JPH10337005A - Converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce voltage applied to a switch element, by connecting together a diode bridge, a transformer having first, second and third terminals and a switch element. SOLUTION: One side of a primary winding and one side of a secondary winding of a transformer 9 are connected to one of outputs of a diode bridge 2, other side of the primary winding is connected to the other of the output of the diode bridge 2 through a switch element 7, and the other of the secondary winding is connected to an anode of a diode 8. Since a current flows to the primary winding or secondary winding of the transformer 9 when the switch element 7 is in ON state or in OFF state, a voltage and a current corresponding to the turn ratio of respective winding occur. When the turn ratio of the transformer 9 is 1:n, if n>1 occurs, then a voltage applied to a switch element and a current peak value of a diode 8 can be suppressed to a small values when the switch element 7 is off. If n<1 occurs, a current peak value during ON of the switch element 7 can be suppressed to a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter using an AC power supply as an input.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram of a conventional capacitor input system. This is a system in which an AC power supply 1 is input, rectified and smoothed by a diode bridge 2 and a capacitor 3, and supplied to a load 4. FIG. 8 is a diagram showing an input waveform in the capacitor input method. As shown in FIG. 8, the input current flows only in the vicinity of the peak of the input voltage and contains many harmonic components of the commercial power supply frequency, and thus has an adverse effect on other devices, power transmission equipment, and the like.

Various methods have been proposed at present to suppress the harmonic current. One of the methods is to insert a boost chopper circuit called a converter between a diode bridge and a capacitor. FIG. 9 is a circuit configuration diagram of a conventional boost chopper system. The AC power supply 1 is input to the diode bridge 2 and the diode bridge 2
Is connected to one end of the reactor 6, and the other end of the reactor 6 is connected to the anode of the diode 8.
The cathode of the diode 8 is connected to one end of the capacitor 3, and the other end of the capacitor 3 is connected to the other output of the diode bridge 2. The load 4 is connected to both ends of the capacitor 3. The switch element 7 is connected between a connection point between the other end of the reactor 6 and the anode of the diode 8 and the other output of the diode bridge 2. The switch 7 is turned on / off by a control circuit (not shown) that detects the output voltage of the circuit and controls the output voltage to a predetermined value. The capacitor 5 is connected across the output of the diode bridge 2. In FIG. 9, a reactor 6, a switch 7, and a diode 8 constitute a boost chopper circuit.
The capacitor 5 has a small capacity (for example, 1 μF) and flows a harmonic current accompanying the switching of the boost chopper circuit, and has almost no effect on the commercial frequency.

There are several methods for controlling the boost chopper circuit, one of which is a method called boundary value mode control. FIG. 10 is a diagram showing a theoretical waveform in the boundary value mode control of the boost chopper circuit. In the boundary value mode control, the reactor current operates at the boundary between the continuous mode and the discontinuous mode. The switch element is turned on / off at a higher frequency than the AC input power supply. At this time, if the peak value of the reactor current is controlled so as to be proportional to the input voltage vi (t), for example, k × vi (t) in FIG. 10, the average value of the reactor current, that is, the input current becomes k × v (t).
i (t) / 2, which is proportional to the input voltage. As a result, in the case of an AC power supply, the input current waveform also becomes a sine wave, and harmonic components can be suppressed. At this time, since the output voltage V0 of the converter is a step-up chopper circuit, it can be set to any value as long as it is equal to or higher than the input voltage.

[0005]

In the prior art, when the value of the output voltage is set to V0, the rated voltages of the switch element 7 and the diode 8 in FIG. Is a sine wave having a peak value of I, a rated current for a current peak value of 2I is required. Accordingly, a first object of the present invention is to reduce voltage or current stress applied to a switching element or to increase the degree of freedom in selecting an element to be used.

In the converter of the boundary value mode control, since the input current waveform is controlled by the control circuit so as to be similar to the input voltage waveform, the input current is theoretically a complete sine wave. However, in practice, when the current does not flow near the zero crossing of the input voltage due to the forward voltage of the diode bridge, or when the waveform is disturbed by noise or the like when detecting the waveform with the control circuit, the waveform does not become a complete sine wave. And harmonic components cannot be completely suppressed. Therefore, a second object of the present invention is to further suppress harmonic components.

Further, in the boundary value mode control, since the reactor current is controlled so as to operate at the boundary between the continuous mode and the discontinuous mode, the switching frequency is not constant, but is constant during one cycle of the input voltage. It changes with the frequency width of. Therefore, a third object of the present invention is to facilitate measures against noise generated from a chopper.

[0008]

According to the present invention, there is provided a boost chopper converter utilizing a boundary value mode, comprising: a diode bridge having an AC power supply as an input; A transformer having a second terminal and a third terminal; and a switching element, wherein the first terminal is connected to one of outputs of the diode bridge, and the second terminal is connected to the switching element via the switching element. The converter is connected to the other output of the diode bridge and the third terminal is connected to a current smoothing circuit.

Alternatively, in the transformer, one of a primary winding and a secondary winding is connected to each other and used as the first terminal, and the other of the primary winding is used as the second terminal. The other end of the winding was the third terminal. Alternatively, the transformer is a single-turn transformer having a center tap, one of the windings being the first terminal, the center tap being the second terminal, and the other being the third winding.
Terminal.

Alternatively, in the transformer, the other end of the winding is used as the second terminal, and a center tap is used as the third terminal. Further, the converter is configured such that a capacitor is connected to both ends of the output of the diode bridge. By using a transformer structure for the reactor, the voltage generated in the reactor or the current flowing in the reactor in the conventional method is changed by the turns ratio of the transformer, and the voltage generated in the switch element or the diode and the flowing current are changed. Stress reduction on
The degree of freedom in element selection can be improved). Also, by changing the apparent inductance of the reactor when the switch element is on and off, the input current waveform is improved (suppression of harmonic current) and the switching frequency band is changed (easiness of noise countermeasures). Can be achieved.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of the present invention. The difference from FIG. 9 is that a transformer 9 is used in place of the reactor 6, and a connection portion connecting one of the primary winding and the secondary winding of the transformer 9 is connected to one of the outputs of the diode bridge 2. The other end of the primary winding is connected to the other output of the diode bridge 2 via the switch element 7, and the other end of the secondary winding is connected to the anode of the diode 8. Other components are shown in FIG.
Is the same as In addition, as the switch element 7, a bipolar transistor, a MOSFET, or the like is used. Although not shown, the switch 7 is turned on / off by a control circuit that detects the output voltage of the circuit and controls the output voltage to a predetermined value.

FIG. 2A is a diagram showing a current flow when the switch element 7 is turned on in FIG.
FIG. 2B is a diagram showing a current flow when the switch element 7 is off in FIG. As shown in FIG. 2, the current flows through the primary winding or the secondary winding of the transformer 9 when the switch element 7 is on and off, so that the voltage and the current correspond to the turns ratio of each winding. Becomes When the turns ratio is 1: 1, the operation is equivalent to that of the conventional circuit.

When the turns ratio of the transformer 9 is 1: n,
When n> 1, the voltage applied to the switch element when the switch element 7 is off can be reduced, and the peak current value of the diode 8 can be reduced. When n <1, the current peak value when the switch element 7 is turned on can be reduced. The current waveform input from the AC power supply is expressed by the following equation.

[0014]

(Equation 1) From this equation, the state of the change of the input current with respect to the turns ratio n is as follows. When n = 1, the input current is a sine wave, and when n <1, the input current is near the peak of the input voltage (wt = around 90 °).
When n> 1, the input current decreases near the peak of the input voltage (around wt = 90 °). FIG. 3 illustrates this state. By applying the theoretical change of the waveform in this way, it is possible to correct the distortion of the input current in the actual converter when it occurs.

Further, the boost ratio is set to M (= Vin / V0). Further, the switching frequency changes in the converter of the boundary value mode control, and the maximum value and the minimum value are fmax and fmin, respectively. FIG. 4 is a diagram illustrating a change in the maximum value / minimum value of the switching frequency with respect to the boosting ratio. In FIG. 4, when the turns ratio n is reduced, the change in frequency can be reduced, and when the turns ratio n is increased, the change in frequency can be increased.

FIG. 5 is a circuit diagram showing another embodiment of the present invention where n> 1. The differences from FIG. 1 are as follows. The transformer 10 is a single-turn transformer having a center tap. One of the windings of the transformer 10 is connected to one of the output portions of the diode bridge 2, and the other winding is connected to the anode of the diode 8. The center tap is configured to be connected to one end of the switch element 7.

FIG. 6 is a circuit diagram showing another embodiment of the present invention where n <1. The differences from FIG. 5 are as follows. The other end of the winding of the transformer 11 is connected to one end of the switch element 7, and the center tap is connected to the anode of the diode 8.

[0018]

As described above, the turns ratio of the transformer n>
When 1 is set, the voltage applied to the switch element when the switch element is turned off is small, and the current peak value of the diode can be suppressed small. When n <1, the current peak value when the switch element is turned on can be suppressed small. So
By appropriately selecting the turns ratio of the transformer, the voltage and current ratings of the switch element and the diode can be reduced, and the range of component selection such as low-cost components or easily available components can be widened.

Further, by appropriately selecting the turns ratio of the transformer, the distortion of the input current can be corrected, so that the effect of suppressing the harmonic current can be enhanced. Also, by properly selecting the turns ratio of the transformer,
By narrowing the frequency band of the switching frequency, it is possible to reduce the noise generation band associated with switching, and also reduce the frequency band of the noise suppression filter. Conversely, by increasing the frequency band of the switching frequency, the noise generation band associated with switching is widened, so that the noise intensity at a specific frequency can be reduced.

[Brief description of the drawings]

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

2A and 2B are diagrams showing a current flow when the switch element of FIG. 1 is turned on / off, FIG. 2A is a diagram showing a current flow when the switch element is turned on, and FIG. The figure which shows the current flow at the time.

FIG. 3 is a diagram showing an input current waveform.

FIG. 4 is a diagram showing a change in the maximum value / minimum value of the switching frequency with respect to a boost ratio.

FIG. 5 is a circuit diagram showing another embodiment of the present invention when n> 1.

FIG. 6 is a circuit diagram showing another embodiment of the present invention when n <1.

FIG. 7 is a circuit diagram of a conventional capacitor input system.

FIG. 8 is a diagram showing an input waveform in a capacitor input method.

FIG. 9 is a circuit configuration diagram of a conventional boost chopper system.

FIG. 10 is a diagram showing theoretical waveforms in the boundary value mode control of the boost chopper circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC power supply, 2 ... Diode bridge, 3,5 ... Capacitor, 4 ... Load, 6 ... Reactor, 7 ... Switch element, 8 ... Diode, 9,10,11 ... Transformer.

Claims (5)

[Claims] 1. A step-up chopper type converter using a boundary value mode, comprising: a diode bridge to which an AC power is input; a transformer having first, second, and third terminals; and a switch element. The first terminal is connected to one of the outputs of the diode bridge; the second terminal is connected to the other of the outputs of the diode bridge via the switch element;
A terminal connected to a current smoothing circuit. 2. The secondary winding according to claim 1, wherein one of a primary winding and a secondary winding is connected to each other and used as the first terminal, and the other of the primary winding is used as the second terminal. The other terminal of the wire is used as the third terminal.
Converter according to. 3. The transformer is a single-turn transformer having a center tap, one of windings serving as the first terminal,
The converter according to claim 1, wherein a center tap is the second terminal, and the other of the windings is the third terminal. 4. The converter according to claim 3, wherein the other terminal of the winding is the second terminal, and a center tap is the third terminal. 5. A device according to claim 1, wherein a capacitor is connected across the output of said diode bridge.
Converter according to.