JP5168955B2 - Electric motor control device - Google Patents

Description

  The present invention is necessary for a motor in a motor control device in which a smoothing circuit composed of a capacitor and a reactor having a remarkably small capacity is connected to an output terminal of a rectifier circuit, and the output voltage pulsates greatly at twice the frequency of the AC power supply frequency. An object is to protect the device by restricting the flow of the above current.

  Conventionally, a smoothing circuit is configured in an electric motor control device in which a smoothing circuit composed of a capacitor and a reactor having a remarkably small capacity is connected to the output terminal of the rectifier circuit and the output voltage pulsates greatly at twice the frequency of the AC power supply frequency. The maximum value of the motor current when the motor is driven at the same rotation speed and load condition is higher than that of a motor control device having a large capacity of capacitors and reactors and almost no output voltage pulsation.

FIG. 13 shows an output voltage waveform from the smoothing circuit in the electric motor control device described in Patent Document 1, and there is a period Tdrop during which the supply voltage to the orthogonal transformation circuit that drives the electric motor drops significantly. For this reason, compared to the case where a stable and constant voltage is supplied, the amount of current supply increases and the maximum value of the motor current is higher because the voltage supply is insufficient to maintain the drive torque of the motor. Become.
JP-A-10-150795

  For this reason, in the drive by the conventional motor control device, a current more than necessary for maintaining the drive torque of the motor is supplied, and there is a possibility that the motor performance may be deteriorated due to demagnetization of the magnet or the component device may be destroyed. Had.

  The present invention solves the above problems, and provides an electric motor control device that limits electric motor current when the electric motor current exceeds a predetermined current value and prevents deterioration of electric motor performance and destruction of component devices due to demagnetization of magnets. With the goal.

In order to solve the above-mentioned conventional problems, an electric motor control apparatus according to the present invention includes a rectifier that rectifies an AC power supply, a smoothing means that pulsates an output voltage from the rectifier at a frequency twice the AC power supply frequency, and an electric motor. Orthogonal transformation means for converting a smooth voltage into a desired AC voltage for driving, current detection means for detecting the current of the motor, and phase calculation means for calculating the rotational phase of the motor based on the detection value of the current detection means A rotation speed command means for instructing the rotation speed of the electric motor, a current command calculation means for calculating a current command value from an instruction rotation speed from the rotation speed command means and an actual rotation speed calculated from the phase calculation means, A voltage command calculation means for calculating a voltage command value based on a current command value from the current command calculation means; a PWM signal generation means for generating a signal for driving an orthogonal transformation means from the voltage command value; Current limiting means for limiting the motive current, temperature detecting means for detecting the temperature of the motor, and limiting current value setting means for setting a limiting current value for limiting the motor current based on a detection value from the temperature detecting means. In the motor control device, the limit current value correction for correcting the limit current value set by the limit current value setting means according to the drive rotation speed of the motor and setting the limit current value low when the drive rotation speed becomes high First, in order to limit the motor current so that the motor current does not exceed a predetermined current value, the fluctuation amount of the current command value during one rotation of the motor from the current command calculation means is decreased to obtain a predetermined fluctuation amount. If the motor current value is less than the maximum allowable value, the motor current is limited next. Lower the motor speed of the eye, when said motor speed has reached below the predetermined rotational speed is provided with the said current limiting means for stopping the motor.

  According to the motor control device of the present invention, it is possible to realize motor driving in which the motor current is limited in the motor control device in which the output voltage from the smoothing circuit pulsates greatly at twice the frequency of the AC power supply frequency.

The first invention includes a rectifying means for rectifying an AC power supply, a smoothing means in which an output voltage from the rectifying means pulsates at a frequency twice the AC power supply frequency, and a smoothing voltage to a desired AC voltage for driving an electric motor. Orthogonal transformation means for converting, current detection means for detecting the current of the motor, phase calculation means for calculating the rotational phase of the motor based on the detection value of the current detection means, and a rotational speed command for instructing the rotational speed of the motor Based on the current command value from the current command calculation means, the current command calculation means for calculating the current command value from the command rotation speed from the rotation speed command means and the actual rotation speed calculated from the phase calculation means A voltage command calculating means for calculating a voltage command value; a PWM signal generating means for generating a signal for driving an orthogonal transformation means from the voltage command value; a current limiting means for limiting a motor current; and the electric motor In the motor control device comprising temperature detection means for detecting the temperature of the motor and limit current value setting means for setting a limit current value for limiting the motor current based on a detection value from the temperature detection means, the limit current value set by the limit current value setting means corrects I'm a limit current value correcting means for setting low said limit current value when the drive speed becomes higher, the motor current is given First, in order to limit the motor current so as not to exceed the current value, the fluctuation amount of the current command value during one rotation of the motor from the current command calculation means is lowered, and when the motor rotation speed reaches less than the predetermined fluctuation amount, the motor rotation speed is set to a predetermined value. If the motor current value still exceeds the allowable maximum value, the motor speed for limiting the motor current is then lowered, and the motor speed is When reaching the constant less than the rotational speed is obtained by a said current limiting means for stopping the motor.

As a result, even if the current detection accuracy by the current detection means decreases due to the increase in the frequency component of the motor current, it is possible to realize motor driving that suppresses the flow of more current than necessary to the motor. In addition, the current can be limited in accordance with the driving state of the motor, and the motor driving can be realized while suppressing the deterioration of the motor performance and the destruction of the constituent devices due to the current exceeding the allowable amount flowing in the motor. In addition, it is possible to realize motor driving that does not perform motor driving in a region other than the rotation speed range in which motor driving is guaranteed while limiting the motor current.

According to a second invention, in the first motor control device, the smoothing means includes a capacitor and a reactor, and sets a resonance frequency obtained from the capacitor and the reactor to be 40 times or more of an AC power supply frequency. is there. Thereby, high performance of the power supply harmonic characteristic of the input current to the rectifying means can be realized.

According to a third aspect of the present invention, in the first or second motor control device, a film capacitor is used as a capacitor constituting the smoothing means. As a result, the use environment can be selected without worrying about the influence of the temperature on the life characteristics.

According to a fourth aspect of the invention, in any one of the first to third electric motor control devices, a one-piston rotary compressor having a DC motor using a permanent magnet (ferrite magnet) is applied to the electric motor.

  As a result, when driving inexpensive standard compressors that are widely used in the global market, the motor current is limited regardless of the drive speed from low to high, and the demagnetizing current at low temperature (-20 ° C). It is possible to realize a safe drive that suppresses a decrease in motor performance due to demagnetization of the ferrite magnet whose value is lower than normal temperature (+ 20 ° C.).

  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 configuration diagram of an electric motor control device according to Embodiment 1 of the present invention.

  In the motor control device, the rectifier circuit 2 is configured by a diode bridge, and full-wave rectifies the AC power supplied from the AC power source 1 such as a commercial power source that is a single-phase AC power source. The smoothing circuit 3 is a smoothing circuit that smoothes the voltage rectified by the rectifying circuit 2, and its output voltage pulsates greatly at a frequency twice that of the AC voltage.

  The orthogonal transformation circuit (DC-AC conversion circuit) 4 is constituted by a semiconductor switching element, and converts the output voltage from the smoothing circuit 3 into a desired AC voltage for driving the motor. The current detection circuit 6 detects a current flowing through the electric motor 5. The phase calculation circuit 7 calculates the rotational phase of the electric motor 5 based on the detection value from the current detection circuit 6. The rotation speed command circuit 8 gives a command value for the motor rotation speed.

  The current command calculation circuit 9 calculates a current command value for driving the electric motor 5 based on the rotation speed command value from the rotation speed command circuit 8 and the actual rotation speed calculated by the phase calculation circuit. The voltage command calculation circuit 10 calculates a voltage command value based on the current command value calculated by the current command calculation circuit 9. The PWM signal generation circuit 11 generates a signal for driving the orthogonal transformation circuit 4 from the voltage command value calculated by the voltage command calculation circuit 10.

  The current limiting circuit 12 stops the motor 5 when the current detection circuit 6 detects a motor current equal to or greater than a predetermined value, lowers the motor rotation speed for a predetermined time, and performs a single rotation of the motor from the current command calculation circuit 9. The motor current is limited by at least one of the methods for reducing the fluctuation amount of the current command value.

  The temperature detection circuit 13 detects the temperature of the electric motor 5. The limit current value setting circuit 14 sets a limit current value that limits the motor current based on the detection value from the temperature detection circuit 13. The limit current value correction circuit 15 corrects the limit current value set by the limit current value setting circuit 14 according to the drive rotation speed of the electric motor 5.

  Here, the current detection circuit 6 is not limited to directly detecting the phase current of the electric motor 5 with a current sensor or the like, but includes estimation detection from the bus current of the orthogonal transformation circuit 4.

  Further, the smoothing circuit 3 has a small-capacitance capacitor set so that the resonance frequency is 40 times or more of the AC power supply frequency and a reactor for lowering the peak value of the inrush charging / discharging current to the capacitor.

  Note that the reactor constituting the smoothing circuit 3 is inserted between the AC power supply 1 and the capacitor constituting the smoothing circuit 3, so that it may be either before or after the rectifier circuit 2.

  Furthermore, the electric motor 5 has a DC motor using a ferrite magnet having a demagnetizing current that varies depending on the temperature.

  About the motor control apparatus comprised as mentioned above, the operation | movement and an effect | action are demonstrated below.

  First, when a commercial power supply with an AC power supply frequency of 50 Hz is used for the AC power supply 1, the values of the reactor and the capacitor constituting the smoothing circuit 3 are such that the resonance frequency fc = 1 / (2π × √ (L1 × C1)) is AC. The power supply frequency is set to 40 times or more, that is, 2000 Hz or more. For this reason, by using a reactor and a capacitor having a reactance value of 0.5 mH and a capacitance value of 10 μF, fc (= 2250 Hz)> 40 × AC power supply frequency (50 Hz).

  In this way, the capacitor capacity of the smoothing circuit 3 is remarkably reduced to cause a large pulsation (ripple ratio of 80% or more) at twice the AC power supply frequency. In this way, when the output voltage from the smoothing circuit 3 pulsates greatly, the capacitance of the capacitor constituting the smoothing circuit 3 is sufficiently large (for example, several hundred μF or more), compared with the case where the output voltage becomes a stable DC voltage with almost no pulsation. However, the peak current value of the motor current becomes large at the same motor speed and output torque.

  For this reason, in motor driving using a permanent magnet or a semiconductor element that causes performance degradation due to demagnetization at a predetermined current value or more, drive control that limits the maximum current value flowing through the motor is required.

  Next, an actual drive command and a current limiting method will be described. 2 to 4 are diagrams showing the relationship between the command rotational speed, the command current value, and the actual rotational speed depending on the presence or absence of torque pulsation during one rotation of the electric motor.

  In an electric motor with a small torque pulsation during one rotation from a low speed to a high-speed rotation speed region such as a scroll compressor, a command current value I_tgt_m with almost no fluctuation during one rotation is given to the command rotation speed F_tgt as shown in FIG. Thus, it is possible to realize motor driving at a stable rotational speed Vm without pulsation.

  On the other hand, in the case of an electric motor having a large torque pulsation during one rotation at a low speed, such as a one-piston rotary compressor, when it is driven to rotate at a low speed, the fluctuation during one rotation with respect to the command rotational speed F_tgt as shown in FIG. When the command current value I_tgt_m having almost no is given, the actual rotation speed pulsates greatly (Vm ± ΔV) during one rotation, which becomes vibration and leads to shaking of the apparatus.

  In order to suppress this vibration, as shown in FIG. 4, in order to suppress the pulsation of the actual rotational speed with respect to the command rotational speed F_tgt, I_tgt_up from the command current value I_tgt_m in the section where the actual rotational speed decreases due to insufficient torque. On the contrary, in a section where the actual rotational speed increases due to excessive torque, the pulsation of the actual rotational speed is suppressed by reducing I_tgt_down from the command current value I_tgt_m, and stable driving at Vm is realized.

  Next, a method for limiting the motor current will be described with reference to FIGS.

  First, the detection accuracy of the motor current will be described. When the motor current is detected by digital sampling, for example, when current detection is performed in the carrier cycle of a PWM signal that drives a general orthogonal transformation circuit in this type of motor control device, the detection accuracy depends on the motor drive rotation speed, The detection accuracy decreases as the drive rotational speed increases.

  FIG. 5 is a diagram in which sampling points when a 6-pole motor is driven at a carrier frequency of 7 kHz and the motor current is sampled at the carrier cycle are plotted for each of the motor rotation speeds of 50 rps and 100 rps. FIG. 6 is a diagram showing a relationship of limiting current value correction based on the driving rotational speed.

  As shown in FIG. 5, when 100 rps drive is performed with respect to 50 rps drive, the number of times of current sampling in one cycle of the motor current is halved, so that detection accuracy is lowered particularly when trying to detect the maximum value of the motor current. Therefore, as shown in FIG. 6, the current limit start current can be made substantially constant regardless of the rotation speed by correcting the current limit start current with the rotation speed in consideration of the detection accuracy based on the drive rotation speed.

  Next, FIG. 7 is a diagram showing a change in the demagnetization current value depending on the temperature of the permanent magnet (ferrite magnet) provided in the electric motor 5. As shown in FIG. 7, the ferrite magnet has a lower demagnetizing current level at a low temperature (−20 ° C.) than that at room temperature (+ 20 ° C.), for example. The demagnetization current level at a temperature Tb (> Ta) higher than that is Ib (> Ia).

  Therefore, by switching the current value for starting the limitation of the motor current based on the detection value by the temperature detection circuit 13 using a switching operation example of the limiting current value as shown in FIG. The driving within the current value guaranteed by the electric motor 5 is realized until the driving after sufficiently rising.

  For example, if the motor temperature is lower than Tc ° C., the current value for starting the current limit is IA, and if it is Tc ° C. or higher, the current value is IB. After the limit value is switched, switching is not performed for a certain period of time. As shown, an unnecessary hunting operation is prevented by providing a hysteresis width ΔT to the switching temperature.

  Here, for the sake of simplicity, the case where the limit current value has two levels has been described, but it may have more switching stages. Alternatively, the limit current value may be changed linearly with temperature.

  Next, FIG. 10 is a diagram showing the change over time in the commanded rotational speed when the current is limited by the rotational speed control. Here, the detected motor current value is I, the current value for starting current limitation by the rotational speed control is Ilim (f) (Ilim = IA when the motor temperature is lower than Tc ° C., Ilim = IB when Tc ° C. or higher, and the motor is driven. The maximum value of the motor current that can be allowed by the motor 5 is Imax (Imax> Ilim).

  First, in a motor drive that gives a substantially constant command current value with respect to the command rotational speed with a small torque pulsation during one rotation like a scroll compressor, when the motor current value I satisfies I> Ilim at t1, FIG. Thus, the maximum value of the motor current is suppressed by lowering the motor rotation speed for a predetermined time, that is, by lowering the motor rotation speed by ΔF_tgt.

  After lowering the motor speed, if I <Ilim at t2, the motor speed is returned to the original command speed F_tgt. Thereafter, when I> Ilim again at t3, the motor rotational speed is decreased by ΔF_tgt.

  When I> Ilim at t4 when the motor rotation speed is lowered by ΔF_tgt, the motor rotation speed is further lowered by ΔF_tgt to suppress the maximum value of the motor current. Thereafter, if I <Ilim at t5, the command rotational speed is increased to restore the motor rotational speed to the original command rotational speed F_tgt.

  If I> Ilim at t6 while the command rotational speed is increasing, the motor rotational speed is decreased by ΔF_tgt and the maximum value of the motor current is suppressed. After decreasing the motor speed, if I <Ilim at t7, the command speed is increased to restore the motor speed to the original command speed F_tgt.

  As described above, a motor that limits the maximum value of the motor current value in the vicinity of Ilim by performing the rotation speed control that increases or decreases the motor rotation speed based on the comparison result between the motor current value I detected by the current detection circuit and the current value Ilim. Drive.

  However, when the motor current value I satisfies I> Imax, and when the motor rotation speed by the rotation speed control is less than the minimum rotation speed F_tgt_min that guarantees motor driving, the motor is stopped and the motor current is limited. To do.

  Next, the torque pulsation during one rotation is large like a one-piston rotary compressor in the low-speed rotation region, and in order to suppress the vibration due to this torque pulsation, the command current value is pulsated according to the torque pulsation to suppress the vibration. The current limiting method in the electric motor drive currently performed is demonstrated.

  Thus, in the motor drive that suppresses vibration due to torque pulsation, the motor current is effectively increased by increasing / decreasing the amount of fluctuation of the command current value from the rotation speed control that increases / decreases the rotation speed as a method of limiting the maximum value of the motor current. The maximum value of can be limited.

  FIG. 11 is a diagram showing an increase / decrease adjustment of the fluctuation amount of the command current value. As shown in FIG. 11A, the command current value is increased by I_tgt_up1 in a section where the torque is insufficient from the command current value I_tgt_m in accordance with the torque pulsation, and the command current value is decreased by I_tgt_down1 in the section where the torque is excessive. It becomes a command current value in a driving state in which the rotation speed is stabilized and vibration due to electric motor driving is suppressed.

  When I> Ilim in such an electric motor drive, as shown in FIG. 11B, the increment of the command current value to be increased in the torque deficient section is I_tgt_up2 (<I_tgt_up1), and the command current is decreased in the excessive torque section. The maximum value of the motor current is limited by reducing the amount of fluctuation so that the decrease in value becomes I_tgt_down2 (<I_tgt_down1).

  FIG. 12 is a diagram illustrating a change over time in the variation amount of the command current value when the current limit is performed by controlling the variation amount of the command current value. Here, for the sake of simplicity, the amount of change in the command current value is such that the increment I_tgt_up and the decrease I_tgt_down are the same value I_tgt_updown.

  When the motor current I becomes I> Ilim at t1 while the motor is being driven, the maximum value of the motor current is suppressed by lowering the fluctuation amount of the command current value by ΔI_tgt_updown. After reducing the fluctuation amount of the command current value, if I <Ilim at t2, the fluctuation amount of the command current value is returned to the original fluctuation amount I_tgt_updown.

  Thereafter, when I> Ilim again at t3, the fluctuation amount of the command current value is decreased by ΔI_tgt_updown. When I> Ilim at t4 where the fluctuation amount of the command current value is lowered by ΔI_tgt_updown, the fluctuation amount of the command current value is further lowered by ΔI_tgt_updown. At t5, if I> Ilim, the fluctuation amount of the command current value is further decreased by ΔI_tgt_updown.

  At t6 when the fluctuation amount of the command current value adjusted by the motor current reaches I_tgt_updown_min that is almost zero, if I> Ilim, current control based on the rotation speed control described above is performed.

Thereafter, after returning to the original rotational speed, when I <Ilim at t7, the fluctuation amount of the command current value is increased by ΔI_tgt_updown. When I <Ilim at t8, the fluctuation amount of the command current value is further increased by ΔI_tgt_updown. If> Ilim, the fluctuation amount of the command current value is decreased by ΔI_tgt_updown to suppress the maximum value of the motor current.

  Thereafter, if I <Ilim, the fluctuation amount of the command current value is increased from t10 to return to the original I_tgt_updown. Based on the comparison result between the detected motor current value I and the current value Ilim, the amount of change in the command current value is increased or decreased, and the motor drive is performed to limit the maximum value of the motor current value in the vicinity of Ilim.

  However, when the motor current value I satisfies I> Imax, and after the fluctuation amount of the command current value reaches less than I_tgt_updown_min and shifts to the current limit by the rotation speed control, the motor rotation speed ensures the motor drive. When it becomes less than the minimum rotation speed F_tgt_min, the motor is stopped to limit the motor current.

  As described above, in the present embodiment, the output voltage from the smoothing circuit 3 is provided by including the limiting current value correction circuit 15 that corrects the limiting current value for starting the limiting control on the motor current according to the driving rotational speed of the motor 5. Realizes motor drive that does not flow more than the current value guaranteed to the motor in accordance with the drive rotation speed and drive state of the motor 5 in the motor control device in which the motor pulsates at a frequency twice the AC power supply frequency. It can be made.

  As described above, the motor control device according to the present invention can effectively limit the motor current within the guaranteed current value according to the driving state, and can reduce the cost and size of the device. Therefore, the present invention can be applied to any motor control device that requires cost reduction and downsizing of the device.

Block configuration diagram of the motor control device according to the first embodiment of the present invention. The figure which shows the example 1 of a relationship of instruction | command rotation speed in the Embodiment 1 of this invention, instruction | command electric current value, and real rotation speed. The figure which shows the example 2 of a relationship of instruction | command rotation speed, instruction | command electric current value, and actual rotation speed in Embodiment 1 of this invention. The figure which shows the example 3 of a relationship of instruction | command rotation speed, instruction | command electric current value, and actual rotation speed in Embodiment 1 of this invention. The figure which shows the sampling plot example of the motor current in Embodiment 1 of this invention The figure which shows the relationship of the limiting current value correction | amendment by the drive rotation speed in Embodiment 1 of this invention Temperature characteristic diagram of electric motor demagnetization current value in Embodiment 1 of the present invention The figure which shows the switching operation example 1 of the limiting current value in Embodiment 1 of this invention The figure which shows the switching operation example 2 of the limiting current value in Embodiment 1 of this invention The figure which shows the operation example 1 of the current limiting circuit in Embodiment 1 of this invention. The figure which shows the operation example 2 of the current limiting circuit in Embodiment 1 of this invention. The figure which shows the operation example 3 of the current limiting circuit in Embodiment 1 of this invention. The figure which shows an output voltage waveform from the smoothing circuit in the conventional motor control apparatus

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectification circuit 3 Smoothing circuit 4 Orthogonal transformation circuit 5 Electric motor 6 Current detection circuit 7 Phase calculation circuit 8 Rotation speed command circuit 9 Current command calculation circuit 10 Voltage command calculation circuit 11 PWM signal generation circuit 12 Current limit circuit 13 Temperature detection Circuit 14 Limiting current value setting circuit 15 Limiting current value correction circuit

Claims (4)

Rectifying means for rectifying the AC power supply, smoothing means in which the output voltage from the rectifying means pulsates at twice the frequency of the AC power supply frequency, and orthogonal transform means for converting the smoothed voltage to a desired AC voltage for driving the motor Current detection means for detecting the current of the motor, phase calculation means for calculating the rotation phase of the motor based on the detection value of the current detection means, rotation speed command means for instructing the rotation speed of the motor, and the rotation speed A voltage command value is calculated based on a current command calculation means for calculating a current command value from an instruction rotation speed from the command means and an actual rotation speed calculated from the phase calculation means, and a current command value from the current command calculation means. A voltage command calculating means; a PWM signal generating means for generating a signal for driving the orthogonal transform means from the voltage command value; a current limiting means for limiting the motor current; and detecting the temperature of the motor. That a temperature detector, wherein the electric motor controller with limited current value setting means for setting the limit current value to limit the motor current value detected by from said temperature detecting means, I by the driving rotation speed of the electric motor Limiting current value set by the limiting current value setting means, and limiting current value correcting means for setting the limiting current value low when the drive speed becomes high, and the motor current exceeds a predetermined current value First, in order to limit the motor current, the amount of fluctuation of the current command value during one rotation of the motor from the current command calculation means is reduced to limit the motor current, and when the motor reaches less than the predetermined fluctuation amount, the motor rotation speed is lowered for a predetermined time. If the motor current value still exceeds the maximum allowable value, the motor speed for limiting the motor current is then lowered, and the motor speed is not set to the predetermined speed. When reaching, the motor control device and a said current limiting means for stopping the motor. The electric motor control device according to claim 1 , wherein the smoothing means includes a capacitor and a reactor, and a resonance frequency obtained from the capacitor and the reactor is set to be 40 times or more of an AC power supply frequency . The motor control device according to claim 1, wherein a film capacitor is used as a capacitor constituting the smoothing means . The electric motor control device according to any one of claims 1 to 3 , wherein a one-piston rotary compressor including a DC motor using a permanent magnet (ferrite magnet) is used for the electric motor.