JP5266872B2 - Variable speed control device for induction motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the occurrence of ripple torque when shifted from DC braking to a normal operation. <P>SOLUTION: Voltage Vd* which is set in a boost voltage setting part 5 is set to be d-axis voltage and voltage Vq* generated in a V/f setting part 4 is set to be q-axis voltage. Thus, voltage for DC braking and boost voltage are output at a phase delayed from voltage whose V/f is constant and which is output in proportion to an operation frequency by 90 degrees, or a synthetic value of voltage whose V/f is constant and which is output in proportion to the operation frequency and boost voltage reduced in proportion to the operation frequency is output at the phase whose V/f is constant and which is output in proportion to the operation frequency by 90 degrees so that the synthetic value is (linearly) output in proportion to the operation frequency. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a variable speed control device for an induction motor using an inverter of a constant V / f control system, and more particularly to a boost voltage output system.

  One of the methods of variable speed operation of an induction motor (hereinafter abbreviated as IM) with an inverter is a V / f constant control method. This is a method of variable speed driving while maintaining a constant relationship between the primary voltage of the IM (the output voltage of the inverter) and the output frequency. As shown in FIG. 6, the primary impedance of the IM is shown as a T-type equivalent circuit. If the influence can be ignored, the current flowing through the excitation reactance can be made constant regardless of the frequency, and a torque proportional to the slip can be secured throughout the variable speed operation.

  However, as the operating frequency decreases and the primary voltage decreases, the influence of the resistance component mainly on the primary impedance inside the IM and the impedance of the wiring from the inverter output terminal to the motor terminal can no longer be ignored, and sufficient excitation current is secured. It may not be possible and torque may be insufficient. As a countermeasure, boosting control of the output voltage in the low speed operation region is performed based on the idea of keeping the primary induced voltage E1 and the output frequency in a fixed relationship in FIG.

  FIG. 7 shows an example in which the base frequency is 60 Hz and the rated voltage is boosted by 10% at 0 Hz. The basic V / f constant voltage Vo is given by equation (1), the voltage Vb to be boosted is given by equation (2), and the sum of these is the output voltage (primary phase voltage) V1.

Vo = (Vbase / Fbase) * Fout (1)
Vb = (Vb−set / Fbase) * (Fbase−Fout) Equation (2)
V1 = Vo + Vb (3)
However, Vbase is the output voltage at the base frequency (same as the motor rated voltage), Vb-set is the boost voltage set value (output voltage at 0 Hz), Fbase is the base frequency, and Fout is the operating frequency.

  In this torque boost method, the primary induced voltage E1 and the output frequency cannot be kept in a fixed relationship, but the purpose of securing the torque in the low frequency region can be sufficiently achieved, so that it is generally applied to many general-purpose inverters. (See, for example, Patent Document 1 and Patent Document 2).

FIG. 8 shows a circuit configuration diagram of a control device to which a boost voltage is added. The main circuit is composed of a forward conversion circuit (rectifier circuit) 1 and an inverse conversion circuit (inverter) 2, and supplies an output in which the frequency and voltage are controlled to the induction motor 3. The control circuit adds the V / f setting by the basic voltage equation (1) proportional to the frequency and the voltage Vb to be set as the booth by the equation (2) calculated as a function of the frequency to obtain the torque command Vq ^* , The excitation current command Vd ^* is fixed at zero.

In FIG. 8, the control voltage Vo proportional to the frequency f is generated from the frequency command f ^* by the V / f setting unit 4, the boost voltage Vb proportional to the frequency f is generated by the boost voltage setting unit 5, and these voltages are added. The torque command is Vq ^* . Integrating circuit 6 obtains the reference phase theta ^* by integrating the frequency command f ^*. The rotation coordinate conversion unit 7 generates voltage commands Vu ^* , Vv ^* , and Vw ^* that are two-phase / three-phase converted having a reference phase θ ^* from the torque command Vq ^* and the excitation current command Vd ^* . The comparator circuit 8 receives the voltage commands Vu ^* , Vv ^* and Vw ^* as comparison inputs, obtains a PWM waveform gate signal using the triangular wave generation circuit 9 as a comparison reference, and inverts the drive signal generated by the dead time generation circuit 10 with a dead time. On / off control of the two switching elements is performed.
JP-A-7-163188 JP-A-6-165585

In the variable speed drive of IM, the frequency command f ^* may be set to 0 and DC braking may be applied. In this case, the relationship between the primary voltage V1 and the current I1 changes from the state shown in FIG. 9A to the state shown in FIG. 9B and has the same phase.

  At the time of this DC braking, the boost voltage Vb given by the above equation (2) should be applied for the purpose of originally securing the excitation current, but in the method of outputting in the same phase as the equation (1) of the conventional method, The current phase I1 immediately after the transition from DC braking to normal operation becomes the same phase as the constant V / f voltage V1 given by the equation (1), and the excitation current phase becomes the voltage at the moment when the motor starts rotating. Since it fluctuates greatly in the phase delayed about 90 degrees from the axis, pulsating torque may be generated.

  An object of the present invention is to provide a variable speed control device for an induction motor in which generation of pulsation torque when shifting from DC braking to normal operation is reduced.

In order to solve the above-mentioned problem, the present invention outputs a voltage for DC braking and a boost voltage at a phase delayed by 90 degrees from a voltage output in proportion to the operation frequency at a constant V / f , and the operation frequency. The combined value of the boost voltage to be reduced according to the frequency is output (linearly) according to the operating frequency, and has the following configuration.

In the inverter device that drives the induction motor at a variable speed with a constant V / f control method and boosts the output voltage in the low speed operation region,
A control circuit is provided that outputs a boost voltage Vd that is 90 degrees behind the voltage V0 that is output in proportion to the operating frequency at a constant V / f and that is reduced in response to a frequency increase. However, the voltage V1 which is the sum of the voltage V0 and the boost voltage Vd is configured to rise linearly following the increase in the operating frequency.

The control circuit expresses the voltage V0 by the following equation (1), expresses the boost voltage Vd by the equation (2), obtains θ from the equation (1) by θ = sin−1 (V0 / V1), The boost voltage Vd is obtained by substituting θ into the equation (2).
  V0 = V1 * sinθ …… (1)
  Vd = V1 * cosθ (2)

  As described above, according to the present invention, the voltage for DC braking and the boost voltage are output at a phase delayed by 90 degrees from the voltage output at a constant V / f in proportion to the operating frequency, or V / f Constant V / f so that the composite value of the voltage output in proportion to the operating frequency at a constant f and the boost voltage to be reduced in proportion to the operating frequency is output (linearly) in proportion to the operating frequency. Therefore, the output voltage V1 and the excitation current phase during the transition from the DC braking to the normal operation can be secured. Torque pulsation that occurs at the time of start-up or when the rotation direction is switched can be reduced.

(Embodiment 1)
FIG. 1 is a circuit configuration diagram of a variable speed control apparatus showing an embodiment of the present invention. 8 differs from FIG. 8 in that the output voltage Vb of the boost voltage setting unit 5 is used as a magnetic flux command Vd ^* . Thereby, the boost voltage control which ensures the continuity of the voltage and the current phase during the transition from the direct current braking to the normal operation is obtained.

  As shown in FIG. 2 (a), the voltage output V1 at the time of DC braking is output to the axis that is delayed by 90 degrees from the Vo output axis in the expression (1).

In order to realize this, in FIG. 1, the V / f setting (torque command Vq ^* ) of the formula (1), which is a basic voltage proportional to the frequency, is output to the q-axis side of the two-phase / three-phase conversion circuit 7. Then, the voltage Vb desired to be used as a booth is output to the d-axis side (90 degrees delayed from the q-axis) according to the frequency function formula (2).

By doing so, the current I1 during DC braking can flow in the axial direction 90 degrees behind the voltage output shaft. As shown in FIG. 2B, the voltage V1 and the voltage I1 during normal operation are Continuity with the excitation current phase during operation can be ensured. For this reason, generation | occurrence | production of pulsation torque can be suppressed. The output voltage V1 is V1 = (Vo ² + Vb ² ) ^1/2 from FIG. 2B, where Vo can be calculated by equation (1) and Vb can be calculated by equation (2).

  FIG. 3 shows the frequency characteristics of the voltages V1, Vo, and Vb when the base frequency is 60 Hz and the boost setting is 10% to which this embodiment is applied, and the voltage change is smooth when accelerating from the braking state (frequency is 0). It turns out that generation | occurrence | production of pulsation torque can be suppressed.

(Embodiment 2)
Although the continuity of the voltage and the current phase during the transition from the DC braking to the normal operation can be ensured by the method of the first embodiment, the synthesized voltage V1 suddenly approaches Vo as the operation frequency increases. For this reason, it is predicted that the voltage boost is not sufficiently performed and the torque is insufficient.

  In order to improve this torque shortage, in this embodiment, for the boost to the axis that is delayed by 90 degrees from the voltage axis so that the relationship between the output voltage V1 and the operating frequency is as in the conventional method (the dashed line in FIG. 7). A method for outputting the necessary voltage Vd (see FIG. 4B) is proposed. The voltage Vd is obtained by the following procedures (S1) to (S6) according to the operating frequency Fout.

  (S1) A constant V / f voltage to be output to the voltage axis is determined.

Vo = (Vbase / Fbase) * Fout (1)
(S2) A voltage to be boosted is determined.

Vb = (Vb−set / Fbase) * (Fbase−Fout) Equation (2)
(S3) The absolute value of the voltage to be finally output is determined.

V1 = (V0 ² + Vb ² ) ^1/2 Formula (3) ′
(S4) The voltage V0 to be output to the voltage axis and the voltage Vb to be output to the axis 90 degrees behind the voltage axis can be expressed as follows.

Vo = V1 * sin θ (4)
Vd = V1 * cos θ (5)
(S5) θ is obtained from equation (4).

      θ = sin−1 (Vo / V1) (6) (S6) Vd is determined by substituting equation (6) into equation (5).

  According to this embodiment, as shown in the voltage-frequency characteristics in FIG. 5, the boost voltage can be ensured as in the conventional method, and the continuity of the voltage V1 and the excitation current phase is ensured during the transition from DC braking to normal operation. it can.

The circuit block diagram of the variable speed control apparatus which shows Embodiment 1 of this invention. Voltage and current vector diagram during DC braking and normal operation. FIG. 3 is a voltage-frequency characteristic diagram of the first embodiment. Voltage and current vector diagram during DC braking and normal operation. FIG. 6 is a voltage-frequency characteristic diagram of the second embodiment. T type equivalent circuit of induction machine. Example of boost voltage. The circuit block diagram of the conventional variable speed control apparatus. Conventional voltage and current vector diagrams during DC braking and normal operation.

Explanation of symbols

1 Forward conversion circuit (rectifier circuit)
2 Inverse conversion circuit (inverter)
DESCRIPTION OF SYMBOLS 3 Induction motor 4 V / f setting part 5 Boost voltage setting part 6 Integration circuit 7 Rotation coordinate conversion part 8 Comparator circuit 9 Triangular wave generation circuit 10 Dead time creation circuit

Claims (2)

In the inverter device that drives the induction motor at a variable speed with a constant V / f control method and boosts the output voltage in the low speed operation region,
A control circuit is provided that outputs a boost voltage Vd that is 90 degrees behind the voltage V0 that is output in proportion to the operating frequency at a constant V / f and that is reduced in response to a frequency increase. However, the variable speed control device for an induction motor is configured such that the voltage V1 which is the sum of the voltage V0 and the boost voltage Vd rises linearly following the increase in operating frequency . The control circuit expresses the voltage V0 by the following equation (1), expresses the boost voltage Vd by the equation (2), obtains θ from the equation (1) by θ = sin−1 (V0 / V1), 2. The variable speed control device for an induction motor according to claim 1, wherein the boost voltage Vd is obtained by substituting θ into the equation (2) .
V0 = V1 * sinθ …… (1)
Vd = V1 * cosθ (2)

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