JPS62210876A - Control unit of induction machine - Google Patents

Abstract

PURPOSE:To obtain sufficient starting torque and to perform a smooth speed control, by connecting a resistance in series between a power rectifier and a secondary chopper and then by connecting a switching element in parallel to the resistance for shortcircuiting. CONSTITUTION:A power rectifier 2 is connected on the secondary side of an induction machine 1, of which secondary chopper 3 is connected on the output side. The secondary chopper 3 is ON/OFF controlled so that the output current of the power rectifier 2 may become a command value. A series circuit of a diode 4 and a capacitor 5 is connected to the secondary chopper 3 inparallel. A power inverter 8 is provided to regenerate the secondary power of the induction machine 1 to an AC power source. Between the capacitor 5 and the power inverter 8 a regenerating chopper 6 is provided to regulate the current from the capacitor 5 to the power inverter 8 so as to keep the voltage of capacitor in a predetermined value.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a control device for an induction machine capable of secondary excitation control,
In particular, the present invention relates to an induction motor control device suitable for variable speed control of equipment 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 through a DC reactor and an inverse converter (DC-AC converter). This is a device that regenerates power.

In addition, this type of device is related! For example, JP-A-60-156297, JP-A-60-2267,
Publication No. 94, etc. may be mentioned.

(Problems to be solved by the invention) In this device, the capacity of the inverter increases in proportion to the size of the speed control range, and furthermore, in the low slip region, the ignition delay angle is This has the disadvantage that the reactive current is large and the power factor of the entire system is also reduced.

For this reason, this type of device usually has a variable range of 60 to 100.
Take about %.

In the speed range of 0 to 60%, operation is performed by connecting a starting resistor to the secondary winding, but in order to prevent torque discontinuity, a continuously variable resistance value is used, and normally Large-scale equipment such as water resistors is used. Therefore, it is contrary to space saving and maintenance efficiency.

The purpose of the present invention is to minimize the inverter capacity, have a high power factor, obtain sufficient starting torque, and furthermore be able to continuously control the torque from starting to rated speed, and perform smooth speed control. Our objective is to provide a control device for induction motors.

[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 in parallel with the secondary chopper. comprising a series circuit of capacitors and an inverter for regenerating the secondary power of the induction machine to an AC power source, and between the capacitor and the inverter so that the capacitor voltage is maintained at a predetermined value; A regenerative chopper that adjusts the current from the capacitor to the inverse converter is interposed, and a resistor is connected in series between the forward converter and the secondary chopper so that the output current of the forward converter becomes a command value, This is achieved by controlling the secondary chopper on and off.

(Function) When the torque changes as the square of the rotational speed, the current of the regenerative chopper and inverse converter is approximately 1/6 of the rated output current of the forward converter at maximum, and as a result,
3 which makes the element capacitance of the inverter minimum (theoretical minimum value) can be done. Furthermore, by combining the effect of increasing the starting torque through additional resistance with the on/off control of the secondary chopper, sufficient starting torque can be obtained.
Smooth operation from start to rated speed is possible.

〔Example〕

An embodiment of the present invention is shown in FIG.

In Figure 1, 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 transistors, 4 is a reverse current blocking diode, and 5 is a capacitor. It is.

3 and 6 are self-extinguishing elements, transistors, G
T O (Gate Turn off Thyrjst
or). 7 is a freewheeling diode, 7
9 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 chopper operation. Also.

26 is a starting resistor connected in series with the DC circuit, and 27
is a circuit short-circuit opening/closing element for short-circuiting both ends of the resistor after the motor is started, and may be a semiconductor switch made of a semiconductor element or a general FFB (hardwire circuit breaker) contactor.

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. 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; A comparator with a hysteresis characteristic that outputs an on/off control signal, 15 is a transistor 3
This is an amplifier for supplying on/off control signals to the base of the Reference numerals 16 to 21 are control units for controlling the voltage of the capacitor 5 to a constant value, and the same method as 11 to 15 described above is used. That is, 16 is a voltage command circuit, 17 is a voltage detector, 18 is a -114 pressure regulator, 19 is a current detector, 20 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 i6 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, thereby controlling the speed. By the way, while the secondary chopper is off, the capacitor 5 is charged with DC current 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 (6). Next, so that the voltage of capacitor 5 is constant,
The transistor 6 (herein referred to as a regenerative chopper) is turned on and off.

The current flowing while the transistor 6 is on reaches the inverter 8, and as a result, the current flows through the inverter 8 to the AC power supply.
MI secondary power is regenerated.

1, a circuit formed by a transistor 3, a diode 4, a capacitor 5, and a transistor 6 has the function of converting a secondary voltage that fluctuates due to slip, that is, the output voltage of a 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 TM1. 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 is the product of the secondary current, where the secondary power is proportional to the square of the rotational speed (torque), and the secondary voltage, which is proportional to the slip.It shows the maximum value when the slip is 1/3, and that value is the This is because it becomes 1/6 of the output. This secondary power is transferred to the transistor 3 as described above.
, 6 etc., the current of the regenerative chopper and inverse converter is approximately equal to the rated output current of the forward converter 2 (proportional to the rated secondary current of the IMI) at maximum. 1/6, and the capacity of the inverter 8 and converter 9 can be reduced to about 176 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 capacitance and system power factor are independent of the speed control range, so it is
It can be applied to 100% of the entire range.

As mentioned above, the inverter capacity is set to 1/6 of the motor capacity.
When set to , the torque (secondary current) at one rotational speed of zero (slip=1) is limited to the rated value of about 176. In the case of pumps, fans, etc., this is usually sufficient, but in cases where the friction 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.

In general, the torque of an induction machine is secondary human power Pzo (synchronous watt)
is proportional to. The secondary input Pzo is divided into a mechanical output M and a secondary electrical output P2 depending on the slip S.

That is, M = (] -s) P2o ・Old...(1) P2=s meeting P2o...
(2) Furthermore, the relationship between the torque T and the secondary electric output P2 is expressed by the following equation.

p2=□・T...Group・(3) Here, ωS is the full angular frequency, and p is the number of pole pairs.

That is, P2 is determined according to the relationship between the torque T and the torque. P2 is the part that is regenerated into the AC power supply by the operation of the secondary chopper 3, inverter 8, etc., and in this embodiment,
Since the resistor 26 is connected between the forward converter 2 and the secondary chopper 3, the power RId2 currently consumed in the resistor 26 is divided into parts consumed there, and the power RId2 is transferred from P2 to the inverse converter 8. If it is determined to be the remainder after subtracting the maximum regenerative power Pr of , the following equation holds true.

RT d”=Pz −P r −(4)
From this, the resistance value R is as follows. In addition, when using the resistor 26 with a fixed resistance value, R is set to the maximum value of the value of equation (5) in the operating speed range by turning on the resistor.

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. Further, since the output current Id of the forward converter 2 is controlled proportionally to the current command signal j according to the speed deviation from the speed regulator 12, the rotation speed is controlled so as to match the speed command value. be done.

As mentioned above, sufficient torque can be obtained from the time of starting (slip = 1), but if the additional resistor 26 is left connected, unit loss will occur in the resistor and efficiency will decrease. It causes Therefore, it is necessary to short-circuit the resistor at an appropriate point.

This is done by the opening/closing element 27, which is turned on when a predetermined rotational speed is reached. After this, all secondary power is regenerated into AC power by the inverter 8.

As described in -1- above, in this embodiment, a large starting torque can be obtained while minimizing the capacity of the S inverse converter, and the output current of the forward converter is always controlled by the secondary chopper 3. Therefore, the torque can be controlled continuously, and there is no step change in torque when switching the resistance, unlike in the case of a single secondary resistance start, and smooth operation can be performed. Note that the electric motor is not limited to a wound 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. In other words, the first
The winding is used as the primary core of the wound induction machine, and the second winding is used as the secondary winding, and the control device of the present invention is connected to the second winding. In this case, there is an advantage that brushless variable speed control is possible.

FIG. 2 shows another embodiment of the present invention.

The embodiment of FIG. 2 includes the forward converter 2 and transistor 3 of FIG.
and 6, all the semiconductors of the diodes 4 and 7 and the inverter 8 are modularized, and all these elements are mounted on an integrated fin, and the detection parts and PWM shown by 11 to 22 are
The control section is manufactured using one LSI.

In addition, 23 in FIG. 2 is a primary side power supply line of the induction machine 1, and 24 is an electric wire for connecting to the transformer 9.

According to this embodiment, there is an effect that the control device can be manufactured more compactly. For example, even in a several hundred kilowatt class model, the control circuit part (the part surrounded by the dotted line in Figure 1,
25) can be made as small as the current terminal box of the induction machine 1.

〔Effect of the invention〕

, l・゛As above,. According to the present invention, the starting torque of the induction machine can be increased and the torque can be continuously controlled.
At start-up (slip = 1) with the inverter capacity minimized
This has the effect of making it possible to obtain smoother speed control over the entire range up to the maximum speed.

[Brief explanation of drawings]

FIGS. 1 and 2 are configuration diagrams showing embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 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 with hysteresis characteristic, 15... Amplifier, 16... Voltage command, 17.
...Voltage detector, 22...Ignition control circuit, 26...
Starting resistance, 27...Circuit opening/closing Figure 1 Figure 2

Claims (1)

[Claims] 1. An induction machine capable of secondary excitation, a forward converter that converts the secondary voltage of the induction machine into direct current, and a secondary chopper consisting of a self-extinguishing element for adjusting the voltage connected to the forward converter. , a series circuit of a diode and a capacitor is connected in parallel with the secondary chopper, and an inverter is provided for regenerating the secondary power of the induction machine to an AC power supply, and the inverter is connected to the capacitor and the inverse converter. In a control device in which a regenerative chopper made of a self-arc-extinguishing element is interposed in series between the forward converter and the secondary chopper, a resistor is connected in series between the forward converter and the secondary chopper, and a short circuit is connected in parallel with the resistor. A control device for an induction machine, characterized in that an opening/closing element for the purpose is connected.