JP4415832B2 - Motor drive device - Google Patents

Description

  The present invention relates to correction of a current detection offset in a motor drive device.

  Current control using a motor drive device has generally been performed since the era of analog circuits for high-speed, high-response control of servo motors. In recent years, advances in microcomputer and LSI technology have led to digitalization of current control, and analog control has made it possible to perform complex control that was difficult to achieve in terms of design and cost. Contributes greatly to high functionality.

  Here, current control of a general motor drive device will be described with reference to the drawings.

  In FIG. 8, the motor driving device 1 detects a three-phase current of the servo motor 2 using a current detector 11. The current controller 12 uses the three-phase current detection value and the motor position information from the position detector 3 to generate a three-phase voltage command so that the three-phase current follows the current command, and outputs it to the power amplifier 13. The power amplifier 13 controls the input from the main power supply 4 to apply a voltage according to the three-phase voltage command to the servo motor 3.

  Further, the current controller 12 often uses dq control by digital calculation. The three-phase current detection value is converted into a d-axis current and a q-axis current, which are rotational coordinate systems, by a dq converter 121, and a d-axis command, which is a field component, and a q-axis command, which is a torque component, by a PI controller 122. And a d-axis voltage command and a q-axis voltage command are generated by performing PI calculation on the deviation. The inverse dq converter 123 reversely converts the d command and the q-axis voltage command into a three-phase coordinate system, and generates a three-phase voltage command.

  In such a current control system, the current detector 11 is configured by current-to-voltage conversion by a current transformer or a high-precision resistor, amplification by an operational amplifier, etc., discretization and quantization by an A / D converter. Many. The temperature characteristics and transient characteristics of these analog circuits cause an offset between the current detection value and the actual current.

  This current detection offset causes torque fluctuations that are synchronized with the motor's electrical angle cycle. Therefore, in servo motors with basic variable speed control, the frequency of torque fluctuations always changes, and the position control and speed where the normal frequency characteristics are constant. It was very difficult to suppress this by control.

  There have been numerous proposals for improvements to the old problem dating back to the beginning of this current control. These are roughly divided into the following two types.

  1) The current detection value at the timing when the phase current becomes 0 is stored and corrected as an offset value (see, for example, Patent Document 1 or Patent Document 2).

2) Extracting torque fluctuations synchronized with the electrical angular period and adjusting the current detection offset value as needed (see, for example, Patent Document 3 or Patent Document 4).
JP-A-8-47280 JP-A-62-233084 JP 2001-186784 A Special table 2000-014866 gazette

  In the method 1) described above, a control state different from the normal current control state is required in order to create a timing at which the three-phase current is always zero. Therefore, the biggest problem is that it cannot be dealt with when the current detection offset changes in a normal current control state.

  For example, Patent Document 1 includes a voltage command cut-off unit that cuts off voltage application to the motor and creates a state in which the three-phase current is zero. On the other hand, in Patent Document 2, the current detection value at that time is used as an offset value by using the remaining 60 ° section in which the motor is turned off by 120 ° energization.

  Note that many common motor driving devices currently on the market measure the current detection offset when the power is turned on or in a non-energized state immediately before the start of energization. All of these cannot cope with current detection offset fluctuations after the start of energization.

  In the method 2), when the speed of the servo motor is not constant, there is a problem that it is very difficult to extract the component because the torque fluctuation synchronized with the electrical angle cycle does not become a constant frequency. Further, when a position control or speed control loop is configured outside the current control, it is difficult to identify whether the torque fluctuation is caused by an external factor of the current control or a current detection offset.

  For example, in Patent Document 3, as a condition for extracting torque fluctuation, there is a restriction that speed fluctuation and torque fluctuation must be equal to or less than a certain value. Further, in Patent Document 4, the offset measurement process becomes very complicated, such as the design of a variable-frequency bandpass filter for extracting a changing torque fluctuation frequency and the need for non-interference between d-q axes.

  Furthermore, in any method, for example, when the torque fluctuation frequency caused by the current detection offset and the torque fluctuation frequency generated by the resonance point between the motor and the load overlap, the two cannot be distinguished.

  The present invention solves the above-described problems, and an object thereof is to provide a motor control device that suppresses torque fluctuation caused by a current detection offset.

In order to solve the above problems, the present invention provides a current detector that detects each phase current of a three-phase motor, and a current controller that generates each phase voltage command that causes each phase current to follow a given current command. And an integrator that integrates each phase current detection value in one period of an electrical angle in the current controller in a motor drive device including a power amplifier that applies a voltage corresponding to each phase voltage command to a three-phase motor; A correction amount calculator that multiplies the input of the integrator by a motor movement amount during a calculation cycle, and determines an offset amount of each phase current detector from the output of the integrator, and outputs the correction amount calculator The offset value of the current detector is corrected by subtracting it from the detection value of the current detector.

  According to the motor drive device of the present invention, by integrating each phase current detection value for one electrical angle cycle, an output proportional to the current detection offset can be obtained under the condition of constant speed and constant torque command, and normal Since the current detection offset can be corrected while performing the current control, it is possible to cope with a change in the current detection offset during driving.

  Further, even if the motor speed fluctuates during one electrical angle cycle, the integration result is kept almost constant, so that even when the motor speed fluctuation is large, the current detection offset can be corrected.

  A current detector that detects each phase current of the three-phase motor, a current controller that generates each phase voltage command that causes each phase current to follow a given current command, and a voltage corresponding to each phase voltage command is 3 In a motor drive device including a power amplifier for applying to a phase motor, an integrator for integrating each phase current detection value for one electrical angle period in the current controller, and each phase current detector from the output of the integrator A correction amount calculator for determining the offset amount of the current detector, and subtracting the output of the correction amount calculator from the detection value of the current detector to correct the offset value of the current detector.

  The current control block diagram of the motor drive device shown in FIG. 1 is a basic configuration of the present invention. Compared with the current control block (FIG. 8) of a conventional general motor drive device, The difference is that the number of current detectors is the same as that of the current detection offset correctors 124 having the motor position information and the corrected current detection value as inputs and outputting the current detection offset correction values as outputs.

  FIG. 2 shows a block configuration of the current detection offset corrector 124a, in which 5 is an electrical angle 1-cycle integrator that integrates for one electrical angle period, and 6 is a correction that determines the offset amount of each phase current detector. It is a quantity calculator. For explanation, a block diagram showing one phase of the actual servo motor 2 is also added.

  The electrical angle one-cycle integrator 5 calculates an electrical angle from the motor position information θ, and outputs an integration result of the current detection value Iu in a period corresponding to the one cycle. For the reason described later, this integration result becomes a value proportional to the current detection offset Iu_ofs *. Therefore, if the correction amount calculator 6 has a function of outputting a current detection offset correction amount Iu_ofs for controlling this to zero. Good. For example, a value obtained by multiplying the integration result by a certain gain may be output, or a certain amount of correction value may be added or subtracted depending on the sign of the integration result.

  Next, why the integration result of one cycle of the electrical angle of the current detection value Iu is proportional to the current detection offset Iu_ofs * will be described. Here, the value marked with * is a value that cannot be directly observed by the motor drive device.

  FIG. 3 shows the integration results for each waveform and one electrical angle cycle when the current control is completely performed. Since the actual current Iu * is controlled to have a waveform having a DC component that cancels the offset Iu_ofs * by the current control, the current detection value Iu becomes a waveform having no apparent offset, and the integrated value is also zero. In this state, information on Iu_ofs * cannot be read from the integration result of the current detection value Iu. However, there is a delay in the current control system, and it is normal that complete control cannot be realized. Each waveform in that case is shown in FIG. The difference from FIG. 3 is that the actual current waveform Iu * does not have a sufficient DC component that cancels the offset Iu_ofs *. This is because the control is not possible due to the delay existing in the current control system. In this case, the current detection value Iu has an offset of ΔIu−ΔIu ′, and the integration result has a value correlated with Iu_ofs *.

  Therefore, when the current detection offset correction amount Iu_ofs is changed using the correction amount calculator 6, the current detection offset amount ΔIu is reduced so as to approach zero equivalently, and finally all integration results converge to zero. This completes the correction of the current detection offset.

  The second embodiment is effective when the motor speed command is not constant, and the block configuration is different from the current detection offset corrector of the first embodiment.

  As shown in FIG. 5, in addition to the electrical angle one-cycle integrator 5 and the correction amount calculator 6 described in the first embodiment, the current detection offset corrector 124b calculates the motor speed from the difference between the calculation cycles of the motor position θ. Is calculated and multiplied by the current detection value Iu, and the output is input to the electrical angle one-cycle integrator 5.

  By multiplying the motor speed, even when the motor speed is not constant, the same current detection offset correction as when the motor speed is constant can be performed. This will be described with reference to FIG.

  In FIG. 6, a) shows the current detection value Iu when the motor speed is constant at ω0. As described above, the integration result for one electrical angle cycle is T × (ΔIu−ΔIu ′). However, as shown in b), when the motor speed changes to ω0 during the half cycle and changes to ω0 / 2 during the remaining half cycle, the integration result of the first half cycle is 2Au / ω0, but is inversely proportional to the motor speed. Since the half-cycle time in the latter half is doubled, the integration result is −4 Au / ω0. Therefore, the integration result for one cycle of the electrical angle is T × (ΔIu−ΔIu ′) − 2Au / ω0.

  Here, focusing on the fact that the integration result is inversely proportional to the motor speed, it can be seen that the influence of the expansion / contraction of the integration time due to the motor speed can be canceled by multiplying the current detection value Iu by the motor speed ωm. The multiplication result Iu × ωm is shown in c), but the amount that the integration time is doubled because the motor speed is ½ is canceled by the multiplication result being ½. I understand.

  This equivalence can also be expressed in mathematical formulas. Considering the current detection value Iu as a function of the motor position θ, Iu (t) = I (θ (t)). This θ (t) indicates the motor position θ at time t. Since the motor speed ω (t) is a derivative of the motor position θ (t), the multiplication result is Iu (t) × ω (t) = I (Θ (t)) × dθ (t) / dt. Furthermore, when both sides of this equation are indefinitely integrated at time t, ∫ (Iu (t) × ω (t)) dt = ∫ (I (θ (t)) × dθ (t) / dt) dt = ∫ (I (Θ)) dθ.

  Looking at this equation, it can be seen that there is no relationship with time t. That is, even if the speed ω (t) changes, the integration result for one electrical angle cycle of the multiplication result is always the same.

  Since this result can be applied not only to the current detection value Iu but also to all values such as the voltage command Vu that can be expressed by a function of the electrical angle, the values of each part in FIG. 5 can be expressed as shown in FIG. It is important that the horizontal axis is replaced from time to position, indicating that the dependence on motor speed has been removed.

  As is clear from each of the above-described embodiments, it is possible to cope with a change in current detection offset during driving in real time, so that it is possible to greatly suppress torque fluctuations synchronized with the electrical angular period caused by the current detection offset. it can. In addition, it is possible to realize current detection offset measurement that is robust against fluctuations in motor speed during acceleration and deceleration.

  The motor drive device of the present invention is not limited to a three-phase motor, but is useful for a linear motor or a DC motor that performs current feedback control.

Current control block diagram in the motor drive device of the present invention 1 is a block diagram of a current detection offset corrector in Embodiment 1 of the present invention. Explanatory drawing of each waveform when there is no delay in the current control system in Example 1 of the present invention Explanatory drawing of each waveform when there is a delay in the current control system in Embodiment 1 of the present invention Block diagram of a current detection offset corrector in Embodiment 2 of the present invention (A) Explanatory view of effect of speed multiplier at constant speed, (b) Explanatory view of effect of speed multiplier when speed is not constant, (c) Explanatory view of effect of speed multiplier when multiplied by motor speed Explanatory drawing of measurement operation in Example 4 of the present invention Current control block diagram in a conventional motor drive device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor drive device 11 Current detector 12 Current controller 121 dq converter 122 PI controller 123 Inverse dq converter 124, 124a, 124b Current detection offset corrector 13 Power amplifier 2 Three-phase motor 3 Position detector 4 Main power supply 5 Electric angle 1 period integrator 6 Correction amount calculator 7 Speed multiplier

Claims (1)

A current detector that detects each phase current of the three-phase motor, a current controller that generates each phase voltage command that causes each phase current to follow a given current command, and a voltage corresponding to each phase voltage command is 3 In a motor drive device including a power amplifier for applying to a phase motor, an integrator for integrating each phase current detection value for one electrical angle period in the current controller, and a motor for an operation period at an input of the integrator A correction amount calculator that multiplies the amount of movement and determines the offset amount of each phase current detector from the output of the integrator, and subtracts the output of the correction amount calculator from the detection value of the current detector. A motor drive device that corrects the offset value of the detector.

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