JPH11285252A - Charger - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable restraining the peak value of a charging current within a previously set value when the voltage of an AC input power source is changed, protecting elements constituting a charging circuit from overcurrents, and reduc ing the element capacity, without increasing overload capacity of the elements. SOLUTION: This charger comprises a rectifying circuit 2 the AC power source of which is its input a switch 4, a resistor 5 connected in parallel with the switch 4, and a smoothing circuit which closes the switch 4 when a DC voltage exceeds a specified value, and makes a current flow in a capacitor 6. The charger is provided with a computing element which operates the difference between the peak voltage of the AC input power source and a voltage applied to the capacitor, a previously set voltage setting apparatus, and a comparator 16 which compares both of them. The switch 4 is made to be shorted or opened by the output of the comparator 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for a power converter such as an inverter or a converter, which rectifies an AC power source to obtain a DC power source and charges a capacitor for smoothing the power source.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory view showing a conventional method.
In FIG. 3, an AC input power supply 1 is supplied to a rectifier 2,
This output is converted to a DC power supply. Generally, a capacitor 6 is connected to smooth this DC. Since the capacitor 6 has a large capacity, the charging current is limited by the resistor 5 connected in series to the charging circuit, and the rectifier 2, the switch 4 connected in parallel with the resistor 5, and the capacitor 6 are protected from overcurrent. The voltage detection circuit 15 detects that the DC voltage has risen by charging the capacitor 6, and the resistor 5 is short-circuited by an electromagnetic contactor or a semiconductor switch (hereinafter referred to as a switch 4). The short circuit is performed when the voltage applied to the capacitor increases until it is estimated that the current determined by the potential difference between the AC power supply and the voltage applied to the capacitor and the wiring impedance does not damage the equipment constituting the charging circuit. When the short-circuited switch is opened, the switch is set lower than the short-circuited potential so as to have a hysteresis characteristic, thereby preventing the switch from chattering.

FIG. 4 is a waveform chart showing the operation of FIG. FIG. 4 shows the capacitor voltage and charging current waveforms when the AC input power supply 1 is turned on, the switch 4 is short-circuited, and the AC power supply 1 is lost and restored after the switch short-circuit. The short-circuit voltage level Von and the voltage level Voff at which the switch 4 is opened are generally levels set in advance without depending on the power supply voltage. As described above, the level at which the switch 4 is short-circuited should be raised to a voltage as close as possible to the saturation level of the power supply voltage in order to protect elements constituting the charging circuit from overcurrent. However, devices generally applied to industries such as power converters have a rated voltage of +10.
Operation must be guaranteed in the range of%, -10%. The short-circuit level is set assuming that the power supply is the lowest.

[0004] Therefore, when the power supply voltage is the highest, the potential difference between the short-circuit level and the power supply level may be extremely large, and when the wiring impedance 3 is low, the overcurrent may damage the charging circuit element. Further, the potential for opening the short-circuited switch 4 must be set to a level below the level at which the operation of the device is guaranteed. The operation guarantee level is often set to about -15% of the minimum rated voltage, and the open level must be set lower. For example, if the rated voltage of the inverter is 400 V to 46
A trial calculation will be made by taking the case of the range of 0 V as an example. The minimum voltage is 360 V, which is -10% of the rated voltage of 400 V, and the DC voltage at this time is 507 assuming no-load peak charging.
V, and when the short-circuit level is set to about 480-490V, the potential difference is 17-27V. However, the power supply is 46
The maximum voltage at 506V which is + 10% of 0V is 713V
, And the potential difference at the time of the short circuit increases to 223 V to 233 V. Further, the open-circuit voltage level must be set to 479 V or less, considering -15% of 400 V in consideration of the operation guarantee voltage. When 470v is set to the open voltage, the potential difference at the time of short circuit becomes 243V at the maximum.

[0005]

As described above, when the power supply voltage is compared between the minimum and the maximum, a difference in current of 9 to 14 times occurs, which may possibly damage the device. Further, it is necessary to increase the overcurrent withstand capability of the device so as not to be damaged. In particular, if the power supply recovers from a power failure when the capacitor charging voltage drops to just before the Voff level, the semiconductor may be damaged due to overcurrent since there is no current limitation by the resistor. The present invention has been made in view of the above points, and its purpose is to
An object of the present invention is to provide a charging device that solves these drawbacks.

[0006]

Means for achieving the object are as follows: 1) A rectifier circuit having an AC power supply as an input, a switch, and a resistor connected in parallel with the switch. And a smoothing circuit that conducts the current to the capacitor by turning on the switch when the DC voltage exceeds a predetermined voltage, and calculates a difference between the peak value of the AC input power supply and the voltage applied to the capacitor. And a comparator for comparing the two with each other, wherein the switch is short-circuited or opened by the output of the comparator.

2) In claim 2, the charging time elapses so as to be negligible compared to the charging time constant of the capacitor, and the DC voltage is averaged when the voltage rise of the capacitor reaches the equivalent of the AC input voltage. The charging device according to claim 1, wherein a voltage obtained by estimating an AC input voltage from the processed voltage is replaced with a peak voltage of the AC input power supply.

That is, the DC voltage level at which the charging circuit is short-circuited or opened is varied according to the magnitude of the voltage of the AC input power supply. As a result, the potential difference between the AC input power supply level and the DC voltage is kept constant, and the maximum charging current at the time when the switch is short-circuited protects the equipment constituting the charging circuit from overcurrent. As mentioned above, the present invention requires measuring or estimating the AC power supply voltage. The measures are as follows: 1) Measure the AC voltage directly, and obtain the DC voltage when charging is completed. 2) If the switch is opened after a sufficient time has passed since the completion of charging, the average value immediately before opening is used.

Means for detecting or estimating the peak voltage of the AC input power supply 1 will be described. The DC voltage Vdcp obtained by rectifying the AC voltage becomes equal to the peak voltage Vac of the AC voltage when there is no load, and is expressed by the equation (1). Vdcp = √2 * Vac --------------- (1) Therefore, it can be obtained by measuring the AC input power supply. When the capacitor is sufficiently charged, the DC voltage Vdc and the peak voltage of the AC input power supply are substantially equal. Therefore, it is only necessary to average the capacitor applied voltage Vdc.

Assuming that the DC voltage sample values immediately before the opening are Vdc1, Vdc2,..., Vdcn, the average value is obtained as follows: Vdc0 = (vdc1 + vdc2 + ---. Vdcn) / n , The peak voltage of the AC input power supply 1 can be estimated. The difference (hereinafter referred to as ΔV) between the peak voltage value of the AC input power supply 1 obtained by the above-described equations (1) and (2) or the estimated value thereof and the voltage applied to the capacitor during charging is obtained. The charging current Ic is obtained by equation (3). The impedance Z is a combination of impedances of a wiring, a rectifier diode, a power supply, and the like. Ic = {V / Z ----------------- (3) Prevent the charging current Ic from damaging the above-described device and element. It is clear that V should be determined. Less than,
An embodiment of the present invention will be described in detail with reference to the drawings.

[0011]

FIG. 1 is a block diagram showing an inverter main circuit and a capacitor charging control according to an embodiment of the present invention. In FIG. 1, 1 is an AC input power supply, 2 is a rectifier, 4
Is a switch, 5 is a resistor, 6 is a smoothing capacitor, 7 is a discharge resistor, 8 is an inverter circuit, and 9 is a load. 3 is an impedance existing between the input power supply and the capacitor. The capacitor 6 is charged in a path from the AC input power supply 1 through the resistor 5, and the voltage applied to the capacitor rises with time. Peak voltage Vp of AC input power supply 1
Is measured by the voltage detection circuit 21 and the DC voltage detection circuit 15 to measure the capacitor applied voltage Vdc.
Can be obtained. The value Vs of the setting device 14 is compared with the ΔV by the comparator 16. When the ΔV becomes smaller than Vs, the switch 4 is short-circuited by the output of the comparator 16 via the drive circuit 18. The output of the comparator is switch 4
In order to shift to the release, the hysteresis circuit 17 operates to make the value larger than the value of ΔV when the switch 4 is short-circuited, thereby preventing the chattering of the switch operation.

FIG. 2 is a block diagram showing another embodiment of the present invention for determining a voltage level at which the switch 4 should be opened when the AC input power supply 1 is lost after charging.
Those having the same reference numerals as have the same functions. In FIG. 2, the average value of the DC voltage Vdc is always stored by the averaging processor 11 irrespective of operation or stop. Also V
dc is input to an AC power loss determiner 12 which can determine that the AC input power 1 has been lost. When it is determined by the AC power loss determiner 12 that the AC input power supply 1 has been lost, the voltage averaged by the averaging processor 11 is stored, and the difference between the voltage Vdc0 immediately before the loss and the voltage Vdc after the loss is obtained. V is obtained by the voltage deviation detection circuit 20. When the power is restored, the comparator 16 compares the current ΔV with the value Vs of the setter 14, and if ΔV is larger than the hysteresis width Vhs, the switch 4 is opened. If smaller, do not open the switch. As shown in FIG. 4, the AC power loss determiner 12 can easily detect the loss of power because the rate of decrease of Vdc becomes significantly larger than before the loss. For example, Vdc can be sampled at regular intervals to determine the change in the reduction rate from the difference between before and after.

[0013]

As described above, according to the present invention, the peak value of the charging current can be suppressed to a predetermined value even if the magnitude of the AC input power source changes, and the elements constituting the charging circuit can be reduced. Can protect against overcurrent. This also eliminates the need to increase the overload capability of the element, and can reduce the element capacity.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inverter main circuit and a capacitor charging control showing an embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention for determining a voltage level at which a switch should be opened when AC input power is lost after charging.

FIG. 3 is a block diagram showing an example of the related art.

FIG. 4 after the AC input power is turned on and the switch is short-circuited
Capacitor voltage when AC power is lost and returned again,
It is a charging current waveform diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier 3 Wiring impedance 4 Switch 5, 7 Resistance 6 Capacitor 8 Inverter circuit 9 Load 11 Average processor 12 AC power supply loss judgment device 13 Average voltage storage circuit 14 Setting device 15, 21 Voltage detection circuit 16 Comparator 17 Hysteresis Circuit 18 Switch drive circuit 20 Voltage deviation detection circuit

Claims (2)

[Claims] A rectifier circuit having an AC power supply as an input, a switch, a resistor connected in parallel with the switch, and a switch which is turned on when a DC voltage exceeds a predetermined voltage to supply a current to a capacitor. A charging device including a flowing smoothing circuit includes a calculator for calculating a difference between a peak value of an AC input power supply and a voltage applied to a capacitor, a voltage setter set in advance, and a comparator for comparing these two. A charging device characterized in that the switch is short-circuited or opened by an output of a charger. 2. The charging time elapses so as to be sufficiently negligible compared to the charging time constant of the capacitor, and when the voltage rise of the capacitor reaches the equivalent of the AC input voltage, the DC voltage is averaged, and the processing is performed. The charging device according to claim 1, wherein a voltage obtained by estimating an AC input voltage from the obtained voltage is replaced with a peak voltage of the AC input power supply.