KR870004066Y1 - Thyristor Control - Google Patents

Abstract

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Description

Thyristor Control

1 (a) -1 (f) are waveform diagrams associated with conventional thyristors.

Figure 2 is a schematic circuit diagram showing a power factor control device using a trigger control circuit of the present invention in the form of some blocks.

3 (a) -3 (m) are waveform diagrams associated with the apparatus of FIG.

[Technical Background of Design]

The present invention relates to a switching circuit of a thyristor used in a power factor control device of an inductive load such as an electric motor.

U.S. Patent Nos. 4,052,648 and 4,266,177 describe power factor controls that are particularly useful for induction motors. These power factor controllers, which sample the line voltage and current flowing into the motor, include a thyristors that control the lamp power input in proportion to the detected phase difference between the sampled voltage and current, thereby reducing the motor load. In response, less power is supplied to the motor.

As is well known in the art, the thyristors, ie SCRs or triacs, will be switched on when current pulses of only a few microseconds are supplied to their gate electrodes and will remain on until the anode current is at zero level. If this thyristor is used to control the sinusoidal current of a resistive load, the trigger pulse can be applied to any part of the sinusoidal since the current will be exactly in phase with the voltage.

However, in inductive loads, the current is significantly delayed with respect to voltage, which causes problems in triggering the thyristor. In particular, if a firing or trigger pulse is generated when the residue flows from the first half cycle, due to the current phase nature, then the triac will be already turned on. Furthermore, when the current goes to zero and the triac is off, the triac will remain off for half a cycle. As a result, the trigger pulse becomes useless, and the drawback of such an operation in the thyristor control is obvious.

In the above-described power factor control apparatus, this problem is solved by supplying the thyristor gate current using a fixed level signal rather than a trigger pulse. However, supplying a fixed level signal consumes significantly more power than supplying a trigger pulse. Moreover, it has been found that for some power factor control devices using triacs where the gate power is derived directly from the line voltage, it is necessary to use civilian gate pilot triacs to turn on the main power triacs.

[Outline of Design]

According to the present invention, there is provided a thyristors trigger circuit that uses a trigger pulse for firing the thyristors and suppresses the generation of the trigger pulses when the current flows from the first half cycle.

This circuit is particularly suitable for use in power factor control because it uses signals existing in the power factor control to suppress the firing pulses. Therefore, the trigger circuit of the present invention solves the problems associated with the above-described pulse firing, while still having the advantages of the fixed-level firing, without the need for a pilot triac.

According to an embodiment of the present invention, a trigger circuit is provided to a thyristor control apparatus for an AC input for a load that is not completely resistive (i.e., a load having a phase difference between the load current and the voltage waveform). A pulse generator for generating a firing pulse for firing a device, a device for inducing a control signal of the thyristors based on a phase difference between load current and voltage, and firing until the load current does not flow from the first half cycle of the AC input. And a device responsive to the control signal to suppress the generation of the pulse. The pulse generating device includes an electronic switching element such as a transistor, and the firing pulse suppressing device preferably controls the "on" time of the transistor.

The firing pulse suppression apparatus has an advantage of setting a reference point for triggering a triac based on the phase difference signal and suppressing the generation of the firing pulse in advance of the reference point. The base of the control transistor of the thyristors is wired to receive the first signal from the suppressor and the second signal from the thyristors control circuit, and the thyristors are connected so that they are turned on only when the signals are negative. . The firing angle of the second signal controls the turn-on time of the transistor as long as it appears after that reference angle, and thus controls the thyristor, but when the firing angle is ahead of the reference angle, the transistor does not turn on until it reaches the reference angle. Do not.

[Description of Preferred Embodiment]

A description of a preferred embodiment of the present invention is described below with reference to the first (a) -1 (f) with respect to the waveform associated with the operation of the prior art thyristors, using the trigger control circuit of the present invention The part corresponding to the prior art in the circuit diagram (Fig. 2) of the power factor controller will be described first.

1 (a) -1 (f) show waveforms associated with the operation of a conventional thyristor. When the thyristors are connected to an alternating pressure and supply an output current when the trigger is “on” or ignited, the input current and voltage are as shown in Fig. 1 (a) and the firing pulses of the thyristors are shown in Fig. 1 (b). If it occurs at the time shown in Fig. 1, the output current will be as shown in Fig. 1 (c). If the firing pulse coincides with the zero crossing of the current waveform as shown in figure 1 (d) in time, an exponential current will flow. That is, the current becomes as shown in FIG. 1 (a). However, as the firing pulse is further ahead in time as shown in Figure 1 (e), a firing pulse occurs when the current is still flowing in the first half cycle, and when the thyristor is already in the "on" state, the current goes to zero. Since the thyristor is turned off and the firing pulse has already ended, the thyristor will remain off for the next half cycle as shown in FIG. 1 (f). This is the problem the present invention seeks to solve. However, before describing the present invention in more detail, a general configuration of the control device in which the present invention is used will be described first.

2 illustrates an embodiment of the present invention for use in a power factor control device similar to that described in US Pat. No. 4,266,177.

Since the apparatus shown in FIG. 2 is similar to that described in the patent, it is described here with reference to the contents of the patent used in the present invention device.

The apparatus of FIG. 2 accepts an input waveform, typically 115 volts alternating current as shown in FIG. 3 (a), and includes a power supply circuit 14, a winding thyristor (triac) 18 and a current of the electric motor 16. And input terminals 10 and 12 connected to both ends of the series connection of the detection resistor 20. The input terminal 10 also has positive and negative voltage square wave shaping circuits 24, which generate the opposite phase propagation, square outputs “f” and “g,” respectively shown in FIGS. 3 (f) and 3 (g). 22). In order to indicate the mode of operation of the representative triac 18 in FIG. 3 (b) and in order to indicate the mode of operation of the triac 18 in succession in FIG. The signal voltage shown is shown across the current detection resistor 20 to indicate the continuous mode of operation triac 18 is always on, which signal is propagated in a square wave shaping circuit 26 and 28. Is applied to. The square wave shaping circuit 26 responds only to the positive half cycle of the terminal current waveform and generates the square output waveform " h " shown in FIG. 3 (h) in response to the signal shown in FIG. In contrast, the square wave shaping circuit 28 responds only to a negative half cycle of the current waveform and generates a square output waveform " i " shown in FIG.

The output terminals " g " and " f " of the voltage square wave shaping circuits 22 and 24 generate negative spikes used to trigger the ramp generating circuit 32 connected to the output terminal of the detector 30. Is connected to a pulse detector (30). The output end of the ramp generation circuit 32 is connected to the positive (non-inverting) input end of the operational amplifier 34, which acts as a zero crossing detector. The control signal described below is connected to the negative (inverting) input terminal of the operational amplifier 34.

The above mentioned control signal

(1) a signal based on a phase difference between a current and a voltage applied to the electric motor 16,

(2) It is a function of the command or reference signal described below.

The phase difference signal is induced by a predetermined combination of the outputs of the square wave shaping circuits 22, 24, 26 and 28. In particular, the outputs of the square wave shaping circuits 22 and 26 are added in the addition circuit 36, and the outputs of the square wave shaping circuits 24 and 28 are added in the adding circuit 38. The signal thus produced is rectified by diodes 40 and 42 and polymerized at point 43 to supply the output signal “j” shown in FIG. 3 (j). The pulses shown in FIG. 3 (j) are constant in amplitude and varying in width. The width or duration of this pulse depends on the phase difference between the input voltage and the current.

The pulse signal shown in FIG. 3 (j) is applied to the other operational amplifier 46 and the capacitor 48 through the resistor 44. The operational amplifier 46 and the capacitor 48 are connected to the integrator (50). ).

The above mentioned command signal is derived from the potential difference 52 set with the unloaded vibrator 16 and the maximum power factor at which the motor will operate for the load range to be applied as described in US Pat. No. 4,266,177. Selects the power factor or phase angle between the voltage currents determined by the minimum phase difference between current and voltage. The tap of potentiometer 52 is connected to negative input of amplifier 46 via resistor 54. The positive input terminal is grounded through resistor 56.

The output of the integrator 50 is the control signal mentioned above and is connected to the negative (inverting) input of the operational amplifier 34.

The present invention relates to a thyristor control apparatus incorporating a trigger circuit in the circuit of US Pat. No. 4,266,177, described above.

According to the present invention, another operational amplifier 58 is provided, in which the positive (non-inverting) input of the operational amplifier is connected to the addition point 43 and the negative (inverting) input terminal is formed by the resistors 60 and 62. And to receive a positive bias, or reference voltage, represented by the voltage divider.

The output voltage of the amplifier 58 is connected via a resistor 64 to the norm 66 which is connected to the base of the control transistor 68. The output of the operational amplifier 34 is connected through the resistor 70 to the Norwood 66 and the transistor 86.

The emitter of transistor 68 is connected to the gate electrode of triac 18 via resistor 72 while the collector of transistor 68 is an Rc time circuit formed by resistor 74 and capacitor 76. Is connected to.

Considering the operation of the apparatus of FIG. 2, the phase difference signal at point 43 (shown in FIG. 3 (j)) is adjusted by being supplied to the non-inverting input of the operational amplifier 58. As described above, a positive bias voltage is applied to the inverting input of amplifier 58 through a voltage divider formed by resistors 60 and 62. The resulting output waveform “k” is shown in FIG. 3 (k). This voltage is added to the output of the amplifier 34 at the Norwood 66, which is a fixed level firing pulse as shown in FIG. 3 (e) and ramp output “d” (zero). Derived from the control signal output of the integrator 50). As can be seen by comparing the third (d) and the third (e) degrees, the firing angle θf is controlled by the intersection of the ramp “d” and the control signal output of the integrator 50. Since the emitter of transistor 68 is essentially a ground potential, transistor 68 is turned on when its base drive is negative. Thus, both input signals “e” and “k” must be negative at the same time to turn on transistor 68. If both inputs are positive, transistor 68 is off, while if one is negative and the other is positive, the two inputs are added as shown by comparing the waveforms shown in FIGS. 3 (e) and 3 (k). Becomes zero, and thus the transistor 68 is turned off again. Thus, the base current will not flow with 0 volt base driving, so the signals “k” and “e” will be effectively “AND” and transistor 68 will only turn on when all are negative.

When transistor 68 is turned on, triac 18 is also turned on, and the gate current is from its ground terminal, indicated at 18a, to gate terminal 18b, resistor 72, transistor 68 and resistor 74. ) And the RC circuit formed by the capacitor 76 flows to the negative power. The amount of current, typically 50-100 milliamps, is determined by the value of resistor 72. The time that this current flows is typically 10 microseconds, and is determined by the RC time constant. In this regard, a flow of 100 milliamps of current for 10 microseconds can be readily supplied by a filter capacitor (not shown) coupled with the power source 14. Resistor 74 provides the discharge path of capacitor 76 for each half cycle.

Triac 18 if the firing angle θf shown in FIG. 3 (e) changed by the power factor control device in response to the changing load is greater than the reference angle θR shown in FIG. 3 (k). The turn on time of will correspond to the firing angle θf. As the load of the motor 16 increases, the firing angle or point [theta] F will advance in time. That is, the on-time of the transistor 68 is increased until the firing angle θF is equal to or larger than the reference angle θR by moving to the left side in FIG. 3 (e).

Such a situation is shown in FIG. 3 (I) and shown by the dashed line waveforms in the firing angle [theta] F 'and in FIG. 3 (e). In such a situation, the base drive of the transistor 68 is the signal shown in FIG. 3 (m). Since the base drive voltage is zero at the firing angle [theta] F, the transistor 68 is not turned on at that time, and both signals “i” and “k” are negative to turn the transistor 68 to turn on the triac 16. It will remain at zero until θR is turned on.

Claims (6)

In a die Lister control apparatus for an AC input including a thyristor for controlling a current flowing through a load having a phase difference between a load current and a voltage waveform, a pulse generator (68) for generating a firing pulse for firing the die lister (68). 74, 76), based on the phase difference between the load current and the voltage, the thyristors until the current does not flow from the first half cycle of the AC input in response to a control signal and the control signal inducing device 50 for the pulse generator. And a suppressor (58) for suppressing generation of a firing pulse. 2. The apparatus of claim 1, wherein the pulse generator comprises an electronic switching element (68) and a device (74, 76) for controlling the ON time of the electronic switching element. A control device as claimed in claim 1 or 2, characterized in that said suppression device comprises means (58) for responding to said control signal to suppress the generation of the firing pulse in advance during half cycle and to set a reference point at which the firing pulse is generated. Thyristor control device. 2. The pulse generator according to claim 1, comprising a pulse generator as the transistor 68, wherein the suppressor prevents the transistor from turning on before the reference point [theta] R time according to the phase difference between the load current and the voltage. And means (58) for supplying a pulse for turning on the transistor (68) at the reference point (θR). The base of the transistor 68 is connected to receive a first signal from the suppressor 58 and a second signal from the control circuits 30, 32, 34 which determine the firing angle of the firing pulses. And the first and second signals have the same polarity before the transistor is turned on. 2. The apparatus of claim 1, wherein the control signal inducing device (50) is connected to the existing device to respond to a phase difference signal provided by the devices (33,36) existing in the power factor control device.