JPH0667255B2 - Inverter control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a controller for an inverter that feeds a motor current to an induction motor that drives a pulsating torque load by connecting a flywheel.

[Conventional technology]

FIG. 4 shows a conventional system in which a reciprocating compressor, which is a pulsating torque load, is operated at a variable speed using a variable frequency inverter. In the figure, 1
Is a power source of the inverter, 2 is a variable frequency inverter (hereinafter,
3 is a three-phase induction motor M, 4 is a flywheel, 5 is a reciprocator, and a compressor (hereinafter referred to as pulsating torque load).

In this way, the flywheel 4 is provided so that the pulsation of the torque of the pulsating torque load 5 is prevented from being directly transmitted to the induction motor 3 by the GD ² , and the torque pulsation of the induction motor 3 is smoothed. However, the degree of smoothness is
It depends on the slip characteristics of the induction motor 3. That is, the slip characteristic (speed-torque characteristic) of the induction motor 3
High slip characteristics can enhance the smoothing effect and greatly reduce the torque pulsation, but the efficiency of the induction motor 3 decreases conversely and the required capacity of INV2 increases. is there. Of course, if the low slip characteristic is used, the smoothing effect is low, the torque pulsation does not become so small, and the required capacity of INV2 becomes large.

Therefore, in order to reduce the required capacity of INV2 and make the system economical, it is necessary to make the slip characteristic of the induction motor 3 appropriate, but this slip characteristic is unique to the induction motor. Since it cannot be changed arbitrarily, it is difficult to construct an economical system.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an inverter control device capable of giving a desired slip characteristic by the inverter output characteristic.

[Means for solving problems]

In order to achieve the above object, the present invention is provided with a current drooping characteristic imparting circuit, adds the output of the current drooping characteristic imparting circuit to the speed setting signal in the same polarity as the speed feed back signal, and creates a torque command value. A limiter that applies an upper limit to the current command value is provided.

[Action]

In the present invention, when the required torque of the induction motor increases and the inverter output current increases, the speed of the induction motor decreases due to the function of the current drooping characteristic imparting circuit, and the peak value of the pulsating torque of the induction motor due to the action of the limiter. Therefore, the speed-torque characteristic of the induction motor is controlled by the inverter. In this way, since the slip characteristics can be given from the control side, it is possible to cause the induction motor to operate the pulsating torque load drive system optimally in terms of efficiency.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 6 denotes a current detection circuit, which detects the output current i of INV2 and sends out a current feedback signal i. A speed detection circuit 7 detects the speed of the induction motor 3 and sends out a speed feedback signal V _S. A speed setting circuit 8 sends out a speed setting signal V _N ^* . 9
Is a current drooping characteristic applying circuit, which takes in the current feedback signal i and outputs a voltage signal V _KI (actually, it is preferable to apply a bias in proportion to the torque) proportional to the current feedback signal i. create.
Reference numeral 10 is a torque command circuit, in which the speed setting signal V _N ^* is a + sign, the speed feed back signal V _S is a − sign, and a voltage signal.
V _KI is taken in by the-sign and these are added to create the torque command signal T ^* . A torque / current conversion circuit 11 takes in the torque command signal T ^* , calculates a current command value from the value, and creates a current command signal I ^* . 12 is an upper limit limiter command circuit, which is a torque / current conversion circuit
The upper limit value I _MAX is given to the output of 11. A current control circuit 13 amplifies a deviation ε _I between the current command signal I ^* and the current feedback signal i to generate a control signal, which is supplied to the base drive circuit 14. The base drive circuit 14 has a deviation ε
Based on _I , the base signal supplied to the transistor forming INV2 is created.

In this configuration, the speed setting signal V _N ^* has a + sign, and the speed feed back signal V _S and the voltage signal V _KI are added as a − sign in the torque command circuit 10. Therefore, the output current i of INV2 is
Is increased, that is, when the required torque of the induction motor 3 is increased, the speed setting value V _N ^* is constant, but the output frequency f _{0 of} INV2 is decreased and the speed of the induction motor 3 is decreased. Further, if the required torque of the induction motor 3 increases, the torque /
The output I ^* is a current converter circuit 11 increases, but when the value reaches the upper limit Rimitsuto I _MAX, saturated at this level.

That is, the current command signal I ^* is relative to the speed of the induction motor 3,
Since the current drooping characteristic and the upper limit limit characteristic are provided, by adjusting the input / output characteristics of the current drooping characteristic applying circuit 9,
The induction motor 3 can be made to follow, for example, the speed-torque characteristic as shown in FIG. 2 (a) (B is due to the bias), and under this characteristic, the torque T _{M of the} induction motor 3 is
Pulsates with respect to the load torque T _L of the pulsating torque load 5 as shown by the dotted line in FIG.

The current drooping characteristic can be arbitrarily changed by adjusting the input / output characteristic of the current drooping characteristic applying circuit 9, and the induction motor 3 has an optimum speed-torque characteristic in view of the economic efficiency of the system. Can drive.

Further, in this embodiment, the maximum torque T _{M MAX} of the induction motor 3 is limited by the operation of the upper limit limiter command circuit 12, so that the capacity of INV2 and the capacity of the induction motor 3 can be reduced.

The pulsating torque load 5 carries out a leveling operation at an extremely low speed at the start of its operation. In this case, it is desirable that the speed of the induction motor 3 hardly changes. While the required torque of the induction motor 3 is equal to or less than the predetermined value, the drooping characteristic imparting circuit 9 does not output the speed-torque characteristic as shown in FIG. 2 (b).

In the above embodiment, the current feed back i is introduced as the input to the current drooping characteristic applying circuit 9, but the same effect can be obtained even if the torque command signal T ^* and the current command signal I ^* are introduced. You can

〔The invention's effect〕

As described above, according to the present invention, the speed-torque characteristic of the induction motor is given by the control of the output characteristic of the inverter, so that the energy of the flywheel can be fully utilized without reducing the power efficiency of the induction motor. Since the torque pulsation of the induction motor can be smoothed and the maximum torque can be limited, the capacities of the induction motor and the inverter can be reduced as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are speed-torque characteristic diagrams for explaining the operation of the above embodiment, and FIG. 3 is a load in the above embodiment. FIG. 4 is a diagram showing the relationship between the torque and the torque of the induction motor, and FIG. 4 is a configuration diagram of the pulsating torque load drive system. 2 ... Inverter, 3 ... Induction motor, 5 ... Pulsating torque load, 6 ... Current detection circuit, 7 ... Speed detection circuit, 8
...... Speed setting circuit, 9 …… Current drooping characteristic applying circuit, 10 ・ ・ ・
… Torque command circuit, 11 …… Torque / current conversion circuit, 12…
… Upper limiter command circuit, 13 …… Current control circuit.

Claims (2)

[Claims] 1. A controller of an inverter for supplying an electric motor current to an induction motor for driving a pulsating torque load by connecting a flywheel, wherein a current drooping characteristic imparting circuit is provided.
For the speed setting signal, the output of the current drooping characteristic applying circuit is added to the same polarity as the speed feed back signal to create a torque command value, and the upper limit of the current command value calculated based on the torque command value is set. A control device for an inverter, which is provided with a limiter for turning on. 2. The inverter control device according to claim 1, wherein the input of the current drooping characteristic imparting circuit is a current feedback value of an inverter output current, a torque command signal, or a current command signal.