JPH077953A - Overcurrent limit circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Reactor 03
A rectifying device having a step-up converter that is intermittently switched by a switching element 04 via a smoothing capacitor 05 to obtain a step-up DC voltage, and outputs a DC current command value that makes a DC output 07 a constant voltage. Multiplier 2 for multiplying the current command value and full-wave rectified voltage to obtain a current command value in phase with AC input 01, and a control signal is sent via current error amplifier 4 to match current I1 with the output command value of multiplier 2. PW
The switching element 04 is given to the PW by giving it to the M comparator 08.
This is a rectifier device that opens and closes in the M method to set the AC input current to a power factor of 1, and the overcurrent limit value by the amplifier 3 is 100V for the AC input
Switching according to the system or the 200V system, the current is limited at the constant power point to increase the reliability of the device. [Structure] A system voltage of AC input is detected by a detection circuit 10, and a reference voltage switching circuit 11 sets a reference voltage for current limitation to an amplifier 3 to 1/2 of a 100V system in a 200V system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifying device for rectifying and smoothing an AC input voltage into a DC voltage, which has a step-up converter type active filter circuit for improving the power factor to nearly one. The present invention relates to an overcurrent protection circuit.
In the drawings below, the same reference numerals indicate the same or corresponding parts.

[0002]

2. Description of the Related Art FIG. 2 is a block circuit diagram showing a configuration example of a rectifying device of this type. In the figure, 01 is AC input,
Reference numeral 02 is a rectifier for full-wave rectifying this AC input, 03 is a reactor, 04 is a switching element composed of a power MOSFET, 05 is a smoothing capacitor, 06 is a diode for blocking a reverse current from the smoothing capacitor 05, and 07 is a DC output.

As is well known, the means of 02 to 06 constitute a boost converter. That is, switching element 0
When 4 is turned on, the reactor 03 is energized by the full-wave rectified voltage of the AC input 01. Next, switching element 0
When 4 is turned off, the reactor 03 generates a voltage in a direction to maintain its exciting current, and the smoothing capacitor 05 boosts the voltage through the diode 06 by the sum voltage of this reactor induced voltage and the full-wave rectified voltage of the AC input 01. Be charged.

By the way, the switching element 04 is a PWM
According to the (pulse width modulation) method, the open / close control is performed at a high frequency of 75 KHZ in this example so that the AC input current to this rectifier has the same phase as AC input 01 (that is, power factor ≈ 1), and a so-called active filter is configured. is doing. Next, the control circuit of the switching element 04 will be described. 08 is a PWM comparator for driving the switching element 04,
Reference numeral 09 is an oscillator that oscillates and outputs a triangular wave having a constant amplitude of 75 KHZ.

A voltage error amplifier 6 compares the voltage of the DC output 07 with the reference voltage 7 and performs a widening operation on the difference voltage so that the difference voltage becomes 0, and as a DC current command value. It is given to the multiplier 2. The multiplier 2 inputs the full-wave rectified voltage of the AC input 01 (that is, the voltage at the point A in FIG. 2) and the output of the voltage error amplifier, and outputs the product of the two, that is, the AC input 01.
Outputs a current command value having the same waveform as the full-wave rectified waveform of, but having its amplitude proportional to the output of the voltage error amplifier 6 (DC current command value) (however, in this example, the negative side is the increasing direction). .

Rs is a resistor for detecting an input current I1 obtained by full-wave rectifying the AC input current of the circuit of FIG.
Is a current error amplifier, which compares the detected value of the input current I1 with the current command value output from the multiplier 2, and outputs the difference voltage to the PWM comparator 08 by increasing the calculation so that this difference becomes zero. To do. PWM comparator 08 is oscillator 0
The triangular wave having a constant amplitude output by 9 is compared with the output signal of the current error amplifier 4 (the diode 8 connecting the output of the PWM comparator 08 and the output of the current error amplifier 4 is normally turned on by the bias means (not shown). State)),
The switching element 04 is turned on while the latter (output of the error amplifier 4) is larger than the former (output of the oscillator 09).

In this way, the PWM comparator 08 outputs a pulse train having a cycle of 75 KHZ and a pulse width proportional to the momentary output of the current error amplifier 4, and turns on the switching element 04 during the period of this pulse width. As a result, the circuit of FIG.
We have realized a rectifier that takes in C input current.

FIG. 3 (1) shows the voltage waveform at point A in FIG. 2 obtained by full-wave rectifying the AC input 01, and FIG. 3 (2) shows A.
The waveform of the current I1 obtained by full-wave rectifying the C input current at a normal time is shown. In this way, the two are in phase. 2 is an overcurrent detection amplifier which constitutes an overcurrent limiting circuit. The negative input terminal of this amplifier 3 has a reference voltage Er.
Similarly, the detection value of the input current I1 by the current detection resistor Rs is input to the positive input terminal of the amplifier 3 as well.

Now, when the load becomes heavy and the current I1 becomes large and the voltage drop across the resistor Rs tries to exceed the reference voltage Er, the output of the amplifier 3 becomes lower than the output level of the current error amplifier 4. As a result, the diode 9 connecting the output of the amplifier 3 and the PWM comparator 08 becomes conductive, the diode 8 on the output side of the current error amplifier 4 is blocked, and the current I1 is limited. As a result, the current I1 has a waveform with its tip cut as shown in FIG.

[0010]

The active filter circuit of FIG. 2 is characterized in that the input voltage range can be widened, and it is common to share the AC100V system and the AC200V system. However, conventionally, since the overcurrent limiting reference voltage Er is fixed, there is a problem in that the output power value at which the overcurrent limiting starts to operate greatly changes in the AC100V system and the 200V system. That is, the output power Po and the input voltage have the following relationship.

[0011]

[Equation 1] Po = Vin · Iin · η where Vin: effective value of AC input voltage Iin: effective value of input current η: conversion efficiency of converter (usually about 0.9 to 0.95) Therefore, when Vin = 200V The current may be half of the current when Vin = 100V. In other words, I100R at AC100V
If Er is set so that the current is limited at the point of s = Er, the current limitation does not operate unless the load is increased to twice the electric power at AC200V, which is a safety problem of the power supply.

Therefore, it is an object of the present invention to provide an overcurrent limiting circuit which can make the output power almost constant when the overcurrent is limited even when the input voltage is switched from the 100V system to the 200V system. To do.

[0013]

In order to solve the above-mentioned problems, an overcurrent limiting circuit according to claim 1 is a rectifying device for converting the voltage of an AC power supply (AC input 01 or the like) into a DC voltage. The current (I
1) and the like) in a rectifying device having means (such as overcurrent detection amplifier 3) for limiting the set value to a set value (means for detecting input voltage detection circuit 10, etc.)
And means for switching the set value so as to be in inverse proportion to the detected system nominal voltage (such as the reference voltage switching circuit 11).

The overcurrent limiting circuit according to a second aspect is the current limiting circuit according to the first aspect, wherein the AC power supply system has nominal voltages of 100V and 200V. Further, in the overcurrent limiting circuit according to claim 3, in the current limiting circuit according to claim 1 or 2, the rectifying device performs full-wave rectification of the voltage of the AC power supply (full-wave rectifier 02 or the like).
And a switching means (such as a switching element 04) which opens and closes this full-wave rectified voltage at a predetermined frequency (such as the output frequency of the oscillator 09) higher than the frequency of the AC power supply via the reactor (03 or the like) in order to boost the voltage. )When,
Means (voltage error amplifier 6, multiplier 2, current 2) for controlling the closing time of the switching means by pulse width modulation so that the current supplied from the AC power supply to the rectifier becomes a sine wave current with a power factor of approximately 1. Aller amplifier 4, PWM comparator 08, etc.).

[0015]

Operation: The nominal voltage of the AC input system is from 100V to 20V.
When the voltage changes to 0V, the overcurrent limiting reference voltage value is switched so that the overcurrent limiting operates at a certain power point.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block circuit diagram showing a configuration as an embodiment of the present invention and corresponds to FIG. 1 is different from FIG. 2 in that the reference voltage of the overcurrent detection amplifier 3 is not a fixed voltage Er but is switchably provided by the input voltage detection circuit 10 and the reference voltage switching circuit 11.

In FIG. 1, whether the power distribution system of the AC input 01 is a 100V system by the input voltage detection circuit 10
It is distinguished whether it is a 0V system. Then, the detection output of the input voltage detection circuit 10 switches the reference voltage to the overcurrent limiting amplifier 3 via the reference voltage switching circuit 11. That is, according to the detection signal of the input voltage detection circuit 10, the reference voltage switching circuit 11 generates a reference voltage which is half that at the time of AC 100V input at the time of AC 200V input, and the overcurrent detection amplifier 3
Give to.

[0018]

According to the present invention, there is provided a rectifier using a boost converter type active filter, which has a function of limiting an overcurrent of an AC input current.
It is detected whether the AC input voltage system is 100V system or 200V system, and the limit value of the overcurrent is 10 for the 200V system.
Since it is switched to 1/2 of 0V system, even if the rectifier of the present invention is shared by AC100V system and 200V system, overcurrent limitation can be applied at a substantially constant output power point.
The reliability of the power factor correction circuit (active filter circuit) can be improved.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a configuration as an embodiment of the present invention.

FIG. 2 is a conventional block circuit diagram corresponding to FIG.

FIG. 3 is a waveform diagram for explaining an operation of a main part of FIG.

[Explanation of symbols]

 01 AC input 02 Full wave rectifier circuit 03 Reactor 04 Switching element 05 Smoothing capacitor 06 Backflow prevention diode 07 DC output 08 PWM comparator 09 Oscillator Rs Current detection resistor 2 Multiplier 3 Overcurrent detection amplifier 4 Current error amplifier 6 Voltage error amplifier 7 Reference voltage 8 Diode 9 Diode 10 Input voltage detection circuit 11 Reference voltage switching circuit

Claims (3)

[Claims] 1. A rectifying device for converting the voltage of an AC power supply into a DC voltage, the rectifying device comprising means for limiting a current supplied from the AC power supply to the rectifying device to a set value. And a means for switching the set value so as to be inversely proportional to the detected system nominal voltage. 2. The current limiting circuit according to claim 1, wherein the AC power supply system has nominal voltages of 100V and 200V.
A current limiting circuit characterized by being set to V. 3. The current limiting circuit according to claim 1, wherein the rectifying device includes means for full-wave rectifying the voltage of the AC power supply, and this voltage for boosting the full-wave rectified voltage. And a switching means for opening and closing via a reactor at a predetermined frequency higher than the frequency of the AC power supply, and closing the switching means so that the current supplied from the AC power supply to the rectifier becomes a sine wave current with a power factor of approximately 1. An overcurrent limiting circuit comprising means for controlling time by pulse width modulation.