JPS635998B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control system for an induction motor, and in particular, the present invention relates to a control method for an induction motor, and in particular, the invention relates to a control system for an induction motor, and in particular, a power conversion device that can independently control the field current component and torque current component of the induction motor, which is a load, is used to control the induction motor. The present invention relates to a control method for driving a .

There are various control methods for variable speed operation using induction motors, but squirrel cage induction motors have a wide control range, can be operated at any speed under any load conditions, and are robust and maintenance-free as induction motors. The primary frequency control method is often used because it allows the use of FIG. 1 is a typical block diagram of the primary frequency control system, which becomes a load through a power converter 12 that converts power obtained from an AC power source 11 into AC power of any frequency, voltage, and current. This is a configuration for driving an induction motor 13.
When the power conversion device 12 is used as an AC power supply having a certain frequency and a certain voltage, there are various circuit examples, but the following is an example of a circuit that should realize the control method for an induction motor that is the object of the present invention. Shown in Figure 2. In the figure, electric power obtained from an AC power source 11 is converted to DC via a rectifier circuit 121, and smoothed by a DC reactor 122.
Furthermore, this DC power is converted back into AC power by an inverter circuit 123, and the induction motor 13 becomes a load.
is driving. The inverter circuit 123 is a current source inverter device called a series diode type, but since it is not a circuit particularly limited to the present invention, a detailed explanation thereof will be omitted. This second
The reason why the current source inverter device shown in the figure is effective for the induction motor control method of the present invention is that the instantaneous output alternating current and phase, which will be described later, can be controlled. The reason is that the current is in the rectifier circuit 12
1, the phase can be controlled by the inverter circuit 123.

In order to make the following explanation easier to understand, the principle of independently controlling the field current component and torque current component of the induction motor will be described. In an induction motor, primary current vector ₁ and secondary magnetic flux vector 〓 ₂
The relationship with is expressed as (1+T ₂ P+jω _S T ₂ )〓 ₂ =M ₁ (1). However, T ₂ is the motor secondary time constant,
M is the primary and secondary mutual inductance, ω _S is the slip angular velocity, and P is a differential operator. FIG. 3 illustrates this relationship. In the same figure
_1〓 If _{the biaxial} component is ₁ d and its orthogonal component is ₁ q, the generated torque T and secondary magnetic flux Φ ₂ in the induction motor are as follows: T=M/L ₂ Φ _{2 1} q ...(2) Φ ₂ = M/1 + T ₂ P ₁ d ...(3). However, L ₂ is the secondary self-inductance. From (2) and (3), the torque T and the secondary magnetic flux Φ ₂ can be controlled by ₁ q・₁ d,
₁ d is called the field current component, and ₁ q is called the torque current component. Also, the slip angular velocity is expressed from (1) and (2) as ω _S =M/T ₂ Φ _{2 1} q = L ₂ /T ₂ Φ ² / ₂ T (4). Therefore, in order to operate an induction motor with torque and secondary magnetic flux that match the torque standard T* and secondary magnetic flux standard Φ ₂ *, from (2) and (3)
Primary current ₁ of induction motor combining ₁ q and ₁ d
It can be seen that it is sufficient to supply an alternating current having the formula (4) and the resultant angular velocity ω ₁ =ω _n +ω _S of the operating angular velocity ω _n of the induction motor.

FIG. 4 shows a control block diagram in which the above explanation is implemented in a current source inverter device. In the figure, an operating angular velocity reference 14 (ω _n
*) and the operating angular velocity ω _n from the speed sensor 15 directly connected to the rotating shaft of the induction motor 13 are compared and amplified to obtain the torque reference T* via the speed control 16. The calculation circuit 17 calculates the torque reference T* according to equation (2).
This is a circuit that calculates the torque current component _1q . Further, the secondary magnetic flux reference Φ ₂ * given by the secondary magnetic flux reference 18 is calculated in accordance with equation (3) via the calculation circuit 19 to obtain the field current component ₁ d. Torque current component
A current control circuit 20 that controls the output current of the power converter 12 according to a primary current reference ₁ * obtained by combining ₁ q and a field current component ₁ d uses the current reference and the feedback from the current detection circuit 21. This is a circuit that generates a control signal by amplifying the error of the signal. On the other hand, the signal obtained from the arithmetic circuit 22 which calculates according to equation (4) from the torque reference T* and the secondary magnetic flux reference Φ ₂ * is the slip angular velocity ω _S , and the frequency control circuit 23 calculates ω ₁ =
A control signal for supplying a frequency corresponding to ω _n +ω _S from the power conversion device 12 is generated. Therefore, the induction motor can be operated at an operating angular velocity and secondary magnetic flux that match the operating angular velocity reference ω _n * and the secondary magnetic flux reference Φ ₂ *. A logic circuit 51 that supplies a signal to the current control circuit 20 has a function of operating or disabling the current control circuit 20 according to a switch 52 that commands the operation or stop of the power conversion device 12. When stopped, the current flowing to the induction motor 13 is throttled so as not to flow, and when the power conversion device 12 is in operation, the current is controlled to flow to the induction motor 13.

In the control circuit shown in FIG.
Consider the case of driving in the pattern shown in the figure. In the same figure, operation starts at time t ₁ and accelerates -
It stops at time t ₂ with a pattern of acceleration completion - constant speed - deceleration. The pattern is that the operation is stopped from time t ₂ to time t ₃ and operation starts again from time t ₃ . In such an operation pattern, operation and stop are frequently repeated, but in the control circuit shown in FIG. ₁ , an excessive current must be passed to start up the field of the induction motor 13 at the start of operation. This current corresponds to the vector T ₂ P〓 ₂ in FIG. 3, and the larger the capacity of the induction motor serving as the load, the larger the time constant T ₂ and therefore the larger the required current. In addition, since time t ₁ is the start of acceleration, a torque current component is also required in order to obtain sufficient acceleration torque. The disadvantage was that it required a power converter with

This invention was made to eliminate the above-mentioned drawbacks, and by supplying only the field current component even when the induction motor serving as a load is stopped, the excessive capacity required only at the start of operation can be suppressed. The object of the present invention is to provide an economical and highly reliable control method for an induction motor that is compatible with the load capacity.

FIG. 6 shows an embodiment of the present invention. The difference between FIG. 6 and FIG. 4 is that a logic circuit 51 that supplies a signal to the current control circuit 20 is connected in parallel with a switch 52 that instructs the normal power converter 12 to stop operating for a short period of time or for a predetermined period. The current control circuit 20 is operated during a period during which the current of the field current component flows before the acceleration time of the load induction motor, for example, during the period from t2 to t3 in FIG.
The addition of a switch 53 that commands the release of the throttle, and the operation angular velocity reference ω* in response to the switch 53
The point is that a switch 54 is provided to turn on and off. The operation of the figure can be explained as follows. Normal operation is stopped by the switch 52, but as mentioned above, during the period TP in which only the field current component current flows, the switch 53 opens to release the throttling of the current control circuit 20. , the driving angular velocity reference ω* is separated and becomes a command equivalent to the zero speed command. Further, when the electric motor is stopped, the speed feedback signal is also zero because a brake (not shown) is normally applied. Therefore, the current of the torque current component does not flow because the torque reference T* becomes a zero command, and only the current of the field current component flows.

FIG. 7 shows another embodiment of the invention. The difference between this figure and FIG. 6 is that the speed sensor 15
Induction motor 1 using the operating angular velocity ω _n from
A switching circuit 24 generates a switch switching command _S3 when motor 3 stops and switches the secondary magnetic flux reference, and an induction motor 1
This is because a switch 26 is added which operates in accordance with the secondary magnetic flux reference 25 at the time of stop of No. 3 and the switch switching command _S3 of the above-mentioned switching circuit 24 to switch the secondary magnetic flux reference. The effect shown in FIG. 6 is the addition of switching the secondary magnetic flux reference in order to lower the field current component current during stoppage to the effect shown in FIG. In this example, it is necessary to increase the capacity by the component current (corresponding to T ₂ P 〓 ₂ in Fig. 3) that increases the secondary magnetic flux that is lowered when stopped when accelerating, but the field current when stopped is There is an advantage that it can be lowered.

As explained above, by supplying only the field current component even when the induction motor serving as a load is stopped, it is possible to provide an induction motor control system having the following features.

(1) Since it is not necessary to flow the field current component current to raise the secondary magnetic flux when the induction motor of the load starts accelerating, the capacity of the power converter corresponding to the capacity of the induction motor of the load can be sufficiently accelerated. It can be used as torque, making it possible to control an induction motor economically and with quick response.

(2) Furthermore, by weakening the secondary magnetic flux when the induction motor serving as a load is stopped, it becomes possible to control the induction motor economically, although there is a slight increase in the field current component.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of primary frequency control of an induction motor, Fig. 2 is a configuration diagram showing an example of the power conversion device in Fig. 1, Fig. 3 is a vector diagram of the current supplied to the induction motor, and Fig. 4 is a block diagram of the primary frequency control of an induction motor. FIG. 5 is an explanatory diagram of an operation pattern, FIG. 6 is a block diagram showing one embodiment of the present invention, and FIG. 7 is a block diagram showing another embodiment of the present invention. 11...AC power supply, 12...power converter, 13...
Induction motor, 14... Operating angular velocity reference, 15... Speed sensor, 16... Speed control circuit, 17... Arithmetic circuit, 18... Secondary magnetic flux reference, 19... Arithmetic circuit, 20
...Current control circuit, 21...Current detection circuit, 22...Arithmetic circuit, 23...Frequency control circuit, 24...Switching circuit, 25...Secondary magnetic flux reference, 26...Switch, 51
...Logic circuit, 52, 53, 54...switch.

Claims (1)

[Scope of Claims] 1. In an induction motor that is driven to repeatedly start and stop using a power conversion device that independently controls the field current component and torque current component of the induction motor serving as a load. . A control method for an induction motor, characterized in that a field current component current is caused to flow even when the induction motor is stopped. 2. In an induction motor that is driven to repeatedly start and stop using a power conversion device that independently controls the field current component and torque current component of the induction motor serving as a load, the operation of the induction motor A control method for an induction motor characterized by flowing a current having a field current component smaller than a field current component in a high-speed range when stopped.