JP2019083595A - Motor drive device, and refrigerator using the same - Google Patents

Abstract

To provide a motor drive device having a high efficiency and a high reliability, and to provide an apparatus utilizing the device.SOLUTION: A motor drive device comprises: a brushless DC motor 4; an inverter circuit 3 configured by six switching elements for supplying power to the brushless DC motor 4; position detection means 5 that detects a rotational position of a rotor of the brushless DC motor 4; PWM control means 11 that on/off-controls an output voltage of the inverter circuit 3 by the switching elements of the inverter circuit 3 at a high frequency, to adjust to be supplied to the brushless DC motor 4; energization phase control means 8 that decides an energization phase of a three-phase coil of the brushless DC motor 4 so that a time ratio of an ON time period of the switching elements in the inverter circuit 3 by PWM control becomes the maximum; and input voltage detection means 15 that detects an input voltage to the inverter circuit 3. To a change in the input voltage to the inverter circuit 3, the time ratio of the ON time period of PWM control is set.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, this type of motor drive device drives a brushless DC motor on the basis of 120-degree rectangular wave conduction of PWM (Pulse Width Modulation) control, and when the on-duty of PWM control becomes 100%, the conduction interval is 120 degrees or more The high-speed and high-load drive area is expanded by expanding the above into (see, for example, Patent Document 1).

  FIG. 9 shows a motor drive device described in Patent Document 1. As shown in FIG. As shown in FIG. 9, when the switching elements 3a to 3f constituting the inverter circuit 3 shift from off to on, the on-timing control means 103 controls the advance angle, and shifts from on to off. When the advance timing control is not performed by the off timing control unit 104, the 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 a target power value, thereby enabling high output and high rotation while reducing loss (see, for example, Patent Document 2). FIG. 10 shows a motor drive device described in Patent Document 2. As shown in FIG. As shown in FIG. 10, the drive control means 201 of the brushless DC motor has a power detection means 202 for detecting the drive power, and a conduction pulse signal generation control means 203 for generating the drive signal pattern of the inverter and setting the inverter input voltage. The inverter input voltage value and the conduction angle and the lead angle are controlled so that the drive power matches the target set power value.

JP, 2006-50804, A JP, 2008-167525, A

  However, in the configuration of Patent Document 1 described above, it is possible to extend the high load and high speed drive region by accelerating the turn-on of the switching element and widening the power supply section to the brushless DC motor to 120 degrees or more. In order to control, loss accompanying ON / OFF of a switching element occurs. Furthermore, high frequency switching by PWM control has a problem that the increase in motor iron loss is accompanied.

  Further, in the configuration described in Patent Document 2 above, since the speed control is performed by increasing or decreasing the conduction angle of the brushless DC motor, the timing at which the speed control is possible is commutation at which the conduction angle is changed (for example, 1 rotation in the case of a 4-pole motor). Limited to 12). Therefore, when the inverter input voltage fluctuates (especially rises) due to a disturbance, the response is delayed, and the step-out stop of the brushless DC motor due to a large delay phase state due to excessive application of voltage or large current It had a problem on reliability such as demagnetization failure of the permanent magnet of the rotor.

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

  In order to solve the above-mentioned conventional problems, a motor drive device according to the present invention comprises a brushless DC motor, an inverter formed of six switching elements for supplying power to the brushless DC motor, and rotation of the brushless DC motor. Position detection means for detecting the rotational position of the child; PWM control means for adjusting the voltage supplied to the brushless DC motor by turning on / off the output voltage of the inverter at a high frequency with the switching element of the inverter; Energizing phase control means for determining the energizing phase of the three-phase winding of the brushless DC motor so that the ratio of the on time of the switching element of the inverter by the PWM control means becomes maximum, and the input for detecting the input voltage of the inverter Voltage detection means, and the PWM control means is adapted to change the input voltage of the inverter And, so that setting the duty ratio of the ON time of the PWM control.

  Thus, in the stable drive state, the ratio of the on time of the PWM control is 100%, and the switching loss of the inverter can be significantly reduced. Furthermore, the high frequency current by PWM control can be greatly suppressed, and motor iron loss can be reduced. In addition, when the input voltage is greatly increased, by decreasing the ratio of the on time of PWM control, it is possible to suppress a sharp rise in voltage applied to the motor and to suppress step-out due to excessive voltage application and generation of large current. .

  The motor drive device of the present invention achieves high efficiency by reducing the loss of the inverter and the brass DC motor, and can perform stable drive even when the input voltage fluctuates, and ensures high reliability.

Block diagram of motor drive device according to the first embodiment of the present invention (A), (b) is a waveform of each part in Embodiment 1 of this invention, respectively, and a timing chart figure Switching element off timing adjustment control start judgment flowchart Transition flowchart from PWM control to off timing adjustment control Operation flow chart at the time of inverter input voltage rise Flow chart showing the operation of off timing adjustment control (A), (b), (c) and (d) show the terminal voltage waveforms of the brushless DC motor respectively Diagram showing phase current waveform of brushless DC motor Block diagram of motor drive device of patent document 1 Control block diagram of motor drive device of patent document 2

  According to a first aspect of the present invention, there is provided a brushless DC motor, an inverter comprising six switching elements for supplying electric power to the brushless DC motor, position detection means for detecting a rotational position of a rotor of the brushless DC motor, and PWM control means for adjusting the voltage supplied to the brushless DC motor by turning on / off the inverter's output element at high frequency to adjust the output voltage of the inverter, and the ratio of the on time of the switching element by PWM control to be maximum It has an energized phase control means for determining an energized phase of a three-phase winding of a brushless DC motor, and an input voltage detecting means for detecting an input voltage of an inverter, and the PWM control means performs PWM according to a change in the input voltage of the inverter. Set the time ratio of control on time. As a result, the switching element does not perform on / off operation at high frequency in a stable driving state, so that the switching loss of the inverter and the iron loss of the motor can be significantly reduced, and when the input voltage is greatly increased, PWM control By reducing the time ratio of the on time, it is possible to suppress a sharp rise in the voltage applied to the motor and to suppress step-out and generation of a large current due to excessive voltage application, thereby providing a highly efficient and highly reliable motor drive device. .

  According to a second aspect of the invention, the PWM control means of the motor drive device of the first aspect of the invention is configured such that the input voltage of the brushless DC motor becomes equal before and after the change when the inverter input voltage changes. The on-time duty ratio is set. As a result, even when the input voltage rises rapidly, the speed fluctuation of the brushless DC motor can be made extremely small, so that the reliability can be further improved by suppressing the vibration and noise due to the speed fluctuation.

  A third invention relates to the motor drive device according to the first or second invention, a rectifier circuit for converting an AC voltage to a DC voltage, and a smoothing circuit for setting the output of the rectifier circuit to a stable DC voltage with small voltage fluctuation. The PWM control means has a switching time ratio of the on time of the switching element when it has a switch unit for switching the rectification method of the rectification circuit to full wave rectification and voltage doubler rectification, and switches from full wave rectification to voltage doubler rectification by the switch unit. I try to lower it. As a result, high-efficiency drive with reduced inverter loss at full-wave rectified input for low-speed, low-load drive of brushless DC motor, high-output drive with double voltage input at high speed and high load, and optimum according to drive condition It becomes possible to drive. Furthermore, even if the input voltage rises sharply due to the switching from full-wave rectification to voltage doubler rectification, the step-out stop of the brushless DC motor, the demagnetization due to an overcurrent, or the rapid speed fluctuation of the brushless DC motor is suppressed. Thus, it is possible to provide a highly reliable motor drive device.

  In a fourth aspect of the invention, a brushless DC motor driven by the motor drive device according to any one of the first to third aspects of the invention drives a compressor of a refrigeration cycle. By this, 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.

  A fifth invention is a refrigerator having a compressor driven by the motor drive device according to any one of the first to fourth inventions. Thus, a highly efficient and reliable refrigeration cycle can provide a low power consumption and highly reliable refrigerator. Furthermore, the noise of the high frequency band accompanying high frequency switching is suppressed, and noise reduction of a refrigerator is attained.

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

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

  In FIG. 1, an AC power supply 1 is a general commercial power supply, and in Japan, it has an effective value of 100 V 50 Hz or 60 Hz. Converter circuit 2 converts AC power supply 1 into a DC voltage. The converter circuit 2 in FIG. 1 includes a rectifier circuit 2a in which four diodes are bridge-connected, a smoothing circuit 2b with a capacitor, and a switch unit 2c that switches the output voltage, thereby doubling output voltage and full wave rectification. It is configured to switch to the stage.

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

  The brushless DC motor 4 is constituted by 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 detection means 5 detects the magnetic pole position of the brushless DC motor 4. In the first embodiment, the phase (zero cross point) of the induced voltage generated in the stator winding by the rotation of the rotor from the motor terminal voltage. Is a method of detecting However, a method using a position sensor such as a Hall IC or 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, and 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 crossing period of the voltage.

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

  Based on the signal from the position detection means 5, the conduction phase control means 8 sets a phase for supplying power to the stator winding of the brushless DC motor 4 within a conduction angle range of 90 degrees or more and 150 degrees or less. In addition, since the conduction phase control means 8 includes the on timing control unit 9 for setting the timings to turn on and off the switching elements 3a to 3f and the off timing control unit 10, the turning on of the switching elements of the inverter circuit 3; Each timing of off 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 drive at a target speed. Here, the PWM on-time ratio is larger than the value obtained by dividing "120 times the electrical angle by 2 times the minimum electrical angle supplying power to the brushless DC motor winding" by "120 electrical degrees". When driving, the off-timing control unit 10 makes the turn-off timing of the switching element earlier so that the PWM control unit 11 has the maximum value (100%) of the on-time ratio. Specifically, when the minimum value of the on interval of each switching element is 90 degrees, (90 degrees × 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 made earlier so that the on time ratio becomes 100%.

  It is desirable that the change of the turn-off timing be gradually advanced in order to prevent a rapid change to the operating state of the brushless DC motor 4, but there is no particular problem if it is performed in one control cycle. The speed control of the brushless DC motor 4 in the on-time ratio adjustment by the PWM control means 11 is limited to the case where driving is performed 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 of low load drive and double voltage input. In other stable drive states, the PWM control means 11 adjusts the off timing of the switching element by the conducting phase control means 8 to perform speed control of the brushless DC motor 4 so that the on time ratio becomes 100%. .

  The waveform synthesizing means 12 synthesizes the PWM signal generated by the PWM control means 11 and the signal generated by the conducting phase control means 8 and the drive means 13 turns on each of the switching elements 3a to 3f of the inverter circuit 3 based on the synthesized signal. Alternatively, in the off state, any generated three-phase AC voltage is supplied to and driven by the brushless DC motor 4.

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

  When the PWM control means 11 detects that the input voltage has changed sharply (in particular, has risen), it 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 that voltage (voltage At the time of rising, the duty ratio is lowered) and output to the waveform synthesis means 12. That is, when the inverter input voltage rises rapidly, the on-time ratio of PWM control is instantaneously reduced so that the input voltage of the brushless DC motor does not change significantly, and the drive is performed by PWM control at any conduction angle. . Thereafter, the off timing of the switching element is advanced by the off timing control unit 10 of the conduction 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 sharply drops, the PWM control on-time ratio is increased according to the decrease degree of the input voltage when performing the PWM control. Although it is possible to suppress the change of the input voltage, it is not possible to cope with driving at 100% duty ratio. 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 charge accumulated in the smoothing circuit 2b, so that a sharp voltage drop is avoided. Therefore, the step out of the brushless DC motor 4 due to a sharp drop in voltage is hard to occur, and it is not particularly necessary to suppress the change in input voltage.

  The compression element 16 is connected to the shaft of the rotor of the brushless DC motor 4 and sucks, compresses and discharges the refrigerant gas. The brushless DC motor 4 and the compression element 16 are housed in the same sealed container to constitute a compressor 17. The discharge gas compressed by the compressor 17 constitutes a refrigeration air conditioning system that returns to the suction of the compressor 17 through the condenser 18, the pressure reducer 19, and the evaporator 20. Since heat absorption is performed, heating and heat absorption can be performed. In addition, a blower etc. may be used for the condenser 18 and the evaporator 20 as needed, and heat exchange may be further promoted. In the first embodiment, the refrigeration air conditioning system is used as a refrigeration cycle of the refrigerator 21, and the evaporator 20 is used to cool the inside of the food storage room 23 surrounded by the heat insulating wall 22.

  The operation and action 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. 2 (a) is a drive waveform and timing chart at a general 120-degree conduction, and FIG. 2 (b) is a diagram when the brushless DC motor 4 is driven by adjusting the off timing of the switching element by the off timing controller 10. The waveform and timing are shown. 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. Although both waveforms show only the U-phase, the V-phase and W-phase waveforms have the same shape with the phase shifted by 120 degrees. The drive signals of the switching devices 3a, 3b and 3c connected to the high voltage side are indicated as U +, V + and W +, and the drive signals of the switching devices 3d, 3e and 3f connected on the low voltage side are 180 from the drive signals of the high voltage side SW devices. The waveform is out of phase.

  In order to detect 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 no voltage is applied to the phase winding (in the U phase shown in FIG. 2, both switching elements 3a and 3d are turned off). A point (P1, P2) at which the magnitude relationship between the induced voltage and the half of the inverter input voltage Vdc is inverted is detected. Therefore, a position signal is generated every electrical angle of 60 degrees, twice for each phase, six times for a total of three phases, in one electrical angle cycle.

  Looking at the conduction patterns (U +, V +, W +) of the switching elements (high-voltage side connections 3a, 3b, 3c) at 120 ° conduction shown in FIG. 2A, W + after 30 ° electrical angle after position detection (P1) By turning on U + (switching element 3a) at the same time as turning off, any of the windings of three phases is always energized in the full range of 360 degrees of electrical angle. On the other hand, in FIG. 2B, after position detection (P1), W + (switching element 3c) is turned off before 30 degrees of electrical angle elapses, and then U + is turned on after 30 degrees of electrical angle.

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

  Furthermore, the timing at which the switching element is turned off can be reliably commutated at the position detection (P1) from immediately after position detection to after 30 electrical degrees have passed after position detection (range A1 range with respect to position detection P1) It is considered that the torque decrease due to the delay phase does not occur by setting the lead phase to the induction voltage in the above range.

  Thus, by setting the off timing of the switching elements (3a to 3f) within 30 degrees immediately after position detection, the power supply section to the three-phase winding is adjusted to 90 degrees or more and 120 degrees or less, and power supply is suspended. As the section (A1, A2, A3) is shorter, a larger advance angle B (1/2 of the electrical angle of the no-power supply section) is automatically added. As a result, although the motor torque is increased and there is a section where no power is supplied, stable driving without step-out or the like is possible.

  When the off timing of the switching element becomes 30 degrees after the position detection due to an increase in load, etc., this is the maximum load that can be driven by 120 degrees conduction. At this time, the off timing is fixed at a position of 30 degrees after position detection, and the on timing is advanced to a maximum of 30 degrees in a state where the on time ratio of PWM control is 100% (that is, commutation simultaneously with position detection signal acquisition) Thus, the conduction angle can be expanded to 150 degrees. At this time, the input current of the brushless DC motor 4 is increased by about 17% at the maximum, and the drive region can be expanded.

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

  FIG. 3 is a flow chart for judging the start of the 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 a predetermined value, and if larger than the predetermined value, the process proceeds to S12 and the off timing adjustment control is started. If the value is smaller than a predetermined value, PWM control is performed. In the first embodiment, since the minimum on section of each switching element is set to an electrical angle of 90 degrees, the predetermined value of the on time ratio is 50% from {(90 degrees × 2) −120 degrees} / 120 degrees. However, select an appropriate value depending on the application.

  As described above, by combining the start of off timing adjustment control of the switching element with the PWM control as being at a predetermined PWM on time ratio or higher, the drive speed is extremely low at startup, etc., or extremely slow at low speed drive. When the load is low, when the load is relatively light at double-voltage input or when the load is relatively slow, etc., start-up failure due to the power supply section to the winding becoming extremely short or unstable operating condition or extreme It prevents torque drop etc. and enables stable driving under any load condition.

  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 according to the flow shown in FIG. 3, the off timing of the switching element is advanced earlier in S21, and the speed control is performed by PWM control in S22. By shortening the off timing, the power supply section to the brushless DC motor 4 becomes shorter, so that the on time ratio of the PWM control increases. When the on-time ratio by PWM control is less than 100 in S23, the process returns to S21 and continues the operation. When the on-time ratio reaches 100% in S23, the process proceeds to S24, the on-time ratio is maintained at 100%, and thereafter the brushless DC motor 4 reaches the target speed by adjusting the off timing of the switching element in S25. Speed control to drive at. Furthermore, when the off timing of the switching element becomes 30 degrees after position detection (ie, 120 degrees conduction state), on timing control is performed to adjust the on timing from immediately after position detection to 30 degrees after position detection. , Extend the drivable area of the brushless DC motor and drive at the target speed.

  Here, the operation in the case where the input voltage to the inverter circuit 3 rapidly rises will be described. This assumes that a momentary power failure occurs in the commercial power supply when the inverter circuit 3 recovers from an input voltage drop state, or when the rectification method of the converter circuit 2 switches from full-wave rectification to voltage doubler rectification.

  FIG. 5 is an operation flowchart in the case where the input voltage to the inverter circuit 3 in the first embodiment of the present invention is largely increased, and the operation will be described in conjunction with FIG.

  First, in S31, the input voltage detection means 15 detects the input voltage of the inverter circuit 3 from the voltage acquired from the voltage detection circuit 14. Next, in S32, the PWM control means 11 checks whether or not the input voltage of the inverter circuit 3 has risen by a prescribed value or more from the previously detected value, and if there is no rise above the prescribed value, the present detection value is 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 PWM control according to the detected input voltage is calculated. In the on-time ratio calculation in the first embodiment of the present invention, the on-time ratio [%] = (previously detected voltage [V] so that the applied voltage of the brushless DC motor 4 is equalized before and after the voltage fluctuation occurs. ] / PWM detection means stores the current detection value as the previous value in S35 after outputting the PWM waveform with the on-time ratio calculated in S34. .

  As described above, when the input voltage to the inverter circuit 3 suddenly rises, the on time ratio of PWM control such that the input voltage to the brushless DC motor 4 before and after the change of the input voltage to the inverter circuit 3 becomes equal. By calculating and outputting instantaneously, the rapid change of the input voltage to the brushless DC motor is suppressed, and the occurrence of the overcurrent which causes the step out and the demagnetization of the rotor permanent magnet is prevented.

  Further, even when the output voltage of the brushless DC motor 4 is expanded by changing the input voltage to the inverter circuit 3 from full wave rectification to double voltage rectification, the brushless DC motor 4 may be switched without stopping. As it is possible, it is possible to provide a very easy-to-use motor drive device.

  The detection cycle of the input voltage is most preferably performed with a PWM timer cycle in order to improve responsiveness to voltage fluctuations, but it is set in consideration of the calculation capability of the processor used, the A / D conversion speed, etc. Do.

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

  FIG. 6 is an operation flowchart of off timing adjustment control of the switching element according to the first embodiment. In FIG. 6, firstly in S41, the deviation between the driving speed of the brushless DC motor 4 detected by the speed detecting means 6 and the target speed is detected by the speed error detecting means 7, and if it is faster than the target speed, the process proceeds to S42. In S42, the on-time ratio 100% in the PWM control means 11 is held, and it is judged by the off-timing control unit 10 whether or not the off-timing can be advanced, and if possible, the off-time of the switching element Speed control to reduce the speed of the brushless DC motor 4 by reducing the power supply section to the winding (S43), and if not possible, use the PWM control in the PWM control means 11 together (S44) ). In the first embodiment, it is determined whether it is possible to advance the off timing earlier if the off timing of the switching element is immediately after the position detection. In the first embodiment, since the advance angle is 0 degrees, the minimum power supply section to the stator winding is 90 degrees in electrical angle.

  When it is determined that the driving speed of the brushless DC motor 4 is slower than the target speed (S45), the process proceeds to S46, and it is determined whether the switching element is turned off by 30 degrees after the position detection. If the off timing is performed before the electrical angle of 30 degrees, the process proceeds to S47, the off timing of the switching element is delayed to increase the power supply section to the windings of the brushless DC motor, and the driving speed is increased. Take control. If it is determined in S46 that the off timing of the off switching element is at a position where the electrical angle is 30 degrees, the process proceeds to S48. In S48, if the off timing of the switching element is delayed more than this, the applied voltage phase is delayed with respect to the induced voltage, and the motor torque may decrease and the out-of-step due to this may occur. The power supply section to the winding is increased and the speed control is performed so that the driving speed of the brushless DC motor is increased.

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

  If the driving speed is equal to the target speed, the control is exited at S45.

  Further, in the first embodiment, since the advance angle is 0 degree, the off timing and the on timing of the switching element are conducted at the same timing at 30 degrees after the position detection with the electrical angle of 120 degrees. In the IPM motor in which the permanent magnet is embedded inside the stator, it is necessary to set the optimum lead angle for the optimum drive realization. Therefore, the off timing adjustment range of the switching element is the position where "(electrical angle 30 degrees)-(advance angle)" has elapsed from the position detection timing immediately after position detection so that any motor such as IPM motor can be driven optimally. . The ON timing of the switching element is the timing when "(electrical angle 30 degrees)-(advance angle)" has passed from the position detection timing (for example, in the case of an advance angle of 10 degrees, the turn-off And turn on after 20 degrees of electrical angle after position detection) and set the sum of the electrical angle from position detection to turn off and the electrical angle from position detection to turn on less than 60 degrees, turn on turn off The angle can be adjusted in an arbitrary range from 0 degree to 30 degrees, and lead angle and on / off timing can be freely set between position detection and 30 degrees of electrical angle.

  Note that the ON interval of each switching element when the advance angle is added is adjusted in the range of "90 degrees + advance angle" to 120 degrees in electrical angle.

  Furthermore, when the brushless DC motor 4 is driven at high speed and high load, position detection is performed immediately after position detection, with the turn-off timing as "(electrical angle 30 degrees)-(advance angle)" elapsed from position detection. The ON interval of each switching element can be adjusted in the range of 120 degrees of electrical angle to 150 degrees of electrical angle of advance by adjusting the range of the timing after "electrical angle of 30 degrees of advance-advanced angle" has elapsed.

  Therefore, by adjusting the turn-on and turn-off timing of the switching element, the power supply section to the brushless DC motor can be adjusted in the range of 90 degrees to 150 degrees electrical angle (at an advance angle of 0 degree). It can handle driving under a wide range of load conditions, from driving to driving at high speed and high load.

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

  As shown in FIGS. 7 (a) and 7 (b), in FIG. 2 (a) showing a waveform in PWM control of 120-degree conduction, a high frequency PWM carrier frequency component (period f) is superimposed. Further, as shown in FIG. 7A, in the C1 section, at the moment when the PWM control is turned on, a ringing noise component due to the influence of the motor winding and the stray capacitance is also superimposed. In section C1, the terminal voltage Vu of the brushless DC motor and half of the inverter input voltage are compared, and the point at which the magnitude relationship is reversed is detected as the zero cross point (point P) of the induced voltage of the brushless DC motor. Due to the noise component, the Px point is erroneously detected. The position detection deviation causes pulsations or vibrations in the driving speed of the brushless DC motor, an increase in noise, a reduction in driving efficiency, and the like.

  On the other hand, as shown in FIG. 7C, when the on-time ratio of PWM control is 100%, an induced voltage waveform appears in the terminal voltage Vu, and the position detection at the correct zero cross point (point P) It is possible to realize low noise, low vibration and low loss stable driving.

  Also, in the section F1 section, as shown in FIG. 7 (b), switching loss occurs with the on / off of the switching element at high frequency by PWM control, but as shown in FIG. 7 (d) Since switching operation is not performed in% driving, no switching loss occurs, and high efficiency can be realized by reducing circuit loss.

  Further, the current flowing to the brushless DC motor is shown in FIG. FIG. 8A shows a waveform in PWM control with 120-degree conduction, and it can be seen that high frequency current components accompanying switching on / off of the switching element in PWM control are superimposed. While this high frequency current component causes a motor iron loss, there is no generation of a high frequency current component in the operation at the ON time ratio 100% of the PWM control shown in FIG. 8 (b). The efficiency of the device can be improved.

  The refrigerator which has a cooling system which drives a compressor with the motor drive device comprised as mentioned above is demonstrated.

  In recent years, with the improvement of heat insulation technology such as the use of a vacuum heat insulating material, the heat infiltration from the outside is extremely reduced. Therefore, except in the morning and evening housekeeping hours during which the door is 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 refrigeration capacity. It is 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, in a state in which the brushless DC motor is driven at low speed and low load, high frequency on / off control by PWM control is not performed, and the PWM on time ratio is 100%. The drive speed control of the brushless DC motor is performed while adjusting the on or off timing of the switching element. As a result, the inverter circuit 3 can significantly improve the circuit efficiency of the inverter without occurrence of switching loss due to PWM control.

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

  As mentioned earlier, the refrigerator is driven at low speed and low load for most of the day, so the current flowing to the brushless DC motor is low. Therefore, when using the motor drive device of this invention for the compressor of a refrigerator, using a MOSFET for the switching element of the inverter circuit 3 is very effective for reducing the power consumption of the refrigerator.

  Further, by not performing the on / off control by the PWM control, there is no high frequency current component in the winding current of the brushless DC motor, the motor iron loss can be largely suppressed, and the motor efficiency can be improved.

  Further, in PWM control, switching operation is generally performed at a PWM frequency of about 1 kHz to about 20 kHz, and this frequency component is generated as noise. Quiet design is very important because the refrigerator is operating day and night all day. The motor drive device according to the first embodiment is 100% of the on-time ratio, and there is no generation of noise due to PWM control, which is very effective for noise reduction design of a refrigerator. In addition, 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 when the compressor is temporarily stopped. Even when the input voltage suddenly rises, stable driving can be continued without stopping, so a stable cooling state can be maintained without an increase in the temperature inside the chamber due to the stop of the compressor.

  Furthermore, even if it is desired to perform an operation with increased refrigeration capacity by high-speed drive as the load on the refrigerator increases, the input voltage of the brushless DC motor can be switched without loss of internal cooling due to the stop of the compressor.

  As described above, the motor drive device according to the present invention can reduce circuit loss of the motor drive device, improve motor efficiency, achieve high reliability, and reduce drive noise and vibration, so a refrigerator, an air conditioner, a washing machine, It can be applied to any equipment using a brushless DC motor such as a pump, a fan, a fan, a vacuum cleaner and the like.

Reference Signs List 3 inverter 4 brushless DC motor 5 position detection means 8 energized phase control means 11 PWM control means 17 compressor 21 refrigerator

Claims (5)

  A brushless DC motor, an inverter composed of six switching elements for supplying electric power to the brushless DC motor, position detecting means for detecting a rotational position of a rotor of the brushless DC motor, and an output voltage of the inverter PWM control means for adjusting the voltage supplied to the brushless DC motor by turning on / off the switching element of the inverter at a high frequency, and the ratio of the on time of the switching element of the inverter by PWM control is maximized And an input voltage detection means for detecting an input voltage of the inverter, wherein the PWM control means changes the input voltage of the inverter. The motor is characterized by setting the time ratio of the PWM control on time. It operated device.   The PWM control means sets the duty ratio of the on time of the switching element of the inverter so that the input voltage of the brushless DC motor does not change before and after the input voltage changes when the inverter input voltage changes. The motor drive device according to claim 1.   A rectifier circuit for converting an AC voltage into a DC voltage, a smoothing circuit for converting the output of the rectifier circuit into a stable DC voltage with small voltage fluctuation, and a switching means for switching the rectification system of the rectifier circuit to full wave rectification and voltage doubler rectification The PWM control means reduces the duty ratio of the on time of the switching element when the switching means switches the rectification system of the rectification circuit from full-wave rectification to voltage doubler rectification by the switching means. Or the motor drive device of Claim 2.   The motor drive device according to any one of claims 1 to 3, wherein the brushless DC motor drives a compressor of a refrigeration cycle.   A refrigerator having a compressor driven by the motor drive device according to any one of claims 1 to 4.

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