JPS6042713B2 - Inverter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction motor (hereinafter referred to as a motor) using an inverter.

) related to power-saving operation, in particular, correcting the frequency so that the motor primary current is minimized while ensuring the torque required for the load, and operating at the point where the torque-current efficiency is maximized. It is. More specifically, the present invention has a speed control loop as a major loop, a torque control loop and a frequency control loop as minor loops, and the torque control loop controls the torque required by the speed control loop to a constant value. Under these conditions, the motor primary current is observed and the command value of the Veri frequency control loop is automatically corrected so that it reaches the minimum value. In general, there is a relationship between torque T, slip frequency Fs, and primary current 1 of an electric motor as shown in Figure 1, and the torque is Tl, T2, T3.
take constant values, respectively, and the primary current is 11, 1 when the suberi frequency is Fsl, fs9, fs3, respectively.
Take the minimum value of 2,13. , so such FSl,
It is preferable to operate at a frequency such as fS2 and fS3 that minimizes the primary current from the viewpoint of torque current efficiency and power saving. The present invention scans the Veri frequency under the Torque constant condition, and corrects the scanning direction so that the current decreases as judged from the differential value of the primary current.

According to this, the current can be automatically converged to the minimum value. On the other hand, it is also possible to memorize the relationship between the torque that minimizes the primary current and the Veri frequency as a pattern in advance, and select the optimal Veri frequency depending on the operating condition. The characteristics must be memorized each time, and the handling is complicated, which impairs generality.

Furthermore, since the characteristics shown in FIG. 1 vary greatly depending on the motor temperature, it is necessary to perform some kind of temperature compensation in order to ensure accuracy, making it increasingly complicated and impractical. On the other hand, in the present invention, the optimum value is inserted while measuring the actual characteristics, so the circuit becomes somewhat complicated, but there is no need to adjust each motor individually, and temperature characteristics are automatically taken into account. It is becoming.

FIG. 2 is a diagram showing the configuration of the present invention, in which 1 is a speed setting device, 2
is a speed detector that converts the motor rotation frequency signal generated by the gear 28 and pulse pickup 29 attached to the motor 27 into an appropriate level of DC voltage, and other types of speed detectors may be used as long as they have the same function. For example, a speedometer generator may be used.

3 is a subtracter, 4 is a speed control amplifier, 1 to 4 form a speed control loop, and the motor speed is controlled to match the output of the speed setter 1.

The output of the speed control amplifier 4 operates as a torque command, and is amplified by the torque control amplifier 7 from which the motor generated torque detected by the torque pickup 30 and the torque detector 5 is subtracted by the subtractor 6. 5 to 7 form a torque control loop, and the detected torque is controlled to match the output of the speed control amplifier 4.

The torque detector is assumed to be a mechanical pickup using a strain gauge, but it may also be calculated from the motor current, rotation speed, etc. 8 and 9 are positive and negative power supplies, respectively, and 10 1 is a current detector that rectifies the output of the current transformer 26 and converts it into a DC voltage of an appropriate level, 11 and 15 are differentiators, and are a first-order lag circuit with an appropriate time constant to remove high frequency noise. It is assumed that they are combined. 12 is a comparator that produces an output when the input is positive; 13 is a T-type flip-flop circuit that inverts the output state each time an input signal is applied; and 14a and 14b are electronic switches whose opening and closing are controlled by the output of the flip-flop 13. The A and B contacts, 16, are absolute value circuits and also have appropriate wave characteristics.

17 is a comparator that produces an output when the input is greater than or equal to a certain value;
18 is an electronic switch that opens when there is an output from the comparator 17, and 19 is an integrator.

8 to 19 form the Suberi frequency correction circuit, of which 1
5 to 18 are for determining whether or not the torque command value of the output of the speed control amplifier 4 is in a steady state, and when there is a large change in the torque command value, the electronic switch 18 is opened to stop the correction circuit. It is.

20 is a torque frequency converter that converts a torque command value into a frequency command value; 21 and 22 are adders;
, 20 to 22 form a frequency control loop, and the frequency of the motor 27 is controlled to match the output of the adder 21.

23 uses the output of the torque control amplifier 7 as a voltage command, and the adder 22
The inverter control circuit receives the output as a frequency command and provides a drive signal to the switching elements of the inverter 25, and the output voltage and output frequency of the inverter 25 are controlled according to the voltage command and frequency command, respectively.

25 is a power supply device that supplies power to the inverter 25; 31
is the load.

The circuit operation of FIG. 2 is as follows.

Now, assuming that the output of the integrator θ unit 19 is always zero, 8 to 1
The circuit 9 has torque control loops 5 to 7 and 2 inside the speed control loops 1 to 4 without affecting the operation in any way.
, 20 to 22 can be considered as a control system having all frequency control loops as minor loops. The motor torque is controlled according to the output of the speed control amplifier 4, and the subtraction frequency is controlled according to the output of the adder 21. The pattern of the Torkusberg frequency converter 20 is created to minimize the motor primary current for each torque value, but as mentioned above, it may not be possible to obtain a completely optimal value due to differences in the characteristics of individual motors, temperature characteristics, etc. Therefore, the gist of the present invention is to use the integrator 19 to correct this deviation from the optimum value. 15 to 17 are for determining whether or not the torque command is in a steady state. If the torque command is in a steady state, the differentiator 15 produces no output. Therefore, the absolute value circuit 16 also produces no output, and the comparator 17 is electronic. A close signal is applied to the switch 18 to perform a correction operation for the full frequency.

When the torque command fluctuates up and down, the differentiator 15 produces positive and negative outputs, which are converted into positive values by the absolute value circuit 16. When this exceeds a certain value, comparator 17 produces an output which opens electronic switch 18, stopping the full frequency correction operation. Now considering the case where the torque command is in a steady state,
If the electronic switch 14a is closed, the voltage of the positive power supply 8 is integrated in the positive direction by the integrator 19, and the VERY frequency increases.
If the electronic switch 14b is closed, a similar operation will reduce the over frequency. 10 to 13 are for controlling the rise and fall of the subway frequency, and if we consider the case where the torque T in Fig. 1 is rising near T2, the subway frequency L or FSl, the primary current 1 will decrease. Differentiator 1
1 output becomes negative, the comparator 12 produces no output, the flip-flop circuit 13, and therefore the electronic switches 14a and 14b maintain this state, and the frequency continues to rise.

When the full frequency Fs is decreasing near FSL, the primary current increases, the output of the differentiator 11 becomes positive, the comparator 12 produces an output, and the state of the flip-flop circuit 13 and therefore the electronic switches 14a and 14b is changed. is reversed, causing the suberi frequency to rise. After all, the very frequency Fs is FS
In the vicinity of l, it operates to increase the veri frequency no matter what state it is in at first. Based on the same idea, when the subtraction frequency L is around FS3, the subtraction frequency is lowered and converged to the current minimum point of FS2. In this way, the circuit shown in FIG. 2 is automatically adjusted to the perfect frequency that minimizes the primary current while the torque remains constant. As described above, according to the present invention, in a steady state, it is possible to operate at the maximum torque-current efficiency, and there is no need to adjust the circuit for each motor individually, and changes in characteristics due to motor temperature are automatically corrected, resulting in power saving of induction motors. It is extremely useful for driving.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between torque, slip frequency, and primary current of an induction motor, and FIG. 2 is a diagram showing the configuration of the present invention.

Claims (1)

[Claims] 1 In an induction motor drive system using a variable voltage/variable frequency inverter, a speed setter 1 generates a voltage corresponding to the set speed of the motor, a speed detector 2 generates a voltage proportional to the speed of the motor, and a speed detector 2 that generates a voltage proportional to the speed of the motor, and a a speed control loop comprising a subtractor 3 for comparison, a speed control amplifier 4 for amplifying the output of the subtractor 3; a torque detector 5 for generating a voltage proportional to the output torque of the motor; A subtracter 6 that compares the output voltage of the speed control amplifier 4 and the output voltage of the torque detector, which constitute a torque command with the output of the loop, and a torque control amplifier 7 that amplifies the output of the subtracter 6. It has a torque control loop consisting of a torque control loop that controls the detected torque to match the torque command, and further includes positive and negative power supplies 8 and 9, a current detector 10 that converts the current transformer output into a DC voltage, A differentiator 11 that differentiates the output of the current detector, a comparator 12 that produces an output when the input is positive, a T-type flip-flop circuit 13 that inverts the output every time an input signal is applied, and the output controls opening and closing. electronic switch contacts 14a, 14b, a differentiator 15 for differentiating the output of the speed control amplifier 4, an absolute value circuit 16 connected to the output, and an absolute value circuit 16 connected to the output when the input is above a certain value. It is provided with a slip frequency correction circuit comprising a comparator 17 that generates an output, an electronic switch 18 that is opened by the output of the comparator 17, and an integrator 19, and is supplied with the output of the speed control amplifier 4, which is the torque command value. , a torque-slip frequency converter 20 that converts this command value into a slip frequency command value, an adder 21 that adds the output of this converter and the output of the integrator 19, and an adder 21.
an adder 22 that adds the output of the speed detector 2 and the output of the speed detector 2;
The inverter 25 is controlled by these control loops and the inverter control circuit 23, and the induction motor primary current is minimized while the induction motor output shaft torque is maintained at a constant value. An inverter control device characterized by automatically correcting a slip frequency so as to increase the torque, and controlling the slip frequency correction value to be held constant by a slip frequency correction circuit while the torque is changing.