JP2007267512A - Drive controller of ac motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of noise while preventing overheat of an inverter when an AC motor is locked. <P>SOLUTION: When an AC motor is locked, vector switching control is performed to vary the current vector of the AC motor such that loss of an inverter is reduced by increasing loss of the AC motor thus avoiding concentration of current on a specific switching element of the inverter. In the vector switching control, torque of the AC motor is held constant by switching a command current vector in the order of current vectors i0, i1 and i2 thereby increasing reactive power of the AC motor periodically. The current vector i0 generates a torque slightly smaller than the maximum torque, and the current vectors i1 and i2 generate a torque identical to that of the current vector i0 and increase reactive power as compared with the current vector i0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an AC motor drive control device for driving a synchronous multiphase AC motor with an inverter.

  Conventionally, as an AC motor drive control technology such as a three-phase permanent magnet synchronous motor, there is one that drives an AC motor by controlling switching of an inverter by sinusoidal PWM control or the like. However, in an electric vehicle equipped with an AC motor as a power source of the vehicle, a desired torque is generated when the wheel is locked and the AC motor is locked (when the rotational speed of the AC motor becomes almost zero). If it tries to do so, current may concentrate on a specific switching element among the switching elements of each arm provided in the inverter, and the switching element may be overheated.

  As a countermeasure, as described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-69761), when the AC motor is locked, the PWM control carrier frequency (the frequency of the carrier signal) is switched to a low frequency, and the inverter By switching the switching frequency to a low frequency, the inverter switching loss is reduced to prevent overheating of the inverter (switching element).

  However, if the carrier frequency (inverter switching frequency) is lowered to a level where overheating of the inverter can be prevented, there is a problem that magnetic noise or the like enters the audible region and noise is generated.

Therefore, as described in Patent Document 2 (Japanese Patent Laid-Open No. 2000-134990), when the AC motor is locked, the inverter may be damaged due to the torque command value of the AC motor and the temperature of the inverter. The frequency is lowered by switching the carrier frequency (inverter switching frequency) to a lower protection frequency when the inverter is in a high risk of thermal damage. There is one that can shorten the period during which noise is generated.
JP 2000-69761 A (pages 2 to 3 etc.) JP 2000-134990 A (5th page, FIG. 4 etc.)

  However, even in the technique of Patent Document 2 described above, the situation of lowering the carrier frequency (inverter switching frequency) in order to prevent overheating of the inverter when the AC motor is locked remains unchanged. There is a drawback that the generation of noise cannot be sufficiently prevented.

  The present invention has been made in view of such circumstances. Accordingly, the object of the present invention is to provide an AC that can prevent noise generation while preventing overheating of the inverter when the AC motor is locked. The object is to provide a motor drive control device.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided an AC motor drive control device comprising a synchronous multi-phase AC motor and an inverter for driving the AC motor. When the speed is lower than the rotation speed, vector switching control is performed to change the current vector that is applied to the AC motor or the voltage vector that is applied to the AC motor so as to increase the loss of the AC motor and decrease the loss of the inverter. Is.

  In this configuration, when the AC motor is locked and the rotation speed of the AC motor becomes equal to or lower than the predetermined rotation speed, vector switching control is executed to increase the AC motor loss and decrease the inverter loss. By changing the current vector or voltage vector of the motor, it is possible to change the current path of the inverter (that is, the switching element through which the current flows) to avoid current concentration on a specific switching element. ) Overheating. In addition, since it is not necessary to lower the switching frequency of the inverter, it is possible to prevent the generation of noise due to the lower frequency.

  By the way, it is not necessary to perform vector switching control because there is no concern about overheating of the inverter when the rotational speed of the alternating current motor exceeds a predetermined rotational speed when the alternating current motor is operated from a stop instead of locking the alternating current motor. Absent.

  Therefore, as in the second aspect, the vector switching control may be executed when the rotational speed of the AC motor is equal to or lower than the predetermined rotational speed and the torque command value is equal to or higher than the predetermined torque. That is, when the rotational speed of the AC motor is equal to or lower than the predetermined rotational speed and the torque command value is equal to or higher than the predetermined torque, it is determined that the AC motor is locked, and the vector switching control is executed, so that the rotational speed of the AC motor is predetermined. When it is higher than the rotational speed or when the torque command value is lower than the predetermined torque, it is determined that the AC motor is not locked, and the vector switching control is not executed. In this way, it is possible to avoid executing the vector switching control when the AC motor is stopped (when the rotational speed of the AC motor is equal to or lower than the predetermined rotational speed and the torque command value is lower than the predetermined torque).

  Further, as in claim 3, during the vector switching control, the torque of the AC motor is kept constant by periodically switching the current vector or the voltage vector so as to periodically increase the reactive power of the AC motor. You may do it. In this way, it is possible to avoid current concentration on a specific switching element of the inverter while keeping the torque of the AC motor constant, and without causing unpleasant torque fluctuations and torque shortages. Overheating can be prevented.

Hereinafter, an embodiment in which the best mode for carrying out the present invention is applied to an electric vehicle or a hybrid vehicle using an AC motor as a power source will be described.
First, the overall configuration of the AC motor drive control device will be schematically described with reference to FIG. The AC motor 11 is a three-phase permanent magnet type synchronous motor used as a power source for a vehicle, and is equipped with a permanent magnet, and a rotor rotational position sensor 12 for detecting the rotational position θ of the rotor is mounted. . The AC motor 11 is driven by a voltage-controlled three-phase inverter 13. The inverter 13 is provided with switching elements corresponding to the respective phases on the upper and lower arms, a driving circuit for driving these switching elements, a smoothing capacitor for smoothing a DC voltage and absorbing a surge voltage, etc. (Not shown). The inverter 13 generates a three-phase DC voltage supplied from a DC power source 15 such as a secondary battery based on three-phase voltage command signals UU, UV, UW output from the inverter control device 14 (motor control means). The AC motor 11 is driven by converting into AC voltages U, V, and W. The U-phase current iu and the W-phase current iw of the AC motor 11 are detected by current sensors 16 and 17, respectively.

  The vehicle ECU 18 is a computer that comprehensively controls the entire vehicle, and includes an accelerator sensor that detects an accelerator operation amount, a shift switch that detects a shift operation, a brake switch that detects a brake operation, a vehicle speed sensor that detects a vehicle speed, and the like. The output signals of various sensors (not shown) and switches are read to detect the driving state of the vehicle. The vehicle ECU 18 transmits and receives control signals and data signals to and from the inverter control device 14, and controls the inverter 13 according to the driving state of the vehicle by the inverter control device 14 to control the operation of the AC motor 11.

  At that time, the inverter control device 14 executes a motor control program shown in FIG. 3 to be described later in order to control the torque of the AC motor 11, whereby the torque command value T * output from the vehicle ECU 18 and the AC motor 11 are controlled. Based on the U-phase current iu and the W-phase current iw (output signals of the current sensors 16 and 17) and the rotor rotation position θ of the AC motor 11 (output signal of the rotor rotation position sensor 12), a three-phase sine wave PWM control method is used. The voltage command signals UU, UV, UW are generated as follows.

  First, the rotational speed N of the AC motor 11 is calculated based on the rotor rotational position θ of the AC motor 11. Thereafter, in the dq coordinate system set as the rotation coordinates of the rotor of the AC motor 11, the torque command value T * of the AC motor 11 is used to independently control the d-axis current id and the q-axis current iq. And a command current vector i * (d-axis command current id *, q-axis command current iq *) corresponding to the rotation speed N and a map or a mathematical formula.

  Thereafter, an actual current vector i (d-axis current id, q-axis current iq) is calculated based on the U phase and W phase currents iu, iw of the AC motor 11 and the rotor rotational position θ of the AC motor 11, and d The d-axis command voltage Vd * is calculated by PI control so that the deviation Δid between the axis command current id * and the actual d-axis current id is small, and the q-axis command current iq * and the actual q-axis current iq The q-axis command voltage Vq * is calculated by PI control so that the deviation Δiq is small. Then, the d-axis command voltage Vd * and the q-axis command voltage Vq * are converted into three-phase voltage command signals UU, UV, UW, and these three-phase voltage command signals UU, UV, UW are output to the inverter 13. Thus, torque control for controlling the torque of the AC motor 11 is executed so as to realize the torque command value T * output from the vehicle ECU 18.

  By the way, when the wheel is locked and the AC motor 11 is locked (when the rotational speed of the AC motor 11 becomes substantially zero), if an attempt is made to generate a desired torque while continuing normal motor control, an inverter There is a possibility that the current concentrates on a specific switching element among the switching elements of each arm provided in 13 and the switching element is overheated.

  Therefore, when the AC motor 11 is locked, the inverter control device 14 periodically changes the current vector supplied to the AC motor 11 so as to increase the loss of the AC motor 11 and decrease the loss of the inverter 13. By executing the switching control as follows, overheating of the inverter 13 is prevented.

  As shown in FIG. 2, the dq coordinate system set as the rotation coordinates of the rotor of the AC motor 11 (a coordinate system in which the d axis is defined in the field direction of the rotor and the q axis is defined in the direction orthogonal to the field direction). ), The current limit circle A is a circle representing a current limit value (maximum current), and the maximum torque curve B is a current that can maximize the generated torque for the same current (current that generates torque most efficiently). ). Therefore, the intersection of the current limiting circle A and the maximum torque curve B becomes a current vector i that generates the maximum torque.

The constant torque curve C is a curve representing a current that generates the same torque, and can be represented by the following equation.
iq = T / {φ + (Ld−Lq) × id}
Here, φ is a magnetic flux, Ld is a d-axis inductance, and Lq is a q-axis inductance, which are device constants of the AC motor 11, respectively.

  The current vector i0 is a current vector on the maximum torque curve B, and is a current vector that generates torque slightly smaller than the current vector i (that is, torque slightly smaller than the maximum torque). The current vector i1 and the current vector i2 are current vectors that are intersections of the constant torque curve C representing the current that generates the same torque as the current vector i0 and the current limit circle A. That is, the current vector i1 and the current vector i2 are current vectors that generate the same torque as the current vector i0 and increase reactive power compared to the current vector i0.

  In the vector switching control of this embodiment, the command current vector i * is periodically switched in the order of the current vectors i0, i1, and i2, so that the reactive power of the AC motor 11 is periodically increased and the torque of the AC motor 11 is increased. Hold constant.

  Hereinafter, processing contents of the motor control program of FIG. 3 executed by the inverter control device 14 will be described. When this program is started, after the initialization process is executed in step 101, the processes after step 102 are repeatedly executed at a predetermined cycle.

  First, in step 102, the torque command value T * output from the vehicle ECU 18 is read, and then the process proceeds to step 103, where the AC motor is based on the rotor rotational position θ of the AC motor 11 (the output signal of the rotor rotational position sensor 12). 11 rotation speed N is calculated.

  Thereafter, the process proceeds to step 104 where a command current vector i * (d-axis command current id *, q-axis command current iq *) corresponding to the torque command value T * and the rotational speed N of the AC motor 11 is mapped or represented by a mathematical formula or the like. Calculate by

  Thereafter, the process proceeds to step 105, where it is determined whether the AC motor 11 is locked, whether the rotation speed of the AC motor 11 is equal to or lower than a predetermined rotation speed (for example, 0 or a slightly higher rotation speed than 0) and the torque of the AC motor 11. The determination is made based on whether or not the command value T * is equal to or greater than a predetermined torque.

  If it is determined in step 105 that the AC motor 11 is not locked (that is, if it is determined that the rotational speed of the AC motor 11 is higher than the predetermined rotational speed, or the torque command value T * of the AC motor 11). Is determined to be lower than the predetermined torque), the routine proceeds to step 106, where a variable n for current vector switching described later is reset to zero.

  Thereafter, the routine proceeds to step 111, where current control is executed based on the command current vector i *. In this current control, the d-axis command voltage Vd * is calculated by PI control so that the deviation Δid between the d-axis command current id * and the actual d-axis current id is small, and the q-axis command current iq * After calculating the q-axis command voltage Vq * by PI control so that the deviation Δiq from the q-axis current iq is small, the d-axis command voltage Vd * and the q-axis command voltage Vq * are converted into three-phase voltage command signals UU, UV, These are converted into UW, and these three-phase voltage command signals UU, UV, UW are output to the inverter 13.

  On the other hand, if it is determined in step 105 that the AC motor 11 is locked (that is, the rotational speed of the AC motor 11 is equal to or lower than the predetermined rotational speed and the torque command value T * of the AC motor 11 is equal to the predetermined torque). If it is determined that the above is satisfied, the process proceeds to step 107, and the current vector switching variable n is incremented by 1. Then, the process proceeds to step 108, and whether the current vector switching variable n is 3 or not. Determine.

  If it is determined in step 108 that the current vector switching variable n is 3, the process proceeds to step 109, the current vector switching variable n is reset to 0, and then the process proceeds to step 110. Set vector i * to current vector i0. As shown in FIG. 2, the current vector i0 is a current vector that generates torque slightly smaller than the current vector i (that is, torque slightly smaller than the maximum torque).

  On the other hand, if it is determined in step 108 that the variable n for current vector switching is not 3 (that is, the variable n is 1 or 2), the process proceeds to step 110, where the variable n for current vector switching is When 1, the command current vector i * is set to the current vector i1, and when the current vector switching variable n is 2, the command current vector i * is set to the current vector i2. As shown in FIG. 2, the current vector i1 and the current vector i2 are current vectors that generate the same torque as the current vector i0 and increase the reactive power compared to the current vector i0. The command current vector i * is periodically switched in the order of the current vectors i0, i1, and i2 by the processing of these steps 108-110.

  Thereafter, the process proceeds to step 111, and the reactive power of the AC motor 11 is periodically increased by executing current control based on the command current vector i * that periodically switches in the order of the current vectors i0, i1, and i2. Thus, vector switching control for periodically switching the current vector is executed. Thereby, the loss of the AC motor 11 is increased while the torque of the AC motor 11 is kept constant, and the loss of the inverter 13 is decreased.

  Thereafter, the process proceeds to step 112, where it is determined whether or not the power source of the vehicle ECU 18 has been turned off. If the power source has not been turned off, the processes in and after step 102 are repeatedly executed. Thereafter, when it is determined in step 112 that the power source of the vehicle ECU 18 is turned off, this program is terminated.

  In the present embodiment described above, when it is determined that the AC motor 11 is locked, the current vector of the AC motor 11 is periodically changed so as to increase the loss of the AC motor 11 and decrease the loss of the inverter 13. Since the vector switching control to be changed to is executed, when the AC motor 11 is locked, the current path of the inverter 13 (that is, the switching element through which the current flows) is changed to concentrate the current on a specific switching element. Can be avoided, and overheating of the inverter 13 (switching element) can be prevented. In addition, since it is not necessary to lower the switching frequency of the inverter 13, it is possible to prevent the generation of noise due to the lower frequency.

  Further, in this embodiment, during vector switching control, the torque of the AC motor 11 is kept constant by periodically switching the current vector so that the reactive power of the AC motor 11 is periodically increased. Therefore, it is possible to avoid current concentration on a specific switching element of the inverter 13 while keeping the torque of the AC motor 11 constant, and the inverter 13 is overheated without causing unpleasant torque fluctuation or torque shortage. Can be prevented.

  In this embodiment, when it is determined that the rotational speed of the AC motor 11 is equal to or lower than the predetermined rotational speed and the torque command value T * is equal to or higher than the predetermined torque, it is determined that the AC motor 11 is locked. When the vector switching control is executed and it is determined that the rotational speed of the AC motor 11 is higher than the predetermined rotational speed, or when it is determined that the torque command value T * of the AC motor 11 is lower than the predetermined torque. Since it is determined that the AC motor 11 is not locked and the vector switching control is not executed, when the AC motor 11 is stopped (the rotational speed of the AC motor 11 is equal to or lower than the predetermined rotational speed, the torque command value is predetermined). It is possible to avoid executing the vector switching control when the torque is lower than the torque.

  In the above embodiment, when the command current vector i * is switched between the current vectors i0, i1, and i2 by executing the vector switching control, the constant torque curve C and the current limit that generate the same torque as the current vector i0 are used. The current vectors at the intersections with the circle A are the current vectors i1 and i2. However, the present invention is not limited to this, and the current vectors i1 and i2 are not limited to the current vector i0. The current vector may be the current vectors i1 and i2. In short, when the command current vector i * is switched between the current vectors i0, i1 and i2, the current path of the inverter 13 (that is, the switching element through which the current flows). The current vectors i1 and i2 are set so that the angle formed by the current vector i1 and the current vector i2 is an electrical angle that is equal to or greater than a predetermined angle (for example, 60 °). If may.

  Further, instead of the current vector i0, the current vector i that generates the maximum torque is used to switch the command current vector i * between the current vectors i, i1, and i2 during the vector switching control. good.

  In the above embodiment, the command current vector i * is changed during the vector switching control. However, the command voltage vector may be changed. In this case, when the current control is temporarily opened and the command voltage vector V * is changed between the voltage vectors V, V1, and V2, the voltage vector V (voltage corresponding to the current vector i or i0) is obtained. Alternatively, feedback control may be performed.

  In addition, the present invention is not limited to an AC motor drive control device mounted on an electric vehicle or a hybrid vehicle, and can be applied to various devices using an AC motor as a drive source.

It is a block diagram which shows schematic structure of the whole drive control apparatus of the alternating current motor in one Example of this invention. It is a figure for demonstrating the vector switching control of a present Example. It is a flowchart which shows the flow of a process of the motor control program of a present Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... AC motor, 12 ... Rotor rotational position sensor, 13 ... Inverter, 14 ... Inverter control device (motor control means), 15 ... Power source, 16, 17 ... Current sensor, 18 ... Vehicle ECU

Claims (3)

In an AC motor drive control device comprising a synchronous multiphase AC motor and an inverter for driving the AC motor,
When the rotational speed of the AC motor is equal to or lower than a predetermined rotational speed, a current vector for energizing the AC motor or a voltage vector applied to the AC motor so as to increase the loss of the AC motor and decrease the loss of the inverter An AC motor drive control device comprising motor control means for executing vector switching control for changing the motor.   2. The AC motor according to claim 1, wherein the motor control unit executes the vector switching control when a rotation speed of the AC motor is equal to or lower than a predetermined rotation speed and a torque command value is equal to or higher than a predetermined torque. Drive control device.   The motor control means makes the torque of the AC motor constant by periodically switching the current vector or the voltage vector so as to periodically increase the reactive power of the AC motor during the vector switching control. The AC motor drive control apparatus according to claim 1, wherein the AC motor drive control apparatus holds the AC motor.

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