WO2019082682A1

WO2019082682A1 - Motor drive device and refrigerator using this

Info

Publication number: WO2019082682A1
Application number: PCT/JP2018/038019
Authority: WO
Inventors: 田中　秀尚; 義典竹岡
Original assignee: パナソニックＩｐマネジメント株式会社
Priority date: 2017-10-27
Filing date: 2018-10-12
Publication date: 2019-05-02
Also published as: CN111034011B; JP2019083594A; JP6979568B2; CN111034011A

Abstract

This motor drive device (30) is provided with a brushless DC motor (4) which has a rotor, an inverter circuit (3) which is configured comprising six switching elements (3a-3f) and which supplies power to the brushless DC motor (4), a position detection unit (5) which detects the rotation position of the rotor, and a PWM control unit (11) which performs PWM control for adjusting the voltage applied to the brushless DC motor (4) by turning the switching elements (3a-3f) ON and OFF at a high frequency. The motor drive device (30) further comprises an energized phase control unit (8) which sets the energized state of each phase of the brushless DC motor (4) while maximizing the ON time ratio of the switching elements (3a-3f) from the PWM control, and a control quantity adjustment unit (8c) which adjusts the control quantity in control of the drive speed of the brushless DC motor (4). The control quantity adjustment unit (8c) adjusts the control quantity depending on the state of power supply to the brushless DC motor (4).

Description

Motor drive device and refrigerator using the same

The present disclosure relates to a motor drive device that drives a brushless DC motor by inverter control, and a refrigerator using the same.

Conventionally, in the drive device of this type of brushless DC motor, the conduction state of each phase of the brushless DC motor is controlled by PWM (Pulse Width Modulation) control.

Specifically, the rectangular wave in PWM control is controlled so that the conduction interval of each phase is basically 120 degrees, and the brushless DC motor is driven. Further, when the on-duty (duty ratio) of the PWM control becomes 100%, the conduction interval is extended to 120 degrees or more. As a result, the drivable area of the brushless DC motor in the case of high speed and high load is expanded (see, for example, Patent Document 1).

FIG. 9 shows a block diagram of the motor drive device of Patent Document 1. As shown in FIG. As shown in FIG. 9, the inverter circuit 103 includes switching elements 103a to 103f. When each of the switching elements 103a to 103f shifts from off to on, the on-timing control means 104a performs lead angle control. On the other hand, when the switching elements 103a to 103f shift from on to off, the advance timing control by the off timing control means 104b is not performed. Thus, the overlap energization is performed.

Further, in another conventional motor drive device, the conduction angle and the advance angle of the switching element and the input DC voltage to the inverter are controlled such that the power supplied to the motor becomes the target power value. As a result, high output of the motor drive device can be realized, and high rotation of the motor can be achieved. In addition, the loss of the motor drive device is reduced (see, for example, Patent Document 2).

FIG. 10 shows a block diagram of the drive control means 201 of the motor drive device of Patent Document 2. As shown in FIG. As shown in FIG. 10, the drive control means 201 of the brushless DC motor has a power detection means 202 for detecting drive power, and a conduction pulse signal generation control means 203. The energization pulse signal generation control unit 203 generates a drive signal pattern of the inverter and sets an inverter input voltage. Then, the input voltage value, the conduction angle, and the advance angle of the inverter are controlled such that the drive power matches the target set power value.

However, in the conventional motor drive device, there is still room for improvement in the improvement of the efficiency and the reliability.

Unexamined-Japanese-Patent No. 2006-50804 JP 2008-167525 A

An object of the present disclosure is to suppress the loss of a motor drive device and to improve the efficiency of a brushless DC motor. Another object of the present invention is to realize a low vibration and low noise motor drive device and to improve the reliability of the motor drive device.

Specifically, the motor drive device according to the present disclosure is configured to include a brushless DC motor having a rotor, and six switching elements, and supplies an electric power to the brushless DC motor, and the position of the rotor It has a position detection part to detect, and a PWM control part which performs PWM control which adjusts a voltage applied to a brushless DC motor by turning on and off the switching element at high frequency. The motor drive apparatus further includes an energized phase control unit that sets the energized state of each phase of the brushless DC motor while maximizing the on time ratio of the switching element by PWM control, and the drive speed of the brushless DC motor. And a control amount adjustment unit that adjusts a control amount in control, and the control amount adjustment unit adjusts the control amount according to the state of power supply to the brushless DC motor.

With such a configuration, it is possible to suppress the loss of the motor drive device and to improve the efficiency of the brushless DC motor. Further, it is possible to realize a low vibration and low noise motor drive device and to improve the reliability of the motor drive device.

FIG. 1 is a block diagram of a motor drive device according to a first embodiment of the present disclosure. FIG. 2A is a diagram showing drive waveforms and a timing chart of the motor drive device according to Embodiment 1. FIG. 2B is a diagram showing another drive waveform and timing chart of the motor drive device in the first embodiment. FIG. 3 is a flowchart for determining the start of off timing adjustment control of the switching element. FIG. 4 is a flowchart in which the transition from PWM control to off timing adjustment control is determined. FIG. 5 is a flowchart showing off timing adjustment control. FIG. 6 is a flowchart showing adjustment of the control amount. FIG. 7A is a diagram showing a terminal voltage waveform of the section C1 in FIG. 2A. FIG. 7B is a diagram showing a terminal voltage waveform of the section F1 in FIG. 2A. FIG. 7C is a diagram showing a terminal voltage waveform of the section C3 in FIG. 2B. FIG. 7D is a diagram showing a terminal voltage waveform of the section F2 in FIG. 2B. FIG. 8A is a diagram showing phase current waveforms of the brushless DC motor when PWM control is performed. FIG. 8B is a diagram showing a phase current waveform of the brushless DC motor when the on-time ratio is 100%. FIG. 9 is a block diagram of a motor drive device of Patent Document 1. As shown in FIG. FIG. 10 is a block diagram of a motor drive device of Patent Document 2. As shown in FIG.

(Findings that formed the basis of this disclosure)
The inventors of the present disclosure obtained the following findings as a result of intensive studies to improve the performance and reliability of the motor drive device.

In the configuration of Patent Document 1 described above, the driveable region can be expanded in the case of high load and high speed by advancing the turn-on of the switching element and widening the power supply section to the brushless DC motor to 120 degrees or more. . However, in the drive region in the low load and low speed case, a loss occurs with the on / off switching operation of the switching element by PWM control. Also, the switching operation at high frequency by PWM control is accompanied by an increase in motor iron loss.

Further, in the control of the speed by the increase and decrease of the conduction angle of the brushless DC motor described in Patent Document 2 described above, the timing at which the control is possible is commutation (for example, in a 4-pole motor, 12 times during one rotation of the motor) Limited to

In the motor drive device described in Patent Document 2, the conduction angle increased or decreased in control is always constant. However, the amount of change in motor current per unit angle of the conduction angle to be increased or decreased is different between the case where the conduction angle is less than 120 degrees and the case where the conduction angle is 120 degrees or more. For this reason, as in the configuration of Patent Document 2, when controlled by a uniform control cycle or control amount, the acceleration of the brushless DC motor becomes uneven, so that the motor is out of step due to rapid acceleration, and the brushless DC motor The inventors have found that there is a problem of stopping. In addition, the slow acceleration or deceleration of the brushless DC motor due to uneven acceleration causes vibration and noise of the brushless DC motor when the rotational frequency of the brushless DC motor passes through the resonance frequency band of the device. The inventors found that there was a problem.

Based on these new findings, the present inventors have come to the following disclosure.

A motor drive device according to an aspect of the present disclosure includes: a brushless DC motor having a rotor; and an inverter circuit that supplies electric power to the brushless DC motor including six switching elements; and a rotational position of the rotor And a PWM control unit that performs PWM control to adjust a voltage applied to the brushless DC motor by turning on and off the switching element at a high frequency. The motor drive apparatus further includes an energized phase control unit that sets the energized state of each phase in the brushless DC motor while maximizing the on time ratio of the switching element by PWM control, and the driving speed of the brushless DC motor. The control amount adjustment unit adjusts the control amount in control, and the control amount adjustment unit adjusts the control amount according to the state of supply of power to the brushless DC motor.

With such a configuration, it is possible to reduce the switching loss of the switching element by PWM control and to improve the efficiency of the motor drive device. In addition, stable acceleration performance can be obtained regardless of the driving state of the brushless DC motor. Therefore, generation of noise and vibration at the time of acceleration or deceleration of the brushless DC motor can be suppressed, and the reliability of the motor drive device can be improved.

In the motor drive device according to another aspect of the present disclosure, the control amount adjustment unit may be configured to switch the control amount at an electric angle of 120 degrees in a section where power is supplied to the brushless DC motor. .

With such a configuration, it is possible to equalize the acceleration when the driving of the brushless DC motor is performed at an energization angle of 120 degrees or more and the acceleration when the driving is performed at an energization angle of less than 120 degrees. it can. Therefore, it is possible to suppress the vibration and noise of the brushless DC motor when the driving frequency of the brushless DC motor passes the resonance frequency band of the device. Further, by suppressing the vibration of the brushless DC motor, the failure of the device due to the vibration is avoided, and the reliability of the motor drive device is improved.

In a motor drive device according to another aspect of the present disclosure, the brushless DC motor of the above-described motor drive device may drive a compressor provided in a refrigeration cycle.

Such a configuration can improve the COP (Coefficient Of Performance) of the compressor. Moreover, the damage by piping which comprises a refrigerating-cycle apparatus can be prevented by the vibration by resonance being suppressed. Therefore, a highly efficient and reliable refrigeration cycle apparatus can be provided.

Moreover, in the refrigerator which concerns on this indication, the above-mentioned motor drive device may be used.

This can provide a refrigerator with low power consumption and high reliability. In addition, it is possible to suppress the vibration and noise of the refrigerator during acceleration or deceleration of the brushless DC motor.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited by the present embodiment.

Embodiment 1
[1. overall structure]
FIG. 1 shows a block diagram of a motor drive device according to a first embodiment of the present disclosure.

Motor drive device 30 includes an inverter circuit 3 and a DC brushless DC motor 4. Further, a DC voltage is supplied to the motor drive device 30, for example, by the converter circuit 2 or the like.

In FIG. 1, an alternating current power supply 1 is a general commercial power supply. The commercial power supply has an effective value of 100 V and a power supply frequency of 50 Hz or 60 Hz in Japan.

Converter circuit 2 converts AC power supply 1 into a DC voltage. Converter circuit 2 includes, for example, a rectifier circuit 2a and a smoothing circuit 2b. The converter circuit 2 may also include a switching unit that switches the output voltage.

The converter circuit 2 in FIG. 1 includes a rectifier circuit 2a in which four diodes are bridge-connected, a smoothing circuit 2b having a capacitor, and a switch (switching unit) 2c that switches an output voltage. The switch 2c switches the output voltage in two stages of voltage doubler rectification and full wave rectification.

The inverter circuit 3 is composed of six switching elements 3a to 3f. In the present embodiment, a MOSFET is used for each of the switching elements 3a to 3f. The switching elements 3a to 3f are connected in a three-phase bridge. By turning on and off any switching element, the input DC voltage of the inverter circuit 3 is converted into a three-phase AC voltage.

The brushless DC motor 4 is configured to include a stator and a rotor having permanent magnets. The stator has three stator windings corresponding to three phases. The brushless DC motor 4 is driven by three-phase AC power supplied from the inverter circuit 3.

Further, the motor drive device 30 has a position detection unit 5. The position detection unit 5 detects the magnetic pole position of the brushless DC motor 4. In the first embodiment, position detection is performed by detecting the zero crossing point of the induced voltage generated in the stator winding of the brushless DC motor 4 based on the terminal voltage of the motor. The induced voltage is generated by the rotation of the rotor of the brushless DC motor 4. The position detection method may be a method using a position sensor such as a Hall IC or a method based on current detection using a current sensor or the like.

Further, the motor drive device 30 may have the speed detection unit 6. The speed detection unit 6 detects the driving speed of the brushless DC motor 4 from the output signal of the position detection unit 5. In the present embodiment, the driving speed of the brushless DC motor 4 is calculated based on the cycle of the zero cross point of the induced voltage generated in the stator winding of the brushless DC motor 4.

Further, the motor drive device 30 may have the speed error detection unit 7. The speed error detection unit 7 detects the difference between the driving speed of the brushless DC motor 4 obtained by the speed detection unit 6 and the target speed.

[2. Conducted phase control section]
As shown in FIG. 1, the motor drive device 30 has an energized phase control unit 8. The energization phase control unit 8 sets which stator winding of the three stator windings of the brushless DC motor 4 is to be supplied with power based on the signal from the position detection unit 5. Electric power is supplied to each stator winding in a range of 90 degrees or more and 150 degrees or less.

The energized phase control unit 8 includes an on timing control unit 8a and an off timing control unit 8b. The on-timing control unit 8a sets timing (hereinafter, on-timing) to turn on the switching elements 3a to 3f. The off-timing control unit 8b sets the timing (hereinafter referred to as off-timing) to turn off the switching elements 3a to 3f. That is, the on timing and the off timing of each of the switching elements 3a to 3f of the inverter circuit 3 are set individually.

The energization phase control unit 8 sets the energization state of each phase as described above. Then, the conduction phase control unit 8 sets the range (power supply section) of the power supply section to the brushless DC motor 4 by setting the on timing and the off timing of each of the switching elements 3a to 3f. Thus, speed control is performed such that the brushless DC motor 4 is driven at the target speed.

Moreover, the conduction phase control unit 8 has a control amount adjustment unit 8c. The control amount adjustment unit 8c adjusts the control amount in the speed control. In the present embodiment, the increase / decrease amount of the section with respect to the power supply section set by the power supply phase control unit 8 corresponds to the control amount. The control amount adjustment unit 8c adjusts the control amount according to the set value of the length of the power supply section by adjusting the on timing and the off timing of the switching element at the time of acceleration or deceleration.

[3. Control of Drive Speed of Brushless DC Motor]
As shown in FIG. 1, the motor drive device 30 has a PWM control unit 11. The PWM control unit 11 adjusts the three-phase AC output voltage from the inverter circuit 3 by PWM control. Thereby, the brushless DC motor 4 is controlled to drive at the target speed.

The on-time ratio (Duty Ratio) of PWM control of the brushless DC motor 4 is “(minimum value of electrical angle when power is supplied to the stator winding of the brushless DC motor) × 2- (electrical angle 120 degrees When the brushless DC motor 4 is driven in a state larger than the value obtained by dividing “A” by “120 electrical degrees”, the off-timing control unit 8b determines that the on-time time ratio of the PWM control is the maximum value. The off timing of the switching element is advanced so as to be 100%.

Specifically, for example, when the power supply section to the brushless DC motor 4 has an electrical angle of 90 degrees, which is the minimum value of the power supply section, (90 degrees × 2-120 degrees) 20120 degrees = 50 [%] It becomes. Therefore, when the brushless DC motor 4 is driven in a state where the on time ratio of PWM control is 50% or more, the off timing control unit 8b advances the off timing of the switching element and the on time ratio is Make it 100%.

When the drive speed of the brushless DC motor 4 is slower than the target speed in a state where the power supply interval is 120 degrees and the PWM control on time ratio is 100%, the PWM control on time ratio is 100%. In the state maintained in the on-timing control unit 8a, the on-timing of the switching element is advanced. As a result, the brushless DC motor 4 is energized in an overlap manner, and the drive region of the brushless DC motor 4 is expanded.

Here, in order to prevent an abrupt change in the operating state of the brushless DC motor 4, it is desirable that the off timing and the on timing be gradually changed. For example, the change of the off timing may be divided into a plurality of times and may be advanced from the previous off timing. However, the off timing and the on timing may be changed within one control cycle.

The speed control of the brushless DC motor 4 is performed by adjusting the on-time ratio by the PWM control unit 11 when the brushless DC motor 4 is driven at the above-described on-time ratio of PWM control or less. Limited. Therefore, PWM control is performed when the brushless DC motor 4 is driven in a relatively low load or low speed state, such as at startup, low speed drive, low load drive, and double voltage input at the start of the brushless DC motor 4. To be done.

In other stable drive states, the off phase and on timing of the switching element are controlled by the conduction phase control unit 8 so that the on time ratio of PWM control is 100%. As a result, the power supply section to the brushless DC motor 4 is adjusted while the on-time ratio of the switching element by PWM control is maximized (100% in the stable driving state in the present embodiment). Control of the drive speed of the brushless DC motor 4 is performed.

The waveform synthesis unit 12 illustrated in FIG. 1 synthesizes the PWM signal generated by the PWM control unit 11 and the signal generated by the conduction phase control unit 8. The drive unit 13 turns on or off the switching elements 3a to 3f of the inverter circuit 3 based on the signal synthesized by the waveform synthesis unit 12. This generates an arbitrary three-phase AC voltage. The generated three-phase AC voltage is supplied to the brushless DC motor 4 to drive the brushless DC motor 4.

[4. Compressor using motor drive]
FIG. 1 shows an example in which the motor drive device 30 described above is used for the compressor 17.

As shown in FIG. 1, the compressor 17 constitutes a refrigeration cycle together with the condenser 18, the pressure reducer 19 and the evaporator 20. In FIG. 1, the refrigerator 21 is shown as an example of the refrigerating cycle apparatus using a refrigerating cycle.

The compressor 17 has a brushless DC motor 4 and a compression element 16. The brushless DC motor 4 and the compression element 16 are housed in the same closed container.

The compression element 16 of the compressor 17 is connected to the shaft of the rotor of the brushless DC motor 4, sucks the refrigerant gas, and compresses and discharges the sucked refrigerant gas. The refrigerant gas discharged from the compressor 17 is again drawn into the compressor 17 through the condenser 18, the pressure reducer 19 and the evaporator 20. This constitutes a refrigeration cycle. Since heat is released in the condenser 18 and heat absorption is performed in the evaporator 20 during the refrigeration cycle, the refrigeration cycle apparatus can perform heating or heat absorption.

In addition, a blower is used for the condenser 18 and the evaporator 20 as needed. This promotes heat exchange in the condenser 18 and the evaporator 20.

Moreover, the refrigerator 21 has the food storage room 23 enclosed by the heat insulation wall 22, as shown in FIG. The evaporator 20 is used to cool the inside of the food storage room 23.

The operation and action of the motor drive device 30 configured as described above will be described below.

[5. Operation of motor drive]
[5-1. Drive waveform and timing chart]
FIG. 2A and FIG. 2B are drive waveforms and timing charts of the motor drive device according to the present embodiment.

FIG. 2A is a drive waveform and timing chart in the case of general energization at an electrical angle of 120 degrees. FIG. 2B is a drive waveform and a timing chart in a state in which the off timing of the switching element is adjusted.

In FIGS. 2A and 2B, the induced voltage generated by the rotation of the brushless DC motor 4 is shown as Vu, which is the terminal voltage of the U phase among the E phases (U phase, V phase and W phase). Moreover, FIG. 2A and FIG. 2B have shown only the waveform about U phase. The waveforms of the induced voltage and the terminal voltage of the V phase and the W phase are waveforms of the same shape in which the phases are respectively shifted by 120 degrees from the waveforms of the induced voltage and the terminal voltage of the U phase.

In FIG. 2A and FIG. 2B, the timing chart of the drive signal about switching element 3a, 3b, 3c connected to the high voltage | pressure side of the inverter circuit 3 is each shown as U +, V +, W +. The drive signals of the switching elements 3d, 3e, 3f connected to the low voltage side of the inverter circuit 3 have respective phases from the drive signals of the switching elements 3a, 3b, 3c on the high voltage side corresponding to the switching elements 3d, 3e, 3f. It will be 180 degrees off.

The position detection unit 5 detects the position of the rotor of the brushless DC motor 4 directly or indirectly. Based on the detected rotor position information, the timing (not shown) for switching the energized phase in the stator winding is adjusted.

In the present embodiment, the position detection unit 5 detects the relative position of the magnetic poles of the rotor. Specifically, the position detection unit 5 detects the zero cross point of the induced voltage as a position signal.

C1 is a section where voltage is not applied to the stator winding of the corresponding phase (a section in which both switching elements 3a and 3d are turned off in the U phase shown in FIG. 2A and FIG. 2B) when detecting the zero cross point. , C2, C3, C4), points (P1, P2) at which the magnitude relationship between the induced voltage appearing in the stator winding and the half of the inverter input voltage Vdc is inverted are detected.

Therefore, the position signal of the zero crossing point is detected twice for each phase per electrical angle cycle. That is, in all three phases, position signals are detected six times in total at every electrical angle of 60 degrees.

In the energization pattern by drive signals U +, V +, and W + shown in FIG. 2A, U + is turned on simultaneously with the turning off of W + at the time when an electrical angle of 30 degrees passes after the position detection of the zero crossing point (P1). The element 3a is turned on. Thereby, the stator winding of any one of the three phases is always energized in the entire range of the electrical angle of 360 degrees.

On the other hand, in the energization pattern shown in FIG. 2B, after the position detection of the zero cross point (P1), W + is turned off and the switching element 3c is turned off before the electrical angle of 30 degrees elapses. At the time when the temperature passes, U + is turned on, and the switching element 3a is turned on.

The induced voltage appears in the stator winding in the section C1 to C4 only during the period when the switching element of the other phase is on, that is, the ON period of the switching element by PWM control. Therefore, the turn-off of the switching element is controlled to be performed earlier than the turn-on, whereby the power supply interval to the brushless DC motor 4 is controlled to be short. As a result, the number of times the switching element is turned on and off due to PWM control is reduced, so that the loss of the inverter circuit 3 is suppressed.

Further, as the power supply section of the stator winding becomes shorter, the on time of the switching element by PWM control becomes longer. As a result, the period during which the position detection unit 5 can acquire the position detection signal of the zero cross point is extended. Therefore, the accuracy of position detection by the position detection unit 5 is improved.

Furthermore, as shown in FIGS. 2A and 2B, the off timing of the switching element is from immediately after the position detection of the zero cross point (P1) to the time when an electrical angle of 30 degrees elapses ( Range). This enables reliable commutation based on the result of position detection of the zero cross point (P1). Further, since the drive waveform is in the lead phase with respect to the induced voltage, the occurrence of the torque drop due to the delay phase is avoided.

As described above, by setting the off timings of the switching elements 3a to 3f to the time when an electrical angle of 30 degrees passes immediately after the position detection of the zero cross point, the conduction angle to the three-phase stator winding is 90 degrees. The above is adjusted to 120 degrees or less. In addition, as the idle section (A1, A2, A3) of the power supply is shorter, a larger advance angle B (1/2 of the electrical angle of the non-powered section) is automatically added.

As a result, the torque of the brushless DC motor 4 is increased, and even if there is no power supply section where power is not supplied to the brushless DC motor 4, step-out or the like of the brushless DC motor 4 is avoided. It becomes possible to drive the brushless DC motor 4 stably.

When the load increases and the off timing of the switching element becomes 30 ° electrical angle after the position detection of the zero cross point, the load is the maximum load that can be driven by the conduction at 120 °. In this case, after the position detection, the off timing is fixed when an electrical angle of 30 degrees elapses, and the on timing is advanced to a maximum of an electrical angle of 30 degrees while the on time ratio of PWM control is 100%. That is, commutation occurs simultaneously with the acquisition of the position detection signal. As a result, the conduction angle of each phase can be expanded to an electrical angle of 150 degrees, and the range of loads that can be driven by the motor drive device 30 can be expanded.

5-2. Details of Speed Control]
Next, speed control of the brushless DC motor 4 by adjusting the on timing and off timing of the switching element described above will be described in detail using a flowchart.

FIG. 3 is a flowchart for determining the start of off timing adjustment control of the switching element.

First, it is determined whether the on-time ratio of the switching element generated by the PWM control unit 11 is larger than a predetermined value (S11). If the on time ratio is larger than the predetermined value (Yes in S11), the off timing adjustment control described later is performed (S12). When the on-time ratio is equal to or less than the predetermined value (No in S11), PWM control is performed (S13).

In the present embodiment, the minimum value of the power supply section to the stator winding of the brushless DC motor 4 is set to an electrical angle of 90 degrees. For this reason, the predetermined value of the on-time time ratio is set to 50% from {(90 degrees × 2) −120 degrees} / 120 degrees. The predetermined value of the on time ratio is set to an appropriate value in consideration of the application of the motor drive device.

As described above, in the present embodiment, the off-timing adjustment control of the switching element is started when the ratio is greater than or equal to the predetermined on-time period. At this time, off timing adjustment control and PWM control are used in combination. As a result, when the drive speed is extremely low, such as when the brushless DC motor 4 is started, or when the load is extremely low at low speed driving, or when the load is relatively light at doubled voltage input or at low speed, etc. In addition, a failure in starting of the brushless DC motor 4 due to an extremely short power supply section to the stator winding, an unstable operating condition, or an extreme torque drop can be prevented. Therefore, the brushless DC motor 4 can be stably driven under all load conditions.

FIG. 4 is a flowchart in which the transition from PWM control to off timing adjustment control is determined.

When the start of the off timing adjustment control is determined by the flow shown in FIG. 3, the off timing of the switching element is advanced by an arbitrary time (S21). Further, speed control is performed by PWM control (S22). When the off timing is advanced, as described above, it may be divided into a plurality of times and may be advanced from the previous off timing.

Here, since the off timing of the switching element is advanced (S21), the power supply section to the brushless DC motor 4 becomes short. Therefore, the PWM control will increase the on time ratio.

When the on-time ratio by PWM control is less than 100% (Yes in S23), the off timing of the switching element is advanced (S21) and PWM control is performed (S22).

When the on-time ratio reaches 100% (No in S23), the on-time ratio is maintained at 100% (S24). That is, in this case, the PWM control is not performed. Further, off timing adjustment control of the switching element is performed (S25). That is, when the on-time ratio becomes 100%, the PWM control is shifted to the off-timing adjustment control. Thereby, the drive speed of the brushless DC motor 4 is controlled so that the brushless DC motor 4 is driven at the target speed.

In addition, when the off timing of the switching element has reached the time when the electrical angle of 30 degrees (that is, the state of being energized at 120 degrees) elapses after the position detection of the zero cross point, speed control by on timing control It may be done. In the on-timing control, the on-timing of the switching element is advanced up to an electrical angle of 30 degrees. As a result, the drivable area of the brushless DC motor 4 is expanded, and the brushless DC motor 4 is appropriately driven at the target speed.

Next, speed control of the brushless DC motor 4 after transition to off timing adjustment control of the switching element will be described with reference to FIGS. 1 and 5.

FIG. 5 is a flowchart showing off timing adjustment control.

The deviation between the driving speed of the brushless DC motor 4 detected by the speed detection unit 6 and the target speed is detected by the speed error detection unit 7.

In FIG. 5, when the driving speed of the brushless DC motor 4 is faster than the target speed (Yes in S31), it is determined whether the off timing control unit 8b can advance the off timing of the switching element (S32). At this time, the on-time ratio in the PWM control unit 11 is held at 100%.

If the off timing can be advanced (Yes in S32), the off timing of the switching element is advanced (S33). As a result, the power supply section to the stator winding is reduced, and speed control is performed such that the driving speed of the brushless DC motor 4 is reduced. If it is not possible to advance the off timing (No in S32), PWM control is performed by the PWM control unit 11 (S34).

In the present embodiment, the determination as to whether or not the off timing of the switching element can be advanced is performed as follows.

If the off timing of the switching element is immediately after the position detection of the zero cross point, it is determined that the off timing can not be further advanced.

In the present embodiment, since the advance angle is 0 degrees, the minimum value of the conduction angle to each stator winding is 90 electrical degrees. Here, when the conduction angle is less than 120 degrees, a non-power supply section having twice the electrical angle of the non-conduction section occurs. Therefore, when the conduction angle is 90 degrees, the non-conduction section is 30 degrees and a non-power supply section of 60 degrees occurs. That is, the output when the conduction angle is 90 degrees is 50% of the output when the conduction angle is 120 degrees.

When it is determined that the drive speed of the brushless DC motor 4 is slower than the target speed (Yes in S35), the off timing of the switching element is between immediately after the detection of the zero cross point position and the time when the electrical angle is 30 degrees. It is determined whether there is any (S36).

If the off timing of the switching element is earlier than the elapse of 30 electrical degrees (Yes in S36), the off timing of the switching element is delayed (S37). As a result, the power supply section to the stator winding of the brushless DC motor 4 is increased, and the speed control is performed so that the driving speed of the brushless DC motor 4 is increased.

On the other hand, when the off timing of the switching element is after the lapse of the electrical angle of 30 degrees (No in S36), when the off timing of the switching element is further delayed, the applied voltage phase is delayed with respect to the induced voltage. A decrease in motor torque and an associated step out may occur. Therefore, the on timing of the switching element is advanced (S38). As a result, the power supply section to the stator winding is increased, and speed control is performed such that the driving speed of the brushless DC motor 4 is increased.

In the present embodiment, the upper limit of the range in which the on-timing of the switching element can be advanced is immediately after the position detection of the zero cross point. The maximum value of the power supply section to the stator winding when the off timing of the switching element is immediately after the position detection of the zero cross point is 150 degrees of electrical angle. At this time, the current flowing through the brushless DC motor 4 is increased by 17% with respect to the current when the conduction angle is 120 degrees. Accordingly, the maximum output of the brushless DC motor 4 also increases by about 17%.

When the driving speed of the brushless DC motor 4 is equal to the target speed (No in S35), the flow ends.

Further, in the present embodiment, as described above, the advance angle is set to 0 degrees. Therefore, when the conduction angle is 120 degrees in electrical angle, the off timing and on timing of the switching element coincide with each other at an electrical angle of 30 degrees after the position detection of the zero cross point.

Here, it is desirable that the motor drive device 30 can optimally drive various motors, including an IPM motor (Interior Permanent Magnet Motor). For example, permanent magnets are embedded in the rotor of the IPM motor. For this reason, in order to realize the optimum drive of the IPM motor, it is necessary to provide an appropriate advance angle.

In the present embodiment, the range of the off timing adjustment of the switching element and the range of the on timing adjustment are set as follows.

That is, the off timing of the switching element is in the range from immediately after the detection of the position of the zero cross point to the time when ((electrical angle 30 degrees) − (advance angle)) has elapsed.

Further, the on timing of the switching element is the time when ((electrical angle 30 degrees) − (advance angle)) has elapsed after the position detection of the zero cross point.

Therefore, for example, when the advance angle is 10 degrees, the off timing of the switching element is adjusted in the range from immediately after the position detection of the zero cross point to the time of the electrical angle of 20 degrees, and the on timing is the position detection of the zero cross point It is adjusted when the electrical angle of 20 degrees has passed. Further, the sum of the electrical angle from the time of detecting the position of the zero cross point to the off timing and the electrical angle from the time of detecting the position of the zero cross point to the on timing is set to 60 degrees or less. Furthermore, the off timing is adjusted in an arbitrary range from the on timing to the time when the electrical angle is 0 degrees to 30 degrees. As a result, the advance angle, the on timing, and the off timing can be freely set in the range from immediately after the detection of the position of the zero cross point to the time when the electrical angle of 30 degrees has elapsed.

The conduction angle to the stator winding when the advance angle is added is adjusted in the range from "(electrical angle 90 degrees) + (advance angle)" to 120 electrical angle.

When the brushless DC motor 4 is driven at high speed and with a high load, the on timing and off timing of the switching element may be adjusted as follows.

That is, the off timing of the switching element is adjusted when "(electrical angle 30 degrees)-(advance angle)" has elapsed after the position detection of the zero cross point. Further, the on timing of the switching element is adjusted in the range from immediately after the detection of the position of the zero cross point to the time when ((electrical angle 30 degrees) − (advance angle)) has elapsed. As a result, the conduction angle to each stator winding of the brushless DC motor 4 can be adjusted within the range of “(electric angle 150 degrees) − (advance angle)” from 120 electrical degrees.

As described above, by adjusting the on timing and off timing of the switching element, the conduction angle is adjusted in the range of 90 ° to 150 ° electrical angle (in the case of 0 ° advance angle), and the brushless DC motor 4 is adjusted. Power supply is regulated. Therefore, the motor drive device 30 according to the present embodiment can drive the brushless DC motor 4 in a wide range from the low speed and low load state to the high speed and high load state. is there.

Next, control at the time of acceleration or deceleration of the brushless DC motor 4 will be discussed.

As described above, in the case of conduction at 90 degrees where the conduction angle is reduced by 30 degrees with respect to the output power in the case of conduction at an electrical angle of 120 degrees, the output power decreases to 50% and the conduction angle is 30 degrees In the case of the increased 150 degree conduction, the output power increases by about 17%. That is, the amount of increase or decrease in the output power per unit conduction angle differs at the time of conduction at an electrical angle of 120 degrees. Therefore, when the conduction angle is increased or decreased at the same rate, the acceleration in the case of conduction at an electrical angle of 120 degrees or more is about 1/3 of the acceleration in the case of conduction at a conduction angle of less than 120 degrees.

In equipment using a motor drive, when the brushless DC motor is driven at a resonance frequency specific to the equipment, vibration and noise increase. The increased vibration may cause equipment failure. For this reason, in general the drive of the motor at the resonance frequency specific to the device is avoided.

As the acceleration decreases, the time for the drive frequency to pass through the resonance frequency band unique to the device increases. For this reason, a reduction in acceleration can be a source of vibration and noise. In addition, if acceleration or deceleration is frequently performed and the drive frequency frequently passes through the resonant frequency band of the device, the generated vibration may cause the device to fail.

In the present embodiment, as described below, the amount of change (control amount) of the on timing and the off timing of the switching element in speed control is corrected according to the conduction angle. This avoids a decrease in acceleration during acceleration or deceleration and provides a constant acceleration.

FIG. 6 is a flowchart showing adjustment of the control amount.

First, according to the flowchart shown in FIG. 5, the on timing and off timing of the switching element in the conduction phase control unit 8 are set (S41).

Next, it is determined from the set on timing and off timing of the switching element whether the conduction angle is 120 degrees or more (S42). If the conduction angle is 120 degrees or more (Yes in S42), Rate 1 is selected (S43). On the other hand, if the conduction angle is smaller than 120 degrees (S42: No), Rate 2 is selected (S44).

Rate 1 and rate 2 are increase / decrease rates of the power supply section of the brushless DC motor. In the present embodiment, the rate 1 is set to three times the rate 2. That is, in the case of energization at an electrical angle of 120 degrees or more, a conduction angle three times as large as the conduction angle to be increased or decreased in the case of less than 120 degrees is increased or decreased.

For example, at the time of acceleration or deceleration, if the conduction angle is less than 120 degrees, the conduction angle is increased or decreased by 0.1 degree per control cycle. On the other hand, when the conduction angle is 120 degrees or more, the conduction angle is increased or decreased by 0.3 degree per control cycle. As a result, substantially constant acceleration can be obtained regardless of the driving state of the brushless DC motor 4.

In this manner, the control amount is adjusted in accordance with the supply state (the power supply section in the present embodiment) of the power to the brushless DC motor 4.

Next, terminal voltages of the brushless DC motor according to the present embodiment will be described with reference to FIGS. 7A to 7D.

FIGS. 7A and 7B respectively show terminal voltage waveforms in section C1 and section F1 in FIG. 2A. FIGS. 7C and 7D respectively show terminal voltage waveforms in section C3 and section F2 in FIG. 2B.

As shown in FIG. 7A and FIG. 7B, a high frequency PWM carrier frequency component (period f) is superimposed on the waveform in the case of PWM control shown in FIG. 2A.

Further, as shown in FIG. 7A, in the section C1, at the moment when the PWM is turned on, a ringing noise component due to the influence of the stator winding or the stray capacitance is also superimposed.

In section C1, the terminal voltage Vu of the brushless DC motor 4 and half of the inverter input voltage Vdc are compared, and the point at which the magnitude relationship is reversed is the zero cross point of the induced voltage of the brushless DC motor 4 (point P). Is detected as

However, as shown in FIG. 7A, since the ringing noise component is superimposed on the terminal voltage Vu, the point Px is erroneously detected as the zero cross point. Such erroneous position detection causes pulsation of the driving speed of the brushless DC motor 4, increases in vibration and noise of the device, and reduction in driving efficiency.

On the other hand, as shown in FIG. 7C, when the on-time ratio of PWM control is 100%, an induced voltage waveform appears at the terminal voltage Vu. For this reason, it is possible to accurately detect the position of the zero cross point (point P). Therefore, stable driving of the brushless DC motor 4 with low noise, low vibration and low loss can be realized.

Further, as shown in FIG. 7B, in the section F1, a switching loss occurs with the on / off of the switching element at high frequency by PWM control. On the other hand, as shown in FIG. 7D, when the on-time ratio is driven at 100%, no switching loss occurs because the switching operation of the switching element is not performed. Therefore, the circuit loss of the motor drive device 30 is reduced, and high efficiency of the motor drive device 30 can be realized.

FIG. 8A is a diagram showing phase current waveforms of the brushless DC motor when PWM control is performed. FIG. 8B is a diagram showing a phase current waveform of the brushless DC motor when the on-time ratio is 100%.

FIG. 8A shows a waveform in the case of energization at an electrical angle of 120 degrees. As shown in FIG. 8A, high-frequency current components accompanying switching on and off of the switching element by PWM control are superimposed on the phase current waveform when PWM control is performed. This high frequency current component causes the motor iron loss.

On the other hand, as shown in FIG. 8B, when the brushless DC motor 4 is driven with the PWM on-time ratio being 100%, no high frequency current component is generated. For this reason, the motor loss of the motor drive device 30 is reduced, and high efficiency of the motor drive device 30 can be realized.

[6. Refrigerator using motor drive]
A refrigeration cycle apparatus using a compressor 17 driven by the motor drive device 30 configured as described above will be described. Here, a refrigerator will be described as an example of the cooling cycle device.

In recent years, a vacuum heat insulating material is adopted for a refrigerator, etc., and the heat insulation performance of the refrigerator is improved, and the penetration of heat from the outside of the refrigerator is very small. For this reason, the interior of the refrigerator is in a stable cooling state during most of the day, except during the morning and evening when doors are frequently opened and closed as household chores are performed. At this time, the compressor 17 is driven at low speed and low load with low refrigeration capacity. Therefore, in order to reduce the power consumption of the refrigerator, it is very effective to increase the efficiency when the brushless DC motor 4 included in the compressor 17 is driven at low speed and low load.

In the present embodiment, in a state where the brushless DC motor 4 is driven at low speed and low load, the switching operation of the switching element at high frequency by the PWM control is not performed. Instead, the drive timing is controlled by adjusting the on timing or off timing of the switching element such that the on time ratio of the PWM control is 100%. As a result, the occurrence of switching loss of the inverter circuit 3 due to PWM control is avoided, and the circuit efficiency of the inverter circuit 3 is significantly improved.

In the present embodiment, a MOSFET is used as a switching element of the inverter circuit 3. The MOSFET does not have a PN junction in the path of the output current when it is on. For this reason, the on-state loss, especially at low current output of the MOSFET, is very low compared to that of other power devices such as IGBTs.

As described above, the refrigerator is driven at low speed and low load during most of the time of day, and the current flowing to the brushless DC motor 4 is small. Therefore, when the motor drive device 30 of the present disclosure is used to drive the compressor 17 of the refrigerator as described above, the power consumption of the refrigerator is effectively reduced by using the MOSFET as the switching element of the inverter circuit 3. Be done.

Further, regardless of the state of the power supply to the brushless DC motor 4, by accelerating or decelerating the brushless DC motor 4 with a constant acceleration, noise and vibration at the time of changing the driving speed can be suppressed. In addition, since the drive frequency of the brushless DC motor 4 quickly passes through the resonance frequency band unique to the device, the occurrence of damage or the like of the piping of the compressor 17 is avoided, and the reliability of the compressor 17 and the device is improved Can.

Also, by setting the on time ratio of the PWM control to 100% and preventing the on and off switching operation by the PWM control from being performed, the phase current flowing in the stator winding of the brushless DC motor 4 is high frequency. It can be avoided that current components are superimposed. As a result, motor iron loss can be significantly reduced, and motor efficiency can be improved.

Further, in PWM control, switching operation of the switching element is generally performed at a PWM frequency of about 1 kHz to about 20 kHz, and noise due to a frequency component of the switching operation is generated. It is very important to improve the silent performance of the refrigerator, since the refrigerator is operated all day regardless of day and night. In the motor drive device 30 of the present embodiment, since the on-time ratio is set to 100%, generation of noise due to PWM control can be avoided, and noise reduction performance of the refrigerator can be improved.

As described above, the motor drive device according to the present disclosure can improve circuit efficiency and improve the efficiency of the brushless DC motor, as well as improve the reliability. In addition, it is possible to reduce the driving noise of the brushless DC motor and the vibration of the device. Therefore, the present invention can be applied to any device in which a brushless DC motor is used, such as a refrigerator, an air conditioner, a washing machine, a pump, a fan, a fan, and a vacuum cleaner.

1 AC power supply 2 converter circuit

2a rectifier circuit

2b smoothing circuit 2c switch (switching unit)
DESCRIPTION OF SYMBOLS 3

inverter circuit

3a, 3b, 3c, 3d, 3f switching element 4 brushless DC motor 5 position detection part 6 speed detection part 7 speed error detection part 8 energized phase control part 8c control amount adjustment part 11 PWM control part 12 waveform composition Part 13 Drive part 16 Compression element 17 Compressor 18 Condenser 19 Depressurizer 20 Evaporator 21 Refrigerator 22 Heat insulation wall 23 Food storage room 30 Motor drive

Claims

A brushless DC motor having a rotor;
An inverter circuit configured to have six switching elements and supplying power to the brushless DC motor;
A position detection unit that detects the position of the rotor;
A motor drive device comprising: a PWM control unit that performs PWM control to adjust a voltage applied to the brushless DC motor by turning on and off the switching element at a high frequency;
The motor drive further comprises:
An energized phase control unit that sets the energized state of each phase in the brushless DC motor while maximizing the on time ratio of the switching element by the PWM control;
A control amount adjustment unit configured to adjust a control amount in control of the drive speed of the brushless DC motor;
The control amount adjustment unit adjusts the control amount according to the supply state of the power to the brushless DC motor.
Motor drive.
The motor drive device according to claim 1, wherein the control amount adjustment unit switches the control amount with respect to a section where the electric power is supplied to the brushless DC motor, at an electrical angle of 120 degrees.
The brushless DC motor drives a compressor provided in a refrigeration cycle,
The motor drive device of Claim 1 or Claim 2.
A refrigerator using the motor drive device according to claim 3.