JP4680701B2 - Control method of permanent magnet synchronous motor - Google Patents

Description

  The present invention relates to a method for controlling a permanent magnet synchronous motor using a permanent magnet as a field, and more particularly to a method for controlling a permanent magnet synchronous motor using a PWM inverter.

  One type of synchronous motor is a rotating field type synchronous motor that uses a permanent magnet for the rotor (rotor), and is called a DC brushless motor because it does not require a brush for power supply. Therefore, it is advantageous as a relatively small motor, and for this reason, in recent years, it has been frequently used in, for example, air conditioners.

  In this rotating field type permanent magnet synchronous motor, a rotation detector or a magnetic pole position detector is used to detect the magnetic pole position of the rotor and switch the armature current to generate a rotating magnetic field, thereby generating torque to the rotor. At this time, in recent years, a so-called PWM inverter driven permanent magnet synchronous motor in which the armature current is switched by a PWM (pulse width modulation) inverter is generally used.

  By the way, in the case of such a permanent magnet synchronous motor, if the rotor shaft is locked at the time of start-up or immediately after start-up, the signal from the rotation detector or the magnetic pole position detector will not change. The output voltage phase in the PWM signal generation section of this will not change and will be locked. When the output voltage phase of the inverter is locked in this way, the output voltage of the inverter becomes a DC voltage, and thus a DC current continues to flow through a specific switching element of the inverter.

  Here, when the motor is rotating, the output voltage phase does not lock and changes according to the frequency synchronized with the rotation of the motor, so that a direct current does not continue to flow through a specific switching element. Since an alternating current flows through the element, there is no possibility that the switching element suddenly generates heat by alternately storing and releasing heat in a short time.

  At this time, the rated current value of the switching element is generally defined as a value that allows a direct current to flow continuously. However, in the case of a PWM inverter, the switching element is several KHz higher than the frequency of the commercial AC power supply. Since switching is performed with a carrier (carrier wave signal) of (kilohertz) frequency, transient loss due to switching operation is added in addition to steady loss due to on-resistance of the switching element, etc. Become.

  For this reason, when the switching element is controlled by PWM, when the DC current state is locked, the switching element suddenly even if the average current value at this time is a value within the rated current value of the switching element. There is a risk that the temperature of the will rise.

  By the way, as protection in such a case, conventionally, when the output current of the inverter exceeds a predetermined value, a method of shutting off the output by the overcurrent protection device, or an electronic thermal mounted on the control device for protection of the motor When a protection device is used and the operation frequency is low, a method for protecting the protection operation quickly by setting the characteristic so that the protection operation becomes sensitive is applied.

Furthermore, a method of protecting a large current from flowing through the switching element by setting the set current value to be equal to or lower than the rated current by a current suppression function has been conventionally known (for example, see Patent Document 1). In this case, a method of reducing the carrier frequency of the inverter at this time is also conventionally known (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 9-140154 JP-A-9-70195

  The above prior art does not consider the fact that a current switched at the carrier frequency is passed through the switching element, and there is a problem that heat is concentrated on a specific switching element when the motor is locked. .

  As described above, when starting with the rotor shaft of the motor locked, if the rotor shaft is locked immediately after starting the flag, a DC current continues to flow through a specific switching element of the PWM inverter. However, since the current passed through the switching element at this time is switched at the carrier frequency, the loss of the switching element increases, and there is a risk of thermal destruction of the switching element due to heat accumulation.

  At this time, even in the conventional technique disclosed in Patent Document 1, nothing is described as a countermeasure when the rotor shaft is locked. In the conventional technique disclosed in Patent Document 2, the carrier frequency is not set. The current command value is used for the condition to reduce.

  An object of the present invention is to provide a control method for a permanent magnet synchronous motor in which protection of a switching element of a PWM inverter can be reliably obtained even when a motor rotor shaft is locked.

The above object is to provide a permanent magnet synchronous motor control method that detects the rotor magnetic pole position of the permanent magnet synchronous motor and controls the PWM inverter to switch the armature current. detecting the carrier frequency of the PWM inverter at the time of locking is reduced from the frequency for ordinary operation, reducing the amount of the carrier frequency at the time of the lock, the length size and the energization time of the output current of the switching elements of the PWM inverter It is achieved at the so that calculated from the.

Here, when the carrier frequency is reduced, the set current value of the current suppression function may be increased according to the reduction amount of the carrier frequency.

  In the above means, when the rotor shaft is locked at the time of starting the motor, if the output current exceeds the carrier frequency reduction start current value in the control device, the carrier frequency serving as a reference for generating the PWM signal is set. It shall be reduced below the carrier frequency set at startup.

  In this case, after the carrier frequency reduction process, the carrier frequency reduction start current value is obtained again by the changed carrier frequency and compared with the detected output current value. When the detected direct current is larger in output current than the carrier frequency reduction start current value, the carrier frequency is reduced again.

  When the detected output current is larger than the carrier frequency reduction start current value obtained as described above, the carrier frequency is reduced. The lower limit value of the carrier frequency can be determined by the use environment and the device configuration of the control device.

  If the output current exceeds the carrier frequency reduction start current value even if the carrier frequency is reduced to the carrier frequency reduction lower limit value, the switching element junction temperature, steady loss, switching element, cooling capacity of the control device, and Based on the relationship between the output current value and the carrier frequency, a time during which a direct current due to switching can be continuously flowed is obtained, and the current is monitored.

  As a result, in a control device that drives a permanent magnet motor having a speed detector or a magnetic pole position detector using the signal of the detector, the rotor shaft is locked at startup and the output current becomes DC and becomes a specific switching element. Even in the case of flowing, the switching element can be protected by shutting off the output before the switching element reaches thermal destruction.

  According to the present invention, since protection of the switching element in consideration of loss due to PWM switching can be obtained, it is possible to maintain higher reliability as compared with the prior art.

  Hereinafter, a method for controlling a permanent magnet synchronous motor according to the present invention will be described in detail with reference to embodiments shown in the drawings.

  FIG. 3 is an example of a permanent magnet synchronous motor control device to which an embodiment of the present invention is applied. As shown in the figure, in this embodiment, first, AC power supplied from the commercial power supply 100 is converted to the forward conversion unit 110. Is converted into direct current and then smoothed by the smoothing unit 120 and then supplied to the inverse conversion unit 130, where PWM control is performed to obtain the drive power necessary for driving the rotating field permanent magnet synchronous motor. The drive power is converted and supplied to the motor M, that is, the rotating field permanent magnet synchronous motor 140.

  At this time, the permanent magnet synchronous motor 140 is provided with a magnetic pole position detector 150 as a sensor for detecting the rotational position of the rotor, and the rotor position signal R detected thereby is input to the controller 160. ing. At this time, the controller 160 is provided with a PWM signal generator 180 and a carrier signal generator 170, which operate under the control of the controller 160.

  Therefore, the control unit 160 controls the carrier signal generation unit 170 and the PWM signal generation unit 180 based on the rotor position signal R, whereby the carrier signal generation unit 170 supplies the carrier frequency to the PWM signal generation unit 180. The PWM signal generator 180 generates a PWM signal from the carrier frequency and supplies the PWM signal to the switching element of the inverse converter 130 so that the driving power is supplied to the permanent magnet synchronous motor 140.

  At this time, a current detector 190 such as a CT (current transformer) is provided between the reverse conversion unit 130 and the permanent magnet synchronous motor 140 so that the output current of the reverse conversion unit 130 is detected. The output current signal C detected here is also input to the controller 160.

  Then, as described above, the control unit 160 not only executes rotation control of the permanent magnet synchronous motor 140 based on the rotor position signal R, but also performs processing such as locking of the rotor shaft and detection of output current. For this reason, it is composed of a microcomputer (microcomputer) on which a predetermined program is mounted.

  Next, FIG. 4 is also an example of a permanent magnet synchronous motor control device to which an embodiment of the present invention is applied. This is an example of the case where the output current is detected on the PWM inverter main circuit side. For this reason, for example, a current detector 190 a such as a shunt resistor is provided between the smoothing unit 120 and the inverse conversion unit 130, and the output current signal C detected thereby is input to the control unit 160.

  Next, the operation of the embodiment of the present invention by the permanent magnet synchronous motor control device of FIGS. 3 and 4 will be described with reference to flowcharts. First, FIG. 1 shows processing necessary for the control method according to the first embodiment of the present invention. This processing is executed by the microcomputer of the control unit 160, and as shown in FIG. This is started when the synchronous motor 140) is started and started, and thereafter executed every predetermined time, for example, every 10 milliseconds.

First, when a specific switching element is switched with a preset normal operation carrier frequency f ₀ , the maximum value of the direct current that can be continuously passed through the switching element is calculated and the carrier is calculated. The frequency reduction start current I ₀ is set (step 200).

Here, the carrier frequency reduction start current I ₀ is determined by the microcomputer of the control unit 160 according to a known physical law from the junction temperature of the switching element, the steady loss, the switching loss, and the cooling capability of the inverse conversion unit 130. Can be calculated. The normal operation carrier frequency f ₀ at this time is determined by the operation conditions and the operation environment, but is normally set to a frequency of about 8 KHz (f ₀ = 8 KHz).

  Next, lock detection is performed and it is determined whether or not lock detection is detected (step 210). Here, when the rotor shaft is locked, the rotor position signal R does not change even though the rotor is activated. Therefore, in this case, it is determined to be locked, and the result is YES. If the lock is not determined, the result is NO.

First, when the result is NO, the carrier frequency is kept at the carrier frequency f ₀ during normal operation (step 220).

On the other hand, if it is determined to be locked, the result is YES. Next, the maximum value of the time during which DC current switched at the carrier frequency f ₀ during normal operation can be continuously flowed, that is, the allowable maximum continuous DC energization time T _{m is obtained.} Is obtained (step 230).

This allowable maximum continuous DC energization time _Tm is the current value by the output current signal C of the current detector 190 or the current detector 190a and the current carrier frequency, the steady loss of the switching element, the switching loss, the junction temperature, and the inverse conversion unit. It can be calculated from the cooling capacity of 130 by the microcomputer of the control unit 160 according to a known physical law.

Next, the energization time T is calculated by integrating the detected current value (step 240), and the calculated energization time T is compared with the allowable maximum continuous DC energization time _Tm to determine the output cutoff (step 250). . If the result is NO, that is, if the energization time T is equal to or greater than the allowable maximum continuous DC energization time T _m (T ≧ T _m ), the control unit 160 shuts off the output of the inverse conversion unit 130 and stops the operation (step 290). .

On the other hand, when the result is YES, that is, when the energization time T is less than the allowable maximum continuous DC energization time T _m (T <T _m ), subsequently, Step 260 and Step 270 are executed to determine the carrier frequency reduction.

First, when the determination result in step 260 is YES, that is, when the current I detected by the current detector 190 or the current detector 190a is equal to or greater than the carrier frequency reduction start current I ₀ (I ₀ ≦ I), and If the determination result in step 270 is also YES, that is, if the current carrier frequency f is not lower than the carrier frequency lower limit value f _L (f _L <f), the carrier frequency is reduced (step 280).

The carrier frequency reduction lower limit value f _{L at} this time is determined by the specific configuration and use environment of this apparatus, but is normally set to a value of about 1 KHz. On the other hand, the reduction of the carrier frequency in step 280 may be set to about 0.5 KHz per time, for example. In this case, the maximum value of the carrier frequency reduction processing count in step 280 is f ₀ = 8000 and f _L = 1000, so 7000 (8000−1000) ÷ 500 = 14.

On the other hand, when the determination result of step 260 is NO, that is, when the detection current I is less than the carrier frequency reduction start current I ₀ (I ₀ > I), when the determination result of step 270 is NO, that is, If the current carrier frequency f exceeds the carrier frequency lower limit value f _L (f _L <f), the carrier frequency reduction process in step 280 is not performed, and in this case, the maximum allowable value in steps 230, 240, and 250 is performed. Protection is provided by the process of obtaining the continuous DC energization time and the process of monitoring the energization time.

  Here, as described above, the process of FIG. 1 is executed at predetermined time intervals. Therefore, according to this embodiment, the rotor shaft of the permanent magnet synchronous motor 140 is locked at the time of startup. As a result, when a direct current flows through the switching element of the reverse conversion unit 130 and there is a risk of thermal destruction in the switching element, the switching loss is suppressed by reducing the carrier frequency, and as a result, the switching element is passed. Heat generation of the switching element can be suppressed without reducing the current value.

  Here, in the process of FIG. 1, the reason why the output cutoff determination based on the allowable maximum continuous DC energization time and the energization time in step 250 is performed before the carrier frequency reduction process in and after step 260 is to reduce the carrier frequency. This is because the protection when the thermal destruction limit level of the switching element is reached in the state is taken into consideration, and thus more reliable protection can be obtained.

  Next, FIG. 2 shows the processing necessary for the control method according to the second embodiment of the present invention, which is the control of the present invention when the control unit 160 has a current suppression function. In this embodiment, the current suppression function refers to a duty ratio (current flow) by PWM of the reverse conversion unit when the output current exceeds a preset current value (set current value) during operation of the motor. Rate) to prevent the output current from exceeding the set current value.

  By the way, as the set current value at this time, a value unique to the control device itself is generally set as a fixed value. Here, in the second embodiment, setting in the current suppression function is performed. The current value is a variable value instead of a fixed value.

  As described above, the present invention is designed to reduce the carrier frequency and reduce the switching loss when the motor is locked, but the reduction of the switching loss due to the reduction of the carrier frequency at this time should be viewed. In other words, it means that the current value that can be passed through the switching element can be relatively increased accordingly.

  Therefore, in the second embodiment, this is utilized so that a larger starting torque can be generated when the electric motor is started. For this reason, as shown in FIG. Step 300 is provided after the carrier frequency reduction processing step 280 in the processing according to the embodiment (FIG. 1), and other configurations are the same as those in the embodiment of FIG.

  At this time, in step 300, an increase amount of the current value corresponding to the step loss of the switching element reduced by lowering the carrier frequency in step 280 is calculated, and this increase amount is added to the set value of the current suppression function. Execute the process.

  As already described, the process of step 280 and the subsequent process of step 300 are executed when the rotor shaft is locked. Therefore, according to the embodiment of FIG. When the shaft is locked, the carrier frequency is automatically reduced and the set current value of the current suppressing function is increased. As a result, the starting torque of the permanent magnet synchronous motor 140 is increased, and the starting characteristic is increased. Improvement will be obtained.

  Here, it is as follows if the effect by the above embodiment is enumerated. First, by reducing the carrier frequency, the switching frequency of the PWM signal flowing through the switching element can be reduced, and the heat generation due to current loss in the switching element can be reduced, and if the heat generation can be reduced in this way, the switching element Problems related to thermal breakdown of can also be improved.

  Next, since the loss of the switching element is reduced by reducing the carrier frequency, the operation time can be lengthened without changing the current value flowing through the switching element. Increases the chance of getting out of the state.

  Further, reducing the carrier frequency of the switching element to reduce the current loss means that the current value that can be passed can be increased by that amount. Therefore, while reducing the carrier frequency, the current value passed through the switching element can be increased within the allowable range of the switching element, and thus the starting torque can be increased when starting the motor. it can.

  At this time, when a specific switching element is switched in the control unit immediately after the motor is started, a carrier frequency reduction start current value which is the maximum value of the direct current that can be continuously passed through the switching element is obtained. The carrier frequency reduction start current value at this time can be obtained by the control unit based on the junction temperature of the switching element, the steady loss, the switching loss, and the cooling capacity of the control device.

3 is a flowchart for explaining an operation according to an embodiment of a method for controlling a permanent magnet synchronous motor according to the present invention. 6 is a flowchart for explaining an operation according to another embodiment of the method for controlling a permanent magnet synchronous motor according to the present invention. It is a block block diagram which shows an example of the permanent magnet synchronous motor control apparatus with which one Embodiment of the control method of the permanent magnet synchronous motor by this invention was applied. It is a block block diagram which shows another example of the permanent magnet synchronous motor control apparatus with which one Embodiment of the control method of the permanent magnet synchronous motor by this invention was applied.

Explanation of symbols

100: Three-phase AC power supply 110: Forward conversion unit 120: Smoothing unit 130: Reverse conversion unit 140: Permanent magnet motor 150: Magnetic pole position detector 160: PWM signal generation unit 170: Carrier signal generation unit 180: Control unit 190: Current detector (CT)
190a: Current detector (shunt resistor)

Claims (2)

In the control method of the permanent magnet type synchronous motor of the method of detecting the rotor magnetic pole position of the permanent magnet type synchronous motor and controlling the PWM inverter to switch the armature current,
Detecting the lock of the permanent magnet type synchronous motor, and reducing the carrier frequency of the PWM inverter from the frequency for normal operation at the time of the lock ;
The reduction amount of the carrier frequency at the time of locking, the control method of a permanent magnet type synchronous motor is calculated from the length of the size and energizing time of the output current, characterized in Rukoto of switching elements of the PWM inverter. In the control method of the permanent magnet type synchronous motor according to claim 1,
A control method for a permanent magnet synchronous motor , wherein when the carrier frequency is reduced, a set current value of a current suppression function is increased in accordance with a reduction amount of the carrier frequency .

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