JP5396969B2 - Motor drive device, compressor and refrigerator - Google Patents

Description

  The present invention relates to a device for driving a brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding by means of an inverter that supplies power to the three-phase winding. The present invention relates to a brushless DC motor driving apparatus that is optimal for driving a compressor such as an air conditioner.

In order to extend the operating range of the brushless DC motor, the conventional motor drive device performs speed control by PWM feedback control while detecting the rotational position of the brushless DC motor at low load, and at a constant cycle at high load. Synchronous driving for switching the energized phase of the brushless DC motor is performed. (For example, see Patent Document 1)
FIG. 13 is a block diagram showing a conventional motor driving device described in Patent Document 1. In FIG.

  In FIG. 13, the power source 1 is a general commercial power source. In Japan, the power source 1 is a 50 Hz or 60 Hz AC power source having an effective value of 100V. The rectifying / smoothing circuit 2 converts the AC voltage into a DC voltage using the AC power supply 1 as an input. The inverter 3 is composed of a switching element (3a to 3f) and a diode (3g to 3l) connected in antiparallel in a three-phase full bridge configuration, and converts the DC input from the rectifying and smoothing circuit 2 into AC power. An AC output having an arbitrary voltage and frequency is supplied to the brushless DC motor. The brushless DC motor 4 is composed of a rotor having a permanent magnet and a stator having a three-phase star-connected winding.

  The counter electromotive voltage detection circuit 105 detects the relative position of the rotor from the counter electromotive voltage generated in the stator winding of the brushless DC motor 4.

The drive circuit 106 turns on / off the switching elements (3a to 3f) of the inverter 3.
The commutation circuit 107 determines which element of the inverter 3 is turned on by the output of the back electromotive voltage detection circuit 105 when the brushless DC motor 4 is in steady operation.

  The synchronous drive circuit 108 outputs a predetermined frequency and a predetermined voltage (predetermined duty) when the brushless DC motor 4 is operated as a synchronous motor.

  The switching circuit 109 switches the signal sent to the drive circuit 106 between the signal of the commutation circuit 107 and the signal of the synchronous drive circuit 108.

  The PWM control circuit 110 performs PWM (pulse width modulation) control by chopping only the switching elements of the upper arm or the lower arm of the switching elements (3a to 3f) of the inverter 3. The output voltage can be increased / decreased by increasing / decreasing the duty of the pulse width (ratio of the ON period in the pulse period).

  The load state determination circuit 111 determines the load state of the brushless DC motor 4 and determines the switching of the operation mode by the switching circuit 109.

  The first timer circuit 112 starts a timer when the operation is switched to the operation by the synchronous drive circuit 108, and ends the timer when a predetermined time t1 has elapsed.

The duty determination circuit 113 detects the maximum load when the duty reaches the maximum (100%).

  The phase determination circuit 114 can detect the phase difference between the signal of the back electromotive voltage detection circuit 105 and the signal of the synchronous drive circuit 108 and know the current load state.

  The frequency adjustment circuit 115 detects the phase difference between the signal of the back electromotive voltage detection circuit 106 and the signal of the synchronous drive circuit 108, and when the phase difference becomes smaller than a predetermined value, the output frequency from the synchronous drive circuit 105 Lower.

  With the above configuration, when the load applied to the brushless DC motor increases in the conventional motor driving device, the predetermined speed cannot be maintained by the feedback control while detecting the rotor of the brushless DC motor. Then, switch to synchronous drive by open loop control, and switch to commutation with a constant rotation speed.

  As a result, the motor rotor follows the commutation timing, and the terminal voltage phase advances relative to the induced voltage phase. As a result, since the current phase is also advanced from the induced voltage phase, the operating range of the brushless DC motor can be easily expanded by being in the same state as the weak magnetic flux control during synchronous driving.

As a result, even with a low torque motor that sacrifices the maximum number of revolutions to increase the motor efficiency, the operating range can be expanded so that the desired number of revolutions can be obtained at the maximum load point. A more efficient motor.
JP-A-9-88837

  However, in the above conventional configuration, the brushless DC motor at high speed or high load is synchronously driven in an open loop, so that the phase relationship between the induced voltage, voltage, and current of the brushless DC motor is in a constant phase state within a certain load range. However, if the load is larger than a certain level, the rotor will be delayed with respect to commutation (ie, the applied voltage phase and current The phase becomes a leading phase with respect to the induced voltage phase of the rotor), and the magnetic flux is weakened and synchronized with the commutation cycle. The rotor is accelerated and the leading angle of the current phase is decreased by the acceleration of the rotor. There is a possibility that the driving state (driving speed) will not converge to the stable state after all, as the rotor repeatedly decelerates. In such a driving state, the rotational speed of the brushless DC motor fluctuates, and there is a concern about the occurrence of “beating noise” accompanying this. In addition, the occurrence of “current pulsation” in which the motor current increases or decreases due to periodic acceleration / deceleration, the possibility of stopping overcurrent protection due to the current pulsation, and the possibility of finally causing a step-out stop of the brushless DC motor. Yes.

  In order to avoid the possibility of such a problem, in the conventional technique, the load state of the brushless DC motor is monitored, and the drive speed is reduced until the drive state becomes unstable.

  Furthermore, the load state determination circuit of the conventional motor drive device determines the load state from the phase difference between the phase of the counter electromotive voltage generated by the rotation of the brushless DC motor detected by the counter electromotive voltage detection circuit and the drive signal of the synchronous drive circuit. Since the determination is made, the upper limit of the drivable load is the time when the counter electromotive voltage becomes a detectable phase difference (30 degrees when 120 degrees energization).

  Therefore, the high-speed and high-load driving of the brushless DC motor is eventually limited, and there is a problem that the driving area cannot be sufficiently expanded.

The present invention solves the above-described conventional problems, and enhances the stability of a brushless DC motor at a high load and high speed driving to expand the driving range, and also suppresses an unstable state due to an external factor and has high reliability. Providing a brushless DC motor drive system With the expansion of the drive range due to the stability of high-speed and high-load drive, high-efficiency low-torque motors can be driven at high speed and high-load, resulting in high efficiency, low noise, and high torque. It aims at realizing a motor drive device.

  In order to solve the above-described conventional problems, a motor driving device according to the present invention supplies a power to a brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding, and the three-phase winding. The inverter has an inverter, detects the phase of the current flowing through the winding of the brushless DC motor from either the current flowing through the brushless DC motor winding or the output terminal voltage of the inverter, and performs a predetermined winding of the brushless DC motor. The brushless DC motor is driven by switching the windings energized to the brushless DC motor so that the current phase of the line and the voltage phase maintain a predetermined phase relationship.

  As a result, even when the brushless DC motor is driven at high speed by synchronous driving, the current and voltage phase of the brushless DC motor are maintained in an appropriate phase relationship with respect to the induced voltage phase, and are driven in an appropriate current and voltage advance state. Is done. For this reason, the stability in synchronous driving is improved, and the influence on the change in phase relationship when a disturbance occurs can be suppressed.

  According to the motor drive device of the present invention, the stability of a brushless DC motor can be increased by increasing the stability of the brushless DC motor at a high load and at a high speed, and an unstable state caused by an external factor can be suppressed. A drive device can be provided. Furthermore, along with the expansion of the drive range due to the stability of high-speed and high-load drive, high-efficiency low-torque motors can be driven at high speed and high-load, and high-efficiency, low-noise and high-torque motor drive devices can be provided. .

The invention according to claim 1 is a brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding, and an inverter for converting a DC voltage into an AC voltage and supplying electric power to the brushless DC motor. And a position detecting means for detecting a relative position of the rotor of the brushless DC motor from the output terminal voltage, and a voltage detecting unit for detecting the output terminal voltage of the inverter, and the brushless based on a signal from the position detecting means. First commutation means for generating a signal for switching a winding for energizing the DC motor, current detection means for detecting a current flowing in the winding of the brushless DC motor, current detected by the current detection means or voltage detection a current phase detection means for detecting the phase of the current flowing from the detected voltage in parts to the brushless DC motor, the output terminal voltage of the load torque Ri determined so as to hold the phase relation between the motor current phase and an inverter output terminal voltage phase, second rolling to produce a signal for switching the windings energizing the brushless DC motor the duty of the PWM control at a constant synchronous operation Switching means, load determination means for determining the load state of the brushless DC motor, and switching of the drive signal source of the inverter to either the first commutation means or the second commutation means by the load determination means. The motor driving device has switching means and detects the phase of the current flowing through the winding of the brushless DC motor for one phase and detects a zero cross point. As a result, even when driving without detecting the rotor position of the brushless DC motor, the relationship between the motor current phase and the voltage phase is always stable, so the driving range of the brushless DC motor can be expanded.

In the present invention, the current phase is detected for one phase. Normally, in feedback control that estimates the rotor position from the motor current, it is necessary to detect at least two-phase currents in order to separate the three-phase currents, but one phase for detecting the reference phase of a specific phase. Therefore, the motor drive device can be reduced in size and cost.

Further, in the present invention, the phase of the current flowing through the winding of the brushless DC motor detects the zero cross point of the current. As a result, the current phase can be reliably detected by a very simple method, so that the motor drive device can be simplified, and the cost can be reduced and the reliability can be improved.

Further, according to the present invention, the commutation means can be switched according to the load state of the brushless DC motor. Therefore, when the load is large and driving at high load / high speed is necessary, high torque operation is performed. Energy-saving drive through high-efficiency operation is possible. Further, since the phase of the voltage applied to the brushless DC motor is determined based on the phase of the current flowing through the stator winding of the brushless DC motor, the relationship between the current phase and the voltage phase of the brushless DC motor is stabilized, and the second commutation is performed. By improving the driving stability by the means, the load area and speed area in which the brushless DC motor can be driven can be greatly expanded.

According to a second aspect of the present invention, in the first aspect of the present invention, the current phase detection unit detects a current flowing through the brushless DC motor detected by the current detection unit or an output terminal voltage of the inverter obtained by the voltage detection unit. Is selected to detect the phase of the current flowing through the brushless DC motor. As a result, the current phase of the brushless DC motor can be acquired reliably and easily, and the cost can be reduced by improving the reliability of the motor driving device and simplifying the device.

According to a third aspect of the present invention, in the invention according to any one of the first and second aspects, a current transformer is used as the current detecting means. As a result, the circuit loss due to the current detection means can be reduced as much as possible, so that a highly efficient motor drive device can be provided.

According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, when the current phase detection unit cannot detect a current phase by the terminal voltage detection unit, the current detection unit The current phase is detected by the current detected by. As a result, the current phase can always be detected in any driving state regardless of the load state or the driving speed state, and the stability improvement in the synchronous driving of the brushless DC motor and the further expansion of the driving region can be realized.

According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the duty determination unit determines that the duty of the output waveform of the first commutation means is maximized. When the output of the first commutation means becomes maximum, the drive drive signal source of the inverter is switched from the first commutation means to the second commutation means. As a result, when the load is such that the PWM duty is maximized in driving by the first commutation means at low load, it is possible to switch to driving by the second commutation means. The driveable load area can be expanded.

Phase difference the invention according to claim 6 to the invention described in any one of claims 1 to 5, for detecting the phase difference between the signal of the signal and the second commutation means of said position detecting means A determination unit is provided to switch the output from the second commutation means to the output from the first commutation means when the phase difference becomes smaller than a predetermined value. As a result, when the second commutation means is in the driving state, it is possible to accurately recognize that the load is reduced and the first commutation means can drive the first commutation means. The frequency of performing high-efficiency operation by the commutation means is increased, and the power consumption of the motor drive device can be reduced.

The invention described in claim 7 is the brushless DC motor according to any one of claims 1 to 6 , wherein the brushless DC motor is a rotor in which a permanent magnet is embedded in an iron core of the rotor, and has saliency. It has the rotor which has. This makes it possible to effectively use the reluctance torque due to the saliency as well as the magnet torque due to the permanent magnet in driving the brushless DC motor. Is possible.

The invention according to an eighth aspect is the invention according to any one of the first to seventh aspects, wherein a compressor is used as a driving load of the brushless DC motor. In the drive control of the compressor, high-precision rotation speed control, acceleration control, position control, etc. are not required unlike industrial servo motor control. In addition, the compressor has a relatively large load of inertia, and the reciprocating type that reciprocates in particular has a very heavy inertia because the rotor is connected to a heavy metal crankshaft and piston. It can be said that the fluctuation of the speed in a large and short time is a very small load. Therefore, even if the detection of the current phase is only one phase, the control accuracy such as speed fluctuation does not deteriorate, so it can be said that it is one of the very effective applications of the motor drive device of the present invention. In addition, by extending the drive area of the brushless DC motor compared to the conventional motor drive device, even when the same compressor as the conventional motor drive device is used, the refrigeration capacity can be increased, so the high-capacity refrigeration cycle can be downsized. Low price can be realized. Furthermore, if the motor drive device of the present invention is replaced with a refrigeration cycle using a conventional motor drive device, a compressor using a higher efficiency motor can be used, and the refrigeration cycle can be further improved in efficiency. Can be realized.

A ninth aspect of the present invention is a compressor including a motor driven by the motor driving device according to any one of the first to eighth aspects. Thereby, the load range and speed range in which the compressor can be driven can be expanded. When the load is low, it is possible to provide a compressor capable of high-efficiency operation at low speed drive and high refrigeration capacity operation at high speed drive when the load is large.

A tenth aspect of the present invention is a refrigerator including the compressor according to the ninth aspect . With the expansion of the compressor's drivable load range and speed range, for example, a compressor using a motor with a high-efficiency low-torque design that increases the number of stator windings with the aim of increasing efficiency in the low-load region, By switching the commutation means to the second commutation means, it is possible to drive at high speed and high load.

  Therefore, high-efficiency operation is required in the stable cooling state that occupies most of the day, such as a refrigerator, while the door temperature is frequently used in housework hours in the morning and evening, summertime, etc. It is a very rational and effective means that can satisfy conflicting requirements for devices that require temporary high-speed and high-load drive to quickly cool, such as when the temperature rises. is there.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. In FIG. 1, the same components as those of the conventional technique are denoted by the same reference numerals, and description thereof is omitted.

In FIG. 1, the position detection means 5 detects the relative position of the rotor of the brushless DC motor 4, and from the voltage detection unit 5a for detecting the output terminal voltage of the inverter 3 and the output waveform of the voltage detection unit 5a, The position detection unit 5b detects the zero cross point of the induced voltage of the brushless DC motor. Position detecting means 5 detects the zero cross point from the induced voltage appearing at the inverter output terminal during the period when the upper and lower switching elements (for example, U-phase switching elements 3a and 3b) of any phase of inverter 3 are off. I am doing so. Specifically, the output terminal voltage of the inverter 3 and the midpoint potential of the stator three-phase winding of the brushless DC motor 4 or a half of the input DC voltage of the inverter 3 are compared by a comparison circuit constituted by a comparator circuit or the like. And the timing at which the magnitude relationship is inverted is detected.

  The first commutation means 6 measures the commutation timing of the brushless DC motor 4 by feedback control, and the speed command means 7 instructs the drive speed of the brushless DC motor. The first commutation means 6 detects the current drive speed of the brushless DC motor from the generation cycle of the position signal obtained by the position detection means 5, and detects the detected drive speed and the command speed instructed by the speed command means 7. From the deviation, the voltage applied to the inverter 3 and the application timing are measured. Specifically, in the case of 120-degree rectangular wave drive, when a voltage is applied from the timing at which an electrical angle of 30 degrees has elapsed from the zero cross point detection time point of the induced voltage (that is, the position detection time point), the induced voltage and the terminal voltage are in phase, The optimum timing can be obtained by arbitrarily adjusting the voltage application timing from the position detection timing based on the type and characteristics of the motor or the load state. The voltage value can be easily adjusted by PWM control. When the drive speed is slower than the command speed, the PWM duty is increased so as to increase the applied voltage, and when the drive speed is faster than the command speed, the duty is decreased to adjust the voltage applied to the brushless DC motor. This results in speed control of the brushless DC motor, and feedback control is performed by detecting the induced voltage.

  The current detection means 8 detects the phase current of the brushless DC motor, and is installed between the output of the inverter 3 and the stator winding in this embodiment. As a method for detecting the motor phase current, current detection is performed between the lower switching element (3b, 3d, 3f) of the inverter 3 and the inverter input N side (that is, the anode side of the diodes 2c, 2d of the rectifying and smoothing circuit 2). There may be a method of attaching a shunt resistor and detecting from the voltage generated in the resistor, but the loss due to the resistance increases. Therefore, in the embodiment of the present invention, a current sensor is used, and there is almost no increase in loss. An efficient motor drive device has been realized.

  The current phase detection means 9 includes a current phase detection switching unit 9a and a current phase detection unit 9b. The current phase detection means 9 receives the output of the terminal voltage detection means 9c for detecting the output terminal voltage of the inverter 3 and the output of the current detection means 8. In this embodiment, the voltage detection unit 5a of the position detection means 5 is connected to the current phase detection means 9. By sharing the terminal voltage detection means, it is not necessary to add a separate circuit, and the device is reduced in size and cost.

  In the current phase detection switching unit 9a, the detection of the current phase is detected based on the output of the current detection unit or the detection based on the output of the voltage detection unit according to the input waveform state from the voltage detection unit 5a and the current detection unit 8. Select to switch. The current phase detection unit 9b detects an arbitrary phase of the phase current flowing through the brushless DC motor from the method selected by the current phase detection switching unit. In this embodiment, the zero cross point of the current waveform is detected.

  The second commutation means 10 has a predetermined commutation period based on the motor drive speed instructed by the speed command means 7 with the zero cross point as a reference as an arbitrary phase of the brushless DC motor phase current detected by the current phase detection means 9. The commutation timing of the switching element of the inverter 3 is measured with a duty of.

  Here, the operation of the current phase detection means 9 will be described with reference to FIGS. 1, 2, 3, and 4.

  FIG. 2 shows the waveform of each part of the U phase in the drive by the first commutation means in the first embodiment. Since PWM feedback control is performed in the drive in the first commutation means, the PWM carrier component is superimposed on the waveform of each part. However, in FIG. 2, the PWM duty is 100% and the description is simplified.

In FIG. 2, (c) shows the output waveform of the voltage detector 5a, the output terminal voltage of the inverter shown in (b) (the U-phase output terminal voltage in FIG. 2), and the brushless DC motor stator. A magnitude relationship with the midpoint potential of the three-phase winding or half of the inverter input voltage Vin is output. (In this embodiment, the terminal voltage is compared with Vin / 2, and the voltage detector 5a outputs Hi when the terminal voltage is higher than Vin / 2, and outputs Lo when it is lower.)
Sections A and B are timings when the switching elements 3a and 3b in FIG. 1 are turned off. At this time, an induced voltage accompanying the rotation of the brushless DC motor 4 appears in the terminal voltage. The timing at which this induced voltage becomes equal to Vin / 2 is the zero cross point of the induced voltage, and the output level of the voltage detector 5a is inverted. The position detector 5b in the position detector 5 acquires this output inversion timing as the position detection timing and outputs it to the first commutator. In the sections A and B, when the switching element is turned off, a spike voltage generated when the energy stored in the winding is released through the diodes 3g (section A) and 3h (section B) appears, and voltage detection is performed. The signal of the part 5a changes. However, since the position detection unit 5b reliably acquires the zero cross point of the induced voltage, the signal voltage of the voltage detection unit 5a is ignored for a certain period after the switch element is turned off. Is preventing.

  FIG. 3 is a waveform of each part of the U phase in the driving by the second commutation means in the first embodiment. FIG. 3A is a driving at a relatively high load, and FIG. 3B is a driving at a relatively low load. State.

  3A and 3B, (C) shows the output waveform of the voltage detector 5a, and the comparison result between the terminal voltage shown in (B) and Vin is output as described above.

  In FIG. 3A, in the section A, the U-phase upper switching element 3a is in the ON state, and the motor current flows into the motor via the switching element 3a. The section B is a section in which the clamp diode 3h is turned on as the switching element 3a is turned off, and the section C is a section in which the clamp diode 3g is turned on. Here, the boundary point that changes from the section B to the section C is the point at which the direction of the motor current (the U phase in the present embodiment) changes at the timing when the diode 3g is turned off and the diode 3h is turned on. is there. Therefore, when there is a point where the output state of the voltage detection unit 5a changes after the switching element (3a) is turned off (that is, when a spike voltage is generated), the current phase detection switching unit outputs the output of the voltage detection unit 5a. 3 is selected, and the timing at which the output of the voltage detector 5a is inverted after the switch element is turned off is acquired as the zero cross point of the motor current, as shown in FIG.

  On the other hand, in the driving state shown in FIG. 3B, the terminal voltage waveform shown in FIG. 3B is a rectangular waveform of 180 degrees one pulse. Naturally, in this case, the output waveform of the voltage detector 5a is also in a one-pulse shape, and it is difficult to detect the phase of the current from the output of the voltage detector 5a. Therefore, at this time, the current phase detection switching unit selects to detect the current phase from the output from the current detection means 8.

  The detection of the current phase by the current detection means 8 is performed by periodically A / D converting the output of the current detection means 8 with a microcomputer or the like (for example, every 20 μsec), and the point where the current value becomes maximum or minimum, or zero This phase (zero cross) can be easily detected by software. In the present embodiment, in order to simplify the control, a current zero cross is detected and is made the same as the phase detection point in the voltage detection unit.

  In addition, as a specific phase detection by hardware, a method of detecting the rising and falling edges of the photocoupler output signal as a zero cross by inputting the output of the current detection means to the photocoupler, and the falling and rising of the photocoupler output signal are detected. It is also possible to easily detect the intermediate point as a phase where the current becomes the maximum or minimum point.

  Here, in the motor drive device according to the embodiment of the present invention, the current information obtained by the current detection means 8 is used to detect the phase of the current, and does not detect the current value. Therefore, it is not necessary to use highly accurate current detection means such as a DC current sensor, and in this embodiment, a very inexpensive AC current sensor 8a (generally called an AC current transformer or ACCT) is used to drive the motor. The cost of the device is reduced.

  In selecting an alternating current sensor, the cost can be further reduced by using a general type for a commercial power supply (50 or 60 Hz). In the present embodiment, since the alternating current sensor is not used for detecting the current value, output accuracy is not particularly required, so that low-cost parts can be selected from the viewpoint of good yield. However, with regard to frequency characteristics, there is no problem in changing the output accuracy with respect to the current frequency, but naturally it is necessary to select a type that can acquire a specific phase stably from the minimum frequency to the maximum frequency of the phase current. is there. Next, the case of the current waveform shown in FIG. 4 will be described.

  FIG. 4 is a waveform of each part of the U-phase in a state in which the energization angle is relatively narrow with a low load driven by the second commutation means in the first embodiment.

  The current waveform shown in FIG. 4 (a) has a period in which the current is zero when both the upper and lower switching elements (3a and 3b) of the U phase are in the OFF state. In the present embodiment, since the zero cross phase of the current is detected, there is a possibility that the detection timing of the detection phase point varies and the detection timing becomes unstable in the zero cross detection by the current detecting means. Furthermore, when an alternating current sensor is used as the current detection means, detection becomes very difficult during a period when the current is zero. Therefore, in the case of such a current waveform, if the point at which the output of the voltage detector changes (that is, the timing at which the spike voltage disappears) is detected after the switching elements (3a and 3b) are turned off, the current is zero as the specific phase. Can be acquired reliably and stably.

  As described above, the current phase detection switching unit selects the current phase detection from the terminal voltage (voltage detection unit) when it detects a point where the output of the voltage detection unit changes (ie, spike voltage) after the switching element is turned off. In the case of a waveform in which the current phase cannot be detected from the inverter output terminal voltage, such as a 180-degree one-pulse rectangular waveform, by selecting the current phase detection by the current detection means, the current zero cross point can be stabilized even in various drive states And it is possible to detect reliably.

  In addition, even when a constant deviation in detection timing occurs due to a constant variation in hardware or a noise removal filter in zero cross detection, the motor driving device of the present invention only needs to determine an arbitrary reference phase of the motor current. Thus, it is possible to realize a motor drive device that has very little influence on circuit variations and the like.

  The load determination means 11 is for determining the load state of the brushless DC motor, and the phase relationship between the duty determination unit 12 for determining the PWM duty state, the position detection timing, and the commutation signal generated by the second commutation means. The phase difference determination unit 13 for determination is configured.

  The switching unit 15 switches whether the output of the inverter 3 is performed by the first commutation unit 6 or the second commutation unit 10 based on the determination result of the load state by the load determination unit 11.

  The drive unit 16 turns on / off the switching element of the inverter 3, and the switching timing of the on / off state of the switching element is the first commutation means 6 or the second commutation means 10 selected by the switching means. Based on the commutation timing generated by.

  The operation of the motor driving apparatus configured as described above will be described.

  FIG. 5 is a flowchart showing the operation in the present embodiment.

  In FIG. 5, first, at step 1, speed control is performed by PWM feedback control with the speed designated by the speed command means 7 as a target based on the rotor relative position of the brushless DC motor detected by the position detection means 5. Since this control is a general driving method, detailed description is omitted, but the commutation timing is controlled so as to achieve the most efficient driving state in order to perform position detection feedback control. Next, in step 2, it is confirmed whether or not the drive speed has reached the target speed. If the drive speed has reached the target speed, the process returns to step 1. If the target speed has not been reached, the process proceeds to step 3, and the duty determination unit 12 in the load determination unit 11 checks whether the PWM duty has reached the maximum duty (generally 100%). If the PWM duty is less than 100%, the speed control by the PWM duty control is possible, and the process returns to step 1. Here, when the PWM duty width reaches the maximum, the supply voltage to the brushless DC motor cannot be increased any more. That is, it is in the limit load state in the drive by the first commutation means 6.

  Accordingly, at this time, the switching means 15 switches the first commutation means to the second commutation means 10 and drives the brushless DC motor by the second commutation means at step 4.

  Here, driving by the second commutation means will be described.

  FIG. 6 shows the phase relationship between the phase current and the terminal voltage when a brushless DC motor is driven in an open loop by a synchronous drive circuit in a conventional motor drive device.

  In FIG. 6, the horizontal axis represents time, the vertical axis represents the phase based on the induced voltage phase (that is, the phase difference from the induced voltage), (A) represents the phase current, (B) represents the terminal voltage, and (C). Is the phase difference between the phase current and the terminal voltage. FIG. 6A shows a stable operation state at a relatively low load, and FIG. 6B shows a state at the drive limit in the conventional motor drive device. Further, since the current phase is advanced from the terminal voltage phase in both (a) and (b), it can be seen that the brushless DC motor is driven at a very high speed and the induced voltage is high.

  As shown in FIG. 6A, when the driving state is stable by synchronous driving, the rotor is delayed by an angle corresponding to the load state with respect to the commutation, that is, when viewed from the rotor (induced voltage). The commutation (i.e., voltage and current phase) becomes the leading phase and the predetermined relationship is maintained. Since this is the same state as the magnetic flux weakening control, it is possible to drive at high speed.

On the other hand, as shown in (b), in a state where the load is large with respect to the driving speed, as in (a), “the rotor is delayed with respect to the commutation so that the magnetic flux is weakened and the commutation cycle is synchronized. The rotor accelerates, but the advance angle of the current phase decreases due to the acceleration of the rotor, and the rotor decelerates. The rotor is accelerated ... ", and the driving state (driving speed) is not stable after all. That is, as shown in (b), since the rotation of the brushless DC motor fluctuates with respect to the commutation performed at a constant cycle, the terminal voltage phase fluctuates when the induced voltage phase is used as a reference. The state becomes unstable. This is because, because of the open loop drive, when the motor rotor is out of synchronization, its position cannot be grasped, and the phase of the terminal voltage (that is, the commutation timing) cannot be fixed with respect to the induced voltage. Therefore, stable driving performance can be obtained by always fixing the phase relationship between the induced voltage and the terminal voltage in the synchronous driving state.

  FIG. 7 is a graph showing a phase state with respect to a load when the brushless DC motor is synchronously driven. In FIG. 7, the horizontal axis indicates the motor torque, and the vertical axis indicates the phase difference based on the induced voltage phase. When the phase is positive, the phase is positive with respect to the induced voltage phase. Further, (b) in FIG. 7 is the motor current, and (b) is the phase of the motor terminal voltage, indicating a stable state in the synchronous operation. Since the current phase is ahead of the terminal voltage phase, it can be seen that the driving is performed at a high speed with a high induced voltage. As is clear from the relationship between the phase current phase and the phase voltage phase shown in FIG. 7, the change in the current phase with respect to the load torque is very small. On the other hand, since the terminal voltage phase changes linearly, the phase difference between the current and the voltage changes almost linearly according to the load torque. Here, as described above, in the state of stable driving by synchronous driving, the phases of the induced voltage, the motor current, and the terminal voltage are stable while maintaining a constant relationship as shown in FIG. That is, the motor current phase and the terminal voltage phase are balanced in an appropriate phase relationship according to the load. Therefore, the motor current phase and voltage phase are always maintained and fixed in an appropriate phase relationship according to the load, thereby avoiding the unstable phenomenon in the high-speed and high-load drive that occurs in the conventional motor drive device. It can be said that it can be expanded.

  Here, a method for stabilizing the phase difference between the motor current phase and the terminal voltage phase according to the load state will be described. FIG. 8 is a timing chart showing commutation timing by the second commutation means in the present embodiment. In FIG. 8, (A) indicates the timing of the reference phase of the U-phase current (in this embodiment, the zero-cross point at which the U-phase current changes from negative to positive polarity), and (B), (C), and (D) respectively. The U-phase, V-phase, and W-phase upper switching element states are shown. In this timing chart, a rectangular wave of 120 degrees is energized. Tfrq in FIG. 8 is a commutation cycle. In the synchronous drive by the second commutation means, the commutation is repeated at a constant period based on the command speed by the speed command means 7.

  T0 to Tn + 1 is an elapsed time from the reference phase of the motor phase current (the U-phase zero cross point in the present embodiment) to the commutation of the arbitrary phase (the U-phase upper switching element is turned on in the present embodiment). The second commutation means 10 always measures this time.

  TW0 to TWn + 1 are timings at which an arbitrary phase is commutated after the motor phase current reference phase is detected (in this embodiment, the W-phase lower switching element 3f is turned on).

  Here, a method for determining the commutation timing will be described with reference to FIG. FIG. 9 is a flowchart showing a method for determining the commutation timing of the second commutation means 10 of the motor drive device according to the present embodiment.

First, at step 11, the time Tn from the current reference phase to the commutation of an arbitrary phase (in this embodiment, the U phase is on) is acquired. In step 12, the acquired time Tn is compared with the average time Tav of the past n pieces of data (from T0 to Tn-1) to calculate a difference. In step 13, the commutation timing correction amount is calculated based on the calculated difference. The correction amount is calculated by using an optimum correction formula or the like based on the motor characteristics, load characteristics, etc. In step 14, based on the correction amount calculated in step 13, the correction amount is added to the commutation cycle in the synchronous drive to set the commutation cycle of any phase (in this embodiment, the energization time TWn + 1 of the W-phase upper switching element 3f). In step 15, the average time Tav from the phase current reference phase to the commutation cycle of the arbitrary phase is updated in consideration of the data Tn acquired this time.

  Since the correction amount of the commutation timing is determined as described above, when the load or the like is stable and the driving of the brushless DC motor is in a stable state, the difference between the acquired data Tn and the past n average times Tav is very small. The correction amount of the commutation timing is also a very small value and is hardly corrected, and the phase relationship is stabilized.

  On the other hand, when the load increases in a stable drive state, the rotation of the rotor is delayed with respect to the commutation cycle as described above, the phase difference between the phase current phase and the terminal voltage phase is reduced, and the time Tn in FIG. 8 is shortened. Become. Therefore, Tn becomes smaller than Tav, and the difference between Tav and Tn increases. At this time, the commutation period is made closer to the rotation of the rotor (that is, the phase current phase and the terminal voltage phase are always kept constant). In this embodiment, Tav and Tn are set in the direction of delaying the W-phase commutation period. A correction amount based on the difference is added. At this time, commutation of other phases is not corrected, and commutation based on the command speed is repeated. This operates so that the time from the phase current reference phase to the commutation of the specific phase (hereinafter referred to as Tm as a representative time) approaches the average time Tav.

  Accordingly, the load increases and the rotor starts to be delayed from commutation, so that the phase difference between the phase current phase and the terminal voltage is reduced, and Tm is shortened. As a result, Tav, which serves as a reference for the commutation timing correction amount, is gradually shortened, so that Tm and Tav are balanced and the relationship between the phase current phase and the terminal voltage phase according to the load state is maintained. The driving state is stabilized by obtaining the angle.

  When the load is reduced, the difference between Tav and Tn increases with the opposite sign to that when the load increases, and the commutation timing is also corrected in the opposite sign direction. It is the same.

  As described above, by correcting the commutation timing so as to maintain the phase relationship between the motor phase current and the terminal voltage according to the load state, the motor induced voltage (that is, motor rotation) phase, the phase current phase, and the terminal voltage phase are changed. As a result, the stability of the high speed and high load driving of the brushless DC motor can be improved, and the high load and high speed driving performance can be expanded.

  As described above, when the brushless DC motor is driven in a relatively low speed and low load state where the PWM duty is 100% or less, the first commutation means 6 performs speed control based on the rotor relative position by PWM feedback control. In the load state in which the PWM duty is 100% due to relatively high speed and high load, and the first commutation means cannot be driven at the target speed, the phase current / terminal by the second commutation means is realized. Realizes high torque drive with drive control that maintains the phase relationship that matches the voltage phase to the load state, expands the drive range further than conventional motor drive devices, and stable high-speed and high-load drive performance that is less susceptible to disturbances Is realized.

  In addition, the phase detection of the motor phase current is performed only for one phase, but if the commutation timing correction is performed by acquiring phase information of two phases or all three phases, correction control with higher sensitivity is possible. However, in this embodiment, the cost performance of the motor drive device is improved by performing the operation in only one phase.

  Next, the operation of the phase difference determination unit of the load determination unit 11 will be described.

The driving by the second commutation means performs synchronous driving with a constant PWM duty regardless of the load state of the brushless DC motor. Therefore, when the load state drops from the state of being driven by the second waveform generating unit under a high load state, and the load state is enabled to be driven by the first commutation unit, the brushless DC is applied by applying an excessive voltage. The motor rotor tries to drive at a higher speed than the target speed. Even in this state, the synchronous driving always performs commutation at a constant speed based on the target speed, so that the driving is performed while the brake is being applied while the speed is being suppressed. At this time, the current of the brushless DC motor is increased, while the motor torque is extremely decreased.

  In order to avoid such a state, in the embodiment of the present invention, when driving by the second commutation unit, by confirming the load state, the first commutation means can be driven. At this time, the drive at the first commutation portion is promptly shifted.

  FIG. 10 is an output signal timing chart of the voltage detector 5a of the position detector 5 when the brushless DC motor is driven. 10A is a U-phase terminal voltage waveform, FIG. 10B is an output signal of the voltage detector 5a of the position detector 5, and FIG. 10C is a U-phase upper drive signal. Although FIG. 10 shows the U-phase signals, it is needless to say that the V-phase and W-phase signals have the same waveform although there is a phase shift of ± 120 degrees.

  As described above, in the synchronous driving by the second commutation means, the current and voltage advance angle corresponding to the driving state are stabilized. Therefore, the position of the zero cross point of the induced voltage appearing in the terminal voltage shown in FIG. 10 (a) changes with respect to the phase of the drive signal depending on the advance angle state (that is, the drive state). This also changes the phase of the output signal (b) of the position detector.

  Specifically, as shown in FIG. 10 (b), when the voltage advance angle increases, the output signal of the voltage detector 5a shifts to the right and the phase difference with the drive signal increases, and the advance proceeds when 120 degrees energization occurs. When the angle is 30 degrees or more, the maximum phase difference is constant at 30 degrees. If the advance angle is reduced, the voltage detector shifts to the left and the phase difference from the drive signal becomes smaller.When the load further decreases after the phase difference becomes zero, the phase is delayed from the induced voltage. Finally, a delayed phase of 30 degrees is obtained.

  In other words, the zero crossing of the induced voltage can be detected in the range where the phase difference of the drive signal with respect to the induced voltage is from −30 ° C. to + 30 ° C. (However, if a spike voltage is generated, If the phase difference is +30 degrees or less, it is a load state that can be driven by the first commutation means. Therefore, by determining the phase difference load state between the signal of the voltage detection unit of the position detection means and the drive signal, it is possible to determine whether the drive by the first commutation means is possible, and the drive by the first commutation means accurately. It becomes possible to shift to.

  In the present embodiment, the detection of the phase difference between the voltage detection unit signal and the drive signal is performed when the voltage detection unit signal and the drive signal change (in FIG. 10, the output of the voltage detection unit changes from L to H). The difference between the changing timing and the timing at which the U-phase upper drive signal becomes H (ON) is used.

  In FIG. 10, φ indicates the time difference between the ON timing of the drive signal and the rising edge of the output signal of the voltage detector 5a, which includes phase difference information of both signals. For example, in the case of 120-degree energization, if the angle from the rising edge of the voltage detector 5a output to commutation is 20 degrees, the phase difference is 10 degrees.

When the load is large and the first waveform generator cannot be driven, the rotation of the brushless DC motor is delayed with respect to the drive signal (ie, commutation timing) (the terminal voltage is induced based on the induced voltage phase). When the voltage detector 5a rises and the rising edge of the drive signal approaches (that is, φ approaches 0), the output of the voltage detector and the drive by the second commutation means The phase difference from the signal increases).

  Further, when the load increases and 120 ° energization has an advance angle of 30 ° or more with respect to the induced voltage, the zero cross of the induced voltage is buried in the terminal voltage, and the rising edge of the drive signal and the voltage detector 5a The rising edges are simultaneous (that is, φ = 0, and the phase difference between the output of the voltage detector and the drive signal from the second commutation means is constant at 30 degrees). In such a load state, the driving by the first commutation means while detecting the zero cross of the induced voltage is naturally not possible. Therefore, the load state exceeds the drive limit of the first commutation means, and the second commutation means Drive by.

  Next, a case where the load is reduced when the load is large and driving by the second commutation means is performed will be described.

  As described above, in the drive by the second commutation unit in the high load state that cannot be driven by the first waveform generation unit, the advance angle state of 30 degrees or more is obtained at 120 degrees energization. Here, when the load is reduced, the advance angle also decreases, and when the advance angle state is less than 30 degrees, the induced voltage zero cross point of the brushless DC motor appears in the terminal voltage, and the first commutation unit can be driven. It becomes a load state. Referring to FIG. 10, the output of the voltage detector 5a of the position detecting means 5 is inverted at the induced voltage zero cross. The inversion timing is different from the on-timing of the U-phase drive signal (φ ≠ 0), and the lead angle becomes smaller as the load becomes lighter, so φ becomes larger (that is, the voltage detection unit output and the second commutation means). The phase difference from the drive signal due to (approaching 0) approaches 0).

  That is, the phase difference between the voltage detection unit output and the drive signal by the second commutation means can be monitored from the timing difference between the change timing of the voltage detection unit 5a output and the commutation timing, and the load that can be driven by the first commutation unit It can be easily detected whether or not it is in a state. In the present embodiment, when the difference φ between the output change timing and the commutation timing of the voltage detection unit 5a becomes larger than the predetermined difference φmax, the driving by the second waveform generation unit is changed to the driving by the first waveform generation unit. I try to migrate. Note that the value of φmax may be an arbitrarily set value such as an advance value set in the drive by the first waveform generator.

  A method of shifting from the driving by the second commutation means described above to the first commutation means will be described with reference to FIGS.

  When driving by the second commutation means in step 4, the output change timing of the voltage detection unit 5a of the position detection unit 5 in step 5 (in FIG. 10, the timing at which the voltage detection unit output of the position detection unit rises for the U phase) And whether the difference φ between the commutation timing (ON timing on the U phase in FIG. 10) is larger or smaller than φmax. If φ is smaller than φmax at this time, it returns to step 4 to continue driving by the second commutation means because the load is large.

  On the other hand, when φ becomes larger than φmax, it is determined that the load state can be driven by the first commutation unit, and the process returns to step 1, and the first commutation unit based on position detection (induced voltage zero cross detection) feedback control is performed. Drive with.

  As a result, when the load is reduced during driving by the second commutation means, when the load state that can be driven by the first commutation means is reached, this timing is accurately detected, and the first commutation means is detected. Is switched to high-efficiency driving by PWM feedback control while detecting the rotor relative position of the brushless DC motor.

In order to prevent hunting in bidirectional switching between the first commutation means and the second commutation means, it is desirable to provide hysteresis or the like in setting the transition timing.

  Next, the structure of the brushless DC motor 4 will be described.

  FIG. 11 is a structural diagram of the rotor of the brushless DC motor according to the first embodiment of the present invention.

  The rotor core 4a is formed by stacking punched thin steel sheets of about 0.35 mm to 0.5 mm. The four magnets 4b to 4e are embedded in the rotor core 4a in a reverse arc shape. This magnet is usually a ferrite type, but when a rare earth magnet such as neodymium is used, a plate structure may be used.

  In a rotor having such a structure, assuming that the axis from the rotor center to the magnet center is the d axis and the axis between the rotor center and the magnet is the q axis, the inductances Ld and Lq in the respective axial directions are reversed. It has saliency and will be different. That is, this means that the motor can effectively use torque (reluctance torque) using reverse saliency in addition to torque (magnet torque) due to magnetic flux of the magnet. Therefore, the torque can be used more effectively as a motor. As a result, the motor is a highly efficient motor.

  Further, when the control of the present embodiment is used, since the current is operated in the leading phase when the second commutation means 10 is driven, the reluctance torque is greatly utilized, so that the reverse collision occurs. The motor can be operated at a higher rotational speed than a motor having no polarity.

  The brushless DC motor 4 is a rotor in which the permanent magnets 4b to 4e are embedded in the iron core of the rotor 4a and has reverse saliency. By using reluctance torque in addition to the magnet torque of the permanent magnet, As a matter of course, the efficiency at low speed is increased, and the high-speed driving performance is further increased.

  Also, by adopting a rare earth magnet such as neodymium as the permanent magnet to increase the ratio of magnet torque, or increase the ratio of reluctance torque by increasing the difference between inductances Ld and Lq, the optimum conduction angle can be changed. Efficiency can be increased.

  In applications where it is required to use a brushless DC motor in a very wide range from a low load at low speed to a high load at high speed, for example, if the load occupying most of the drive is low load to medium load, If a brushless DC motor having a torque design that can be driven by the first commutation means with a duty of 100% near the most frequently used speed and load is used, a further increase in efficiency can be achieved.

(Embodiment 2)
FIG. 12 is a block diagram showing a refrigerator using the motor drive device according to the second embodiment of the present invention. In FIG. 12, the same components as those in FIG.

  The brushless DC motor 4 is connected to the compression element 16 to form a compressor 17. In the present embodiment, the compressor is used in the refrigeration cycle, and the high-temperature and high-pressure refrigerant discharged from the compressor is sent to the condenser 18 to be liquefied, reduced in pressure by the capillary 19, evaporated by the evaporator 20, and returned to the compressor again. I have to. Furthermore, in this Embodiment, the refrigerating cycle using the motor drive device 22 is used for the refrigerator 21, and the evaporator 20 cools the inside 23 of the refrigerator 21. FIG.

As described above, in the second embodiment, the brushless DC motor drives the compression mechanism of the compressor of the refrigeration air conditioning cycle. For example, in particular, a reciprocating (reciprocating type) compressor has a structure in which a metal crankshaft and a piston having a large mass are connected to a brushless DC motor, and the load is very large. For this reason, fluctuations in speed in a short time are very small regardless of the compressor process (suction process, compression process, etc.) as the drive speed is high. Therefore, even if the commutation timing is determined based on the current phase of only one arbitrary phase, a stable driving performance can be obtained without increasing the speed fluctuation. Furthermore, since the control of the compressor does not require high-precision rotation speed control or acceleration / deceleration control, the motor driving device of the present invention can be said to be one of the very effective applications for driving the compressor.

  In addition, since the drive region can be expanded compared to when the compressor is driven by a conventional motor drive device, the refrigeration capacity of the refrigeration cycle can be increased by driving at a higher speed. Thereby, even if it is the same cooling system as before, it can be applied to a system that requires higher refrigeration capacity. That is, a refrigeration cycle that requires high refrigeration capacity can be reduced in size and provided at low cost.

  Further, even if a compressor having a refrigerating capacity one rank smaller (for example, a compressor cylinder volume is small) than a conventional refrigeration cycle using a motor drive device, the compressor using the motor drive device of the embodiment of the present invention is used. By rotating at a high speed, it becomes possible to secure the necessary refrigeration capacity, and further, the cooling cycle can be reduced in size and cost.

  In this embodiment, since the compressor is used to cool the inside of the refrigerator, the refrigerator has a high frequency of opening and closing the door only in the morning and evening due to the characteristics of the product. The inside of the refrigerator is in a stable cooling state, and the brushless DC motor is driven in a very low load state. Therefore, to reduce the power consumption of the refrigerator, it is effective to improve the efficiency of driving the brushless DC motor at low speed and low output. In the present invention, since the high-speed and high-load efficiency of the brushless DC motor can be greatly expanded, the compressor using the brushless DC motor that sacrifices the motor torque (high-speed rotation performance) to increase the number of windings of the stator and increase the efficiency. The maximum refrigeration capacity required for the refrigerator is secured by improving the high-load and high-speed driving performance of the refrigerator. This can further reduce power consumption due to high efficiency in a low load area that occupies most of the day.

  As a specific motor winding design, when driving at the most frequently used rotation speed and load state (for example, 40 Hz rotation speed and compressor input power of about 80 W) as a refrigerator, the first rotation is used. If the current means 6 is designed to have a duty ratio of 100% at a conduction angle of 120 to 150 degrees, the iron loss of the brushless DC motor and the switching loss of the inverter 3 can be reduced, so that the circuit efficiency is also the highest efficiency. Can be pulled out. Therefore, power consumption as a refrigerator can be minimized.

  In addition, since the motor drive device of the present invention can expand the high-speed and high-load drive region of the compressor, it will increase the refrigeration capacity of the refrigeration cycle, such as when the door of the refrigerator is frequently opened, after defrosting, or immediately after installation. The conventional motor drive unit is used for "high-speed freezing" that is performed when the chamber temperature is high and the load is high, or when hot food is put into the chamber and the food is to be rapidly cooled (frozen). It is possible to cool the inside and food in a short time from the refrigerator of the refrigeration cycle.

  Furthermore, the improvement in the refrigeration capacity of the refrigeration cycle will enable the capacity of the refrigerator to be increased even with a compact refrigeration cycle, and the cost reduction of the refrigerator will be realized and the volumetric efficiency in the refrigerator (food storage relative to the refrigerator volume) will be realized. The ratio of part volume) can also be improved.

The motor drive device of the present invention extends the drive area of a brushless DC motor and improves drive stability at high load and high speed drive. As a result, the load range of the brushless DC motor can be expanded, and the high-efficiency motor can be driven at high speed and high load, so that the power consumption of the device can be reduced. Therefore, it can be applied to various uses using brushless DC motors such as washing machines, water heaters, pumps, etc., as well as electric devices using compressors such as air conditioners, vending machines, food showcases, heat pump water heaters.

1 is a block diagram of a motor device according to Embodiment 1 of the present invention. Waveform diagram of each part of U phase in driving by first commutation means in embodiment 1 of the present invention Waveform diagram of each part of U phase in driving by second commutation means in embodiment 1 of the present invention Waveform diagram of each part of the U phase in the state where the conduction angle is relatively narrow at a low load in the second commutation means in Embodiment 1 of the present invention. Operation flowchart of motor drive device of the present invention Phase relationship graph during synchronous drive with conventional motor drive Phase relationship graph by load during synchronous driving of brushless DC motor Timing chart of commutation timing by the second commutation means The flowchart which showed the determination method of the commutation timing of a 2nd commutation means Timing diagram of output signal of position detection means Structure diagram of rotor of brushless DC motor according to embodiment 1 of the present invention Block diagram of a refrigerator provided with a motor drive device in Embodiment 2 of the present invention Block diagram showing a conventional motor drive device

DESCRIPTION OF SYMBOLS 3 Inverter 4 Brushless DC motor 5 Position detection means 5a Voltage detection part 6 1st commutation means 8 Current detection means 9 Current phase detection means 10 2nd commutation means 11 Load determination means 12 Duty determination part 13 Phase difference determination part 15 Switching Means 17 Compressor 21 Refrigerator 22 Motor drive device

Claims (10)

A brushless DC motor comprising a rotor having a permanent magnet and a stator having a three-phase winding; an inverter for converting a DC voltage into an AC voltage and supplying power to the brushless DC motor; and an output terminal voltage of the inverter. A position detecting means for detecting the relative position of the rotor of the brushless DC motor from the output terminal voltage, and a winding for energizing the brushless DC motor based on a signal from the position detecting means are switched. A first commutation means for generating a signal; a current detection means for detecting a current flowing in the winding of the brushless DC motor; and the brushless DC based on the current detected by the current detection means or the voltage detected by the voltage detection unit. a current phase detection means for detecting the phase of the current flowing in the motor, the motor current phase determined by an output terminal voltage of the load torque To preserve the phase relationship between the inverter output terminal voltage phase, and a second commutation means for generating a signal for switching the windings energizing the brushless DC motor the duty of the PWM control at a constant synchronous operation, the brushless Load determination means for determining a load state of the DC motor, and switching means for switching the drive signal source of the inverter to either the first commutation means or the second commutation means by the load determination means, The motor driving device detects the phase of the current flowing through the winding of the brushless DC motor for one phase and detects the zero cross point. The current phase detection means selects either the current flowing through the brushless DC motor detected by the current detection means or the output terminal voltage of the inverter obtained by the voltage detection section, and flows through the winding of the brushless DC motor. The motor driving device according to claim 1, wherein the motor driving device detects a phase of a current. The motor driving apparatus according to claim 1, wherein the current detection unit is a current transformer. 4. The motor according to claim 1, wherein the current phase detection unit detects the current phase based on the current detected by the current detection unit when the current phase cannot be detected by the terminal voltage detection unit. 5. Drive device. A duty determination unit configured to determine that the duty of the output waveform of the first commutation means is maximized, and when the duty of the waveform output from the first commutation means is maximized, The motor driving device according to any one of claims 1 to 4, wherein a drive signal source is switched from the first commutation means to the second commutation means. An output from the second commutation means when the phase difference is no smaller than a predetermined value, the phase difference determination section detecting a phase difference between the signal of the voltage detection section and the signal of the second commutation means; The motor drive device according to any one of claims 1 to 5, wherein the motor is switched to an output by the first commutation means. The brushless DC motor according to any one of claims 1 to 6, wherein the brushless DC motor is a rotor in which a permanent magnet is embedded in an iron core of a rotor and has a saliency. Drive device. The motor driving device according to any one of claims 1 to 7, wherein the brushless DC motor drives a compressor. The compressor provided with the motor driven by the motor drive device as described in any one of Claims 1-8. A refrigerator comprising the compressor according to claim 9.