JPS6211914A - Dead load control method for converter - Google Patents

Abstract

PURPOSE:To reduce the electric power loss during the light load and to improve the reduction effect especially in a parallel operation mode and at the same time to prevent a hunting phenomenon due to the hysteresis characteristics, by providing a dead load and a variable impedance element connected in series. CONSTITUTION:When the output voltage level rises up to a dead load application point A in a light load state, an operational amplifier 7 delivers a difference signal having a level equivalent to the difference between the reference voltage level and the detecting voltage level of the output voltage to a driving circuit 8. The circuit 8 applies a control signal having a level corresponding to said difference signal to a variable impedance element 4 for linear control of the impedance. Thus the impedance of the element 4 is controlled so that the sum of the load current flowing to a load 2 and the dead load current flowing via a dead load 5 connected in series to the element 4 is approximately equal to the current I3 at a point A within a range between the point A and a no-load point. Therefore the output voltage is approximately equal to the voltage V3 at the point A within a range between the point A and the no-load point. This reduces the electric power loss and especially improves the reduction effect in a parallel operation mode. Then it is possible to prevent a hunting phenomenon caused by the hysteresis characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling dead load in a converter device such as a rectifier device or a DC-DC co/verter.

[Conventional technology]

It is generally known that in converter devices, when the load becomes lighter, the output voltage of the converter increases as shown in FIG. In order to completely suppress the rise in output voltage during light loads, it has been conventionally done to completely turn on the dead load. 59-18
There is one disclosed in Japanese Patent No. 5160.

This conventional example f: will be explained with reference to FIG. 6 and FIG.
5 is a dead load, and 11 is a comparison circuit having hysteresis characteristics as shown in FIG. The operation of this circuit will be explained using FIGS. 4 and 5. When the output voltage of converter 1 becomes larger than IV, l, the output voltage of comparator circuit 11 becomes VH, and switch 4' is closed. A current flows through the dead load 5. At this time, by selecting the resistance value of the column load 5 to an appropriate value, the output voltage of the converter 1 can be set between '1lv21 and I'41, so that the switch can be switched while in a light load or no-load state. 4' is in the closed state.

When the load becomes normal and the output voltage becomes smaller than 1v21, the output voltage of the comparator 6 becomes ■.

Then, the switch 4' is opened. This causes no current to flow through the column load. Therefore, no current flows through the column load 5 when the load is normal.

[Problem that the invention seeks to solve]

However, such conventional devices have hysteresis characteristics in applying and removing column loads, and therefore have the following drawbacks. In FIG. 5, when the output voltage of converter 1 rises at 3 (output current I) according to load curve X1, p-series load 5 is applied as described above, and
As the current (I2-I, ) flows through , the output voltage of converter 1 drops to ■2. The converter output drops from point A to point B, and as the load becomes lighter, the converter output increases according to another song MAX2 that has been changed. Dead load 5 due to the voltage lower than the critical point A of input
After the complete disconnection, the hysteresis is fully utilized to prevent pinch hunting so as not to return to the vicinity of point A on the original load curve When the load 5 descends to point DK, the column load 5 must be separated and returned to an arbitrary point DK on the original load curve The sum of the current flowing through load 5 is
(The load current is IC), and the large current (I,
-Ic) flows into the column load 5, causing a large stain force loss. If the hysteresis is small, a hunting phenomenon will occur and the operation of the device will become unstable; if the hysteresis is large, the release of the dead cap will be delayed and the current flowing to the column load will increase, resulting in a large power loss. [Means for solving all problems] A converter is equipped with a column load and a variable impedance element connected in series between the output terminals, and when the output voltage reaches the dead load application voltage, the impedance of the variable impedance element is changed. Control according to output voltage.

[For production]

In the range between the dead load application voltage and the no-load voltage, the sum of the load current flowing through the load and the current flowing through the string load is approximately equal to the current value corresponding to the dead load application voltage,
The impedance of the variable impedance element is controlled. [Embodiment] An embodiment of the present invention will be fully explained with reference to FIG. 21 and FIG. 2. In FIG. 1, the same symbols as those shown in FIG. 5 are assumed to be the same, 4 is a variable impedance element such as a tracker/raster, 6 is a reference voltage circuit common to the load control system and AVR system, and this is the reference power supply E1 resistor R, .
It consists of a constant voltage diode ZD, a resistor R1, an impedance element z1, and a resistor R6 connected in series between both ends of the constant voltage diode ZD. Further, 7°8 is an operational amplifier and a drive circuit for the dead load control system, respectively, and 9 and 10 are an operational amplifier and a drive circuit for the AVR system, respectively.For easy explanation, the output voltage detection input terminals of operational amplifiers 7 and 9 are shown. (
The non-inverting terminals) are connected to the same point, and the inverting input terminals are connected to the connection point between resistor R4 and impedance element 2 biased by the same reference voltage source, and the connection point between impedance element 2 and resistor R6. are connected to 9 respectively.
The reference voltage at the inverting terminal of the operational amplifier 7 is always set to be higher than the reference voltage at the inverting terminal of the operational amplifier 90.

Therefore, when one load voltage rises to a certain first set level, the operational amplifier 9 and drive circuit 10 of the AVR control system act on the converter to lower the output voltage, but the operational amplifier 7 and drive circuit of the dead load control system act on the converter to reduce the output voltage. 8 does not apply a control signal to the variable impedance regulator 4 unless the output voltage rises to a certain second set level that is higher than the first set level. The light load condition progresses, and even though the operational amplifier 9 and drive circuit 10 of the AVR control system are controlling the converter 1 to operate at the minimum pulse width, the output voltage is
When the set level of 1-1 rises to the load application point A,
The operational amplifier 7 outputs a difference signal of a magnitude corresponding to the difference between the reference voltage and the detection voltage of the output voltage to a full drive circuit 8, and the drive circuit 8 outputs a control signal of a magnitude corresponding to the difference signal to a fully variable impedance element. 4 and linearly control its impedance. As a result, in the range between the dead shell loading point A and the no-load point, the sum of the load current flowing through the load 2 and the dead shell current flowing through the variable impedance element 4 and the column load 5 is:
The current at dead shell loading point A is approximately equal to ■3.
The impedance of variable impedance element 4 is controlled. Therefore, as shown in FIG. 2, in the range from the dead shell loading point A to the no-load point, the output voltage is maintained at a voltage approximately equal to the voltage 3 at the dead shell loading point A.

Although the above embodiments have been described for the case where the converter is operated alone, it can also be applied to the case where two or more converters are operated in parallel. [Effect of the Invention] According to the present invention, in the range from the dead shell loading point to the no-load point, the sum of the load current and the dead shell loading current is equal to the current at the dead shell loading point. Since it is maintained at a value approximately equal to , it is possible to completely reduce power loss during light loads, and this effect is particularly significant when all converters are operated in parallel.

Furthermore, there is no need to provide a hysteresis characteristic as in the conventional case, and there is no occurrence of H/CH/G caused by the hysteresis characteristic.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing an apparatus for carrying out an embodiment of the present invention, FIG. 2 is a diagram for fully explaining the present invention, and FIGS. 3 to 5 are diagrams for fully explaining a conventional example. It is a diagram. 1... Converter 2... Load 6... Voltage divider circuit 4... Variable impedance element 5... Column load 6.
...Reference voltage circuit 7,9...Arithmetic circuit 8.10
...Drive circuit to Nippon Telegraph and Telephone Corporation tan? -Ken 5 Wang 1;-1)←

Claims (1)

[Claims] In a converter device including a series-connected dead load and a variable impedance element between the output terminals of a converter, as the load becomes lighter, the output voltage of the converter increases to reach a predetermined dead load application voltage. When this happens, control of the impedance of the variable impedance element is started, and the sum of the load current and the dead load current is approximately equal to the current value corresponding to the dead load application voltage in the range between the dead load application voltage and the no-load voltage. A dead load control method for a converter, characterized in that the impedance of the variable impedance element is controlled so as to be equal.