turns B becomes insufficient in voltage at the rotation speed less than the rated rotation speed. It is shown. Therefore, to use the number of turns B, it is necessary to output a boosted voltage by the boosting circuit 3.

FIG. 11 shows an induced voltage when the connection state of the motor 500 is a star connection and an induced voltage when the connection state of the motor 500 is a delta connection. The horizontal axis indicates the number of rotations of the motor 500, and the vertical axis indicates various voltages. In FIG. 11, in consideration of the efficiency characteristics shown in FIG. 9, the connection state of the motor 500 is a star connection in a low-speed region and a delta connection in a high-speed region. In FIG. 11, it is assumed that the star connection and the delta connection are switched at the first rotational speed shown in FIG.

The induced voltage between terminals in the star connection is √3 times the induced voltage between terminals in the delta connection. Accordingly, changing the connection state from the delta connection to the star connection is equivalent to increasing the number of windings by √3 times. Also, if it is assumed that the number of turns is changed between star connection and delta connection without changing the number of windings and only the winding connection state is changed, the gradient of the induced voltage with respect to the rotation speed in the star connection is the gradient of the induced voltage with respect to the rotation speed in the delta connection. √3 times the slope.

In FIG. 11, the levels of the rectified voltage and the two boosted voltages, that is, the first voltage and the second voltage are indicated by broken lines. As described above, the rectified voltage is the output voltage of the booster circuit 3 when the booster circuit 3 is not operated. In other words, the rectified voltage is an output voltage of the booster circuit 3 that does not involve the switching operation of the switching element of the booster circuit 3.

Here, in the first embodiment, two boosting modes are defined. One is a boosting mode in which the boosting circuit 3 performs a boosting operation and outputs a first voltage. This boost mode is defined as “first boost mode”. The other is a boosting mode in which the boosting circuit 3 performs a boosting operation and outputs a second voltage. This boost mode is defined as “second boost mode”.

In the first boost mode, the boost circuit 3 operates in the simple switching mode described above, and generates the first voltage as shown in FIG. The first voltage is an output voltage of the booster circuit 3 that is boosted by the switching operation of the switching element of the booster circuit 3.

In the second boost mode, the boost circuit 3 operates in the above-described PWM control mode, and generates the second voltage as shown in FIG. The second voltage is an output voltage of the booster circuit 3 that is boosted by the switching operation of the switching element of the booster circuit 3 and is higher than the first voltage. When the level difference between the second voltage and the first voltage is small, the generation of the second voltage may be performed in the first boost mode, that is, the simple switching mode.

所 要 In FIG. 11, the required bus voltage is indicated by a bold dashed line. The required bus voltage indicates a level at which the voltage does not become insufficient when the connection state of the motor 500 is switched according to an increase in the rotation speed.

For example, in a star connection, the rotation speed increases and the induced voltage needs to be boosted to the first voltage in the second rotation speed at which the induced voltage reaches the rectified voltage and in the rotation speed section in which the rotation speed of the motor 500 is the first rotation speed. There is. As illustrated, the second rotation speed is a lower rotation speed than the first rotation speed. In actual operation control, it is needless to say that the voltage is raised to the first voltage at a preset rotation speed before reaching the second rotation speed in consideration of a margin.

Further, in the delta connection, in the rotation speed section between the third rotation speed at which the induced voltage reaches the rectified voltage and the fourth rotation speed at which the induced voltage reaches the first voltage, the voltage must be raised to the first voltage. is there. As illustrated, the third speed and the fourth speed are higher than the first speed and lower than the rated speed. The fourth rotation speed is a rotation speed higher than the third rotation speed. Needless to say, in actual operation control, the voltage is increased to the first voltage at a preset rotation speed before reaching the second rotation speed in consideration of a margin.

Further, in the delta connection, in the rotation speed section between the fourth rotation speed at which the induced voltage reaches the first voltage and the rated rotation speed at which the induced voltage reaches the second voltage, the voltage must be raised to the second voltage. is there. In the actual operation control, it is needless to say that the voltage is raised to the second voltage at a preset rotation speed before reaching the fourth rotation speed in consideration of a margin.

As described above, the motor driving device 100 according to the first embodiment operates at the first rotation speed which is the switching speed at which the connection state of the winding of the motor 500 is switched between the star connection and the delta connection. The output voltage of the booster circuit 3 is configured to be able to be boosted to a first voltage higher than the output voltage of the booster circuit 3 when the booster circuit 3 is not operated. With this configuration, it is possible to further improve the efficiency in the low-speed rotation range using the star connection.

理由 The reason why the efficiency is further improved in the low-speed rotation range is as follows.

(4) As described above, in the connection switching motor, it is necessary to pay attention to both the voltage shortage so that the voltage shortage in the star connection and the voltage shortage in the delta connection do not occur. Further, the conventional booster circuit has a large loss at the time of boosting, and there is a restriction in increasing the number of turns. In particular, boosting in a star connection, in which loss at an intermediate load becomes a problem, was forgotten.

On the other hand, in the first embodiment, since the synchronous rectification is performed when the booster circuit 3 performs the passive operation, the loss caused by the conventional diode rectification can be improved. Further, since synchronous rectification is performed even in the two boost modes, the loss due to the boost operation can be compensated for by the loss improvement due to the synchronous rectification during the boost operation. As a result, even in the star connection where the loss at the intermediate load becomes a problem, it is possible to improve the efficiency in the low-speed rotation region using the star connection by using the synchronous rectification together. In addition, this makes it possible to improve the efficiency without impairing the effect of increasing the number of windings by the connection switching motor.

Next, a hardware configuration for realizing the function of the control unit 10 according to the first embodiment will be described with reference to FIGS. 12 and 13. FIG. 12 is a block diagram illustrating an example of a hardware configuration that implements the function of the control unit 10 according to the first embodiment. FIG. 13 is a block diagram illustrating another example of a hardware configuration that implements the function of the control unit 10 according to the first embodiment.

When implementing all or a part of the functions of the control unit 10 according to the first embodiment, as shown in FIG. 12, a processor 300 for performing an operation, a memory 302 for storing a program read by the processor 300, And an interface 304 for inputting and outputting signals.

The processor 300 may be an arithmetic unit such as an arithmetic unit, a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The memory 302 includes 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), an EEPROM (registered trademark) (Electrically EPROM). Examples include a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, and a DVD (Digital @ Versatile @ Disc).

The memory 302 stores a program for executing all or a part of the functions of the control unit 10. The processor 300 transmits and receives necessary information via the interface 304, and controls the booster circuit 3 and the inverter circuit 18 by executing the program stored in the memory 302 by the processor 300.

The processor 300 and the memory 302 shown in FIG. 12 may be replaced with a processing circuit 305 as shown in FIG. 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 thereof.

Embodiment 2 FIG.
FIG. 14 is a diagram illustrating a configuration example of an air conditioner 200 according to Embodiment 2. The air conditioner 200 according to Embodiment 2 includes the motor drive device 100 described in Embodiment 1. In the air conditioner 200, the compressor 251 including the motor 500 according to Embodiment 1; the four-way valve 259; the outdoor heat exchanger 252; the expansion valve 261; A separate type air conditioner is equipped with a refrigeration cycle attached. Note that components having functions similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

圧 縮 A compression mechanism 250 for compressing the refrigerant and a motor 500 for operating the compression mechanism 250 are provided inside the compressor 251. A refrigeration cycle for cooling and heating is configured by circulating a refrigerant between the compressor 251 and the outdoor heat exchanger 252 and between the compressor 251 and the indoor heat exchanger 257. The configuration shown in FIG. 14 is applicable not only to an air conditioner but also to a refrigeration cycle apparatus having a refrigeration cycle such as a refrigerator or a freezer.

Next, the operation of the main part of the air conditioner 200 according to Embodiment 2 will be described with reference to FIG. FIG. 15 is a time chart illustrating an example of an operation method of the air conditioner 200 according to Embodiment 2. It is assumed that the connection state of the windings of the motor 500 is star connection, which is the default connection state, as a premise of the description of FIG. In FIG. 15, a bold solid line indicates the number of rotations, and a bold broken line indicates a bus voltage.

{Circle around (1)} At time t1, energization of the air conditioner 200 is started, and the air conditioner 200 is started at time t2. In addition, between the time t1 and the time t2, the connection state of the winding is switched from the star connection to the delta connection.

モ ー タ The motor 500 is accelerated between the time t2 and the time t5. In addition, since a shortage of the bus voltage is predicted, the first boosting is performed at time t3, and the bus voltage is changed to the first voltage. Further, after the bus voltage is changed to the first voltage, further shortage of the bus voltage is predicted. Therefore, at time t4, the second boosting is performed, and the bus voltage is changed to the second voltage. The first boosting is performed in the first boosting mode, and the second boosting is performed in the second boosting mode.

で は At time t5, the rated load is reached, and during the period from time t5 to time t6, constant rotation speed control is performed. Further, between time t5 and time t6, control unit 10 of motor drive device 100 determines whether or not the absolute value of the temperature difference between the target temperature and room temperature is less than the threshold. If the temperature difference is less than the threshold value, the operation shifts to a deceleration operation for restarting. Note that in the example of FIG. 15, the operation shifts to the deceleration operation at time t6.

At the time t7 between the time t6 and the time t8, the boosting operation stops and the bus voltage becomes the rectified voltage in order to increase the efficiency. At time t8, the winding is stopped, and the connection state of the winding is switched from delta connection to star connection.

再 Restarted at time t9, the motor 500 accelerates between time t9 and time t11. At time t10 when a voltage shortage is expected, the boost is performed, and the bus voltage is changed to the first voltage. At time t11, the load reaches the intermediate load, and during the period from time t11 to time t12, control at a constant rotational speed is performed. In addition, the operation of the intermediate load is performed between the time t11 and the time t12, and the boosting to the second voltage is not necessary.

At time t12, for example, a stop command is input from a remote controller (not shown), and the operation shifts to a deceleration operation. At time t13 between time t12 and time t14, the boosting operation is stopped and the bus voltage becomes a rectified voltage in order to increase efficiency. The operation stops at time t14, and the energization ends at time t15.

The above is an example of the operation pattern in the air conditioner 200 according to Embodiment 2. The following supplements some of the operations.

First, the information on the room temperature required for the determination between the time t5 and the time t6 can be grasped by a function normally included in the air conditioner 200.

Also, from time t5 to time t6, the absolute value of the temperature difference between the target temperature and room temperature is compared with the threshold value, but the present invention is not limited to this. The absolute value of the temperature difference is an example of a determination index, and another determination index may be used. Whether or not the value is smaller than the threshold is an example of a condition determined by the determination index, and another condition may be used. Here, this condition is referred to as a “first condition”. That is, it is sufficient to determine whether the determination index satisfies the first condition from the time t5 to the time t6.

Also, in the example of FIG. 15, the connection state of the winding is switched from the star connection to the delta connection at the first startup. However, if the determination index satisfies the first condition, the connection state of the winding is changed to the star connection. It is not necessary to switch from the connection to the delta connection, and it is only necessary to start with the delta connection.

Further, the example of FIG. 15 is an embodiment in which the connection state of the winding is not switched in both the period from the start to the stop and the period from the restart to the stop. The connection state of the line may be switched. The sudden change in the load is assumed to be a case where the temperature difference suddenly changes due to opening and closing of a door and a window, and cooking in a kitchen. When the winding is performed during the operation of the air conditioner 200, it is preferable that the threshold value of the temperature difference has hysteresis so that the connection state is not frequently switched.

As described above, when the determination index does not satisfy the first condition, the air conditioner 200 according to Embodiment 2 is started by switching the winding connection state to the delta connection, and the determination index is changed to the first index. Is satisfied, the motor driving device 100 is stopped and then the winding connection state is switched to the star connection and restarted. As a result, operation utilizing the characteristics of the star connection and the delta connection can be performed, and the efficiency of the air conditioner 200 can be increased as compared with a case where a connection switching motor is not used.

It should be noted that the configuration shown in the above-described embodiment is an example of the content of the present invention, and can be combined with another known technology, and the configuration is not deviated from the gist of the present invention. Can be omitted or changed.

1 AC power supply, 2 reactor, 3 booster circuit, 3a, 3b, 3c, 3d, 26a, 26b, 26c connection point, 4 capacitor, 5, 7 voltage detector, 10 control unit, 12a, 12b DC bus, 18, 18X Inverter circuit, 18A, 18B, 18C leg, 18a transistor, 18DS shunt resistor, 18UP, 18VP, 18WP upper arm element, 18UN, 18VN, 18WN lower arm element, 18US, 18VS, 18WS lower arm shunt resistor, 18b, D1, D2 , D3, D4} diode, 18S} current detector, 31} first leg, 32} second leg, 33U1, 33U2, 502U U phase winding, 33V1, 33V2, 502V {V phase winding, 33W1, 33W2, 502W} W phase Winding, 60 ° connection switching unit, 62 U-phase switch, 62V V-phase switch, 62W W-phase switch, 100 motor drive, 200 air conditioner, 250 compression mechanism, 251 compressor, 252 outdoor heat exchanger, 257 indoor heat exchanger, 259 4 way valve, 261 expansion Valve, 262 refrigerant line, 300 processor, 302 memory, 304 interface, 305 processing circuit, 311 first upper arm element, 312 first lower arm element, 321 second upper arm element, 322 second lower arm element , 500 motor, Q1, Q2, Q3, Q4 switching element.

Claims (9)

1. A booster circuit having at least one switching element, converting and boosting an AC voltage output from an AC power supply to a DC voltage by opening and closing the switching element,
   A capacitor for smoothing the DC voltage output from the booster circuit,
   An inverter circuit that converts the power stored in the capacitor into AC power and supplies the AC power to the motor;
   With
   The motor has a plurality of windings,
   Both ends of the winding are open, and the connection state of the winding can be switched between a first connection state and a second connection state by changing a connection destination of the both ends,
   The motor applied voltage in the first connection state is higher than the motor applied voltage in the second connection state under the same motor rotation speed,
   At a first rotation speed, which is a rotation speed at a switching point at which the connection state of the winding is switched between the first connection state and the second connection state, the output voltage of the booster circuit causes the booster circuit to perform a boost operation. A motor drive device capable of boosting to a first voltage higher than a rectified voltage which is an output voltage of the booster circuit when not performed.
2. 2. The motor according to claim 1, wherein when a connection state of the winding is switched to the second connection state, an output voltage of the booster circuit can be boosted to a second voltage higher than the first voltage. Drive.
3. The output voltage of the booster circuit is
   In the first connection state, the rectified voltage or the first voltage is set,
   The motor drive device according to claim 2, wherein the rectified voltage, the first voltage, or the second voltage is set in the second connection state.
4. The first connection state is a star connection,
   The motor drive device according to any one of claims 1 to 3, wherein the second connection state is a delta connection.
5. The motor drive device according to any one of claims 1 to 4, wherein the switching element is formed of a wide band gap semiconductor.
6. The motor driving device according to claim 5, wherein the wide band gap semiconductor is silicon carbide, gallium nitride, gallium oxide, or diamond.
7. An air conditioner driven by the motor drive device according to claim 4,
   When the determination index does not satisfy the first condition, the connection state of the winding is switched to the delta connection and activated.
   When the determination index satisfies the first condition, the air conditioner restarts by stopping the motor drive device, switching the connection state of the winding to the star connection, and restarting.
8. An air conditioner driven by the motor drive device according to claim 4,
   In the initial state, the winding is switched to the star connection,
   When the determination index does not satisfy the first condition, the connection state of the winding is switched to the delta connection and activated.
   When the judgment index satisfies the first condition, the air conditioner starts up while the connection state of the windings remains in the star connection state.
9. The determination index is an absolute value of a temperature difference between the target temperature and room temperature,
   The air conditioner according to claim 7, wherein the time when the determination index satisfies the first condition is when the absolute value of the temperature difference is less than a threshold.

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