JPS6356196A - Control unit of inductor - Google Patents

Abstract

PURPOSE:To increase starting torque and to perform continuous control of torque, by connecting a resistance and the secondary chopper in parallel to a power rectifier connected to the secondary side of an inductor. CONSTITUTION:A power rectifier 2 is connected to the secondary side of an inductor 1. The secondary chopper 3 is connected to the output side of the power rectifier 2. In parallel to this secondary chopper 3 a series circuit of a diode 4 and a capacitor 5 is previded, where a reverse converter 8 is provided. Between the power rectifier 2 and the secondary chopper 3 a resistor 26 and a switch 27 are provided in parallel. In starting, the resistor 26 is connected in parallel to the secondary chopper 3, so that sufficient starting torque is obtained. After the starting is finished, the resistor 26 is separated by the switch 27, while the secondary chopper 3 is kept on actuating. At this moment, no torque fluctuation is caused, as the motor current is controlled so as to make it continuous.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a control device for an induction machine capable of secondary excitation control, and particularly to a control device suitable for variable speed control of a machine that requires starting torque. .

[Conventional technology]

Servius devices have been used for variable speed driving of pumps and fans. This connects a forward converter (AC-DC converter) to the secondary winding of a wound induction machine, and then converts the secondary power into AC via a DC reactor and an inverse converter (DC-AC converter). This is a device that regenerates power. In this device, the capacity of the inverter increases in proportion to the size of the speed control range, and furthermore, in the low velocity range, the ignition delay angle of the inverter operates at α; 0°, so it is invalid. The drawback is that the current is large and the power factor of the entire system is reduced. For this reason, this type of device usually has a variable speed range of 60 to
Set it to about 100%. In the speed range of 0 to 60%, a starting resistor is connected to the secondary winding for operation, but in order to prevent torque discontinuity, the resistance value is continuously variable. Usually, large-scale devices such as water resistors are used. Therefore, it is contrary to space saving and maintenance efficiency.

Incidentally, related devices of this type include, for example, Japanese Patent Application Laid-Open Nos. 156297-1982 and 226794-1980.

[Problem that the invention seeks to solve]

The object of the present invention is to eliminate the drawbacks of the prior art described above, to provide a minimum inverter capacity, a high power factor, and sufficient starting torque in a speed control range of 0 to 100%.
Furthermore, it is an object of the present invention to provide a secondary excitation control device that can continuously control torque from startup to rated speed and can perform smooth speed control.

[Means for solving problems]

The above purpose is to connect an induction machine capable of secondary excitation, a forward converter to the secondary side of the induction machine, connect a secondary chopper to its output side, and connect a diode and a capacitor in parallel with the secondary chopper. It is equipped with an inverter for regenerating the secondary power of the induction machine into an AC power supply, and is further provided with a series circuit between the forward converter and the secondary chopper in a low speed region below a predetermined speed. , connect a resistor, and the output current of the forward converter is.

This is achieved by controlling the secondary chopper on and off so that the command value is achieved.

[Effect]

During start-up, a resistor is connected in parallel with the secondary chopper. Then, the output current of the forward converter is detected, and the secondary chopper is controlled on and off to control the current so that it is proportional to the current command value from the speed regulator. When the rotational speed of the electric motor exceeds a predetermined value and the start is completed, the resistor is disconnected by the opening/closing element, the secondary chopper is operated continuously, and the variable speed control of the induction machine is performed by the secondary excitation operation. be exposed. Since the secondary chopper always operates continuously, even when disconnecting the resistor, 1! Since the motive current is controlled to be continuous, torque fluctuations do not occur. Therefore, the torque and speed are continuously controlled from startup to steady operation.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is a wound induction motor (hereinafter referred to as IM);
2 is a forward converter that converts the secondary voltage of IMI to DC; 3 and 6 are self-extinguishing elements, including a transistor, GT○(
Although any transistor such as a gate turn off thyristor may be used, a transistor will be described here. 4 is a backflow blocking diode, and 5 is a capacitor. 7 is a freewheeling diode, 8 is a thyristor inverter for regenerating the secondary power of the IMI to an AC power source, and 9 is a transformer.

In this circuit, transistors 3 and 6 perform a chopper operation. Further, 26 is a resistor connected in parallel with the transistor 3, and 27 is a circuit opening/closing element for disconnecting the resistor from the circuit after starting the motor, and is a semiconductor switch or contactor made of semiconductor elements. configured. In addition.

The opening/closing element 27 is configured to be closed when the induction machine is started (when the rotational speed is below a predetermined value).

The above is the main circuit configuration.

Next, the detection section and control circuit section will be explained.

10 is a speed detector directly connected to the IMI, 11 is a speed command circuit, and 12 is a speed regulator that amplifies the deviation between the signal of the speed detector 10 and the speed command signal and outputs a current command signal is. Reference numeral 13 denotes a current detector for detecting the output current of the forward converter 2; 14 compares the current command signal sent from the speed regulator 12 with the current detection signal obtained from the current detector 13; 15 is an amplifier for supplying the on/off control signal to the base of the transistor 3. Reference numerals 16 to 21 are control units for controlling the voltage of the capacitor 5 to a constant level, and the method is almost the same as that of 11 to 15 described above. That is, 16 is a voltage command circuit, 17 is a voltage detector, 18 is a voltage regulator, 19 is a current detector, 2
0 is a comparator with hysteresis characteristics, and 21 is a base amplifier.

22 is a circuit for controlling the firing of the inverter 8 at a constant firing phase.

The basic operation of this embodiment is as follows.

In response to the output signal i of the speed regulator 12, the transistor 3 (herein referred to as a secondary chopper) is turned on.

The output current id of the forward converter 2 is controlled by turning it off, thereby controlling the secondary current 12 of the IMI and the torque which is proportional to this to perform speed control. By the way, the secondary chopper is on an off period.

The DC current is charged to the capacitor 5 via the diode 4. At this time, the secondary power of the IMI is sent to the capacitor 5, where it is converted into direct current with a substantially constant voltage. to operate on and off.

The current flowing during the on period of the transistor 6 reaches the inverter 8.

As a result, the secondary power of the IMI is regenerated to the AC power source via the inverter 8.

The circuit formed by the transistor 3, the diode 4, the capacitor 5, and the transistor 6 has the function of converting the secondary voltage that fluctuates due to slippage, that is, the output voltage of the forward converter, into a constant voltage of direct current.

Naturally, if circuit losses are ignored, the power transferred to the inverter side will be equal to the secondary power of the IMI. Therefore, for loads such as pumps and fans whose torque changes as the square of the rotational speed, the power handled by the inverter can be at most 1/6 of the motor output. This means that the secondary power is the product of the secondary current, which is proportional to the square of the rotation speed, and the secondary voltage, which is proportional to the slip.It reaches its maximum value when the slip is 1/3, and that value is 1/2 of the motor output. /6. This secondary power is supplied to transistors 3 and 6 as described above.
Because the current of the primary regenerative chopper and inverse converter is converted to DC with a constant voltage by the effects of
The capacity of the inverter 8 and the transformer 9 can be reduced to about 1/6 of the motor capacity.

In addition, since the inverter 8 is controlled with a constant firing phase,
The power factor is always a constant high value (0.7~0
．． 8) is maintained. Especially at rated speed (slip is almost zero)
In the vicinity, the current of the inverter 8 is almost zero (secondary power is almost zero), so there is no generation of reactive power from the inverter 8, and the entire system can operate with high power factor and high efficiency. I can do it. Therefore, the inverter capacity and the system power factor are independent of the speed control range, so the speed range can be taken over the entire range from 0 to 100%.

However, as mentioned above, if the inverter capacity is set to 1/6 of the motor capacity, the torque (secondary current) at one rotational speed of zero (slip = 1) is limited to approximately 1/6 of the rated value. . In the case of pumps, fans, etc., this is usually sufficient, but in cases where the load torque at the time of starting is large, this becomes insufficient torque. Increasing the capacity of the inverter would solve this torque shortage, but it would be uneconomical, so the method of the present invention as described below is adopted.

Generally, the torque of an induction machine is proportional to the secondary input Pxo (synchronous watt). Secondary human power P20 is according to Suberi S,
It is divided into mechanical output M and secondary electrical output P2. That is, M = (1-s) P2O-(1) Pz= 5-Pro, = (2
) Furthermore, the relationship between the torque T and the secondary electrical output P2 is expressed by the following equation.

Here, ws: angular frequency, p: number of pole pairs. That is, P2 is determined according to the relationship between torque T and slip.

P2 is determined by the operation of the secondary chopper 3, inverse converter 8, etc.
Since the resistor 26 is connected between the forward converter 2 and the secondary chopper 3 in this embodiment, it is divided into the part that is regenerated by the AC power supply, and the part that is consumed there. If it is determined that the remaining power is obtained by subtracting the maximum regenerative power Pr of the inverse converter 8, the following equation holds true.

(s-F!do)2 ”P2-Pr... (4) where R: resistance value, 5-Edo secondary chopper output end voltage,
From this, the resistance value is z-Pr. In addition, when using the resistor 26 with a fixed resistance value, R is set to the minimum value of the value of equation (5) in the operating speed range in which the resistor is applied.

When the resistor 26 having such a resistance value is connected as described above and the output current of the forward converter 2 is controlled by the secondary chopper 3, the regenerative power of the inverse converter 8 is suppressed within the upper limit value. , the required torque can be obtained. Furthermore, since the output current id of the forward converter 2 is controlled in proportion to the current command signal is according to the speed deviation from the speed regulator 12, the rotational speed is controlled to match the speed command value. Ru.

As described above, according to the present invention, sufficient torque can be obtained in a low speed rotation range such as during startup (slip = 1), but if the additional resistor 26 is left connected, Joule loss will occur in the resistor. This causes a decrease in efficiency.

Therefore, it is necessary to disconnect the resistor at an appropriate point. This is accomplished by the opening/closing element 27, which operates at the point at which a predetermined rotational speed is reached. After this, the secondary power.

All of the power is regenerated into AC power by the inverter 8.

As described above, in this embodiment, a large starting torque can be obtained while minimizing the inverse converter capacity, and since the forward converter output current is constantly controlled by the secondary chopper 3, the torque can be controlled continuously, and even if the resistor is a fixed resistance, the torque can be controlled to a desired value and smooth speed control can be performed. Further, as in the case of a simple secondary resistance start, the step change in torque when the resistance is turned on and off is softened according to the action of the speed regulator. In other words, when the motor current changes as the resistor turns on and off, the torque changes and the speed also changes, so the current command signal that is the output signal of the speed regulator changes, and as a result, the motor current changes. is suppressed in a short period of time, torque fluctuations are alleviated, and smooth operation is possible.

Note that the electric motor is not limited to a single-winding induction machine, but any induction machine having a secondary excitation function may be used. For example, JP-A-59
It is also possible to apply a brushless squirrel cage induction machine of -129588. That is, the first winding wound around the stator core is used as the primary winding of the wound induction machine, the second winding is used as the secondary winding, and the control of the present invention is applied to this second winding. It connects devices. In this case, there is an advantage that brushless variable speed control is possible.

In the above embodiment, the current command signal and the signal from the current detector are compared using a comparator with hysteresis characteristics to control the chopper on and off. In addition to the P-I controlled current regulator, its output signal and chopper on,
Similar control can be performed even if a carrier wave signal that determines the off frequency is applied to a comparator and the output pulse signal is used to control the chopper on and off.

In short, any configuration can perform the required operation as long as it can control the current according to the current command signal.

〔Effect of the invention〕

As described above, according to the present invention, the starting torque of the induction machine can be increased and the torque can be continuously controlled.
This has the effect of making it possible to obtain smoother speed control characteristics over the entire range up to the maximum speed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of an induction machine control device according to the present invention. 1... Wound induction motor (IM), 2... Forward converter. 3...Transistor, 4...Reverse current blocking diode, 5...Smoothing capacitor, 6...Transistor,
8... Inverse converter, 9... Transformer, 10... Speed detector, 11... Speed command, 12... Comparator, 13...
・Current detector, 14... Comparator, 15... Amplifier,
16... Voltage command, 17... Voltage detector, 22...
- Ignition control circuit, 26... resistor, 27... circuit switching element.

Claims (1)

[Claims] 1. An induction machine capable of secondary excitation, a forward converter for exchanging the secondary voltage of the induction machine to direct current, and a secondary chopper consisting of a self-extinguishing element for current adjustment connected to the forward converter. , a series circuit of a diode and a capacitor is connected in parallel with the secondary chopper, and an inverse converter is provided for regenerating the secondary power of the induction machine into an AC power source via a transformer. 1. A control device for an induction machine, characterized in that a circuit in which a resistor and a switching element are connected in series in parallel is inserted between the forward converter and the secondary chopper.