JP5168925B2 - 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. 8 shows an output voltage waveform from the smoothing circuit in the 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 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, the current more than necessary is supplied in order to maintain the drive torque of the motor, and there is a problem 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-described problems, an electric motor control apparatus according to the present invention drives a rectifier that rectifies an AC power supply, a smoothing means that an output voltage from the rectifier pulsates at twice the frequency of the AC power supply frequency, and an electric motor. Therefore, an orthogonal transform unit that converts a smooth voltage into a desired AC voltage, a current detection unit that detects a current of the motor, a phase calculation unit that calculates a rotation phase of the motor based on a detection value of the current detection unit, 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, and the current Voltage command calculation means for calculating a voltage command value based on a current command value from the command calculation means, and PWM signal generation means for generating a signal for driving the orthogonal transformation means from the voltage command value In the motivation control device, the motor control device further includes a current limiting unit that limits the motor current, and the current limiting unit first reduces a fluctuation amount of the current command value during one rotation of the motor from the current command calculation unit in order to limit the motor current. When the motor speed reaches a predetermined fluctuation amount, control is performed to reduce the motor speed for a predetermined time. If the motor current value still exceeds the allowable maximum value, the motor speed is then reduced to limit the motor current. When the motor speed reaches less than a predetermined speed, the motor is stopped .

  As a result, 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 motor drive that suppresses the deterioration of the motor performance and the breakdown of the component devices caused by flowing an excessive current to the motor. Can be realized.

  The motor control device according to the present invention can 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 An electric motor control apparatus comprising: a voltage command calculating means for calculating a voltage command value; and 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 said current limiting means, first to lower the amount of variation of the current command value in the motor revolution from the current command calculating means for limiting the motor current, and reaches below a predetermined change amount If the motor speed is controlled to decrease for a predetermined time and the motor current value is still greater than or equal to the allowable maximum value, then the motor speed for limiting the motor current is decreased and the motor speed is set to the predetermined speed. When it reaches less than the number, the electric motor is stopped .

As a result, it is possible to realize motor driving that suppresses deterioration of motor performance and destruction of component devices caused by excessive current flowing in 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.

The second invention is the motor control apparatus of the first aspect of the invention, the smoothing means is a capacitor and the reactor is set to be the resonance frequency obtained from the capacitor and the reactor over 40 times the AC power source frequency Is. Thereby, high performance of the power supply harmonic characteristic of the input current to the rectifying means can be realized.

According to a third invention, in the motor control device of the first or second invention, 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 present invention, in the electric motor control device according to any one of the first to third aspects, a one-piston rotary compressor including a DC motor using a permanent magnet is applied to the electric motor. As a result, in the driving of an inexpensive standard compressor widely used in the global market, it is possible to realize a safe driving in which the motor current is limited and the deterioration of the motor performance due to the demagnetization of the permanent magnet is suppressed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to this embodiment.

(Embodiment 1)
FIG. 1 shows a block diagram of an electric motor control device according to a first embodiment of the present invention.

  The motor control device is supplied with power from an AC power source 1 such as a commercial power source that is a single-phase AC power source, and includes a rectifier circuit 2 configured by a diode bridge that performs full-wave rectification of the supplied AC power source, and a rectifier circuit 2 The output voltage from the smoothing circuit 3 pulsates greatly at twice the frequency of the AC voltage, and the orthogonal transformation circuit 4 comprising a semiconductor switching element that converts the output voltage from the smoothing circuit 3 into a desired AC voltage for driving the motor. A current detection circuit 6 for detecting the current flowing through the motor 5, a phase calculation circuit 7 for calculating the rotation phase of the motor 5 based on a detection value from the current detection circuit 6, and a command value for the motor rotation speed. Current command calculation for calculating a current command value for driving the motor from the rotation speed command circuit 8 and the rotation speed command value from the rotation speed command circuit 8 and the actual rotation speed calculated from the phase calculation circuit A voltage command calculation circuit 10 that calculates a voltage command value based on the current command value, a PWM signal generation circuit 11 that generates a signal for driving the orthogonal transformation circuit 4 from the voltage command value, and a motor current greater than or equal to a predetermined value. Is detected from the current detection circuit 6, at least of the methods of stopping the motor 5, lowering the motor rotation speed for a predetermined time, and reducing the fluctuation amount of the current command value during one rotation of the motor from the current command calculation circuit 9. It has a current limiting circuit 12 that limits the motor current by one method.

  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.

  In addition, since the reactor which comprises the smoothing circuit 3 is inserted between the alternating current power supply 1 and the capacitor | condenser which comprises the smoothing circuit 3, it may be either before and after the rectifier circuit 2. FIG.

  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 show 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, in a section where the actual rotational speed decreases due to insufficient torque, the command current value I_tgt_m By increasing I_tgt_up and conversely when 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, thereby realizing stable driving at Vm.

  Next, a method for limiting the motor current will be described with reference to FIGS. FIG. 5 shows the change over time in the commanded rotational speed when current limitation is performed by rotational speed control. Here, it is assumed that the detected motor current value is I, the current value for starting current limitation by the rotational speed control is Ilim, and the maximum motor current allowable by the motor is Imax (Imax> Ilim).

  First, in the case of an electric motor drive that gives an almost 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 becomes 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. 6 shows increase / decrease adjustment of the fluctuation amount of the command current value. In FIG. 6A, the actual rotation speed is stabilized by increasing the command current value I_tgt_up1 in the section where the torque is insufficient from the command current value I_tgt_m in accordance with the torque pulsation, and decreasing the command current value I_tgt_down1 in the section where the torque is excessive. The command current value in a driving state in which vibration due to electric motor driving is suppressed is shown.

  When I> Ilim in such an electric motor drive, as shown in FIG. 6B, the increase in 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. 7 shows a change over time in the amount of change in the command current value when the current is limited by controlling the amount of change in 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 electric motor 5 is stopped based on the detection value from the current detection circuit 6, the electric motor rotation speed is lowered for a predetermined time, and the electric current command value during one rotation of the electric motor from the electric current command calculation circuit 9 Motor control apparatus in which the output voltage from the smoothing circuit 3 greatly pulsates at twice the frequency of the AC power supply frequency by providing a current limiting circuit that limits the motor current by at least one of the methods for reducing the fluctuation amount of In this case, it is possible to realize motor driving without flowing a current exceeding the guaranteed current value in the motor 5.

  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, it can be applied to any motor control device that requires cost reduction and downsizing of the device.

Block diagram of electric motor control apparatus according to Embodiment 1 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 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 the 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 Rotational speed command circuit 9 Current command calculation circuit 10 Voltage command calculation circuit 11 PWM signal generation circuit 12 Current limit 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. In a motor control device comprising a voltage command calculating means and a PWM signal generating means for generating a signal for driving the orthogonal transform means from the voltage command value, a current limit for limiting the motor current Comprises a stage, said current limiting means, first to lower the amount of variation of the current command value in the motor revolution from the current command calculating means for limiting the motor current, motor speed is reached below a predetermined change amount If the motor current value still exceeds the allowable maximum value, the motor rotation speed for limiting the motor current is then decreased, and the motor rotation speed is less than the predetermined rotation speed. An electric motor control device that stops the electric motor when reaching the electric motor. 2. 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 or 2 , wherein a film capacitor is used as a capacitor constituting the smoothing means . 4. The motor control device according to claim 1, wherein a one-piston rotary compressor including a DC motor using a permanent magnet is used for the motor .

Images