JP2011193585A - Motor drive and electric equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reliable motor drive suppressing an unstable state due to an external factor by obtaining stable drive performance even if driving a brushless DC motor at a high speed and with a high load. <P>SOLUTION: An advance correction means 10 sets a terminal voltage advance value to maintain a current value detected by a current detection means 9 to be constant. A second waveform generation part 11 outputs a motor drive signal while keeping duty constant by the set advance value and a command frequency set according to a system state, thus achieving stable drive without any position detection, and hence achieving stable drive even in high-speed drive and high-load drive where the position detection of the brushless DC motor 4 is difficult. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a motor driving device that drives a brushless DC motor and an electric device using the same.

  For example, as disclosed in Patent Document 1, a conventional motor driving device drives a motor by switching to either speed feedback driving or speed open loop driving according to a current value or a driving speed. FIG. 12 shows a conventional motor driving apparatus described in Patent Document 1.

  In FIG. 12, a DC power supply 201 inputs DC power to an inverter 202. The inverter 202 is configured by connecting six switching elements in a three-phase bridge. The inverter 202 converts the input DC power into AC power having a predetermined frequency and inputs the AC power to the brushless DC motor 203.

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

  The position calculation unit 206 calculates information on the magnetic pole position of the rotor 203 a of the brushless DC motor 203 based on the signal from the position detection unit 204. Both the self-limiting driving unit 207 and the other braking / driving unit 210 output a signal indicating the timing for switching the current flowing through the three-phase winding of the brushless DC motor 203. These timing signals are signals for driving the brushless DC motor 203. These timing signals output from the self-limiting drive unit 207 are for driving the brushless DC motor 203 by feedback control, and are signals obtained based on the magnetic pole position of the rotor 203a obtained from the position calculation unit 206 and the speed command unit 213. It is.

  On the other hand, these timing signals output by the other braking / driving unit 210 are for driving the brushless DC motor 203 by open loop control, and are signals obtained based on the speed command unit 213. The selection unit 211 selects and outputs either the signal input from the self-limiting driving unit 207 or the timing signal input from the other braking / driving unit 210. That is, the selection unit 211 selects whether the brushless DC motor 203 is driven by the self-braking drive unit 207 or the other braking / driving unit 210. The drive control unit 212 outputs a control signal for the switching element of the inverter 202 based on the signal output from the selection unit 211.

  When the brushless DC motor 203 is driven at a high speed or driven with a high load, the conventional motor driving device switches from self-limiting driving by feedback control to other braking driving by open loop control. As a result, the drive range of the brushless DC motor 203 is extended from low speed driving to high speed driving, or from low load driving to high load driving.

JP 2003-219681 A

  However, the conventional configuration drives the brushless DC motor 203 by open loop control in the case of driving at high speed or high load (hereinafter referred to as high speed / high load). For this reason, when the load is small, stable driving performance can be obtained, but when the load is large, there is a problem that the driving state becomes unstable.

  The present invention solves the above-described conventional problems, and extends the driving range by obtaining stable driving performance even when a brushless DC motor is driven at high speed / high load. Thus, an unstable state due to an external factor is suppressed, and a highly reliable motor driving device is provided.

  The motor drive device of the present invention is a motor drive device that drives a brushless DC motor. The present invention further includes an inverter that supplies power to the brushless DC motor, and a terminal voltage acquisition unit that acquires the terminal voltage of the brushless DC motor. Furthermore, the present invention includes a first waveform generation unit that outputs a first waveform signal having a waveform with a conduction angle of 120 degrees to 150 degrees. The present invention further includes current detection means for detecting at least one phase current flowing through the brushless DC motor. The present invention further includes an advance correction means for changing the terminal voltage advance angle of the brushless DC motor so as to keep the current value detected by the current detection means constant. Furthermore, the present invention outputs a second waveform signal having a constant duty and a waveform having an advance angle value set by the advance angle correction means and an arbitrarily set frequency and a conduction angle of 120 degrees to less than 180 degrees. A second waveform generator. Furthermore, the present invention includes a switching determination unit that switches the output of the first waveform signal and the second waveform signal according to an operating state. Furthermore, the present invention provides a drive unit that outputs to the inverter a drive signal that indicates the supply timing of the power that the inverter supplies to the three-phase winding based on the first or second waveform signal output from the switching determination unit. Have.

  According to this configuration, the brushless DC motor can be driven based on the first waveform signal having a waveform with a conduction angle of 120 degrees or more and 150 degrees or less if the load or speed is low and the position can be detected. Done. On the other hand, in an operating state where position detection is impossible at high speed / high load, the brushless DC motor has a second waveform having a conduction angle of 120 degrees or more and less than 180 degrees according to an arbitrarily set frequency. Driving based on the signal is performed.

  The motor driving apparatus of the present invention is stable in driving and extended in driving range even when driving at high speed / high load. As a result, it is possible to provide a highly reliable motor drive device that suppresses an unstable state due to an external factor.

1 is a block diagram of a motor drive device according to Embodiment 1 of the present invention. Timing chart of motor drive device in same embodiment The figure explaining the optimal conduction angle of the motor drive device in the embodiment Another timing chart of the motor drive device in the same embodiment The figure which shows the relationship between the torque at the time of the synchronous drive of the brushless DC motor in the embodiment, and a phase The figure explaining the phase relationship of the phase current and terminal voltage of the brushless DC motor in the embodiment The figure explaining the relationship between the phase current and torque of the brushless DC motor in the same embodiment (A) The figure explaining the phase relationship of the brushless DC motor in the embodiment (B) The figure explaining the other phase relationship of the brushless DC motor in the embodiment The flowchart which shows operation | movement of the 2nd waveform generation part of the motor drive device in the embodiment The figure which shows the relationship between the rotation speed of the brushless DC motor in the same embodiment, and a duty Sectional drawing of the principal part of the brushless DC motor in the same embodiment Block diagram of a conventional motor drive device

  A first invention is a motor drive device for driving a brushless DC motor including a rotor and a stator having a three-phase winding, wherein an inverter for supplying power to the three-phase winding, and a conduction angle are A first waveform generator that outputs a first waveform signal having a waveform of 120 degrees or more and 150 degrees or less, current detection means that detects at least one-phase current flowing in the brushless DC motor, and detection by the current detection means An advance angle correction means for changing the terminal voltage advance angle of the brushless DC motor so as to keep the current value constant, and a duty is constant, and an advance angle value corrected by the advance angle correction means is arbitrarily set. A second waveform generator that outputs a second waveform signal having a waveform with a conduction angle of 120 degrees or more and less than 180 degrees at a frequency, and the output of the first waveform signal and the second waveform signal according to an operating state. And a switching determination unit for switching the drive signal, and a drive signal for instructing a supply timing of power supplied to the three-phase winding by the inverter based on the first or second waveform signal output from the switching determination unit. The drive unit that outputs to the motor enables stable driving without detecting the position of the motor. Therefore, stable driving is possible even at high speed / high load where the position of the brushless DC motor is difficult to detect. It becomes possible.

  According to the second aspect of the invention, in particular, the fact that the current value of the first aspect of the invention is kept constant, the average of the current values detected by the current detection means is set as a target, and the current value is brought closer to the target. The motor is driven at the most stable current value, and more stable driving is possible.

  In the third invention, in particular, the current value handled by the advance angle correction means of the first or second invention is set to the peak value of the current value detected by the current detection means. Since it is only necessary to compare whether or not the period is the maximum every time the current is detected, the calculation load necessary to keep the current constant can be reduced, and an inexpensive microcomputer can be realized.

  In the fourth aspect of the invention, in particular, the current value handled by the advance angle correction means of the first or second aspect of the invention is an integration result of an arbitrary phase range of the current value detected by the current detection means. Since only a limited range necessary for stable driving is detected, stable driving with higher accuracy is possible.

  In the fifth invention, in particular, when the advance angle correction means according to any one of the first to fourth inventions has a current value detected by the current detection means larger than a target current to be kept constant. Generating a second waveform by reducing the terminal voltage advance angle of the brushless DC motor and keeping the current constant by increasing the terminal voltage advance angle of the brushless DC motor when the terminal voltage advance angle is smaller than the target current. It is possible to control by a very simple method with only the commutation timing of the part, and it becomes possible to improve the maintainability of the software and realize it with an inexpensive microcomputer.

In a sixth aspect of the present invention, in particular, the brushless DC motor according to any one of the first to fifth aspects of the present invention,
The rotor has a permanent magnet embedded in the rotor core and has a rotor with saliency. This makes it possible to effectively use the reluctance torque due to the saliency as well as the magnet torque due to the permanent magnet in driving the brushless DC motor. Is possible.

  In the seventh invention, in particular, a compressor is used as a driving load of the brushless DC motor of the first invention. In the drive control of the compressor, high-precision rotation speed control, acceleration control, and the like are not required unlike industrial servomotor control. Further, the compressor has a load with a relatively large inertia, and it can be said that the fluctuation of the speed in a short time is a very small load. Therefore, even if the detection of the current phase is only one phase, the control accuracy such as speed fluctuation does not deteriorate, so it can be said that it is one of the very effective applications of the motor drive device of the present invention. In addition, by extending the drive area of the brushless DC motor compared to the conventional motor drive device, even when the same compressor as the conventional motor drive device is used, the refrigeration capacity can be increased, so the high-capacity refrigeration cycle can be downsized. Low price can be realized. Furthermore, if the motor drive device of the present invention is replaced with a refrigeration cycle using a conventional motor drive device, a compressor using a higher efficiency motor can be used, and the refrigeration cycle can be further improved in efficiency. Can be realized.

  In the eighth invention, in particular, the compressor of the seventh invention is a reciprocating compressor. As a result, the reciprocating type that performs reciprocating motion has a very large inertia, a larger inertia, and a high-speed torque because the rotor is structurally connected with a metal and heavy crankshaft and piston. Since the pulsation is small, it can be stably operated at a high speed.

  In the ninth invention, in particular, the refrigerant used in the compressor according to the seventh invention is R600a. As a result, the cylinder volume is increased in order to obtain the refrigerating capacity, the inertia is increased, and stable driving that is less likely to fluctuate depending on the speed and load becomes possible.

  The tenth aspect of the invention is an electric device using the motor driving device of any one of the first to fifth aspects of the invention. Thereby, when it uses for a refrigerator as an electric equipment, since load fluctuation | variation is not sudden, the more stable drive is attained. In addition, when used in an air conditioner as an electrical device, it can handle a wide driving range from the lowest load during cooling to the maximum load during heating, and can reduce power consumption particularly at low loads below the rating. .

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

(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 general commercial power source, and in Japan, a power source of 50 or 60 Hz with an effective value of 100V. The motor driving device 22 is connected to the AC power source 1 and drives the brushless DC motor 4. Hereinafter, the motor drive device 22 will be described.

  The rectifying and smoothing circuit 2 rectifies and smoothes AC power into DC power with the AC power supply 1 as an input, and includes four rectifying diodes 2a to 2d connected in a bridge and smoothing capacitors 2e and 2f. In the present embodiment, the rectifying / smoothing circuit 2 is configured by a voltage doubler rectifying circuit, but the rectifying / smoothing circuit 2 may be configured by a full-wave rectifying circuit. Further, in the present embodiment, the AC power source 1 is a single-phase AC power source, but when the AC power source 1 is a three-phase AC power source, the rectifying and smoothing circuit 2 is configured by a three-phase rectifying and smoothing circuit.

The inverter 3 converts the DC power from the rectifying / smoothing circuit 2 into AC power. Inverter 3
Is configured by connecting six switching elements 3a to 3f in a three-phase bridge connection. The six return current diodes 3g to 3l are connected to the switching elements 3a to 3f in the reverse direction.

  The brushless DC motor 4 includes a rotor 4a having a permanent magnet and a stator 4b having a three-phase winding. The brushless DC motor 4 rotates the rotor 4a when the three-phase alternating current generated by the inverter 3 flows in the three-phase winding of the stator 4b.

  The position detection unit 5 acquires the terminal voltage of the brushless DC motor 4 in the present embodiment. That is, the magnetic pole relative position of the rotor 4a of the brushless DC motor 4 is detected. Specifically, the position detector 5 detects the relative rotational position of the rotor 4a based on the induced voltage generated in the three-phase winding of the stator 4b. As another position detection method, there is a method of estimating the magnetic pole position by performing vector calculation on the detection result of the motor current (phase current or bus current).

  The first waveform generator 6 generates a first waveform signal for driving the switching elements 3 a to 3 f of the inverter 3. The first waveform signal is a rectangular wave signal with an energization angle of 120 degrees to 150 degrees. In order to smoothly drive the brushless DC motor 4 having the three-phase winding, the energization angle needs to be 120 degrees or more. On the other hand, in order for the position detection unit 5 to detect the position based on the induced voltage, an interval of 30 degrees or more is necessary as the ON / OFF interval of the switching element. For this reason, the upper limit of the conduction angle is 150 degrees obtained by subtracting 30 degrees from 180 degrees. The first waveform signal may be a waveform conforming to a rectangular wave, even if it is other than a rectangular wave. For example, it is a trapezoidal wave having a slope at the rise / fall of the waveform.

  The first waveform generation unit 6 generates a first waveform signal based on the position information of the rotor 4 a detected by the position detection unit 5. The first waveform generator 6 further performs pulse width modulation (PWM) duty control in order to keep the rotation speed constant. As a result, the brushless DC motor 4 is efficiently driven with an optimum duty based on the rotational position.

  The speed detector 7 detects the speed (that is, the rotational speed) of the brushless DC motor 4 based on the position information detected by the position detector 5. For example, 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 an arbitrary frequency required by the system. The duty is constant and the frequency is set by changing only the frequency.

  The current detecting means 9 detects a predetermined one-phase current value among the currents flowing through the brushless DC motor 4. In the present embodiment, a U-phase current is detected. The detected result is output to the advance correction means 10.

The advance angle correction means 10 sets a target current value from the current value detected by the current detection means 9, and corrects the terminal voltage advance angle of the brushless DC motor 4 according to the difference between the target value and the detected current value. Set the amount. The current value can be a peak of one cycle, an integrated current value in a specific range, or the like. The peak of the current value can be easily obtained by, for example, periodically sampling the current value at a sufficiently short interval of 1/10 or less of the current period, and comparing the maximum value within one period with the sampled value, An inexpensive configuration is possible. Further, the integrated current value can be calculated by periodically sampling the current value at a sufficiently short interval of, for example, 1/10 or less of the current cycle, and obtaining the sum of the positive current period, and suppressing variation. It can be obtained with high accuracy. In the present embodiment, the current value that matches the target is the current peak value. Further, the current target value is updated once in one cycle of the current, and a low pass filter or an average of the past several times is used. In the present embodiment, an average value of current peak values is set as a target current value. The average is, for example, the current peak value for each current cycle is stored for the past 10 times, the new current peak value is replaced with the oldest current peak value data, and the total of the 10 times of data is the total number. It is possible to calculate by dividing by 10, and can be easily calculated.

  The second waveform generation unit 11 generates a second waveform signal for driving the switching elements 3 a to 3 f of the inverter 3 based on the frequency from the frequency setting unit 8 and the position information from the position detection unit 5. To do. The second waveform signal is a rectangular wave signal having a conduction angle of 120 degrees or more and less than 180 degrees. As with the first waveform generator 6, the brushless DC motor 4 has a three-phase winding, so that the conduction angle needs to be 120 degrees or more for smooth and efficient driving. On the other hand, the second waveform generator 11 does not require the ON / OFF intervals of the switching elements, so the upper limit is set to less than 180 degrees. The second waveform signal may be a waveform that conforms to a rectangular wave. For example, it may be a sine wave or a distorted wave. In the present embodiment, the duty is at a maximum or close to the maximum (a constant duty of 90 to 100%).

  The switching determination unit 12 switches the signals from the first waveform generation unit 6 and the second waveform generation unit 11 according to the operation state and outputs the signals to the drive unit 13. Specifically, during driving with the signal of the first waveform generation unit 6, the speed of the speed detection unit 7 is lower than the frequency set by the frequency setting unit 8 and the maximum that can be output by the first waveform generation unit 6. When the duty and the energization angle are set, the signal is switched to the signal of the second waveform generation unit 11 and output to the drive unit 13. When these conditions are not satisfied, the signal output of the first waveform generator 6 is continued. If the signal from the position detector 5 becomes detectable during driving with the signal from the second waveform generator 11, the signal waveform is switched to the first waveform generator 6. While the signal from the position detector 5 cannot be detected, the signal of the second waveform generator 11 is output to the drive unit.

  Based on the waveform signal output from the switching determination unit 12, the drive unit 13 outputs a drive signal that instructs the supply timing of the power that the inverter 3 supplies to the three-phase winding of the brushless DC motor 4. Specifically, the drive signal turns on or off (hereinafter referred to as on / off) the switching elements 3a to 3f of the inverter 3. As a result, optimum AC power is applied to the stator 4b, the rotor 4a rotates, and the brushless DC motor 4 is driven.

  Next, an electric device using the motor driving device 22 in the present embodiment will be described. A refrigerator 21 will be described as an example of the electric device.

  Although the compressor 21 is mounted on the refrigerator 21, the rotational motion of the rotor 4a of the brushless DC motor 4 is converted into reciprocating motion by a crankshaft (not shown). A piston (not shown) connected to the crankshaft reciprocates in a cylinder (not shown) to compress the refrigerant in the cylinder. That is, the compressor 17 is constituted by the brushless DC motor 4 and the crankshaft, piston and cylinder.

  As a compression method (mechanism method) of the compressor 17, an arbitrary method such as a rotary type or a scroll type is used. In this embodiment, the case of the reciprocating type will be described. The reciprocating compressor 17 has a large inertia. For this reason, when the brushless DC motor 4 of the compressor 17 is driven synchronously, the drive of the compressor 17 is stabilized.

The refrigerant used for the compressor 17 is generally R134a or the like, but in the present embodiment, R600a is used as the refrigerant. R600a has a lower global warming potential than R134a, but has a low refrigeration capacity. In the present embodiment, the compressor 17 is constituted by a reciprocating compressor, and the cylinder volume is increased in order to ensure the refrigerating capacity. Since the compressor 17 having a large cylinder volume has a large inertia, the brushless DC motor 4 is rotated by the inertia even when the power supply voltage is lowered. As a result, fluctuations in the rotational speed are reduced, and more stable synchronous driving is possible. However, since the compressor 17 with a large cylinder volume has a large load, it is difficult to drive with the conventional motor drive device. The motor drive device 22 according to the present embodiment is optimal for driving the compressor 17 using R600a because the drive range particularly at high loads is expanded.

  The refrigerant compressed by the compressor 17 constitutes a refrigeration cycle in which the refrigerant passes through the condenser 18, the decompressor 19, and the evaporator 20 in this order and returns to the compressor 17 again. At this time, since the condenser 18 radiates heat and the evaporator 20 absorbs heat, cooling and heating can be performed. A refrigerator 21 is configured with this refrigeration cycle. Here, as another example of the electric device, an air conditioner is provided with a blower in the condenser 18 or the evaporator 20.

  The operation of the motor drive device 22 configured as described above will be described. First, the operation when the speed of the brushless DC motor 4 is low and the first waveform generator 6 is driving (at low speed) will be described. FIG. 2 is a timing chart of the motor driving device 22 in the present embodiment. In particular, FIG. 2 is a timing diagram of signals for driving the inverter 3 at a low speed. The signal for driving the inverter 3 is a drive signal output from the drive unit 13 to turn on / off the switching elements 3 a to 3 f of the inverter 3. In this case, the drive signal is obtained based on the first waveform signal. The first waveform signal is output from the first waveform generator 6 based on the output of the position detector 5.

  In FIG. 2, signals U, V, W, X, Y, and Z are drive signals for turning on / off switching elements 3a, 3c, 3e, 3b, 3d, and 3f, respectively. Waveforms Iu, Iv, and Iw are respectively U-phase, V-phase, and W-phase current waveforms of the winding of the stator 4b. Here, in driving at low speed, commutation is sequentially performed in intervals of 120 degrees based on a signal from the position detection unit 5. The signals U, V, and W perform duty control by PWM control. Waveforms Iu, Iv, and Iw, which are U-phase, V-phase, and W-phase current waveforms, are sawtooth waveforms as shown in FIG. In this case, commutation is performed at an optimal timing based on the output of the position detector 5. For this reason, the brushless DC motor 4 is driven most efficiently.

  Next, the optimum energization angle will be described with reference to FIG. FIG. 3 is a diagram for explaining an optimum energization angle of the motor drive device 22 in the present embodiment. In particular, FIG. 3 shows the relationship between the energization angle at low speed and the efficiency. In FIG. 3, line A shows circuit efficiency, line B shows motor efficiency, and line C shows total efficiency (product of circuit efficiency A and motor efficiency B). As shown in FIG. 3, when the energization angle is larger than 120 degrees, the motor efficiency B is improved. This is because the effective value of the phase current of the motor decreases (that is, the power factor increases) and the motor efficiency B increases as the copper loss of the motor decreases as the conduction angle increases. However, when the energization angle is larger than 120 degrees, the number of times of switching increases, and the switching loss may increase. In such a case, the circuit efficiency A decreases. From the relationship between the circuit efficiency A and the motor efficiency B, there is a conduction angle at which the overall efficiency C is the best. In the present embodiment, 130 degrees is the conduction angle at which the overall efficiency C is the best.

  Next, the operation when the speed of the brushless DC motor 4 is high and driven by the second waveform generator 11 (at high speed) will be described. FIG. 4 is a timing chart of the motor drive device 22 in the present embodiment. In particular, FIG. 4 is a timing diagram of drive signals for driving the inverter 3 at high speed. In this case, the drive signal is obtained based on the second waveform signal. The second waveform signal is output from the second waveform generator 11 based on the output of the frequency setting unit 8.

Signals U, V, W, X, Y, Z and waveforms Iu, Iv, Iw in FIG. 4 are the same as those in FIG. Each signal U, V, W, X, Y, and Z is commutated by outputting a predetermined frequency based on the output of the frequency setting unit 8. In this case, the conduction angle is 120 degrees or more and less than 180 degrees. FIG. 4 shows a case where the conduction angle is 150 degrees. By increasing the conduction angle, the current waveforms Iu, Iv, and Iw of each phase approximate to a sine wave.

  By increasing the frequency while keeping the duty constant, the maximum rotational speed can be significantly increased as compared with the conventional case, and the rotational speed is increased. When the rotational speed is increased, the motor is driven as a synchronous motor, and the current increases as the drive frequency increases. In this case, the peak current is suppressed by expanding the conduction angle to less than the maximum of 180 degrees. Therefore, even if the brushless DC motor 4 is driven at a higher current, it is operated without overcurrent protection.

  Here, the second waveform signal generated by the second waveform generator 11 will be described. FIG. 5 is a diagram showing the relationship between torque and phase when the brushless DC motor 4 is driven synchronously. In FIG. 5, the horizontal axis represents the motor torque, and the vertical axis represents the phase difference based on the phase of the induced voltage. When the phase is positive, the phase is positive with respect to the phase of the induced voltage. 5 showing the stable state in the synchronous drive, the line D1 indicates the phase of the phase current of the brushless DC motor 4, and the line E1 indicates the phase of the terminal voltage of the brushless DC motor 4. Here, since the phase of the phase current is ahead of the phase of the terminal voltage, it can be seen that the brushless DC motor 4 is driven at high speed by synchronous driving. As is clear from the relationship between the phase of the phase current and the phase of the terminal voltage shown in FIG. 5, there is little change in the phase of the phase current with respect to the load torque. On the other hand, since the phase of the terminal voltage changes linearly, the phase difference between the phase current and the terminal voltage changes almost linearly according to the load torque.

  Thus, in synchronous driving, the driving of the brushless DC motor 4 is stabilized in relation to the phase of the appropriate phase current and the phase of the terminal voltage in accordance with the driving speed and the load. FIG. 6 shows the relationship between the terminal voltage phase and the phase current phase in this case. In particular, FIG. 6 is a vector diagram showing the relationship between the phase of the phase current due to the load and the phase of the terminal voltage on the dq plane.

  In the synchronous drive, when the load increases, the phase of the terminal voltage vector Vt changes in the advance direction while keeping the magnitude almost constant. Referring to FIG. 6, the terminal voltage vector Vt rotates in the direction of arrow F. On the other hand, when the load increases, the current vector I changes in magnitude as the load increases (for example, the current increases as the load increases) while maintaining a substantially constant phase. This relationship is shown in FIG. In FIG. 7, the horizontal axis represents the motor torque, and the vertical axis represents the current value. A line H1 represents an average of current peaks for each cycle of a predetermined phase flowing through the brushless DC motor. As shown in FIG. 7, the current value increases as the torque increases. In this way, the phase relationship between the vectors is determined in an appropriate state in which the voltage vector and the current vector are in accordance with the driving environment (input voltage, load torque, driving speed, etc.).

Here, a temporal change in phase at a certain load or speed when the brushless DC motor 4 is synchronously driven in an open loop will be described with reference to the drawings. FIGS. 8A and 8B are diagrams for explaining the phase relationship of the brushless DC motor 4 and the current peak value at that time. In both figures, the line D2 indicates the phase of the phase current, the line E2 indicates the phase of the terminal voltage, and the line H2 indicates the peak value for each period of the phase current. Further, the horizontal axis represents time, the vertical axis represents the phase based on the phase of the induced voltage (that is, the phase difference from the induced voltage) for the lines D2 and E2, and the current value for the line H2. . FIG. 8A shows a driving state at a low load, and FIG. 8B shows a driving state at a high load. Further, since the phase of the phase current is advanced from the phase of the terminal voltage in both FIGS. 8A and 8B due to the difference from the phase of the induced voltage, the brushless DC motor 4 is very It turns out that it is driving at high speed.

  As shown in FIG. 8A, in the synchronous drive when the load is small with respect to the drive speed, the rotor 4a is delayed by an angle corresponding to the load with respect to the commutation. That is, when viewed from the rotor 4a, commutation advances and becomes a phase, and a predetermined relationship in which the current value is constant is maintained. That is, when viewed from the induced voltage, the phase of the terminal voltage and the phase current becomes a leading phase, and a predetermined relationship is maintained. Since this is the same state as the magnetic flux weakening control, high-speed driving is possible.

  On the other hand, as shown in FIG. 8B, when the load is large with respect to the driving speed, the rotor 4a is delayed with respect to the commutation, so that the magnetic flux is weakened, the phase current is increased, and the rotor 4a is increased. Accelerates to synchronize with the commutation cycle. Thereafter, due to the acceleration of the rotor 4a, the phase current decreases due to the decrease of the lead phase of the terminal voltage, and the rotor 4a decelerates. This state is repeated, and the rotor 4a repeats this acceleration and deceleration. As a result, the drive state (drive speed) is not stabilized eventually. That is, as shown in FIG. 8B, the rotation of the brushless DC motor 4 fluctuates with respect to the commutation performed at a constant cycle. For this reason, when the phase of the induced voltage is used as a reference, the phase of the terminal voltage varies. In such a driving state, the rotation of the brushless DC motor 4 fluctuates, and a swell sound is generated accordingly. Further, since the current pulsates, it is determined that the current is an overcurrent, and the brushless DC motor 4 may be stopped.

  Therefore, when the brushless DC motor 4 is synchronously driven in an open loop, the brushless DC motor 4 is stably driven when the load is small. However, the above disadvantage occurs when the load is large. That is, when the brushless DC motor 4 is synchronously driven in an open loop, it cannot be driven at high speed / high load, and the driving range is not expanded.

  Therefore, the motor drive device 22 in the present embodiment drives the brushless DC motor 4 in a state in which the phase of the phase current and the phase of the terminal voltage are kept in a phase relationship corresponding to the load as shown in FIG. . A method for maintaining the phase relationship between the phase of the phase current and the phase of the terminal voltage will be described below.

  The motor driving device 22 corrects the commutation timing (commutation with a constant period) so as to keep the current value that stabilizes the phase current flowing through the brushless DC motor 4 constant, and the phase of the phase current is calculated. The commutation timing that maintains the phase relationship with the terminal voltage phase is determined. Specifically, when the load on the brushless DC motor 4 increases and the rotor 4a starts to be delayed with respect to commutation, and the current increases due to the weakening magnetic flux effect, the weakening magnetic flux effect is reduced in order to decrease the current. Therefore, the terminal voltage advance angle is reduced. That is, commutation is delayed. Conversely, when the current decreases with respect to the target, the terminal voltage advance angle is increased in order to increase the current. That is, the commutation is accelerated. These advance angles may be changed once or more for one current cycle. Further, the target current value is increased when the load increases and the current value increases, and conversely when the current decreases, the target current is also decreased. However, the target must be a change amount sufficiently smaller than the advance angle adjustment cycle. In the present embodiment, the amount of change is 1/10 or less. The target current can be set according to the load by changing the target. These corrections are calculated by the advance angle correction means 10, and the second waveform generator 11 determines the commutation timing. Therefore, the waveform generated based on the commutation timing, that is, the second waveform signal is a waveform in which an appropriate torque is output with a current value corresponding to the load. The second waveform generator 11 outputs the generated second waveform signal to the drive unit 13. The operation of the advance angle correction means 10 will be described with reference to the flowchart of FIG.

  First, in step 101, the current detection means 9 detects the phase current flowing through the brushless DC motor, and the process proceeds to step 102.

In step 102, the advance angle correction means 10 determines whether or not the current value detected this time by the current detection means 9 is larger than the maximum current of one phase current of the brushless DC motor 4. If the current value is larger than the maximum current (Yes in step 102), the process proceeds to step 103. If the current value is equal to or less than the maximum current (No in step 102), the process proceeds to step 104.

  In step 103, since the current value detected this time is larger than the maximum current, the maximum current is updated. As a result, the maximum current is always substituted for the maximum current, and the peak of the current of the brushless DC motor 4 can be detected. Next, proceed to step 104.

  In step 104, it is determined whether or not the specific phase current flowing through the brushless DC motor 4 is commutated at a timing that does not necessarily peak. In this embodiment, the characteristic phase is the U phase, and the switch on the W phase is turned on as the commutation timing at which the U phase current does not necessarily reach the peak. That is, if it is the timing when the switching element 3e is turned on (Yes in step 104), the process proceeds to step 105. If not (No in step 104), the process returns to step 101 and the process is repeated.

  In step 105, it is determined whether or not the maximum current that is the current peak value of the current cycle is larger than the current average value that is the average value of the current peak values that are targets for making the current constant. If larger (Yes in step 105), the process proceeds to step 106.

  In step 106, since the current peak is larger than the target value, it is necessary to reduce the current value, and the correction amount is determined so as to reduce the magnetic flux weakening effect by reducing the advance angle (that is, by setting the commutation timing). This correction amount is determined according to the difference between the current average value as the target value and the maximum current as the current peak value. If the difference is large, the correction amount is increased, and if the difference is small, the correction amount is decreased. This enables driving that absorbs fluctuations in the strength of the weakening magnetic flux of the motor. Next, the routine proceeds to step 107.

  In step 107, the current average value is updated. If the target of the current to be stabilized is always constant, the current corresponding to the load cannot be output, so the current average needs to be updated. The average is obtained from the maximum current for the past 10 times, and the new current average value is calculated including the maximum current detected this time, excluding the oldest current average value. As a result, the target current average value increases as the load increases, and the target current average value decreases as the load decreases. Therefore, a target value corresponding to the load can be set. In addition, the change amount is 1/10 of the correction amount and does not become unstable. Next, the routine proceeds to step 108.

  In step 108, the maximum current is cleared to zero. Since this is executed once in one cycle, the maximum current has a peak value of one cycle of current.

  On the other hand, in step 105, it is determined whether or not the maximum current, which is the current peak value of the current cycle, is large. If small (No in step 105), the process proceeds to step 109. In step 109, since the current peak is smaller than the target value, it is necessary to increase the current value, and the correction amount is determined so as to increase the advance angle (that is, advance the commutation timing). This correction amount is determined according to the difference between the current average value as the target value and the maximum current as the current peak value. If the difference is large, the correction amount is increased, and if the difference is small, the correction amount is decreased. As a result, it is possible to perform driving that absorbs fluctuations in the weakening of the magnetic flux weakening of the motor. Next, the routine proceeds to step 107.

By executing these series of processes at least once in one cycle of current, a necessary current corresponding to the load state of the brushless DC motor 4 is output, and the second waveform generator that enables stable driving outputs. Next, the switching operation by the switching determination unit 12 will be described.

  FIG. 10 is a diagram illustrating the relationship between the rotation speed and the duty of the brushless DC motor 4 in the present embodiment.

  In FIG. 10, when the rotational speed of the brushless DC motor 4, that is, the rotational speed of the rotor 4 a is 50 r / s or less, the brushless DC motor 4 is driven based on the first waveform signal from the first waveform generator 6. Is done. The duty is adjusted to the most efficient value according to the rotational speed by feedback control.

  The rotation speed is 50 r / s, the duty is 100%, and the driving based on the first waveform generator 6 cannot be further rotated. That is, the limit is reached. In this state, when the rotation speed (in this case, 75 r / s) set by the frequency setting unit 8 exceeds 50 r / s, the duty is constant until the rotation speed command, and the frequency (that is, the commutation cycle). ) Only, and the brushless DC motor 4 is driven.

  On the other hand, when a command of 50 r / s or less (here 45 r / s) is generated from the frequency setting unit 8 during driving at 75 r / s, the second waveform generation unit 11 gradually decreases the frequency of the drive signal. . When the position reaches 50 r / s, the position detection unit 5 can detect the position detection signal of the brushless DC motor 4 and is input to the switching determination unit 12. Here, since the position detection signal is input to the switching determination unit 12, the drive signal is switched from the second waveform generation unit 11 to the drive signal of the first waveform generation unit 6. Accordingly, the second waveform generator 11 capable of high speed / high load operation and the first waveform generator 6 having high stability at low speed or low load can be switched and operated. By setting the upper limit frequency in advance by the system, an optimal motor that can drive the upper limit frequency can be selected, and reliability can be ensured.

  In addition, when switching from the second waveform generation unit to the drive signal of the first waveform generation unit 6, hysteresis such as switching at a frequency further lowered by 2 Hz after the position detection signal is input to the switching determination unit 12. By providing, the 1st waveform generation part 6 can drive stably more reliably.

  Next, the structure of the brushless DC motor 4 of the present embodiment will be described. FIG. 11 is a cross-sectional view showing a cross section perpendicular to the rotation axis of the rotor of the brushless DC motor 4 in the present embodiment.

  The rotor 4a includes an iron core 4g and four magnets 4c to 4f. The iron core 4g is configured by stacking punched thin steel sheets of about 0.35 to 0.5 mm. As the magnets 4c to 4f, arc-shaped ferrite permanent magnets are often used, and as illustrated, the magnets 4c to 4f are arranged symmetrically with the arc-shaped concave portions facing outward. On the other hand, when rare earth permanent magnets such as neodymium are used as the magnets 4c to 4f, they may be flat.

  In the rotor 4a having such a structure, an axis extending from the center of the rotor 4a toward the center of one magnet (for example, 4f) is defined as a d-axis, and one magnet (for example, 4f) is connected to the center of the rotor 4a. The axis that goes to the magnet adjacent to (for example, 4c) is the q axis. The inductance Ld in the d-axis direction and the inductance Lq in the q-axis direction have opposite saliency and are different. That is, this can effectively use torque (reluctance torque) using reverse saliency as well as torque (magnet torque) due to magnetic flux of the magnet. Therefore, torque can be used more effectively as a motor. As a result, a highly efficient motor is obtained as the present embodiment.

In the control of the present embodiment, when driving is performed by the frequency setting unit 8 and the second waveform generation unit 11, the phase current becomes a leading phase. For this reason, since this reluctance torque is largely used, it can be driven at a higher rotation than a motor without reverse saliency.

  Further, the brushless DC motor 4 of the present embodiment has a rotor 4a in which permanent magnets 4c to 4f are embedded in an iron core 4g and has saliency. In addition to the magnet torque of the permanent magnet, reluctance torque due to saliency is used. This not only improves efficiency at low speeds, but also improves high-speed drive performance. Also, if a rare earth magnet such as neodymium is used as the permanent magnet to increase the ratio of magnet torque, or the difference between inductances Ld and Lq is increased to increase the ratio of reluctance torque, the optimum conduction angle can be changed. Can increase efficiency.

  Next, the case where the compressor 17 is driven using the motor drive device 22 of the present embodiment for the refrigerator 21 and the air conditioner will be described. In the case of a conventional motor driving device, it is necessary to use a brushless DC motor that secures a necessary torque by reducing the number of windings in order to support high-speed / high-load driving. Such a brushless DC motor has a large motor noise. If the motor drive device 22 of the present embodiment is used, even if the brushless DC motor 4 in which the winding amount of the winding is increased and the torque is reduced is used, it can be driven at high speed / high load. As a result, the duty when the rotational speed is low can be made larger than when the conventional motor driving device is used. Therefore, motor noise, particularly carrier sound (corresponding to a frequency in PWM control, for example, 3 kHz) can be reduced.

  In addition, since the compressor 17 is a reciprocating compressor, the inertia is larger and the torque pulsation at a high speed is small. Therefore, the compressor 17 can be stably operated at a high speed. Further, when the compressor 17 is mounted on the refrigerator 21, the load of the refrigerator 21 is not suddenly changed, so that the change in the phase difference between the phase of the phase current and the phase of the terminal voltage is small, and more stable driving is possible. .

  In the case of driving the compressor 17 of the air conditioner using the motor driving device 22 of the present embodiment, it is possible to cope with a wide driving range from the lowest load during cooling to the maximum load during heating. It is possible to reduce power consumption at a low load below the rating.

  As described above, the present invention is a motor driving apparatus for driving a brushless DC motor 4 including a rotor 4a and a stator 4b having a three-phase winding, and an inverter that supplies power to the three-phase winding. 3, a first waveform generator 6 that outputs a first waveform signal having a waveform with a conduction angle of 120 degrees or more and 150 degrees or less, and current detection means 9 that detects at least one-phase current flowing in the brushless DC motor 4. The advance angle correction means 10 for changing the terminal voltage advance angle of the brushless DC motor 4 so as to keep the current value detected by the current detection means 9 constant, and the duty is constant and set by the advance angle correction means 10 A second waveform generator 11 that outputs a second waveform signal having a waveform with a conduction angle of 120 degrees or more and less than 180 degrees at an advance angle value and an arbitrarily set frequency; a first waveform signal 6; Waveform signal The switching determination unit 12 that switches the output of 10 according to the operating state, and the drive that instructs the supply timing of the power that the inverter 3 supplies to the three-phase winding based on the first or second waveform signal output from the switching determination unit Since the drive unit 13 that outputs a signal to the inverter 3 has stable driving without detecting the position of the motor, the position of the brushless DC motor 4 is difficult to detect at high speed / high load. Even if it is, stable driving is possible.

  In the present invention, the current value is kept constant. The average current value detected by the current detection means 9 is set as a target, and the current value is brought close to the target, so that the motor is driven at the most stable current value. Thus, more stable driving is possible.

Further, according to the present invention, since the current value handled by the advance angle correction means 10 is set to the peak value of the current value detected by the current detection means, the calculation load necessary for constant current can be reduced, and an inexpensive microcomputer Realization is possible.

  In addition, since the current value handled by the advance angle correction means 10 is made constant in the integration result of an arbitrary phase range of the current value detected by the current detection means 9, only a limited range necessary for stable driving is obtained. Since this is detected, stable driving with higher accuracy is possible.

  Further, the present invention reduces the terminal voltage advance angle of the brushless DC motor 4 when the advance angle correction means 10 has a current value detected by the current detection means 9 larger than a target current to be kept constant, When the current is kept constant by increasing the terminal voltage advance angle of the brushless DC motor 4 when the current is smaller than the target current, the control can be performed only by the commutation timing of the second waveform generator 11. It becomes possible to improve maintainability and to realize with a low-cost microcomputer.

  In the present invention, the brushless DC motor 4 is a rotor in which a permanent magnet is embedded in the iron core of the rotor 4a and has a rotor having saliency. This makes it possible to effectively use the reluctance torque due to the saliency as well as the magnet torque due to the permanent magnet in driving the brushless DC motor. Is possible.

  In the present invention, the compressor 17 is used as a driving load of the brushless DC motor 4. The drive control of the compressor 17 does not require high-precision rotation speed control, acceleration control, or the like, unlike industrial servo motor control. Further, the compressor 17 is a load having a relatively large inertia, and it can be said that the fluctuation of the speed in a short time is a very small load. Therefore, even if the detection of the current phase is only one phase, the control accuracy such as speed fluctuation does not deteriorate, so it can be said that it is one of the very effective applications of the motor drive device of the present invention. In addition, by extending the drive area of the brushless DC motor compared to the conventional motor drive device, even when the same compressor as the conventional motor drive device is used, the refrigeration capacity can be increased, so the high-capacity refrigeration cycle can be downsized. Low price can be realized. Furthermore, if the motor drive device of the present invention is replaced with a refrigeration cycle using a conventional motor drive device, a compressor using a higher efficiency motor can be used, and the refrigeration cycle can be further improved in efficiency. Can be realized. Furthermore, since a higher torque than that of the conventional driving method can be output, a brushless DC motor in which the amount of winding is increased to reduce the torque can be used to reduce motor noise, particularly carrier noise.

  In the present invention, the compressor 17 is a reciprocating compressor. As a result, the reciprocating type that performs reciprocating motion has a very large inertia, a larger inertia, and a high-speed torque because the rotor is structurally connected with a metal and heavy crankshaft and piston. Since the pulsation is small, it can be stably operated at a high speed.

  In the present invention, the refrigerant used in the compressor 17 is R600a. As a result, the cylinder volume is increased in order to obtain the refrigerating capacity, the inertia is increased, and stable driving that is less likely to fluctuate depending on the speed and load becomes possible.

  Further, the present invention is an electric device using the motor driving device 22. Thereby, when it uses for the refrigerator 21 as an electric equipment, since the load fluctuation | variation is not steep, the more stable drive is attained. In addition, when used in an air conditioner as an electrical device, it can handle a wide driving range from the lowest load during cooling to the maximum load during heating, and can reduce power consumption particularly at low loads below the rating. .

The present invention also relates to an electric device using the motor drive device having the above-described configuration. Thereby, when it uses for a refrigerator as an electric equipment, since load fluctuation | variation is not sudden, the more stable drive is attained. In addition, when used in an air conditioner as an electrical device, it can handle a wide driving range from the lowest load during cooling to the maximum load during heating, and can reduce power consumption particularly at low loads below the rating. .

  The motor drive device of the present invention is intended to improve the drive stability of a brushless DC motor at high speed / high load and to extend the drive range. Thereby, it can be applied not only to refrigerators and air conditioners but also to higher efficiency of compressors in vending machines, showcases, and heat pump water heaters. In addition, the present invention can be applied to energy saving of electric devices using brushless DC motors such as washing machines, vacuum cleaners, and pumps.

3 Inverter 4 Brushless DC motor 4a Rotor 4b Stator 4c, 4d, 4e, 4f Magnet (permanent magnet)
4g Iron core 5 Position detector (terminal voltage acquisition unit)
6 First waveform generation unit 8 Frequency setting unit 9 Current detection unit 10 Advance angle correction unit 11 Second waveform generation unit 12 Switching determination unit 13 Drive unit 17 Compressor 21 Refrigerator (electric equipment)
22 Motor drive device

Claims (10)

A motor driving apparatus for driving a brushless DC motor including a rotor and a stator having a three-phase winding, wherein an inverter that supplies power to the three-phase winding and a conduction angle of 120 degrees to 150 degrees A first waveform generator that outputs a first waveform signal that is a waveform of the current, a current detector that detects at least one-phase current flowing in the brushless DC motor, and a current value detected by the current detector is constant. The advance angle correction means for correcting the terminal voltage advance angle of the brushless DC motor so as to maintain the current, and the advance angle value corrected by the advance angle correction means and the arbitrarily set frequency, while maintaining the duty constant, A second waveform generator that outputs a second waveform signal having a waveform of 120 degrees or more and less than 180 degrees, and the output of the first waveform signal and the second waveform signal are switched depending on the operating state. Based on the switching determination unit to be switched and the first or second waveform signal output from the switching determination unit, a drive signal for instructing the supply timing of power supplied to the three-phase winding by the inverter is sent to the inverter. A motor drive unit having an output drive unit. The motor driving device according to claim 1, wherein keeping the current value constant means that the current value is brought close to a target with an average of the current values detected by the current detecting means as a target. The motor drive device according to claim 1 or 2, wherein the current value that the advance angle correction means tries to keep constant is a peak value of the current value detected by the current detection means. 3. The motor driving device according to claim 1, wherein the current value that the advance angle correction unit tries to keep constant is an integration result of an arbitrary phase range of the current value detected by the current detection unit. The advance angle correction means decreases the terminal voltage advance angle of the brushless DC motor when the current value detected by the current detection means is larger than a target current to be kept constant, and is less than the target current. 5. The motor driving device according to claim 1, wherein the current is kept constant by increasing a terminal voltage advance angle of the brushless DC motor when the voltage is small. 6. The motor drive device according to claim 1, wherein the rotor of the brushless DC motor is configured by embedding a permanent magnet in an iron core, and further has a saliency. 6. The motor driving apparatus according to claim 1, wherein the brushless DC motor drives a compressor. The motor driving device according to claim 7, wherein the compressor is a reciprocating compressor. The motor driving device according to claim 7, wherein the refrigerant used in the compressor is R600a. An electric device comprising a brushless DC motor driven by the motor drive device according to claim 1.