JP3214687B2 - Step-down high power factor converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-down high power factor converter for rectifying AC power, improving the power factor and outputting the rectified AC power.

[0002]

2. Description of the Related Art FIG. 6 is a circuit diagram showing a configuration of a conventional step-down type high power factor converter.
When N is reached, a current flows through the path of the single-phase AC power supply S-transistor Tr-choke coil Lr-single-phase AC power supply S,
Energy is stored in the choke coil Lr. When the transistor Tr is turned off, the energy of the choke coil Lr becomes equal to the choke coil Lr−the smoothing capacitor Cd−
The current circulates through the path of the diode D-choke coil Lr, the current of the choke coil Lr gradually decreases, and the energy of the choke coil Lr is transmitted to the smoothing capacitor Cd. At this time, the current waveform of the choke coil Lr becomes a discontinuous waveform, and the input current waveform becomes a triangular pulse train. However, by passing through an LC filter including the inductor Ls and the capacitor Cs, a waveform close to a sine wave can be obtained. . The current flows from the power supply in a region where the instantaneous value es of the power supply voltage is higher than the DC output voltage Ed.

[0003]

As described above, in the conventional high power factor converter, the current from the power supply flows through the transistor Tr in a region where the instantaneous value es of the power supply voltage is larger than the DC output voltage Ed. As the DC output voltage Ed increases, the distortion of the input current Is increases. In addition, since the transistor Tr, which is a switching element, is turned on / off in a state where a current is flowing, noise is generated when the transistor Tr is turned off and switching loss is large, thereby reducing the conversion efficiency of the high power factor converter. And high frequency noise increases. Further, the operating life of the switching element is relatively short.

The present invention has been made in view of the above-mentioned current situation of a high power factor converter, and an object of the present invention is to perform a control operation for improving a power factor smoothly without switching loss, and to realize a switching element. An object of the present invention is to provide a step-down high power factor converter capable of extending the operating life.

[0005]

In order to achieve the above object, a first embodiment of the present invention is a first embodiment of a single-phase AC power supply S.
The switching element T, the choke coil Lr, and the load L are connected in series between the rectification output terminal t1 and the second rectification output terminal t2, and a connection point between the switching element T and the choke coil Lr and the second A diode D is connected between the rectification output terminals t2, a smoothing capacitor Cd is connected between the connection point of the choke coil Lr and the load L, and the second rectification output terminal t2, and the switching element T The first rectified output terminal t1,
Between a connection point of the choke coil Lr and the diode D, a series connection circuit of a first transistor Tr1 and a second diode Dc2 and a series connection circuit of a first diode Dc1 and a second transistor Tr2 are parallel to each other. And a resonance capacitor Cr is connected between a connection point between the first transistor Tr1 and the second diode Dc2 and a connection point between the first diode Dc1 and the second transistor Tr2. It is characterized by having been done.

In order to achieve the above object, a second embodiment is the same as the first embodiment, except that the first transistor Tr1 and the second transistor Tr2
Are simultaneously controlled on / off.

In order to further achieve the above object, a third embodiment is the same as the first embodiment, except that the first transistor Tr1 and the second transistor Tr2
Is constant over one cycle of the commercial frequency.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a step-down high power factor converter according to the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing the configuration of the embodiment, and FIG. 2 is a circuit diagram showing the embodiment.
3A to 3E are diagrams showing the operation of each mode, FIG. 3 is an operation waveform diagram of each part of the present invention, FIG. 4 is a diagram showing VI characteristics of the switching element, and FIG. FIG. 5B is a VI characteristic diagram of a switching element of a conventional converter, and FIG. 5 is a characteristic diagram showing a relationship between a duty factor and a DC output voltage of the converter of the present invention.

In the present invention, as shown in FIG. 1, a switching element T, a choke coil Lr, and a load L are connected between a first rectified output terminal t1 and a second rectified output terminal t2 of a single-phase AC power supply S. Connected in series, the switching element T
A diode D is connected between the connection point of the choke coil Lr and the second rectification output terminal t2.
A smoothing capacitor Cd is connected between the connection point of r and the load L and the second rectified output terminal t2. Here, the switching element T includes a series connection circuit of a first transistor Tr1 and a second diode Dc2 between a first rectification output terminal t1 and a connection point of the choke coil Lr and the diode D, and a first diode. Dc1 and a series connection circuit of the second transistor Tr2 are connected in parallel with each other,
First transistor Tr1 and second diode Dc2
And a connection point between the first diode Dc1 and the second transistor Tr2 is connected to a resonance capacitor Cr.

The operation of the present invention having such a configuration will be described. No current flows through the choke coil Lr, and the first
The transistor Tr1 and the second transistor Tr2 are turned off, and each mode of the switching operation will be described based on FIG. 2 with an initial state in which the voltage of the resonance capacitor Cr is equal to the voltage Ed of the smoothing capacitor Cd. If the sum of the instantaneous value es of the power supply voltage and the voltage of the resonance capacitor Cr is lower than the DC output voltage, the first transistor T
r1, even if the second transistor Tr2 is turned on,
There is no change in the state and the initial state is maintained.

When the first transistor Tr1 and the second transistor Tr2 are simultaneously turned on in a state where the sum of the instantaneous value es of the power supply voltage and the voltage of the resonance capacitor Cr is higher than the DC output voltage Ed, an initial state is obtained. 2A, the choke coil Lr and the resonance capacitor Cr resonate, and the resonance capacitor Cr starts discharging. However, since the resonance capacitor Cr is turned on with zero current, zero current switching ( ZCS) operation is performed.

When the resonance capacitor Cr finishes discharging and the voltage becomes zero, the mode shifts to the mode of FIG.
Transistor Tr1-second diode Dc2 and second transistor Tr2-first diode Dc1.
Since the current of the choke coil Lr is shunted through one route, overheating due to the current of the switching element is reduced.
In FIG. 2B, energy is continuously stored in the choke coil Lr.

When the first transistor Tr1 and the second transistor Tr2 are simultaneously turned off, FIG.
The current flowing through the choke coil Lr is changed to the first diode Dc1-the resonance capacitor Cr.
Flowing through the second diode Dc2, the resonance capacitor C
r is charged, the first transistor Tr1, the second transistor Tr1,
Of the transistor Tr2 does not rise sharply. At this time, since the switching element is turned off at zero voltage, a zero voltage switching (ZVS) operation is performed.

When the resonance capacitor Cr is charged up to the instantaneous value es of the power supply voltage, the diode D becomes conductive, and
In the mode (d), the input power supply side and the output load side are separated, and the energy of the choke coil Lr is supplied to the load L. When the current flowing through the choke coil Lr becomes zero, the mode shifts to the mode of FIG. 2E, which is equal to the initial state, and the first transistor Tr1 and the second transistor T
When r2 is turned on again, the next cycle starts.

A maximum rating of 200 as a switching element
FIG. 3 shows the operation waveforms of the respective parts in the simulation performed when the duty factor is 20% using MOSFETs (MOS1 and MOS2) of V and 25A and other elements as ideal elements. When the switching element is turned on at time t0, the resonance capacitor Cr starts discharging, and at time t1, the voltage of the resonance capacitor Cr becomes zero. At time t2, when the switching element is turned off, the resonance capacitor Cr
Starts charging, the voltage of the resonance capacitor Cr becomes equal to the instantaneous value es of the power supply voltage at time t3, and the current of the choke coil Lr becomes zero at time t4. Next, one cycle is performed until the switching element is turned on. Here, Tb is one cycle of the switching operation. In order to make the current of the choke coil Lr discontinuous, the time tb
The condition that the period from 0 to time t4 is shorter than one period Tb is required.

The switching element M of the converter of the present invention
FIG. 4A shows the VI characteristics of OS1 and MOS2, and FIG.
FIG. 4B shows the -I characteristic. In a switching element of a conventional converter, as shown in FIG. 4B, the locus drawn by the VI characteristic has an area, and in the converter of the present invention, the locus drawn by the VI characteristic is It is almost zero. The loss of the switching element is expressed by V-
Since the converter is proportional to the area of the locus drawn by the I-characteristic, the converter of the present invention realizes a reduction in loss by the zero current switching (ZCS) operation and the zero voltage switching (ZVS) operation as compared with the conventional converter. It is clear that

Further, when the current waveform of the converter of the present invention is subjected to Fourier analysis and the change in the duty factor for each nth-order component of the harmonic is obtained, the fundamental wave component becomes larger than that of the conventional converter. The amplitudes of the harmonic components become substantially equal. That is, in the converter of the present invention, the harmonic component relative to the fundamental wave is relatively reduced, and the current waveform is improved. Further, in the converter of the present invention, as shown in FIG. 5, the DC output voltage Ed with respect to the duty factor dF is made higher than that of the conventional converter within a range where the current of the choke coil Lr maintains the discontinuous state. Can be. In this case, the resonance capacitor Cr is 0.1 μF.

In the converter of the present invention, the ripple rate of the DC output voltage for the same duty factor dF is the same as that of the conventional converter, and the resonance capacitor C
When the capacity of r is small, the DC output voltage increases with an increase in the capacity, but when the capacity becomes 0.3 μF or more, the DC output voltage does not increase, but the output value is always higher than that of the conventional converter. Has been maintained.

As described above, in the converter of the present invention, when the current of the choke coil is operated discontinuously, a sine wave current having a constant duty factor is obtained, the switching element is turned on by the ZCS operation, and the turn-off is performed by the ZV operation.
In S operation, the current capacity increases due to the shunting of the current of the choke coil, the overheating of the switching element is prevented, and the charging voltage of the resonance capacitor Cr is added to the power supply voltage, so that the DC output voltage can be increased. become.

[0020]

According to the present invention, the first phase of the single-phase AC power
Between the rectified output terminal t1 and the connection point of the choke coil Lr and the diode D, a series connection circuit of a first transistor Tr1 and a second diode Dc2, and a series connection of a first diode Dc1 and a second transistor Tr2. Circuit is connected in parallel with each other, and the first transistor Tr
Since a resonance capacitor Cr is connected between a connection point between the first and second diodes Dc2 and a connection point between the first diode Dc1 and the second transistor Tr2 to form a switching element, the choke coil Lr Is operated discontinuously, a sine wave current with a constant duty factor is obtained, and the turn-on of the switching element is Z
CS operation, turn-off becomes ZVS operation, current capacity increases due to shunting of the current of the choke coil Lr, overheating of the switching element is prevented, generation of noise at the time of turn-on is reduced, switching loss is reduced, As a result, the operating life of the switching element can be extended, and the charging voltage of the resonance capacitor Cr is added to the power supply voltage, so that the DC output voltage can be increased.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a step-down high power factor converter according to the present invention.

FIGS. 2A to 2C are circuit diagrams of an embodiment of the present invention, wherein FIGS.
(E) is a figure which shows operation | movement in each mode.

FIG. 3 is an operation waveform diagram of each section of the present invention.

FIG. 4 is a diagram showing VI characteristics of a switching element.
(A) is a characteristic diagram of the switching element of the converter of the present invention, and (b) is a characteristic diagram of the switching element of the conventional converter.

FIG. 5 is a characteristic diagram showing a relationship between a duty factor and a DC output voltage of the converter of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a conventional converter.

[Explanation of symbols]

 S Single-phase AC power supply t1 First rectified output terminal t2 Second rectified output terminal Tr1 First transistor Tr2 Second transistor Dc1 First diode Dc2 Second diode Cr Resonance capacitor D Diode Lr Choke coil Ls Choke Coil MOS1 Switching element MOS2 Switching element Cd Smoothing capacitor L Load

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-39149 (JP, A) JP-A-5-343222 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/217 H02M 1/08 331 H02M 3/155

Claims (3)

(57) [Claims] 1. A first rectified output terminal t of a single-phase AC power supply S
A switching element T, a choke coil Lr, and a load L are connected in series between the first and second rectification output terminals t2, and a connection point between the switching element T and the choke coil Lr and the second rectification output terminal A diode D is connected between t2, a smoothing capacitor Cd is connected between a connection point of the choke coil Lr and the load L, and the second rectification output terminal t2, and the switching element T is connected to the first rectifying output terminal t2. Rectified output terminal t
1, a series connection circuit of a first transistor Tr1 and a second diode Dc2 between a connection point of the choke coil Lr and the diode D, and a first diode Dc
A series connection circuit of the first and second transistors Tr2 is connected in parallel with each other; a connection point of the first transistor Tr1 and the second diode Dc2; and a connection point of the first diode Dc1 and the second transistor Tr2 A step-down type high power factor converter, wherein a resonance capacitor Cr is connected between the connection points of the above. 2. The step-down high power factor converter according to claim 1, wherein the first transistor Tr1 and the second transistor Tr2 are simultaneously ON / OFF controlled. 3. The step-down high power factor converter according to claim 1, wherein the ON duty of the first transistor Tr1 and the second transistor Tr2 is constant over one cycle of a commercial frequency.