CN111886791A

CN111886791A - Motor driving device and refrigerator using the same

Info

Publication number: CN111886791A
Application number: CN201980019457.8A
Authority: CN
Inventors: 竹冈义典; 田中秀尚
Original assignee: Panasonic Intellectual Property Management Co Ltd
Current assignee: Panasonic Intellectual Property Management Co Ltd
Priority date: 2018-05-22
Filing date: 2019-05-17
Publication date: 2020-11-03
Also published as: JPWO2019225486A1; WO2019225486A1

Abstract

A motor drive device includes an inverter (4) having switching units (4 a-4 f), which switches input power by the switching units (4 a-4 f) and supplies the input power to a brushless DC motor, and a control unit (8) which controls the inverter (4). A control unit (8) intermittently acquires positional information of the rotation of the brushless DC motor (5), generates a PWM control signal based on the positional information, and switches the switching units (4 a-4 f) based on the PWM drive signal. The switches (4 a-4 f) are controlled to be on for each predetermined number of carriers based on the PWM drive signal, and are controlled to be on for a period from the start of the predetermined carrier at which the switches (4 a-4 f) are controlled to be on to at least the time point at which the control unit (8) first acquires the position information.

Description

Motor driving device and refrigerator using the same

Technical Field

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

Background

In the related art, in such a motor driving device, the motor is driven by PWM control. In the PWM control, the applied voltage to the motor is controlled by increasing or decreasing the PWM on ratio by changing the on width of the PWM control. Therefore, the PWM on ratio is lower as the current rotation speed of the motor is lower, and the PWM on ratio is higher as the current speed is higher. Further, the PWM on-ratio is lower as the load is lighter, and the PWM on-ratio is higher as the load is heavier.

In the PWM control, there are asynchronous PWM control and synchronous PWM control. Asynchronous PWM control is a method in which the motor is operated asynchronously between the drive frequency and the carrier frequency of PWM. Synchronous PWM control is a method of synchronizing a carrier frequency of PWM with an integral multiple of a driving frequency of a motor.

The synchronous PWM control is used for suppressing a temperature rise of an inverter circuit (for example, see patent document 1), for example, at the time of high load or at the time of high-speed driving. Further, as a position detection method in the synchronous PWM control, there are a method of using a sensor such as a resolver or a hall element and using an offset of a current value flowing in the motor (for example, see patent document 2), a method of detecting a current value and estimating the current value by using dq coordinate conversion or the like (for example, see patent document 3), and the like.

Fig. 5 shows a conventional motor driving device described in patent document 2. As shown in fig. 5, the motor drive device includes an inverter 102 including 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 an angle of brushless DC motor 101; a current detection unit 104 that detects a current flowing through brushless DC motor 101; a current offset amount calculation unit 105 that calculates a current offset amount indicating a deviation from a target current from the angle of the brushless DC motor detected by the angle detection unit 103 and the current value detected by the current detection unit 104; a drive signal generation unit 106 for PWM-controlling the brushless DC motor 101; and a phase signal correction unit 107 for correcting the drive signal generated by the drive signal generation unit 106 based on the current offset amount calculated by the current offset amount calculation unit 105, and switching the inverter 102.

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

However, patent document 1 does not disclose details about detection of the phase of the motor.

Further, the motor drive device of patent document 2 has a problem of high cost because an angle sensor such as a resolver is used to acquire phase information of the motor.

Further, the motor drive device of patent document 3 performs sensorless control without using a sensor, but requires a current detector for current detection, a processor for performing advanced calculation, and the like, which causes a problem of high cost.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2016-134950

Patent document 2: japanese laid-open patent application No. 2001-298992

Patent document 3: japanese laid-open patent publication No. 2012-110079

Disclosure of Invention

The invention provides a motor driving device which can detect the position information of a brushless DC motor by using a cheap structure and stably drive the motor.

The motor driving device of the invention comprises: an inverter having a switching unit, which switches input power and supplies the switched input power to the brushless DC motor; and a control unit for controlling the inverter. And a control unit for intermittently acquiring position information of rotation of the brushless DC motor, generating a PWM drive signal for driving the switching unit based on the position information, and switching the switching unit based on the PWM drive signal. The switch unit is controlled to be on for every predetermined number of carriers based on the PWM drive signal, and is controlled to be on for a period of time from the start of the predetermined carrier on which the switch unit is controlled to be on to at least the time point when the control unit first acquires the position information.

Drawings

Fig. 1 is a block diagram of the overall configuration including a motor drive device in the embodiment of the present invention.

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

Fig. 3 is a waveform diagram of a PWM drive signal in the case where the switching interval in the 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 driving device.

Detailed Description

An electric motor driving device according to an aspect of the present invention includes: an inverter having a switching unit, which switches input power and supplies the switched input power to the brushless DC motor; and a control unit for controlling the inverter. And a control unit for intermittently acquiring position information of rotation of the brushless DC motor, generating a PWM drive signal for driving the switching unit based on the position information, and switching the switching unit based on the PWM drive signal. The switch unit is controlled to be on for every predetermined number of carriers based on the PWM drive signal, and is controlled to be on for a period of time from the start of the predetermined carrier on which the switch unit is controlled to be on to at least the time point when the control unit first acquires the position information.

According to such a configuration, a sensor for detecting the phase of the brushless DC motor is not required. Further, a processor for performing a calculation for detecting a complicated timing of the phase of the brushless DC motor is not required. Therefore, the position information of the brushless DC motor shown in the on state of the PWM control can be detected with an inexpensive configuration. Further, the position information of the brushless DC motor can be reliably acquired. Therefore, stable driving of the brushless DC motor can be achieved.

In the motor drive device according to another aspect of the present invention, the switch unit may be controlled to be off from on during a period from a time point when the control unit first acquires the position information to a time point when a carrier next to the predetermined carrier starts.

With this configuration, the position information can be reliably acquired, and the on ratio of the PWM control can be changed.

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

With this configuration, the position information of the brushless DC motor can be detected, and the motor can be stably driven.

In the motor driving device according to the still another aspect of the present invention, each carrier segment of the continuous carrier may be synchronized with a segment of 60 degrees per electrical angle with reference to 0 degrees in electrical angle when the brushless DC motor is driven.

In the motor drive device according to the still another aspect of the present invention, the switching unit may be controlled to be on continuously 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.

With this configuration, the position information can be reliably acquired, and the on ratio of the PWM control can be increased.

In the motor drive device according to the still another aspect of the present invention, the control unit may determine the carrier cycle of the predetermined carrier based on the position information obtained first from the start of the predetermined carrier.

With this configuration, the motor can be stably driven.

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

With this configuration, the calculation required for detecting the rotational position of the brushless DC motor is simplified, and the motor drive device can be configured at low cost.

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

With this configuration, the time indicated by the zero crossing of the induced voltage serving as a reference for each phase of the brushless DC motor is in the on period in the PWM control. Therefore, the position of the brushless DC motor can be detected with high accuracy.

An electric motor driving device according to an aspect of the present invention includes: an inverter having a switching unit, which switches input power and supplies the switched input power to the brushless DC motor; and a control unit for controlling the inverter. The control unit includes: a position detection unit for detecting a reference position of a brushless DC motor for driving a load; and a PWM generating unit for generating a waveform for driving the brushless DC motor based on the information of the reference position from the position detecting unit, wherein the signal output from the PWM generating unit is turned on at least before the position detecting unit detects the information of the reference position of the brushless DC motor.

With this configuration, the position information of the brushless DC motor indicated in the on state of the PWM control can be reliably detected, and the brushless DC motor can be stably driven.

In the motor driving device according to the still another aspect of the present invention, the brushless DC motor driven by the motor driving device may be a motor that drives the compressor.

According to such a configuration, even when the brushless DC motor that drives the compressor in the high-temperature closed space is used, the position can be detected without a sensor, and therefore the motor driving device can be configured at low cost.

A refrigerator according to one aspect of the present invention includes a refrigeration cycle circuit in which a compressor having a brushless DC motor, a condenser, a decompressor, and an evaporator are connected. The brushless DC motor is driven by any of the motor driving devices described above.

With this configuration, the power consumption of the refrigerator having a high operation rate at the low speed of the compressor can be reduced, and the power consumption of the refrigerator can be effectively reduced with an inexpensive configuration.

(embodiment mode)

[1. Overall Structure ]

Fig. 1 is a block diagram of the overall configuration including a motor drive device according to an embodiment of the present invention.

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 includes switching units 4a to 4 f. The inverter switches input power by the switching units 4a to 4f to supply the input power to the brushless DC motor 5.

The following description will be made in more detail.

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

The rectifier circuit 2 receives ac power from the ac power supply 1. The rectifier circuit 2 rectifies the input ac power into dc power. The rectifier circuit 2 is constituted by 4 rectifier diodes 2a to 2d which are bridged.

The smoothing unit 3 is connected to the output side of the rectifier circuit 2 to smooth the output of the rectifier circuit 2. The smoothing section 3 is constituted by a smoothing capacitor, a reactor (inductor), and the like. The smoothing unit 3 may be configured by only a smoothing capacitor for simplifying the circuit configuration as shown in fig. 1.

In addition, in the case of using a reactor, the reactor may be interposed between the ac power supply 1 and the capacitor. The reactor may be inserted before or after the rectifier diodes 2a to 2d, that is, on either of the input side and the output side of the rectifier circuit 2. In the case of using a reactor, when a common mode filter constituting a high-frequency removing means is provided in a circuit, it is necessary to consider a composite component of the reactor and a reactance component of the high-frequency removing means.

In the present embodiment, the inverter 4 converts the dc power from the smoothing unit 3 into ac power. The inverter 4 includes 6 switching elements 4a to 4f as a switching unit, and these switching elements 4a to 4f3 are bridged. In the present embodiment, 6 diodes 4g to 4l for a return current are connected in parallel to the switching elements 4a to 4f so as to be in opposite directions with respect to the conduction directions of the switching elements 4a to 4 f.

The brushless DC motor 5 has a rotor 5a having a permanent magnet and a stator 5b having 3-phase windings. The 3-phase alternating current generated in the inverter 4 flows to the 3-phase winding of the stator 5b of the brushless DC motor 5, and thereby the rotor 5a rotates. The number of poles of the brushless DC motor 5 is determined according to required characteristics. The number of poles of brushless DC motor 5 is 4 in the present embodiment, but the number is not limited to this, and a number of poles other than 4 may be used.

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

In the present embodiment, control unit 8 intermittently acquires position information, which is information of a phase angle of rotation of 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. The control unit 8 controls the switching unit to be on for each predetermined carrier based on the PWM drive signal, and controls the switching unit to be on for a period from the start of the predetermined carrier to at least a time point at which the position information is first acquired.

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 driver unit 12.

Position detecting unit 6 detects the magnetic pole position of rotor 5a as the rotational position information of 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 3-phase winding of the stator 5 b. More specifically, position detecting unit 6 detects a value of a terminal voltage of brushless DC motor 5, thereby acquiring a magnetic pole relative position of rotor 5a of brushless DC motor 5. Position detecting unit 6 may be configured to continuously detect the value of the terminal voltage of brushless DC motor 5, or may be configured to detect the value of the terminal voltage for a certain period including the time when the positional information of the rotation of brushless DC motor 5 is acquired.

In the present embodiment, the position detection unit 6 detects the relative rotational position of the rotor 5a by comparing the induced voltage generated in the 3-phase winding of the stator 5b with a reference voltage (reference voltage) and detecting a zero crossing. Here, the reference voltage to be compared with the zero crossing of the induced voltage may be defined by a virtual midpoint of the terminal voltages of the 3 phases, or may be defined by a dc bus voltage obtained by obtaining the voltage. In the present embodiment, the value of the virtual midpoint is used as the reference voltage. As in the present embodiment, when a method of detecting the position of brushless DC motor 5 based on the induced voltage is used, it is not necessary to use a hall element or the like, and the structure is simple. Therefore, the motor drive device can be configured more inexpensively.

The speed detection unit 7 detects the rotation speed of the brushless DC motor 5. In the present embodiment, speed detector 7 calculates the current driving speed (rotation speed) and the average speed (rotation speed) of the previous rotation of brushless DC motor 5 from the position information detected by position detector 6. Specifically, for the current speed, the time of the detection interval of the zero crossing of the induced voltage is measured, from which the current speed is calculated. Further, as for the average speed of the past one revolution, the time of the detection interval of the zero crossing of the induced voltage is recorded by the amount of one revolution of the brushless DC motor 5, and the average speed of the past one revolution is calculated from the sum of the times of the detection intervals of the amount of one revolution. These calculations are performed each time the position detector 6 detects a zero crossing of the induced voltage.

The PWM generating unit 10 sets an on ratio (Duty) in the PWM control and generates a PWM signal. Here, the on ratio (Duty) in the PWM control is a ratio of an on period in a carrier period of 1 carrier. The PWM signal is a rectangular wave having information of a carrier period and an on ratio. The carrier cycle will be described later.

In the present embodiment, PWM generating unit 10 compares the average speed of one revolution detected by speed detecting unit 7 with the target speed input from the outside every time position detecting unit 6 detects the zero crossing of the induced voltage. When the target speed is higher than the average speed of one revolution, PWM generating unit 10 sets the on ratio of PWM control so as to increase the voltage applied to brushless DC motor 5. On the other hand, when the target speed is slower than the average speed of one revolution, PWM generating unit 10 sets the on ratio of the PWM control so as to reduce the voltage applied to brushless DC motor 5. When the target speed matches the average speed of one revolution, PWM generating unit 10 sets the on ratio of the PWM control so as to maintain the voltage applied to brushless DC motor 5. Thereby controlling the average speed of 1 rotation of the brushless DC motor 5.

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

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

In the present embodiment, since the brushless DC motor 5 is a 3-phase motor, the combination of the energized phases changes every 60 degrees in electrical angle. Further, during the energization of one phase, energization by substantially 120 degrees in electrical angle and thereafter disconnection by 60 degrees are repeated.

The

switching elements

4a, 4c, and 4e sequentially start energization so as to be shifted by an electrical angle of 120 degrees. Similarly, the switching elements 4b, 4d, and 4f are sequentially energized so as to be shifted in electrical angle by 120 degrees. Further, the switching element 4a and the switching element 4b start energization every 180 degrees in electrical angle. Similarly, the switching element 4c and the switching element 4d start energization every 180 degrees in electrical angle, and the switching element 4e and the switching element 4f start energization every 180 degrees in electrical angle. Thereby, a rotating magnetic field is formed, and the rotor 5a of the brushless DC motor 5 rotates.

Further, the PWM generating section 10 calculates the frequency (carrier frequency) of the PWM signal. The carrier frequency is calculated from the current driving speed of the brushless DC motor 5.

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

In the present embodiment, the start timing of the PWM period (carrier period) is synchronized with the timing of switching the conduction phase of brushless DC motor 5. That is, in the present embodiment, each carrier segment of the continuous carrier is synchronized with a segment of 60 degrees per electrical angle with reference to 0 degrees in electrical angle when brushless DC motor 5 is driven. Therefore, the switch 4a is turned on at the same timing as the start timing of the predetermined carrier. Then, at least until the position detector 6 first detects the zero crossing of the induced voltage, the PWM output is turned on to the switch 4 a. That is, the switch unit 4a is turned on for every predetermined number of carriers based on the PWM drive signal, and is turned on at least until the time point when the position information is first acquired from the start of the predetermined carrier at which the switch unit 4a is controlled to be on. Similarly, the switches 4b to 4f are also turned on for every predetermined number of carriers based on the PWM drive signal, and are turned on at least until the time point when the position information is first acquired from the start of the predetermined carrier at which the switches are controlled to be on. This allows the position information of brushless DC motor 5 to be detected, and brushless DC motor 5 to be driven stably. The predetermined carriers are different from each other among the switches 4a to 4 f.

In the present embodiment, since the brushless DC motor 5 is a 3-phase motor as described above, the combination of the energized phases is changed every 60 degrees in electrical angle. Therefore, PWM generating unit 10 generates and outputs a PWM drive signal so that switches 4a to 4f are controlled to be on every 6 carriers by PWM control as a predetermined number of carriers.

At the start of a carrier cycle of a predetermined carrier wave of PWM control, a carrier frequency of PWM control of the predetermined carrier wave is in an undetermined state. The PWM is turned on until the position detector 6 detects the zero crossing of the induced voltage. When the zero crossing of the induced voltage occurs, the carrier period (carrier frequency) of the PWM control of the predetermined carrier and the start time of the off of the PWM control are determined based on the acquired position information.

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

The driver 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 generating unit 10. More specifically, the driver unit 12 generates a drive signal based on the PWM drive signal generated by the PWM generating unit 10, and inputs the drive signal to the control terminals of the switching elements 4a to 4 f.

The motor drive device 13 may include the rectifier circuit 2 and the smoothing unit 3 in addition to the inverter 4. The motor drive device 13 may be connected to the ac power supply 1. The motor drive device 13 may include the position detection unit 6, the speed detection unit 7, the PWM generation unit 10, and the driver unit 12 as the control unit 8. The motor drive device 13 configured as described above drives the brushless DC motor 5.

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

In the reciprocating compressor 20, the rotational motion of the rotor 5a is converted into a reciprocating motion by a crankshaft (not shown) connected to the rotor 5a of the brushless DC motor 5. A piston (not shown) as a compression member connected to the crankshaft reciprocates in a cylinder (not shown). Thereby, the refrigerant in the cylinder is compressed.

Further, the reciprocating compressor has less leakage of refrigerant during compression, and particularly has high efficiency at low speed. In addition, the reciprocating compressor can reliably follow the speed change even when the current driving speed fluctuates due to the load pulsation. Therefore, the driving can be performed at an appropriate timing, so that the efficiency is high and the power consumption can be suppressed. In particular, in low-speed driving, even when the current driving speed varies greatly, the carrier cycle of the PWM control can be changed in accordance with the change in the current driving speed, and thus stable driving can be achieved.

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, radiates heat in the condenser 21 and absorbs heat in the evaporator 23. Therefore, cooling and heating by heat exchange with the refrigerant can be performed.

Refrigerator 30 has a refrigeration cycle circuit including compressor 20, condenser 21, decompressor 22, and evaporator 23, and cools the inside of the casing by sending air cooled by evaporator 23 to the refrigerating chamber and the freezing chamber.

[2. Motor drive device ]

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, and the current and terminal voltage of the brushless DC motor in the present embodiment.

First, changes in the PWM drive signal, the current between the brushless DC motor 5 and the switching element 4a of the inverter 4, and the terminal voltage will be described with reference to fig. 2.

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

On the horizontal axis of fig. 2, intervals of T1 to T2, T2 to T3, T3 to T4, T4 to T5, T5 to T6, and T6 to T7 represent carrier periods of 1 carrier to which PWM control is applied, respectively. In each of these intervals, at least 1 of the 3 phases is switched.

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

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 period (carrier cycle) during which switching is performed. For example, the predetermined carrier for the switching element 4a is a segment carrier corresponding to T4 to T5. Similarly, predetermined carriers for the respective 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. The switching elements 4a to 4f may be driven with high activity. The switching elements 4a to 4f are continuously turned on (100% on) in a section of the carrier wave next to the predetermined carrier wave on which switching is performed, and are energized at 100%.

Accordingly, when each of the switching elements 4a to 4f is turned off, the motor current flows back, and the balance between the current during on and the current during off becomes good, thereby performing efficient motor drive control.

In addition, the 6-carrier period of T7 in T1 corresponds to 1 cycle in electrical angle of brushless DC motor 5. Among the switching elements 4a to 4f, the

switching elements

4a, 4c, and 4e, which are the upper switching elements of the inverter 4, are switched on the basis of waveforms that are shifted from each other every 120 degrees in electrical angle. The switching elements 4b, 4d, and 4f, which are the switching elements on the lower side of the inverter 4, are also switched on the basis of waveforms that are shifted from each other by 120 degrees in electrical angle in the same manner. This can produce a rotating magnetic field and rotate the brushless DC motor 5. Further, since brushless DC motor 5 of the present embodiment has 3 phases and 4 poles, electrical angle 2 cycles correspond to one rotation of brushless DC motor 5. Further, by repeating the energization pattern of electrical angle 1 cycle, brushless DC motor 5 continues to rotate.

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

In the interval from T5 to T6, the switching element 4a is turned on at 100%, but the current increases and decreases because the switching element 4f performs switching.

In the interval from T6 to T7, since the switching element 4a is off, the current converges to 0 during the period from T6 to T9 as shown in fig. 2 (g). During the period 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 return current. Therefore, as shown in fig. 2(h), the terminal voltage between switching element 4a and brushless DC motor 5 is a potential difference between the ground and the terminal voltage, which is only diode 4h for the return current. Therefore, the terminal voltage goes around 0V, and no induced voltage appears at the terminal voltage.

In the interval from T6 to T7, the current flowing from the switching element 4a to the brushless DC motor 5 becomes 0 during the period from T9 to T10 as shown in fig. 2 (g). As shown in fig. 2(h), the switching elements 4c and 4f are turned on but not connected to the terminal voltage. Therefore, the intersection (T10) of the midpoint of the dc bus-to-bus voltage of the inverter 4 (the one-dot chain line shown in fig. 2 h) and the induced voltage is detected as an induced voltage zero crossing.

In the present embodiment, the switching element 4c is turned on by PWM control at least until the zero crossing of the induced voltage is detected in the period from T9 to T10. 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 1 revolution. This enables reliable position detection. In addition, the position detection is performed 1 time and the switch is performed 1 time, and the switching loss is very small. Therefore, the accuracy of detecting the magnetic pole position of brushless DC motor 5 can be improved, the loss can be reduced, and the driving can be performed at an arbitrary speed according to the load.

When the position detector 6 detects the zero crossing of the induced voltage, the PWM generator 10 calculates a carrier frequency for PWM control. Therefore, in the example shown in fig. 2, the carrier frequency is determined at the time of T10 when the zero crossing of the induced voltage is detected in the interval from T6 to T7.

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

In fig. 2, the on ratio of the PWM control is shown as 50%, but the on ratio is not limited thereto. For example, the switches 4a to 4f may be controlled to be turned off from on during a period from a time point when the position information is first acquired from a start time of a predetermined carrier to a start time of a carrier next to the predetermined carrier. This can change the on ratio of the PWM control.

The switches 4a to 4f may be controlled to be on continuously 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 switches 4a to 4f may be controlled so that the PWM on ratio becomes 100% in the continuous 2 carriers.

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

Next, the difference between the switching sections will be described with reference to fig. 2 and 3.

Fig. 3 is a waveform diagram of a PWM drive signal in the case where the switching interval in the PWM control is changed. Fig. 3 shows driver signals (drive signals) of the switching elements 4a to 4f in fig. 3(a) to (f), respectively, as in fig. 2. Fig. 3(g) shows a current flowing from the switching element 4a to the brushless DC motor 5, and fig. 3(h) shows a terminal voltage between the switching element 4a and the brushless DC motor 5.

As described above, in fig. 2, the switching element 4a is switched in the first half of the current-carrying interval of 120 degrees in electrical angle (T4 to T5) and is switched at 100% in the second half of the current-carrying interval of 60 degrees in electrical angle (T5 to T6). On the other hand, in fig. 3, the switching element 4a is energized at 100% in the first half of the interval (T404 to T405) of 60 degrees in electrical angle among the energization intervals of 120 degrees in electrical angle, and is switched in the second half of the interval (T405 to T406) of 60 degrees in electrical angle. That is, in the section (T405 to T406) of the switching section at 60 degrees in electrical angle, the first half (T405 to T408) is turned on and the second half (T408 to T406) is turned off, as in T4 to T8 in fig. 2.

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

In the case shown in fig. 3, in the interval of 120 degrees in electrical angle from T404 to T406, the on and off of the switch are each 1 time, and therefore the switching loss of the inverter 4 is lower.

The terminal voltage shown in fig. 2(h) is different from the terminal voltage shown in fig. 3 (h). However, in the section T9 to T10 of fig. 2 and the section T409 to T410 of fig. 3, which are sections in which position detection is performed, the waveforms of the terminal voltages are similar to each other. Therefore, also in the case shown in fig. 3, the position can be accurately detected as in the case shown in fig. 2. In addition, the waveform shown in fig. 2(g) and the waveform shown in fig. 3(g) have substantially the same waveform with respect to the current, and the same torque can be obtained.

[3. speed control of Motor ]

Next, the speed control of the brushless DC motor 5 by the PWM control will be described in detail with reference to fig. 4.

Fig. 4 is a flowchart regarding speed control of the motor based on speed detection and PWM control.

First, it is determined whether or not the zero crossing of the induced voltage as a reference of the magnetic pole position of brushless DC motor 5 has been detected (step 101). As a result of the determination, if the zero crossing of the induced voltage is not detected, the process proceeds to step 101 again, and the determination is performed again (No in step 101). For example, the position detector 6 detects the zero crossing of the induced voltage, and the speed detector 7 makes this determination.

On the other hand, if the zero crossing of the induced voltage is detected, the process proceeds to step 102 (Yes at step 101).

Next, the current driving speed of brushless DC motor 5 is calculated from the detection interval of the zero crossing of the induced voltage (step 102). Since the brushless DC motor 5 is a 3-phase 4-pole motor, the zero crossing of the induced voltage occurs 12 times during one rotation of the motor. That is, control unit 8 intermittently acquires position information of brushless DC motor 5. Thus, by dividing 1 second by 12 times the position detection interval of the zero crossing, the current driving speed, which is the number of rotations per 1 second of brushless DC motor 5, can be calculated. At this time, the average speed of 1 rotation is also calculated. The average speed of 1 rotation can be calculated by counting and inverting the position detection intervals of 12 times, which is the number of position detections during 1 rotation. When 1 second is divided by the summed position detection intervals, the average speed of 1 revolution per 1 second can be calculated. For example, in the present embodiment, speed detecting unit 7 calculates the current driving speed of brushless DC motor 5. When the calculation is finished, the process proceeds to step 103.

Next, it is determined whether the average speed of 1 rotation calculated in step 102 is higher than the target speed inputted from the outside (step 103). The target speed is input from the outside, but is determined, for example, in the refrigerator 30, based on the temperature in the refrigerator 30. For example, if the interior temperature of the refrigerator 30 is higher than a target temperature determined in advance as a temperature suitable for food preservation (STPE103, no), a high target speed is set to improve the cooling capacity. On the other hand, if the interior temperature of 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 in a state where the interior is not cooled, such as when the power of the refrigerator 30 is turned on. If the average speed of the current 1 rotation is faster than the target speed (yes in step 103), the process proceeds to step 104.

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

At step 105, the PWM carrier period of PWM generator 10 is calculated from the on ratio of PWM control by PWM generator 10 and the current driving speed of brushless DC motor 5 detected by speed detector 7. Then, the timing at which PWM control is turned on and the commutation timing at which the energization pattern to be switched to brushless DC motor 5 is switched are calculated and set.

For example, the current driving speed calculated at step 102 is 20 Hz. In this case, 12.5/3ms, which is the inverse of the product of the number of position detections for 1 rotation, 12 and 20Hz, is the time from the switching time of the current phase of the previous brushless DC motor 5 to the switching time of the next current phase, and is defined as the PWM carrier period. Then, the reciprocal of the PWM carrier period becomes the carrier frequency.

In step 106, the off timing of the PWM control of the current carrier (predetermined carrier) is determined from the carrier period calculated in step 105 and the PWM on ratio determined by the PWM generating unit 10. For example, the current driving speed of the brushless DC motor 5 is 20Hz, and the on ratio of the PWM control is 60%. In this case, 2.5ms, which is the product of 12.5/3ms and 60%, is the on-time from the start of the PWM control of the current carrier, and the time when this time elapses is the time when the switching is off. Then, the time point of switching to off calculated in this way is set, and the process is exited.

On the other hand, in step 103, if the average speed of 1 rotation of brushless DC motor 5 detected by speed detecting unit 7 is slower than the target speed or matches the target speed (no in step 103), the process proceeds to step 107.

At step 107, it is determined whether the average speed of 1 rotation of brushless DC motor 5 detected by speed detecting unit 7 is slower than the target speed. If the average speed is slower than the target speed (YES in step 107), the process proceeds to step 108.

In step 108, since the average speed of 1 rotation of brushless DC motor 5 is increased, the on ratio (Duty) of the PWM control generated by PWM generating unit 10 is increased. Then, the process proceeds to step 105 and step 106 in this order.

On the other hand, when the target speed coincides with the average speed of 1 rotation of brushless DC motor 5 in step 107 (no in step 107), the on ratio of PWM control by PWM generator 10 is maintained, and the process proceeds to step 105 and step 106.

By repeating these processes, PWM generating unit 10 can accelerate when the speed of 1 rotation of brushless DC motor 5 is insufficient for the target speed and acceleration is required. When the speed of 1 rotation of brushless DC motor 5 is excessive with respect to the target speed and deceleration is required, deceleration is performed. Further, if the speed of 1 rotation of the brushless DC motor 5 coincides with the target speed, the average speed of 1 rotation can be maintained.

Further, the PWM generating section 10 switches the energization phase every 60 degrees in electrical angle. Thereby, a rotating magnetic field for rotating the brushless DC motor 5 is generated.

Before the processing of the flow of fig. 4 is performed, a pattern of switching of the power-on phase is generated. Then, what degree of voltage is applied to each conducting phase is determined according to the flow of fig. 4 at which timing the conducting phase is switched.

The lower limit of the on ratio of the PWM control by the PWM generating unit 10 may be 50%. Thus, the PWM control is turned on at least until the time of detection of the zero crossing of the induced voltage by the position detector 6. Thus, the zero crossing of the induced voltage can be detected.

Further, the PWM generator 10 cannot perform the speed control at the lower limit of the on ratio of the PWM control performed by the PWM generator 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, increasing the magnetic force of the rotor 5a, or the like. Accordingly, even when the minimum speed and the minimum load are required for the normal operation of the system, the on ratio of the PWM control by the PWM generator 10 can be made higher than the lower limit.

Since the motor drive device 13 of the present invention turns on the current at the timings of detecting the electrical angles 0 degrees and 180 degrees, which become the references of the respective phases of the brushless DC motor 5, that is, turns on the respective predetermined carrier switches 4a to 4f, it is not necessary to perform complicated calculation of the timing for sensorless detection of the phase of the brushless DC motor 5. Therefore, the position information of brushless DC motor 5 shown in the on period in PWM control can be reliably detected, and stable driving of brushless DC motor 5 can be performed.

When a sensor cannot be disposed for sensorless position detection, brushless DC motor 5 can be driven even in a high-temperature closed space or the like.

Further, the number of switching times for driving the brushless DC motor 5 is small. Therefore, the present invention can be applied to driving of brushless DC motor 5 at a low speed at which switching loss is dominant among losses of motor drive device 13, and thus can effectively reduce power consumption.

[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 disposed in a high-temperature atmosphere, a refrigerant atmosphere, and an oil atmosphere. Therefore, it is significantly difficult to mount the position sensor on the brushless DC motor 5. Therefore, a sensorless technique capable of detecting the magnetic pole position for motor driving without using a sensor is required in many cases.

The motor drive device 13 can detect the magnetic pole position of the rotor 5a of the brushless DC motor 5 housed inside the compressor 20 by using the induced voltage of the brushless DC motor 5 that can be detected outside the compressor 20. In the present embodiment, specifically, the position detection unit 6 detects the magnetic pole position of the rotor 5 a.

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

In the present embodiment, the compressor 20 employs a reciprocating compression system. Therefore, the efficiency is very high 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, large torque pulsation is periodically generated. Therefore, when the responsiveness of the control is poor, the energization to the stator 5b and the position of the rotor 5a are deviated, and the efficiency is deteriorated. Therefore, in motor drive device 13 of the present embodiment, the current drive speed of brushless DC motor 5 is detected in order to improve the responsiveness of the control. Specifically, the speed detection unit 7 detects the current driving speed based on the induced voltage zero crossing detection interval shown in fig. 2 or 3 for each induced voltage zero crossing detected by the position detection unit 6. Further, by changing the on-time and carrier frequency of the PWM control by the PWM generating unit 10, it is possible to instantaneously cope with a periodic torque change and a speed change.

[5. refrigerator ]

Next, the refrigerator 30 using the compressor 20 described above 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 greatly varies depending on the load in the refrigerator, the outside air temperature, and the like. The operation state of the refrigerator 30 is an operation state in which the load in the interior of the food or the like is sufficiently cooled at a time-maximum ratio. In such an operating state, the compression load of the compressor 20 is reduced, and the brushless DC motor 5 is operated at a low speed and a low load. Further, the conduction loss of the inverter 4 is smaller as the speed is lower and the load is lower, and the proportion of the switching loss in the entire loss of the inverter 4 is larger.

In the present embodiment, brushless DC motor 5 is driven in a cycle of 1 carrier in which the magnetic pole position of brushless DC motor 5 is detected with high accuracy and the switching of the conduction phase of brushless DC motor 5 is performed. Therefore, brushless DC motor 5 can be driven with a very small number of switching times. Therefore, particularly in a low-speed or low-load region where the proportion of switching loss of the inverter 4 is large, the energy saving performance of the refrigerator 30 to which the motor drive device 13 is applied can be greatly improved.

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

Industrial applicability of the invention

The motor driving device of the present invention can reduce the loss of the inverter circuit during low-speed operation, and therefore can be applied to motors for driving compressors in refrigerators, air conditioners, vending machines, showcases, heat pump water heaters, and the like.

Description of the reference numerals

1 AC power supply

2 rectification circuit

2a, 2b, 2c, 2d rectifier diodes

3 smooth part

4 inverter

4a, 4c, 4e switching elements (switching parts)

4b, 4d, 4f switching elements (switching parts)

4g, 4i, 4k diode

4h, 4j, 4l diode

5 brushless DC motor

5a rotor

5b stator

6 position detecting part

7 speed detection part

8 control part

10 PWM generating part

12 driver part

13 Motor drive device

20 compressor

21 condenser

22 pressure reducer

23 evaporator

30 a refrigerator.

Claims

1. A motor drive device characterized by comprising:

an inverter having a switching unit, wherein input power is switched by the switching unit and supplied to the brushless DC motor; and

a control unit for controlling the inverter, wherein the inverter is connected to the inverter,

the control part is used for controlling the operation of the motor,

intermittently acquiring position information of rotation of the brushless DC motor,

generating a PWM driving signal for driving the switching part based on the position information,

switching the switching part based on the PWM driving signal,

the switch unit is controlled to be on for every predetermined number of carriers based on the PWM drive signal, and is controlled to be on for a period of time from a start of the predetermined carrier on which the switch unit is controlled to be on to at least a time point until the control unit first acquires the position information.

2. The motor drive device according to claim 1, wherein:

the switch unit is controlled to be off from on during a period from the time point when the control unit first acquires the position information to a time point when a next carrier of the predetermined carrier starts.

3. The motor drive device according to claim 1, wherein:

the switch unit is continuously controlled to be on during a period from a start time of the predetermined carrier to an end time of a next carrier, and is controlled to be off at the end time of the next carrier.

4. A motor drive device according to any one of claims 1 to 3, wherein:

the start time of each of the continuous carriers is synchronized with the switching time of the power-on phase.

5. The motor drive device according to any one of claims 1 to 4, wherein:

each carrier segment of the continuous carrier is synchronized with a segment of 60 degrees per electrical angle with reference to 0 degrees in electrical angle when the brushless DC motor is driven.

6. The motor drive device according to any one of claims 1 to 5, wherein:

the control unit determines a carrier cycle of the predetermined carrier based on the position information obtained first from the start of the predetermined carrier.

7. The motor drive device according to any one of claims 1 to 6, wherein:

the PWM driving signal is a rectangular wave.

8. The motor drive device according to any one of claims 1 to 7, wherein:

the control unit acquires information of a magnetic pole position of the brushless DC motor from an induced voltage of the brushless DC motor as the position information of the rotation of the brushless DC motor.

9. A motor drive device characterized by comprising:

the control unit includes:

a position detection unit that detects a reference position of the brushless DC motor that drives a load; and

a PWM generating section for generating a waveform for driving the brushless DC motor based on the information of the reference position from the position detecting section,

the signal output by the PWM generating unit is turned on at least before the position detecting unit detects the information of the reference position of the brushless DC motor.

10. The motor drive device according to any one of claims 1 to 9, wherein:

the brushless DC motor is a motor that drives a compressor.

11. A refrigerator characterized in that:

comprises a refrigeration cycle circuit formed by connecting a compressor with a brushless DC motor, a condenser, a pressure reducer and an evaporator,

the brushless DC motor is driven by the motor driving device according to any one of claims 1 to 10.