JP5428746B2 - Brushless DC motor driving apparatus and electric apparatus using the same - Google Patents

Description

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

  A conventional motor drive device is provided with a step of switching between speed feedback operation and speed open loop operation according to a current state and a speed state to drive the motor (for example, Patent Document 1). FIG. 12 shows a conventional motor driving apparatus described in Patent Document 1. In FIG.

  In FIG. 12, a DC power source 201 inputs six switching elements to an inverter 202 having a three-phase bridge configuration, and the inverter 202 converts the input DC voltage into an AC voltage having an arbitrary frequency, and a brushless DC motor 203. To enter.

  The position detector 204 detects the relative position of the rotor 203 a of the brushless DC motor 203 based on the induced voltage information generated by the rotation of the brushless DC motor 203 from the output terminal voltage of the inverter 202. The control circuit 205 receives the position signal output from the position detection unit 204 and generates a control signal for the switching element of the inverter 202.

  The position calculation means 206 calculates magnetic pole position information of the rotor 203a of the brushless DC motor 203 from the signal of the position detection unit 204. Based on the magnetic pole position of the rotor 203a obtained from the position calculating means 206 and the speed command value, the self-regulating operation means 207 switches the current flowing through the three-phase winding of the brushless DC motor 203 by feedback control of the brushless DC motor. The other driving operation means 210 performs open-loop driving by switching the current flowing through the three-phase winding of the brushless DC motor based on the speed command, and the selection means 211 performs the self-limiting operation of the brushless DC motor. It is selected whether to drive by means or other driving means.

  The drive control means 212 generates a control signal for the switching element of the inverter 202 based on the operation means selected by the selection means 211.

  As described above, the conventional motor drive device can change the operation range of the brushless DC motor by switching from the self-regulated operation by the feedback control to the other control operation that performs the open loop drive when the brushless DC motor is driven at a high speed or a high load. It has been expanded.

JP 2003-219681 A

  However, the above-described conventional configuration drives the brushless DC motor in an open loop during high-speed or high-load operation, so that stable driving performance can be obtained with a relatively small load. If it becomes larger, it may fall into an unstable driving state.

  FIG. 7 shows the phase relationship between the phase current and the terminal voltage when the brushless DC motor is driven in an open loop synchronous manner. In FIG. 7, the horizontal axis represents time, the vertical axis represents the phase based on the induced voltage phase (that is, the phase difference from the induced voltage), (A) represents the phase current, (B) represents the terminal voltage, and (C). Is the phase difference between the phase current and the terminal voltage. FIG. 7 (a) shows a relatively low load state, and FIG. 7 (b) shows a high load state. In both cases (a) and (b), the current phase advances from the terminal voltage phase due to the difference from the induced voltage phase. Therefore, it can be seen that the driving is performed at a very high speed (that is, the induced voltage is high) by the synchronous driving.

  As shown in FIG. 7 (a), in synchronous driving when the load is relatively small with respect to the driving speed, the rotor is delayed by an angle corresponding to the state of the load with respect to commutation, that is, the rotor (induced voltage). ), The commutation (that is, the voltage and current phase) becomes the leading phase and the predetermined relationship is maintained, so that the same state as the flux-weakening control is achieved, and high-speed driving is possible. On the other hand, as shown in (b), in a state where the load is large with respect to the driving speed, as in (a), “the rotor is delayed with respect to the commutation so that the magnetic flux is weakened and the commutation cycle is synchronized. Thus, the acceleration of the rotor and the acceleration of the rotor repeatedly reduce the current phase lead angle and the rotor decelerates ", and the drive state (drive speed) is not stabilized after all. That is, as shown in (b), since the rotation of the brushless DC motor fluctuates with respect to the commutation repeated at a constant period, the terminal voltage phase fluctuates when the induced voltage phase is used as a reference. In such a driving state, occurrence of problems such as the occurrence of “swelling noise” accompanying fluctuations in the rotational speed of the brushless DC motor and the possibility of overcurrent stop due to current pulsation is expected.

  Therefore, in order to avoid the possibility of the above-mentioned problems, it can be dealt with by reducing the load or reducing the speed until the rotational state of the brushless DC motor becomes unstable. This limits the high-speed and high-load driving of the DC motor, and has a problem that it is difficult to sufficiently expand the driving area.

  Furthermore, in the above conventional configuration, since the motor current phase and voltage phase are determined by speed and load, the motor current and voltage phase states are ideal in an ideal environment where the load and input voltage of the brushless DC motor are very stable. However, the rotation fluctuation phenomenon described above is affected by the driving speed and the load size, and the load fluctuation (the motor during one rotation of the motor such as a compressor) is affected. (Including load fluctuations) and input voltage fluctuations (including ripple voltage associated with AC voltage rectification and smoothing). Had problems.

  The present invention solves the above-described conventional problems, and enhances the stability of a brushless DC motor at a high load and high speed driving to expand the driving range, and also suppresses an unstable state due to an external factor and has high reliability. A brushless DC motor driving apparatus is provided.

  In addition, the drive range can be expanded due to the stability of high-speed and high-load drive, enabling high-efficiency, low-torque motors to be driven at high speed and high load by increasing the number of stator windings and sacrificing high-speed drive performance. An object of the present invention is to realize a motor drive device with high efficiency and high torque.

  In order to solve the above-described conventional problems, the motor driving method of the present invention is configured such that the energization angle of the brushless DC motor is 120 degrees to 150 degrees at low speed, 120 degrees to less than 180 degrees at high speed, and a predetermined frequency is set at high speed. The energization timing is achieved at a constant duty while maintaining the phase relationship with the phase current corresponding to the speed and load state of the brushless DC motor. As a result, the phase current and terminal voltage phase of the brushless DC motor are maintained in an appropriate phase relationship with respect to the induced voltage phase depending on the driving speed, load state, input voltage state, etc., and stable when a disturbance occurs. Can be driven.

  The motor driving method according to the present invention can provide a highly reliable motor driving device that can extend the operable range by improving the stability of high-speed and high-load driving of a brushless DC motor.

  In addition, by expanding the operating range, high-efficiency motors that increase the number of motor turns and sacrifice high-speed drive performance can be driven at high loads and high speeds, while maintaining the same load drive range as before. Efficiency can be improved.

  In addition, when the motor driving device of the present invention is used for driving a compressor of a refrigeration cycle, it is possible to increase the efficiency of the device, particularly when driving at a low speed, and to save energy of the electric device.

1 is a block diagram of a brushless DC motor driving apparatus according to Embodiment 1 of the present invention. Timing chart of inverter driving at low speed in Embodiment 1 of the present invention Energization angle at low speed = Efficiency characteristic diagram in Embodiment 1 of the present invention Timing chart of inverter drive at high speed in Embodiment 1 of the present invention The graph which shows the phase state with respect to the load at the time of the synchronous drive of a brushless DC motor Vector diagram showing phase relationship between phase current and terminal voltage depending on load condition A graph showing the phase relationship when a brushless DC motor is driven in an open loop synchronous manner The flowchart which shows the operation | movement of the 2nd waveform generation part in Embodiment 1 of this invention. Rotation speed = duty characteristic diagram in Embodiment 1 of the present invention Timing chart of rotation speed and duty in Embodiment 1 of the present invention Structure diagram of rotor of brushless DC motor according to embodiment 1 of the present invention Block diagram of a conventional motor drive 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 power to the three-phase winding, and a current of the brushless DC motor. A current phase detector that detects a phase; a first waveform generator that outputs a rectangular wave having a conduction angle of 120 degrees to 150 degrees or a waveform equivalent thereto; and a frequency setting section that changes only a predetermined frequency with a constant duty. a second waveform generator for power output at a predetermined frequency determined square wave and sine wave under conduction angle is 120 degrees or more 180 degrees, or a waveform based on those by the frequency setting unit, in the low-speed first waveform the output of the generator, the high-speed possess a switching determination unit for selecting the outputs of the second waveform generator, wherein in the driving according to the second waveform generator, reference current phase A phase difference in which the current phase and the voltage phase of the brushless DC motor are inevitably determined according to the driving state by converging and stabilizing the time from the phase point to the commutation for switching the current winding to a predetermined time difference. Since the brushless DC motor can be appropriately driven according to the driving state, the brushless DC motor can always be in the optimum driving state. Further, in the driving by the second waveform generator, the phase of the voltage to be applied is determined based on the phase of the stator winding current of the brushless DC motor, so that the relationship between the current phase and the voltage phase of the brushless DC motor is stabilized, By improving the driving stability by the two commutation units, it is possible to greatly expand the load area and speed area in which the brushless DC motor can be driven.

The invention according to claim 2 has a position detection unit that detects the rotational position of the rotor, and at low speed, the inverter is driven based on the rotational position of the rotor by the position detection unit. Can be done. According to a third aspect of the present invention, in the first or second aspect of the present invention, the brushless DC motor is temporarily corrected at a predetermined timing with respect to the energization time of the three-phase winding of the brushless DC motor. The current phase and voltage phase of the motor are held in a predetermined phase relationship. As a result, the phase relationship between the current phase and the voltage phase of the brushless DC motor can be maintained in an appropriate state according to the load state, and the phase relationship can be maintained. It is possible to improve and extend the driveable load range. According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects of the present invention, the switching of the energized winding of the three-phase winding of the brushless DC motor is performed by the brushless DC motor. This is performed at an arbitrary timing based on the current phase. As a result, the motor current phase and the voltage phase can be reliably held in a predetermined phase relationship.

According to a fifth aspect of the present invention, there is provided the frequency limiting unit according to any one of the first to fourth aspects , wherein the upper limit frequency of the predetermined frequency is set and the output of the frequency equal to or higher than the upper limit frequency is prohibited. By having it, it is possible to prevent the brushless DC motor from stepping out or falling into an unstable driving state by preventing driving at a frequency exceeding the driving limit frequency, and to improve the reliability of the apparatus.

According to a sixth aspect of the invention, there is provided an upper limit frequency setting unit configured to set the upper limit frequency by a maximum frequency output by the first waveform generation unit in the invention according to any one of the first to fifth aspects. Therefore, it is possible to set the maximum frequency according to the driving situation, and it is possible to perform more stable and high-speed driving.

According to a seventh aspect of the invention, in the invention according to any one of the first to sixth aspects, after a predetermined time has elapsed, the drive from the frequency setting unit is temporarily changed to the drive from the commutation unit. By switching automatically, by having an upper limit frequency changing unit for resetting the upper limit frequency, it is possible to operate at the optimum maximum speed even when the load state changes with time.

The invention according to claim 8 is the invention according to any one of claims 1 to 7 , wherein the brushless DC motor is a rotor formed by embedding a permanent magnet in the iron core of the rotor, and has saliency. In the drive of brushless DC motor, reluctance torque due to saliency can be effectively used in driving a brushless DC motor, so high-efficiency driving at low speed and high-efficiency high-speed The driving performance can be further extended.

According to a ninth aspect of the invention, in the invention according to any one of the first to eighth aspects, the brushless DC motor drives the compressor, and the compressor has high efficiency and low noise. This is one of the most important applications that can realize driving.

The invention described in claim 10 is a refrigerator using the invention described in claim 9 for driving the compressor of the cooling system, and it is possible to improve the cooling performance by increasing the efficiency of the cooling system and expanding the drive region. The power consumption of the refrigerator can be reduced and the cooling time can be shortened when the internal temperature is high.

The invention of claim 11 is an air conditioner using the invention described in claim 9. As a result, the power consumption of the air conditioner can be reduced by increasing the efficiency of the refrigerating and air-conditioning cycle, and the heating capacity when the outside air temperature is very low can be improved, so that driving in a wide load range is possible.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block diagram showing a brushless DC motor driving apparatus according to Embodiment 1 of the present invention.

  In FIG. 1, an AC power source 1 is a commercial power source having 50 or 60 Hz and an effective value of 100 V in Japan. The rectifying / smoothing circuit 2 receives the AC power supply 1 as an input and rectifies and smoothes the DC power supply. The rectifying / smoothing circuit 2 includes four bridge-connected rectifier diodes (2a to 2d) and smoothing capacitors (2e and 2f). Although the voltage doubler rectifier circuit is used in this embodiment, a full wave rectifier circuit may be used. Furthermore, in this embodiment, the AC power source is a single phase, but when a three-phase AC power source is used, a three-phase rectifying / smoothing circuit may be used as the rectifying / smoothing circuit.

  The inverter 3 converts the DC power into AC power using the DC voltage of the rectifying and smoothing circuit 2 as an input, and is configured by connecting six switching elements (3a to 3f) in a three-phase bridge. Further, although a diode for return current is connected in the reverse direction of each switching element, it is omitted in this figure.

  The brushless DC motor 4 is composed of a rotor 4a having a permanent magnet and a stator 4b having a three-phase winding, and the three-phase alternating current generated by the inverter 3 flows through the stator winding 4b. The child 4a can be rotated. The rotational motion of the rotor 4a is converted into a reciprocating motion by a crankshaft (not shown), and a piston (not shown) reciprocates in a cylinder (not shown) to drive a compressor that compresses the refrigerant. Do.

  The position detector 5 detects the relative magnetic pole position of the rotor 4a of the brushless DC motor 4, and in this embodiment, the relative position of the rotor 4a is determined from the induced voltage generated in the three-phase winding of the stator 4b. Rotating position is detected. As a method for detecting the stator position, the magnetic pole position may be estimated through the vector calculation from the detection of the motor current (phase current or bus current).

The first waveform generator 6 generates a signal for driving the switching element of the inverter 3 based on the position information of the rotor 4 a obtained by the position detector 5. This driving signal is based on rectangular wave energization, and the energization angle is 120 degrees or more and 150 degrees or less. However, there is no problem even if the waveform other than the rectangular wave is a trapezoidal wave having a slight slope in the rising / falling as a waveform conforming thereto.

  The first waveform generator 6 further performs PWM duty control in order to keep the rotation speed constant. As a result, it is possible to operate with an optimum duty according to the rotational position, and the brushless DC motor can be most efficiently operated.

  The speed detector 7 detects the speed of the brushless DC motor 4 from the output signal of the position detector 5. As a specific method, it can be easily detected by measuring a signal from the position detection unit 5 generated at a constant period.

  The frequency setting unit 8 outputs only the frequency with a constant output duty, and the frequency limiting unit 9 limits the frequency of the frequency setting unit 8 so as not to exceed the upper limit.

  The second waveform generator 10 generates a signal for driving the switch element of the inverter 3 based on the output signal of the frequency limiter 9 and the output signal of a current phase detector 16 described later. This driving signal is a rectangular wave having a conduction angle of 120 degrees or more and less than 180 degrees. However, there is no problem even if the waveform conforms to a rectangular wave such as a trapezoidal wave, or a distorted waveform conforms to a sine wave or sine wave. Here, driving is performed with the maximum duty, which is a constant duty of 90 to 100%.

  The switching determination unit 11 determines low / high speed based on the speed detected by the speed detection unit 7 and switches the waveform for operating the inverter 3 between the first waveform generation unit 6 and the second waveform generation unit 10. Specifically, when the rotational speed is low, the signal from the first waveform generator 6 is selected, and when the rotational speed is high, the signal from the second waveform generator 10 is selected to operate the inverter 3.

  Here, the determination of whether the rotation speed is low or high may be determined from the actual speed detected by the speed detector 7, or may be determined from the set rotation speed or the duty. Since the determination by the duty is the maximum duty (generally 100%) and the maximum speed in driving by position detection, the waveform generation unit can be switched under this condition.

  The drive unit 12 drives the switch elements (3 a to 3 f) of the inverter 3 by the output signal from the switching determination unit 11. By this driving, an optimal AC output can be applied from the inverter 3 to the brushless DC motor 4, so that the rotor 4a can be rotated.

  The upper limit frequency setting unit 13 sets the upper limit frequency based on the maximum rotation speed (when the duty is 100%) when driven from the first waveform generation unit 6. In the present embodiment, the upper limit frequency (that is, the upper limit rotational speed of the brushless DC motor) is set to 1.5 times the maximum rotational speed. For example, 75 r / s is set when the maximum rotation speed is 50 r / s. The upper limit rotational speed set by this upper limit frequency is used for frequency limitation of the frequency limiting unit 9.

The upper limit frequency is set as follows. When driving by the frequency setting unit 8 and the second waveform generation unit 10, the brushless DC motor 4 is operated as a synchronous motor in which the rotor 4 a is attached to the commutation of the inverter 3, and is fixed to the commutation. Due to the delay of the child, the induced voltage phase is delayed with respect to the current phase. That is, when the induced voltage phase is considered as a reference, since the motor current phase is driven with respect to the induced voltage phase (that is, the magnetic flux is weakened), the first waveform generator 6 is driven at a duty of 100%. Furthermore, high-speed rotation is possible. However, when this advance angle becomes large (that is, when the stator is largely delayed with respect to commutation), the motor is out of synchronization and stepped out. Therefore, the reliability of the motor drive device is improved by setting the upper limit frequency in advance so as to be lower than the rotational speed at which this step-out is performed.

  The upper limit frequency changing unit 14 forcibly switches the switching determination unit to the first waveform generating unit 6 when the switching determination unit 11 continues driving by the second waveform generation unit 10 for a predetermined time (for example, 30 minutes). The upper limit frequency by the setting unit 13 is reset.

  The current detector 15 detects an instantaneous value of the current flowing through the brushless DC motor, and the current phase detector 16 detects the phase of the motor current of the brushless DC motor. In the present embodiment, the current phase detection unit 16 inputs the output of the current detection unit 15 configured by a current sensor or the like to the comparator and detects the zero cross timing. The current detector 15 may be a DC current sensor, an AC current sensor, or any current detector such as a fixed resistor having a very small resistance value.

  As another method of current phase detection, A / D conversion is performed on the current detected by the current detection unit 15 at a predetermined sampling period (for example, carrier period), and the current phase detection unit determines the maximum from the result of the A / D conversion. It is also possible to detect the phase of the current from the value, minimum value, current zero point, and the like.

  Next, the operation in Embodiment 1 of the present invention will be described.

  First, the operation at low speed will be described. FIG. 2 is a timing diagram of inverter driving at low speed in Embodiment 1 of the present invention. When the rotation speed of the brushless DC motor 4 is low, the brushless DC motor 4 is driven by a signal from the first waveform generator 6 that operates according to the output of the position detector 5, and the operation is as shown in FIG.

  In FIG. 2, U is a drive signal for the switch element 3a, V is a drive signal for the switch element 3c, W is a drive signal for the switch element 3e, X is a drive signal for the switch element 3b, Y is a drive signal for the switch element 3d, and Z Is a drive signal for the switch element 3f, and Iu, Iv, and Iw indicate currents of U phase, V phase, and W phase of each winding of the stator 4b. In driving at low speed, commutation is performed sequentially in intervals of 120 degrees in accordance with the signal from the position detection unit 5. The upper arm drive signals U, V, and W are duty controlled by PWM control. At this time, the current waveform is a sawtooth waveform as shown in FIG. At this time, since the commutation is performed at an optimum timing based on the output of the position detector 5, the brushless DC motor can be driven most efficiently.

  Next, the optimum energization angle will be described with reference to FIG. FIG. 3 is a conduction angle = efficiency characteristic diagram at low speed in Embodiment 1 of the present invention. In FIG. 3, the solid line indicates the motor efficiency, the broken line indicates the circuit efficiency, and the alternate long and short dash line indicates the total efficiency (motor efficiency × circuit efficiency). As shown in FIG. 3, when the energization angle is larger than 120 degrees, the motor efficiency is improved. This is because the effective angle of the motor current decreases (that is, the power factor increases) and the motor efficiency increases as the copper loss of the motor decreases as the conduction angle increases. However, in the circuit, the number of times of switching increases and the switching loss increases, so that the circuit efficiency decreases. Therefore, the point with the highest overall efficiency appears. In the present embodiment, it can be said that 130 degrees is the most efficient point.

  Next, the operation at high speed will be described. FIG. 4 is a timing diagram of inverter driving at high speed in the first embodiment of the present invention. When the rotation speed of the brushless DC motor 4 is high, the brushless DC motor 4 is driven by a signal from the second waveform generation unit 10 that operates according to the output of the frequency setting unit 8 and operates as shown in FIG.

  The symbols in FIG. 4 are the same as those in FIG. Each drive signal is commutated so as to output a predetermined frequency in accordance with the output of the frequency setting unit 8. At this time, the conduction angle is set to 120 degrees or more and less than 180 degrees. In FIG. 4, this conduction angle is shown as 150 degrees, but by increasing the conduction angle, the current waveform of each phase approximates a sine wave.

  By increasing the frequency while keeping the duty constant, the number of revolutions can be significantly increased as compared with the prior art. In this state where the rotational speed is increased, the brushless DC motor 4 is operated as a synchronous motor, and the current increases as the drive frequency increases. At this time, by increasing the conduction angle to less than 180 degrees at the maximum, the peak current value can be suppressed, and a higher current can be operated without overcurrent protection.

  Here, the timing for turning on the switching element by the second waveform generator will be described. FIG. 5 is a graph showing a phase state with respect to a load when the brushless DC motor is synchronously driven. In FIG. 5, the horizontal axis indicates the motor torque, and the vertical axis indicates the phase difference based on the induced voltage phase. When the phase is positive, it indicates that the phase is forward with respect to the induced voltage phase. Further, (a) in FIG. 5 is the motor phase current, and (b) is the phase of the motor phase voltage, which shows a stable state in the synchronous operation. Since the current phase is ahead of the terminal voltage phase even in a low load state, it can be said that the brushless DC motor is driven at high speed by synchronous driving. As is clear from the relationship between the phase current phase and the phase voltage phase shown in FIG. 5, the change in the current phase is small with respect to the load torque, and the terminal voltage phase changes linearly. It can be seen that the phase difference between and changes substantially linearly.

  As described above, in the synchronous drive, it is stable at an appropriate current and voltage phase relationship according to the drive speed and load of the brushless DC motor. FIG. 6 shows the relationship between the terminal voltage and the current phase at this time. FIG. 6 is a vector diagram showing the phase relationship between the current and the terminal voltage depending on the load state in a dq plane.

  As shown in FIG. 6, in the synchronous drive, the phase of the terminal voltage vector changes in the advance direction while keeping the magnitude almost constant when the load increases. On the other hand, the current vector changes its magnitude as the load increases while maintaining a substantially constant phase (current increases as the load increases). In this way, the phase relationship between the vectors is determined in an appropriate state in which the voltage and current vectors are in accordance with the driving environment (input voltage, load torque, driving speed, etc.).

  Here, the temporal change of the phase state in a certain load state / speed state will be described with reference to FIG. As described in the problem of the prior art, when the driving state is stable by synchronous driving, the phase difference between the phase current phase and the terminal voltage phase is constant as shown by the waveform (c) in FIG. Kept stable.

  On the other hand, when the load is extremely large, or when the driving state is unstable due to disturbance or the like (when fluctuations in rotational speed occur), current and terminal voltage based on the induced voltage phase due to fluctuations in the rotor speed The phase relationship between the current and the terminal voltage also varies because the variation in the terminal voltage phase is larger than the variation in the current phase.

  In other words, when an unstable phenomenon occurs in synchronous drive, the phase relationship between the induced voltage, motor terminal voltage, and motor current is in an unstable (fluctuating) state, and is unstable once in an open loop drive. When falling into a phase state, it is difficult to converge to a phase relationship commensurate with load and speed. Therefore, by maintaining the phase difference between the current phase and the terminal voltage in an appropriate phase relationship corresponding to the load as shown in FIG. 5, it is possible to suppress an unstable phenomenon due to synchronous driving.

  As a method of maintaining the phase relationship between the terminal voltage and the phase current, in this embodiment, the reference phase of the terminal voltage (that is, the commutation reference position of the drive signal) and the reference point of the current phase are detected, and the open loop synchronization is performed. The commutation timing in driving (commutation with a fixed period) is corrected.

  Now, a method for determining the control timing of the switching element of the inverter 3 will be described with reference to the flowchart showing the operation of the second waveform generator in FIG.

  First, in step 101, the ON timing of a specific switch element is waited. In this embodiment, the on-timing of the U-phase upper switch element, that is, the switch element 3a of the inverter 3 is awaited. If it is the ON timing of the switch element 3a, the process proceeds to step 102, and the time from when the switch element 3a is turned on until the current reaches a predetermined phase is measured. In the present embodiment, the U-phase current is detected by the current detection unit 15 using a current sensor, and the current phase detection unit uses the zero cross point at which the current changes from the negative direction to the positive direction as a reference for the current phase. The time from the on timing of 3a to the timing at which the U-phase current changes in the positive direction is measured. In order to detect the current zero cross point, the input of the current sensor is input to a comparator circuit configured to invert the output in accordance with the direction of current flow, and the output edge of the comparator circuit is detected.

  In step 103, the difference between the measured time and the average time so far is calculated, and in step 104, the commutation timing correction amount is calculated based on the difference.

  The commutation timing correction amount is for correcting the commutation timing with respect to the basic commutation period based on the command speed set by the frequency setting unit 8. Therefore, when a large correction amount is added, it causes overcurrent and step-out stop. Therefore, in determining the correction amount, a sudden change in commutation timing is suppressed by performing a correction amount calculation after adding a low-pass filter or the like. As a result, even when the current zero cross detection fails (false detection) due to the influence of noise or the like, the influence on the correction amount can be reduced, and the driving stability can be further improved. Furthermore, suppressing a sudden change in the correction amount calculation also slows down the change in commutation timing during acceleration / deceleration of the brushless DC motor, so the command speed is greatly changed and the commutation cycle by the frequency setting unit is greatly increased. Even when changed to, the change in commutation timing becomes gradual, and smooth acceleration / deceleration performance with suppressed current disturbance can be obtained.

  Specifically, the commutation timing is corrected so that the phase difference always approaches the average time (the phase difference can be maintained at the average time). For example, if the load increases, the current phase is delayed due to a decrease in the rotor speed, and the measurement time is longer than the average time from the terminal voltage reference phase to the phase current reference phase, the commutation timing is extended (the measurement time because the current phase was delayed). Therefore, the commutation timing is corrected so that the commutation timing is delayed to delay the terminal voltage phase, and the phase difference from the current phase is brought closer to the average time. Alternatively, when the measurement time is shorter than the average time from the terminal voltage reference phase to the phase current phase when the load is reduced, the rotor speed is increased and the current phase is advanced, the commutation timing is temporarily shortened. (Since the current phase is accelerated and the measurement time is shortened, the commutation timing is advanced to advance the terminal voltage phase, and the phase difference of the current phase approaches the average time).

  Further, the commutation timing is corrected as an arbitrary timing of a specific phase (for example, only switching on the U phase) (such as once per rotation of the rotor), and the commutation of other phases is based on the target rotational speed. Perform in time by cycle. As a result, the phase relationship between the phase current and the terminal voltage phase can be optimally maintained according to the load, and the driving speed of the brushless DC motor can be maintained.

  Next, in step 105, it is calculated and updated as an average time taking into account the time from the commutation obtained in step 102 to the specific phase of the current.

  In step 106, the commutation timing is determined by adding a correction amount to the commutation cycle of the switch element based on the driving speed set by the frequency setting unit. If it is not the commutation timing of the specific switch element (switch element 3a in the present embodiment) in step 101, the commutation timing is determined in step 106 with the correction amount set to 0.

  In this embodiment, since the commutation cycle is corrected only by the ON timing of the U-phase upper switch element 3a, the correction is performed once during the electrical angle cycle. However, the application of the motor drive device, the inertia of the motor, etc. In consideration of the above, the correction may be performed once per rotation, twice in one electrical angle cycle, or at each timing when each switch element is turned on.

  Next, the switching operation of the waveform generation unit by the switching determination unit 11 will be described.

  FIG. 9 is a graph showing the rotational speed = duty characteristics in the first embodiment of the present invention.

  In FIG. 9, when the rotational speed is 50 r / s or less, the first waveform generator 6 is driven. The duty is automatically adjusted to the most efficient point by feedback control according to the rotation speed.

  At 50 r / s, the duty becomes 100%, and the drive by the first waveform generator 6 reaches a limit that cannot be rotated any further. In this state, the upper limit frequency setting unit 13 sets 75 r / s, which is 1.5 times as high, as the upper limit frequency based on 50 r / s. When the output signal from the frequency setting unit 8 exceeds 75 r / s, the frequency limiting unit 9 is prevented from outputting higher frequency according to the upper limit frequency 75 r / s. The duty is fixed between 50 r / s and 75 r / s, and only the rotational speed (that is, the commutation cycle) is increased.

  Next, the operation of the upper limit frequency changing unit 14 will be described. When this device is used in a compressor such as a refrigerator, a high-efficiency motor with reduced torque can be used, and high-efficiency operation can be performed when a low-speed rotation with a stable internal temperature is required. When the internal temperature is high and high speed rotation is required, the rotation speed can be easily increased, which is optimal for application of this technology. Thus, when this apparatus is used for a compressor such as a refrigerator, the load torque hardly changes suddenly and takes a relatively long time to change the load torque. At this time, it is necessary to change the upper limit frequency.

  FIG. 10 shows a timing diagram of the rotational speed and duty in the first embodiment of the present invention.

  In FIG. 10, the brushless DC motor 4 starts at time t0. Here, it is assumed that the rotational speed command is instructed to be 80 r / s. The inverter 3 supplies electric power to the brushless DC motor 4 to increase the duty, and at the same time, the rotational speed is sequentially increased by the driving by the feedback from the position detection unit 5 and the first waveform generation unit 6.

  At time t1, the maximum duty is 100%, and the rotational speed cannot be increased any more by the driving by feedback by the position detector 5 and the first waveform generator 6. At this time, the rotation speed of the brushless DC motor 4 is 50 r / s, and based on this rotation speed, the upper limit frequency setting unit 13 sets the upper limit frequency to 1.5 times 75 r / s.

Next, the switching determination unit 11 switches to driving by the frequency setting unit 8 and the second waveform generation unit 10. Thereafter, the duty is constant 100%, and the frequency setting unit 8 increases the frequency to increase the rotation speed of the brushless DC motor 4. At time t2, the rotation speed command is instructed to be 80 r / s, but the upper limit frequency determined by the upper limit frequency setting unit 13 is 75 r.
Therefore, the rotation speed is limited to 75 r / s by the frequency limiting unit 9.

  Next, at time t3 (time t3-t2 is 30 minutes as an example), when used in a compressor such as a refrigerator, the load state may be changed, so the maximum number of revolutions is confirmed. This detects that the upper limit frequency changing unit 14 has reached a predetermined time (30 minutes in the present embodiment), and switches the switching determination unit 11 to drive from the first waveform generation circuit 6. Then, the number of rotations decreases, and the maximum number of rotations operable from the normal first waveform generation circuit 6 can be measured from the rotation number detection unit 7.

  In the present embodiment, the load state at time t3 is lighter than the load state at time t2, and the maximum rotational speed increases to 55 r / s. As a result, the upper limit frequency setting unit 13 resets the upper limit frequency, but 1.5 times 82.5 r / s is set as the upper limit frequency.

  Thereafter, similarly, the switching determination unit 11 is switched to driving from the frequency setting unit 8 and the second waveform generation unit 10 to increase the rotational speed again. At this time, since the upper limit frequency is 82.5 r / s with respect to the command rotational speed 80 r / s, the operation is continued at a desired 80 r / s. In this way, an optimum operation according to the load state can be realized by detecting the load state again at regular intervals and correcting the upper limit frequency with respect to the load fluctuation.

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

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

  The rotor core 20 is formed by stacking punched thin steel sheets of about 0.35 mm to 0.5 mm. The four magnets 21a to 21d are embedded in the rotor core 20 in a reverse arc shape. This magnet is usually a ferrite type, but if a rare earth magnet such as neodymium is used, a plate structure may be used.

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

  Further, when the control according to the present embodiment is used, the current is operated in the leading phase when driving by the frequency setting unit 8 and the second waveform generation unit 10, so that the reluctance torque is greatly utilized. Therefore, the motor can be operated at a higher rotational speed than a motor without reverse saliency.

As described above, the brushless DC motor driving method according to the present embodiment supplies power to the brushless DC motor including the rotor having the permanent magnet and the stator having the three-phase winding, and the three-phase winding. Inverter, a rectangular wave having a conduction angle of 120 ° to 150 ° at a low speed or a waveform corresponding thereto, and a rectangular wave and a sine wave having a conduction angle of 120 ° to less than 180 ° at a high speed, or a waveform corresponding thereto, Driving at a predetermined frequency according to a phase relationship with the phase current of the DC motor and changing only the predetermined frequency while keeping the duty constant makes it possible to further improve the stability during high-speed driving by synchronous driving. The area can be expanded.

  In addition, since the relationship between the phase current phase and the terminal voltage phase is fixed according to the load and speed, it can be driven stably against disturbances such as load fluctuations and voltage fluctuations, so that the reliability of the motor drive device is improved. Can do.

  In addition, since the current peak can be kept low by wide-angle energization with high-speed driving at high load, the current rating of the inverter can be lowered, and the cost of the motor drive device can be reduced.

  Also, at low speed, it has a position detection unit that detects the rotational position of the rotor, and speed feedback control is performed while the relative position of the brushless DC motor rotor is detected by the position detection unit, so that the motor drive device is driven with high efficiency. I can do it.

  Furthermore, in the low-speed drive region, by outputting a rectangular wave with an energization angle of 120 degrees or more and 150 degrees or less, or a waveform corresponding thereto (for example, a trapezoidal wave), the copper loss is reduced by reducing the effective current, the circuit loss is reduced, Operation in the lowest loss state that balances with an increase in switching loss is possible, and operation at the highest efficiency is possible. In general, sinusoidal drive is said to have good motor efficiency, but since the conduction angle is 180 degrees, the switching loss of the circuit increases. The driving method is superior.

  The brushless DC motor 4 is a rotor 4a in which permanent magnets 21a to 21d are embedded in the iron core of the rotor 4a, and has a rotor 4a having saliency. In addition to the magnet torque of the permanent magnet, By using reluctance torque due to saliency, the efficiency at low speeds is naturally increased, and the high-speed driving performance is further increased. In addition, by adopting a rare earth magnet such as neodymium as the permanent magnet to increase the ratio of magnet torque, or to increase the ratio of reluctance torque by increasing the difference between inductances Ld and Lq, the optimum conduction angle is changed. Efficiency can be increased.

  In addition, the use of the motor driving device of the present embodiment for driving the compressor increases the winding amount of the winding and reduces the torque (that is, lowers the maximum number of rotations than the brushless DC motor used in the conventional motor driving device). Since the DC motor can be driven at a predetermined high speed, the duty at a low rotation speed can be made larger than that of the conventional driving method, so that motor noise, particularly carrier noise (equivalent to the frequency of PWM control, for example, 3 kHz) can be reduced. This is a very important application.

  In addition, since the frequency limiting unit 9 that sets the upper limit frequency of the predetermined frequency and prohibits the output of the frequency higher than the upper limit frequency is prevented, the drive at the rotation exceeding the drive upper limit capability is prevented. Is secured. Accordingly, it is possible to prevent a cooling system such as a refrigerator from being stopped unexpectedly and not being cooled due to a stop due to motor step-out.

  Furthermore, by having an upper limit frequency setting unit that sets the upper limit frequency according to the maximum frequency output by the first waveform generator, even when the load state changes over time, an appropriate maximum drive frequency can be set according to the driving situation. It becomes possible, and the high-speed drive capability according to the load state can be utilized to the maximum.

In addition, after a predetermined time has elapsed, by having an upper limit frequency changing unit that temporarily switches from driving from the frequency setting unit 8 to driving from the position detection unit 5 and resets the upper limit frequency, the load state is increased over time. Even if has changed, it can be reset to an appropriate maximum speed. When driving a compressor of a cooling system, the load state changes very slowly, so there is no need to frequently correct the maximum speed, and correcting the maximum speed over time is a very effective method. It is.

  In this embodiment, the brushless DC motor drives the compressor of the refrigerator. However, even when driving the compressor of the air conditioner, the high-efficiency driving at low speed and the high-load high-speed driving are similarly performed. It is possible to cover a wide driving range from the lowest load during cooling to the maximum load during heating, and in particular, it is possible to reduce power at a relatively low load below the rating.

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

DESCRIPTION OF SYMBOLS 3 Inverter 4 Brushless DC motor 5 Position detection part 6 1st waveform generation part 8 Frequency setting part 9 Frequency restriction part 10 2nd waveform generation part 11 Switching determination part 13 Upper limit frequency setting part 14 Upper limit frequency change part 16 Current phase detection part 17 Compressor 21 Refrigerator

Claims (11)

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 current phase detecting unit for detecting a current phase of the brushless DC motor; A first waveform generator that outputs a rectangular wave with a conduction angle of 120 degrees or more and 150 degrees or less, or a waveform corresponding thereto, a frequency setting section that changes only a predetermined frequency with a constant duty, and a conduction angle of 120 degrees or more and 180 degrees less than the square wave and sine wave, or a second waveform generator for power output at a predetermined frequency determined by the waveform of the frequency setting unit based on those, the output of the first waveform generator is at a low speed, said high speed the output of the second waveform generator possess a switching determination unit for selecting each, in the drive by the second waveform generation unit, switching the conduction winding from the reference phase point of current phase By converging and stabilizing the time until commutation to a predetermined time difference, the current phase and the voltage phase of the brushless DC motor are stably driven with a phase difference that is inevitably determined according to the driving state. The brushless DC motor drive device. 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 current phase detecting unit for detecting a current phase of the brushless DC motor; The position detector for detecting the rotational position of the rotor and the output of the position detector at a low speed output a rectangular wave and a sine wave having a conduction angle of 120 degrees to less than 150 degrees or a waveform corresponding to them at a predetermined frequency. A first waveform generator for driving the inverter, a frequency setting unit for changing only a predetermined frequency with a constant duty at high speed, and a rectangular wave having a conduction angle of 120 degrees or more and less than 180 degrees or a waveform corresponding thereto. have a second waveform generator for power output at a predetermined frequency determined by the parts, it said in the driving according to the second waveform generation unit, the current phase of the reference phase By converging and stabilizing the time from commutation to switching the current winding to a predetermined time difference, the current phase and voltage phase of the brushless DC motor are stabilized to a phase difference that is inevitably determined according to the driving state. A brushless DC motor drive device. By temporarily correcting the energization time of the three-phase winding of the brushless DC motor at a predetermined timing, the winding current phase and voltage phase of the brushless DC motor are changed to drive speed, load torque, input voltage, etc. The brushless DC motor drive device according to claim 1 , wherein the drive device is held in a phase relationship determined by a drive state of the brushless DC motor . 4. The brushless DC motor according to claim 1 , wherein the winding to be energized in the three-phase winding of the brushless DC motor is switched at a predetermined timing with reference to the phase of the winding current of the brushless DC motor. 5. Drive device . 5. The brushless DC motor drive device according to claim 1 , further comprising a frequency limiting unit that sets an upper limit frequency of the predetermined frequency and prohibits output of a frequency equal to or higher than the upper limit frequency. 6. The brushless DC motor driving apparatus according to claim 1, further comprising an upper limit frequency setting unit that sets the upper limit frequency based on a maximum frequency output by the first waveform generation unit. 7. After a predetermined time has elapsed, by switching from driving by the frequency setting unit in manner temporarily driven by the first waveform generator, claim 1 having an upper limit frequency changing unit to reset the upper limit frequency to claim 6 The brushless DC motor drive device described. 8. The brushless DC motor according to claim 1 , wherein the brushless DC motor is a rotor in which a permanent magnet is embedded in an iron core of the rotor, and has a rotor having saliency. 9. Drive device. The brushless DC motor driving device according to at least one of claims 1 to 8, wherein the brushless DC motor drives the compressor. A refrigerator using the brushless DC motor drive device according to claim 9 . An air conditioner using the brushless DC motor drive device according to claim 9 .