JP3672637B2 - Compressor motor control device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a control device for an electric motor for a compressor (particularly a brushless motor) used in a refrigeration system such as a refrigerator or an air conditioner.
[0002]
[Prior art]
Brushless motors are widely used because they are highly efficient and the number of revolutions can be controlled by voltage control. In particular, since a method for detecting a rotational position from a back electromotive voltage generated in a winding voltage of a motor has been proposed as a technique that eliminates the need for a position detecting element for detecting the rotational position of a brushless motor in recent years, compression used particularly in a refrigeration system is proposed. It has come to be used frequently even in places where the operating environment is extremely poor, such as in machines where there are refrigerants and oil inside.
[0003]
For example, it describes in the case of applying to a refrigerator in Unexamined-Japanese-Patent No. 3-55478 etc. A conventional compressor motor control device will be described below with reference to the drawings.
[0004]
FIG. 10 is a block diagram of a conventional compressor motor control device. In FIG. 10, reference numeral 101 denotes a brushless motor, which operates the compression mechanism 102 via a shaft.
[0005]
Reference numeral 103 denotes a commercial power supply, for example, an AC power supply of 100 V 60 Hz in a general household. Reference numeral 104 denotes a rectifier circuit for rectifying the commercial power supply 103. Here, a voltage doubler rectification system is adopted, and AC 100V is input and DC 250V is output.
[0006]
Reference numeral 105 denotes an inverter, which has a configuration in which switching elements are connected in a three-phase bridge, converts the DC output of the rectifier circuit 103 into an output of an arbitrary voltage and an arbitrary frequency of three phases, and supplies power to the brushless motor 101.
[0007]
Reference numeral 106 denotes a counter electromotive voltage detection circuit that detects the relative position of the rotor rotation from the counter electromotive voltage of the stator winding of the brushless motor 101. Reference numeral 107 denotes a drive circuit that turns on / off the switching element of the inverter 105.
[0008]
Reference numeral 108 denotes a commutation circuit, which determines which element of the inverter 105 is turned on by the output of the back electromotive voltage detection circuit 106 when the brushless motor 101 is in steady operation.
[0009]
Reference numeral 109 denotes a PWM control circuit, which chops only the switching elements of the upper arm or the lower arm of the switching element of the inverter 105 and performs PWM (pulse width modulation) control. The output voltage can be increased / decreased by increasing / decreasing the duty of the pulse width (ratio of the ON period in the pulse period).
[0010]
Next, the operation of the compressor motor control device configured as described above will be described.
[0011]
When the brushless motor 101 is started from a stopped state, no back electromotive voltage is generated, and therefore position detection is impossible. Accordingly, a low frequency, low duty output is forcibly output from the inverter 105 to forcibly start rotation (generally referred to as low frequency synchronous start).
[0012]
When the rotation increases to some extent, a counter electromotive voltage is generated in the stator winding of the brushless motor 101, and the position detection signal from the counter electromotive voltage detection circuit 106 is processed by the commutation circuit 108 and applied to the drive circuit 107. Thus, an operation as a normal DC motor (closed loop control by a position signal) is performed.
[0013]
In the DC motor, the rotational speed can be controlled by changing the voltage. When the duty from the PWM control circuit 109 is increased, the rotational speed increases, and conversely, when the duty is decreased, the rotational speed decreases.
[0014]
Since the output of the position detection signal of the back electromotive voltage detection circuit 106 is completely synchronized with the rotation of the rotor, the rotation speed of the motor can be controlled by detecting the rotation speed from this signal and adjusting the duty. .
[0015]
The characteristics when operating as a DC motor will be described next. FIG. 11 is a torque characteristic diagram of the DC motor. The horizontal axis represents torque, and the vertical axis represents the rotational speed and the current flowing through the motor.
[0016]
R1 is the torque = rotational speed characteristic when the duty is 100% (maximum voltage). As the torque increases, the rotational speed decreases. I1 is a current flowing through the motor at that time, and increases substantially in proportion to the torque.
[0017]
Lm is the maximum load point in the refrigeration system, which is the maximum torque Tm and the maximum rotation speed Rm. In this respect, in order to secure the refrigeration performance, it is necessary to secure the rotation speed Rm.
[0018]
Therefore, when designing a motor, the design is performed so that the maximum load point can be operated. That is, the design is performed such that the rotational speed characteristic R1 is located above the maximum load point Lm (in this case, it is necessary to set a margin in consideration of an influence such as a decrease in input voltage).
[0019]
[Problems to be solved by the invention]
However, the conventional configuration has the following problems.
[0020]
In order to be able to obtain the maximum load point Lm in FIG. 11, the motor is designed as R1, but since the motor is a high output, the motor current itself inevitably increases as a whole. Therefore, there is a problem that the motor current increases even at the torque Tn for normal operation, and the efficiency of the inverter deteriorates.
[0021]
In order to solve this problem, for example, by reducing the motor output and designing a motor having the rotation speed characteristic R2 and current characteristic I2 in FIG. 11, the current decreases and the efficiency becomes high, but at this time the maximum load point Lm is cleared. This is not possible and the rotational speed will decrease.
[0022]
The present invention solves the conventional problems, and provides a highly efficient compressor motor control device that can expand the operating range so that a desired rotational speed can be obtained at the maximum load point even with a motor with improved rotational speed characteristics. The purpose is to do.
[0023]
Another object of the present invention is to provide a compressor motor control device capable of detecting a load, switching the operation method optimally, preventing the rotation speed from decreasing, and ensuring the refrigerating capacity.
[0024]
Another object of the present invention is to provide a compressor motor control device that can stabilize the operation even in the vicinity of switching of the operation method.
[0025]
Another object of the present invention is to provide a compressor motor control device that can quickly return to the original operating state when the load becomes light by detecting the load during operation corresponding to a high load. The purpose is to do.
[0026]
Another object of the present invention is to detect the load at the time of operation corresponding to a high load, thereby further reducing the number of revolutions before the motor reaches a stop because the load further increases. It is an object of the present invention to provide a compressor motor control device that can avoid the above.
[0027]
[Means for Solving the Problems]
In order to achieve this object, the compressor motor control device of the present invention isA commutation circuit for generating a waveform for driving the inverter from a signal of the back electromotive voltage detection circuit, a synchronous drive circuit for generating a waveform for operating a brushless motor as a synchronous motor, and a waveform output from the inverter for the commutation circuit or And a switching circuit for switching to one of the synchronous drive circuits.
[0028]
Also,A commutation circuit for generating a waveform for driving an inverter from a signal of a back electromotive voltage detection circuit, a synchronous drive circuit for generating a waveform for operating a brushless motor as a synchronous motor, and a load state for determining a load state of the brushless motor And a switching circuit for switching a waveform output from the inverter by the load state determination circuit to either the commutation circuit or the synchronous drive circuit.
[0029]
In addition, it is configured from a duty determination circuit that determines that the duty is maximized and outputs a waveform output from the inverter from the synchronous drive circuit.
[0030]
In addition, a duty determination circuit that determines that the duty is maximized and outputs the waveform output from the inverter from the synchronous drive circuit, and a commutation circuit that starts counting when the synchronous drive circuit is switched over and a certain time has elapsed And a first timer circuit for outputting from the first timer circuit.
[0031]
Also, the duty determination circuit that determines that the duty is maximized and outputs the waveform output from the inverter from the synchronous drive circuit, and the phase difference between the signal of the counter electromotive voltage detection circuit and the signal of the synchronous drive circuit are detected. When the phase difference disappears, the phase determination circuit switches to the output from the commutation circuit.
[0032]
And a frequency adjustment circuit that detects a phase difference between the signal of the back electromotive voltage detection circuit and the signal of the synchronous drive circuit and reduces the output frequency from the synchronous drive circuit when the phase difference becomes smaller than a predetermined value. Yes.
[0033]
[Action]
The compressor motor control device of the present invention detects a load state of a brushless motor by a load state determination circuit, and when it is in a high load state, it switches to operate as a synchronous motor, and even a motor with improved rotational speed characteristics. The operating range can be expanded so that a desired number of revolutions can be obtained at the maximum load point, and high-efficiency operation is possible at normal loads.
[0034]
In addition, it can be said that it is a limit that the DC motor cannot produce any more capacity when the duty becomes maximum, so the load is detected from this duty, and when the duty becomes maximum, the operation method is switched to operation as a synchronous motor, The number of rotations does not decrease, and the refrigerating capacity can be secured.
[0035]
Further, once the operation as the synchronous motor is switched, the operation can be stabilized even in the vicinity where the operation method is switched by operating the first timer circuit and continuing the operation for a certain time.
[0036]
Also, when operating as a synchronous motor, the load is predicted by detecting the phase difference between the signal of the back electromotive voltage detection circuit and the signal of the synchronous drive circuit, and when the phase difference disappears, By returning to the operation of the DC motor, it is possible to quickly return to the original operation state when the load is light.
[0037]
Also, when operating as a synchronous motor, if the phase difference is smaller than a predetermined value, the out-of-step torque can be improved by lowering the output frequency from the synchronous drive circuit, and the load increases. The worst state of motor stop can be avoided by reducing the rotation speed before the motor stops.
[0038]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0039]
FIG. 1 is a block diagram of a compressor motor control apparatus according to an embodiment of the present invention. In FIG. 1, 1 is a compressor. Reference numeral 2 denotes a shell of the compressor 1.
[0040]
Reference numeral 3 denotes a brushless motor, which includes a rotor 3a and a stator 3b. The rotor 3a has permanent magnets arranged around it (for example, in the case of 4 poles, an NSNS pole is placed every 90 degrees).
[0041]
A shaft 4 is fixed to the rotor 3a and rotates in the bearing 5 when the rotor 3a rotates. An eccentric portion 4 a is provided at the lower portion of the shaft 4. Further, an oil supply pump 6 is provided at the lower part.
[0042]
Reference numeral 7 denotes a piston, and the rotational movement of the shaft 4 is changed to a reciprocating movement by the eccentric portion 4a, and the piston 7 reciprocates in the cylinder 8 to compress the refrigerant. The compressed refrigerant exits from the discharge pipe 9 and is discharged from the suction pipe 10 into the shell 2 of the compressor 1 through a cooling system (not shown) such as a condenser, an expander, and an evaporator.
[0043]
Reference numeral 11 denotes a commercial power source, for example, a 100 V 60 Hz AC power source in a general home. Reference numeral 12 denotes a rectifier circuit for rectifying the commercial power supply 11, which employs a voltage doubler rectification method, with AC 100V as an input and DC 250V as an output.
[0044]
Reference numeral 13 denotes an inverter, which has a configuration in which switching elements are connected in a three-phase bridge, converts the DC output of the rectifier circuit 12 into an output of a three-phase arbitrary voltage and arbitrary frequency, and supplies power to the brushless motor 3.
[0045]
Reference numeral 14 denotes a counter electromotive voltage detection circuit that detects the relative position of the rotation of the rotor 3a from the counter electromotive voltage of the winding of the stator 3b of the brushless motor 3. A drive circuit 15 turns on / off the switching element of the inverter 13.
[0046]
Reference numeral 16 denotes a commutation circuit which determines which element of the inverter 13 is turned on by the output of the back electromotive voltage detection circuit 14 when the brushless motor 3 is in steady operation.
[0047]
Reference numeral 17 denotes a synchronous drive circuit, which outputs a predetermined frequency and a predetermined voltage (predetermined duty) when the brushless motor 3 is operated as a synchronous motor.
[0048]
Reference numeral 18 denotes a switching circuit that switches a signal to be sent to the drive circuit between the signal of the commutation circuit 16 and the signal of the synchronous drive circuit 17.
[0049]
Reference numeral 19 denotes a PWM control circuit, which chops only the switching elements of the upper arm or the lower arm of the switching element of the inverter 13 to perform PWM (pulse width modulation) control. The output voltage can be increased / decreased by increasing / decreasing the duty of the pulse width (ratio of the ON period in the pulse period).
[0050]
A load state determination circuit 20 determines the load state of the brushless motor 3 and determines the switching of the operation mode by the switching circuit 18.
[0051]
Reference numeral 21 denotes a first timer circuit which starts a timer when the operation is switched to the synchronous drive circuit 17 and ends when a predetermined time t1 elapses.
[0052]
Reference numeral 22 denotes a duty determination circuit, which detects the maximum load when the duty reaches a maximum (100%).
[0053]
Reference numeral 23 denotes a phase determination circuit that detects the phase difference between the signal of the back electromotive voltage detection circuit 14 and the signal of the synchronous drive circuit 17 and can know the current load state.
[0054]
Reference numeral 24 denotes a frequency adjustment circuit that detects the phase difference between the signal of the back electromotive voltage detection circuit 14 and the signal of the synchronous drive circuit 17 and outputs a signal from the synchronous drive circuit 17 when the phase difference becomes smaller than a predetermined value. Reduce the output frequency.
[0055]
The operation of the compressor motor control apparatus configured as described above will be described below with reference to FIG.
[0056]
When the brushless motor 3 is started from a stopped state, no back electromotive voltage is generated, so position detection is impossible. Therefore, a low frequency, low duty output is forcibly output from the inverter 13 to forcibly start rotation (generally referred to as low frequency synchronous activation).
[0057]
After that, when acceleration is performed and the rotation increases to some extent (about 10 r / sec), a counter electromotive voltage is generated in the stator winding of the brushless motor 3, and position detection by the counter electromotive voltage detection circuit 14 becomes possible.
[0058]
A position detection signal from the back electromotive voltage detection circuit 14 is processed by the commutation circuit 16 and applied to the drive circuit 15 via the switching circuit 18 to perform an operation as a normal DC motor (closed loop control based on the position signal). It becomes.
[0059]
In operation as a DC motor, the rotational speed can be controlled by changing the voltage. Increasing the duty from the PWM control circuit 19 increases the rotational speed, and conversely, decreasing the duty decreases the rotational speed. Become.
[0060]
The PWM control is called pulse width modulation and adjusts the voltage by duty. The duty is ON cycle / carrier cycle and takes a value of 0 to 100%.
[0061]
The carrier period is determined by the carrier frequency, and is generally several kHz to several tens of kHz. The voltage increases as the duty value increases.
[0062]
The synchronous drive circuit 17 outputs an output when the brushless motor is operated as a synchronous motor, and can output an output with a predetermined frequency and a predetermined duty. At this time, it becomes a characteristic as a synchronous motor.
[0063]
The load state determination circuit 20 determines the load state of the brushless motor 3. When the load state is determined and it is determined that the load is high, the operation is switched to the operation by the synchronous drive circuit 17.
[0064]
Further, since the output of the position detection signal of the back electromotive voltage detection circuit 14 is completely synchronized with the rotation of the rotor, the rotation speed of the motor is detected by detecting the rotation speed from this signal and adjusting the duty of the PWM control circuit 19. The number can be controlled.
[0065]
The characteristics obtained by performing the operation as described above will be described with reference to FIG. FIG. 2 is a characteristic diagram showing the operating range of the brushless motor in the present embodiment. The horizontal axis represents torque and the vertical axis represents the rotational speed.
[0066]
R2 is a torque = rotational speed characteristic at a duty of 100% (maximum voltage) of a motor designed to reduce the output in order to increase efficiency as described in the conventional example.
[0067]
When the brushless motor is operated only as a DC motor, the region where the rotational speed can be controlled is the region A shown in FIG. 2, and the maximum rotational speed and the maximum torque are limited due to the characteristic R2. Understand.
[0068]
Therefore, the operation in the region B is also possible by operating the brushless motor as a synchronous motor. The lack of a region with high rotation speed and high torque in region B indicates that the step-out torque of the synchronous motor is in this part.
[0069]
Next, the operation of the present embodiment will be described in more detail with reference to FIGS. FIG. 3 is a flowchart of the compressor motor control device in this embodiment.
[0070]
In FIG. 3, in STEP1, the brushless motor is operated as a DC motor. That is, the output from the inverter 13 is selected by the switching circuit 18 from the commutation circuit 16.
[0071]
Next, in STEP2, the duty determination circuit 22 determines whether or not the duty output from the PWM control circuit 19 is 100% (maximum). If the duty is less than 100%, it is determined that there is still a margin in performance, and the operation as STEP 1, that is, the DC motor is continued. If the duty is 100%, the process proceeds to STEP3.
[0072]
Next, in STEP 3, it is determined whether or not the current actual rotational speed is lower than the target rotational speed. If it is not lowered, it is determined that the duty is 100%, which is the maximum state, but is still at the limit, and the operation as STEP 1, that is, the DC motor is continued.
[0073]
If the rotational speed is reduced, it is determined that the operating range of the DC motor is no longer exceeded due to the load, and the process proceeds to STEP4.
[0074]
Next, in STEP 4, the switching circuit 18 switches to the operation in the synchronous drive circuit 17. At this time, the frequency of the signal output from the synchronous drive circuit 17 corresponds to the target rotational speed (for example, a frequency of 140 Hz if 70 r / sec is the target and a 4-pole motor), and the duty is 100%.
[0075]
Next, in STEP5, the time from the start of operation as a synchronous motor is counted, and if the predetermined time t1 has not elapsed, the operation of STEP4 as a synchronous motor is repeatedly continued.
[0076]
When the predetermined time t1 elapses, the process returns to STEP1, the operation as the DC motor is executed again, and the process is repeated from STEP1. At this time, if the load is still high, the operation as a synchronous motor is resumed in the same procedure, and if the load is light, the operation as a DC motor is resumed.
[0077]
Next, characteristics when the operation shown in FIG. 3 is performed will be described with reference to FIG. FIG. 4 is a motor characteristic diagram showing the operation in this embodiment.
[0078]
In FIG. 4, the horizontal axis represents torque, and the vertical axis represents the rotational speed. R2 is a torque = rotational speed characteristic at a duty of 100% (maximum voltage) of a motor designed to reduce the output in order to increase efficiency as described in the conventional example.
[0079]
When the torque is in the range from T1 to T2, the rotational speed control is sufficiently possible by the operation as a DC motor. When the torque is T2, the operation is performed with a duty of 100%, but the rotation speed can still maintain the maximum rotation speed Rm (target rotation speed).
[0080]
When the torque further increases and reaches T3, the operation limit of the DC motor is no longer exceeded, so the rotational speed decreases along the motor characteristic R2. Here, the operation is switched to a synchronous motor. Then, the rotational speed becomes the maximum rotational speed Rm again, and the rotational speed can be maintained.
[0081]
Further, even if the load increases, the motor operates as a synchronous motor, so that the maximum rotational speed Rm can be maintained even at the maximum load point Lm, that is, the torque Tm.
[0082]
However, even when operating as a synchronous motor, there is a limit to the torque, and in this description, when the torque increases to the torque T4 (step-out torque), the motor will step out and stop.
[0083]
Next, this operation will be described in detail with reference to FIG. FIG. 5 is a timing chart of the operation according to this embodiment. The horizontal axis indicates time. (A) shows the rotation speed, (b) shows the load torque, and (c) shows the duty.
[0084]
At time t2, the load torque is also low, and the rotation speed can be sufficiently controlled by operation as a DC motor. Thereafter, the duty is increased in order to maintain the rotational speed as the load torque increases.
[0085]
Further, the load torque is increased, and the operation is performed with a duty of 100% at time t3. When the load further increases, the rotational speed decreases at time t4. Therefore, the operation as the synchronous motor is switched and the count of the first timer circuit 21 is started.
[0086]
Since the first timer circuit 21 is operating as a synchronous motor while counting the time t1 (time t4 to t5), the rotational speed is maintained even when the load torque increases. At time t5 when the first timer circuit 21 finishes counting, the operation once returns to the DC motor.
[0087]
However, although the load torque is still high and the duty is maintained at 100%, the rotational speed drops, so the operation immediately switches to the operation as a synchronous motor, and the first timer circuit starts to operate again.
[0088]
Since the first timer circuit 21 is operating as a synchronous motor while counting the time t1 (time t5 to t6), the rotational speed is maintained even when the load torque increases. At time t6 when the first timer circuit 21 finishes counting, the operation as the DC motor is resumed.
[0089]
Here, the load torque is low, and at the moment of switching, the rotational speed increases, and the duty is decreased by rotational speed control so that the rotational speed becomes the target rotational speed. Therefore, after time t6, a normal DC motor operation is performed.
[0090]
Next, the operation of the second embodiment will be described with reference to FIGS. FIG. 6 is a flowchart of the compressor motor control apparatus according to the second embodiment.
[0091]
In FIG. 6, in STEP 11, the brushless motor is operated as a DC motor. That is, the output from the inverter 13 is selected by the switching circuit 18 from the commutation circuit 16.
[0092]
Next, in STEP 12, the duty determination circuit 22 determines whether the duty output from the PWM control circuit 19 is 100% (maximum). If the duty is less than 100%, it is determined that there is still a margin in performance, and the operation as STEP 11, that is, the DC motor is continued. If the duty is 100%, the process proceeds to STEP3.
[0093]
Next, in STEP 13, it is determined whether or not the current actual rotational speed is lower than the target rotational speed. If it is not lowered, it is determined that the duty is 100%, which is in the maximum state but is still at the limit, and the operation as STEP 11, that is, the DC motor is continued.
[0094]
If the rotational speed is reduced, it is determined that the operating range of the DC motor is no longer exceeded due to the load, and the process proceeds to STEP14.
[0095]
Next, in STEP 14, the switching circuit 18 switches to the operation in the synchronous drive circuit 17. At this time, the frequency of the signal output from the synchronous drive circuit 17 corresponds to the target rotational speed (for example, a frequency of 140 Hz if 70 r / sec is the target and a 4-pole motor), and the duty is 100%.
[0096]
Next, in STEP 15, the phase determination circuit 23 detects the phase difference between the signal from the back electromotive voltage detection circuit 14 and the signal from the synchronous drive circuit 17. Here, the phase difference indicates the phase difference of the signal of the counter electromotive voltage detection circuit 14 with respect to the signal of the synchronous drive circuit 17, which means advance when the value is positive and delay when the value is negative.
[0097]
Here, if the phase difference is 0 or more in the determination in STEP 15, the operation as a synchronous motor is terminated, the operation returns to STEP 11, the operation as a DC motor is executed again, and the operation is repeated from STEP 11. If it is determined in STEP 15 that the phase difference is less than 0, the process proceeds to STEP 16.
[0098]
In STEP 16, the phase difference is further determined. If it is −φm or more, the process is repeated from STEP 14, and if it is less than −φm, the process proceeds to STEP 17.
[0099]
In STEP 17, the frequency adjustment circuit 24 adjusts the synchronization frequency and lowers the output frequency from the synchronization drive circuit 17, thereby lowering the output frequency from the inverter 13.
[0100]
Next, this phase difference will be described in more detail with reference to FIG. FIG. 7 is a timing diagram of signals in the second embodiment.
[0101]
In FIG. 7, (a) to (f) are outputs of the synchronous drive circuit 17 that determines ON / OFF of each power element of the inverter 13. (G) to (i) are position detection signals of the counter electromotive voltage detection circuit 14.
[0102]
There is a delay of the phase difference φ1 between the rise of the U-phase upper arm signal and the rise of the position detection signal X. Further, the rising of the U-phase lower arm signal and the falling of the position detection signal X cause a delay of the phase difference φ2.
[0103]
Similarly, a delay of the phase difference φ3 occurs between the rise of the V-phase upper arm signal and the rise of the position detection signal Y. Further, the rising of the V-phase lower arm signal and the falling of the position detection signal Y cause a delay of the phase difference φ4.
[0104]
Further, the rising of the W-phase upper arm signal and the rising of the position detection signal Z are delayed by a phase difference φ5. Further, a delay of the phase difference φ6 occurs between the rise of the W-phase lower arm signal and the fall of the position detection signal Z.
[0105]
When the operation as a synchronous motor is performed, the rotor phase is delayed with respect to the rotating magnetic field from the stator at a high load, and thus a delayed phase is generated.
[0106]
On the other hand, at a light load, the rotor rotates in the opposite direction with respect to the rotating magnetic field from the stator, so that it becomes a leading phase.
[0107]
Note that when operating as a DC motor, signals to be driven according to the position detection signals X, Y, and Z are generated, so that φ1 to φ6 are all zero. Thus, when operating as a synchronous motor, the state of the load can be known by detecting the phase difference.
[0108]
Next, characteristics when the operation shown in FIG. 7 is performed will be described with reference to FIG. FIG. 8 is a characteristic diagram showing the operation in the second embodiment.
[0109]
In FIG. 8, the horizontal axis represents torque, and the vertical axis represents the rotational speed. R2 is a torque = rotational speed characteristic at a duty of 100% (maximum voltage) of a motor designed to reduce the output in order to increase efficiency as described in the conventional example.
[0110]
When the torque is in the range from T1 to T2, the rotational speed control is sufficiently possible by the operation as a DC motor. When the torque is T2, the operation is performed with a duty of 100%, but the rotation speed can still maintain the maximum rotation speed Rm (target rotation speed).
[0111]
When the torque further increases and reaches T3, the operation limit of the DC motor is no longer exceeded, so the rotational speed decreases along the motor characteristic R2. Here, the operation is switched to a synchronous motor. Then, the rotational speed becomes the maximum rotational speed Rm again, and the rotational speed can be maintained.
[0112]
Further, even if the load increases, the motor operates as a synchronous motor, so that the maximum rotational speed Rm can be maintained even at the maximum load point Lm, that is, the torque Tm.
[0113]
However, even when operating as a synchronous motor, there is a limit to the torque, and in this description, when the torque increases to the torque T4 (step-out torque), the motor will step out and stop.
[0114]
In order to prevent the step-out, the operating frequency of the synchronous motor is lowered at the torque T5 (T5 <T4), and the rotational speed is lowered. When the rotational speed decreases, the step-out torque increases as is apparent from the characteristics of the synchronous motor.
[0115]
Therefore, even if the torque T6 (T6> T4) is reached, the motor can be continuously operated without being stepped out. In order to know the state of the load, the operating state is appropriately determined by determining the phase difference.
[0116]
Further, since the load state can be easily understood, the phase becomes zero, and it is possible to easily return to the operation as the DC motor.
[0117]
Next, this operation will be described in detail with reference to FIG. FIG. 9 is an operation timing chart according to the second embodiment. The horizontal axis indicates time. (A) is the rotation speed, (b) is the load torque, (c) is the duty, and (d) is the phase difference.
[0118]
At time t7, the load torque is also low, and the rotation speed can be sufficiently controlled by the operation as a DC motor. Thereafter, the duty is increased in order to maintain the rotational speed as the load torque increases.
[0119]
Further, the load torque increases, and the operation is performed with a duty of 100% at time t8. When the load further increases, the rotational speed decreases at time t9. Therefore, the operation is switched to a synchronous motor, and the rotation speed is maintained. At this time, since the load is slightly high, the phase difference is slightly delayed.
[0120]
As the load increases further, the phase difference becomes more delayed. Since the phase difference tends to be larger than −φm at time t10, the rotational frequency is lowered by lowering the output frequency from the synchronous drive circuit 17. This rotational speed is maintained when the load is large.
[0121]
At time t11, the load is lightened and the phase difference is smaller than −φm, and the operation returns to the original synchronous frequency. When the load becomes lighter and the phase difference becomes zero, the operation as a DC motor is resumed.
[0122]
As described above, the compressor motor control apparatus according to the present embodiment includes the load state determination circuit 20 that determines the load state of the brushless motor, and the waveform output from the inverter 13 by the load state determination circuit 20 as the commutation circuit 16 or the synchronization. By providing a switching circuit 18 for switching to one of the drive circuits 17, the load state of the brushless motor is detected by the load state determination circuit 20, and when it is in a high load state, switching is performed so as to operate as a synchronous motor. Even with a motor with improved number characteristics, the operating range can be expanded so that a desired rotational speed can be obtained at the maximum load point, and high-efficiency operation is possible at normal loads.
[0123]
Further, by providing the duty determination circuit 22 that determines that the duty is maximized and outputs the waveform output from the inverter from the synchronous drive circuit, if the duty becomes maximum, the DC motor cannot perform further. Since it can be said that it is a limit, the state of the load is detected from this duty, and when the duty reaches the maximum, the operation method is switched to the operation as a synchronous motor, the rotation speed does not decrease, and the refrigerating capacity can be secured.
[0124]
Also, the duty is determined when the duty is maximized and the waveform output from the inverter is output from the synchronous drive circuit 17, and the count is started when the synchronous drive circuit 17 is switched, and after a certain time has elapsed. By providing the first timer circuit 21 to be output from the commutation circuit 16, once the operation as a synchronous motor is switched, the first timer circuit 21 is operated and the operation is continued for a certain period of time. The operation can be stabilized without frequently switching even in the vicinity of the switching.
[0125]
Further, the duty determination circuit 22 that determines that the duty is maximized and outputs the waveform output from the inverter 13 from the synchronous drive circuit 17, the signal of the counter electromotive voltage detection circuit 14, and the signal of the synchronous drive circuit 17 By detecting the phase difference of the current and detecting the phase difference, the phase determination circuit 23 for switching to the output from the commutation circuit 16 when the phase difference disappears is provided. Predicting by detecting the phase difference between the signal of the circuit 14 and the signal of the synchronous drive circuit 17, and returning to the normal operation of the DC motor when the phase difference disappears, promptly when the load becomes light It is possible to return to the original operating state.
[0126]
The frequency adjustment circuit 24 detects the phase difference between the signal of the back electromotive voltage detection circuit 14 and the signal of the synchronous drive circuit 17 and lowers the output frequency from the synchronous drive circuit 17 when the phase difference becomes smaller than a predetermined value. When the operation as a synchronous motor is performed, if the phase difference is smaller than a predetermined value, the step-out torque can be improved by reducing the output frequency from the synchronous drive circuit 17, Further, the worst state of stopping the motor can be avoided by reducing the rotational speed before the load becomes large and the motor stops.
[0127]
【The invention's effect】
As described above, the compressor motor control device of the present invention isBy providing a switching circuit that switches the waveform output from the inverter to either the commutation circuit or the synchronous drive circuit, the load state of the brushless motor is detected by the load state determination circuit. Even with a motor that has been switched for operation and has improved rotational speed characteristics, the operating range can be expanded so that a desired rotational speed can be obtained at the maximum load point, and high-efficiency operation is possible at normal loads.
[0128]
Also,By providing a load state determination circuit that determines the load state of the brushless motor and a switching circuit that switches the waveform output from the inverter to either the commutation circuit or the synchronous drive circuit by the load state determination circuit, the load state of the brushless motor Is detected by the load condition judgment circuit, and when it is in a high load condition, the operation range is changed so that the motor can be operated as a synchronous motor and the desired speed can be obtained at the maximum load point even with a motor with improved speed characteristics. In addition, high efficiency operation is possible under normal load.
[0129]
In addition, by providing a duty determination circuit that determines that the duty is maximized and outputs the waveform output from the inverter from the synchronous drive circuit, the limit that the DC motor cannot produce any more when the duty is maximized Therefore, the state of the load is detected from this duty, and when the duty reaches the maximum, the operation method is switched to the operation as a synchronous motor, the rotation speed does not decrease, and the refrigerating capacity can be secured.
[0130]
In addition, a duty determination circuit that determines that the duty is maximized and outputs the waveform output from the inverter from the synchronous drive circuit, and a commutation circuit that starts counting when the synchronous drive circuit is switched over and a certain time has elapsed By providing the first timer circuit to output from the motor, once switching to the operation as a synchronous motor, by operating the first timer circuit and continuing the operation for a certain period of time, frequently even in the vicinity where the operation method is switched The operation can be stabilized without switching.
[0131]
Also, the duty determination circuit that determines that the duty is maximized and outputs the waveform output from the inverter from the synchronous drive circuit, and the phase difference between the signal of the counter electromotive voltage detection circuit and the signal of the synchronous drive circuit are detected. By providing a phase determination circuit that switches to the output from the commutation circuit when the phase difference disappears, when operating as a synchronous motor, the load of the back electromotive voltage detection circuit and the synchronous drive circuit By detecting the phase difference with the signal of, and returning to normal DC motor operation when the phase difference disappears, it is possible to quickly return to the original operating state when the load is light it can.
[0132]
There is also provided a frequency adjustment circuit that detects the phase difference between the signal of the counter electromotive voltage detection circuit and the signal of the synchronous drive circuit and lowers the output frequency from the synchronous drive circuit when the phase difference becomes smaller than a predetermined value. Thus, when operating as a synchronous motor, if the phase difference is smaller than a predetermined value, the step-out torque can be improved by lowering the output frequency from the synchronous drive circuit, and the load becomes larger. The worst state of motor stop can be avoided by reducing the rotation speed before the motor stops.
[Brief description of the drawings]
FIG. 1 is a block diagram of a compressor motor control apparatus according to an embodiment.
FIG. 2 is a characteristic diagram showing the operating range of the brushless motor in the embodiment.
FIG. 3 is a flowchart of a compressor motor control apparatus in the embodiment.
FIG. 4 is a motor characteristic diagram showing the operation in the embodiment.
FIG. 5 is an operation timing chart according to the embodiment.
FIG. 6 is a flowchart of a compressor motor control device according to a second embodiment.
FIG. 7 is a timing diagram of signals in the second embodiment.
FIG. 8 is a motor characteristic diagram showing the operation in the second embodiment.
FIG. 9 is an operation timing chart according to the second embodiment.
FIG. 10 is a block diagram of a conventional compressor motor control device.
FIG. 11 is a torque characteristic diagram of a DC motor.
[Explanation of symbols]
3 Brushless motor
13 Inverter

Claims (6)

An inverter that converts a DC voltage into an AC voltage, a brushless motor driven by the inverter, a counter electromotive voltage detection circuit that detects a rotational position of a rotor from a counter electromotive voltage of the brushless motor, and a counter electromotive voltage detection circuit A commutation circuit for generating a waveform for driving the inverter from a signal, a synchronous drive circuit for generating a waveform for operating the brushless motor as a synchronous motor, and a waveform output from the inverter for the commutation circuit or the synchronous drive circuit And a switching circuit for switching to any one of the compressor motor control device for switching the switching circuit to operate the brushless motor as a synchronous motor when in a high load state. An inverter that converts a DC voltage into an AC voltage, a brushless motor driven by the inverter, a counter electromotive voltage detection circuit that detects a rotational position of a rotor from a counter electromotive voltage of the brushless motor, and a counter electromotive voltage detection circuit A commutation circuit for generating a waveform for driving the inverter from a signal, a synchronous drive circuit for generating a waveform for operating the brushless motor as a synchronous motor, a load state determination circuit for determining a load state of the brushless motor, A compressor motor control device comprising: a switching circuit that switches a waveform output from the inverter by the load state determination circuit to either the commutation circuit or the synchronous drive circuit. An inverter that converts a DC voltage into an AC voltage, a brushless motor driven by the inverter, a counter electromotive voltage detection circuit that detects a rotational position of a rotor from a counter electromotive voltage of the brushless motor, and a counter electromotive voltage detection circuit A commutation circuit for generating a waveform for driving the inverter from a signal, a synchronous drive circuit for generating a waveform for operating the brushless motor as a synchronous motor, a load state determination circuit for determining a load state of the brushless motor, A switching circuit that switches the waveform output from the inverter to either the commutation circuit or the synchronous drive circuit by the load state determination circuit, and synchronously drives the waveform output from the inverter after determining that the duty is maximized A compressor motor control device having a duty determination circuit for outputting from the circuit. An inverter that converts a DC voltage into an AC voltage, a brushless motor driven by the inverter, a counter electromotive voltage detection circuit that detects a rotational position of a rotor from a counter electromotive voltage of the brushless motor, and a counter electromotive voltage detection circuit A commutation circuit for generating a waveform for driving the inverter from a signal, a synchronous drive circuit for generating a waveform for operating the brushless motor as a synchronous motor, a load state determination circuit for determining a load state of the brushless motor, A switching circuit that switches the waveform output from the inverter to either the commutation circuit or the synchronous drive circuit by the load state determination circuit, and synchronously drives the waveform output from the inverter after determining that the duty is maximized The duty judgment circuit to output from the circuit and the synchronous drive circuit were switched to Compressor motor control device having a first timer circuit for the output from a certain time after the commutation circuit starts counting the can. An inverter that converts a DC voltage into an AC voltage, a brushless motor driven by the inverter, a counter electromotive voltage detection circuit that detects a rotational position of a rotor from a counter electromotive voltage of the brushless motor, and a counter electromotive voltage detection circuit A commutation circuit for generating a waveform for driving the inverter from a signal, a synchronous drive circuit for generating a waveform for operating the brushless motor as a synchronous motor, a load state determination circuit for determining a load state of the brushless motor, A switching circuit that switches the waveform output from the inverter to either the commutation circuit or the synchronous drive circuit by the load state determination circuit, and synchronously drives the waveform output from the inverter after determining that the duty is maximized A duty determination circuit for output from the circuit, and a signal of the back electromotive voltage detection circuit; Serial detect compressor motor control device and a phase determining circuit for switching the output from the commutation circuit when it is no longer the phase difference a phase difference between the signals of the synchronous drive circuit. An inverter that converts a DC voltage into an AC voltage, a brushless motor driven by the inverter, a counter electromotive voltage detection circuit that detects a rotational position of a rotor from a counter electromotive voltage of the brushless motor, and a counter electromotive voltage detection circuit A commutation circuit for generating a waveform for driving the inverter from a signal, a synchronous drive circuit for generating a waveform for operating the brushless motor as a synchronous motor, a load state determination circuit for determining a load state of the brushless motor, A switching circuit that switches the waveform output from the inverter to either the commutation circuit or the synchronous drive circuit by the load state determination circuit, and synchronously drives the waveform output from the inverter after determining that the duty is maximized A duty determination circuit for output from the circuit, and a signal of the back electromotive voltage detection circuit; Serial compressor motor control device and a frequency adjustment circuit phase difference detecting a phase difference lowers the output frequency from the synchronous driving circuit when it becomes smaller than a predetermined value between the signals of the synchronous drive circuit.

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