KR102212816B1 - Dc-dc converter and switching method thereof - Google Patents

Abstract

The DC-DC converter and its switching method according to an embodiment of the present invention are inventions capable of minimizing power loss by controlling the synchronization timing of the switching element of the inverter unit and the switching element of the rectifier unit, and are connected to the input terminal, An inverter unit including a fourth switching element; A transformer whose primary side receives a voltage from the inverter unit; A rectifying unit connected to the secondary side of the transformer and including fifth and sixth switching elements, and is disposed counterclockwise in the order of the first, second, fourth and third switching elements, and a closed loop And the secondary side of the transformer and the fifth and sixth switching elements are DC-DC converters forming a closed loop in a clockwise direction, and a turn-on time of the third and fourth switching elements, and A delay that is a difference time between the turn-on time of the third and fourth switching elements and the turn-off time of the fifth and sixth switching elements by synchronizing the turn-off time of the fifth and sixth switching elements Detecting time; The present invention relates to a DC-DC converter including the step of compensating the turn-off timing of the fifth and sixth switching elements by the delay time and a switching method thereof.

Description

DC-DC converter and its switching method {DC-DC CONVERTER AND SWITCHING METHOD THEREOF}

The present invention relates to a DC-DC converter and a switching method thereof.

The present invention relates to a DC-DC converter and a switching method thereof.

Hybrid vehicles equipped with both an engine and an electric motor as a power source are popular.

Hybrid vehicles are equipped with low-voltage (for example, 12V) batteries for engine and electronic equipment, and high-voltage (for example, 300V) batteries for electric motors.

In hybrid cars, since it is not common to have an alternator for charging low-voltage batteries, it is a step-down, insulated DC-DC that uses a high-voltage battery as an input power source for charging low-voltage batteries and for supplying power to electrical equipment. You need a converter. Since the recent increase in electrical equipment has increased its power consumption, it is necessary to convert the power of the KW order in this DC-DC converter.

In this case, heat generation due to losses in the DC-DC converter also increases, and the cooling device added for heat dissipation measures becomes larger and more weighty, thereby increasing the vehicle weight. Therefore, it is necessary to reduce the loss of the DC-DC converter not only for improving conversion efficiency, but also for reducing the amount of heat generated and reducing the weight of the cooling device.

There are many types of DC-DC converters, and a full-bridge method is known as a method suitable for high power conversion as an insulated switching method.

1 shows a circuit diagram of a conventional phase shift full bridge type DC-DC converter.

In the DC-DC converter 1 shown in Fig. 1, a series circuit made of switching elements QA and QB and a series circuit made of switching elements QC and QD are each of the input power supply Vin (input voltage vin). It is connected to both ends.

The transformer T is provided with a primary winding Np and a secondary winding Ns.

A resonant coil (Lr) is connected in series to the primary winding (Np), and one end of this series circuit (in this case, the resonant coil (Lr) side) is connected to the connection point of the switching elements (QA, QB), and the other end is It is connected to the connection point of the switching elements QC and QD.

The switching elements (QA, QB, QC, QD) are power MOSFETs for power, and the description is omitted, but includes an internal capacitance between the drain and the source and a body diode whose direction from the source to the drain is in the forward direction. Further, the gate, which is a control terminal, is connected to a control circuit not shown.

One end of the secondary winding Ns provided in the transformer T is connected to the negative electrode of the rectifying diode D1, and the other end is connected to the negative electrode of the rectifying diode D2.

The positive poles of the rectifying diodes Dl and D2 are connected to each other and at the same time connected to one end (+ side) of the output terminal Vout through a choke coil La. Further, the secondary winding Ns is divided into secondary windings Ns1 and Ns2 through an intermediate tap, and the intermediate tap is connected to the other end (1 side) of the output terminal Vout.

A smoothing capacitor Ca is connected between one end of the output terminal Vout and the other end.

Furthermore, a series circuit consisting of a resistor (R1) and a capacitor (C1) is connected in parallel to the rectifier diode (D1), and a series circuit consisting of the resistor (R2) and a capacitor (C2) is parallel to the rectifier diode (D2). Is connected to.

The series circuit consisting of this resistor and a capacitor constitutes RC snubber circuits 2 and 3, respectively.

In the DC-DC converter (1) configured in this way, switching elements (QA and QB) are alternately turned on and off with almost 50% duty by having a short dead time to be turned off. Repeat. The switching elements (QC and QD) are similarly turned on and off with 50% duty. The switching frequency is constant on either side.

When the switching elements (QA and QD) are on, the switching elements (QB and QC) are turned off, and the resonance coil (Lr) side is in the series circuit between the resonance coil (Lr) and the primary winding (Np). The input voltage vin is applied as positive.

Conversely, when the switching elements QB and QC are on, the switching elements QA and QD are turned off, and the resonance coil Lr side is applied as negative.

When the switching elements (QA and QC) are on and the switching elements (QB and QD) are off, and the switching elements (QB and QD) are on, the switching elements (QA and QC) are When it is off, the potentials at both ends of this series circuit become equal, so no voltage is applied to this series circuit.

The relationship between the on and off timing of the switching elements QA and QB and the on and off timing of the switching elements QC and QD is not fixed, and the illustration is omitted. By controlling this through the output voltage detection & feedback means, the power transmission amount is changed and the output voltage is stabilized.

For example, if the switching element QA is turned on and the switching element QD is immediately turned on, until the next switching element QA is turned off. Since the input voltage is applied to the primary winding Np, the amount of power transmission increases.

Conversely, if the switching element QD is in the same relationship as not being turned on until immediately before the switching element QA turns off, the time for applying the input voltage to the primary winding Np is shortened. , The amount of power transmission becomes small.

This driving method does not directly control the duty of each switching element, but only controls the timing of switching of the switching elements (QA, QB) and the switching elements (QC, QD), and the phase shift control method It is called.

Further, the DC-DC converter 1 has a resonance coil Lr connected in series to the primary winding Np, but this resonance coil Lr includes each switching element QA, QB, QC, QD. It is installed for zero voltage switching (ZVS).

That is, it is configured to turn on when the voltage between both ends of the switching element (the voltage between the drain and the source is almost zero) by using the internal capacitance of each switching element and the resonance with the resonance coil Lr. The inductance value of Lr) is determined based on the relationship with the size of the internal capacitance of the switching element.

As described above, in the phase shift full-bridge DC-DC converter, zero voltage switching of the switching element can be achieved relatively simply by installing the resonance coil Lr.

In addition, in a full-bridge DC-DC converter that performs phase shift control while realizing such zero voltage switching, it is necessary to appropriately control four switching elements. This control method is already common and is used for controlling IC is also commercially available (for example, UC3875 manufactured by Texas Instruments). By the way, the secondary side of the DC-DC converter 1 is a center-tap type rectifier circuit using two general rectifier diodes.

When a voltage with the resonant coil (Lr) side positive is applied to the primary side, a voltage that makes the rectifier diode (D1) forward is generated in the secondary winding (Ns), and the secondary winding (Ns1) → rectifier diode ( A current flows in the path of D1) → choke coil (La) → load (not shown) → secondary winding (Ns1).

This current increases with time.

Next, when the voltage on the primary side disappears, current flows in the same path, but the current value decreases with time.

Next, when a voltage with a negative resonant coil (Lr) is applied to the primary side, on the contrary, a voltage in which the rectifier diode (D2) goes forward is generated in the secondary winding (Ns), thereby flowing through the rectifier diode (D1). The current quickly becomes zero, and on the contrary, the current flows in the path of the secondary winding (Ns2) → rectifier diode (D2) → choke coil (La) → load (not shown) → secondary winding (Ns2). And this repeats itself.

Among the above operations, the current flowing through the rectifier diode D1 does not stop when the forward current becomes zero, and the current (reverse recovery current) flows in the reverse direction only for the reverse recovery time of the diode.

This reverse recovery current is the rectifier diode (D1) → secondary winding (Ns1) → secondary winding (Ns2)

→ It becomes a short circuit path called rectifier diode (D2) → rectifier diode (D1).

Since this reverse recovery current stops abruptly, a surge voltage is generated in the secondary winding Ns1 by this, and is applied to the rectifier diode D1 in the reverse direction.

Rectifier diodes having a high withstand voltage such as those capable of withstanding this surge voltage generally tend to have a large forward voltage drop (Vf).

When the forward voltage drop Vf increases, the loss when current flows in the forward direction increases, which is undesirable in terms of conversion efficiency and heat generation.

Therefore, the RC snubber circuit 2 in which the resistor R1 for absorbing the surge voltage and the capacitor C1 are connected in series is provided in the rectifier diode D1.

Similarly, in order to absorb the surge voltage caused by the reverse recovery current of the rectifier diode D2, a RC snubber circuit 3 in which a resistor R2 and a capacitor C2 are connected in series is installed in the rectifier diode D2.

In this case, the current due to the surge voltage flows through the resistor R1 (or R2) and is converted into heat.

This is a loss for the entire DC-DC converter, but since a relatively small forward voltage drop can be used as the rectifier diodes (D1 and D2), the loss when current flows in the forward direction can be reduced, and the RC snubber circuit is Compared to the case where there is no, it is possible to reduce the overall loss.

Since the conventional DC/DC converter uses a hard switching method for controlling the output voltage, there is a limit to improving the efficiency of power conversion due to a switching loss that occurs when a switching element is turned on or off.

In addition, such a hard-switching DC/DC converter has a disadvantage in that power conversion efficiency decreases due to an increase in the number of switching frequencies to reduce switching stress and ripple voltage, and when the switching element is'on' or'off', current or voltage The slope of is very large, so there is a limit to the efficiency improvement.

Recently, in designing a DC/DC converter, there is a need to provide a DC/DC converter for improving power conversion efficiency by minimizing switching loss or rectification loss.

The DC-DC converter and its switching method according to an embodiment of the present invention provide a DC-DC converter capable of minimizing power loss by controlling the synchronization timing of the switching element of the inverter unit and the switching element of the rectifying unit and a switching method thereof.

A DC-DC converter switching method according to an embodiment of the present invention includes: an inverter unit connected to an input terminal and including first to fourth switching elements; A transformer whose primary side receives a voltage from the inverter unit; A rectifying unit connected to the secondary side of the transformer and including fifth and sixth switching elements, and is disposed counterclockwise in the order of the first, second, fourth and third switching elements, and a closed loop And the secondary side of the transformer and the fifth and sixth switching elements are DC-DC converters forming a closed loop in a clockwise direction, and a turn-on time of the third and fourth switching elements, and A delay that is a difference time between the turn-on time of the third and fourth switching elements and the turn-off time of the fifth and sixth switching elements by synchronizing the turn-off time of the fifth and sixth switching elements Detecting time; And compensating for the turn-off time of the fifth and sixth switching elements by the delay time.

A DC-DC converter switching method according to an embodiment of the present invention, wherein the transformer is a tap transformer DC-DC converter switching method.

In the DC-DC converter switching method according to an embodiment of the present invention, the DC-DC converter further comprises an L-C filter connected between the tap of the tap transformer and the sixth switching element.

In the DC-DC converter switching method according to an embodiment of the present invention, the delay time is a duty ratio of a time taken by a duty ratio for generating a required output voltage per cycle and a time at which the fifth and sixth switching elements are turned off. DC-DC converter switching method that corresponds to the range between the time occupied per cycle.

In the DC-DC converter switching method according to an embodiment of the present invention, the delay time is a DC-DC that varies according to a leakage inductance and a commutating inductor included in the inverter or a leakage inductance of the transformer. Converter switching method.

In the DC-DC converter switching method according to an embodiment of the present invention, the sixth switching element is turned on at the turn-on time of the first switching element, and the fifth switching element is turned on at the turn-on time of the second switching element. DC-DC converter switching method.

In the DC-DC converter switching method according to an embodiment of the present invention, a DC-DC converter switching method in which the turn-off time of the fifth and sixth switching elements is delayed by the delay time.

A DC-DC converter according to an embodiment of the present invention includes an inverter unit connected to an input terminal and including first to fourth switching elements; A transformer whose primary side receives a voltage from the inverter unit; A rectifier connected to the secondary side of the transformer and including fifth and sixth switching elements; And a control unit for controlling the turn-on/off timing of the first to sixth switching elements, and are arranged counterclockwise in the order of the first, second, fourth, and third switching elements and constitute a closed loop. , The secondary side of the transformer and the fifth and sixth switching elements form a closed loop in a clockwise direction, and the control unit includes a time point when the third and fourth switching elements are turned on, and the fifth and sixth switching elements The fifth and sixth switching elements are turned off by a delay time that is a difference time between a turn-on time of the third and fourth switching elements and a turn-off time of the fifth and sixth switching elements by synchronizing turn-off time of DC-DC converter that compensates for the point in time.

In the DC-DC converter according to an embodiment of the present invention, the control unit delays the turn-off time of the fifth and sixth switching elements by the delay time.

In the DC-DC converter according to an embodiment of the present invention, the transformer is a tap transformer, and the DC-DC converter further comprises an LC filter connected between the tap of the tap transformer and the sixth switching element. .

In the DC-DC converter according to an embodiment of the present invention, the delay time is a duty ratio of a time taken by a duty ratio for generating a required output voltage per cycle and a time at which the fifth and sixth switching elements are turned off per cycle. DC-DC converters corresponding to the range between the occupied times.

In the DC-DC converter according to an embodiment of the present invention, the delay time is a DC-DC converter that varies according to a leakage inductance and a commutating inductor included in the inverter or a leakage inductance of the transformer.

In the DC-DC converter according to an embodiment of the present invention, the control unit turns on the sixth switching element at a turn-on time of the first switching element, and the fifth switching element is turned on at a turn-on time of the second switching element. DC-DC converter that turns on.

In a DC-DC converter according to an embodiment of the present invention, the controller turns off the sixth switching element after a delay time when the third switching element is turned on.

In the DC-DC converter according to an embodiment of the present invention, the control unit turns off the fifth switching element after a delay time when the fourth switching element is turned on.

The DC-DC converter and its switching method according to an embodiment of the present invention have an effect of minimizing power loss by controlling the synchronization timing of the switching element of the inverter unit and the switching element of the rectifying unit.

1 is a circuit diagram of a conventional phase shift full-bridge type DC-DC converter.
2 is a circuit diagram of a DC-DC converter according to an embodiment of the present invention.
3 is a graph showing an operation waveform of the DC-DC converter according to FIG. 2.
4 to 7 are circuit diagrams showing the operation of the DC-DC converter according to an embodiment of the present invention.
8 is a graph of a switching method of a DC-DC converter according to an embodiment of the present invention.
9 is a circuit diagram showing a DC-DC converter according to an embodiment of the present invention.

Hereinafter, with reference to the drawings of a DC-DC converter and a switching method thereof according to an embodiment of the present invention will be described in detail. The following embodiments are provided as examples in order to sufficiently convey the spirit of the present invention to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In addition, in the drawings, the size and thickness of the device may be exaggerated for convenience. Throughout the specification, the same reference numbers indicate the same elements.

2 is a circuit diagram of a DC-DC converter according to an embodiment of the present invention.

Referring to FIG. 2, a DC-DC converter 100 according to an embodiment of the present invention may include an inverter unit 200, a tap transformer 400, a rectifier 500, and an L-C filter 600.

Additionally, the inductor Lc connected between one side of the tap transformer 400 and one side of the first switching element 110 may be an inductor formed according to leakage inductance and commutating inductor, and may be intentionally added. I can.

3 is a diagram illustrating an operation waveform of the DC-DC converter according to FIG. 2.

The inverter unit 200 may be connected to both ends of the input voltage Vin and may switch the input voltage Vin to output a voltage to be input to the tap transformer 400 below.

In addition, the inverter unit 200 may be composed of four Insulated Gate Bipolar Transistors (IGBTs), or may be composed of a MOSFET.

In the inverter unit 200, a switch is connected in a full-bridge form, so that a pair of switches are alternately turned on (ON) and off (OFF), and the input voltage Vin can be supplied to the tap transformer 400. have.

In more detail, the inverter unit 200 includes a first switch 110, a second switch 120, a third switch 130, and a fourth switch 140, and the first switch 110 and The second switch 120 is connected in series with each other, and the third switch 130 and the fourth switch 140 are connected in series with each other and in parallel with the first switch 110 and the second switch 120. Can be connected to.

That is, the first switch 110 and the second switch 120, the third switch 130, and the fourth switch 140 are connected in series, respectively, and are connected in parallel to the input voltage Vin. It can be a form.

The first to fourth switching elements 110, 120, 130, 140 constitute a closed loop, and the first switching element 110, the second switching element 120, the fourth switching element 140, and the fourth 3 Switching elements 130 may be arranged counterclockwise in order.

In addition, an end between the first switch 110 and the second switch 120, the third switch 130 and the fourth switch 140 are connected to both ends of the input side of the tap transformer 400 It can form a full-bridge.

In addition, the first switch 110 and the fourth switch 140 are simultaneously ON or OFF, and the second switch 120 and the third switch 130 are simultaneously turned on. It is (ON) or off (OFF), the first switch 110 and the fourth switch 140 may be alternately turned on (ON) or off (OFF) with each other.

That is, when the first switch 110 and the fourth switch 140 are turned on (ON), the second switch 120 and the third switch 130 are turned off (OFF), the first When the switch 110 and the fourth switch 140 are turned off, the second switch 120 and the third switch 130 may be turned on.

In addition, the sixth switching element 160 is turned on when the first switching element 110 is turned on, and the fifth switching element is switched on when the second switching element 120 is turned on. The device 150 may be turned on.

In addition, the graph of FIG. 3 shows the switching waveforms of the first to fourth switches 110, 120, 130, and 140. As shown, the first switch 110 and the fourth switch 140 It can be seen that the second switch 120 and the third switch 130 are alternately turned on (ON) or off (OFF).

When summarized in a table, it is shown in Table 1.

Meanwhile, the tap transformer 400 may serve to increase or decrease the voltage to a predetermined voltage by receiving the AC voltage output from the inverter unit 200.

In addition, the tap transformer 400 is a transformer provided with a tap 410 that divides the output on the output side and allows a user to adjust the output.

In addition, the tap transformer 400 may be provided as an insulated transformer, and by insulating the inverter unit 200 and the rectifying unit 500, the input side and the output side can be safely protected from burnout or power accident. have.

The rectifier 500 may full-wave rectify the output voltage of the tap transformer 400, and the L-C filter 600 may smooth the full-wave rectified output voltage to output a DC voltage.

In addition, the rectifier 500 may be composed of a MOSFET switch, may include a fifth switching element 150 and a sixth switching element 160, each switching element is a tap of the tap transformer 400 Output voltages alternately output from both sides based on 410 may be output to the LC filter 600, respectively. Accordingly, the rectifying unit 500 may reduce the number of switching elements compared to when the switching elements are configured as a full-bridge.

Meanwhile, the secondary side of the transformer 400 and the fifth and sixth switching elements 150 and 160 may form a closed loop in a clockwise direction in the order listed above.

One end of the fifth switching element 150 is connected to one end of the tap transformer 400, and the sixth switching element 160 has one end connected to the other end of the fifth switching element 150, , The other end may be connected to the other end of the tap transformer 400.

In addition, one end of the L-C filter 600 may be connected to the tab 410 and the other end may be connected to one end of the sixth switch element 160.

Referring to FIG. 3, the fifth switching element 150 is turned on and off in synchronization with the second and fourth switching elements 120 and 140 of the inverter unit 200, and the fifth switching element 150 is 6 The switching element 152 may be turned on or off in synchronization with the first and third switching elements 110 and 123.

Specifically, the fifth switching element 150 is turned on when the second switching element 120 is turned on, and is turned off when the fourth switching element 140 is turned on. Can be. In addition, the sixth switching element 160 is turned on when the first switching element 120 is turned on, and is turned off when the third switching element 130 is turned on. I can.

<Operation relationship of the embodiment of the present invention>

4 to 7 are circuit diagrams showing the operation of the DC-DC converter according to an embodiment of the present invention.

Referring to Table 1 and FIGS. 2 to 7, an operation method of the DC-DC converter 100 according to an embodiment of the present invention will be described.

First, an operation method of the DC-DC converter 100 according to the On/Off operation of the switching elements 110, 120, 130, 140, 150, and 160 will be described.

<Mode 1>

Referring to Table 1 and FIGS. 2 and 4, looking at the case of mode 1, the first switching element 110 and the fourth switching element 140 are turned off, and the second switching element 120 and the third switching element When 120 is ON, the fifth switching element 150 is ON and the sixth switching element 160 is OFF, as shown in FIG. 4.

In this case, the voltage Vab may be the sum of the positive inductor voltage (VL) and the negative input voltage (Vin).

In the graph of FIG. 3, it can be seen that the voltage Vab has a negative voltage.

In this case, mode 1 may be divided into two time periods, a first time period T1 and a second time period T2.

In the first time period T1, a voltage across the capacitor is formed due to a rapid increase in the magnitude of the current flowing through the primary-side transformer. Therefore, the voltage Vab has the first voltage.

In the second time period T2, a steady state is reached, and the voltage Vab has a second voltage.

The magnitude of the first voltage is smaller than the magnitude of the second voltage. (However, considering the negative sign, the first voltage is higher than the second voltage)

<Mode 2>

Referring to Table 1, Figures 3, and 5, looking at the case of mode 2, the first switching element 110 and the third switching element 130 are turned on, and the second switching element 120 and the fourth switching element When 140 is OFF, the fifth switching element 150 is ON, and the sixth switching element 160 is ON, as shown in FIG. 5.

In this case, the voltage Vab has a potential of zero, and the magnitude of the current flowing through the primary-side transformer decreases.

<Mode 3>

Referring to Table 1 and FIGS. 3 and 6, looking at the case of mode 3, the first switching element 110 and the fourth switching element 140 are turned on, and the second switching element 120 and the third switching element When 130 is OFF, the fifth switching element 150 is OFF, and the sixth switching element 160 is ON, as shown in FIG. 6.

In this case, the voltage Vab has a positive voltage.

At this time, mode 3 may be divided into two time periods, a third time period T3 and a fourth time period T4.

In the third time period T3, a voltage across the capacitor C is formed due to a rapid increase in the magnitude of the current flowing through the primary-side transformer. Therefore, the voltage Vab has a third voltage.

In the fourth time period T4, a steady state is reached, and the voltage Vab has a fourth voltage.

The magnitude of the third voltage is smaller than the magnitude of the fourth voltage.

<Mode 4>

Referring to Table 1, Figures 3, and 7, in the case of mode 4, the first switching element 110 and the third switching element 130 are turned off, and the second switching element 120 and the fourth switching element When 140 is ON, the fifth switching element 150 is ON, and when the sixth switching element 160 is ON, as shown in FIG. 7.

In this case, the voltage Vab has zero potential, and the magnitude of the current flowing through the primary transformer decreases.

As described above, it can be confirmed that the fifth and sixth switching elements 150 and 160 are switched in synchronization with the first to fourth switching elements 110, 120, 130 and 140.

Switching losses can be reduced according to this synchronization method.

Comparing the rectification losses of the fifth and sixth switching elements 150 and 160 of the rectifying unit 500 and the body diode elements of the fifth and sixth switching elements 150 and 160, the rectification of the body diode element The loss is expressed as the product of the voltage across the body diode (V _F ) and the output current (i _D ), and is shown in Equation 1 below.

In addition, the rectification loss of the MOSFET switch is expressed as the product of the equivalent resistance (R _DS ) and the output current (io) when the MOSFET switch is'ON', and is shown in Equation 2 below.

Comparing Equations 1 and 2 above, since the R _DS value is very small, the fifth and sixth switching elements 150 and 160 have a small value of R _DS instead of a body diode having a high V _F in the ON period. Loss of the fifth and sixth switching elements 150 and 160 may be reduced by passing a furnace current.

However, referring to the graph of FIG. 3, it can be seen that an additional loss still occurs during the Td time period between the first time section and the third time section.

Specifically, referring to FIG. 3, looking at VDS_E, which is the voltage across both ends of the fifth switching element 150, when the fifth switching element 150 is turned off in Mode 3, the fifth switching element ( A voltage Vf, which is a drop voltage of the body diode, is applied to 150), and a current flows through the fifth switching element 150.

That is, it can be seen that an additional loss occurs during the time Td, which is the third time period T3.

In addition, after Mode 4, looking at VDS_F, which is the voltage across both ends of Fig. 2 and the sixth switching element 160 in Mode 1, when the sixth switching element 160 is OFF in Mode 1, during the first time period T1. A voltage Vf, which is the drop voltage of the body diode, is applied to the sixth switching element 160 and a current flows through the sixth switching element 160. Therefore, an additional loss occurs during time Td, which is the first time period T1.

In order to solve this and minimize the loss, the fifth and sixth switching elements 150 and 160 are turned on during the Td time period. It is necessary to control OFF.

This will be described in detail through Table 2 and Fig. 8, which is a graph of a switching method of a DC-DC converter according to an embodiment of the present invention.

According to the graph of FIG. 3, an additional loss occurs during a time Td, which is a third time period T3.

Therefore, as shown in FIG. 8, the OFF time point of the fifth switching element 150 is the start time point of the fourth time section T4, which is the time point at which the third time section T3 ends, that is, after a Td time delay. Adjust by the viewpoint.

Through this, the fifth switching element 150 is turned on even in the Td period, which is the third time period T3, thereby reducing losses caused by current flowing through the body diode, thereby maximizing the efficiency of the DC-DC converter.

In addition, after Mode 4, when returning to Mode 1, additional loss occurs during Td time, which is the first time period T1 as shown in the graph of FIG. 3, so that the first time period T1 as shown in FIG. The time point of OFF of the sixth switching element 160 is adjusted to a time point at which the first time period T1 ends, that is, a time point after time Td, which is the start time point of the second time period T2.

Through this, the sixth switching element 160 is turned on even in the Td period, which is the first time period T1, thereby reducing losses caused by current flowing through the body diode, thereby maximizing the efficiency of the DC-DC converter.

In this way, by changing the synchronization method of the DC-DC converter 100 having the above-described synchronization method, that is, in synchronization with the ON/OFF time of the primary switching elements 110, 120, 130, 140, the secondary switching elements Instead of determining ON/OFF of (150, 160), by determining OFF of the secondary switching elements 150 and 160 after compensation for Td time, the secondary switching elements 150, 160) is turned ON, reducing the loss caused by the current flowing through the body diode and maximizing the efficiency of the DC-DC converter.

A method of determining the Td time will be described.

The Td time is defined as a delay time.

The turn-on time of the third and fourth switching elements by synchronizing the turn-on time of the third and fourth switching elements and the turn-off time of the fifth and sixth switching elements And a difference time between the turn-off time of the fifth and sixth switching elements is defined as a delay time.

Specifically, by synchronizing a turn-on time of the third switching element 130 and a turn-off time of the sixth switching element 160, the third switching element 130 The turn-on time and the turn-off time of the sixth switching element 160 are not synchronized with each other, and are different by the delay time Td.

Similarly, by synchronizing the turn-on time of the fourth switching element 140 and the turn-off time of the fifth switching element 150, the turn-on of the fourth switching element 140 The time point and the turn-off time point of the fifth switching element 150 are not synchronized with each other, and differ by a delay time Td. Accordingly, the turn-off timing of the fifth and sixth switching elements 150 and 160 is compensated for by the delay time Td, that is, the body diode is turned off by delaying the delay time Td for the delay time Td. It can minimize the loss that occurs in

The delay time (Td) is a range between a time taken by a duty ratio for generating a required output voltage per cycle and a time taken by a duty ratio of the turn-off times of the fifth and sixth switching elements 150 and 160 per cycle DC-DC converter equivalent to.

In order to specifically describe a method of deriving the delay time Td, it will be described through Equations 3 to 5 below.

The output voltage can be expressed by Equation 3 below according to the input/output relationship.

Vo is the output voltage, Vin is the input voltage, Np is the number of turns on the primary side of the transformer, Ns is the number of turns on the secondary side, Dc is the command duty to generate the required output voltage, Ts is the switching period, Ts /2 means the half cycle of switching.

In FIGS. 3 and 8, the second and fourth time periods T2 and T4, that is, the turn-off time of the fifth and sixth switching elements 150 and 160 may be defined as an effective duty time period.

When the effective duty time period is expressed by D _eff , it can be expressed by Equation 4 below.

Therefore, it can be expressed by Equation 5 below from the above equations.

The Dc is the duty ratio for generating the output voltage, and in Dc, c is the acronym of Command.

The T _d is as a delay because of a leakage inductance of an inductor (Lc) component and the leakage inductance (leakage inductance), and the current inductor (commutating inductor), the transformer (400) included in the inverter unit 200, the T _d time vary I can.

Accordingly, if the switching timing of the secondary-side switch elements 150 and 160 is determined according to the relational expression regarding Td, power efficiency can be maximized by reducing losses.

That is, duty loss due to leakage inductance Lc of the transformer can be minimized.

9 is a circuit diagram showing a DC-DC converter according to an embodiment of the present invention.

Referring to FIG. 9, the DC-DC converter 100 may further include a control unit 300.

According to an embodiment of the present invention, the inverter unit 200 connected to the input terminal to which the input voltage is supplied and including the first to fourth switching elements 110, 120, 130, 140, the primary side transformer and the secondary side Including a transformer, having a turn ratio of Np: Ns, the primary side is connected to the transformer 400 receiving a voltage from the inverter unit 200, the secondary side of the transformer 400, the fifth and sixth switching Including the rectifier 500 including the elements 150 and 160, the turn-on/off time of the first to sixth switching elements 110, 120, 130, 140, 150, 160 It may further include a control unit 300 to control.

In addition, the first, second, fourth, and third switching devices 110, 120, 140, and 130 are arranged in a counterclockwise direction in order, and a closed loop may be formed.

The secondary side of the transformer 400 and the fifth and sixth switching elements 150 and 160 may form a closed loop in a clockwise direction.

The controller 300 turns on the sixth switching element 160 at a turn-on time of the first switching element 110, and turns on the fifth switching element 150 at a turn-on time of the second switching element 120. ) Can be controlled to turn on.

In addition, the control unit 300 synchronizes the turn-on time of the third and fourth switching elements 130 and 140 with the turn-off time of the fifth and sixth switching elements 150 and 160, And a delay time (Td) that is a difference time between the turn-on time of the fourth switching elements 130 and 140 and the turn-off time of the fifth and sixth switching elements 150 and 160. 150, 160) can be compensated for the turn-off time.

In this way, the controller 300 delays the turn-off times of the fifth and sixth switching elements 150 and 160 by a delay time Td and then turns them off, so that the fifth and sixth switching elements 150 and 160 Power loss that occurs when 160 is forcibly turned off in synchronization with the third and fourth switching elements 130 and 140, that is, during the delay time Td, can be prevented.

In the detailed description of the present invention described above, it has been described with reference to preferred embodiments of the present invention, but those skilled in the art or those of ordinary skill in the relevant technical field of the present invention described in the claims to be described later It will be understood that various modifications and changes can be made to the present invention without departing from the spirit and technical scope. Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be determined by the claims.

2, 3 RC snubber circuit
100 DC-DC converters
110 first switching element
120 second switching element
130 third switching element
140 fourth switching element
150 5th switching element
160 sixth switching element
200 inverter unit
300 control unit
400 transformer
500 rectifier
600 LC filter part

Claims (15)

An inverter unit connected to the input terminal and including first to fourth switching elements;
A transformer whose primary side receives a voltage from the inverter unit;
Including; a rectifier connected to the secondary side of the transformer and including fifth and sixth switching elements,
The first, second, fourth and third switching elements are arranged in a counterclockwise direction in order and constitute a closed loop,
The secondary side of the transformer and the fifth and sixth switching elements are DC-DC converters forming a closed loop in a clockwise direction,
The turn-on time of the third and fourth switching elements by synchronizing the turn-on time of the third and fourth switching elements and the turn-off time of the fifth and sixth switching elements Detecting a delay time that is a difference time between the turn-off time of the fifth and sixth switching elements;
And compensating for the turn-off time of the fifth and sixth switching elements by the delay time. The method of claim 1,
The transformer is a tap transformer DC-DC converter switching method. The method of claim 2,
The DC-DC converter further comprises an LC filter connected between the tap of the tap transformer and the sixth switching element. The method of claim 1,
The delay time is a DC-DC converter switching that corresponds to a range between the time that the duty ratio for generating the required output voltage takes per cycle and the duty ratio of the turn-off times of the fifth and sixth switching elements per cycle. Way. The method of claim 4,
The delay time varies according to a leakage inductance and a commutating inductor included in the inverter unit or a leakage inductance of the transformer. The method of claim 1,
The DC-DC converter switching method in which the sixth switching element is turned on when the first switching element is turned on, and the fifth switching element is turned on when the second switching element is turned on. The method of claim 1,
The DC-DC converter switching method in which the turn-off timing of the fifth and sixth switching elements is delayed by the delay time. An inverter unit connected to the input terminal and including first to fourth switching elements;
A transformer whose primary side receives a voltage from the inverter unit;
A rectifier connected to the secondary side of the transformer and including fifth and sixth switching elements; And
Including; a control unit for controlling the turn on / off timing of the first to sixth switching elements,
The first, second, fourth and third switching elements are arranged in a counterclockwise direction in order and constitute a closed loop,
The secondary side of the transformer and the fifth and sixth switching elements form a closed loop in a clockwise direction,
The control unit,
The third and fourth switching elements synchronize the turn-on time and the turn-off time of the fifth and sixth switching elements, so that the third and fourth switching elements turn-on time and the fifth and sixth switching elements A DC-DC converter that compensates for the turn-off time of the fifth and sixth switching elements by a delay time that is a difference time between the turn-off time. The method of claim 8,
The control unit is a DC-DC converter for delaying the turn-off timing of the fifth and sixth switching elements by the delay time. The method of claim 8,
The transformer is a tap transformer,
The DC-DC converter further comprises an LC filter connected between the tap of the tap transformer and the sixth switching element. The method of claim 8,
The delay time is a DC-DC converter corresponding to a range between a time taken by a duty ratio for generating a required output voltage per cycle and a time taken by a duty ratio of a turn-off time of the fifth and sixth switching elements per cycle. The method of claim 8,
The delay time is a DC-DC converter that varies depending on a leakage inductance and a commutating inductor included in the inverter or a leakage inductance of the transformer. The method of claim 8,
The control unit,
A DC-DC converter in which the sixth switching element is turned on when the first switching element is turned on, and the fifth switching element is turned on when the second switching element is turned on. The method of claim 13,
The control unit,
A DC-DC converter for turning off the sixth switching element after a delay time when the third switching element is turned on.
The method of claim 13,
The control unit,
DC-DC converter for turning off the fifth switching element after a delay time when the fourth switching element is turned on.

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