JP2008160950A - Motor driver and refrigerator possessing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor driver which is possible of high-efficiency and high-torque operation and high-speed drive in inverter drive control. <P>SOLUTION: The motor driver has a brushless DC motor 6 which comprises a rotor having a permanent magnet and a stator having three-phase winding, and an inverter 5 which supplies the above three-phase winding with power. It reduces the switching loss of the inverter 5 by outputting rectangular waves or sine waves or waveform corresponding to them so that PWM duty may be maximum within the range from 60°to less than 180° in energization angle, thereby achieving the higher efficiency of the motor driver. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a motor driving device that drives and controls a brushless motor by an inverter, and a refrigerator that includes the motor driving device.

  FIG. 8 is a system configuration diagram showing a conventional inverter device for driving a brushless DC motor. As shown in FIG. 8, the conventional inverter device includes a converter 202 that converts an alternating current into a direct current with a commercial power supply 201 as an input, and an inverter 203 that converts a direct current that is the output of the converter into a pseudo alternating current. The brushless DC motor 204 is driven with the output of the above as an input.

FIG. 9 shows the energization timing waveform to the brushless DC motor 204 in the conventional inverter device, where (a) is the U-phase energization timing waveform of the brushless DC motor 204 and (b) is fixed by the rotation of the rotor. This is an induced voltage waveform generated in the child winding. The angle between the permanent magnet of the rotor and the field winding facing each other is 0 ° and 180 °, and centered on 0 ° and 180 ° regardless of the PWM duty width. By controlling the energization width to 120 ° or less, the power of the motor is controlled by reducing the switching frequency of the inverter unit, and the efficiency of the inverter system is improved.
JP-A-9-191683

  However, in the above conventional configuration, since the power supply to the brushless DC motor 204 has a conduction angle of 120 ° or less, in applications that require high load and high speed driving, the predetermined rotational speed cannot be secured due to insufficient torque. Had.

  In addition, the energization timing is a target waveform centered on the angle at which the permanent magnet of the rotor and the field winding are directly facing each other, and is driven in a state where the induced voltage phase and the current phase coincide with each other. Reluctance torque cannot be used effectively for motors with saliency, such as embedded magnet type motors embedded in the stator, and high torque drive cannot be performed because the drive is mainly based on magnet torque. It had the problem that. Further, the magnetic flux cannot be controlled by driving in a state where the current phase and the induced voltage phase coincide with each other, and there is a problem that high-speed driving is limited.

  The present invention solves the above-described conventional problems, and an object thereof is to provide a motor drive device capable of high efficiency, high torque, and high speed drive.

  In order to solve the above-described problems, a motor driving device of the present invention includes a brushless DC motor and an inverter that supplies electric power to the brushless DC motor, and the inverter has a rectangular wave or sine with a conduction angle of 90 degrees or more and less than 180 degrees. By outputting a wave or a waveform corresponding thereto, the power utilization rate of the brushless DC motor is increased, and high torque and high speed driving are possible.

  Further, the inverter supplies power to the brushless DC motor so that the PWM duty becomes maximum, so that the switching loss and motor iron loss of the inverter can be reduced, and a highly efficient motor drive device can be provided.

  The motor drive device of the present invention can drive the brushless DC motor with high torque and high speed, reduce the loss of the inverter and the motor, and provide a highly efficient motor drive device.

  Furthermore, a refrigerator with low power consumption can be provided by driving the compressor of the refrigerator with the motor driving device.

  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, an inverter for supplying electric power to the three-phase winding, and a conduction angle of 60 degrees or more. Waveform generating means for outputting a rectangular wave or sine wave of less than 180 degrees or a waveform equivalent thereto is provided, and the brushless DC motor is driven by the waveform output generated by the waveform generating means.

  As a result, the power utilization factor of the brushless DC motor can be increased, and a motor drive device capable of rotating the brushless motor with high torque and high speed can be provided.

  According to a second aspect of the present invention, when the brushless DC motor is started, the brushless DC motor is started at an arbitrary conduction angle in a range of 90 ° to less than 180 °.

  By performing such PWM duty control, it is possible to prevent a failure due to an overcurrent of the circuit, a demagnetization of the permanent magnet of the brushless DC motor, and the like by preventing the occurrence of an overcurrent at the time of starting, and improving the reliability. be able to.

  According to a third aspect of the present invention, when the PWM duty becomes a predetermined width after startup, the energization angle at which the PWM duty width becomes maximum is determined from the energization angle and the duty width at that time, and the brushless DC motor is energized. To do.

  As a result, switching loss of the inverter and motor iron loss can be reduced, and the efficiency of the motor drive device can be improved.

  According to a fourth aspect of the present invention, when there is a difference between the actual rotational speed of the brushless DC motor and the target speed, the PWM duty is set to the maximum state and the energization width is variable and output within a range of 60 ° to less than 180 °. Thus, the speed control of the brushless DC motor is performed.

  This makes it possible to control the speed by changing the voltage applied to the brushless DC motor, and to drive and control the motor with high efficiency over a wide load range and speed range.

  According to a fifth aspect of the present invention, the phase difference between the voltage applied to a predetermined phase of the brushless DC motor and the induced voltage in the same phase is in the range of 0 degree to less than 90 degrees.

  As a result, the current phase can be advanced from the induced voltage phase of the brushless DC motor, and further high-speed driving can be performed by the flux weakening control.

  According to a sixth aspect of the present invention, the brushless DC motor has a structure in which a permanent magnet is embedded in an iron core of a rotor and has saliency.

  In this way, the permanent magnet is embedded in the iron core of the rotor of the brushless DC motor, the optimum current phase is selected and driven using the rotor having saliency, and the highest efficiency suitable for the application of the brushless DC motor. Operation, maximum torque operation, etc. can be performed.

  In the seventh aspect of the present invention, the brushless DC motor drives a compressor forming a refrigeration cycle, and a highly efficient cooling system can be provided.

  The invention according to claim 8 is a refrigerator including the motor driving device according to any one of claims 1 to 7, which can increase the efficiency of the cooling system of the refrigerator and Electric power can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by this Embodiment.

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

  In FIG. 1, an AC power source 1 is a commercial power source. In Japan, AC 100V, 50 or 60 Hz is standard.

  The converter 2 includes a rectifier circuit 3 in which four diodes 3a, 3b, 3c, and 3d are bridge-connected, and a smoothing circuit 4 that smoothes a rectified voltage including pulsation that is an output of the rectifier circuit 3.

  The inverter 5 has a configuration in which a set of diodes 5g, 5h, 5i, 5j, 5k, and 5l connected in the opposite direction to the switching elements 5a, 5b, 5c, 5d, 5e, and 5f are connected in a 6-circuit three-phase bridge connection. It is. In this embodiment, FET is used, but the inverter 5 may be IGBT or bipolar transistor. Furthermore, if a silicon carbide semiconductor or a gallium nitride semiconductor is employed for the switching element instead of a general silicon semiconductor, the loss when the switch element is on can be greatly reduced.

  The motor 6 is driven by the three-phase output of the inverter 5. The motor 6 is a brushless DC motor constituted by a stator having a winding wound in a three-phase star connection and a rotor having a permanent magnet. The stator winding may be concentrated winding or distributed winding. Further, the arrangement of the permanent magnets of the rotor may be a surface magnet type (SPM) or a magnet embedded type (IPM), but in this embodiment, a concentrated winding IPM motor is used.

  A position detector 7 attached to the motor 6 is a position sensor such as an encoder and outputs position information and speed information of the stator to the position detection means 8. The position detection means 8 recognizes the stator position and the current drive speed from the input stator position and speed information, and outputs them to the waveform generator 9.

  The waveform generator 9 receives input from the position detector 8 and controls on / off of the switching elements 5a, 5b, 5c, 5d, 5e, and 5f of the inverter 5 so as to drive the motor 6 at a predetermined speed by pseudo alternating current. I do.

  Next, the structure of the rotor of the motor 6 will be described.

  FIG. 2 is a schematic diagram of the rotor of the brushless DC motor according to Embodiment 1 of the present invention.

  In FIG. 2, 6a, 6b, 6c, and 6d are permanent magnets, which are arranged so as to have polarities as shown in the figure. Although this rotor has a two-pole pair four-pole motor configuration, it may be a so-called six-pole motor in which six permanent magnets are arranged depending on the number of slots of the stator winding. Further, the permanent magnet may be a ferrite type or a rare earth type.

  6e is a silicon steel plate, and 6f, 6g, 6h, 6i, 6j, 6k, 6l and 6m are non-magnetic materials.

  As shown in FIG. 2, the brushless DC motor according to the first embodiment is an embedded magnet motor (hereinafter referred to as an IPM motor) in which a permanent magnet is embedded in a rotor, and a current in a predetermined direction flows through a stator winding. In the magnetic path Ψd of the magnetic flux in the d-axis direction that is sometimes created, a permanent magnet having the same magnetic resistance as that of the air gap is present and the magnetic flux is difficult to pass, but the magnetic flux Ψq in the q-axis direction passes through the silicon steel plate. The magnetic resistance is small, and the inductance in the d-axis direction has a saliency smaller than the inductance in the q-axis direction.

  FIG. 3 is a diagram showing the torque / advance characteristic of the motor in the first embodiment, and shows that the motor torque changes depending on the advance angle, that is, the phase of the current.

  In such a brushless DC motor having saliency, the optimum control according to the application, such as maximum torque drive, maximum efficiency drive, and flux weakening control, is achieved by optimally controlling the current phase and amplitude according to the position of the stator. It is generally known that accurate control is possible.

  Next, the energization timing to the brushless DC motor will be described with reference to FIG.

  FIG. 4 is an explanatory diagram showing the timing of voltage application to the motor in Embodiment 1 of the present invention.

  In the first embodiment, the position of the rotor is detected by the position sensor 7 and the position detecting means 8, and the waveform generation unit 9 detects the position of the motor 6, the speed, and the use as shown in FIG. 4. Timing is set.

  That is, by applying to the inverter 5 the voltage (a) whose phase is advanced in the range of 0 ° to 90 ° according to the load state, speed or application of the motor 6 with respect to the induced voltage (b) phase, The motor 6 is optimally driven such that the angle is controlled in the range of 0 ° to 90 °.

  The drive loss in this type of motor drive device is mainly caused by the converter 2, the inverter 5, and the motor 6. In the inverter 5, the switching elements 5a, 5b, 5c, 5d, 5e, and 5f are turned on and off. The main loss is the accompanying switching loss and the on loss due to the voltage drop when the switching element is ON. In the motor 6, the iron loss and the copper loss are the main losses.

  In the first embodiment, the waveform generator 9 controls the motor speed by adjusting the energization width so that the PWM duty width is maximized. Therefore, the number of times the inverter 5 is switched is very small. Further, by using a silicon carbide-based or gallium nitride-based semiconductor for the switching elements 5a, 5b, 5c, 5d, 5e, and 5f, the inverter loss can be greatly reduced, and the inverter efficiency can be greatly improved.

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

  FIG. 5 is a flowchart when the motor is started in the motor drive apparatus according to the first embodiment of the present invention.

  In FIG. 5, the motor start instruction is awaited at step 101, and when the start instruction is received, the process proceeds to step 102, and the motor 6 is driven at a predetermined energization angle of 90 ° or more and less than 180 ° (120 ° in the first embodiment). Start up.

  At this time, it is conceivable to reduce the energization angle and increase the non-energization period at the time of motor startup and low-speed driving immediately after startup. In such a case, since the motor inertia is small, there is a possibility of starting failure (motor step-out). Further, the energization angle at the time of start-up is reduced to, for example, 60 ° energization, and the PWM duty width is increased to 10% at 60 ° energization, for example, when the start-up duty width at 120 ° energization is 5%. However, since there is no motor induced voltage at the time of starting the motor, an overcurrent flows through the motor winding, and there is a risk of demagnetization of the stator permanent magnet.

  Therefore, in the first embodiment, after setting the energization angle to the motor 6 to 120 ° in step 102, the duty width is adjusted in step 103, and the energization angle and duty width are adjusted to predetermined values in step 104. The As a result, stable driving can be realized by driving with 120 ° energization at the time of startup, and the reliability of the apparatus can be improved.

  FIG. 6 is a flowchart for determining the energization width and energization rate in the waveform generation unit according to the first embodiment of the present invention.

  In FIG. 6, at step 111, the current drive speed is detected from the position sensor 7 and the position detection means 8, and it is determined whether or not the vehicle is driven at the commanded speed. As a result, when the current speed of the motor 6 coincides with the command speed, the current ratio and the current angle are maintained at step 112 and the motor driving is continued.

  If there is a difference between the drive speed and the command speed at step 111 (ie, when acceleration or deceleration is required), the routine proceeds to step 113, where it is determined whether the current energization angle is at the minimum energization angle (for example, 60 °). When driving at an energization angle larger than the minimum energization angle, energization angle control is performed at step 114. Specifically, control is performed to decrease the energization angle if the drive speed is faster than the command speed, and to increase the energization angle if the drive speed is slower than the command speed.

  If the energization angle is the minimum energization angle at step 113, the routine proceeds to step 115 where duty control is performed. Specifically, if the drive speed is faster than the command speed, the duty is decreased, and if the drive speed is slower than the command speed, the duty is increased, and the process proceeds to step 116.

  By providing the minimum energization angle in this way, an increase in vibration due to speed fluctuations due to the lengthening of the non-energization section is prevented without taking an extremely long non-energization period for the motor 6.

  In step 116, it is confirmed whether or not the duty width is maximum (for example, 100%). If not, the process returns to step 111 to repeat the above-described operation. When acceleration of the motor 6 is necessary and the maximum duty width is reached by duty control (duty increase), the conduction angle control is performed at step 117, and the speed control is performed so that the rotation of the motor approaches the commanded rotation speed. .

  As described above, the waveform generation unit 9 reduces the loss of the inverter 5 by driving the motor 6 so that the switching of the inverter 5 is reduced with a waveform that maximizes the duty. Increasing the PWM duty width and reducing the number of times of switching will suppress the pulsation of the motor current due to PWM switching, reduce the motor iron loss, and increase the efficiency of the motor drive device. be able to.

  As described above, in the present embodiment, a motor (brushless DC motor) 6 including a rotor having a permanent magnet and a stator having a three-phase winding, and an inverter 5 that supplies power to the three-phase winding. And a rectangular wave or sine wave with an energization angle of 60 degrees or more and less than 180 degrees or a waveform corresponding thereto is output, so that the power utilization rate of the motor 6 can be increased and the motor 6 can be operated at high torque and high speed. A motor drive device can be provided.

  In addition, when starting the motor 6 in the first embodiment, it is possible to start the motor 6 at an arbitrary energization angle of 90 ° or more and less than 180 °, thereby realizing a reliable start of the motor 6 and improving the reliability of the apparatus. is doing.

  Further, in the first embodiment, since the brushless DC motor is driven at a conduction angle that maximizes the PWM duty, the switching loss and motor iron loss of the inverter 5 can be reduced, and high efficiency is achieved. A simple motor driving device can be provided.

  Furthermore, when there is a difference between the brushless DC motor rotation speed and the target speed with the PWM duty at the maximum, the voltage applied to the motor 6 can be varied by changing the energization angle in the range of 60 degrees to less than 180 degrees. Thus, it is possible to provide a motor drive device that can control the speed of the brushless DC motor and obtain high efficiency over a wide load range and speed range.

  In the first embodiment, the phase difference between the applied voltage to the predetermined phase of the brushless DC motor and the induced voltage of the same phase is set to 0 degree or more and less than 90 degrees, so that the induced voltage phase of the brushless DC motor is Since the current phase can be advanced, further high-speed driving can be achieved by the flux weakening control.

  Furthermore, by using a motor 6 having a saliency in which a permanent magnet is embedded in a rotor core in a brushless DC motor and selecting and driving an optimum current phase, the highest efficiency operation, the highest torque operation, etc. are possible. Optimal driving suitable for the application can be performed.

(Embodiment 2)
Next, a refrigerator provided with the motor drive device shown in the first embodiment will be described. Here, the same constituent elements as those of the first embodiment will be described with the same reference numerals.

  FIG. 7 is a block configuration diagram of the refrigerator in the second embodiment of the present invention.

  In FIG. 7, a compression element 10 is connected to a rotor shaft of a motor (brushless DC motor) 6 and is driven by the motor 6 to suck in refrigerant gas, compress it, and discharge it. The motor 6 and the compression element 10 are accommodated in the same hermetic container to constitute the compressor 11.

  The discharge gas compressed by the compressor 11 circulates back to the suction of the compression element 10 through the condenser 12, the decompressor 13, and the evaporator 14, thereby forming a refrigeration air conditioning system. Since the condenser 12 radiates heat and the evaporator 14 absorbs heat, cooling and heating can be performed. If necessary, a fan or the like may be added to the condenser 12 or the evaporator 14 to further promote heat exchange.

  In the second embodiment, the interior 15 of the refrigerator is cooled by the evaporator 14. The position estimating means 16 estimates the relative position of the rotor of the brushless DC motor.

  As described above, in the second embodiment, since the motor 6 drives the compression element 10, the operating environment is very severe under a sealed high-temperature refrigerant atmosphere and exposed to high-temperature oil.

  Therefore, providing a position sensor such as an encoder or a hall sensor for detecting the position of the stator has a problem in reliability of the components. Therefore, in the second embodiment, the phase current of the motor 6 is input to the position estimation unit 16, and the position estimation unit 16 thereby estimates the relative position of the rotor based on the current and outputs it to the waveform generation unit 9. .

  As a result, the waveform generation unit 9 can generate a rectangular wave or a sine wave of 60 ° or more and less than 180 ° based on the stator position estimated by the position estimation means 16 or a waveform corresponding thereto and output the generated waveform to the inverter 5. And sensorless driving is possible.

  In the second embodiment, the rotor position is estimated from the phase current of the motor 6, but the current value is detected by a current sensor or the lower switching elements 5b, 5d, 5f of the inverter 5. Any current detection method such as detection of a current value flowing through a shunt resistor inserted in series with the shunt resistor may be used.

  Further, as a method for estimating the position of the stator, various methods have been proposed, such as a method of detecting the current flowing through the inverter buses L1 and L2 from the shunt resistance and a method of detecting from the motor induced voltage appearing at the output terminal of the inverter 6. However, any method may be used as long as the position of the stator can be estimated.

  In the motor drive device of the present invention, when the energization angle is less than 120 °, a period in which power is not supplied to the brushless DC motor occurs, and during this period, the motor 6 rotates due to inertial force due to its own rotation. .

  In the second embodiment, the motor 6 drives the compressor 11 and has a feature that the inertia is very large. Therefore, even when there is a period in which electric power is not supplied to the motor 6 by driving at an energization angle of less than 120 °, the inertial force hardly changes the speed of the motor 6 and stable driving characteristics can be obtained. It can be said that (especially the reciprocating compressor) 11 is very suitable as a target application of the motor drive device of the present invention.

  As described above, in the second embodiment, a highly efficient cooling system can be provided by using the motor 6 for driving a compressor that forms a refrigeration cycle.

  Furthermore, by adopting the cooling system in the refrigerator, the efficiency of the cooling system can be increased, and as a result, the power consumption of the refrigerator can be reduced.

  As described above, since the motor drive device according to the present invention can provide a highly efficient motor drive device, home appliances using motors such as air conditioners, washing machines, and vacuum cleaners, AV equipment such as DVD players, Furthermore, it can be applied to a wide range of equipment using brushless DC motors, such as industrial equipment such as hydraulic pumps.

1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. Schematic diagram of the rotor of the brushless DC motor in the first embodiment Torque / advance angle characteristic diagram of motor in the first embodiment Explanatory drawing which shows the voltage application timing to the motor in the first embodiment Flowchart at motor start-up in the first embodiment Flowchart of operation in waveform generation unit in the first embodiment The block block diagram of the refrigerator in Embodiment 2 of this invention System configuration diagram of a conventional motor drive device Voltage application timing waveform diagram of a conventional motor drive device

Explanation of symbols

5 Inverter 6 Motor (Brushless DC motor)
8 Position detection means 9 Waveform generation section 11 Compressor 15 Refrigerator 16 Position estimation means

Claims (8)

  A brushless DC motor including a rotor having a permanent magnet and a stator having a three-phase winding, an inverter for supplying power to the three-phase winding, and a rectangular wave or a sine wave having a conduction angle of 60 degrees or more and less than 180 degrees Alternatively, a motor drive device comprising waveform generation means for outputting a waveform equivalent thereto, and driving the brushless DC motor by the waveform output generated by the waveform generation means.   The motor drive device according to claim 1, wherein when the brushless DC motor is started, the brushless DC motor is started at an arbitrary energization angle in a range of 90 ° to less than 180 °.   3. When the PWM duty becomes a predetermined width after startup, an energization angle that maximizes the PWM duty width is determined from the energization angle and the duty width at that time, and the brushless DC motor is energized. The motor drive device described.   When there is a difference between the actual rotational speed of the brushless DC motor and the target speed, the PWM duty is set to the maximum state, and the energization width is variable within the range of 60 ° to less than 180 °, and output to control the speed of the brushless DC motor. The motor drive device according to claim 1, wherein the motor drive device is performed.   The motor drive according to any one of claims 1 to 4, wherein a phase difference between an applied voltage to a predetermined phase of the brushless DC motor and an in-phase induced voltage is in a range of 0 degree or more and less than 90 degrees. apparatus.   The motor drive device according to any one of claims 1 to 5, wherein the brushless DC motor has a configuration in which a permanent magnet is embedded in an iron core of a rotor and has saliency.   The motor drive device according to any one of claims 1 to 6, wherein a compressor that forms a refrigeration cycle is driven by the brushless DC motor.   The refrigerator provided with the motor drive device according to any one of claims 1 to 7.

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