JP2004135410A - Current control device for electric motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current control device for an electric motor which simultaneously satisfies the improvement of current response performance and reduction in current ripple. <P>SOLUTION: This current control device for the electric motor comprises a current controller 3 for generating a voltage command by variation between a current detecting value and a current command value detected in a current detector 1; a PWM pulse generator 6 for converting the voltage command into the PWM pulse; and an inverter 7 for supplying an electric power to the electric motor M by switching a semiconductor element by using the PWM pulse. An average voltage in a sampling cycle based on the pulse voltage supplied from the PWM pulse to the electric motor M is calculated. A current correction means 10 for obtaining an electric current correction quantity from a difference value between the average voltage and an induced voltage of the electric motor, the current command value and an electric characteristic of the electric motor is provided. The current of the electric motor is detected by conducting sampling at a cycle which is earlier than a carrier frequency of the PWM pulse generator 6. The correction current detecting value obtained by subtracting the current correction value from the current detecting value is inputted into the current controller 3 as the current detecting value. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a current control device for a motor including an inverter device that supplies power to the motor with a PWM pulse.
[0002]
[Prior art]
FIG. 4 shows the configuration of a current control device for a motor having a conventional inverter device.
This device has a current detector 1 for detecting the current of the electric motor M, dq-axis conversion means 2 for converting a current detection value detected by the current detector 1 into orthogonal dq-axis components, and dq-axis conversion. A current controller 3 that creates a voltage command by comparing the current detection values id_fb, iq_fb with the current command values iq_ref, id_ref; a voltage FF compensator 4 that performs voltage feedforward correction on the output of the current controller 3 , A dq-axis voltage command into a three-phase voltage command value, a voltage converting means 5, a PWM pulse generator 6 converting the voltage command into a PWM pulse, and switching using a PWM (pulse width modulation) pulse to produce an electric motor. An inverter 7 for supplying electric power and a voltage compensating means 8 for compensating voltage for a three-phase voltage command value are provided. In the figure, reference numeral 9 denotes a differentiator for differentiating the output of the pulse generator PG for detecting the angle θ of the electric motor M and outputting each speed ω.
[0003]
In this device, a phase detector is detected by a current detector 1 and a dq-axis current value is obtained by a dq-axis converter 2. The obtained dq-axis current value is compared with a current command for each of the dq axes, and current control is performed by the current controller 3. The current controller 3 normally performs PI control. A voltage FF compensation value created from the current commands iq_ref and id_ref by the voltage FF compensator 4 is added to the output of the current controller 3 to obtain a dq axis voltage command. The obtained dq-axis voltage command value is converted by the voltage conversion means 5 into a three-phase voltage command value. The voltage compensating means 8 calculates a voltage disturbance component such as a dead time of the PWM pulse generator 6 and a voltage drop of the switching element of the inverter 7, and adds the disturbance to the three-phase voltage command value obtained by the voltage converting means 5. The components are compensated and set in the PWM pulse generator 6. The inverter 7 supplies electric power to the electric motor M according to the pulse generated from the PWM pulse generator 6.
In general, the current detector 1 captures a current with a small ripple component by performing sampling at the timing of the peak of the waveform of the PWM carrier wave of the PWM pulse generator 6, and controls the current.
On the other hand, in order to improve the response of the current control, a method of increasing the carrier frequency has been adopted. When importance is placed on the response, the sampling cycle may be made faster than the carrier frequency of the PWM pulse.
In Patent Document 1, sampling is performed at the peak of the PWM carrier wave and at a timing intermediate or divided into four to detect the current, and the gain at the detected current from the top of the carrier wave is compared with the current at a point other than the top of the carrier wave. A method has been proposed in which the multiplied values are integrated and added to the detected current as a correction value.
[0004]
[Patent Document 1]
JP-A-9-154283
[Problems to be solved by the invention]
However, when the carrier frequency of the PWM pulse increases, the loss in the semiconductor element of the inverter 7 increases, causing thermal destruction. Therefore, an upper limit is set for the carrier frequency. That is, in the current control by carrier frequency synchronization, the upper limit is determined from the limit of the semiconductor element.
Also, if the current sampling period is made faster than the carrier frequency with emphasis on responsiveness, ripples will occur in current detection due to the influence of the pulse voltage due to the PWM pulse, and the current will be controlled with the current containing the ripple component, thus amplifying the ripple. In some cases. An increase in the current ripple is not preferable because it causes rotation unevenness and vibration of the electric motor.
Furthermore, the method proposed in Patent Document 1 has a problem that it is difficult to select a gain for current correction, and that ripples cannot be reduced depending on a change in a PWM pattern.
Therefore, an object of the present invention is to provide a current control device for a motor that simultaneously satisfies the improvement of the current response performance and the reduction of the current ripple.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is a current detector that detects the current of the electric motor, a current controller that creates a voltage command by comparing the current detection value and the current command value detected by the current detector, In a current control device for a motor, comprising: a PWM pulse generator that converts the voltage command into a PWM pulse; and an inverter device that switches a semiconductor element using the PWM pulse and supplies power to the motor.
An average voltage during a sampling period is calculated based on a pulse voltage supplied to the motor from a pulse generated by the PWM pulse generator, and a difference value between the average voltage and an induced voltage generated by the motor is calculated. A command value and current correction means for obtaining a current correction amount from the electric characteristics of the electric motor are provided,
The current of the motor is sampled at a cycle faster than the carrier frequency of the PWM pulse generator to perform current detection, and the current correction value obtained by the current correction means is subtracted from the current detection value to obtain a corrected current detection value. And the correction current detection value is input to the current controller as a current detection value.
[0007]
Further, the current correction means calculates a Laplace operator from the current detection value i_det, the average voltage V_av up to the next sampling time of the pulse voltage, the induced voltage E, the inductance L of the motor, and the armature resistance R by s. The current change estimated value i_hat at the next sampling time is calculated as i_hat = {1 / (Ls + R)} (V_av-E)
Or, if Ls >> R,
i_hat = (1 / Ls) (V_av-E)
Asked by
The ideal current change i_ideal from the current ideal value i_ideal0 of the current time T0 calculated last time, the time T1 of the next peak of the carrier wave of the PWM pulse generator and the current command value i_ref to the next sampling time Ts is Δi_ideal = {(I_ref-i_ideal0) / (T1-T0)} Ts
And a difference between the ideal current change amount Δi_ideal and the current change amount estimation value i_hat is used as a current correction value.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram illustrating a configuration of a current control device for an electric motor according to the present embodiment. FIG. 2 is an explanatory diagram illustrating an example of a current change in one sampling cycle by a PWM pulse according to the present embodiment. FIG. 4 is an explanatory diagram illustrating an example of a current change in a certain continuous time by a PWM pulse according to the embodiment.
This embodiment is characterized in that a current correction unit 10 is added to the configuration of the conventional example shown in FIG.
[0009]
In the present embodiment, similarly to the conventional configuration shown in FIG. 4, a phase detector is detected by the current detector 1, a dq-axis current value is obtained by the dq-axis conversion means 2, and a dq-axis current value is calculated for each dq axis. , Current control is performed by the current controller 3 in comparison with the current command. The current controller 3 normally performs PI control. A voltage FF compensation value created from the current commands iq_ref and id_ref by the voltage FF compensator 4 is added to the output of the current controller 3 to obtain a dq axis voltage command. The obtained dq-axis voltage command value is converted by the voltage conversion means 5 into a three-phase voltage command value. The voltage compensating means 8 calculates a voltage disturbance component such as a dead time of the PWM pulse generator 6 and a voltage drop of the switching element of the inverter 7, and adds the disturbance to the three-phase voltage command value obtained by the voltage converting means 5. The components are compensated and set in the PWM pulse generator 6. The inverter 7 supplies electric power to the electric motor M according to the pulse generated from the PWM pulse generator 6.
[0010]
The current correction means 10 includes three components: a voltage conversion means 11, a current change amount calculation means 12, and a current correction amount calculation means 13.
The voltage conversion unit 11 generates a PWM pulse voltage from the three-phase voltage command generated by the voltage conversion unit 5, changes the average voltage during the sampling period, and then performs dq-axis conversion to output a dq-axis voltage command V_av.
The current change calculating means 12 calculates an induced voltage E from the motor angular velocity ω obtained by differentiating the motor angle θ detected by the pulse generator PG with the differentiator 9 and the induced voltage constant, and obtains the voltage by the voltage converting means 11. Compared with the obtained dq-axis voltage command V_av, the current change estimated value i_hat is obtained from the motor circuit constants L and R,
i_hat = {1 / (Ls + R)} (V_av-E) [Equation 1]
Or, if Ls >> R,
i_hat = (1 / Ls) (V_av-E) [Equation 2]
Ask by. Note that s is a Laplace operator.
The current correction amount calculating means 13 calculates the current ideal value i_ideal0 of the current time T0 calculated last time, the time T1 of the next peak of the carrier wave of the PWM pulse generator 6, and the current command value i_ref until the next sampling time Ts. The ideal current change amount Δi_ideal is represented by Δi_ideal = {(i_ref−i_ideal0) / (T1−T0)} Ts [Equation 3]
From the ideal current change amount Δi_ideal and the current change amount estimation value i_hat, i_cmp = i_hat−Δi_ideal [Equation 4]
To determine the current correction value i_cmp. This corresponds to the ripple component of the current, and by subtracting this from the current detection value i_fb, a current from which the ripple component has been removed can be obtained. The effect is the same even if the current correction value i_cmp is added to the current command value i_ref.
[0011]
FIG. 2 shows an example of a current change in one sampling cycle by a PWM pulse. In the same figure, an ideal current change amount Δi_ideal from an ideal current i_ideal0 (n) at a certain sampling time point (n) to a next sampling time point (n + 1) after elapse of the time Ts, and an estimated current change amount estimated from the voltage command i_ref. The i_fb is corrected using the difference i_cmp from i_hat. Then, the ideal current value at time (n + 1) is i_ideal (n + 1) = i_ideal (n) + Δi_ideal.
FIG. 3 shows an example of a current change of a certain phase at a certain continuous time by a PWM pulse. i_fb indicated by a is a current detection value, i_ref indicated by b is a current command value, and i_ideal indicated by c is an ideal current. The current correction amount i_cmp in FIG. 3 is the distance between the curve i_ideal and (i_ideal + i_hat). The result of subtracting i_cmp from i_fb is the result of adding the distance between curve i_fb and (i_ideal + i_hat) to curve i_ideal, and a current from which a ripple component has been removed is obtained. When the current command changes during the carrier cycle, the responsiveness can be ensured because the slope of the broken line portion i_ideal in FIG. 3 is corrected.
[0012]
【The invention's effect】
According to the present invention, an average voltage between sampling periods is calculated based on a pulse voltage supplied to a motor from a pulse generated by a PWM pulse generator, and a difference value between the average voltage and an induced voltage generated by the motor is calculated. And a current correction means for obtaining a current correction amount from the current command value and the electric characteristics of the motor, and performs current detection by sampling the current of the motor at a cycle faster than the carrier frequency of the PWM pulse generator. By subtracting the current correction value obtained by the current correction means from the current detection value to create a correction current detection value and inputting the correction current detection value to the current controller as a current detection value, Since the ripple component of the current is estimated and removed in advance, even if the current sampling period is set to a period faster than the PWM carrier frequency, the current ripple is removed. Current control of high response, not excessively amplify Le can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a current control device for a motor according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing an example of a current change in one sampling cycle by a PWM pulse according to the present embodiment.
FIG. 3 is an explanatory diagram illustrating an example of a current change in a continuous time by a PWM pulse according to the present embodiment;
FIG. 4 is a block diagram illustrating a configuration of a current control device for a motor including a conventional inverter device.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 current detector 2 dq axis conversion means 3 current controller 4 voltage FF compensator 5 voltage conversion means 6 PWM pulse generator 7 inverter 8 voltage compensator 9 differentiator 10 current correction means 11 voltage conversion means 12 current change amount calculation means 13 Current correction amount calculation means

Claims (2)

A current detector for detecting a current of the electric motor, a current controller for creating a voltage command by comparing a current detection value detected by the current detector with a current command value, and a PWM for converting the voltage command into a PWM pulse A current control device for a motor, comprising: a pulse generator; and an inverter device for switching a semiconductor element using the PWM pulse to supply power to the motor.
An average voltage during a sampling period is calculated based on a pulse voltage supplied to the motor from a pulse generated by the PWM pulse generator, and a difference value between the average voltage and an induced voltage generated by the motor is calculated. A command value and current correction means for obtaining a current correction amount from the electric characteristics of the electric motor are provided,
The current of the motor is sampled at a cycle faster than the carrier frequency of the PWM pulse generator to perform current detection, and the current correction value obtained by the current correction means is subtracted from the current detection value to obtain a corrected current detection value. A current control device for an electric motor, wherein the current control device is configured to input the corrected current detection value as a current detection value to the current controller. The current correction unit calculates the Laplace operator as s from the current detection value i_det, the average voltage V_av up to the next sampling time of the pulse voltage, the induced voltage E, the inductance L of the motor, and the armature resistance R. The current change estimated value i_hat at the time of sampling is represented by i_hat = {1 / (Ls + R)} (V_av-E)
Or, if Ls >> R,
i_hat = (1 / Ls) (V_av-E)
Asked by
The ideal current change amount Δi_ideal from the current ideal value i_ideal0 calculated at the previous time T0, the next peak time T1 of the carrier wave of the PWM pulse generator, and the current command value i_ref to the next sampling time Ts is represented by Δi_ideal = {(I_ref-i_ideal0) / (T1-T0)} Ts
The current control device for an electric motor according to claim 1, wherein a difference between the ideal current change amount Δi_ideal and the current change amount estimation value i_hat is set as a current correction value.

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