JP2008017564A - Boost chopper - Google Patents

Abstract

The number of components is reduced while reducing switching loss.
The circuit 1 includes a first reactor L1 and a first diode D1 connected in series to a positive line of a DC power supply VS, a connection point a between the first reactor L1 and the first diode D1, and a DC power supply VS. The main switching element SW1 connected between the negative electrode line and switching based on the on / off control signal generated by the controller, and the smoothing first connected between the output terminal of the first diode D1 and the negative electrode line. 1 capacitor C1, and a zero voltage switching circuit 10 that causes the main switching element SW1 to perform a zero voltage switching operation when the main switching element SW1 is turned off.
[Selection] Figure 1

Description

  The present invention relates to a boost chopper that boosts a voltage of DC power to a predetermined voltage.

  It is known that the loss of the step-up chopper accounts for a large proportion of the loss related to the switching element. The loss of the switching element includes an on-loss (loss generated during the on period) and a switching loss (loss generated at the moment of turning on and off). In particular, in the case of a step-up chopper with a large step-up ratio, the voltage on the output side is high, so that the voltage applied to the switching element at the moment of turning on and off becomes high and the switching loss increases.

  Among them, the switching loss at the time of off is considerably large because the voltage that is applied to the switching element suddenly cuts off the current that has flown up to now and is the maximum in a series of operation processes, that is, V × I is large. It is common. On the other hand, the switching loss at ON is relatively small because it is an operation that suddenly flows out the current that has not flowed until now, and the current cannot increase suddenly due to the inductance of the electric circuit or other components. Met.

  Conventionally, what was described in patent document 1 is known as a technique which suppresses such switching loss. In this system-connected inverter, a zero voltage switching means is connected between the boosting means and the inverter means in the grid-connected inverter, and all switching elements are switched at zero voltage by the control unit during the switching operation of the boosting means and the inverter means. As shown, a resonance circuit is formed in the zero voltage switching means. According to this technique, the resonant circuit is operated, soft switching can be realized with zero voltage between the DC positive and negative buses, and switching loss can be reduced.

Japanese Patent No. 3655804

  However, this technique switches all of the switching elements at zero voltage, and eliminates all switching losses regardless of whether the switching elements are on or off. Therefore, there is a problem in that the number of components increases because not only the switching element is turned off but also the on time when the loss is relatively small as described above.

  Therefore, in view of the above problems, the present invention is a boost chopper that can reduce the number of components while significantly reducing the switching loss by switching the switching element to zero voltage only when the switching loss is relatively large at the OFF time. The issue is to provide

  In order to solve the above problems, a step-up chopper according to a first aspect of the present invention includes a first reactor and a first diode connected in series to a positive line of a DC power supply, a connection point between the first reactor and the first diode, and a DC A main switching element connected between a negative line of the power supply and performing a switching operation based on an on / off control signal generated by the control unit; a first capacitor connected between the output terminal of the first diode and the negative line; A zero voltage switching circuit for causing the main switching element to perform a zero voltage switching operation when the main switching element is turned off. The zero voltage switching circuit includes a connection point between the first reactor and the main switching element and a negative electrode of the DC power source. A second capacitor connected to the line via a second diode, and a series of the second diode and the second capacitor. A second reactor and an auxiliary switching element connected in series between the point and the input point of the first reactor, and when the main switching element is turned off by the on / off control signal, the second capacitor The main switching element is charged by the electric charge of the current flowing in the element, and is configured to perform a zero voltage switching operation.

  In the step-up chopper according to the second aspect of the present invention, when the main switching element is turned on by the on / off control signal, the auxiliary switching element is turned on by the on control signal generated by the control unit, and simultaneously with the on operation of the auxiliary switching element. The second capacitor and the second reactor cause the auxiliary switching element to perform a zero current switching operation by discharging the charge charged in the second capacitor in a predetermined discharge time, and after the discharge time has elapsed, the first reactor and the second reactor The two reactors transfer the energy stored in the second reactor to the first reactor at a predetermined transition time, and reduce the current flowing through the second reactor, thereby turning on the auxiliary switching element that has been turned on after the transition time has elapsed. It is configured to be turned off by zero current switching operation. .

  According to a third aspect of the present invention, there is provided a step-up chopper control method according to the second aspect, wherein the control unit is assisted by the on-control signal when the main switching element is turned on by the on-off control signal. The switching element is configured to be turned on.

  According to the first aspect of the present invention, the zero voltage switching circuit causes the main switching element to perform the zero voltage switching operation only during the off operation with a relatively large switching loss, so that the number of components can be reduced while greatly reducing the switching loss. Can be reduced.

  According to the second and third aspects of the invention, since the second capacitor is discharged by the on operation of the auxiliary switching element when the main switching element is on, the zero voltage switching operation when the main switching element is off is continuously performed. Can do. Further, both the ON and OFF operations of the auxiliary switching element can be set to zero current switching operation, and the switching loss can be reduced.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described in detail with reference to the drawings.
FIG. 1 is a circuit diagram showing a step-up chopper (hereinafter referred to as the present circuit) according to the present invention. The circuit 1 is connected between the DC power supply VS and the load RL, and is configured to boost the voltage supplied from the DC power supply VS to a predetermined voltage and output the voltage to the load RL.

  The circuit 1 includes a first reactor L1 and a first diode D1 connected in series to a positive line of the DC power supply VS, a connection point a between the first reactor L1 and the first diode D1, and a negative line of the DC power supply VS. A smoothing first connected between the main switching element SW1 connected between the main switching element SW1 that operates based on an on / off control signal generated by a control unit (not shown) and the output terminal of the first diode D1 and the negative electrode line. The capacitor C1 and a zero voltage switching circuit 10 that causes the main switching element SW1 to perform a zero voltage switching operation when the main switching element SW1 is turned off are configured.

  The zero voltage switching circuit 10 includes a second capacitor C2 connected via a second diode D2 between a connection point a of the first reactor L1 and the main switching element SW1 and a negative line of the DC power supply VS, and a second diode. A second reactor L2 connected in series between a connection point b of D2 and the second capacitor C2 and an input point c of the first reactor L1 and a thyristor SW2 as an auxiliary switching element are configured.

Next, the boosting operation by the circuit 1 having the above configuration will be described.
As shown in FIGS. 2A to 2G, first, when the main switching element SW1 is turned off (the thyristor SW2 is already turned off), the step-up first reactor L1 flowing to the main switching element SW1 The current charges the second capacitor C2 via the second diode D2. At this time, the voltage of the second capacitor C2 rises linearly. Since the voltage of the second capacitor C2 is applied to the main switching element SW1, a zero voltage switching (ZVS) operation is performed. For this reason, the switching loss when the main switching element SW1 is OFF is substantially zero. When the voltage of the second capacitor C2 reaches the output voltage, the current of the first reactor L1 flows to the load side via the first diode D1 and increases the voltage of the load RL.

Next, when the main switching element SW1 is turned on, the current of the first reactor L1 flows again to the main switching element SW1. At this time, since hard switching is performed, the switching loss at the time of ON is the same as that of the prior art.
Simultaneously with the turning on of the main switching element SW1, a short-time on control signal is applied from the control unit to the thyristor SW2, and the thyristor SW2 is also turned on. At this time, the electric charge charged in the second capacitor C2 starts to discharge through the path C2-L2-SW2-VS-C2, but the discharge current I (SW2) increases from zero by the action of the second reactor L2. Therefore, the switching loss when the thyristor SW2 is on becomes zero by the zero current switching (ZCS) operation.

  The voltage of the second capacitor C2 becomes zero after the elapse of the predetermined discharge time t1, but at this time, the discharge current becomes maximum. The discharge from the second capacitor C2 stops here, but the second reactor L2 tries to continuously flow the current, so that part or all of the current flowing in the main switching element SW1 is L2-SW2 -It starts to flow suddenly along the route of L1-D2-L2. This current gradually decreases as the energy stored in the second reactor L2 shifts to the first reactor L1, and after the predetermined transition time t2, the transition is completed and becomes zero. In the meantime, the current of the first reactor L1 flowing through the main switching element SW1 gradually increases, and finally the total current of the first reactor L1 flows again. When the current flowing through the second reactor L2 becomes zero, a reverse voltage is applied to the thyristor SW2 by the action of the second reactor L2, and the thyristor SW2 is turned off. The switching of the thyristor SW2 at this time is also ZCS, and the switching loss is zero. Eventually, the loss of the thyristor SW2 is only the on-loss.

  According to the step-up chopper 1 having the above configuration, the zero voltage switching circuit 10 causes the main switching element SW1 to perform the zero voltage switching operation only during the off operation with a relatively large switching loss. It is possible to reduce the number of parts.

  Further, since the second capacitor C2 is discharged by turning on the thyristor SW2 when the main switching element SW1 is turned on, the zero voltage switching operation when the main switching element SW1 is turned off can be continuously performed. Further, the on / off operation of the thyristor SW2 can be a zero current switching operation, and the switching loss can be reduced.

  FIG. 3 is a circuit diagram showing another embodiment of the step-up chopper according to the present invention. The circuit 21 includes a second capacitor C2 in which a zero voltage switching circuit 20 is connected via a second diode D2 between a connection point a of the first reactor L1 and the main switching element SW1 and a negative line of the DC power supply VS. A second reactor L2 connected in series between a connection point b of the second diode D2 and the second capacitor C2 and an input point c of the first reactor L1, an FETSW3 as an auxiliary switching element, and a third diode D3 It is configured with. Also with the present circuit 21, when the FET SW3 is controlled to be turned on / off simultaneously with the main switching element SW1, the same effects as the circuit 1 of FIG. 1 can be obtained.

  In addition, this invention is not limited to the said embodiment, It is also possible to change suitably the shape and structure of each part in the range which does not deviate from the meaning of this invention. For example, the auxiliary switching elements are not limited to thyristors and FETs, and other types of switching elements may be used. Further, when SW2 in FIG. 3 is only FET and ON / OFF control is performed simultaneously with SW1, another resonance current flows through the path C2-L2-SW2-VS-C2, but when the influence is slight, The same effect as the circuit 1 of FIG. 1 is obtained.

It is a circuit diagram showing one embodiment of the present invention. 1, (a) a current waveform diagram of the first reactor L1, (b) a current waveform diagram of the main switching element SW1, (c) a voltage waveform diagram of the main switching element SW1, (d) a current waveform diagram of the thyristor SW2, e) A voltage waveform diagram of the thyristor SW2, (f) a voltage waveform diagram of the second capacitor C2, and (g) a current waveform diagram of the first diode D1. It is a circuit diagram which shows other embodiment of this invention.

Explanation of symbols

  1 ·· Boost chopper, 10 ·· Zero voltage switching circuit, C1 ·· 1st capacitor, C2 ·· 2nd capacitor, D1 ·· 1st diode, D2 ·· 2nd diode, L1 ·· 1st reactor, L2 .. second reactor, RL .. load, SW1 .. main switching element, SW2 ..thyristor as auxiliary switching element, SW3 ..FET as auxiliary switching element, VS .. DC power supply.

Claims (3)

A first reactor and a first diode connected in series to a positive line of a DC power supply;
A main switching element connected between a connection point of the first reactor and the first diode and a negative electrode line of the DC power supply, and performing a switching operation based on an on / off control signal generated by the control unit;
A first capacitor connected between the output terminal of the first diode and the negative electrode line;
A zero voltage switching circuit for causing the main switching element to perform zero voltage switching operation when the main switching element is turned off;
With
Zero voltage switching circuit
A second capacitor connected via a second diode between the connection point of the first reactor and the main switching element and the negative line of the DC power supply;
A second reactor and an auxiliary switching element connected in series between a connection point of the second diode and the second capacitor and an input point of the first reactor;
With
When the main switching element is turned off by the on / off control signal, the second capacitor is charged by the electric charge of the current flowing through the main switching element to cause the main switching element to perform a zero voltage switching operation.
Boost chopper characterized by that. When the main switching element is turned on by the on / off control signal, the auxiliary switching element is turned on by the on control signal generated by the control unit,
Simultaneously with the ON operation of the auxiliary switching element, the second capacitor and the second reactor cause the auxiliary switching element to perform a zero current switching operation by discharging the charge charged in the second capacitor in a predetermined discharge time,
After the discharge time has elapsed, the first reactor and the second reactor cause the energy stored in the second reactor to shift to the first reactor at a predetermined transition time, thereby reducing the current flowing through the second reactor, thereby reducing the transition time. After the elapse of time, the auxiliary switching element that is turned on is turned off by the zero current switching operation.
The step-up chopper according to claim 1. A method for controlling a step-up chopper according to claim 2,
The control unit turns on the auxiliary switching element by the on control signal when the main switching element is turned on by the on / off control signal.
A step-up chopper control method.

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