RU2653574C2 - Push-pull dc/dc converter with l-inlet - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: device is a push-pull DC/DC converter with an L-inlet. It comprises: a main throttle; a transformer with primary and secondary windings. The primary winding is made with a centre terminal; the first and second power transistors (power controlled keys); a full-wave current rectifier of the secondary winding; an output filter capacitor. The known features of the push-pull DC/DC-converter with the L-inlet are: connection of the first terminal of the main throttle winding to the first power bus and direct connection of the second terminal of this winding to the centre of the primary transformer winding; connection of the first terminal of the primary winding to the second power bus via the output circuit of the first power transistor; connection of the second terminal of the primary winding to the second power bus via the output circuit of the second power transistor; connection of the secondary transformer winding via the full-wave current rectifier of this winding to the output filter capacitor. The characteristic features of the push-pull DC/DC-converter are: introduction of the first, second, third and fourth diodes, additional throttle, as well as the first and second capacitors to the device; connection of four entered diodes according to the diode bridge circuit; direct connection of the first terminal of the output circuit of the mentioned diode bridge to the first power bus; connection of the second terminal of the output circuit of the diode bridge to the second power bus via the additional throttle winding; connection of the first terminal of the input circuit of the diode bridge via the first capacitor to the connection point of the first terminal of the transformer primary winding with the first power transistor; connection of the second terminal of the input circuit of the diode bridge via the second capacitor to the connection point of the second terminal of the transformer primary winding to the second power transistor.

EFFECT: reducing switching loss energy in power transistors during their lock-out, thus increasing the reliability of their operation and increasing the energy efficiency of energy conversion.

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Description

The proposed device relates to power converting equipment and is intended for converting and regulating the energy consumed from a direct current source, and transmitting the converted energy to its receiver using transformer coupling between the source and receiver energy circuits.

Push-pull DC / DC converter with L-input, considered as a prototype [1, p. 77, Fig. 5.1-b], contains:

- main choke;

- a transformer with primary and secondary windings, and the primary winding is made with the conclusion of the midpoint;

- the first and second power transistors (power controlled keys);

- a half-wave rectifier of the current of the secondary winding;

- output filter capacitor.

Known features of a push-pull DC / DC converter with an L input are:

- connecting the first output of the main inductor winding to the first power bus and directly connecting the second output of this winding to the midpoint of the transformer primary winding;

- connecting the first output of the primary winding to the second power bus through the output circuit of the first power transistor;

- connecting the second terminal of the primary winding to the second power bus through the output circuit of the second power transistor;

- connecting the secondary winding of the transformer through a half-wave rectifier of the current of this winding to the capacitor of the output filter.

In the first part of each cycle, both power transistors are closed. In this case, the primary winding is shorted through their output circuits, and the supply voltage is applied to the power winding of the main inductor, which is why energy is accumulated in it.

In the second part of each cycle, one of the two power transistors opens, and through the other transistor one of the two halves of the primary winding of the transformer is connected between the end of the main inductor winding and the second power bus. At the same time, the first power transistor works in a state of high conductivity in the first cycle, and through its output circuit the first half of the transformer primary winding is connected between the end of the main inductor winding and the second power bus. In the second cycle, in a state of high conductivity, the second power transistor operates, and through its output circuit the second half of the transformer primary winding is connected between the end of the main inductor winding and the second power bus.

The presence of the main inductor winding, which is alternately clockwise connected in series with the first or second halves of the transformer primary winding through the first or second power transistors, contributes to a rapid increase in voltage on the primary winding and on the power transistor during its shutdown. As a result, significant switching losses occur in the power transistor.

In real-world transformers, there is a leakage inductance. It prevents the instantaneous transfer of power by the transformer to its secondary winding, due to which short voltage surges occur on the primary winding. If the voltage amplitude at the power transistor, which has switched to a non-conducting state, reaches the value of the breakdown voltage, then additional transistor energy stored in the transformer inductance will be released in this transistor.

High switching losses in transistors reduce the reliability of their operation and, accordingly, the reliability of the device as a whole, as well as reduce the efficiency of electric energy conversion.

The aim of the proposal contained in this invention is to increase the energy efficiency and reliability of the device.

Two variants of the proposed device are presented in FIG. 1 and 2. They differ in the designs of the secondary winding of the transformer, as well as the half-wave rectifier of the current of this winding. In the device of FIG. 1, the secondary winding is made with the conclusion of its midpoint, and the rectifier contains two valve elements (as in the circuit, considered as a prototype). In the device of FIG. 2, the secondary winding is single-phase, and in the current rectifier of this winding, the valve elements are connected according to the bridge circuit.

The noted differences between the two variants of the scheme are not fundamental. The essential known features of the device is only the connection of the secondary winding of the transformer through a half-wave rectifier of the current of this winding to the capacitor of the output filter.

Salient features of the proposed device are that:

- the first, second, third and fourth diodes, an additional inductor, and also the first and second capacitors are introduced into the device;

- the entered four diodes are connected according to the diode bridge circuit;

- a first output terminal of said diode bridge is directly connected to the first power bus;

- the second terminal of the output circuit of the diode bridge is connected to the second power bus through the winding of an additional inductor;

- the first terminal of the input circuit of the diode bridge is connected through the first capacitor to the connection point of the first terminal of the primary winding of the transformer with the first power transistor;

- the second terminal of the input circuit of the diode bridge is connected through the second capacitor to the connection point of the second terminal of the primary winding of the transformer with the second power transistor.

In the device of FIG. 1 between the first power bus 1 and the second power bus 2 the power source 3 is turned on (it is made, for example, in the form of a voltage source). The first output of the winding 4 of the main inductor is directly connected to the power bus 1, and the second output of this winding is connected to the midpoint of the two-phase primary winding 5 of the transformer 6.

The first terminal of the primary winding 5 of the transformer 6 is connected to the second power bus 2 through the output circuit of the first power transistor 7, and the second terminal of the primary winding 5 is connected to this bus through the output circuit of the second power transistor 8.

The secondary winding 9 of the transformer 6 through a half-wave rectifier 10 of the current of this winding is connected to the capacitor 11 of the output filter. Parallel to this capacitor, a load of 12 is connected.

In the device of FIG. 1, the secondary winding 9 is made with the conclusion of the midpoint, and a half-wave rectifier 10 of the current of this winding contains two valve elements. In the device of FIG. 2, the secondary winding 9 contains one section, and four valve elements of a half-wave rectifier 10 are connected according to a bridge circuit.

The first diode 13, the second diode 14, the third diode 15 and the fourth diode 16 form a diode bridge circuit. The first output of the output circuit of the diode bridge is directly connected to the first power bus 1. The second output of the output circuit of the diode bridge is connected to the second power bus 2 through the winding 17 of the additional inductor.

The first output of the input circuit of the diode bridge through the first capacitor 18 is connected to the connection point of the first output of the primary winding 5 of the transformer 6 with the first power transistor 7.

The second output terminal of the input circuit of the diode bridge through the second capacitor 19 is connected to the connection point of the second terminal of the primary winding 5 of the transformer 6 with the second power transistor 8.

The objectives of the technical solution proposed in this invention are achieved through the interaction of significant known and distinctive features of the device.

In the stationary mode of operation of a push-pull DC / DC converter, in the first part of each cycle, both power transistors are in a state of high conductivity (7 and 8). In this case, the primary winding 5 of the transformer 6 is shorted, a supply voltage is applied to the power winding 4 of the main inductor, and energy is accumulated in it.

At the beginning of the first clock cycle, the first power transistor 7 is unlocked, and the second power transistor 8 continues to be in a state of high conductivity.

In the second part of the first cycle, the second power transistor 8 is locked, and the first power transistor 7 continues to be in a state of high conductivity. The main inductor begins to give off energy, and a voltage of "reverse" polarity appears on its winding 4. Accordingly, the potential of the midpoint of the primary winding 5 becomes higher than the potential of the first power bus 1 by the value of the indicated voltage of the "reverse" polarity on the winding 4. In this case, a voltage arises on the first half of the primary winding 5 of the transformer 6, the value of which is almost equal to the potential of the midpoint. Due to the magnetic coupling between the halves of the primary winding 5, the same voltage is set on the second half of the winding 5, and the second capacitor 19 is charged with this voltage, and a positive sign of the voltage is installed on the terminal of the capacitor, which is connected to the second terminal of the primary winding 5.

At the beginning of the second clock, the second power transistor 8 is unlocked, and the first transistor 7 continues to remain in a state of high conductivity. After unlocking the transistor 8, the discharge process of the second capacitor 19 begins. The discharge current is closed along the following circuit: the second capacitor 19 → the second power transistor 8 → the winding 17 of the additional inductor → the fourth diode 16 → the second capacitor 19.

Due to the presence of an additional inductor in the winding circuit 17, the process is oscillatory. The current of the capacitor 19 varies according to the sinusoidal law, and the voltage on this capacitor - according to the law of the cosine wave. At the end of this process, the voltage across the capacitor should have grown to almost the initial value, but opposite in sign. It, as shown earlier, is more than the supply voltage. Therefore, when the positive potential at the anode of the third diode 15 reaches the supply voltage level (more precisely, exceeds it by a small amount of voltage drop across the diode 15 in the forward direction), the diode 15 goes into a conduction state, and the second capacitor 19 is charged to the supply voltage. In this case, the current of the winding 17 of the additional inductor, previously closed through the second capacitor 19, begins to flow along the circuit: the winding 17 of the additional inductor → the fourth diode 16 → the third diode 15 → power supply 3 (towards the EMF of the source) → the winding 17 of the additional inductor. The energy stored in the additional inductor is returned to the power source, and the current of the winding 17 decreases in time.

It is assumed that the inductance of the winding 17 of the additional inductor satisfies two conditions.

The first of them is that the voltage is fixed on the second capacitor 19 at the level of the supply voltage until the first power transistor 7, which occurs in the second cycle, is turned off. In this case, the polarity of the voltage across the capacitor 19: plus - at the terminal of the capacitor connected to the common point of the diodes 15 and 16, minus - at the terminal of the capacitor, which is connected to the second terminal of the primary winding 5 of the transformer 6. The indicated voltage on the second capacitor 19 is stored until the moment of locking the second power transistor 8, which occurs in the first cycle of the next cycle of the circuit.

The second condition is that the winding 17 current decreases to zero before the start of a new cycle of the circuit and by the beginning of each new cycle there is no energy accumulated in the previous cycle in the additional inductor.

The second part of the second clock cycle starts from the moment of locking the first power transistor 7, and the second power transistor 8 continues to be in a state of high conductivity. The main inductor begins to give off energy, and a voltage of "reverse" polarity appears on its winding 4. Accordingly, the potential of the midpoint of the primary winding 5 becomes higher than the potential of the first power bus 1 by the value of the indicated voltage of the "reverse" polarity on the winding 4. In this case, a voltage arises on the second half of the primary winding 5 of the transformer 6, the value of which is almost equal to the potential of the midpoint. Due to the magnetic coupling between the halves of the primary winding 5, the same voltage is set on the first half of the winding 5, and the first capacitor 18 is charged with this voltage, and a positive voltage sign is installed on the terminal of the capacitor, which is connected to the first terminal of the primary winding 5.

At the beginning of the first cycle in the next cycle of the circuit, the first power transistor 7 is unlocked, and the second power transistor 8 continues to be in a state of high conductivity. After unlocking the transistor 7, the discharge process of the first capacitor 18 begins. The discharge current closes along the following circuit: the first capacitor 18 → the first power transistor 7 → the winding 17 of the additional inductor → the second diode 14 → the first capacitor 18.

Due to the presence of an additional inductor in the winding circuit 17, the process is oscillatory. The current of the capacitor 18 varies according to a sinusoidal law, and the voltage on this capacitor - according to the law of the cosine wave. At the end of this process, the voltage across the capacitor should have grown to almost the initial value, but opposite in sign. It, as shown earlier, is more than the supply voltage. Therefore, when the positive potential at the anode of the first diode 13 reaches the supply voltage level (more precisely, exceeds it by a small amount of voltage drop across the diode 13 in the forward direction), the diode 13 goes into a conduction state, and the first capacitor 18 is charged to the supply voltage. In this case, the current of the winding 17 of the additional inductor, previously closed through the first capacitor 18, begins to flow along the circuit: the winding 17 of the additional inductor → the second diode 14 → the first diode 13 → power supply 3 (towards the EMF of the source) → the winding 17 of the additional inductor. The energy stored in the additional inductor is returned to the power source, and the current of the winding 17 decreases in time.

It is assumed that the inductance of the winding 17 of the additional inductor is such that the voltage is fixed at the first capacitor 18 at the level of the supply voltage until the start of turning off the second power transistor 8, which occurs in the first cycle. The voltage polarity across capacitor 18: plus — at the capacitor’s output connected to the common point of the diodes 13 and 14, minus — at the capacitor’s output, which is connected to the first output of the primary winding 5 of transformer 6. The indicated voltage on the first capacitor 18 is maintained until it is locked the first power transistor 7, which occurs in the second cycle of the next cycle of the circuit.

Then, in the first cycle of the second cycle of operation, the second power transistor 8 is turned off. When the transistor 8 is turned off, the voltage on it starts to rise from the zero level, which is caused by the process of recharging the second capacitor 19. During this process, the current of the capacitor 19 is closed along the circuit: winding 4 of the main inductor → the second half of the primary winding 5 of the transformer 6 → the second capacitor 19 → the third diode 15 → the winding 4 of the main inductor. In this case, the voltage at the output circuit of the second power transistor 8 rises with a limited speed. The slew rate is inversely proportional to the capacitance of the capacitor 19.

Similarly, in the second cycle of the second cycle of operation, an increase in voltage at the output circuit of the first power transistor 7 occurs when it is locked.

Further, the processes in the circuit are repeated.

Additional capacitors 18 and 19 are capable of absorbing the energy stored in each cycle in the leakage inductances of the transformer 6. This effectively limits the amplitude of voltage spikes on the primary winding 5 of transformer 6 and, accordingly, the operation of power transistors in breakdown mode is prevented.

Thus, the proposed technical solution causes, at each turn-on of the power transistors, an increase in voltage on them from zero, and the increase occurs at a limited speed, and is also able to prevent the operation of transistors in breakdown mode. This achieves the goal - to reduce switching energy losses in power transistors, which increases the reliability of their work and helps to increase the efficiency of the energy conversion process.

Information sources

1. Meleshin V.I., Ovchinnikov D.A. Management of transistor power converters. - M .: Technosphere, 2011 .-- 576 p.

Claims (1)

 A push-pull DC / DC converter containing a main inductor, a transformer with primary and secondary windings, the primary winding being made with a midpoint output, the first and second power transistors (power controlled keys), a half-wave rectifier of the secondary winding and the capacitor of the output filter, the first output the inductor winding is connected to the first power bus, and the second output of this winding is directly connected to the midpoint of the transformer primary winding, the first output of the primary winding is connected to the W swarm power bus through the output circuit of the first power transistor, and the second output of the primary winding is connected to the second power bus through the output circuit of the second power transistor, characterized in that the first, second, third and fourth diodes, an additional inductor, as well as the first and the second capacitors, four introduced diodes are connected according to the diode bridge circuit, the first output terminal of the diode bridge is directly connected to the first power bus, and the second output terminal of the diode bridge is connected connected to the second power bus through the winding of an additional inductor, the first output of the input circuit of the diode bridge through the first capacitor is connected to the connection point of the first terminal of the primary winding of the transformer with the first power transistor, and the second output of the input circuit of the diode bridge through the second capacitor is connected to the connection point of the second terminal of the primary transformer windings with a second power transistor.

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