KR20160007867A - Full Bridge Low Voltage DC/DC Converter - Google Patents

Abstract

The present invention relates to a full bridge low voltage DC-DC converter and, more specifically, to a full bridge low voltage DC-DC converter enabling common application by the type of vehicle as a buck boost circuit is provided at an input terminal of a low voltage DC-DC converter to respond to a wide range of input voltages. More specifically, the present invention is to provide a full bridge low voltage DC-DC converter enabling common application regardless of the type of vehicle, by improving a low-voltage DC-DC converter for charging a low voltage auxiliary battery to a circuit that can be applied to a wide range of input voltages (a cell voltage of a high voltage battery) and enhancing the low voltage DC-DC converter into a structure which adds a buck boost circuit combining a buck converter and a boost converter, whose polarity is not reversed, to an input terminal of a conventional DC-DC converter.

Description

[0001] The present invention relates to a full bridge low voltage DC / DC converter,

The present invention relates to a full bridge low voltage DC-DC converter, and more particularly, to a full bridge low voltage DC-DC converter having a buck-boost circuit at the input terminal of a low voltage DC-DC converter to cope with a wide input voltage range, DC converter.

Eco-friendly vehicles that use electricity such as hybrid vehicles (HEV), fuel cell vehicles, and fuel cell hybrid vehicles are equipped with low voltage DC / DC converters that supply 12V battery (auxiliary battery) Converter, and LDC).

This green car is equipped with a low-voltage DC-DC converter for charging a low-voltage battery from a high-voltage battery (about 100V to 450V), and the ground for the high-voltage battery and the low- An insulated DC converter with a transformer is used.

The low-voltage DC-DC converter converts a high-voltage direct-current voltage generated from a high-voltage battery into a low-voltage direct-current voltage to provide a full load of the vehicle such as a 12V auxiliary battery, and an insulated full bridge and a forward converter are used .

More specifically, the low-voltage DC-DC converter serves as an alternator of a general gasoline vehicle. The low-voltage DC-DC converter supplies a voltage of 12V by downing the high voltage of the main high-voltage battery. The high- DC) to 12V (DC) to charge the auxiliary battery (12V battery) or to supply the electric field load.

The input voltage of the low-voltage DC-DC converter is a high-voltage battery mounted in an electric vehicle and a hybrid vehicle, and the high-voltage battery voltage range is very different from a minimum of about 100 V to a maximum of 450 V depending on the type of vehicle.

Because of the wide range of high-voltage batteries, the turn ratio of the transformer can be varied from 5: 1 to about 15: 1 for a full bridge converter, and when the turn ratio of the transformer is different The size of the current flowing in the primary side of the insulated converter is changed, so that the specification of the semiconductor device needs to be changed. As a result, it is impossible to share the low-voltage DC-DC converter with the environmentally friendly car, It is necessary to redesign every time, which causes a rise in manufacturing cost.

As a result, it is not possible to commonly use a low-voltage DC-DC converter for each type of vehicle. Thus, the turn ratio and the number of turns of the transformer such as an insulated converter vary depending on the size of the high-voltage battery. There is a problem in that the design specifications of the converter are largely changed for each type.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and it is an object of the present invention to provide a low-voltage DC-DC converter for charging a low-voltage (12 / 24V) battery to a wide input voltage (cell voltage of a high- By improving the structure of the existing low-voltage DC-DC converter with a combination of a buck converter and a boost converter that does not have polarity reversal at the input stage, it can be shared regardless of the type of vehicle. The present invention provides a full-bridge low-voltage DC-DC converter.

According to an aspect of the present invention, there is provided a DC-DC converter including: a switching unit for alternately switching and outputting direct currents; a transformer for lowering the AC voltage output from the switching unit to a level of 12V usable in a vehicle; Wherein a buck-boost circuit capable of outputting a voltage whose polarity is not reversed is connected to an input terminal of the switching unit, wherein the full-bridge low-voltage DC-DC converter includes: to provide.

In particular, the buck-boost circuit of the present invention comprises: a buck switch connected in series with a high voltage battery; An inductor coupled in series with the buck switch; A first diode connected in parallel with the buck switch; A second diode connected in series with an output terminal of the inductor; And a boost switch connected in parallel between the inductor and the second diode.

Advantageously, when the input voltage magnitude of the high voltage battery is greater than the reference voltage, the buck switch is repeatedly turned on / off according to a predetermined duty ratio, while the boost switch is always off.

When the input voltage of the high voltage battery is smaller than the reference voltage, the boost switch is repeatedly turned on and off according to a predetermined duty ratio, and the buck switch is always on.

The present invention provides the following effects through the above-mentioned problem solving means.

First, the input voltage of the full bridge DC / DC converter circuit can be kept constant regardless of the voltage level of the high voltage battery, and the operation can be always performed at a high level of efficiency.

Second, since the input terminal voltage of the full bridge DC / DC converter becomes constant, the low voltage DC-DC converter can be shared regardless of the type of vehicle.

Third, the commonality of low-voltage DC-DC converters makes it possible to share transformers and semiconductor devices, and it is very advantageous to reduce costs when designing products and to reflect them when changing design specifications.

1 is a circuit diagram showing a conventional center cap full bridge converter,
2 is a circuit diagram showing a conventional current doubler full bridge converter,
3 is a circuit diagram showing a full-bridge low-voltage DC-DC converter according to an embodiment of the present invention.
4 is a circuit diagram showing a full-bridge low-voltage DC-DC converter according to another embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, to facilitate understanding of the present invention, the construction of a conventional full bridge converter, which is an example of a low-voltage DC-DC converter, will be described.

FIG. 1 shows a conventional center tap full bridge converter, and FIG. 2 shows a conventional current doubler full bridge converter.

The full bridge converter circuit shown in FIGS. 1 and 2 is a circuit widely used as a low voltage DC-DC converter circuit. Particularly, a full bridge converter is widely used for a DC converter of 1 kW or higher.

These full bridge converters use phase shifting and can be used with high efficiency and wide load range while ensuring Zero Voltage Switching (ZVS) operation by using resonance of parasitic capacitor components of the transformer's leakage inductors and switches.

As shown in FIGS. 1 and 2, the full bridge converter 100 includes a switching unit 20 for alternately switching and outputting a direct current, and a switching unit 20 for switching the AC voltage output from the switching unit 20 down to a level of 12V And a rectifying unit 40 for rectifying the down voltage to a constant voltage.

Since the input voltage of the full bridge converter, that is, the voltage input from the high voltage battery to the switching unit 20 of the full bridge converter 100 is very different from the minimum voltage range of about 100 V to the maximum voltage of 450 V according to the vehicle type, The turn ratio and the number of turns of the transformer vary, and the design specifications of other power parts are inevitably changed.

That is, as the types of environment-friendly cars are diversified, such as hybrid electric vehicles, hydrogen fuel cell vehicles, plug-in hybrids, and electric vehicles, the size of the high voltage battery varies from 100V to 450V by vehicle type, Since the size is different, there is a problem that the low voltage DC-DC converter is difficult to be used in common. As a result, transformer specifications and semiconductor device specifications are different for each vehicle type. And the efficiency characteristics are also different.

In order to solve such a problem, the present invention provides a low-voltage DC-DC converter, in which a low-voltage DC-DC converter is applied to a wide input voltage (high-voltage battery cell voltage) And a boost converter coupled to the boost converter to provide a full bridge low voltage DC-DC converter that can be shared regardless of the type of the high voltage battery.

FIG. 3 is a circuit diagram showing a full bridge low voltage DC-DC converter according to an embodiment of the present invention, and FIG. 4 is a circuit diagram showing a full bridge low voltage DC-DC converter according to another embodiment of the present invention.

3 and 4, the full bridge converter 100 according to the present invention includes a switching unit 20 for alternately switching and outputting direct current, and a switching unit 20 for switching the AC voltage output from the switching unit 20 And a rectifying unit (40) for rectifying the down voltage to a constant voltage. The buck-boost circuit (20) includes a buck-boost circuit (10) are connected to each other.

The buck-boost circuit 10 operates in a buck mode for reducing the input voltage from the high-voltage battery and a boost mode for boosting the input voltage from the high-voltage battery, and the polarity of the circuit is reversed, In the (+) direction constantly.

To this end, the buck-boost circuit 10 comprises a buck switch 11 and a first diode 13 for the buck mode at the input of the low-voltage DC-DC converter, a boost switch 15 for the boost mode, And the inductor 12 connected between the buck switch and the boost switch are connected in an arrangement in which the polarity is not inverted.

More specifically, the buck-boost circuit 10 includes a buck switch 11 connected in series with a high-voltage battery, an inductor 12 connected in series with the buck switch 11, a buck switch 11, A second diode 14 connected in series with an output terminal of the inductor 12 and a second diode 14 connected in parallel between the inductor 12 and the second diode 14. The first diode 13 is connected in parallel between the inductor 12 and the inductor 12, And a boost switch 15 connected to the switch 15.

As the buck-boost circuit 10 is coupled to the input terminal of the full bridge converter, it is possible to increase and decrease the input voltage and to control the step-down of the input voltage. Therefore, regardless of the size of the high- It is possible to use the same circuit and element parts in the input voltage range and to adjust the output voltage (Vdc) value to the input terminal of the full bridge converter constantly.

Hereinafter, the operational flow of the buck-boost circuit having the above-described configuration will be described.

The full bridge converter according to the present invention operates with a fixed duty, and the output voltage can be controlled to a constant level by PWM control in a buck boost circuit.

First, a reference output voltage (Vdc) value output to the input terminal of the full bridge converter, that is, the switching unit 20, is determined in a control unit (not shown), and the high efficiency operation voltage is determined.

At this time, if the magnitude of the input voltage input from the high voltage battery to the buck-boost circuit 10 is greater than the reference output voltage Vdc, the buck-boost circuit 10 controls the buck switch 11 In which the boost switch 15 is always off.

That is, when the input voltage of the high voltage battery is larger than the reference voltage, the buck switch 11 repeatedly turns on / off according to the duty ratio determined by the control unit, The input voltage magnitude of the high voltage battery is reduced and output to the switching unit 20 of the full bridge converter in accordance with the reference output voltage Vdc.

More specifically, when the buck switch 11 is turned on, current flows to the inductor 12, energy is accumulated in the inductor 12, current flows to the capacitor and the switching unit 20, The inductor current, which is the energy stored in the inductor 12, flows through the capacitor and the switching unit 20 when the first diode 13 is turned off and the inductor current is increased until the buck switch 11 is turned on .

When the input voltage of the high-voltage battery is larger than the reference voltage, the buck switch 11 is periodically turned on / off according to a predetermined duty ratio in a state where the boost switch 15 is turned off, Smoothing the voltage of the pulse shape lower than the voltage and outputting it to the switching unit.

When the input voltage input from the high voltage battery to the buck-boost circuit 10 is smaller than the reference output voltage Vdc, the buck-boost circuit 10 controls the boost switch 15, such as a boost converter, The buck switch 11 is always operated in the on mode.

That is, when the input voltage level of the high voltage battery is smaller than the reference voltage, the boost switch 15 repeats on / off according to a duty ratio determined by the control unit, and the buck switch 11 is always turned on So that the input voltage magnitude of the high voltage battery is boosted and output to the switching unit 20 of the full bridge converter in accordance with the reference output voltage Vdc.

More specifically, when the boost switch 15 is turned on while the buck switch 11 is kept on, energy is accumulated in the inductor 12 while current flows through the inductor 12, and at the same time, The energy stored in the capacitor is consumed because the current does not flow to the switching unit 20 through the switching unit 20. On the other hand, when the boost switch 15 is turned off, the energy stored in the inductor 12 is added to the input voltage from the high- The voltage output through the diode 14 increases by the energy voltage accumulated in the inductor so that the voltage is increased.

When the input voltage of the high voltage battery is smaller than the reference voltage, the boost switch 15 is periodically turned on and off according to a predetermined duty ratio in a state where the buck switch 11 is turned on, A voltage higher than the voltage is output to the switching unit.

Thus, by operating the full bridge converter circuit with fixed duty and keeping the output voltage value to the switching unit constant using the buck-boost circuit, the converter can always be operated at a high efficiency operating point.

In addition, even if the specifications of the high-voltage battery are changed according to the type of vehicle, that is, the low-voltage DC-DC converter can be shared regardless of the type of the environmentally friendly vehicle, cost reduction is possible and high efficiency operation can be guaranteed at all times.

10: Buck-boost circuit
11: Buck Switch
12: Inductor
13: first diode
14: second diode
15: Boost switch
20:
30: Transformer
40: rectification part
100: Full bridge converter

Claims (4)

A switching unit 32 for alternately switching and outputting direct currents, a transforming unit 34 for bringing the alternating voltage output from the switching unit 32 down to a level of 12V usable in the vehicle, Voltage DC-DC converter including a rectifying section (36)
And a buck-boost circuit capable of outputting a voltage whose polarity is not inverted is connected to an input terminal of the switching unit.
The method according to claim 1,
The buck-boost circuit comprises:
A buck switch in series with a high voltage battery;
An inductor coupled in series with the buck switch;
A first diode connected in parallel with the buck switch;
A second diode connected in series with an output terminal of the inductor;
A boost switch connected in parallel between the inductor and the second diode;
Voltage DC-DC converter.
The method of claim 2,
Wherein the buck switch repeatedly turns on / off according to a predetermined duty ratio when the input voltage magnitude of the high voltage battery is greater than a reference voltage, while the boost switch always operates off.
The method of claim 2,
Wherein when the input voltage magnitude of the high voltage battery is smaller than the reference voltage, the boost switch repeats on / off according to a predetermined duty ratio, and the buck switch always operates on.

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