JP2008125205A - Motor driver and air conditioner using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a motor driver which can successively operate stably by suppressing a speed variation at a time other than overloading, and further preventing an overcurrent protective device from operating at overloading. <P>SOLUTION: A torque command correcting means is provided, and when the phase current of a brushless motor detected by a current detection means is larger than a preset value, an amount of a torque command decided by a torque control means is decreased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric motor drive device that drives an electric motor such as a brushless DC motor at an arbitrary rotation speed.

  In recent years, in an apparatus for driving an electric motor such as a compressor in an air conditioner, there is an increasing need to reduce power consumption from the viewpoint of protecting the global environment. Among them, as one of the power saving technologies, an inverter that drives a highly efficient electric motor such as a brushless DC motor at an arbitrary frequency is widely used. Furthermore, as a driving technique, a sine wave driving technique that is more efficient and can reduce noise than a rectangular wave driving that is driven by a rectangular wave current is becoming mainstream. In addition, the mainstream of the compressor used is a highly efficient and inexpensive one-piston rotary compressor.

  When driving an electric motor such as a compressor in an air conditioner, it is difficult to attach a sensor for detecting the position of the rotor of the electric motor. A sinusoidal drive technique has also been invented. As a method of estimating the rotor position, there is a method of estimating the induced voltage of the motor, and a method of estimating from the current flowing through the inverter bus (for example, Patent Document 1), or flowing to the motor using a current sensor. A method of estimating from the current (for example, Patent Document 2) has been invented.

  In addition, when driving an electric motor having a large load torque fluctuation generated during one rotation of the rotor of the electric motor, such as a one-piston rotary compressor, a torque control means (for example, a patent) Document 3) has been invented.

  FIG. 4 shows a system configuration for realizing the position sensorless sine wave drive described in Patent Document 1. 1 is a DC power source, 2 is an inverter, 3 is a brushless motor, 4 is a stator, 5 is a rotor, and 6 is a control unit.

  The brushless motor 3 includes a stator 4 to which three phase windings 4u, 4v, 4w Y-connected around a neutral point are attached, and a rotor 5 to which a magnet is attached. A U-phase terminal 8u is connected to the non-connection end of the U-phase winding 4u, a V-phase terminal 8v is connected to the non-connection end of the V-phase winding 4v, and a W-phase terminal 8w is connected to the non-connection end of the W-phase winding 4w.

  The inverter 2 has three series circuits in which a pair of switching elements are connected in series in a relationship between the upstream side and the downstream side of the current, for U phase, for V phase, and for W phase. A DC voltage output from the DC power source 1 is applied to these series circuits. The U-phase series circuit includes an upstream side switching element 12u and a downstream side switching element 13u. The series circuit for V phase includes an upstream side switching element 12v and a downstream side switching element 13v. The series circuit for W phase includes an upstream side switching element 12w and a downstream side switching element 12w. Free wheel diodes 14u, 14v, 14w, 15u, 15v, and 15w are connected in parallel with the switching elements.

  Terminals 8u, 8v, and 8w of the brushless motor 3 are connected to an interconnection point of the switching elements 12u and 13u, an interconnection point of the switching elements 12v and 13v, and an interconnection point of the switching elements 12w and 13w in the inverter 2, respectively. .

The DC voltage applied to the inverter 2 is converted into a three-phase AC voltage by a circuit such as the switching element in the inverter 2 described above, and the brushless motor 3 is thereby driven.

  In order to realize the target speed given from the outside, the PWM signal generating means 9 generates a PWM signal for driving the switching element of the inverter 2 in order to output the output voltage calculated from the error with the current speed. The switching signals 12u, 12v, 12w, 13u, 13v, and 13w operate by being converted by the base driver 10 into drive signals for electrically driving the elements.

  The control unit 6 includes the phase current of the brushless motor 3 detected by the current detection means 7 arranged on the inverter bus, the output voltage calculated by the PWM signal generation means 9 and the DC power source 1 detected by the inverter applied voltage detection means 16. The induced voltage of the brushless motor 3 is estimated by the induced voltage estimation means 17 from the DC voltage output from The estimated induced voltage is compared with the induced voltage determined based on the phase voltage equation of each phase of the brushless motor 3 by the rotor position speed detecting means 18, and the rotor magnetic pole position of the brushless motor 3 is determined based on the comparison result. And estimate the speed.

  FIG. 5 shows a system configuration for realizing the position sensorless sine wave drive described in Patent Document 2, and the means for detecting the phase current of the brushless motor 3 is changed from the current detection means 7 arranged on the inverter bus to the current sensors 20v and 20w. Other configurations and operations are the same as those of the invention described in Patent Document 1.

  FIG. 6 shows a system configuration for realizing torque control described in Patent Document 3. Reference numeral 21 denotes torque control means for controlling the load torque of the brushless motor 3. The torque control means 21 is detected by the rotor position speed detection means 18. The rotor acceleration detecting means 19 for calculating the acceleration using the detected speed and the acceleration control means 20 for controlling the detected acceleration fluctuation to be zero. The torque control means 21 detects the acceleration by the rotor acceleration detection means 19, determines the torque command amount from the current acceleration and the target acceleration by the acceleration control means 20, and outputs it to the PWM signal generation means 9.

  The rotor position speed detection means 18 calculates an estimated current value of the motor from the motor model equation using the current detected by the current detection means 7, the DC voltage output from the inverter 2, and the motor constant of the brushless motor 3. Then, the position of the rotor is estimated by using an error from the current detected by the current detection means 7. Here, the current value detected by the current detection means 7 and the current value estimated from the motor model equation are converted into a current iδ in the axis δ direction of the rotating magnetic field and a current iγ in the axis γ direction of the magnetic flux direction. By controlling it as a direct current value, torque control is easily realized.

  The PWM signal generation means 9 adds or subtracts a torque command amount for realizing the target acceleration to the output voltage calculated from an error from the current speed in order to realize the target speed given from the outside, and drives the switching element of the inverter 2. A PWM signal is generated and further converted into a drive signal for electrically driving the switching element by the base driver 10, and each switching element 12u, 12v, 12w, 13u, 13v, 13w operates.

The drive control of the brushless motor 3 is performed with the circuit configuration as described above.
JP 2003-189670 A JP 2000-350489 A JP 2001-37281 A

  However, when a motor with a large variation in load torque during one rotation of the rotor of the motor, such as a one-piston rotary compressor, is driven using the torque control, a voltage applied to the inverter when the load torque is large When the load torque is small, control is performed to reduce the voltage applied to the inverter. Therefore, the maximum motor current increases compared to when torque control is not used. Had the problem of operating.

  In addition, a general electric motor drive device has an overcurrent protection function for stopping motor operation when a current flowing through the motor exceeds a certain value in order to prevent demagnetization of the motor and overcurrent breakdown of the power device. Therefore, if torque control is performed with a constant torque control amount regardless of the size of the load, the torque control amount cannot be increased due to the need to prevent the overcurrent protection device from operating during overload, There was a problem that speed fluctuations other than overload could not be suppressed.

  The present invention solves the above-mentioned problem, can suppress speed fluctuations other than during overload, can further prevent the overcurrent protection device from operating during overload, and is continuously stable. An object of the present invention is to provide an electric motor drive device that can be operated smoothly.

  In order to solve the above-mentioned conventional problems, the electric motor drive device of the present invention is provided with a torque command correction means, and when the phase current of the electric motor detected by the current detection means exceeds a preset value, the torque control means By reducing the determined torque command amount, it is possible to suppress speed fluctuations except during overload, and motor vibration and noise can also be suppressed. Further, since the torque control amount is limited at the time of overload, the speed fluctuation during one rotation increases, but the overcurrent protection device is prevented from operating.

  The electric motor drive device of the present invention realizes an electric motor drive device capable of suppressing the speed fluctuation of the electric motor having a large torque fluctuation during one rotation of the rotor of the electric motor and capable of continuously operating stably. .

  According to a first aspect of the present invention, there is provided an overload by providing torque command correction means for reducing the torque command amount determined by the torque control means when the phase current of the motor detected by the current detection means exceeds a preset value. Electric motor drive that can prevent the motor from stopping due to the overcurrent protection function operating at the time, and can suppress speed fluctuations other than during overload, enabling continuous stable operation The device is realized.

  In the second invention, in particular, the detection of the phase current flowing through the three-phase motor of the first invention is detected using the current detection means arranged on the inverter bus, and the phase current can be generated at low cost.

  The third aspect of the invention detects the phase current flowing in the three-phase motor of the first aspect of the invention using a current sensor, and can detect the phase current with high accuracy.

  In the fourth aspect of the invention, in particular, the electric motor drive device according to the first to third aspects of the invention is used for driving a compressor of an air conditioner, and a one-piston rotary compressor is used for the compressor of the air conditioner. Thus, an inexpensive and low vibration air conditioner is provided.

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

(Embodiment 1)
FIG. 1 is a block diagram according to the first embodiment of the present invention. 1 is a DC power source, 2 is an inverter, 3 is a brushless motor, 4 is a stator, 5 is a rotor, and 6 is a control unit.

  The brushless motor 3 includes a stator 4 to which three phase windings 4u, 4v, 4w Y-connected around a neutral point are attached, and a rotor 5 to which a magnet is attached. A U-phase terminal 8u is connected to the non-connection end of the U-phase winding 4u, a V-phase terminal 8v is connected to the non-connection end of the V-phase winding 4v, and a W-phase terminal 8w is connected to the non-connection end of the W-phase winding 4w.

  The inverter 2 has three series circuits in which a pair of switching elements are connected in series in a relationship between the upstream side and the downstream side of the current, for U phase, for V phase, and for W phase. A DC voltage output from the DC power source 1 is applied to these series circuits. The U-phase series circuit includes an upstream side switching element 12u and a downstream side switching element 13u. The series circuit for V phase includes an upstream side switching element 12v and a downstream side switching element 13v. The series circuit for W phase includes an upstream side switching element 12w and a downstream side switching element 12w. Free wheel diodes 14u, 14v, 14w, 15u, 15v, and 15w are connected in parallel with the switching elements.

  Terminals 8u, 8v, and 8w of the brushless motor 3 are connected to an interconnection point of the switching elements 12u and 13u, an interconnection point of the switching elements 12v and 13v, and an interconnection point of the switching elements 12w and 13w in the inverter 2, respectively. .

  The DC voltage applied to the inverter 2 is converted into a three-phase AC voltage by a circuit such as the switching element in the inverter 2 described above, and the brushless motor 3 is thereby driven.

  The torque control means 21 detects the current speed at every certain period by the rotor acceleration detection means 19, compares the amount of change in the certain period as acceleration, and compares it with the target acceleration by the acceleration control means 20. The torque command amount for realizing is determined.

  The PWM signal generating means 9 drives the switching element of the inverter 2 by increasing or decreasing the torque command amount for realizing the target acceleration to the output voltage calculated from the error with the current speed in order to realize the target speed given from the outside. PWM signal to be generated is further converted into a drive signal for electrically driving the switching element by the base driver 10, and each switching element 12u, 12v, 12w, 13u, 13v, 13w operates.

  The control unit 6 includes the phase current of the brushless motor 3 detected by the current detection means 7 arranged on the inverter bus, the output voltage calculated by the PWM signal generation means 9 and the DC power source 1 detected by the inverter applied voltage detection means 16. The induced voltage of the brushless motor 3 is estimated by the induced voltage estimation means 17 from the DC voltage output from Further, the rotor position / velocity detecting means 18 estimates the rotor magnetic pole position and speed of the brushless motor 3 from the estimated induced voltage.

  When the phase current of the brushless motor 3 detected by the current detecting means 7 is larger than a preset value, the torque command correcting means 11 reduces the torque command amount determined by the torque control means, so that the torque command correcting means 11 An electric motor drive device that can prevent an overcurrent protection function from operating and stop the motor, further suppresses speed fluctuations other than during overload, and enables stable operation continuously. It is realized.

(Embodiment 2)
FIG. 2 is a block diagram according to the second embodiment of the present invention, which detects the phase current flowing through the brushless motor 3 using the current sensors 22v and 22w, thereby detecting the phase current with high accuracy. Since other configurations and operations are the same as those in the first embodiment, description thereof is omitted.

(Embodiment 3)
FIG. 3 is a block diagram according to the third embodiment of the present invention, in which 23 is an outdoor unit of an air conditioner and 24 is a compressor. By using a 1-piston rotary compressor for the 24 compressors, an inexpensive and low-vibration air conditioner is realized.

  As described above, the electric motor drive device of the present invention reduces the rotor position estimation error and enables stable driving, so it can be used for industrial equipment and products that use a position sensorless brushless DC motor. it can.

The block diagram of the electric motor drive device in Embodiment 1 of this invention Block diagram of an electric motor drive device according to Embodiment 2 of the present invention The block diagram of the air conditioner in Embodiment 3 of this invention Block diagram of a conventional current sensorless motor drive device Block diagram of a conventional motor drive unit with a current sensor Block diagram of an electric motor drive device provided with a conventional torque control means

Explanation of symbols

1 DC power supply 2 Inverter 3 Brushless motor (three-phase motor)
6 Control section 7 Current detection means 9 PWM signal generation means 10 Base driver 11 Torque command correction means 16 Inverter applied voltage detection means 17 Induced voltage estimation means 18 Rotor position speed detection means 19 Rotor acceleration detection means 20 Acceleration control means 21 Torque Control means

Claims (4)

An electric motor comprising a three-phase motor, an inverter, and torque control means for controlling the inverter so that the torque generated by the three-phase motor matches the load torque generated by the load element driven by the three-phase motor In the torque control apparatus, when the current detection means for detecting the phase current flowing through the three-phase motor and the current detected by the current detection means are larger than a preset value, the torque command amount determined by the torque control means An electric motor drive device comprising torque command amount correction means for reducing the torque. The motor drive device according to claim 1, wherein the phase current of the three-phase motor is detected from the inverter bus. The motor driving device according to claim 1, wherein the phase current of the three-phase motor is detected using a current sensor. An air conditioner using the electric motor drive device according to claim 1 and using a 1-piston rotary compressor as a compressor.

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