JP2007288858A - Motor controller, refrigerator, and air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor controller which can ensure durability (long term reliability) of an apparatus while silencing motor drive sound as much as possible. <P>SOLUTION: The motor controller X comprises a mode switching circuit 18 outputting a switching signal based on the detection temperature of a temperature sensor 10 for detecting the temperature of a switching element 20, and a PWM signal output circuit 14 for controlling the switching element 20 based on the switching signal. The PWM signal output circuit 14 performs switching between a three-phase line-to-line modulation mode for switching supply voltage to three phases of a motor M in parallel, and a two-phase line-to-line modulation mode for switching supply voltage to only two phases of a motor M in parallel (supply voltage is fixed for one remaining phase) for every period of a predetermined electric angle (e.g. 120°). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a motor control device that controls a three-phase motor, a refrigerator including the motor control device, and an air conditioner.

In general, a motor control device that controls a three-phase motor used in a compressor of a refrigerator, an air conditioner, or the like generally uses a triangular wave carrier signal and a predetermined comparison target signal (usually, a sine wave current to flow through the three-phase motor. , A sine wave) to generate a PWM signal, and a switching circuit (generally a switching element) provided in the inverter circuit performs switching according to the PWM signal to convert a DC voltage into an AC voltage, and thereby obtain AC voltage to be applied to each phase of the motor.
Here, as a voltage application method to each phase of the motor, there are a three-phase line modulation method (also referred to as a three-phase pulse width modulation method) and a two-phase line modulation method (also referred to as a two-phase pulse width modulation method). is there.
The three-phase line modulation method generates three PWM signals corresponding to the three phases of the three-phase motor, and the switching circuit converts the three AC voltages obtained by switching according to each of the PWM signals into the three-phase. This is a method applied to each phase of the motor. Thereby, switching is performed in parallel for all the supply voltages to the three phases of the three-phase motor.
On the other hand, the two-phase line-to-line modulation method generates two PWM signals corresponding to two of the three phases of the three-phase motor for each predetermined electrical angle period, and the switching circuit uses the two PWM signals. In this method, two AC voltages obtained by switching according to each signal are applied to two phases of a three-phase motor, and the applied voltage to the remaining one phase is fixed. Thereby, switching is performed in parallel only for the supply voltages to the two phases of the three-phase motor for each period of a predetermined electrical angle.
In general, when a three-phase line-to-line modulation method is employed, the motor drive sound is silenced. Therefore, many motor control devices employed in refrigerators and air conditioners control motors using a three-phase line modulation method.
On the other hand, Patent Document 1 discloses a motor control device that switches between a three-phase line modulation method and a two-phase line modulation method according to the number of rotations of the motor in order to increase the efficiency of motor driving.
JP 2005-318702 A

By the way, when the three-phase line modulation method is employed for motor control, the frequency of switching operation of the switching circuit (element) increases, switching loss increases, and the temperature of the switching circuit rises. And when the situation where the temperature of the switching circuit becomes high occurs frequently, there is a problem that the life of the switching circuit is shortened. Furthermore, when the temperature of the switching circuit becomes too high, there is a problem that the switching circuit is destroyed.
On the other hand, as shown in Patent Document 1, when the motor control for switching from the three-phase line-to-line modulation method to the two-phase line-to-line method when the rotational speed of the motor is in a preset range, switching is performed. Even if the temperature of the circuit leads to shortening of its life or destruction, there is a problem that control by the three-phase line modulation method is continued because the motor speed is not within the set range. obtain.
In addition, if the motor rotation speed setting value for switching from the three-phase line modulation method to the two-phase line method is made too small in order to prevent the temperature of the switching circuit from rising, the silent performance of the motor drive is sacrificed. A point is created.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to provide a motor control capable of ensuring the durability (long-term reliability) of the apparatus while minimizing the motor driving sound as much as possible. It is providing a device and a refrigerator and an air conditioner provided with the device.

In order to achieve the above object, the present invention provides a switching means (a switching circuit provided in an inverter circuit) that converts a DC voltage into an AC voltage by switching the DC voltage and supplies three AC voltages to each phase of a three-phase motor. The circuit (or switching element) is applied to a motor control device having a typical example thereof, and includes the following components (1) and (2).
(1) Temperature detection means for detecting the temperature of the switching means (a typical example of which is a switching element).
(2) By controlling the switching means based on the temperature detected by the temperature detection means, a three-phase line-to-line modulation mode (that is, switching in parallel for all the supply voltages to the three phases of the three-phase motor) , An operation mode in the three-phase line modulation method), and a two-phase line modulation mode in which switching is performed in parallel only for the supply voltages to the two phases of the three-phase motor every period of a predetermined electrical angle ( That is, the line modulation control means for switching to the operation mode in the two-phase line modulation method.
More specifically, when the inter-line modulation control unit is in the three-phase inter-line modulation mode, the mode is switched to the two-phase inter-line modulation mode when the temperature detected by the temperature detection unit is equal to or higher than a predetermined temperature. In the two-phase line modulation mode, when the detected temperature of the temperature detecting means becomes lower than a predetermined temperature, the mode is switched to the three-phase line modulation mode.

The motor control device having the components shown in the above (1) and (2) can surely prevent the temperature state of the switching means from becoming a situation that leads to shortening or destruction of its life, and further within that range. Motor drive noise can be reduced as much as possible.
In general, the switching means performs switching in accordance with each of three PWM signals, and the line modulation control means controls the switching means by changing the PWM signal output to the switching means. Is. In addition, it is conceivable to set the predetermined temperature for each switching direction to a different temperature so that the mode switching has hysteresis.
Further, the line modulation control means controls the switching means so that a combination of two phases to be switched in parallel is changed every predetermined electrical angle period in the two-phase line modulation mode. Is desirable.
As a result, the frequency of switching is distributed to each of the three phases, leading to a prolonged life of the switching means.
Further, the motor control device described above is preferably applied to a refrigerator or an air conditioner equipped with a three-phase motor (for example, a compressor motor) controlled thereby.

  According to the present invention, it is possible to reliably prevent the temperature state of the switching means (switching element) from being brought into a situation where the life of the switching means (switching element) is shortened or destroyed, and a highly durable motor control device can be provided. Furthermore, the motor drive sound can be made as quiet as possible within the range in which the durability of the apparatus can be ensured.

Embodiments of the present invention will be described below with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: It is not the thing of the character which limits the technical scope of this invention.
FIG. 1 is a block diagram showing a schematic configuration of a motor control device X according to the present invention, and FIG. 2 explains a generation process of a PWM signal in each state of a three-phase line modulation mode and a two-phase line modulation mode. FIG. 3 is a diagram showing examples of various signal waveforms in the three-phase line modulation mode in the motor control device X, and FIG. 4 is a two-phase line modulation mode in the motor control device X. It is a figure showing an example of these various signal waveforms.

First, the configuration of the motor control device X according to the embodiment of the present invention will be described with reference to the block diagram shown in FIG.
The motor control device X receives a DC voltage from the DC power supply circuit 1, converts the DC voltage into three AC voltages, and converts the three AC voltages to each phase (U, U) of the motor M (an example of a three-phase motor). V, W). The motor M in the present embodiment is a sensorless DC brushless motor.
Here, the DC power supply circuit 1 includes a rectification circuit 2 that rectifies an AC voltage obtained from an AC power supply G (commercial power supply), and electrolytic capacitors 3 and 4 that smooth the rectified voltage.

As shown in FIG. 1, the motor control device X includes an inverter device 5, an inverter control device 6, an induced voltage detection circuit 8, a current detection circuit 9, and a temperature sensor 10.
The inverter device 5 includes a switching element 20 that switches a DC voltage supplied from the DC power supply circuit 1 and a driver circuit 21 that drives the switching element 20 in accordance with a signal from the inverter control device 6.
The switching element 20 performs switching (ON / OFF) of a DC voltage supplied from the DC power supply circuit 1 to convert the DC voltage into an AC voltage to generate three AC voltages. It supplies to each phase.
Three PWM signals supplied from the inverter control device 6 are input to the switching element 20 through the driver circuit 21. The switching element 20 performs switching of the DC voltage supplied from the DC power supply circuit 1 according to each of the three PWM signals.
The temperature sensor 10 is a sensor that detects the temperature of the switching element 20, and is, for example, a thermistor provided in the vicinity of the switching element 20. The temperature sensor 10 may be another sensor (such as a thermocouple or a radiation thermometer) as long as the temperature of the switching element 20 can be detected directly or indirectly.
The induced voltage detection circuit 8 is a circuit that detects an induced voltage (induced voltage generated in the winding) in each phase of the motor M.
The current detection circuit 9 is a circuit that detects a current in each phase of the motor M (current flowing through the winding).

The inverter control device 6 includes a rotation speed detection circuit 11, a rotor position detection circuit 12, a PWM signal output circuit 14, a duty adjustment circuit 16, a temperature detection circuit 17, a mode switching circuit 18, and the like.
The rotation speed detection circuit 11 rotates the motor M based on the rotor position of the motor M detected by the rotor position detection circuit 12 shown below or the induced voltage of each phase of the motor M detected by the induced voltage detection circuit 8. This circuit detects the speed, and the detection result is transmitted to the duty adjustment circuit 16.
The rotor position detection circuit 12 is based on the induced voltage of each phase of the motor M detected by the induced voltage detection circuit 8 or the rotational speed of the motor M detected by the rotational speed detection circuit 11. The position of the piston connected to M) is detected, and the detection result is transmitted to the duty adjustment circuit 16.
The duty adjustment circuit 16 is a circuit that adjusts (sets) the duty ratio of the PWM signal supplied to the inverter device 5 in accordance with the rotational speed of the motor M and the rotor position (piston position). It is transmitted to the output circuit 14. For example, the duty adjustment circuit 16 adjusts the duty ratio by performing feedback control based on the detection result of the rotation speed of the motor M by the rotation speed detection circuit 11 so that the rotation speed of the motor M becomes a set target speed. Thus, the power supply to the motor M is controlled. The duty adjustment circuit 16 adjusts the duty ratio in synchronization with the rotor position of the motor M by the rotor position detection circuit 12 as necessary.

The PWM signal output circuit 14 is a circuit that generates a PWM signal by comparing the triangular wave carrier signal with a predetermined comparison target signal and outputs the PWM signal to the inverter device 5.
The PWM signal output circuit 14 includes a three-phase line modulation mode for outputting a PWM signal for operating the switching element 20 in the above-described three-phase line modulation method according to a switching signal from a mode switching circuit 18 to be described later. The switching element 20 can be switched to a two-phase line modulation mode that outputs a PWM signal for operating the above-described two-phase line modulation method.
In other words, the mode switching circuit 18 and the PWM signal output circuit 14 switch between the three-phase line modulation mode and the two-phase line modulation mode by controlling the switching element 20 based on the temperature detected by the temperature sensor 10. It is an example of a line modulation | alteration control means.

Here, referring to various signal waveforms shown in FIG. 2, the PWM signal in each state of the three-phase line modulation mode (FIG. 2A) and the two-phase line modulation mode (FIG. 2B). A generation process of the PWM signal by the output circuit 14 will be described. Here, both FIG. 2 (a) and (b) has shown the signal waveform (voltage waveform) for predetermined triangular wave Ct1 period. The horizontal axis of each signal waveform is the electrical angle (phase).
In FIG. 2, PWM signals corresponding to the U terminal (U phase), V terminal (V phase) and W terminal (W phase) of the motor M are respectively represented as Eu and Eu ′, Ev and Ev ′, and Ew. Ew '. Since the switching element 20 of the inverter device 5 applies an AC voltage synchronized with the PWM signal to each phase of the motor M, the waveforms of Eu and Eu ′, Ev and Ev ′, and Ew and Ew ′ are as follows. This is equivalent to the waveform of the voltage applied to the U terminal, V terminal and W terminal of the motor M.
In FIG. 2A, each of the comparison target signals Du, Dv, and Dw is a (part of) sine wave signal corresponding to each of the U, V, and W phases of the motor M.
Similarly, in FIG. 2B, each of the comparison target signals Dv ′ and Dw ′ is (a part of) a sine wave signal corresponding to each phase of V and W of the motor M, respectively.

In the three-phase interline modulation mode, the PWM signal output circuit 14 compares the comparison target signal Du and the triangular wave Ct that intersect the triangular wave Ct with a comparator or the like as shown in FIG. A PWM signal Eu corresponding to the V phase is generated and output. As a result, the inverter device 5 outputs a voltage synchronized with the PWM signal Eu to the U terminal of the motor M.
Similarly, in the PWM signal output circuit 14, each of the comparison target signals Dv and Dw and the triangular wave Ct are compared by a comparator or the like, whereby PWM signals Ev and Ew corresponding to the V terminal and W terminal of the motor M are obtained. Is generated and output. Thus, the inverter device 5 outputs a voltage synchronized with each of the PWM signals Ev and Ew to each of the V terminal and the W terminal of the motor M.
As a result, the line voltage Em (UV) between the U terminal and the V terminal of the motor M becomes a voltage synchronized with the difference between the PWM signals Eu and Ev. In the example shown in FIG. 2A, the level is high in the interval t1 and the interval t2.
Similarly, the line voltage Em (U−W) between the U terminal and the W terminal of the motor M is a voltage synchronized with the difference between the PWM signals Eu and Ew. In the example shown in FIG. 2A, the high level is set in the section t3 and the section t4.

On the other hand, in the two-phase line modulation mode, in the PWM signal output circuit 14, as shown in FIG. 2B, one comparison target signal (Du ′ here) does not intersect with the triangular wave Ct in a certain section. Set to level. As a result, the PMW signal Eu ′ corresponding to one phase (here, the U phase) of the motor M becomes a signal that does not change in that section. That is, switching by the switching element 20 is not performed for one of the three phases of the motor M. Therefore, the applied voltage to one phase (here, the U phase) of the motor M does not change during that interval.
On the other hand, for the remaining two phases (here, V phase and W phase), the PWM signal output circuit 14 compares each of the comparison signals Dv ′ and Dw ′ intersecting the triangular wave Ct with the triangular wave Ct. The PWM signals Ev and Ew corresponding to each of the V terminal and the W terminal of the motor M are generated and outputted, for example. Thus, the inverter device 5 outputs a voltage synchronized with each of the PWM signals Ev and Ew to each of the V terminal and the W terminal of the motor M.
As a result, the line voltage Em (UV) ′ between the U terminal and the V terminal of the motor M becomes a voltage synchronized with the difference between the PWM signals Eu ′ and Ev ′. In the example shown in FIG. 2B, the level is high in the section t5.
Similarly, the line voltage Em (U−W) ′ between the U terminal and the W terminal of the motor M is a voltage synchronized with the difference between the PWM signals Eu and Ew. In the example shown in FIG. 2B, the level is high in the section t6.
In these two modes, if T1 + T2 = T5 and T3 + T4 = T6, the line voltage of the motor M is equal in each of the three-phase line modulation mode and the two-phase line modulation mode.
And even if the mode switching is performed, the PWM signal output circuit 14 has the duty ratios of the line voltages Em (U-W) and Em (UV), and Em (U-W) 'and Em (UV). The waveforms of the comparison target signals Du, Dv, Dw, Du ′, Dv ′, and Dw ′ are set so that the duty ratios of “′” become the duty ratios set by the duty adjustment circuit 16. Each of these waveforms is set based on waveform data stored in advance in a storage unit included in the PWM signal output circuit 14.

On the other hand, the temperature detection circuit 17 is a circuit that outputs the temperature detection result by the temperature sensor 10 as an electrical signal (temperature detection signal), and the temperature detection signal is transmitted to the mode switching circuit 18.
The mode switching circuit 18 compares the temperature detected by the temperature sensor 10 with each of a predetermined first set temperature and second set temperature (where the first set temperature> the second set temperature). This is a circuit that outputs a predetermined switching signal to the PWM signal output circuit 14 only during the period from when the detected temperature becomes equal to or higher than the first set temperature to below the second set temperature. The mode switching circuit 18 is configured by a comparator or a logic circuit, for example.
As a result, the PWM signal output circuit 14 that operates according to the switching signal performs two-phase line modulation when the temperature detected by the temperature sensor 10 is equal to or higher than the first set temperature in the three-phase line modulation mode. Switch to mode. Further, the PWM signal output circuit 14 switches to the three-phase line modulation mode when the temperature detected by the temperature sensor 10 is lower than the second set temperature in the two-phase line modulation mode.
Here, the first set temperature is a temperature that is considered to lead to a shortening of the life or destruction of the switching element 20 when the switching element 20 continues or frequently exceeds the temperature.
Further, by setting the mode switching to have a hysteresis (first set temperature> second set temperature), it is possible to prevent frequent mode switching due to fluctuation of the temperature detected by the temperature sensor 10 near the switching temperature. it can.

Next, specific examples of operation states of the motor control device X in each of the three-phase line modulation mode and the two-phase line modulation mode will be described with reference to signal waveforms such as PWM signals shown in FIGS. 3 and 4. To do.
FIG. 3 is a diagram illustrating an example of various signal waveforms when the motor control device X is in the three-phase line modulation mode. The horizontal axis of each signal waveform is the electrical angle (phase).
When the switching signal is not output from the mode switching circuit 18 (the signal is OFF), the PWM signal output circuit 14 generates a triangular wave Ct as shown in FIG. 3 based on the data stored in the storage unit in advance. Then, comparison target signals Dv, Du, Dw (each sine wave) intersecting with the triangular wave Ct are generated and compared by a comparator or the like. Each comparison signal Dv, Du, Dw is a sine wave having the same period and amplitude but different phases.
As a result, three different PWM signals Eu, Ev, Ew corresponding to the respective phases of the motor M are output to the inverter device 5, and the voltages corresponding to the respective PWM signals Eu, Ev, Ew are output to the respective phases (U phase, V phase, W) of the motor M. Phase).
As shown in FIG. 3, the PWM signals Eu, Ev, Ew generated in the three-phase line-to-line modulation mode are in parallel for all the supply voltages to the three phases of the motor M over the entire period of the electrical angle. Thus, the PWM signal is switched (there is an ON / OFF change).
Here, the waveform of the triangular wave Ct and each of the comparison target signals Dv, Du, Dw is set so that the waveform of the line voltage (phase voltage) of the motor M becomes a waveform equivalent to a sine wave.
FIG. 3 shows a waveform of the line voltage Em (uw) between the U terminal and the W terminal of the motor M, that is, a waveform corresponding to a signal of (Eu−Ew). The waveform of the line voltage Em (uw) is a waveform equivalent to a sine wave. The same applies to the waveform (not shown) of the line voltage Em (uv) between the U terminal and the V terminal of the motor M. As a result, a sinusoidal current flows through the stator winding of the motor M.

On the other hand, FIG. 4 is a diagram illustrating an example of various signal waveforms in the motor control device X in the two-phase line modulation mode.
When the switching signal is output from the mode switching circuit 18 (the signal is ON), the PWM signal output circuit 14 generates a triangular wave Ct as shown in FIG. 4 based on the data stored in the storage unit in advance. Then, comparison target signals Dv ′, Du ′, Dw ′ intersecting with the triangular wave Ct are generated and compared by a comparator or the like. Each of the comparison target signals Dv ′, Du ′, and Dw ′ is an irregular wave that has the same waveform that changes periodically, but has a different phase.
As a result, three different PWM signals Eu ′, Ev ′, Ew ′ corresponding to the respective phases of the motor M are output to the inverter device 5, and the voltages corresponding to the respective PWM signals Eu ′, Ev ′, Ew ′ are output to the respective phases of the motor M (U phase, V Phase, W phase).
As shown in FIG. 4, the PWM signals Eu ′, Ev ′, Ew ′ generated in the two-phase line-to-line modulation mode are for one phase of the motor M for each of the sections Wa, Wb, Wc with an electrical angle of 120 °. The supply voltage is fixed, and only the supply voltages to the remaining two phases are switched in parallel (there is an ON / OFF change) PWM signal. Further, the PWM signals Eu ′, Ev ′, Ew ′ generated in the two-phase line-to-line modulation mode are combinations of two phases that are switched in parallel for each of the sections Wa, Wb, Wc having an electrical angle of 120 °. Is set to change.
In the example shown in FIG. 4, the applied voltage is switched only for the U phase and the V phase in the section Wa, only in the U phase and the W phase in the section Wb, and only in the V phase and the W phase in the section Wc.
Thereby, the frequency of switching is distributed to each of the three phases, leading to a longer life of the switching element 20.
Here, also in the two-phase line-to-line modulation mode, the waveform of the triangular wave Ct and each of the comparison target signals Dv ′, Du ′, Dw ′ is a waveform in which the waveform of the line voltage (phase voltage) of the motor M is equivalent to a sine wave. Is set to be
FIG. 4 shows a waveform of the line voltage Em (uw) ′ between the U terminal and the W terminal of the motor M, that is, a waveform corresponding to a signal of (Eu′−Ew ′). The waveform of the line voltage Em (uw) ′ is a waveform equivalent to a sine wave. The same applies to the waveform (not shown) of the line voltage Em (uv) ′ between the U terminal and the V terminal of the motor M. As a result, a sinusoidal current flows through the stator winding of the motor M.

As can be seen from a comparison between FIG. 3 and FIG. 4, in the two-phase line modulation mode, switching does not occur in each phase of the motor M in one third of the operation time. The switching frequency (the total number of switching times) is reduced to one-third with respect to the three-phase line modulation mode.
For this reason, when the temperature of the switching element 20 rises above the first set temperature, the temperature of the switching element 20 can be lowered by switching from the three-phase line modulation mode to the two-phase line modulation mode.
As a result, if the motor control device X is employed, it is possible to reliably prevent the temperature state of the switching element 20 from being brought into a situation where the lifetime is shortened or destroyed.
Furthermore, since the switching element 20 operates in the three-phase line modulation mode as long as the switching element 20 does not exceed the first set temperature, the motor control device X can reduce the motor driving sound as much as possible.

The motor control device X described above is suitable when applied to a refrigerator or an air conditioner equipped with a three-phase motor controlled thereby. For example, it is conceivable to control a motor for driving a compressor constituting a part of a refrigeration cycle of a refrigerator by the motor control device X, or to control a motor for driving a compressor included in an air conditioner.
Thereby, it is possible to provide a refrigerator and an air conditioner that have high durability and quiet motor driving sound.

  The present invention can be applied to a motor control device.

1 is a block diagram showing a schematic configuration of a motor control device X according to the present invention. The figure showing the various signal waveforms for demonstrating the production | generation process of the PWM signal in each state of a three-phase line modulation mode and a two-phase line modulation mode. The figure showing an example of various signal waveforms at the time of the three-phase line modulation mode in motor control device X. The figure showing an example of various signal waveforms at the time of two phase line modulation mode in motor control device X.

Explanation of symbols

X ... motor control device G ... AC power supply M ... motor 1 ... DC power supply circuit 2 ... rectifier circuit 3, 4 ... electrolytic capacitor 5 ... inverter device 6 ... inverter control device 8 ... induced voltage detection circuit 9 ... current detection circuit 10 ... temperature Sensor 11 Rotational speed detection circuit 12 Rotor position detection circuit 14 PWM signal output circuit 16 Duty adjustment circuit 17 Temperature detection circuit 18 Mode switching circuit

Claims (5)

A motor control device comprising switching means for converting a DC voltage into an AC voltage by switching a DC voltage and supplying three AC voltages to each phase of a three-phase motor,
Temperature detecting means for detecting the temperature of the switching means;
By controlling the switching means based on the temperature detected by the temperature detection means, a three-phase line modulation mode in which switching is performed in parallel for all the supply voltages to the three phases of the three-phase motor; Line modulation control means for switching between two-phase line modulation mode for switching in parallel only for the supply voltage to the two phases of the three-phase motor for each angular period;
A motor control device comprising:   The line modulation control means controls the switching means so that a combination of two phases to be switched in parallel is changed for each period of a predetermined electrical angle in the two-phase line modulation mode. Item 2. The motor control device according to Item 1.   When the inter-line modulation control means is in the three-phase inter-line modulation mode, when the detected temperature of the temperature detecting means becomes a predetermined temperature or more, the mode is switched to the two-phase inter-line modulation mode, 3. The motor control device according to claim 1, wherein the motor control device switches to the three-phase line-to-line modulation mode when the temperature detected by the temperature detection unit becomes lower than a predetermined temperature in the modulation mode.   A refrigerator comprising a three-phase motor and the motor control device according to claim 1 for controlling the motor.   An air conditioner comprising a three-phase motor and the motor control device according to claim 1 for controlling the three-phase motor.

Images