JPH04178170A - Power factor improving type rectifying apparatus - Google Patents

Abstract

PURPOSE:To stably supply a current without generating overshoot and prevent voltage breakdown of a load by lowering an output frequency of an oscillator after turning on the power supply and turning and ON and OFF a control element of the chopper circuit. CONSTITUTION:An integrator 32 integrates a boosting start signal 31 to generate an integral circuit 32a which gradually increases. Next, a comparator 33 compares an integral signal 32a with a voltage signal 13a and provides an output 33a. An AND circuit 34 provides an output 34a from the output 33a and pulse signal 18a. Next, an output 34a is inputted to a NOR circuit 23, resetting an SR flip-flop 19. Since an output 19a of the SR flip-flop 19 is inputted to a NOR circuit 23, an output 24a of a drive circuit 24 gradually increases the ON/OFF interval, turning ON and OFF an FET 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power factor improving rectifier that rectifies AC power and supplies it to a load.

[Prior Art] Fig. 4 to Fig. 6 are diagrams showing a conventional rectifier for power factor improvement disclosed in, for example, Japanese Unexamined Patent Publication No. 1-295676. Fig. 4 is a circuit diagram, Fig. 5 and FIG. 6 is an explanatory diagram of the operating principle.

In Figure 4, (1) is AC power supply, (2) is AC power supply (1)
(3) is an inductor connected to the DC side of rectifier (2), and (4) is a switching field effect transistor (hereinafter referred to as "field effect transistor") connected between inductor (3) and rectifier (2). FET), (5) is a diode for the reverse current element connected to the inductor (3), (6
) is a smoothing capacitor connected between the diode (5) and the rectifier (2), and the inductor (3) and F E T
(4), diode (5) and smoothing capacitor (6)
A chopper circuit (7) is formed. (8)
is the load connected to smoothing capacitor (6), and (9) is the current detector that detects the current passing through FET (4).
(9a) is a current signal, (10) is a current detector that detects the current passing through load (7), (11) is a control circuit, (12)
is an input voltage detector connected to the input side of the chopper circuit, (12a) is a sine wave phase signal, (13) is an output voltage detector also connected to the output side, (13a) is a voltage signal, (14) is a DC voltage command value input from the outside, (15) is an operational amplifier, (15a) is an average input current command value, (16) is a multiplier, (17) is a comparator, (
17a) is its output, (18) is r) (Jr
a transmitter that emits a pulse signal (18a) that becomes LJ;
(19) is an SR flip-flop, (19a) is its output, (20) is a reset signal input from the outside,
(21) is an overcurrent detector connected to the current detector (10), (22) is an SR flip-flop, (23) is an N
The OR circuit (24) is a drive circuit connected to the gate of FET (4), and (24a) is its output.

The conventional rectifier for power factor improvement is constructed as described above, and its operation will be explained with reference to FIGS. 5 and 6.

The alternating current of the alternating current power supply (1) is converted to direct current by the rectifier (2), inputted to the chopper circuit (7), smoothed by the smoothing capacitor (6) via the inductor (3) and diode (5), and the ripple is reduced. Less DC power is output and the load (
8). At this time, by controlling FET (4), a boost operation is performed to increase the power factor of the input power source and raise the voltage to the level required for the load (8). The boost operation is divided into two cases: on/off of F E T (4). That is, when F E T (4) is off,
AC power supply (1) → Rectifier (2) → Inductor (3) → Diode (5) → Smoothing capacitor (6) → Rectifier (2)
→In the AC power supply (1) circuit, power is supplied to the load (8) while storing charge in the smoothing capacitor (6).

Also, when FET (4) is on, AC power supply (1) →
Rectifier (2) → Inductor (3) → E F T (4)
→ Rectifier (2) → AC power supply (1) circuit, energy is stored in the inductor (3). During this time, power is supplied to the load (8) by the smoothing capacitor (6). When the inductor (3) discharges, the charged energy turns into voltage. Since this voltage is superimposed on the voltage of the AC power source (1) and applied to the smoothing capacitor (6), a voltage higher than the voltage of the AC power source (1) is generated. In the chopper circuit (7), this voltage is held by the smoothing capacitor (6) while the inductor (3) is charged and discharged by turning on and off the FET (4). The output voltage is boosted.

While the inductor (3) is charging energy, current is supplied from the AC power supply (1) to the inductor (3), so the input current increases, and while the inductor (3) is discharging energy, the input current increases. 3), smoothing capacitor (6
) and the load (8), the input current of the chopper circuit (7) decreases. The control circuit (11) is
The increase or decrease in input current that occurs when the operation changes is controlled so that it becomes a sine wave with the same phase as the input voltage.

That is, the operational amplifier (15) outputs the deviation between the voltage command value (14) and the voltage signal (13a) as an average input current command value (15a) that compensates for the output voltage value. That is, if the output voltage value is smaller than the voltage command value (14),
The average input current command value (15a) is increased to increase the average input current, and the average energy charged in the inductor (3) is increased to increase the output voltage. In addition, if the output voltage value is larger than the voltage command value (14), the average input current command value (15a) is decreased to reduce the average input current and the energy charged in the inductor (3). to lower the output voltage. The multiplier (16) outputs the average input current command value (15a) and the sine wave phase signal (12a).
An instantaneous input current command value (16a) that compensates for the input power factor is output by multiplying by (Fig. S (a)). With this, the instantaneous input current command value (16a) has a value whose average value is determined by the average input current command value (15a), and becomes a sinusoidal command value having the same phase as the power supply voltage. The comparator (17) compares the instantaneous input current command value (16a) and the current signal (9a), and if the current signal (9a) is equal to or higher than the instantaneous input current command value (16a), the output (17a) becomes rH. ”, and the current signal (9
If a) is smaller than the instantaneous input current command value (16a), the output (17a) becomes rlJ (FIG. 5(b)). S
The output (17a) of the R flip-flop (19) is "H"
It is set when the output (19a) becomes r) (J, and is reset when the pulse signal (18a) (Fig. 5 (C)) is "H", and the output (19a) becomes "L". (Figure 5(d)).The output (19a) passes through the NOR circuit (23) and the drive circuit (24) and becomes the output (24a) (
FIG. 5(e)), turn on/off F ET (4).

In this way, by turning on/off FET (4), the input current changes to the instantaneous input current command value (16a
), the current becomes a sinusoidal wave with the same phase as the power supply voltage,
The input power factor is 100%. Further, since the average value of the instantaneous input current command value (16a) is corrected according to the increase/decrease in the output voltage, the output is stably supplied.

Figure 6 shows an extended time scale of Figure 5.
(a) to (e) in FIG. 6 correspond to (a) to (e) in FIG. 5.

Further, the current flowing through the load is detected by an overcurrent detector (21), and when this becomes an overcurrent, its output becomes rHJ and the SR flip-flop (22) is set, its output becomes rHJ, and the drive circuit The output (24a) of (24) becomes "L", and F E T (4) becomes OFF. Note that when the overcurrent inspection device (21) operates, the power supply to the load is cut off, but the details will be omitted.

[Problem to be solved by the invention] In the conventional power factor improving rectifier as described above, the transmitter (
Since FET (4) is turned on/off according to the frequency of 18), the device starts operating immediately after the power is turned on, and the output voltage rises rapidly due to control delays, etc. Overshoot A as shown in f)
wake up As a result, the output voltage causes unstable pulsations at the start of control, making it impossible to supply a stable current.
Sometimes, due to overshoot A, a voltage exceeding its withstand voltage is applied to the load (8), causing problems such as voltage breakdown.

This invention was made to solve the above problems, and even when boosting and input power factor control is started immediately after power is turned on, a stable current can be supplied and voltage breakdown of the load can be prevented. The purpose of the present invention is to provide a power factor improving rectifier.

[Means for Solving the Problems] The power factor improving rectifier according to the present invention outputs a boost start signal through an integrator, compares this output with the output of a chopper circuit, and calculates the boost start signal immediately after power is turned on.

The output frequency of the oscillator signal that turns on/off the control element of the chopper circuit is lowered.

[Function] In this invention, since the output frequency of the oscillator is lowered immediately after power is turned on to turn on/off the control element of the chopper circuit, the on/off interval of the control element gradually increases.

[Example] Figures 1 to 3 are diagrams showing an example of the present invention.
The figure is a circuit diagram, and FIGS. 2 and 3 are diagrams explaining the principle of operation, and parts similar to those of the conventional device are designated by the same reference numerals.

In Figure 1, (31) is a boost start signal input from the outside, (32) is an integrator, (32a) is an integral signal, (3
3) is a comparator with hysteresis characteristics, (33a) is its output, (34) is an AND circuit, and (34a) is its output.

Next, the operation of this embodiment will be explained.

The operating principle is as described above; when FET (4) is on, the inductor (3) is charged with power, and FET
When T (4) is off, the power charged in the inductor (3) is discharged as output. The control circuit (11) controls the increase and decrease of the input current when the inductor (3) is charged and discharged.

The integrator (32) receives the boost start signal (31) (Fig. 2 (X
)) and generates a gradually increasing integral signal (32a) as shown in FIG. 2(y). Then, this integral signal (32
The output voltage at the start of circuit operation is controlled using a) as a reference. The comparator (33) outputs the integral signal (32a) and the voltage signal (
13a), the comparator (33) has a hysteresis characteristic and has an upper limit value Y and a lower limit value Y2 with respect to the reference integral signal (32a). Therefore, the output (33a) of the comparator (33) becomes "L" when the voltage signal (13a) rises above the upper limit value Y1, as shown in FIG. 2 (z), and becomes "L" when it falls below the lower limit value Y2. It becomes rJ.

The AND circuit (34) outputs the output (33a) and the pulse signal (1
8a) and output (34a) shown in Figure 2(d).
becomes. This output (34a) is input to the NOR circuit (23), resets the SR flip-flop (19), and the output (19a) is input to the NOR circuit (23), so the drive circuit (24) Output (24a)
becomes as shown in FIG. 2(e), and turns on/off F E T (4).

As shown in the conventional device, in steady state, the pulse signal (1
Since FET (4) is turned on when 8a) becomes rHJ, the on/off period of FET (4) is determined by the timing of pulse signal (18a). On the other hand, in this embodiment, at the start of the two-circuit operation, the comparator (33) temporarily blocks the transmission of the pulse signal (18a) depending on the value of the output voltage. In other words, when the output voltage rises too much,
After stopping the sending of the pulse signal (18a) and lowering the output voltage, boosting the voltage using the pulse signal (18a) is started again. Therefore, the output voltage becomes as shown in FIG. 3(f), and overshoot due to sudden voltage increase is suppressed.

[Effects of the Invention] As explained above, in this invention, the output frequency of the oscillator is lowered after the power is turned on to turn on/off the control element of the chopper circuit.

The on/off interval of the control element is gradually increased to suppress the voltage increase,
This has the effect of being able to supply a stable current without causing overshoot, and also being able to prevent voltage breakdown of the load.

[Brief explanation of drawings]

1 to 3 are diagrams showing an embodiment of a power factor improving rectifier according to the present invention, and FIG. 1 is a circuit diagram. Figures 2 and 3 are diagrams explaining the operating principle, Figures 4 to 6 are diagrams showing conventional power factor improving rectifiers, Figure 4 is a circuit diagram, and Figures 5 and 6 are diagrams of operation. It is a principle explanatory diagram. In the figure, (1) is an AC power supply, (2) is a rectifier, (4) is a field effect transistor, (6) is a smoothing capacitor, (7)
is a chopper circuit, (8) is a load, (13) is an output voltage detector, (18) is an oscillator, (31) is a boost start signal, (
32) is an integrator, (33) is a comparator, and (34) is a boost control circuit (AND circuit). Note that the same reference numerals in each figure indicate the same or corresponding parts. Figure 2 Time-◆ Figure 3 Figure 5 Figure 6

Claims (1)

[Claims] A rectifier is connected to the AC power supply, and a chopper circuit is connected to the DC side of the rectifier, which has a control element that turns on and off at a constant frequency based on the output of the oscillator, and has a smoothing capacitor.The output of this chopper circuit is connected to the DC side of the rectifier. The device includes an integrator that generates an output that gradually increases when a boost start signal is input, and compares the output of this integrator with the output of the chopper circuit to determine whether the oscillator is activated immediately after power is supplied to the chopper circuit. A power factor improving rectifier characterized by comprising a boost suppression circuit that lowers the output frequency.