JPWO2019225486A1 - Motor drive and refrigerator using this - Google Patents

Abstract

An inverter (4) having switching units (4a to 4f), switching input power by the switching units (4a to 4f) and supplying the brushless DC motor, and a control unit (8) for controlling the inverter (4). , Equipped with. The control unit (8) intermittently acquires the position information of the rotation of the brushless DC motor (5), generates a PWM control signal based on the position information, and the switching unit (4a to 4f) based on the PWM drive signal. Is configured to switch. The switching units (4a to 4f) are controlled to be turned on for each predetermined number of carriers based on the PWM drive signal, and the switching units (4a to 4f) are controlled to be turned on from the start of a predetermined carrier. It is controlled on at least for a period until the time when the control unit (8) first acquires the position information.

Description

The present disclosure relates to a motor drive device for driving a brushless DC motor and a refrigerator using the motor drive device.

Conventionally, in this type of motor drive device, the motor is driven by PWM control. In PWM control, the PWM on ratio is increased or decreased by changing the on width in PWM control, and the voltage applied to the motor is controlled. Therefore, the lower the rotation speed of the current motor, the lower the PWM on ratio, and the higher the current speed, the higher the PWM on ratio. Further, the lighter the load, the lower the PWM on ratio, and the heavier the load, the higher the PWM on ratio.

PWM control includes asynchronous PWM control and synchronous PWM control. Asynchronous PWM control is a method of operating without synchronizing between the drive frequency of the motor and the carrier frequency of PWM. Synchronous PWM control is a method of synchronizing the carrier frequency of PWM with an integral multiple of the drive frequency of the motor.

Synchronous PWM control is used at the time of high load, high speed driving, etc., such as suppressing the temperature rise of the inverter circuit (see, for example, Patent Document 1). Further, as a position detection method in synchronous PWM control, a method using an offset of the current value flowing in the motor in addition to a sensor such as a resolver or a Hall element (see, for example, Patent Document 2) and a current value detection method. However, there is a method of estimating using dq coordinate conversion or the like (see, for example, Patent Document 3).

FIG. 5 is a conventional motor drive device described in Patent Document 2. As shown in FIG. 5, the motor drive device includes an inverter 102 composed of a brushless DC motor 101 and a plurality of switching elements for driving the brushless DC motor 101. Further, the motor drive device includes an angle detection unit 103 that detects the angle of the brushless DC motor 101, a current detection unit 104 that detects the current flowing through the brushless DC motor 101, and an angle of the brushless DC motor detected by the angle detection unit 103. , The current offset amount calculation unit 105 that calculates the current offset amount that represents the deviation between the current value detected by the current detection unit 104 and the target current, the drive signal generation unit 106 that PWM-controls the brushless DC motor 101, and It has a phase signal correction unit 107 that corrects the drive signal generated by the drive signal generation unit 106 according to the current offset amount calculated by the current offset calculation unit 105 and switches the inverter 102.

The drive signal generation unit 106 generates an appropriate drive signal according to the phase angle of the brushless DC motor 101 detected by the angle detection unit 103. The phase signal correction unit 107 corrects the deviation of the phase angle output by the angle detection unit 103, and drives the inverter 102. As a result, a voltage suitable for the phase angle of the brushless DC motor is applied, and the brushless DC motor 101 can be driven stably.

However, Patent Document 1 does not disclose details regarding the detection of the phase of the motor.

Further, in the motor drive device according to Patent Document 2, an angle sensor such as a resolver is used for acquiring the phase information of the motor, and there is a problem that the cost is high.

Further, in the motor drive device according to Patent Document 3, sensorless control without using a sensor is performed, but a current detector for current detection, a processor for performing advanced calculations, and the like are required, and there is a problem that the cost is high. There is.

Japanese Unexamined Patent Publication No. 2016-134950 Japanese Unexamined Patent Publication No. 2001-298992 Japanese Unexamined Patent Publication No. 2012-110079

The present disclosure provides a motor drive device capable of stably driving a motor while detecting position information of a brushless DC motor with an inexpensive configuration.

The motor drive device of the present disclosure includes a switching unit, an inverter that switches input power by the switching unit and supplies the brushless DC motor, and a control unit that controls the inverter. The control unit intermittently acquires the position information of the rotation of the brushless DC motor, generates a PWM drive signal for driving the switching unit based on the position information, and switches the switching unit based on the PWM drive signal. It is composed. The switching unit is controlled to be turned on for each predetermined number of carriers based on the PWM drive signal, and at least the control unit first acquires the position information from the start of a predetermined carrier whose switching unit is controlled to be ON. It is controlled to be on until the time when it is done.

FIG. 1 is a block diagram of an overall configuration including a motor drive device according to the embodiment of the present disclosure. FIG. 2 is a waveform diagram showing the PWM drive signal in the same embodiment, and the current and terminal voltage of the brushless DC motor. FIG. 3 is a waveform diagram of a PWM drive signal when the switching section in PWM control is changed. FIG. 4 is a flowchart relating to speed control of the brushless DC motor. FIG. 5 is a block diagram showing a conventional motor drive device.

The motor drive device according to one aspect of the present disclosure includes a switching unit, an inverter that switches input power by the switching unit and supplies the brushless DC motor, and a control unit that controls the inverter. The control unit intermittently acquires the position information of the rotation of the brushless DC motor, generates a PWM drive signal for driving the switching unit based on the position information, and switches the switching unit based on the PWM drive signal. It is composed. The switching unit is controlled to be turned on for each predetermined number of carriers based on the PWM drive signal, and at least the control unit first acquires the position information from the start of a predetermined carrier whose switching unit is controlled to be ON. It is controlled to be on until the time when it is done.

With such a configuration, a sensor for detecting the phase of the brushless DC motor becomes unnecessary. It also eliminates the need for a processor to perform complex timing calculations to detect the phase of the brushless DC motor. Therefore, the position information of the brushless DC motor that appears during ON in the PWM control can be detected by an inexpensive configuration. In addition, the position information of the brushless DC motor can be reliably acquired. Therefore, the brushless DC motor can be stably driven.

In the motor drive device according to another aspect of the present disclosure, the switching unit is turned on and off from the time when the control unit first acquires the position information to the start of the next carrier of a predetermined carrier. It may be controlled.

With such a configuration, it is possible to change the on ratio of PWM control while surely acquiring the position information.

In the motor drive device according to still another aspect of the present disclosure, the start timing of each carrier of continuous carriers may be synchronized with the switching timing of the energized phase.

With such a configuration, the motor can be stably driven while detecting the position information of the brushless DC motor.

In the motor drive device according to still another aspect of the present disclosure, each carrier section of continuous carriers has a section of every 60 degrees of electric angle with reference to an electric angle of 0 degrees when the brushless DC motor is driven. It may be synchronized.

With such a configuration, the motor can be stably driven while detecting the position information of the brushless DC motor.

In the motor drive device according to still another aspect of the present disclosure, the switching unit is continuously controlled to be on from the start of a predetermined carrier to the end of the next carrier, and the switching unit is of the next carrier. It may be controlled off at the end.

With such a configuration, it is possible to increase the on ratio of PWM control while reliably acquiring the position information.

The motor drive device according to still another aspect of the present disclosure is configured such that the control unit determines the carrier cycle of a predetermined carrier based on the position information first acquired from the start of the predetermined carrier. May be good.

With such a configuration, the motor can be driven stably.

In the motor drive device according to still another aspect of the present disclosure, the PWM drive signal may be a rectangular wave.

With such a configuration, the calculation required for detecting the rotation position of the brushless DC motor becomes simple, and the motor drive device can be made an inexpensive configuration.

In the motor drive device according to still another aspect of the present disclosure, the control unit may acquire information on the magnetic pole position of the brushless DC motor from the induced voltage of the brushless DC motor as the position information of the rotation of the brushless DC motor. ..

With such a configuration, the timing at which the zero cross of the induced voltage, which is the reference for each phase of the brushless DC motor, appears is during the ON period in the PWM control. Therefore, the position of the brushless DC motor can be detected with high accuracy.

The motor drive device according to one aspect of the present disclosure includes a switching unit, an inverter that switches input power by the switching unit and supplies the brushless DC motor, and a control unit that controls the inverter. The control unit includes a position detection unit that detects a reference position of the brushless DC motor that drives the load, and a PWM generation unit that generates a waveform for driving the brushless DC motor based on the information of the position detection unit. The PWM output by the PWM generation unit is turned on at least until the position detection unit detects the reference position of the brushless DC motor.

With such a configuration, it is possible to reliably detect the position information of the brushless DC motor that appears during ON in the PWM control, and to stably drive the brushless DC motor.

The motor drive device according to still another aspect of the present disclosure may be a motor in which a brushless DC motor driven by the motor drive device drives a compressor.

With such a configuration, even in a brushless DC motor that drives a compressor in a high-temperature closed space, position detection can be performed without a sensor, so that the motor drive device can be inexpensively configured.

The refrigerator according to one aspect of the present disclosure includes a refrigeration cycle circuit configured by connecting a compressor having a brushless DC motor, a condenser, a decompressor, and an evaporator. The brushless DC motor is driven by any of the motor drive devices described above.

With such a configuration, the power consumption of the refrigerator having a high operating rate at a low speed of the compressor can be reduced, and the power consumption of the refrigerator can be effectively reduced by the inexpensive configuration.

(Embodiment)
[1. overall structure]
FIG. 1 is a block diagram of an overall configuration including a motor drive device according to an embodiment of the present disclosure.

As shown in FIG. 1, the motor drive device 13 includes an inverter 4 and a control unit 8 that controls the inverter 4.

The inverter 4 has switching units 4a to 4f. The inverter switches the input power by the switching units 4a to 4f and supplies it to the brushless DC motor 5.

Hereinafter, a more detailed description will be given.

The AC power supply 1 shown in FIG. 1 is a general commercial power supply. For example, in Japan, it is a power supply having an effective value of 100 V and a frequency of 50 Hz or 60 Hz.

The AC power from the AC power supply 1 is input to the rectifier circuit 2. The rectifier circuit 2 rectifies the input AC power into DC power. The rectifier circuit 2 is composed of four bridge-connected rectifier diodes 2a to 2d.

The smoothing unit 3 is connected to the output side of the rectifier circuit 2 and smoothes the output of the rectifier circuit 2. The smoothing portion 3 is composed of a smoothing capacitor, a reactor (inductor), and the like. As shown in FIG. 1, the smoothing portion 3 may be composed of only a smoothing capacitor for simplification of the circuit configuration.

When a reactor is used, it may be inserted between the AC power supply 1 and the capacitor. Further, the reactor may be inserted before and after the rectifier diodes 2a to 2d, that is, on either the input side or the output side of the rectifier circuit 2. Further, when a reactor is used and a common mode filter constituting the high frequency removing means is provided in the circuit, it is necessary to consider the synthetic component of the reactance and the reactance component of the high frequency removing means.

In the present embodiment, the inverter 4 converts the DC power from the smoothing portion 3 into AC power. The inverter 4 has six switching elements 4a to 4f, which are switching units, and these switching elements 4a to 4f are connected by a three-phase bridge. Further, in the present embodiment, the six diodes 4g to 4l for the reflux current are connected in parallel with the switching elements 4a to 4f so as to be opposite to the conduction direction of the switching elements 4a to 4f. Will be done.

The brushless DC motor 5 has a rotor 5a having a permanent magnet and a stator 5b having a three-phase winding. The rotor 5a rotates when the three-phase AC current generated by the inverter 4 flows through the three-phase winding of the stator 5b of the brushless DC motor 5. Further, the number of poles of the brushless DC motor 5 is determined according to the required characteristics. The number of poles of the brushless DC motor 5 is 4 poles in the present embodiment, but the number of poles is not limited to this and may be other than 4 poles.

The control unit 8 includes, for example, a storage unit (not shown) for storing the control program and an arithmetic processing unit (not shown) for executing the control program.

In the present embodiment, the control unit 8 intermittently acquires position information, which is information on the phase angle of rotation of the brushless DC motor 5. Further, the control unit 8 generates a PWM drive signal based on the acquired position information. The control unit 8 switches the switching unit based on the generated PWM control signal. Further, the control unit 8 controls the switching unit to be turned on for each predetermined carrier based on the PWM drive signal, and the period from the start of the predetermined carrier to at least the time when the position information is first acquired. Control the switching unit on.

As shown in FIG. 1, the control unit 8 may include, for example, a position detection unit 6, a speed detection unit 7, a PWM generation unit 10, and a drive unit 12.

The position detection unit 6 detects the magnetic pole position of the rotor 5a as the rotation position information of the brushless DC motor 5. In the present embodiment, the position detection unit 6 detects the magnetic pole position of the rotor 5a based on the induced voltage generated in the three-phase winding of the stator 5b. More specifically, the position detection unit 6 detects the value of the terminal voltage of the brushless DC motor 5 and thereby acquires the magnetic pole relative position of the rotor 5a of the brushless DC motor 5. The position detection unit 6 may be configured to continuously detect the value of the terminal voltage of the brushless DC motor 5, or is constant including the timing at which the position information of the rotation of the brushless DC motor 5 is acquired. It may be configured to detect the value of the terminal voltage during the period.

In the present embodiment, the position detection unit 6 compares the induced voltage generated in the three-phase winding of the stator 5b with the reference voltage (reference voltage), detects zero cross, and detects the rotor. The relative rotation position of 5a is detected. Here, the reference voltage to be compared with the zero cross of the induced voltage may be defined by the virtual midpoint of the terminal voltage for three phases, or may be defined by the acquired DC bus voltage. Good. In this embodiment, the value of the virtual midpoint is used as the reference voltage. When a method of detecting the position of the brushless DC motor 5 based on the induced voltage is used as in the present embodiment, it is not necessary to use a Hall element or the like, so that the configuration is simple. Therefore, it is possible to configure the motor drive device at a lower cost.

The speed detection unit 7 detects the rotation speed of the brushless DC motor 5. In the present embodiment, the speed detection unit 7 uses the position information detected by the position detection unit 6 to obtain the current drive speed (rotational speed) of the brushless DC motor 5 and the average speed (rotational speed) of one rotation in the past. To calculate. Specifically, the current velocity is calculated from the time of the zero cross detection interval of the induced voltage. Further, the average speed of one rotation in the past is calculated from the sum of the detection interval times for one rotation by recording the time of the detection interval of the zero cross of the induced voltage for one rotation of the brushless DC motor 5. Then, these calculations are performed every time the position detection unit 6 detects a zero cross of the induced voltage.

The PWM generation unit 10 sets the on ratio (Duty) in the PWM control and generates a PWM signal. Here, the on ratio (Duty) in PWM control is the ratio of the on period in the carrier cycle of one carrier. The PWM signal is a square wave having information on the carrier period and the on ratio. The carrier cycle will be described later.

In the present embodiment, each time the position detection unit 6 detects a zero cross of the induced voltage, the PWM generation unit 10 determines the average speed of one rotation detected by the speed detection unit 7 and the target speed input from the outside. To compare. Then, when the target speed is faster than the average speed of one rotation, the PWM generation unit 10 sets the on ratio of the PWM control so as to increase the voltage applied to the brushless DC motor 5. On the other hand, when the target speed is slower than the average speed of one rotation, the PWM generation unit 10 sets the on ratio of the PWM control so as to lower the voltage applied to the brushless DC motor 5. Further, when the target speed and the average speed of one rotation match, the PWM generation unit 10 sets the on ratio of the PWM control so as to maintain the voltage applied to the brushless DC motor 5. As a result, the average speed of one rotation of the brushless DC motor 5 is controlled.

Further, the PWM generation unit 10 generates a waveform (motor drive waveform) for generating a rotating magnetic field for driving the brushless DC motor 5. In the present embodiment, the motor drive waveform is a rectangular wave. This simplifies the calculation required to detect the rotational position of the brushless DC motor 5, and makes the motor drive device 13 an inexpensive configuration.

The PWM generation unit 10 calculates the energization switching timing from the position detection timing detected by the position detection unit 6 and the current drive speed calculated by the speed detection unit 7. Then, a motor drive waveform is generated so as to switch the energized phase between the phases.

In the present embodiment, since the brushless DC motor 5 is a three-phase motor, the combination of the energizing phases changes every 60 degrees in the electric angle. Then, in the energization period of one phase, basically, energization of 120 degrees at an electric angle and subsequent off of 60 degrees are repeated.

The switching elements 4a, 4c, and 4e are sequentially energized so as to deviate by 120 degrees with respect to the electric angle. Similarly, the switching elements 4b, 4d, and 4f are sequentially energized so as to deviate by 120 degrees in the electric angle. Further, the switching element 4a and the switching element 4b are deviated by 180 degrees in terms of electric angle, and energization is started. Similarly, the switching element 4c and the switching element 4d are started to be energized with a deviation of 180 degrees in the electric angle, and the switching element 4e and the switching element 4f are started to be energized with a deviation of 180 degrees in the electric angle. As a result, a rotating magnetic field is formed, and the rotor 5a of the brushless DC motor 5 rotates.

Further, the PWM generation unit 10 calculates the frequency (carrier frequency) of the PWM signal. The carrier frequency is calculated from the current drive speed of the brushless DC motor 5.

Then, the PWM generation unit 10 generates a PWM drive signal by synthesizing the motor drive waveform and the PWM signal. The PWM drive signal may be a rectangular wave.

In the present embodiment, the start timing of the PWM cycle (carrier cycle) is synchronized with the timing of switching the energizing phase of the brushless DC motor 5. That is, in the present embodiment, each carrier section of the continuous carriers is synchronized with the section every 60 degrees of the electric angle with reference to the electric angle of 0 degrees when the brushless DC motor 5 is driven. Therefore, the switching unit 4a is turned on at the same timing as the start timing of the predetermined carrier. Then, at least until the position detection unit 6 first detects the zero cross of the induced voltage, the PWM output is turned on to the switching unit 4a. That is, the switching unit 4a is turned on for each predetermined number of carriers based on the PWM drive signal, and from the start of the predetermined carrier in which the switching unit 4a is controlled to be turned on to at least the time when the position information is first acquired. It will be turned on for the period of. Similarly, the switching units 4b to 4f are also turned on for each predetermined number of carriers based on the PWM drive signal, and the switching units are controlled to be turned on at least at the first position from the start of the predetermined carriers. It is turned on until the time when the information is acquired. As a result, the brushless DC motor 5 can be stably driven while detecting the position information of the brushless DC motor 5. The predetermined carriers described above are different from each other between the switching units 4a to 4f.

In the present embodiment, since the brushless DC motor 5 is a three-phase motor as described above, the combination of the energizing phases changes every 60 degrees in the electric angle. Therefore, the PWM generation unit 10 generates and outputs a PWM drive signal so that the switching units 4a to 4f are controlled to be turned on by PWM control every 6 carriers as a predetermined number of carriers.

At the start of the carrier cycle of a predetermined carrier of PWM control, the carrier frequency of PWM control in the predetermined carrier is in an undetermined state. PWM is turned on until the position detection unit 6 detects zero crossing of the induced voltage. Then, at the time of zero crossing of the induced voltage, the carrier cycle (carrier frequency) of the PWM control in the predetermined carrier and the off start timing in the PWM control are determined based on the acquired position information.

The drive speed of the brushless DC motor 5 is detected by the speed detection unit 7, for example, as in the present embodiment. The speed detection unit 7 detects the drive speed when the position detection unit 6 detects a zero cross of the induced voltage. The zero cross of the induced voltage is the reference position for driving the brushless DC motor 5.

The drive unit 12 turns on or off (hereinafter, referred to as on / off) the switching elements 4a to 4f of the inverter 4 based on the PWM drive signal generated by the PWM generation unit 10. More specifically, the drive unit 12 generates a drive signal based on the PWM drive signal generated by the PWM generation unit 10, and inputs the drive signal to the control terminals of the switching elements 4a to 4f.

The motor driving device 13 may include a rectifier circuit 2 and a smoothing portion 3 in addition to the inverter 4. Then, the motor drive device 13 may be connected to the AC power supply 1. Further, the motor drive device 13 may be configured to include a position detection unit 6, a speed detection unit 7, a PWM generation unit 10, and a drive unit 12 as the control unit 8. The motor drive device 13 configured in this way drives the brushless DC motor 5.

As the compressor 20, an arbitrary compression method (mechanism) such as a rotary type or a scroll type is used. For example, in the present embodiment, the compressor 20 is a reciprocating type.

In the reciprocating compressor 20, a crankshaft (not shown) connected to the rotor 5a of the brushless DC motor 5 converts the rotational motion of the rotor 5a into a reciprocating motion. Then, a piston (not shown), which is a compression element connected to the crankshaft, reciprocates in the cylinder (not shown). As a result, the refrigerant in the cylinder is compressed.

The reciprocating compressor has less leakage of refrigerant during compression, and is particularly efficient at low speeds. Further, the reciprocating compressor can surely follow the speed change even when the current drive speed fluctuates due to the load pulsation. Therefore, since it can be driven at an appropriate timing, it is efficient and power consumption can be suppressed. Further, especially in low-speed driving, even when the current driving speed fluctuates greatly, the carrier cycle of PWM control can be changed according to the change in the current driving speed, so that stable driving is possible. ..

The refrigerant compressed by the compressor 20 passes through the condenser 21, the decompressor 22, and the evaporator 23 in this order, and returns to the compressor 20 again. The refrigerant, which is a medium constituting the refrigeration cycle, dissipates heat in the condenser 21 and absorbs heat in the evaporator 23. Therefore, cooling and heating can be performed by heat exchange with the refrigerant.

The refrigerator 30 has a refrigerating cycle circuit composed of a compressor 20, a condenser 21, a decompressor 22, and an evaporator 23, and the air cooled by the evaporator 23 is sent to a refrigerating chamber and a freezing chamber to provide a casing. The inside of the body is cooled.

[2. Motor drive]
Next, the motor drive device 13 will be described in detail with reference to the drawings.

FIG. 2 is a waveform diagram showing the PWM drive signal in the present embodiment and the current and terminal voltage of the brushless DC motor.

First, the PWM drive signal, the current between the brushless DC motor 5 and the switching element 4a of the inverter 4, and the change in the terminal voltage will be described with reference to FIG.

FIG. 2A is a drive signal from the drive unit 12 input to the switching element 4a, FIG. 2B is a drive signal from the drive unit 12 input to the switching element 4b, and FIG. c) indicates a drive signal from the drive unit 12 input to the switching element 4c. 2 (d) of FIG. 2 is a drive signal from the drive unit 12 input to the switching element 4d, and FIG. 2 (e) is a drive signal from the drive unit 12 input to the switching element 4e. (F) indicates a drive signal from the drive unit 12 input to the switching element 4f. Further, FIG. 2 (g) shows the current flowing between the switching element 4a and the brushless DC motor 5. Further, FIG. 2H shows the terminal voltage between the switching element 4a and the brushless DC motor 5. The direction of the current (g) in FIG. 2 is positive from the switching element 4a to the brushless DC motor 5.

On the horizontal axis of FIG. 2, the sections T1 to T2, T2 to T3, T3 to T4, T4 to T5, T5 to T6, and T6 to T7 each represent the carrier cycle of one carrier in PWM control. In each of these sections, switching is performed on at least one of the three phases.

Specifically, in the section from T1 to T2, the switching element 4b switches. Similarly, in the section from T2 to T3, the switching element 4e is switching, and in the section from T3 to T4, the switching element 4d is switching. Further, in the section from T4 to T5, the switching element 4a is switching, in the section from T5 to T6, the switching element 4f is switching, and in the section from T6 to T7, the switching element 4c is switching. ing.

Each of the switching elements 4a to 4f is turned on in the first half and turned off in the second half in a predetermined carrier section (carrier cycle) for switching. For example, the predetermined carrier for the switching element 4a is a carrier corresponding to the section from T4 to T5. Similarly, the predetermined carriers for each of the switching elements 4b to 4f are carriers corresponding to the sections T1 to T2, T6 to T7, T3 to T4, T2 to T3, and T5 to T6, respectively. Each of the switching elements 4a to 4f may be driven by high activity. Then, the switching elements 4a to 4f are continuously turned on (100% on) in the section of the carrier next to the predetermined carrier that has been switched, and are 100% energized.

As a result, when each of the switching elements 4a to 4f is off, the motor current recirculates, the balance between the currents during on and off is improved, and efficient motor drive control is performed.

The 6 carrier cycles from T1 to T7 correspond to one electrical angle cycle of the brushless DC motor 5. Of the switching elements 4a to 4f, each of the switching elements 4a, 4c, and 4e on the upper side of the inverter 4 is switched based on a waveform shifted by 120 degrees in terms of electrical angle. Further, each of the switching elements 4b, 4d, and 4f on the lower side of the inverter 4 is similarly switched based on the waveforms shifted from each other by an electric angle of 120 degrees. As a result, a rotating magnetic field can be created to rotate the brushless DC motor 5. Further, since the brushless DC motor 5 of the present embodiment has three phases and four poles, two cycles of the electric angle correspond to one rotation of the brushless DC motor 5. Then, the brushless DC motor 5 is continuously rotated by repeating the energization pattern in one cycle of the electric angle.

In the present embodiment, in the section from T4 to T5, the switching element 4a is turned on during the period from T4 to T8. At this time, as shown in FIG. 2 (g), the current monotonically increases in the section from T4 to T8. Then, during the period from T8 to T5, the switching element 4a is turned off and the current decreases monotonically.

In the section from T5 to T6, the switching element 4a is 100% on, but since the switching element 4f is switching, the current increases or decreases.

Further, since the switching element 4a is turned off in the section from T6 to T7, the current converges to 0 in the period from T6 to T9 as shown in FIG. 2 (g). Until the current becomes 0 (the period from T6 to T9), the current shown in FIG. 2 (g) flows to the brushless DC motor 5 through the diode 4h for the reflux current. Therefore, there is only a potential difference of the diode 4h for reflux current between the terminal voltage between the switching element 4a and the brushless DC motor 5 and the ground shown in FIG. 2 (h). Therefore, the terminal voltage sticks to around 0V, and the induced voltage does not appear in the terminal voltage.

Further, in the section from T6 to T7, during the period from T9 to T10, the current flowing from the switching element 4a to the brushless DC motor 5 becomes 0 as shown in FIG. 2 (g). Further, as shown in FIG. 2H, the switching element 4c and the switching element 4f are turned on, but they do not lead to the terminal voltage. Therefore, the intersection (T10) between the midpoint of the DC bus voltage of the inverter 4 (the alternate long and short dash line shown in FIG. 2H) and the induced voltage is detected as the induced voltage zero cross.

In the present embodiment, the switching element 4c is turned on by PWM control in the period from T9 to T10 until at least the induced voltage zero cross is detected. Then, the on width in the PWM control is increased or decreased according to the difference between the target speed and the average speed of one rotation. This makes it possible to reliably detect the position. In addition, switching is performed once for each position detection, and the switching loss becomes very small. Therefore, it is possible to reduce the loss and drive at an arbitrary speed according to the load while increasing the detection accuracy of the magnetic pole position of the brushless DC motor 5.

The PWM generation unit 10 calculates the carrier frequency for PWM control when the position detection unit 6 detects the induced voltage zero cross. Therefore, in the example shown in FIG. 2, the carrier frequency is determined at the timing of T10 when the induced voltage zero cross is detected in the section from T6 to T7.

The carrier frequency is determined as follows. First, the current drive speed is obtained by the reciprocal of the time from the timing of the previous detection of the induced voltage zero cross to the timing of the detection of the current induced voltage zero cross. Next, the timing at which the energizing phase of the brushless DC motor 5 should be switched and the timing at which the carrier cycle of the next carrier is started (the end of the carrier cycle of the current carrier) is calculated to determine the carrier frequency. Then, from the calculated carrier frequency, the timing of the start of off in PWM control (the end of on in PWM control) is determined. At T10, the switching element 4c starts off in PWM control at the same time as the timing of the induced voltage zero cross. In this case, the PWM on ratio is 50%.

Note that FIG. 2 shows a case where the on ratio of PWM control is 50%, but the on ratio is not limited to this. For example, the switching units 4a to 4f may be controlled from on to off from the time when the position information is first acquired from the start of the predetermined carrier to the start of the next carrier of the predetermined carrier. .. Thereby, the on ratio of PWM control can be changed.

Further, the switching units 4a to 4f may be continuously controlled to be on from the start of a predetermined carrier to the end of the next carrier, and may be controlled to be off at the end of the next carrier. That is, the switching units 4a to 4f may be controlled so that the PWM on ratio is 100% in two consecutive carriers.

As described above, in the present embodiment, after the control unit 8 acquires the position information, the control unit 8 determines the timing of the start (end of on) of the current carrier (predetermined carrier) by PWM control, and the next Determines the on timing by carrier PWM control. Therefore, control with high speed response can be performed.

Next, the difference in the switching section will be described with reference to FIGS. 2 and 3.

FIG. 3 is a waveform diagram of a PWM drive signal when the switching section in PWM control is changed. 3 shows the drive signals (drive signals) of the switching elements 4a to 4f, respectively, in FIGS. 3A to 3F, respectively, as in FIG. Further, FIG. 3 (g) shows the current flowing from the switching element 4a to the brushless DC motor 5, and FIG. 3 (h) shows the terminal voltage between the switching element 4a and the brushless DC motor 5. ..

As described above, in FIG. 2, the switching element 4a switches in the section (T4 to T5) of 60 degrees in the first half of the energization section of 120 degrees in the electric angle, and 60 in the electric angle of the latter half. It is 100% energized in the degree section (T5 to T6). On the other hand, in FIG. 3, the switching element 4a energizes 100% of the section (T404 to T405) having an electric angle of 60 degrees in the first half of the energized section of 120 degrees in the electric angle, and has an electric angle of 60 degrees in the latter half. Switching is performed in the section (T405 to T406). That is, in the section (T405 to T406) with an electric angle of 60 degrees in the switching section, the first half (T405 to T408) is turned on and the second half (T408 to T406) is turned off in the same manner as T4 to T8 in FIG.

In the case shown in FIG. 3, the predetermined carrier for the switching element 4a is a carrier corresponding to the section from T405 to T406. Then, the switching element 4a is controlled to be turned on for a period from T405, which is the start of a predetermined carrier, to at least the time when the control unit 8 first acquires the position information. The other switching elements 4b to 4f are also controlled in the same manner as the switching elements 4a from the start of each predetermined carrier.

Further, in the case of FIG. 3, since the switching is turned on and off once in the section of 120 degrees in the electric angle from T404 to T406, the switching loss of the inverter 4 is further reduced.

Further, the terminal voltage shown in FIG. 2 (h) and the terminal voltage shown in FIG. 3 (h) are different. However, in the section from T9 to T10 in FIG. 2 and the section from T409 to T410 in FIG. 3, which are the sections where the position is detected, the waveforms of the terminal voltages are similar to each other. Therefore, even in the case shown in FIG. 3, the position can be detected accurately as in the case shown in FIG. As for the current, the waveform shown in FIG. 2 (g) and the waveform shown in FIG. 3 (g) have substantially the same waveform, and the same torque can be obtained.

[3. Motor speed control]
Next, the speed control of the brushless DC motor 5 by PWM control will be described in detail with reference to FIG.

FIG. 4 is a flowchart relating to speed control of the motor by speed detection and PWM control.

First, it is determined whether or not the induced voltage zero cross, which is the reference of the magnetic pole position of the brushless DC motor 5, is detected. (STEP101). As a result of the determination, if the induced voltage zero cross is not detected, the process shifts to STEP101 again, and the determination is performed again (STEP101, No). For example, the position detection unit 6 detects the induced voltage zero cross, and the speed detection unit 7 makes the determination.

On the other hand, if the induced voltage zero cross is detected, the process proceeds to STEP 102 (STEP 101, Yes).

Next, the current drive speed of the brushless DC motor 5 is calculated from the detection interval of the induced voltage zero cross (STEP102). Since the brushless DC motor 5 is a three-phase four-pole motor, the induced voltage zero cross occurs 12 times during one rotation of the motor. That is, the control unit 8 intermittently acquires the position information of the brushless DC motor 5. Therefore, the current drive speed, which is the number of revolutions per second of the brushless DC motor 5, can be calculated by dividing 1 second by 12 times the position detection interval of the zero cross. At this time, the average speed of one rotation is also calculated. The average speed of one rotation can be calculated by summing the position detection intervals of 12 times, which is the number of position detections during one rotation, and taking the reciprocal. By dividing 1 second by the total position detection interval, the average speed of one revolution per second can be calculated. For example, in this embodiment, the speed detection unit 7 calculates the current drive speed of the brushless DC motor 5. When the calculation is completed, the process proceeds to STEP103.

Next, it is determined whether or not the average speed of one rotation calculated in STEP 102 is faster than the target speed input from the outside (STEP 103). The target speed is input from the outside, but in the refrigerator 30, for example, it is determined by the temperature inside the refrigerator 30. For example, if the temperature inside the refrigerator 30 is higher than the target temperature determined in advance as a temperature suitable for food storage (STPE103, No), a high target speed is set to improve the cooling capacity. On the other hand, if the temperature inside the refrigerator 30 is lower than the target temperature (STPE103, Yes), a low target speed is set to reduce the cooling capacity. In particular, the target speed is set high when the inside of the refrigerator is not cooled, such as when the refrigerator 30 is turned on. If the current average speed of one rotation is faster than the target speed (STEP103, Yes), the process proceeds to STEP104.

In STEP 104, since the PWM control on ratio (Duty) generated by the PWM generation unit 10 is excessive, the PWM control on ratio is reduced (STEP 104), and the process proceeds to STEP 105.

In STEP 105, the PWM carrier cycle of the PWM generation unit 10 is calculated from the on ratio of the PWM control of the PWM generation unit 10 and the current drive speed of the brushless DC motor 5 detected by the speed detection unit 7. Then, the timing of turning on by PWM control and the commutation timing of switching the energization pattern to the brushless DC motor 5 are calculated and set.

For example, assume that the current drive speed calculated in STEP 102 is 20 Hz. In this case, 12.5 / 3 ms, which is the reciprocal of the product of the number of position detections of one rotation of 12 and 20 Hz, is the time from the switching timing of the energizing phase of the brushless DC motor 5 immediately before to the switching timing of the next energizing phase. This is referred to as the PWM carrier cycle. The reciprocal of this PWM carrier cycle becomes the carrier frequency.

In STEP 106, the off timing of PWM control in the current carrier (predetermined carrier) is determined from the carrier cycle calculated in STEP 105 and the PWM on ratio determined by the PWM generation unit 10. For example, assume that the current drive speed of the brushless DC motor 5 is 20 Hz and the on ratio of PWM control is 60%. In this case, the PWM cycle of 12.5 / 3 ms and 2.5 ms, which is the product of 60%, is the on-time from the start of the PWM control in the current carrier, and the timing at which the time elapses is the timing to switch off. .. Then, the timing for switching off, which is calculated in this way, is set, and the process is exited.

On the other hand, in STEP103, when the average speed of one rotation of the brushless DC motor 5 detected by the speed detection unit 7 is slower than the target speed or matches the target speed (STEP103, No), the process proceeds to STEP107.

In STEP107, it is determined whether or not the average speed of one rotation of the brushless DC motor 5 detected by the speed detection unit 7 is slower than the target speed. If the average speed is slower than the target speed (STEP107, Yes), the process proceeds to STEP108.

In STEP 108, in order to increase the average speed of one rotation of the brushless DC motor 5, the on ratio (Duty) of the PWM control generated by the PWM generation unit 10 is increased. Then, it shifts to STEP 105 and STEP 106 in order.

On the other hand, in STEP107, when the target speed and the average speed of one rotation of the brushless DC motor 5 match (STEP107, No), the on ratio of the PWM control of the PWM generation unit 10 is maintained, and the steps are sent to STEP105 and STEP106. And migrate.

By repeating these processes, the PWM generation unit 10 can accelerate when the speed of one rotation of the brushless DC motor 5 is insufficient with respect to the target speed and acceleration is required. Further, when the speed of one rotation of the brushless DC motor 5 is excessive with respect to the target speed and deceleration is required, the speed can be reduced. Further, if the speed of one rotation of the brushless DC motor 5 matches the target speed, the average speed of one rotation can be maintained.

Further, the PWM generation unit 10 switches the energizing phase every 60 degrees at an electric angle. As a result, a rotating magnetic field for rotating the brushless DC motor 5 is generated.

Before the flow process shown in FIG. 4 is performed, a pattern for switching the energized phase is generated. Then, how much voltage is applied to each energized phase and at what timing the energized phase is switched are determined by the flow of FIG.

Further, the lower limit of the on ratio of the PWM control by the PWM generation unit 10 may be 50%. As a result, the ON by PWM control continues at least until the timing of the induced voltage zero cross detection by the position detection unit 6. Therefore, it is possible to detect the zero cross of the induced voltage.

It should be noted that the PWM generation unit 10 cannot control the speed below the lower limit of the on ratio of the PWM control by the PWM generation unit 10. However, the induced voltage can be adjusted by increasing the number of turns of the winding of the stator 5b of the brushless DC motor 5 or increasing the magnetic force of the rotor 5a. As a result, the on ratio of the PWM control of the PWM generation unit 10 can exceed the lower limit even at the minimum speed required for the normal operation of the system and the minimum load.

The motor drive device 13 of the present disclosure turns on the power at the timing of detecting the electric angles of 0 degrees and 180 degrees, which is the reference of each phase of the brushless DC motor 5, that is, the switching 4a to 4f is performed for each predetermined carrier. Since it is turned on, complicated timing calculation for detecting the phase of the brushless DC motor 5 without a sensor is required. Therefore, the position information of the brushless DC motor 5 that appears during the ON period in the PWM control can be reliably detected, and the brushless DC motor 5 can be stably driven.

Further, since the position is detected without a sensor, the brushless DC motor 5 can be driven even in a high-temperature enclosed space or the like when the sensor cannot be arranged.

In addition, the number of switching times for driving the brushless DC motor 5 is small. Therefore, the power consumption can be effectively reduced by applying it to the driving of the brushless DC motor 5 at a low speed in which the switching loss is dominant among the losses of the motor driving device 13.

[4. Compressor]
Next, a case where the motor drive device 13 is applied to the compressor 20 will be described.

In the compressor 20, the brushless DC motor 5 is arranged in a high temperature atmosphere, a refrigerant atmosphere, and an oil atmosphere. Therefore, it is extremely difficult to attach the position sensor to the brushless DC motor 5. Therefore, in many cases, a sensorless technology that can detect the position of the magnetic pole for driving the motor without using a sensor is indispensable.

The motor drive device 13 detects and acquires the magnetic pole position of the rotor 5a of the brushless DC motor 5 housed inside the compressor 20 by the induced voltage of the brushless DC motor 5 that can be detected outside the compressor 20. can do. Specifically, in the present embodiment, the position detection unit 6 detects the magnetic pole position of the rotor 5a.

Further, at least, the switching unit is turned on by PWM control until the position detection unit 6 detects the induced voltage zero cross. As a result, the position detection unit 6 can reliably detect the induced voltage zero cross. Therefore, the brushless DC motor 5 can be driven with high accuracy even without a sensor.

Further, in the present embodiment, the compressor 20 employs a reciprocating compression method. Therefore, it is very efficient in a system such as a refrigerator that is driven at a low speed for a long time. However, in the reciprocating compression method, since the compression step and the suction step are performed separately, a large torque pulsation is periodically generated. Therefore, when the responsiveness of the control is poor, the energization of the stator 5b and the position of the rotor 5a are deviated, and the efficiency deteriorates. Therefore, in the motor drive device 13 of the present embodiment, the current drive speed of the brushless DC motor 5 is detected in order to enhance the responsiveness of the control. Specifically, the speed detection unit 7 detects the current drive speed for each induced voltage zero cross detected by the position detection unit 6 based on the induced voltage zero cross detection interval shown in FIG. 2 or FIG. Then, by changing the on-time and carrier frequency of the PWM control by the PWM generation unit 10, it is possible to instantly respond to a periodic change in torque and a change in speed.

[5. refrigerator]
Next, the refrigerator 30 using the above-mentioned compressor 20 will be described. As shown in FIG. 1, the compressor 20 of the refrigerator 30 is driven by the motor drive device 13.

The required load of the refrigerator 30 varies greatly depending on the load inside the refrigerator, the temperature of the outside air, and the like. Of the operating states of the refrigerator 30, the operating state in which the load in the refrigerator such as food is sufficiently cooled occupies the largest ratio in terms of time. In such an operating state, the compressive load of the compressor 20 is reduced, and the brushless DC motor 5 is operated at a low speed and a low load. Then, as the speed becomes lower and the load becomes lower, the conduction loss of the inverter 4 decreases, and the ratio of the switching loss to the total loss of the inverter 4 increases.

In the present embodiment, the brushless DC motor 5 is driven with the period in which the magnetic pole position of the brushless DC motor 5 is detected with high accuracy and the energization phase of the brushless DC motor 5 is switched as one carrier. Therefore, the brushless DC motor 5 can be driven in a state where the number of switchings is very small. Therefore, the energy saving performance of the refrigerator 30 to which the motor drive device 13 is applied can be greatly improved, particularly in a low speed or low load region where the ratio of switching loss of the inverter 4 is large.

Although FIG. 1 shows an example in which the motor drive device 13 is provided separately from the refrigerator 30, the motor drive device 13 may be provided integrally with the refrigerator 30.

Since the motor drive device of the present disclosure can reduce the loss of the inverter circuit during low-speed operation, it can be applied not only to a refrigerator but also to a motor for driving a compressor in an air conditioner, a vending machine, a showcase, a heat pump water heater, and the like.

1 AC power supply 2 Rectifier circuit 2a, 2b, 2c, 2d Rectifier diode 3 Smoothing part 4 Inverter 4a, 4c, 4e Switching element (switching part)
4b, 4d, 4f switching element (switching unit)
4g, 4i, 4k Diode 4h, 4j, 4l Diode 5 Brushless DC motor 5a Rotor 5b Stator 6 Position detection unit 7 Speed detection unit 8 Control unit 10 PWM generator 12 Drive unit 13 Motor drive 20 Compressor 21 Condenser 22 Compressor 23 Evaporator 30 Refrigerator

Claims (11)

An inverter that has a switching unit, switches the input power by the switching unit, and supplies it to the brushless DC motor.
A control unit that controls the inverter and
With
The control unit
The position information of the rotation of the brushless DC motor is acquired intermittently.
Based on the position information, a PWM drive signal for driving the switching unit is generated.
It is configured to switch the switching unit based on the PWM drive signal.
The switching unit is based on the PWM drive signal.
It is controlled to be turned on for each predetermined number of carriers, and
It is controlled on for a period from the start of a predetermined carrier in which the switching unit is controlled on to at least the time when the control unit first acquires the position information.
Motor drive. The switching unit is controlled from on to off from the time when the control unit first acquires the position information to the start of the next carrier of the predetermined carrier.
The motor drive device according to claim 1. The switching unit is continuously controlled to be on from the start of the predetermined carrier to the end of the next carrier, and is controlled to be off at the end of the next carrier.
The motor drive device according to claim 1. The start timing of each carrier of successive carriers is synchronized with the switching timing of the energizing phase.
The motor drive device according to any one of claims 1 to 3. Each carrier section of the continuous carrier is synchronized with the section every 60 degrees of the electric angle with reference to the electric angle of 0 degrees when the brushless DC motor is driven.
The motor drive device according to any one of claims 1 to 4. The control unit determines the carrier cycle of the predetermined carrier based on the position information first acquired from the start of the predetermined carrier.
The motor drive device according to any one of claims 1 to 5. The PWM drive signal is a square wave.
The motor drive device according to any one of claims 1 to 6. The control unit acquires information on the magnetic pole position of the brushless DC motor from the induced voltage of the brushless DC motor as the position information of the rotation of the brushless DC motor.
The motor drive device according to any one of claims 1 to 7. An inverter that has a switching unit, switches the input power by the switching unit, and supplies it to the brushless DC motor.
A control unit that controls the inverter and
With
The control unit
A position detection unit that detects the reference position of the brushless DC motor that drives the load, and
A PWM generation unit that generates a waveform that drives the brushless DC motor based on the reference position information from the position detection unit.
Have,
The signal output by the PWM generator is turned on until at least the position detector detects the information on the reference position of the brushless DC motor.
Motor drive. The brushless DC motor is a motor that drives a compressor.
The motor drive device according to any one of claims 1 to 9. It includes a refrigeration cycle circuit configured by connecting a compressor with a brushless DC motor, a condenser, a decompressor and an evaporator.
The brushless DC motor is driven by the motor drive device according to any one of claims 1 to 10.
refrigerator.

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