JPH0130390B2 - - Google Patents

Description

Detailed Description of the Invention a. Technical Field The present invention relates to a current control device for exciting an inductive load.

b. Technical Background and Problems The conventional current control device for exciting an inductive load is shown in the control block diagram of FIG.

1 is an AC power supply, 2 is a controlled rectifier circuit composed of a thyristor 2A that converts AC voltage to DC voltage, 3 is an inductive load excited by the controlled rectifier circuit 2, and 4 is a current flowing through the inductive load 3. 5 is a current detection circuit that detects the current flowing through the inductive load 3; 6 is a current reference circuit that differentially inputs the output signal of the current reference circuit 4 and the output signal of the current detection circuit 5; 7 is a phase control circuit that determines the firing timing of the thyristor of the control rectifier circuit 2 based on the output signal of the current control calculation circuit 6; 8 is a phase control circuit of the phase control circuit 7; A continuous gate pulse generation circuit provides a continuous gate pulse to the gate of the thyristor of the control rectifier circuit 2 by output, and 9 provides a shift command to the phase control circuit 7 in order for the phase control circuit 7 to phase shift the continuous gate pulse to the β limit. 10, 11, 12, 13 are snubber circuits that are connected to both ends of the thyristor and are made up of a resistor and a capacitor to absorb the surge voltage generated across the thyristor. This is a dummy resistor connected to the output side of the control rectifier circuit 2 to facilitate latching when continuous gate pulses are applied to the circuit.

The conventional current control device configured as above is
When the phase throttling circuit 9 cancels the shift command, the phase control circuit 7 generates a trigger pulse from the phase that follows the output signal of the current control calculation circuit 6, and generates a trigger pulse via the continuous gate pulse generation circuit 8 as shown in FIGS. 2b and 2c. The control rectifier circuit 2 outputs continuous gate pulses as shown in
Current control is performed so that the current applied to the gate of the thyristor 2A and flowing to the inductive load 3 follows the setting signal of the current reference circuit 4.

In this case, when starting from a state where the load current is zero, a problem arises in that starting may not be possible in some cases, but this will be explained below with reference to FIG.

Figure 2a shows the voltage waveform of the AC power supply, Figure 2b,
c is a continuous gate pulse applied to the gate of thyristor 2A, and the first rise indicated by P _A is:
This is the thyristor firing timing calculated by the phase control circuit 7. The pulses P _B after P _A are continuously generated by the continuous gate pulse generating circuit 8 until several pulses after the β limit shown at point b in FIG. 2 a after the pulse P _A is generated.

Inductive load 3 using conventional narrow gate pulse
The resistance value of the dummy resistor 14 is selected to be a value that allows a sufficient latch current to flow through the thyristor when a current is caused to flow through the thyristor, but this has the drawback of increasing power loss during operation. Therefore, as shown in FIGS. 2b and 2c, continuous narrow gate pulses are used, and the resistance value of the dummy resistor 14 is selected to be large in order to reduce power loss.

FIG. 2d is a current waveform showing the initial state of the load current when a gate pulse is applied from a state where the load current is zero.

When the gate pulse (FIG. 2b) is applied at time _t1 , the first pulse P _A turns on the thyristor 2A and the load current begins to flow. At this time, the rise of the load current increases in accordance with the time constant of the main circuit impedance including the power supply and load, and the pulse
During the P _A period, the current increases only slightly and the current flowing through the thyristor 2A does not reach the latch current. Therefore, when the gate pulse P _A disappears, the thyristor 2A becomes semi-conductive, forms an inductive load discharge circuit, and operates to hold the increased load current. After that, when the pulse P _B is applied, the thyristor 2A, which is in a semi-conducting state, becomes fully conductive and the load current starts to increase again.If the latch current is not reached during the period of the pulse P _B , the thyristor 2A is turned off again when the pulse P _B disappears. 2A becomes semi-conductive. Thereafter, the load current increases little by little while repeating the same operation every time the pulse P _B is applied.

After that, when the load current increases to the value of _I0 at time _t2 , the current of thyristor 2A reaches the latch current, and from then on, even if the pulse disappears, the load current increases and continues to flow as a continuous current. Enters normal commutation operation.

The above explanation is based on the case where the thyristor 2A can be started normally, but due to an abnormality in the pulse width of the gate pulse, disconnection of the dummy resistor 14, or other causes, the thyristor 2A
The current may not reach the latch current.
In this case, even though gate pulses are continuously applied to the thyristor 2A, the target load current cannot flow, and the thyristor 2A cannot be started.
Furthermore, if this state is left as it is, there is a risk and disadvantage that the resistors of the snubber circuits 10 to 13 will be burned out due to charging and discharging of the capacitors.

c. Object of the Invention In order to eliminate the above-mentioned drawbacks of the conventional art, the object of the present invention is to provide a protection function that can prevent burnout of the resistor of the snubber circuit by providing an unlatching detection circuit that detects the failure of the thyristor to latch. The object of the present invention is to provide a highly reliable current control device.

d.Summary of the Invention The present invention provides a current control device that includes a power conversion circuit using a thyristor that supplies power to an inductive load, and a gate pulse generation circuit that provides firing pulses of the thyristor with a plurality of consecutive pulses. a current level detection circuit that outputs a first logic signal when the load current exceeds a predetermined value; and a timer circuit that outputs a second logic signal after a predetermined time from the timing of starting control of the current control device. and,
A logic circuit is provided for outputting a shift signal for controlling the firing phase of the firing pulse to the delayed side from the first logic signal and the second logic signal, thereby making it possible to prevent burnout of the snubber circuit. This is a current control device.

e Embodiment of the Invention FIG. 3 shows an embodiment of the current control device according to the present invention. It should be noted that circuits having the same functions as the conventional circuit shown in FIG. 1 are given the same reference numerals and explanations thereof will be omitted. 15-18
This is the configuration of the unlatching detection circuit newly provided in the present invention to prevent burnout of the resistor of the snubber circuit.
15 is a current level detection circuit which inputs the output signal of the current detection circuit 5 and detects whether the current flowing through the inductive load 3 exceeds the thyristor latch current; 16 is a cancellation of the shift command from the phase throttle circuit 9; 17 is an AND circuit, and 18 is an OR circuit.

In the current control device configured as described above, normal current control is started when the shift command from the phase throttle circuit 9 is released. After that, if the device starts up smoothly and enters normal operation, a load current greater than the latch current of the thyristor flows after a predetermined period of time, and a logic signal of “0” is detected at the output of the current level detection circuit 15. The output of the timer circuit 16 has a time limit after the shift command is released, and outputs a logic signal of "1". If this time limit is selected to be sufficiently large, the output of the AND circuit 17 will be A logic signal of “1” does not appear.

However, as mentioned above, if the latch current is not reached even after the time limit of the timer circuit 16 has elapsed due to some reason, the output of the current level detection circuit 15 remains in the "1" state, and the output of the timer circuit 16 remains in the "1" state. When the output of the AND circuit 17 becomes "1", the output becomes "1" and this signal is input to the phase control circuit 7 via the OR circuit 18 as a shift command. This action reduces power loss due to charging and discharging of the capacitors in the snubber circuits 10 to 13 due to turning on and off of the thyristors even if the state where the latch current is not reached and the startup is not possible is left.
It is possible to prevent the No. 13 resistor from burning out.

f. Effects of the Invention As explained above, according to the present invention, in a continuous gate pulse type current control device that excites an inductive load, the thyristor cannot latch due to some reason and becomes unable to start. Even if left in this state, a shift command is automatically issued after a predetermined period of time, and the resistance of the snubber circuit is reduced by repeatedly charging and discharging the snubber circuit capacitor by repeatedly turning the thyristor on and off using continuous gate pulses. A current control device that can reduce power loss and prevent burnout can be provided.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional current control device, Figure 2a is a voltage waveform diagram of an AC power supply, Figures 2b and c are continuous gate pulses applied to the gate of the thyristor, and Figure 2d is FIG. 3, a waveform diagram showing the rise of the load current, is a block diagram showing an embodiment of the current control device according to the present invention. 1... AC power supply, 2... Control rectifier circuit, 3...
Inductive load, 4... Current reference circuit, 5... Current detection circuit, 6... Current control calculation circuit, 7... Phase control circuit, 8... Continuous gate pulse generation circuit, 9...
...Phase throttling circuit, 10, 11, 12, 13...
Snubber circuit, 14...Dummy resistor, 15...Current level detection circuit, 16...Timer circuit, 17
...AND circuit, 18...OR circuit.

Claims (1)

[Claims] 1. In a current control device equipped with a power conversion circuit using a thyristor that supplies power to an inductive load, and a gate pulse generation circuit that gives the firing pulse of the thyristor as a plurality of consecutive pulses, the load current is controlled to a predetermined level. a current level detection circuit that outputs a first logic signal when the current level reaches a value greater than or equal to a value of A current control device comprising: a logic circuit that outputs a shift signal for controlling the firing phase of the firing pulse to a delayed side based on the signal and the second logic signal.