JP7312189B2 - Motor drive device and air conditioner - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive device for driving a motor and an air conditioner provided with the motor drive device.

Patent Document 1 below describes a technology for improving 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 star connection and delta connection. A configuration of a motor drive is disclosed. This patent document 1 proposes a technique for expanding the high-speed rotation range and improving efficiency in the low-speed rotation range by using star connection in the low-speed rotation range and delta connection in the high-speed rotation range.

Japanese Patent No. 4619826

However, when the star connection and the delta connection are used with the same bus voltage, the number of turns of the winding is determined based on the motor applied voltage in the delta connection in accordance with the required number of revolutions in the high speed range. For this reason, there is room for improvement in efficiency in the low speed range where star connection is used.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a motor drive device capable of further improving efficiency in a low speed rotation range.

In order to solve the above-described problems and achieve the object, a motor drive device according to the present invention has at least one switching element, and converts an AC voltage output from an AC power supply to a DC voltage by opening and closing the switching element. A booster circuit for conversion and boosting is provided. The motor drive device also includes a capacitor that smoothes the DC voltage output from the booster circuit, and an inverter circuit that converts the power accumulated in the capacitor into AC power and supplies the AC power to the motor. The motor has a plurality of windings, and both ends of the windings are open. can be switched to The voltage applied to the motor in the first connection state is higher than the voltage applied to the motor in the second connection state under the same motor rotation speed condition. At the first rotation speed, which is the rotation speed at which the connection state of the windings is switched between the first connection state and the second connection state, the output voltage of the booster circuit is equal to can be boosted to a first voltage higher than the rectified voltage, which is the output voltage of the .

Advantageous Effects of Invention According to the motor drive device of the present invention, it is possible to further improve the efficiency in the low speed rotation range.

1 is a circuit diagram showing a configuration of a motor drive device according to Embodiment 1; FIG. 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 different from that shown in FIG. 2; FIG. 4 is a diagram for explaining another example of the first and second connection states in the first embodiment; FIG. 4 is a diagram for explaining operation modes 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; Schematic diagram showing current-loss characteristics in a typical switching element FIG. 4 is a diagram showing one current path in the simple switching mode in the booster circuit of the first embodiment; FIG. 4 is a diagram for explaining the relationship between the connection state and the efficiency in the connection switching motor of the first embodiment; FIG. FIG. 4 is a diagram for explaining considerations when configuring the connection switching motor according to the first embodiment; FIG. 4 is a diagram for explaining output voltage control in the booster circuit of the first embodiment; FIG. 2 is a block diagram showing an example of a hardware configuration that implements the functions of the control unit according to Embodiment 1; FIG. 4 is a block diagram showing another example of the hardware configuration that implements the functions of the control unit according to Embodiment 1; FIG. 10 is a diagram showing a configuration example of an air conditioner according to Embodiment 2; Time chart showing an example of a method of operating an air conditioner according to Embodiment 2

A motor drive device and an air conditioner according to embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the present invention is not limited by the embodiments shown below. Also, hereinafter, the electrical connection will be simply referred to as "connection".

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

As shown in FIG. 1, the motor drive device 100 according to Embodiment 1 converts AC power supplied from a single-phase AC power supply 1 into DC power. Further, the motor drive 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 . Examples of the motor 500 are motors built into blowers, compressors, or air conditioners.

In FIG. 1, a motor driving device 100 includes a booster circuit 3, a capacitor 4, a control section 10, an inverter circuit 18 having a current detector 18S, a connection switching section 60, and a voltage detector as a first voltage detector. It comprises a detector 5 and a voltage detector 7 which is a second voltage detector.

The booster circuit 3 is a booster 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, which will be described later. The booster circuit 3 controls, that is, boosts the voltage value of the converted DC voltage when converting the AC voltage into the DC voltage. The AC voltage output from the AC power supply 1 is called "power supply voltage" and represented by "Vs".

The booster circuit 3 includes a 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 on 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 form AC terminals.

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

Although FIG. 1 exemplifies a metal oxide semiconductor field effect transistor (MOSFET) for each of the switching elements Q1, Q2, Q3, and Q4, it is not limited to a MOSFET. A MOSFET is a switching element that allows current to flow bidirectionally between a drain and a source. Any switching element may be used as long as it is a switching element that allows current to flow bidirectionally between the first terminal corresponding to the drain and the second terminal corresponding to the source.

Anti-parallel means that the first terminal corresponding to the drain of the MOSFET and the cathode of the diode are connected, and the second terminal corresponding to the source of the MOSFET and the anode of the diode are connected. A parasitic diode that the MOSFET itself has inside may be used as the diode. A parasitic diode is also called a body diode.

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

Wide bandgap semiconductors generally have higher withstand voltage and heat resistance than silicon semiconductors. Therefore, by using a wide bandgap semiconductor for at least one of the switching elements Q1, Q2, Q3, Q4, the voltage resistance and allowable current density of the switching elements are increased, and the semiconductor module incorporating the switching elements can be miniaturized. can be

Three of the switching elements Q1, Q2, Q3 and Q4 may be diodes instead of switching elements. That is, at least one of the switching elements Q1, Q2, Q3, Q4 should be a switching element. Even with such an alternative configuration, a boosting operation, which will be described later, is possible.

One end of the capacitor 4 is connected to the DC bus 12a on the high potential side. The DC bus 12 a is drawn from a connection point 3 c 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 DC bus 12b on the low potential side. The DC bus 12b is drawn from a connection point 3d between the first lower arm element 312 on the first leg 31 and the second lower arm element 322 on the second leg 32 . In the booster circuit 3, the connection points 3c and 3d form DC terminals. Further, in the booster circuit 3, the side on which the connection points 3c and 3d are located is called the "DC side".

The output voltage of the booster circuit 3 is applied across the capacitor 4 . Capacitor 4 is connected to DC buses 12 a and 12 b and smoothes the output voltage of booster circuit 3 . The voltage generated on the DC buses 12a and 12b is called "bus voltage" and is represented by "Vdc". Also, an alternating current flowing between the alternating current power supply 1 and the booster circuit 3 may be referred to as a "first current".

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

Voltage detector 7 detects bus voltage Vdc and outputs the detected value of bus voltage Vdc to 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 has 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. Leg 18A, leg 18B and leg 18C are connected in parallel with each other. A shunt resistor 18DS is inserted in the DC bus 12b. Shunt resistor 18DS is a component of current detector 18S shown in FIG. The upper arm elements 18UP, 18VP, 18WP and the lower arm elements 18UN, 18VN, 18WN are sometimes called "second switching elements".

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

Upper arm element 18UP includes transistor 18a and diode 18b connected in antiparallel to transistor 18a. Other upper arm elements 18VP, 18WP and 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 booster circuit 3 . means.

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

Although FIG. 2 shows a configuration including three legs in which the upper arm element and the lower arm element are connected in series, the configuration is not limited to this. 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 is , silicon carbide, gallium nitride, gallium oxide, or a wide bandgap semiconductor such as diamond. By using a MOSFET formed of a wide bandgap semiconductor, it is possible to enjoy the effects of withstand voltage and heat resistance.

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 the second phase (eg, V phase) of the motor 500, and the connection point 26c between the upper arm element 18WP and the lower arm element 18WN is connected to the third phase (eg, W phase) of the motor 500. FIG. In the inverter circuit 18, the connection points 26a, 26b, and 26c constitute AC terminals.

Further, an inverter circuit 18X shown in FIG. 3 may be used instead of the inverter circuit 18 shown in FIG. FIG. 3 is a circuit diagram showing a configuration different from that of FIG. 2 of the inverter circuit shown in FIG.

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

Other legs are similar. 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 is composed of an upper arm element 18VP, a lower arm element 18VN and a lower arm shunt resistor 18VS which are connected in series. A lower arm shunt resistor 18WS connected in series to the lower arm element 18WN is provided between the lower arm element 18WN and the DC bus 12b. Thus, the leg 18CB is composed of an upper arm element 18WP, a lower arm element 18WN and a lower arm shunt resistor 18WS which are connected in series.

The lower arm shunt resistor 18US detects the current flowing through the U-phase lower arm. The lower arm shunt resistor 18VS detects the current flowing through the V-phase lower arm. The lower arm shunt resistor 18WS detects the current flowing through the W-phase lower arm. Detected values of the currents flowing through the lower arm shunt resistors 18 US, 18 VS, and 18 WS are sent to the controller 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. Further, FIG. 3 shows a circuit configuration of a so-called 3-shunt current detection system. The circuit of FIG. 3 is preferably used mainly for fan drive motors.

Next, motor 500 in Embodiment 1 will be described. Note that the number of revolutions of the motor 500 is appropriately called "motor number of revolutions". Further, the voltage applied to the motor 500 by the inverter circuit 18 is appropriately called "motor applied voltage" or simply "applied voltage".

In FIG. 1, motor 500 includes U-phase winding 502U, V-phase winding 502V, and W-phase winding 502W. A U-phase winding 502U, a V-phase winding 502V, and a W-phase winding 502W are three windings that the motor 500 has.

Both ends of 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 of the motor 500 between a first connection state and a second connection state. The second connection state is a state in which the voltage applied to the motor is lower than that in the first connection state under the same motor rotation speed condition. Therefore, under the condition of the same motor rotation speed, the voltage applied to the motor in the first connection state is higher than the voltage applied to the motor in the second connection state. In the case of the motor 500 of FIG. 1, the first connection state is star connection, and the second connection state is 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 destination of each open winding. To realize this function, the connection switching section 60 includes a U-phase switch 62U, a V-phase switch 62V, and a W-phase switch 62W. U-phase switch 62U is a switching unit that switches the connection destination of 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.

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 section .

The current contacts of each phase switch are in a state to connect each phase winding of motor 500 to the star connection. That is, the default contact is a state in which each phase winding of the motor 500 is connected in star connection.

In addition, although each phase switch is described as a c-contact switch in FIG. 1, it is not limited to these examples. Each phase switch may be a 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. Also, each phase switch may be a semiconductor switch.

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

In addition, in FIG. 1, although the case where the 1st connection state was star connection and the 2nd connection state was delta connection was illustrated, it is not limited to this. For example, the two connection states shown in FIG. 4 may be switched. FIG. 4 is a diagram for explaining another example of the first and second connection states in the first embodiment.

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

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

In FIG. 4, illustration of a component corresponding to the connection switching unit 60 shown in FIG. 1 is omitted. 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 detectors 5 and 7. FIG. 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. The switching elements Q2 and Q3 are also controlled by the control signal from the control section 10. FIG. The control signals S311 to S322 generated by the control section 10 are input to a gate drive circuit (not shown) within 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 the detected values of the voltage detector 5, the voltage detector 7 and the current detector 18S. . Control signal S1 is a control signal for controlling upper arm element 18UP, and control signal S6 is a control signal for controlling lower arm element 18WN. Other upper arm elements 18VP, WP and other lower arm elements 18UN, VN are also controlled by control signals from the controller 10. FIG. The control signals S1 to S6 generated by the control section 10 are input to a gate driving circuit (not shown) within 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 FIGS. 1 to 8 as appropriate.

FIG. 5 is a diagram for explaining operation modes of motor drive device 100 in the first embodiment. Three modes of operation are shown in FIG. 5: passive synchronous rectification mode, simple switching mode, and pulse width modulation (PWM) control mode. FIG. 6 is a diagram showing one current path in the passive synchronous rectification mode in booster circuit 3 of the first embodiment. FIG. 7 is a diagram schematically showing current-loss characteristics in a general switching element. FIG. 8 is a diagram showing one current path in the simple switching mode in booster circuit 3 of the first embodiment.

The upper part of FIG. 5 shows the power supply voltage and 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 not performing a power supply short-circuit operation. The power supply short-circuit operation will be described later. Synchronous rectification is a control method for turning ON a switching element connected in anti-parallel to a diode in accordance with the timing at which current flows through the diode.

FIG. 6 shows the 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 is at a positive potential. It is also assumed that the polarity of the power supply voltage is negative when the upper terminal of the AC power supply 1 is at a negative potential.

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, the AC power supply Current flows in the order of 1. A diode does not conduct unless a voltage corresponding to the voltage drop is applied in the direction of current flow, that is, in the forward direction. Therefore, as shown in the upper part of FIG. 5, current flows in a period T2 shorter than the half cycle T1 in the period of the positive half cycle T1 of the power supply voltage. In the passive synchronous rectification mode, during the period T2, the switching elements Q1 and Q4 are controlled to be ON in accordance with the conduction timing of the diodes D1 and D4. Therefore, in the period T2, current flows through 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 in this order.

A similar operation is performed in the half cycle in which the power supply voltage is negative. However, during the period T3 in the negative half cycle of the power supply voltage, the switching elements Q2 and Q3 are controlled to be ON in accordance with the conduction timing of the diodes D2 and D3.

FIG. 7 shows the loss characteristics of the diode and the loss characteristics when the switching element is on. As shown in FIG. 7, in region A where the current is smaller than the current value I0, the loss of the diode is greater than the loss of the switching element. Using this characteristic, the motor driving device 100 can be operated with high efficiency by using synchronous rectification that turns on the switching element connected in anti-parallel to the diode in accordance with the timing at which the current flows through the diode.

The middle part of FIG. 5 shows the power supply voltage and power supply current in the simple switching mode. This operation mode is an operation mode in which the power supply short-circuit operation is performed once or several times during the period of the half cycle of the power supply voltage to cause the booster circuit 3 to perform the boosting operation. In the example of the middle part of FIG. 5, the power supply short-circuit operation is performed once during the period of the 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 during the period T4. In this way, current flows through the AC power supply 1, the reactor 2, the switching element Q1, the switching element Q3, and the AC power supply 1 in this order, and electrical energy is accumulated in the reactor 2.

After the period T4, the operation in the passive synchronous rectification mode shown in the upper part of FIG. 5 is performed. Immediately after period T<b>4 , the sum of the voltage of AC power supply 1 and the voltage generated in reactor 2 is applied to booster circuit 3 . Therefore, the diodes D1 and D4 of the booster circuit 3 become conductive. Then, the switching elements Q1 and Q4 are turned ON in synchronization 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 ON-operated, but instead of this, the switching elements Q2 and Q4 may be ON-operated. In this case, the current flows through the AC power supply 1, the reactor 2, the switching element Q2, the switching element Q4, and the AC power supply 1 in that order.

The same is true for the negative half-cycles, after one or several power supply short-circuits, passive synchronous rectification occurs. 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.

The lower part of FIG. 5 shows the power supply voltage and power supply current in the PWM control mode. In this operation mode, a power supply short-circuit operation for accumulating electrical energy in reactor 2 and a charging operation for charging capacitor 4 using the electrical energy accumulated in reactor 2 are alternately repeated. Switching between the power supply short-circuit operation and the charging operation is performed at a high frequency of several kHz to several tens of kHz. Thereby, as shown in the lower part of FIG. 5, the power supply current is controlled to a sinusoidal current. In addition, the time for the boosting operation 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.

The three modes described above are switched according to operating conditions and load conditions. This allows the motor drive device 100 to operate with high efficiency.

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

FIG. 9 is a diagram for explaining the relationship between the connection state and efficiency in the connection switching motor of the first embodiment. 10A and 10B are diagrams for explaining points to be considered when configuring the connection switching motor of Embodiment 1. FIG. FIG. 11 is a diagram for explaining output voltage control in booster circuit 3 of the first embodiment.

FIG. 9 shows the relationship between the number of revolutions of the motor 500 and the efficiency of the motor 500 in the star connection and the delta connection. The horizontal axis indicates the rotation speed of the motor 500, and the vertical axis indicates the efficiency of the motor 500. FIG. As shown in FIG. 9, the efficiency of the motor 500 when the connection state is the star connection is better than that of the delta connection in the low speed region where the rotation speed is small, that is, in the light load region, but in the high speed region where the rotation speed is high. , 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 that of the star connection in the low speed region where the rotation speed is low, but it 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, there is a switching point shown in FIG. 9, and if the connection state is switched at this switching point, efficient operation becomes possible. Note that the switching rotation speed at the switching point may be referred to as "first rotation speed".

One of the applications of the motor drive device 100 is an air conditioner. One of the indexes related to energy saving in air conditioners is annual performance factor (APF). The efficiency of the air conditioner at intermediate load contributes greatly to the APF. It should be noted that the above-described low-speed region or light-load region may be considered to be almost synonymous with intermediate load referred to in APF.

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

In FIG. 10, the induced voltage in the winding with the number of turns A and the winding with the number of turns B are the same except for the number of turns. indicated by a dashed line. There is a relationship of number of turns B>number of turns A between the number of turns A and number of turns B, 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. Also, if the induced voltage is increased by increasing the number of turns of the windings, the motor current can be reduced, so efficiency can be improved. Therefore, it can be understood that increasing the number of turns of the winding is effective in improving the efficiency at an intermediate load.

However, when the induced voltage is increased by increasing the number of turns of the winding, the voltage may be insufficient in the low speed region or the 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 boosted, 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 have a voltage shortage even at the rated rotation speed, but the winding with the number of turns B may have a voltage shortage at a rotation speed lower than the rated rotation speed. It is shown. Therefore, in order to use the number of turns B, it is necessary to output a boosted voltage from the booster circuit 3 .

FIG. 11 shows the induced voltage when the motor 500 is connected in the star connection and the induced voltage when the motor 500 is connected in the delta connection. The horizontal axis indicates the rotation speed of the motor 500, and the vertical axis indicates various voltages. In FIG. 11, in view of the efficiency characteristics shown in FIG. 9, the connection state of the motor 500 is star connection in the low speed region and delta connection in the high speed region. Moreover, in FIG. 11, it is assumed that the star connection and the delta connection are switched at the first rotation speed shown in FIG.

The induced voltage between terminals in star connection is √3 times the induced voltage between terminals in delta connection. Therefore, changing the connection state from delta connection to star connection is equivalent to multiplying the number of winding turns by √3. Also, if the star connection and delta connection are switched only by the connection state of the windings without changing the number of turns, the gradient of the induced voltage with respect to the rotation speed in the star connection is the same as that 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, the first voltage and the second voltage, are indicated by dashed lines. As described above, the rectified voltage is the output voltage of the booster circuit 3 when the booster circuit 3 is not boosted. In other words, the rectified voltage is the output voltage of the booster circuit 3 without the opening/closing operation of the switching element of the booster circuit 3 .

Here, in Embodiment 1, two boost modes are defined. One is a boosting mode in which the boosting circuit 3 is operated to boost and output 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 to output a second voltage. This boost mode is defined as "second boost mode".

In the first boosting mode, the boosting circuit 3 operates in the above-described simple switching mode to generate the first voltage as shown in FIG. The first voltage is the output voltage of the booster circuit 3 boosted by the opening/closing operation of the switching element of the booster circuit 3 .

In the second boosting mode, the boosting circuit 3 operates in the PWM control mode described above to generate the second voltage as shown in FIG. The second voltage is the output voltage of the booster circuit 3 boosted by the switching operation of the switching element of the booster circuit 3, and is a voltage higher than the first voltage. Note that if the level difference between the second voltage and the first voltage is small, the second voltage may be generated in the first boost mode, that is, the simple switching mode.

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

For example, in the star connection, it is necessary to boost the voltage to the first voltage in the second rotation speed where the rotation speed increases and the induced voltage reaches the rectified voltage, and in the rotation speed section where the rotation speed of the motor 500 becomes the first rotation speed. There is As shown, the second rotation speed is a rotation speed lower than the first rotation speed. It goes without saying that in actual operation control, the voltage is boosted to the first voltage at a preset rotational speed before reaching the second rotational speed, with a margin taken into consideration.

Further, in the delta connection, it is necessary to be boosted to the first voltage 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. be. As illustrated, the third and fourth rotation speeds are higher than the first rotation speed and lower than the rated rotation speed. Also, the fourth rotation speed is a rotation speed higher than the third rotation speed. It goes without saying that in actual operation control, the voltage is boosted to the first voltage at a preset number of revolutions before reaching the second number of revolutions in consideration of a margin.

Furthermore, in the delta connection, it is necessary to be boosted to the second voltage 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. be. It goes without saying that in actual operation control, the voltage is boosted to the second voltage at a preset number of revolutions before reaching the fourth number of revolutions, in consideration of a margin.

As described above, the motor drive device 100 according to the first embodiment operates at the first rotation speed, which is the rotation speed at which the connection state of the windings of the motor 500 is switched between the star connection and the delta connection. The output voltage of 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 in boosting operation. With this configuration, it is possible to further improve the efficiency in the low speed rotation range using the star connection.

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

As described above, in the connection-switching motor, it is necessary to pay attention to voltage shortages in both the star connection and the delta connection so as not to cause a voltage shortage. In addition, 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 with a star connection, which poses a problem of loss at intermediate loads, has been postponed.

On the other hand, in Embodiment 1, synchronous rectification is performed when the booster circuit 3 performs passive operation, so that the loss that occurs in the conventional diode rectification can be improved. In addition, since synchronous rectification is performed in both boosting modes, the loss due to the boosting operation can be offset by the loss improvement due to the synchronous rectification during the boosting operation. As a result, even in the case of star connection where loss at intermediate loads is a problem, efficiency can be improved in the low speed rotation region using star connection by using it together with synchronous rectification. Further, this makes it possible to improve the efficiency without impairing the effect of increasing the number of turns by the connection switching motor.

Next, a hardware configuration for realizing the functions of the control unit 10 according to Embodiment 1 will be described with reference to FIGS. 12 and 13. FIG. FIG. 12 is a block diagram showing an example of a hardware configuration that implements the functions of the control section 10 according to Embodiment 1. As shown in FIG. FIG. 13 is a block diagram showing another example of the hardware configuration that implements the functions of the control unit 10 according to the first embodiment.

When realizing all or part of the functions of the control unit 10 in Embodiment 1, as shown in FIG. and an interface 304 for inputting and outputting signals.

The processor 300 may be an arithmetic means such as an arithmetic unit, a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). The memory 302 includes non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), EEPROM (registered trademark) (Electrically EPROM), Examples include magnetic discs, flexible discs, optical discs, compact discs, mini discs, and DVDs (Digital Versatile Discs).

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

Also, the processor 300 and 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. 14 is a diagram showing a configuration example of an air conditioner 200 according to Embodiment 2. As shown in FIG. An air conditioner 200 according to the second embodiment includes the motor drive device 100 described in the first embodiment. Air conditioner 200 includes compressor 251 incorporating motor 500 according to Embodiment 1, four-way valve 259 , outdoor heat exchanger 252 , expansion valve 261 , and indoor heat exchanger 257 via refrigerant pipe 262 . A separate type air conditioner is provided with a refrigerating cycle attached to it. Components having functions similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

A compression mechanism 250 that compresses refrigerant and a motor 500 that operates the compression mechanism 250 are provided inside the compressor 251 . Refrigerant circulates between the compressor 251 and the outdoor heat exchanger 252 and between the compressor 251 and the indoor heat exchanger 257 to form a refrigeration cycle for cooling and heating. Note that the configuration shown in FIG. 14 can be applied not only to air conditioners but also to refrigeration cycle devices such as refrigerators and freezers having a refrigeration cycle.

Next, operations of the main parts of the air conditioner 200 according to Embodiment 2 will be described with reference to FIG. 15 . FIG. 15 is a time chart showing an example of the operating method of the air conditioner 200 according to Embodiment 2. FIG. As a premise for the description of FIG. 15, it is assumed that the wire connection state of the windings of the motor 500 is star connection, which is the default wire connection state. Also, in FIG. 15, the thick solid line represents the number of revolutions, and the thick dashed line represents the bus voltage.

First, at time t1, power supply to the air conditioner 200 is started, and is started at time t2. Between time t1 and time t2, the connection state of the windings is switched from star connection to delta connection.

Motor 500 is accelerated between time t2 and time t5. Moreover, since the voltage shortage of the bus voltage is predicted, at time t3, the first boost is performed and the bus voltage is changed to the first voltage. Further, after the bus voltage is changed to the first voltage, the voltage shortage of the bus voltage is predicted, so at time t4, the second boost 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.

At time t5, the rated load is reached, and control for constant rotation speed is performed between time t5 and time t6. Also, between time t5 and time t6, the controller 10 of the motor drive device 100 determines whether the absolute value of the temperature difference between the target temperature and the room temperature is less than the threshold. If the temperature difference is less than the threshold, the deceleration operation is performed for restarting. In addition, in the example of FIG. 15, the deceleration operation is started at time t6.

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

It is restarted at time t9, and motor 500 is accelerated between time t9 and time t11. At time t10 when the voltage shortage is expected, the voltage is boosted and the bus voltage is changed to the first voltage. At time t11, the engine reaches an intermediate load, and control for constant rotation speed is performed from time t11 to time t12. In addition, between the time t11 and the time t12, the operation is performed with an intermediate load, and boosting up to the second voltage is unnecessary.

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

An example of the operation pattern in the air conditioner 200 according to Embodiment 2 has been described above. Some operations are supplemented below.

First, the room temperature information required for the determination between time t5 and time t6 can be grasped by the functions normally possessed by the air conditioner 200 .

Also, between the time t5 and the time t6, the absolute value of the temperature difference between the target temperature and the 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. Moreover, whether or not the value is less than the threshold is an example of a condition determined by a determination index, and other conditions may be used. Here, this condition is called "first condition". That is, between time t5 and time t6, it is sufficient to determine whether the determination index satisfies the first condition.

In the example of FIG. 15, the connection state of the windings is switched from the star connection to the delta connection at the first startup. There is no need to switch from wire connection to delta connection, just start with delta connection.

The example of FIG. 15 is an embodiment in which the connection state of the windings is not switched during both the period from start to stop and the period from restart to stop. You may switch the connection state of a line. A sudden load change is assumed to be a sudden change in temperature due to the opening and closing of a door or window, cooking in a kitchen, or the like. In addition, when winding is performed while the air conditioner 200 is in operation, it is preferable to provide a hysteresis to the threshold value of the temperature difference 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 switches the connection state of the windings to the delta connection and starts up. When the condition of (1) is satisfied, the motor drive device 100 is stopped and then the connection state of the windings is switched to the star connection and restarted. As a result, the air conditioner 200 can be operated in a way that makes use of the respective features of the star connection and the delta connection, and the efficiency of the air conditioner 200 can be improved as compared with the case where the connection switching motor is not used.

It should be noted that the configuration shown in the above embodiment shows an example of the contents of the present invention, and it is possible to combine it with another known technique, and the configuration can be changed without departing from the gist of the present invention. It is also possible to omit or change part of

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 62U U-phase switch 62V V-phase switch 62W W-phase switch 100 Motor drive device 200 Air conditioner 250 Compression mechanism 251 Compressor 252 Outdoor heat exchanger 257 Indoor heat Exchanger 259 Four-way valve 261 Expansion valve 262 Refrigerant piping 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)

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 operations of the switching element , and performing a synchronous rectification operation of the switching element ;
a capacitor for smoothing the DC voltage output from the booster circuit;
an inverter circuit that converts the power accumulated in the capacitor into AC power and supplies the power to the motor;
with
The motor has a plurality of windings,
Both ends of the winding are open, and by changing connection destinations of the both ends, the connection state of the winding can be switched between a first connection state and a second connection state,
The voltage applied to the motor in the first connection state is higher than the voltage applied to the motor in the second connection state under the same motor rotation speed condition,
The number of rotations at a switching point for switching the connection state of the winding between the first connection state and the second connection state is defined as a first rotation number, and when the winding is in the first connection state, the When the number of revolutions at which the induced voltage, which is the voltage induced in the windings, reaches the rectified voltage, which is the output voltage of the booster circuit when the booster circuit does not perform the boosting operation, is defined as the second number of revolutions. In the section between the first rotation speed, the output voltage of the booster circuit is boosted to a first voltage higher than the rectified voltage,
The second rotation speed is lower than the first rotation speed,
The output voltage of the booster circuit is a rectified voltage in the interval below the second rotation speed.
motor drive. 2. The motor according to claim 1, wherein when the connection state of the windings is switched to the second connection state, the output voltage of the booster circuit can be boosted to a second voltage higher than the first voltage. drive. The output voltage of the booster circuit is
In the first connection state, the rectified voltage or the first voltage,
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. The first connection state is star connection,
The motor driving device according to any one of claims 1 to 3, wherein the second connection state is delta connection. The motor drive device according to any one of claims 1 to 4, wherein the switching element is made of a wide bandgap semiconductor. The motor drive device according to claim 5, wherein the wide bandgap semiconductor is silicon carbide, gallium nitride, gallium oxide, or diamond. An air conditioner driven by the motor drive device according to claim 4,
when the determination index does not satisfy the first condition, switching the connection state of the windings to the delta connection for activation;
The air conditioner is restarted by switching the connection state of the windings to the star connection after stopping the motor drive device when the determination index satisfies the first condition. An air conditioner driven by the motor drive device according to claim 4,
In an initial state, the winding is switched to the star connection,
when the determination index does not satisfy the first condition, switching the connection state of the windings to the delta connection for activation;
When the determination index satisfies the first condition, the air conditioner is started with the connection state of the windings as the star connection. The determination index is the absolute value of the temperature difference between the target temperature and the room temperature,
The air conditioner according to claim 7 or 8, wherein 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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