JP3428256B2 - Induction motor speed controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control apparatus for an induction motor suitable for controlling a pump, a fan and the like at a variable speed. 2. Description of the Related Art As a variable speed driving device such as a pump or a fan, there is known an induction motor speed control device described in Japanese Patent Publication No. 3-41024, for example. FIG.
FIG. 1 shows a circuit configuration diagram of this speed control device. In FIG. 5, a load 17 such as a pump or a fan is directly connected to a winding-type induction motor (hereinafter referred to as an induction machine) 1, and a tachometer 18 is further attached. The secondary AC voltage of the induction machine 1 is converted to DC by the diode rectifier 2. Induction machine 1
The secondary DC current of step-up chopper circuit 5 is composed of a switching element 28 (transistor, GTO, IGBT, etc.) having a self-extinguishing function and a diode 29 for blocking backflow.
Controlled at 0. When the switching element 28 is on, the boost chopper circuit 50 short-circuits the secondary side of the induction machine, increases the output current of the diode rectifier 2 and stores energy in the wiring and the inductance of the induction machine 1. When the switching element 28 is off, the output current of the diode rectifier 2 is cut off and the stored energy is charged to the capacitor 31 via the diode 29. The voltage of the capacitor 31 has a higher value than the rectified voltage of the secondary rated voltage of the induction machine. The inverter 32 regenerates the secondary power of the induction machine 1 charged in the capacitor 31 to the power supply when the switching element 28 is off. In addition, 30 is a reactor, 3
Reference numeral 3 denotes a transformer. To drive the switching element 28, a comparator 37 compares a speed command signal of a speed command circuit 38 with a speed detection signal of the tachometer 18 to obtain a current command signal.
Next, the current command signal and the current detection signal detected by the current detector 34 are compared by a comparator 36 having a hysteresis characteristic to generate an ON / OFF signal of the switching element 28.
The switching element 28 turns off when the current command signal increases by more than a predetermined value (hysteresis width value) from the current detection signal, and turns on when the current command signal decreases below the predetermined value from the current detection signal. The output current of the diode rectifier 2 becomes a DC current having a pulsation width determined by the hysteresis of the comparator 36 as shown in FIG. [0004] In order to increase the capacity of the induction machine, it is common to increase the secondary rated voltage of the induction machine. When the secondary voltage of the induction machine is increased, unless the DC voltage Vcd is higher than the secondary rectified voltage of the induction machine, the boost chopper circuit is not established. [0005] Here, the DC current Id obtained by rectifying the secondary current of the induction machine is expressed by Equation 1 when the switching element is on, and is expressed by Equation 2 when the switching element is off. [0006] [0007] Here, Vd is a voltage obtained by rectifying the secondary voltage of the induction machine, Vcd is a DC voltage R, wiring is a diode rectifier and the resistance Te of the induction machine is wiring, a time constant t of the diode rectifier and the induction machine is an elapsed time induction machine. When the secondary voltage and the capacitor voltage are increased, as can be understood from Equations (1) and (2), the gradient of increase / decrease of the DC current Id increases. Therefore, if the secondary voltage of the induction machine is increased without changing the hysteresis of the comparator, the pulsation width of the output current of the rectifier diode does not change, but the on / off cycle of the signal output from the comparator becomes shorter. That is, the switching amount of the switching element per unit time increases, and the loss due to switching increases. Therefore, due to the increase in the loss, it is necessary to increase the rated current of the switching element. SUMMARY OF THE INVENTION It is an object of the present invention to provide a speed control device for an induction motor capable of suppressing a pulsation width of a current without shortening a switching cycle even when a secondary rated voltage of the induction motor is increased. is there. According to the present invention, a step-up chopper circuit is constructed by connecting two switching elements in series, and a capacitor is connected in parallel with both switching elements to form two switching elements. The elements are turned on and off alternately. In this way, by alternately turning on and off both switching elements, the pulsation width of the output voltage of the boost chopper circuit is at most DC voltage Vcd.
And the pulsation width of the current is also reduced to 1/2 of the conventional value. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Note that FIG.
5, the same components as those in FIG. 5 are denoted by the same reference numerals.
Reference numerals 3 and 4 denote reactors for current smoothing, 5 and 6 denote switching elements (transistors, GTO, IGBT, etc.) connected in series having a self-extinguishing function, 7, 8 denote diodes for preventing backflow, and 9 and 10 denote diodes. Voltage smoothing capacitors connected in series, 11 and 12 are transistors, IGBT, G
Inverter composed of TO etc., 13 and 14 are transformers,
Reference numerals 15 and 16 denote amplifiers for supplying base currents for driving the transistors 5 and 6, 19 a current detector for detecting the output current of the diode rectifier 2, and 20 a control for generating base signals for driving the transistors 5 and 6. Circuit, 2
Reference numerals 1 and 22 denote voltage detectors for detecting the voltages of the capacitors 9 and 10, 23 and 24 denote amplifiers that supply a base current for driving the inverters 11 and 12, and 25 and 26 denote voltage detectors 21 and 22. Upon receiving the voltage detection signal, the capacitor 9,
This is a control circuit for controlling the inverters 11 and 12 so as to keep the voltage of 10 constant. The operation of FIG. 1 is almost the same as that of the apparatus shown in FIG. That is, the secondary current of the induction machine 1 is converted to DC by the diode rectifier 2, and the current is controlled by the boost chopper circuit 51 composed of the transistors 5, 6 and the diodes 9, 10 to control the speed. In the inverters 11 and 12, when the transistor 5 or 6 is turned off, the capacitors 9 and
The secondary power of the induction machine 1 that is charged to 10 is regenerated to a power supply. Specifically, the control circuits 25 and 26 include the voltage detector 2
A voltage for controlling the voltage of the capacitors 9 and 10 to be constant by the voltages of the capacitors 9 and 10 detected in the power supply 1 and 22 and detecting the phase of the power supply, and controlling the current waveform regenerated to the power supply to a sine wave. The base signals of the converters 11 and 12 are created. Amplifiers 23 and 24 amplify the base signal to a level that drives inverters 11 and 12. When the transistors 5 and 6 constituting the boost chopper circuit 51 are simultaneously turned on or off, the pulsation width of the output current of the diode rectifier 2 becomes the same as that of the conventional one.
In the present invention, the transistors 5 and 6 are alternately switched by base signals having a 180 ° phase difference. The base signals of the transistors 5 and 6 are created by the control circuit 20 shown in FIG. In FIG. 2, a speed command signal of the induction machine 1 and a speed detection signal obtained by converting a speed detection value detected by the tachometer 18 into a digital signal by an analog / digital converter (A / D converter) 40 are shown. The speed controller 41 outputs a current command signal according to the deviation of. Current command signal and current detector 1
A / D is the output current of diode rectifier 2 detected at 9
The current controller 43 outputs a voltage command signal normalized by the amplitude of the carrier based on a deviation from the current detection signal converted into a digital signal by the converter 42. The carrier is a triangular wave generator 44
As a result, the cycle is obtained as a triangular wave serving as a switching cycle. Next, 18 using a voltage command signal and a triangular wave.
The operation of creating two types of base signals having different 0 ° phases will be described with reference to FIG. 3 showing the relationship among a triangular wave, a voltage command signal, and a gate signal. 1) Preparation of base signal of transistor 5 A comparator 45 compares the triangular wave with the voltage command signal to generate a carrier comparison PWM type gate signal. (Signal (a)) Note that the carrier comparison PWM method is well known, and a detailed description thereof will be omitted. 2) Preparation of Base Signal of Transistor 6 In order to generate a base signal whose phase is different from that of the base signal of the transistor 5 by 180 °, first, a voltage command signal is subtracted from the amplitude value of the carrier wave, and the value is converted into a triangular wave and a comparator 46. To create the signal (b). By inverting the signal of (b) by the NOT circuit 47, a base signal having a 180 ° phase difference from the base signal of the transistor 5 is obtained. ((C)
When the transistors 5 and 6 are driven by the base signals whose phases are different by 180 °, the transistors 5 and 6 are not turned on or off at the same time, but are always turned on or off one by one. The fluctuation of the output voltage of the boost chopper circuit 51 is as shown in FIG. FIG. 4 shows the relationship between the base signal of the transistor and the output voltage of the boost chopper circuit 51 when the ON time of the transistor is 以下 or less of the switching cycle. In FIG. 4, when one of the transistors 5 and 6 is on and the other is off, the output voltage of the boost chopper circuit 51 is 直流 of the DC voltage Vcd.
It becomes. When both the transistors 5 and 6 are off, the output voltage of the boost chopper circuit 51 becomes Vcd.
For this reason, the pulsation width of the voltage of the conventional boost chopper circuit is the DC voltage Vcd, whereas the pulsation width of the output voltage of the boost chopper circuit 51 is １ ／ of the DC voltage Vcd in the present invention.
It becomes. This relationship is the same when the ON time of the transistor is 以上 or more of the switching period. Therefore, the present invention makes it possible to reduce the pulsation width of the output current of the diode rectifier to 従 来 of the conventional one by reducing the pulsation width of the output voltage of the boost chopper circuit to 従 来 of the conventional one. In the embodiment, the inverters 11 and 12 are arranged in series. However, the same effect can be obtained by using a single inverter using a device having a rated voltage that can withstand Vcd. Obviously, the reactors 3 and 4 need not have the required current pulsation width due to the inductance of the induction machine. Further, in the present embodiment, two kinds of base signals having phases different from each other by 180 ° are created by one kind of carrier wave by operating the voltage command signal, but the phase is changed without operating the voltage command signal. Of course, it can be created by comparing with a base signal different by 180 °. As described above, the present invention relates to, for example, the induction motor 2
When the secondary voltage is doubled, the pulsation width of the secondary rectified current can be suppressed to half of the conventional one at the same switching cycle as the conventional one. Therefore, the pulsation width of the secondary current of the induction machine can be suppressed, and the speed control accuracy can be improved. The pulsation width of the output voltage of the boost chopper circuit is の of the output voltage Vcd. Therefore, the fluctuation width of the voltage per switching element is halved, and the switching loss per switching element can be reduced. That is, the rated current of the element can be reduced. Further, by connecting the switching elements in series and connecting the middle of the elements to the middle of the capacitors connected in series, the DC voltage Vcd is applied to the upper and lower switching elements.
Are applied in half each, so that when an induction machine having the same secondary voltage is connected, the rated voltage of the element is reduced to half that of the conventional device.
It becomes possible to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a speed control device for an induction motor according to an embodiment of the present invention. FIG. 2 is a configuration diagram illustrating an example of a control circuit for generating a gate signal according to an embodiment of the present invention. FIG. 3 is a waveform diagram showing a relationship between a voltage command signal, a carrier, and a base signal. FIG. 4 is a waveform diagram showing a relationship between a base signal and an output voltage of a boost chopper circuit. FIG. 5 is a configuration diagram of a conventional induction motor speed control device. FIG. 6 is an operation explanatory diagram of the conventional device shown in FIG. 5; [Description of Signs] 1 ... Wound induction motor, 2 ... Diode rectifier, 3,4
... Reactor, 7,8 ... Diode, 9,10 ... Capacitor, 11,12 ... Inverter, 13,14 ... Transformer.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadakatsu Kinase 5-2-1 Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi, Ltd. Omika Plant (72) Inventor Kiyotaka Kobayashi 5-chome Omikacho, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi, Ltd. Omika Factory (56) References JP-A-5-284793 (JP, A) JP-A-64-60288 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) H02P 5/28-5/44 H02P 7/36-7/66

Claims (1)

(57) Claims 1. A diode rectifier connected to the secondary side of a wound induction motor, and a self-extinguishing element connected in series with the same polarity between both ends of a DC output of the rectifier. A capacitor connected in parallel to the self-extinguishing element via a diode, and the diode is connected in a direction to guide the output current of the rectifier to the capacitor when the self-extinguishing element is off, and The middle of the upper and lower elements of the arc element is connected to the middle of the upper and lower capacitors of the capacitor, an inverter that regenerates the DC power of the capacitor to the power supply, and the self-extinguishing to control the output current of the rectifier. on the element, the signal causes off, two self is the series
The arc-extinguishing element turns on and off alternately, and one turns off
A signal that is 180 ° out of phase to turn on the other later
A speed control device for an induction motor, comprising a chopper control means that is generated by the operation.