RU2539560C1 - Dc-to-dc voltage converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to conversion equipment, particularly to high-frequency converters for converting dc voltage to high-power dc voltage with galvanic isolation of circuits, and can be used in electrical circuits of dc power sources for various purposes. The disclosed device comprises a control unit and a transformer, the primary coil of which is connected to the middle points of two diagonals of a transistor bridge, each formed by two series-connected transistors, and the secondary coil of the transformer is connected to a load through rectifier diodes and an output capacitor. According to the disclosed solution, the device further includes two transistor diagonals, each consisting of two transistors, and an additional transformer, the primary coil of which is connected to the middle points of additional transistor diagonals, and the secondary coil is connected through additional rectifier diodes to the output capacitor and to the load, wherein the control unit enables to generate four pulse sequences with partial time overlapping of one pulse with two adjacent pulses.

EFFECT: high efficiency, providing transistor switching at virtually zero current, resulting in the multifold reduction of dynamic losses on transistors of the converter.

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Description

The invention relates to a conversion technique, in particular to high-frequency converters of direct voltage to direct voltage of increased power with galvanic isolation of circuits, and can be used in electrical circuits of DC power supplies for various purposes.

In advanced countries, the number of different primary energy sources used is constantly increasing against the background of an even faster growth rate of electricity consumers. This trend creates an urgent need for technical means that convert the energy of primary sources into the form necessary for the work of various consumers. Such technical means are power converting devices, including converters of direct voltage to direct voltage.

Modern industrially used samples of DC / DC converters with galvanic isolation have a coefficient of performance in the range of 85-92%. These numbers mean that the net power loss is between 8 and 15%. Losses in the active elements of the converters are divided into switching (dynamic), which occur when switching power transistors (switches), and losses on conductivity (ohmic). Losses on conductivity are due to the choice of the element base, the magnitude of the current and ripple current in the converter device. Dynamic losses are associated with power losses in transistors and diodes of the converter at switching times.

Reducing dynamic losses in transistors of a converter is one of the urgent tasks when creating new converter devices. This will increase the frequency of operation of the converter, as a result, reduce its dimensions. Reducing dynamic losses on transistors plays a paramount role in increasing the reliability of converter modules. An additional increase in the efficiency of power converters by 1-2% will give a significant saving in energy resources.

Currently, there are a large number of DC-to-DC converters with galvanic isolation that can reduce the dynamic losses in the transistors of these converters.

So, in the patent U.S. 6356462, priority date 08/31/2000, "Phase-controlled bridge converter" has a circuit that allows you to implement a mode of maintaining constant voltage, current and, if necessary, output power. The main disadvantage of this topology is the current circulation in the primary circuit in the pause mode, as well as the high-frequency “ringing” of rectifier keys, associated with the need to use a high transformer dissipation inductance. As a result, losses increase and the level of electromagnetic interference increases. With a decrease in load, transistors exit the switching mode at zero voltage, which leads to a decrease in efficiency and an increase in heat loss.

Known resonant LLC Converter patent U.S. 6344979, priority date 02/09/2001, which provides maximum efficiency at maximum input voltage (up to 95% according to expert estimates).

The disadvantage of this converter is the frequency control, which complicates the control distribution of currents in the case of using several channels connected in parallel, as well as a complicated protection circuit when operating on short circuit or limiting the output current.

U.S. Patent DC / DC Converter is also known. 5563780, priority date 12/08/1993, in which a number of converters are connected in parallel at the input and output with a shift in the operation of one converter relative to another in time. First, the first converter generates the output voltage, then with a slight overlap the second converter generates the output voltage on the total output capacitance, etc. This solution allows you to reduce the ripple of the output voltage at the load, distributes the total power to a number of blocks.

The common disadvantages of these analogues can be attributed to the fact that in the technical solution, each converter, made in the form of a bridge circuit or a resonant circuit or half-bridge circuit, etc., operates as an independent converter, that is, transistors in the diagonals of one converter do not affect dynamic losses in transistors of another converter, with the exception of the effect of the distortion of currents in the converters. The control signals force first the first converter to work out, then the second converter with partial overlap by applying the output voltage to the output capacitance, etc. As a result, the dynamic losses in the transistors remain at a level characteristic of the construction topology of each of the converters combined in parallel.

The closest, taken as a prototype, is a DC-voltage converter containing a transformer, the primary winding of which is connected to the midpoints of the two diagonals of the transistor bridge, each of which is formed by two series-connected valve elements, and the secondary winding of the transformer is connected to the load through rectifier diodes and a smoothing filter (REA power supplies. Handbook edited by G.S. Naivelt. M: Radio and communications, 1986, pp. 360-368).

The disadvantages of the known Converter should include a high level of dynamic losses in the transistors that appear when the transistors switch from a high-resistance state to a low-resistance state and vice versa. At the moment of unlocking the transistor, the voltage across it drops to almost zero in a finite time, while the current through the transistor begins to increase from the moment the switching starts. As a result, during the transition of the transistor to the open state, the power of losses is allocated on it. Also, at the time of locking the key in a known circuit, a loss of power occurs due to the fact that the key goes into a high-resistance state in a finite time, and during this time the load current flows through it. As a result, the active energy of the losses is released on the transistor. The higher the switching frequency of the keys, the greater the losses allocated to the transistors. This leads to the need to remove heat from transistors by installing radiators and / or fans, which in turn increases the dimensions of the power source, increases its cost and reduces reliability.

A common drawback of both analogs and the prototype is that switching losses still occur in the power transistors of the converter, which expose them to a strong load, in particular thermal. As a result, power transistors age quickly, respectively, and their failure rate increases with the duration of operation of the converter circuit. High readiness of the converter circuit for operation, mandatory, for example, in the field of traction, is absent in this case.

The objective of the proposed technical solution is to increase the efficiency, service life and reliability of DC-DC converters to DC voltage, while reducing their size.

This goal is achieved due to the fact that the claimed Converter containing a control unit and a transformer, the primary winding of which is connected to the midpoints of the two diagonals of the transistor bridge, each of which is formed by two series-connected transistors, and the secondary windings of the transformer are connected to the load through rectifier diodes and the output capacitor additionally contains two transistor diagonals, each of which consists of two transistors and an additional transformer, first the secondary winding of which is included in the midpoints of the additional transistor diagonals, and the secondary windings are connected through an additional rectifier diode to the output capacitor and to the load, while the control unit is configured to generate four pulse sequences with a partial overlap in time of one of two adjacent pulses.

In addition, the DC-to-DC converter has such a control unit that is designed to provide alternating pulses to the transistors of the transducer diagonals in the order: to the first diagonal, to the third diagonal, to the second diagonal, to the fourth diagonal, and so on.

The technical result obtained by the implementation of the claimed solution is achieved by creating a converter with an improved circuit for converting DC voltage to DC voltage, which provides a multiple reduction in switching losses, due to the fact that the switching of transistors occurs at almost zero current.

A comparative analysis with the prototype shows that the presence in the circuit is new in the claimed converter:

- 2 transistor diagonals, each of which consists of two transistors;

- an additional transformer, the primary winding of which is included in the midpoints of the additional transistor diagonals, and the secondary winding through additional rectifier diodes is connected to the output capacitor and to the load;

- the control unit is designed to provide the formation of four sequences of pulses with a partial overlap in time of one on two adjacent pulses;

- the control unit is configured to provide alternate pulses to the transistors of the transducer diagonals in the order: to the first diagonal, to the third diagonal, to the second diagonal, to the fourth diagonal and so on, which allows us to conclude that the claimed invention meets the criterion of "novelty."

An analysis of the known DC-DC to DC voltage converters showed that the claimed solution due to a fundamentally new converter circuit, made it possible to obtain a fundamentally new DC-DC to DC converter, which was not previously used. This allows us to conclude that the criterion of "inventive step".

The essence of the invention lies in the fact that due to the proposed topology and control algorithm, interception of the operating current of the closing transistors is achieved, so that the transistors go into a high-resistance state at zero operating current. Transistors open at zero current, since the operating current begins to flow through them at the end of the front of switching to a low-impedance state. As a result of this, the dynamic losses in the transistors of the converter are many times reduced.

The claimed solution is illustrated by drawings.

Figure 1 shows a diagram of a Converter;

Figure 2 shows diagrams of control signals;

Figure 3 shows a diagram of the current through the transistor and voltage drain-source.

The claimed Converter DC to DC voltage according to the circuit in figure 1 contains:

transistors 1-8; transformers 9, 10; diodes 11-14; output capacity 15; control unit 16.

Transistors 1 and 4 form the first diagonal, transistors 2 and 3 form the second diagonal. The primary winding of the transformer 9 is connected to the midpoints of the first and second diagonals, and the secondary winding through the rectifier diodes 11 and 12 is connected to the output capacitor 12. Transistors 5 and 8 form the third diagonal of the circuit. And transistors 6 and 7 are the fourth diagonal of the circuit. The primary winding of the transformer 10 is connected to the midpoints 3 and 4 of the diagonals, and the secondary winding through the rectifier diodes 13 and 14 is connected to the output capacitor 15. The control unit is connected to each of the transistors 1-8.

Figure 2 shows the diagrams of the control signals (hereinafter SU) SU1-SU4 formed by the control unit 16 for controlling the transistors 1-8 of the Converter. Accordingly, the control signal SU1 is supplied to transistors 1 and 4; control signal SU2 is supplied to transistors 5 and 8; control signal SU3 is supplied to transistors 2 and 3; control signal SU4 is supplied to transistors 6 and 7.

Figure 2 shows the time t - the time during which two transistors of the same diagonal of the converter are open. Time tн is the overlap time of adjacent control pulses.

Figure 3 shows a diagram of the current through the transistor and voltage drain-source. It is seen that at the moment the transistor switches to a low-impedance state, the current through the transistor is zero. Also, when switching the transistor to a high-resistance state, we see that the current at the beginning of the switching moment is zero.

The operation of the converter is as follows: a constant voltage Uin is supplied to the primary winding of the transformer 9. Keys 1 and 4 are open. Keys 2, 3, 5-8 are closed. A current flows through the diode 12, charging the output capacitor 15. After time t is the operating time of only the first diagonal, the control pulses from the control unit 16 are fed to transistors 5 and 8. The transistors begin to open. The voltage on the transistors decreases to almost zero, while the current does not flow through the transistors 5 and 8 (with the exception of the idle current of the transformer), since the output diode of the first diagonal 14 does not yet pass current. At the end of the moment of switching transistors 5 and 8, the control signals on transistors 1 and 4 go into the negative region, the transistors begin to close. At this moment, the entire load current begins to flow through the keys 5, 8, transformer 10 and diode 14, and through the diode 12 the load current stops flowing, because it is intercepted by the third diagonal and its rectifier diode 14. Therefore, the current ceases to flow through transistors 1 and 4, which means that the transistors close almost at zero current. A small current is associated with the dissipation inductance of the transformer and can be reduced to almost zero by taking appropriate measures to the design of the transformer.

After time t, the control signals arrive at the second diagonal of the bridge, formed by transistors 2 and 3, they begin to open, but the working current does not flow through them, since the output diode 11 does not conduct current yet. Therefore, they go into the open state at zero current; at the end of the switching moment, the second diagonal intercepts the operating current; the current begins to flow through the diode 11 and transistors 2, 3. At the same time, the current stops flowing through the diode 14, and therefore, the transistors 5 and 8 are closed at zero operating current. The process continues. As a result of this, the dynamic losses in the converter are reduced to almost zero, due to the fact that the transistors turn on and off at almost zero operating current.

The positive effect of the proposed Converter is confirmed by bench tests of a manufactured prototype with a capacity of 1 kW. A low level of losses, high efficiency, and a decrease in the ripple of the output voltage and input current were obtained. Due to this, the level of generated interference was found to be 20-30 dB lower than that of converters of the same power and clock frequency (comparison was made without using an input interference filter).

The advantages of the claimed solution is to increase the efficiency, increase the reliability and life of the converter while reducing its size.

Claims (2)

1. A DC / DC converter containing a control unit and a transformer, the primary winding of which is connected to the midpoints of the two diagonals of the transistor bridge, each of which is formed by two transistors connected in series, and the secondary winding of the transformer is connected to the load through rectifier diodes and an output capacitor, characterized in that it additionally contains two transistor diagonals, each of which consists of two transistors, and an additional trans a formator, the primary winding of which is included in the midpoints of the additional transistor diagonals, and the secondary winding through additional rectifier diodes is connected to the output capacitor and to the load, while the control unit is configured to generate four pulse sequences with a partial overlap in time of one to two adjacent pulses. 2. The DC-DC converter to DC voltage according to claim 1, characterized in that the control unit is configured to provide alternate pulses to the transistors of the converter diagonals in the order: to the first diagonal, to the third diagonal, to the second diagonal, to the fourth diagonal and so on.

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