JP6970871B2 - Motor drive device and refrigerator using it - Google Patents

Description

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

Conventionally, this type of motor drive device drives a brushless DC motor based on PWM (Pulse Width Modulation) controlled square wave 120 degree energization, and when the on-duty of PWM control reaches 100%, the energized section is 120 degrees or more. By expanding to, the high-speed and high-load drive region is expanded (see, for example, Patent Document 1).

FIG. 9 shows the motor drive device described in Patent Document 1. As shown in FIG. 9, when each of the switching elements 3a to 3f constituting the inverter circuit 3 shifts from off to on, the on-timing control means 103 controls the advance angle, and when the switching elements 3a to 3f shift from on to off. By not performing advance angle control by the off-timing control means 104, overlap energization is performed.

Further, the conduction angle, the lead angle, and the inverter input DC voltage are controlled so that the motor drive power becomes the target power value to enable high output and high rotation, while reducing the loss (see, for example, Patent Document 2). FIG. 10 shows the motor drive device described in Patent Document 2. As shown in FIG. 10, the drive control means 201 of the brushless DC motor includes a power detection means 202 for detecting the drive power and an energization pulse signal generation control means 203 for generating the drive signal pattern of the inverter and setting the inverter input voltage. Then, the inverter input voltage value and the energization angle and advance angle are controlled so that the drive power matches the target set power value.

Japanese Unexamined Patent Publication No. 2006-50804 Japanese Unexamined Patent Publication No. 2008-167525

However, in the configuration of Patent Document 1, it is possible to expand the high load / high speed drive region by accelerating the turn-on of the switching element and expanding the power supply section to the brushless DC motor to 120 degrees or more, but PWM. Since the control is performed, a loss occurs due to the on / off of the switching element. Further, high frequency switching by PWM control has a problem that the motor iron loss is increased.

Further, in the configuration described in Patent Document 2, since the speed is controlled by increasing or decreasing the energizing angle of the brushless DC motor, the timing at which the speed control is possible is the time of commutation when the energizing angle is changed (for example, one rotation in the case of a 4-pole motor). Limited to 12 times during). Therefore, when the inverter input voltage fluctuates (especially rises) suddenly due to disturbance, the responsiveness is delayed, the brushless DC motor is detuned due to a large delay phase state due to excessive voltage application, and a large current is generated during detuning. When it occurred, it had a reliability problem such as demagnetization damage of the permanent magnet of the rotor.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to improve the efficiency and reliability of a device by reducing the loss of a motor drive device.

In order to solve the above-mentioned conventional problems, the motor drive device of the present invention includes a brushless DC motor, an inverter composed of six switching elements for supplying power to the brushless DC motor, and rotation of the brushless DC motor. Position detecting means for detecting the rotation position of the child, PWM control means for adjusting the voltage supplied by the brushless DC motor by turning on / off the switching element of the inverter at a high frequency, and PWM. An energizing phase control means that determines the energizing phase of the three-phase winding of the brushless DC motor so that the time ratio of the on-time of the switching element of the inverter by control is maximized, and an input voltage detection that detects the input voltage of the inverter. It has a means , a rectifier circuit that converts an AC voltage into a DC voltage, a smoothing circuit that converts the output of the rectifier circuit to a DC voltage, and a switching means for switching the rectification method of the rectifier circuit between full-wave rectification and double-voltage rectification. When the rectification method of the rectifier circuit is switched from full-wave rectification to double-voltage rectification by the switching means, the PWM control means reduces the time ratio of the on-time of the switching element .

As a result, in a stable drive state, the time ratio of the PWM control on time becomes 100%, and the switching loss of the inverter can be significantly reduced. Furthermore, high-frequency current due to PWM control can be significantly suppressed, and motor iron loss can be reduced. Further, when the input voltage rises significantly, by lowering the time ratio of the on-time of the PWM control, it is possible to suppress a sudden rise in the motor applied voltage, and to suppress step-out and generation of a large current due to excessive voltage application. ..
In addition, when driving a brushless DC motor at low speed and low load, high efficiency drive that suppresses inverter loss with full-wave rectification input, and high output drive with double voltage input at high speed and high load, are optimal according to the drive state. It can be driven. Furthermore, even if the input voltage rises sharply due to the switch from full-wave rectification to voltage doubler rectification, detuning of the brushless DC motor, demagnetization due to overcurrent, or sudden speed fluctuation of the brushless DC motor is suppressed. It is possible to provide a highly reliable motor drive device.

The motor drive device of the present invention aims to improve efficiency by reducing the loss of the inverter and the brassless DC motor, and can stably drive the motor even when the input voltage fluctuates to ensure high reliability.

Block diagram of the motor drive device according to the first embodiment of the present invention. (A) and (b) are waveforms and timing charts of each part in the first embodiment of the present invention, respectively. Switching element off timing adjustment control start judgment flowchart diagram Flow chart of transition from PWM control to off-timing adjustment control Flow chart of operation when the inverter input voltage rises Flow chart showing the operation of off-timing adjustment control (A), (b), (c), (d) are diagrams showing terminal voltage waveforms of brushless DC motors, respectively. The figure which shows the phase current waveform of a brushless DC motor Block diagram of the motor drive device of Patent Document 1 Control block diagram of motor drive device of Patent Document 2

The first invention comprises a brushless DC motor, an inverter composed of six switching elements for supplying power to the brushless DC motor, and a position detecting means for detecting the rotational position of the rotor of the brushless DC motor. When the PWM control means for adjusting the output voltage of the inverter by turning on / off the switching element of the inverter at a high frequency to adjust the voltage supplied by the brushless DC motor and the ON time of the switching element of the inverter by PWM control. An energizing phase control means that determines the energizing phase of the three-phase winding of the brushless DC motor so that the ratio becomes maximum, an input voltage detecting means that detects the input voltage of the inverter, and rectification that converts an AC voltage into a DC voltage. It has a circuit, a smoothing circuit that makes the output of the rectifier circuit a DC voltage, and a switching means for switching the rectification method of the rectifier circuit between full-wave rectification and double-voltage rectification. When switching from full-wave rectification to double-voltage rectification, the PWM control means reduces the time ratio of the on-time of the switching element.
As a result, the switching element is not turned on / off at high frequencies in a stable drive state, so the switching loss of the inverter and the iron loss of the motor can be significantly reduced, and when the input voltage rises significantly, PWM control is performed. By lowering the time ratio of the on-time, it is possible to suppress a sudden rise in the motor applied voltage and suppress step-out and large current generation due to excessive voltage application, so it is possible to provide a highly efficient and highly reliable motor drive device. ..
In addition, when driving a brushless DC motor at low speed and low load, high efficiency drive that suppresses inverter loss with full-wave rectification input, and high output drive with double voltage input at high speed and high load, are optimal according to the drive state. It can be driven. Furthermore, even if the input voltage rises sharply due to the switch from full-wave rectification to voltage doubler rectification, detuning of the brushless DC motor, demagnetization due to overcurrent, or sudden speed fluctuation of the brushless DC motor is suppressed. It is possible to provide a highly reliable motor drive device.

In the second invention, the brushless DC motor driven by the motor drive device of the first invention drives the compressor of the refrigeration cycle. Thereby, the COP of the compressor can be improved by the motor drive device of the present invention, and a highly efficient and highly reliable refrigeration cycle can be provided.

The third invention is a refrigerator having a compressor driven by the motor drive device of the first or second invention. As a result, a highly efficient and highly reliable refrigerating cycle can provide a highly reliable refrigerator with low power consumption. Furthermore, noise in the high frequency band associated with high frequency switching is suppressed, and the refrigerator can be made quieter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 shows a block diagram of a motor drive device according to the first embodiment of the present invention.

In FIG. 1, the AC power supply 1 is a general commercial power supply, and in the case of Japan, the effective value is 100 V 50 Hz or 60 Hz. The converter circuit 2 converts the AC power supply 1 into a DC voltage. The converter circuit 2 in FIG. 1 is composed of a rectifier circuit 2a in which four diodes are bridge-connected, a smoothing circuit 2b using a capacitor, and a switch unit 2c for switching the output voltage, so that the output voltage can be double-voltage rectified and full-wave rectified. It is configured to switch to stages.

The inverter circuit 3 is composed of six switching elements 3a to 3f, and in the first embodiment, a MOSFET is used. Then, each switching element is connected to a three-phase bridge, and the input DC voltage is converted into a three-phase AC voltage by switching on / off of an arbitrary switching element.

The brushless DC motor 4 is composed of a stator having a three-phase winding and a rotor having a permanent magnet, and is driven by three-phase AC power from the inverter circuit 3.

The position detecting means 5 detects the magnetic pole position of the brushless DC motor 4, and in the first embodiment, the phase (zero cross point) of the induced voltage generated in the stator winding due to the rotation of the rotor from the motor terminal voltage. Is used as a method to detect. However, a method using a position sensor such as a Hall IC, a current detection method using a current sensor, or the like may be used.

The speed detecting means 6 detects the driving speed of the brushless DC motor 4 from the output signal of the position detecting means 5. In the first embodiment, the induction generated in the stator winding by the rotation of the rotor of the brushless DC motor 4. Calculated based on the zero cross period of the voltage.

The speed error detecting means 7 detects the difference between the driving speed of the brushless DC motor 4 and the target speed obtained by the speed detecting means 6.

The energizing phase control means 8 sets a phase for supplying electric power to the stator winding of the brushless DC motor 4 in the energizing angle range of 90 degrees or more and 150 degrees or less based on the signal from the position detecting means 5. Further, since the energized phase control means 8 has an on-timing control unit 9 for setting the timing for turning on and off the switching elements 3a to 3f, and an off-timing control unit 10, the switching element of the inverter circuit 3 is turned on. Each off timing can be set individually.

The PWM control means 11 adjusts the three-phase AC output of the inverter circuit 3 by PWM control, and controls the brushless DC motor 4 to be driven at the target speed. Here, with a PWM on-time ratio larger than the value obtained by dividing "the value obtained by subtracting the electric angle 120 degrees from twice the minimum electric angle that supplies power to the brushless DC motor winding" by "electric angle 120 degrees". When the PWM control means 11 is driven, the off-timing control unit 10 early turns off the switching element so that the time ratio of the on-time becomes the maximum value (100%). Specifically, when the minimum value of the on section of each switching element is 90 degrees, (90 degrees x 2-120) ÷ 120 = 50 [%], and the PWM on time ratio is 50% or more. In this case, the off-timing of the switching element is performed early so that the on-time ratio is 100%.

It is desirable to gradually change the turn-off timing in order to prevent a sudden change to the operating state of the brushless DC motor 4, but there is no particular problem even if the turn-off timing is changed in one control cycle. The speed control of the brushless DC motor 4 by adjusting the on-time ratio by the PWM control means 11 is limited to the case where the brushless DC motor 4 is driven at the on-time ratio or less of the PWM control described above. It is performed at relatively low load and low speed drive at the time, low load drive, and double voltage input. In other stable driving states, the PWM control means 11 controls the speed of the brushless DC motor 4 by adjusting the off timing of the switching element by the energization phase control means 8 so that the on-time ratio becomes 100%. ..

The waveform synthesis means 12 synthesizes the PWM signal generated by the PWM control means 11 and the signal generated by the energization phase control means 8, and the drive means 13 turns on the switching elements 3a to 3f of the inverter circuit 3 based on the synthesized signal. Alternatively, it is turned off, and an arbitrary three-phase AC voltage generated is supplied to the brushless DC motor 4 to drive it.

The voltage detection circuit 14 connects a plurality of resistors connected in series to the output section of the smoothing circuit so as to take out the voltage across any resistor. The input voltage detecting means 15 detects the input voltage of the inverter circuit 3 from the voltage taken out from the voltage detecting circuit 14, and inputs the input voltage to the PWM control means 11.

When the PWM control means 11 detects that the input voltage fluctuates sharply (particularly rises), the PWM control means 11 sets the time ratio of the on-time of the switching element of the inverter circuit 3 by PWM control according to the rate of increase of the voltage (voltage). When it rises, the time ratio is lowered) and output to the waveform synthesizing means 12. That is, when the inverter input voltage rises sharply, the on-time ratio of PWM control is instantaneously lowered so that the input voltage of the brushless DC motor does not change significantly, and the drive is performed by PWM control at an arbitrary energization angle. .. After that, the off-timing of the switching element is advanced by the off-timing control unit 10 of the energization phase control means 8 so that the on-time ratio of the PWM control becomes 100%.

When the input voltage to the inverter circuit 3 drops sharply, when PWM control is performed, the on-time ratio of PWM control is increased according to the degree of drop in the input voltage, and the brushless DC motor 4 is used. It is possible to suppress the change in the input voltage, but it cannot be dealt with when driving at a time ratio of 100%. However, when the input voltage drops sharply due to a momentary power failure or the like, power is supplied to the brushless DC motor 4 from the electric charge stored in the smoothing circuit 2b, so that the sharp drop in voltage is avoided. Therefore, step-out of the brushless DC motor 4 due to a sudden drop in voltage is unlikely to occur, and it is not particularly necessary to suppress changes in the input voltage.

The compression element 16 is connected to the shaft of the rotor of the brushless DC motor 4, sucks the refrigerant gas, compresses it, and discharges it. The brushless DC motor 4 and the compression element 16 are housed in the same closed container to form a compressor 17. A refrigerating and air-conditioning system is configured in which the discharged gas compressed by the compressor 17 passes through the condenser 18, the decompressor 19, and the evaporator 20 and returns to the suction of the compressor 17, and the condenser 18 dissipates heat and the evaporator 20. Since heat is absorbed, heating and heat absorption can be performed. If necessary, a blower or the like may be used for the condenser 18 or the evaporator 20 to further promote heat exchange. Further, in the first embodiment, the refrigerating and air-conditioning system is used as a refrigerating cycle of the refrigerator 21, and the evaporator 20 is used to cool the inside of the food storage chamber 23 surrounded by the heat insulating wall 22.

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

FIG. 2 is a timing chart of the motor drive device according to the first embodiment. FIG. 2A is a general drive waveform and timing diagram when energized at 120 degrees, and FIG. 2B is a case where the off-timing of the switching element is adjusted by the off-timing control unit 10 to drive the brushless DC motor 4. It shows the waveform and timing. The induced voltage generated by the rotation of the brushless DC motor 4 is shown as E, and the terminal voltage is shown as Vu. Both waveforms show only the U phase, but the V phase and W phase waveforms have the same shape with their phases shifted by 120 degrees. The drive signals of the switching elements 3a, 3b, and 3c connected to the high voltage side are shown as U +, V +, and W +, and the drive signals of the switching elements 3d, 3e, and 3f connected to the low voltage side are 180 from the drive signals of the respective high voltage side SW elements. The waveform is out of phase.

In order to determine the switching timing (not shown) of the energized phase of the stator winding, the zero cross point of the induced voltage is detected as a position signal in the rotor magnetic pole relative position detection. The detection of the zero cross point appears in the section (C1, C2, C3, C4) in which the voltage is not applied to the phase winding (in the U phase shown in FIG. 2, both the switching elements 3a and 3d are turned off). The point (P1, P2) where the magnitude relationship between the induced voltage and 1/2 of the inverter input voltage Vdc is reversed is detected. Therefore, a position signal is generated every 60 degrees of the electric angle, twice for each phase and six times in total for the three phases per cycle of the electric angle.

Looking at the energization patterns (U +, V +, W +) of the switching element (3a, 3b, 3c connected on the high voltage side) at 120 degree energization shown in FIG. By turning on U + (switching element 3a) at the same time as turning off, any of the three-phase windings is always energized over the entire range of the electric angle of 360 degrees. On the other hand, in FIG. 2B, after the position detection (P1), W + (switching element 3c) is turned off before the electric angle of 30 degrees elapses, and then U + is turned on after the electric angle of 30 degrees.

The induced voltage appears in the C1 to C4 sections only when the switching element of the other phase is on, that is, only during the on period of the PWM control. Therefore, the turn-off of the switching element is performed earlier than the turn-on, and the power supply section to the brushless DC motor 4 is shortened. As a result, the power supply section of the stator winding is shortened, and the number of on / off times by PWM control is reduced, so that the loss of the inverter circuit 3 can be suppressed. Further, by shortening the power supply section, the on-time of the PWM control becomes long, and the acquisition period of the position detection signal becomes long, so that the position detection accuracy is improved.

Further, the timing of turning off the switching element is from immediately after the position detection to after the electric angle of 30 degrees has elapsed after the position detection (the range of the section A1 with respect to the position detection P1), and the commutation can be reliably performed by the position detection (P1). Consideration is given so that the torque does not decrease due to the delayed phase by setting the lead phase with respect to the induced voltage in a wide range.

By setting the off timing of the switching element (3a to 3f) within 30 degrees immediately after the position is detected in this way, the power supply section to the three-phase winding is adjusted to 90 degrees or more and 120 degrees or less, and the power supply is suspended. The shorter the section (A1, A2, A3), the larger the advance angle B (1/2 of the electric angle of the non-power supply section) is automatically added. As a result, the motor torque increases and stable driving without step-out or the like is possible even though there is a non-power supply section.

When the off timing of the switching element reaches 30 degrees after the position is detected due to an increase in the load or the like, the maximum load that can be driven by energizing 120 degrees is the maximum load. At this time, the off-timing is fixed at the position of 30 degrees after the position is detected, and the on-timing is advanced up to 30 degrees with the on-time ratio of PWM control set to 100% (that is, commutation at the same time as the position detection signal is acquired). This makes it possible to widen the energization angle up to 150 degrees. At this time, the input current of the brushless DC motor 4 increases by up to about 17%, and the drive region can be expanded.

Next, the operation of the off-timing adjustment of the switching element will be described using a flowchart.

FIG. 3 is a flowchart for determining the start of off-timing control of the switching element. In FIG. 3, first, in S11, it is confirmed whether the on-time ratio of the switching element generated by the PWM control means 11 is larger than the predetermined value, and if it is larger than the predetermined value, the process proceeds to S12 and the off-timing adjustment control is started. If it is smaller than a predetermined value, PWM control is performed. In the first embodiment, the minimum on section of each switching element is set to an electric angle of 90 degrees, so that the setting of the predetermined value of the on-time ratio is from {(90 degrees × 2) −120 degrees} / 120 degrees to 50%. However, select an appropriate value depending on the application.

By using the start of the off-timing adjustment control of the switching element together with the PWM control when the predetermined PWM on-time ratio or more is used in this way, it is extremely low when the drive speed is extremely low such as at startup or when the drive is at low speed. When the load is low, when the load is relatively light at the time of voltage doubler input, or when the load is low, the power supply section to the winding becomes extremely short, resulting in startup failure, unstable operating conditions, or extreme. It prevents torque reduction, etc., and enables stable driving under all load conditions.

FIG. 4 is a flowchart showing the transition from PWM control to off-timing adjustment. 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 performed earlier in S21 by an arbitrary time, and the speed is controlled by PWM control in S22. By advancing the off timing, the power supply section to the brushless DC motor 4 becomes shorter, so that the time ratio of the on time by PWM control increases. When the on-time ratio by PWM control is less than 100 in S23, the process returns to S21 and the operation is continued. When the on-time ratio reaches 100% in S23, the process proceeds to S24 and the on-time ratio is maintained at 100%. After that, the brushless DC motor 4 moves to the target speed by adjusting the off-timing of the switching element in S25. The speed is controlled so that it is driven by. Furthermore, when the off-timing of the switching element reaches 30 degrees after position detection (that is, 120 degrees energized state), on-timing control is performed to adjust the on-timing from immediately after position detection to 30 degrees after position detection. The driveable area of the brushless DC motor is expanded to drive at the target speed.

Here, the operation when the input voltage to the inverter circuit 3 suddenly rises will be described. This assumes the moment when the inverter circuit 3 recovers from the input voltage drop state due to a momentary power failure in the commercial power supply, or the moment when the rectification method of the converter circuit 2 is switched from full-wave rectification to double-voltage rectification.

FIG. 5 is an operation flowchart when the input voltage to the inverter circuit 3 in the first embodiment of the present invention is greatly increased, and the operation will be described together with FIG.

First, in S31, the input voltage detecting means 15 detects the input voltage of the inverter circuit 3 from the voltage acquired from the voltage detecting circuit 14. Next, in S32, the PWM control means 11 confirms whether the input voltage of the inverter circuit 3 has increased by a specified value or more from the previously detected value, and if there is no increase by the specified value or more, the detected value of this time is set to the previous time in S35. Store as a value and exit the process.

On the other hand, when it is determined in S32 that the voltage rise is large, in S33, the on-time ratio of the PWM control according to the detected input voltage is calculated. In the calculation of the on-time ratio in the first embodiment of the present invention, "on-time ratio [%] = (previous detection voltage [V]" so that the applied voltage of the brushless DC motor 4 is equalized before and after the voltage fluctuation occurs. ] / This time detection voltage [V]) × 100 ”, the PWM control means 11 outputs the PWM waveform at the on-time time ratio calculated in S34, and then stores the current detection value as the previous value in S35. ..

When the input voltage to the inverter circuit 3 rises sharply in this way, the on-time ratio of PWM control is such that the input voltage to the brushless DC motor 4 becomes the same before and after the change in the input voltage to the inverter circuit 3. By instantaneously calculating and outputting, the sudden change in the input voltage to the brushless DC motor is suppressed, and the generation of overcurrent that causes step-out and demagnetization of the inverter permanent magnet is prevented.

Further, even when the input voltage to the inverter circuit 3 is changed from full-wave rectification to voltage doubler rectification to expand the output range of the brushless DC motor 4, the brushless DC motor 4 can be switched without stopping. Therefore, it is possible to provide a motor drive device that is very easy to use.

The input voltage detection cycle is most preferably set by the PWM timer cycle in order to improve the responsiveness to voltage fluctuations, but it is set in consideration of the computing power of the processor to be used and the A / D conversion speed. do.

Next, the operation of the speed control of the brushless DC motor after the shift to the off-timing adjustment control of the switching element will be described with reference to FIGS. 1 and 6.

FIG. 6 is an operation flowchart of the off-timing adjustment control of the switching element of the first embodiment. In FIG. 6, first, in S41, the speed error detecting means 7 detects the deviation between the driving speed of the brushless DC motor 4 detected by the speed detecting means 6 and the target speed, and if the speed is faster than the target speed, the process proceeds to S42. In S42, the on-time ratio of the PWM control means 11 is maintained at 100%, and the off-timing control unit 10 determines whether or not the off-timing can be accelerated, and if possible, the off-time of the switching element. By accelerating the speed, the power supply section to the winding is reduced and the speed is controlled so that the speed of the brushless DC motor 4 decreases (S43). If not possible, the PWM control in the PWM control means 11 is also used (S44). ). In the first embodiment, it is determined whether or not the off timing can be advanced further if the off timing of the switching element is immediately after the position detection. In the first embodiment, since the advance angle is 0 degree, the minimum power supply section to the stator winding is an electric angle of 90 degrees.

When it is determined (S45) that the drive speed of the brushless DC motor 4 is slower than the target speed, the process proceeds to S46, and it is determined whether the switching element is turned off until the electric angle of 30 degrees elapses from the position detection. When the off timing is performed before the lapse of 30 degrees of the electric angle, the process proceeds to S47, the off timing of the switching element is delayed, the power supply section to the winding of the brushless DC motor is increased, and the speed is increased so that the drive speed is increased. Take control. If the off timing of the off-switching element is the elapsed position of the electric angle of 30 degrees in S46, the process proceeds to S48. In S48, if the off-timing of the switching element is further delayed, the applied voltage phase becomes a delayed phase with respect to the induced voltage, and there is a possibility that the motor torque may decrease and the step-out may occur, so the on-timing should be advanced. The speed is controlled so that the drive speed of the brushless DC motor increases by increasing the power supply section to the winding.

In the first embodiment, the upper limit for accelerating the on-timing is immediately after the position is detected, and the maximum power supply section to the winding at this time is an electric angle of 150 degrees, at which time the current of the brushless DC motor increases by about 17%. , The output range can also be expanded.

If the drive speed is equal to the target speed, the control is exited in S45.

Further, since the advance angle is set to 0 degrees in the first embodiment, the off timing and the on timing of the switching element are coincidently performed at the timing of 30 degrees after the position is detected by energizing the electric angle of 120 degrees. In an IPM motor in which a permanent magnet is embedded inside the stator, it is necessary to provide an optimum advance angle in order to realize an optimum drive. Therefore, the off-timing adjustment range of the switching element is the position where "(electric angle 30 degrees)-(advance angle)" has passed from the position detection timing immediately after the position detection so that all motors such as IPM motors can be driven optimally. .. The on-timing of the switching element is the timing when only "(electric angle 30 degrees)-(advance angle)" has elapsed from the position detection timing (for example, in the case of an advance angle of 10 degrees, the turn-off is in the range from the position detection to the elapse of 20 degrees electric angle. Turn-on is performed after 20 degrees of electric angle after position detection), and the sum of the electric angle from position detection to turn-off and the electric angle from position detection to turn-on is 60 degrees or less, and turn-off is electric from turn-on. The angle can be adjusted in an arbitrary range from 0 degrees to 30 degrees, and the advance angle and on / off timing can be freely set from the position detection to the electric angle of 30 degrees.

The on section of each switching element when the advance angle is added is adjusted in the range of "90 degrees + advance angle" to 120 degrees in terms of the electric angle.

Furthermore, when driving the brushless DC motor 4 at high speed and high load, the turn-off timing is set to the timing when "(electrical angle 30 degrees)-(advance angle)" has passed from the position detection, and the turn-on timing is set to the position detection immediately after the position detection. The on section of each switching element can be adjusted in the range of the electric angle of 120 degrees to the electric angle of 150-advance by adjusting the timing within the range of the timing when only the "electric angle of 30 degrees-advance" has elapsed.

Therefore, by adjusting the turn-on and turn-off timings of the switching element, the power supply section to the brushless DC motor can be adjusted in the range of the electric angle of 90 degrees to 150 degrees (when the advance angle is 0 degrees), and the power supply section to the brushless DC motor can be adjusted at low speed and low load. It can handle a wide range of loads and speeds, from driving to high-speed and high-load driving.

Next, the terminal voltage of the brushless DC motor according to the first embodiment will be described with reference to FIG. 7 (a) and 7 (b) show sections C1 and F1 in FIG. 2 (a), and FIGS. 7 (c) and 7 (d) show sections C3 and F2 in FIG. 2 (b).

As shown in FIGS. 7 (a) and 7 (b), FIG. 2 (a) showing a waveform under PWM control of 120-degree energization is superimposed with a high-frequency PWM carrier frequency component (period f). Further, as shown in FIG. 7A, in the C1 section, a ringing noise component due to the influence of the motor winding, stray capacitance, etc. is superimposed at the moment when the PWM control is turned on. In the C1 section, the terminal voltage Vu of the brushless DC motor is compared with 1/2 of the inverter input voltage, and the point where the magnitude relationship is reversed is detected as the zero crossing point (point P) of the induced voltage of the brushless DC motor, but ringing. It is erroneously detected as a Px point due to the noise component. This position detection deviation causes pulsation and vibration of the drive speed of the brushless DC motor, an increase in noise, a decrease in drive efficiency, and the like.

On the other hand, as shown in FIG. 7 (c), when the on-time ratio of PWM control is 100%, an induced voltage waveform appears at the terminal voltage Vu, and the position can be detected accurately at the zero cross point (point P). It is possible, and stable drive with low noise, low vibration, and low loss can be realized.

Further, in the section F1, as shown in FIG. 7 (b), a switching loss occurs due to the on / off of the switching element at high frequency by PWM control, but as shown in FIG. 7 (d), the on-time ratio is 100. Since the switching operation is not performed in the% drive, no switching loss occurs, and high efficiency can be realized by reducing the circuit loss.

Further, the current flowing through the brushless DC motor is shown in FIG. FIG. 8A is a waveform in the PWM control by energizing 120 degrees, and it can be seen that the high frequency current component accompanying the on / off of the switching element in the PWM control is superimposed. While this high-frequency current component causes motor iron loss, the high-frequency current component does not occur during operation at the on-time ratio of 100% for PWM control shown in FIG. 8 (b), so that the motor is driven by reducing the motor loss. The efficiency of the device can be improved.

A refrigerator having a cooling system for driving a compressor with a motor drive device configured as described above will be described.

In recent years, refrigerators have very little heat intrusion from the outside due to improvements in heat insulation technology such as the adoption of vacuum heat insulating materials. For this reason, except for the morning and evening housework hours when doors are frequently opened and closed, the refrigerator is in a stable cooling state for most of the day, and the compressor is driven at low speed and low load with reduced refrigerating capacity. It has been. Therefore, in order to reduce the power consumption of the refrigerator, it is very effective to increase the driving efficiency of the compressor, that is, the brushless DC motor at low speed and low output.

In the first embodiment of the present invention, when the brushless DC motor is driven at a low speed and a low load, the high frequency on / off control by the PWM control is not performed, and the PWM on time ratio is 100%. , The drive speed of the brushless DC motor is controlled while adjusting the on or off timing of the switching element. As a result, the inverter circuit 3 does not generate switching loss due to PWM control, and the circuit efficiency of the inverter can be significantly improved.

In the first embodiment, a MOSFET is used as the switching element of the inverter circuit 3. Due to its structural characteristics, MOSFETs do not have a PN junction in the path of the output current at the time of on, so the loss at the time of on, especially at the time of low current output, is very low compared to other power devices such as IGBTs. ..

As mentioned above, since the refrigerator is driven at low speed and low load for most of the day, the current flowing through the brushless DC motor is low. Therefore, when the motor drive device of the present invention is used for the compressor of the refrigerator, using the MOSFET for the switching element of the inverter circuit 3 is very effective in reducing the power consumption of the refrigerator.

Further, by not performing on / off control by PWM control, the winding current of the brushless DC motor does not have a high frequency current component, the motor iron loss can be significantly suppressed, and the motor efficiency can be improved.

Further, in PWM control, a switching operation is generally performed at a PWM frequency of about 1 kHz to 20 kHz, and this frequency component is generated as noise. Quiet design is very important because the refrigerator runs all day, day and night. The motor drive device of the first embodiment has an on-time time ratio of 100% and does not generate noise due to PWM control, so that it is very effective for a quiet design of a refrigerator. In addition, once the compressor is stopped, it is necessary to delay the restart of the refrigerator until the pressure difference between the low pressure side and the high pressure side is balanced from the viewpoint of the reliability of the mechanical part of the compressor. Even when the input voltage suddenly rises, stable driving can be continued without stopping, so a stable cooling state can be maintained without the rise in the refrigerator temperature due to the compressor stopping.

Further, as the load on the refrigerator increases, the input voltage of the brushless DC motor can be switched without the loss of cooling inside the refrigerator due to the stop of the compressor even when it is desired to perform the operation with the refrigerating capacity increased by high-speed driving.

As described above, the motor drive device according to the present invention can reduce the circuit loss of the motor drive device, improve the motor efficiency, have high reliability, and reduce the drive noise and vibration. Therefore, the refrigerator, the air conditioner, the washing machine, and the like. It can be applied to all devices using brushless DC motors such as pumps, electric fans, fans, and vacuum cleaners.

3 Inverter 4 Brushless DC motor 5 Position detection means 8 Energizing phase control means 11 PWM control means 17 Compressor 21 Refrigerator

Claims (3)

A brushless DC motor, an inverter composed of six switching elements that supply power to the brushless DC motor, a position detecting means for detecting the rotational position of the rotor of the brushless DC motor, and an output voltage of the inverter. The PWM control means for adjusting the voltage supplied by the brushless DC motor by turning on / off the switching element of the inverter at a high frequency and the time ratio of the on-time of the switching element of the inverter by PWM control are maximized. A current-carrying phase control means for determining the current-carrying phase of the three-phase winding of the brushless DC motor, an input voltage detecting means for detecting the input voltage of the inverter, a rectifier circuit for converting an AC voltage into a DC voltage, and the rectifier circuit. a smoothing circuit for the DC voltage output of the rectification of the rectifier circuit has a switching means for switching the full-wave rectification and voltage doubler rectification, rectification method is voltage doubler full wave rectification of the rectifier circuit by the switching means The PWM control means is a motor drive device characterized in that when switching to rectification, the time ratio of the on-time of the switching element is lowered. The motor driving device according to claim 1, wherein the brushless DC motor drives a compressor of a refrigerating cycle. A refrigerator having a compressor driven by the motor driving device according to claim 1 or 2.

Images