KR20100114751A - Bi-directional non-isolated dc-dc converter and control method thereof - Google Patents

Abstract

PURPOSE: The device having the current rate in which the bidirectional non-insulating DC - D C converter and control method low is used and the capacity of the capacitor filter is reduced. CONSTITUTION: The low voltage circuit includes the second switch(D). The high voltage side circuit includes the second inductor. The voltage detecting portion detects the voltage of the high voltage power source and low-voltage power. Controller controls the duty of the first switch to the fourth switch by using the output of the voltage detecting portion.

Description

Bi-Directional Non-isolated DC-DC Converter and Control Method

The present invention relates to a non-isolated DC-DC converter capable of power flow in both directions and a control method thereof, and more particularly, to operate in a continuous conduction mode (CCM) and all switches operate with zero voltage switching (ZVS). A bidirectional non-isolated DC-DC converter for performing the present invention and a control method thereof.

Recently, as a kind of environmentally friendly vehicle, a hybrid vehicle using a conventional internal combustion engine and a battery combined with a power source has been developed. The hybrid vehicle is driven by an electric motor at start and start, and an electric motor and The car is operated by the internal combustion engine.

A general driving system of such a hybrid vehicle and a bidirectional DC-DC converter circuit used therein are illustrated in FIGS. 1 and 2, respectively. In the driving system of FIG. 1, a large capacity high voltage battery is connected to an input side of a power conversion system and a motor is connected to an output side.

In addition, an inverter for driving the motor and a DC-DC converter for boosting the voltage of the high voltage battery to a high voltage are connected between the high voltage battery and the motor.

In this case, the DC-DC converter may perform a boost operation for delivering power to the motor by discharging the high voltage battery when the motor is driven and a buck operation for charging the regenerative energy of the motor with the high voltage battery. Power flow must be possible in both directions.

The bidirectional DC-DC converter according to the related art shown in FIG. 2 has a simple switching configuration, which is easy to control, and when switching is performed in a discontinuous conduction mode (DCM), soft switching is performed at all switches. have.

However, the bidirectional DC-DC converter according to the related art requires a device having a large rating due to a high peak current in a large power application when operating with DCM, a large amount of heat generated by the iron loss of the inductor, and Due to problems such as an increase in the capacity of the capacitor filter due to the large current ripple, there is a big disadvantage in efficiency and volume.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to design a low current ripple of an inductor in a large power application to use a device having a low current rating and to reduce the capacity of a capacitor filter. It is to provide a non-isolated DC-DC converter and a control method thereof.

In addition, another object of the present invention is to operate as a CCM to reduce the heat loss by reducing the inductor iron loss, all the switches by performing a zero voltage switching bidirectional non-isolated DC-DC to improve the operating efficiency by reducing the switching loss It is to provide a converter and a control method thereof.

In order to achieve the above object, the bidirectional non-isolated DC-DC converter according to the present invention is a bidirectional non-isolated DC-DC converter having a low voltage power supply and a high voltage power supply, the first being sequentially connected to the low voltage power supply in series. A low voltage side circuit having an inductor, a first switch and a first capacitor, and a second switch branched at a first contact between the first inductor and the first switch and connected in parallel to the first switch and the first capacitor, wherein A second capacitor connected in series to a high voltage power source, a third switch and a fourth switch connected in parallel to the second capacitor and connected in series with each other, and a second contact point and the first contact point between the third switch and the fourth switch; A first switch to a fourth switch such that the high voltage side circuit having a second inductor for connecting the circuits and the converter are operated by CCM and each switch is turned on by zero voltage switching. Characterized in that a control unit for controlling the operation.

The apparatus may further include a voltage detector configured to detect voltages of the low voltage power and the high voltage power, and the controller controls the duty of the first to fourth switches by using the output of the voltage detector.

The control unit may control the first switch and the third switch to have a duty by complementary switching with respect to the second switch and the fourth switch, respectively.

The controller may control the duty of the second switch and the fourth switch to be the same.

In addition, the first switch to the fourth switch is characterized in that the MOSFET or IGBT.

As described above, the bidirectional non-isolated DC-DC converter and the control method thereof according to the present invention can use a device having a low current rating because the current ripple of the inductor can be designed to be low by the CCM operation of the converter in a large power application. And the capacity of the capacitor filter can be reduced.

In addition, since the bidirectional non-isolated DC-DC converter and the control method thereof according to the present invention operate in the CCM, there is an advantage that the heat generation can be reduced by reducing the iron loss of the inductor.

In addition, the bidirectional non-isolated DC-DC converter and the control method thereof according to the present invention have an advantage that the efficiency of the converter can be improved as a whole by reducing switching losses because all switches perform zero voltage switching.

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

3 is a circuit diagram illustrating a configuration of a bidirectional non-isolated DC-DC converter according to an embodiment of the present invention.

Two-way non-isolated DC-DC converter according to the present invention, the low voltage power source (V _LOW) and the first inductor sequentially connected in series with the low voltage power source _{(V LOW) (L 1)} , the first switch (S1) and the first A branch connected at the first contact between the capacitor C ₁ and the first inductor L ₁ and the first switch S1 and connected in parallel to the first switch S1 and the first capacitor C ₁ ; And a low voltage side circuit having two switches S2.

Further, the second capacitor (C _2), the second capacitor (C ₂₎ a two-way non-isolated DC-DC converter is connected in series with the high voltage power source (V _High), and the high-voltage power supply (V _High) according to the invention The third switch (S3) and the fourth switch (S4) connected in parallel and in series with each other, and connecting the second contact and the first contact between the third switch (S3) and the fourth switch (S4) And a high voltage side circuit having a second inductor L ₂ .

In this case, the low voltage power supply (V _LOW ) is a battery capable of charging and discharging, and the high voltage power supply (V _High ) is an input power supply of a DC / AC inverter (motor driver) for driving a hybrid vehicle. In addition, the first switch (S1) to the fourth switch (S4) is preferably configured as a MOSFET switch, but may also be configured as an IGBT switch, if necessary.

According to the above configuration, the bidirectional non-isolated DC-DC converter according to the present invention has a boost operation in which a battery of _low voltage power supply (V _Low ) is discharged when the motor of the high voltage power supply (V _High ) side is driven, and the regenerative operation of the motor is performed. It is possible to perform a buck operation for charging the battery using energy.

On the other hand, the first switch (S1) to the fourth switch (S4) of the bi-directional DC-DC converter according to the present invention is operated according to the control signal of the controller, the controller is a low voltage power (V _Low ) and high voltage power (V) in the front end of the _High) output and the second inductor (L ₂₎ of the voltage detection section for detecting a voltage by using the output of a current detection unit for detecting the current to control the operation of said switch control signals (that is, gate signal) Create it and pass it to the gate driver.

In this case, the controller controls the duty of each switch using the output of the voltage detector as described below, and allows the duty control to be more precisely controlled using the output of the current detector.

In the bidirectional DC-DC converter according to the present invention, as described below, the controller controls the bidirectional DC-DC converter to operate in CCM and each switch performs zero voltage switching. In order to control the operation of S4, more specifically, the control unit controls the first switch S1 and the third switch S3 to the second switch S2 and the fourth switch S4 for one period. Control to have a duty by asymmetric complementary switching.

In other words, the duty by complementary switching means that the total duty of each of the switches S1 and S2 of the low voltage side circuit is 1 for one cycle and the main switch of the low voltage side circuit is the second switch S2. In this case, when the second switch S2 is controlled to have a duty of D, it means that the first switch S1, which is an auxiliary switch, has a duty of 1-D.

In this case, the two switches are controlled so that there is no overlapping operation time. That is, when the second switch S2 is turned on, the first switch S1 is turned off and when the second switch S2 is turned off, the first switch is turned off. The switch S1 is turned on.

In order to control the operation of each switch as described above, the voltage drop due to the voltage transfer ratio, main duty, voltage of each capacitor, and the duty loss of the discharge in consideration of the duty loss of the bidirectional non-isolated DC-DC converter according to the present invention It can be expressed as Equation 1 to Equation 4 below.

In this case, the duty loss is generated in the second inductor L ₂ , D _eff is an effective duty, ΔD is a duty loss, and ΔV is a voltage drop due to the duty loss.

In addition, the following input voltage (V _i ) and output voltage (V _o ) is a value that is set differently according to the characteristics of the DC-DC converter, but in the case of a hybrid car as an example input voltage (V _i ) is 240 ~ 280V, output voltage (V _o ) is preferably set to 450 to 600V.

In addition, the following main duty is a duty value for obtaining the set voltage transfer ratio when there is no duty loss, which is preferably set in advance in the controller.

Therefore, the controller of the bidirectional non-isolated DC-DC converter according to the present invention compares the voltage transfer ratio obtained by using the output of the voltage detector with the predetermined voltage transfer ratio, and then the effective duty is obtained when the calculated voltage transfer ratio is larger. And decreases vice versa and increases the effective duty to control the operation of each switch.

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On the other hand, in the bidirectional non-isolated DC-DC converter according to the present invention, the voltage drop due to the voltage transfer ratio, the main duty, the voltage of each capacitor and the loss of duty in consideration of the duty loss of the second inductor (L ₂ ) is as follows. It can be expressed as Equation 5 to Equation 8.

In this case, the meaning of each variable value is the same as the description of the above-described discharge, so a detailed description thereof will be omitted.

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Next, the switching scheme of the bidirectional non-isolated DC-DC converter and the optimal design method of the converter according to the present invention will be described with reference to FIGS.

4 is a circuit diagram illustrating a switching method of a converter according to the present invention, FIG. 5 is an equivalent circuit diagram of a converter according to the present invention, and FIG. 6 is a diagram illustrating a voltage applied to a second inductor L ₂ of a converter according to the present invention. Current waveform.

As shown in FIG. 4, in the bidirectional non-isolated DC-DC converter according to the present invention, the second switch S2 becomes the main duty D in the discharge operation, and the first switch S1 is asymmetrically complementary as described above. It is controlled to have a duty of (1-D) by the enemy switching.

At this time, the high voltage side switches are also asymmetrically complementary switching, the fourth switch (S4) is the main duty (D), the third switch (S3) is controlled to have a duty of (1-D).

In addition, in the bidirectional non-isolated DC-DC converter according to the present invention, in the charging operation, the third switch S3 becomes the main duty D, and the fourth switch S4 is formed by asymmetric complementary switching as described above. It is controlled to have a duty of (1-D).

At this time, the low voltage side switches are also asymmetrically complementary switching, the first switch (S1) is the main duty (D), the second switch (S2) is controlled to have a duty of (1-D).

Meanwhile, as shown in FIG. 6, the phase angle Φ of the low voltage side and the high voltage side square wave voltages control the magnitude of the voltage applied to the second inductor L ₂ , thereby determining the zero voltage switching region. The smaller the size of Φ, the smaller the magnitude of the current flowing through the second inductor L ₂ , so that an element having a lower current rating can be used.

Further, the low voltage side half bridge and there is generated for each of the rectangular wave to the second inductor (L ₂₎ jwawoopyeon on the higher-voltage half-bridge, the current waveform of the second inductor (L ₂₎ As can be seen in FIGS. 5 and 6 Is determined by the phase angle, the low voltage side capacitor voltage and the high voltage side capacitor voltage.

Therefore, the optimal design for lowering the current rating of the second inductor L ₂ in the bidirectional non-isolated DC-DC converter according to the present invention is the voltage V _c1 of the first capacitor C ₁ and the second capacitor C _2. It is preferable to make the voltage V _c2 equal to, which can be done by making the magnitudes of the low voltage side duty and the high voltage side duty the same as shown in FIG.

FIG. 7 is a view illustrating main waveforms during one cycle of a discharge (step-up) operation of the bidirectional non-isolated DC-DC converter according to the present invention, and FIG. 8 illustrates the operation principle of each section for explaining the operation of FIG. It is a circuit diagram.

The converter according to the present invention operates in seven modes during one cycle during discharging. Hereinafter, operation of each mode will be described in detail.

1) Mode 1 section

When the second switch S2 is turned on by zero voltage switching as described later in the state where the third switch S3 is turned on, a positive voltage is applied to the first inductor L ₁ of the low voltage side circuit to charge. In addition, a negative voltage is applied to the second inductor L ₂ of the high voltage side circuit to discharge. Thereafter, the control unit turns off the third switch S3 when the duty 1 -D of the third switch S3 is completed, thereby ending Mode 1.

2) Mode 2 section

The section is a dead time section in which all of the switches of the high voltage circuit are turned off. When the third switch S3 is turned off in the Mode 1 section, the internal capacitors of the third switch S3 and the fourth switch S4 are turned off. Are charged and discharged, respectively, and thus the current direction of the second inductor L ₂ is also changed to flow to the second switch S2 like the current of the first inductor L ₁ .

When the internal capacitors of the third switch S3 and the fourth switch S4 complete charging and discharging, current flows to the internal diode of the fourth switch S4. In this case, the fourth switch S4 has a gate voltage. Is applied.

3) Mode 3 section

When the gate voltage is applied to the fourth switch S4 in the mode 2 section, the current flowing through the internal diode of the fourth switch S4 flows in the reverse direction of the switch channel, and the fourth switch S4 naturally switches zero voltage. (ZVS) is achieved and turned on.

That is, the bidirectional non-isolated DC-DC converter according to the present invention naturally achieves zero voltage switching even without a separate control operation by the controller by the charge / discharge operation of the internal capacitor of each switch.

On the other hand, the controller terminates Mode 3 by turning off the second switch S2 after maintaining the main duty D of the second switch S2 to obtain a predetermined voltage transfer ratio as described above.

4) Mode 4 section

The section is a dead time section in which all of the switches of the low voltage side circuit are turned off. When the second switch S2 is turned off in the Mode 3 section, the internal capacitors of the first switch S1 and the second switch S2 are turned off. Are charged and discharged, respectively, and when the internal capacitors of the switches complete charging and discharging, current flows to the internal diode of the first switch S1. At this time, a gate voltage is applied to the first switch S1.

5) Mode 5 section

When the gate voltage is applied to the first switch S1 in the Mode 4 section, the current flowing through the internal diode of the first switch S1 flows in the reverse direction of the switch channel, and the first switch S1 naturally has a zero voltage. The switch ZVS is turned on and turned on, and the current direction of the second inductor L ₂ also changes in the forward direction.

Meanwhile, the controller terminates Mode 5 by turning off the fourth switch S4 after maintaining the main duty D of the fourth switch S4. In the present embodiment, as described above, the second inductor L _In order to lower the current rating of ₂ ), the main duty D of the fourth switch S4 is set to be the same as the main duty D of the second switch S2.

6) Mode 6 section

The section is a dead time section in which all of the switches of the high-voltage circuit are turned off. When the fourth switch S4 is turned off in the mode 5 section, the third switch S3 and the fourth switch S4 are inside. Capacitors charge and discharge, respectively, and when the internal capacitors of the switches complete charging and discharging, current flows to the internal diode of the third switch S3. At this time, a gate voltage is applied to the third switch S3. .

7) Mode 7 section

When the gate voltage is applied to the third switch S3 in the Mode 6 section, current flowing through the internal diode of the third switch S3 flows in the reverse direction of the switch channel, and the third switch S3 naturally switches to zero voltage. (ZVS) is achieved and turned on.

Thereafter, the control unit turns off the first switch S1 at the time when the duty 1-D of the first switch S1 is completed, thereby ending Mode 7. As a result, one cycle ends.

Thereafter, the second switch S2 is turned on by zero voltage switching in the dead time period in which all the switches of the low voltage side circuit are turned off by the same method as described above, and is repeated from Mode 1.

FIG. 9 is a diagram illustrating main waveforms during one cycle of a charging (stepping down) operation of the bidirectional non-isolated DC-DC converter according to the present invention, and FIG. It is a circuit diagram.

The converter according to the present invention operates in seven modes during one cycle during charging. Hereinafter, operation of each mode will be described in detail.

1) Mode 1 section

When the third switch S3 is turned on and the first switch S1 is turned on by zero voltage switching as described below, the current flowing through the second inductor L ₂ is lower than the third switch S3. The flow is divided into the first inductor L ₁ of the side circuit.

Meanwhile, as described above, the control unit maintains the main duty D of the third switch S3 to obtain a predetermined voltage transfer ratio, and then turns off the third switch S3 to end Mode 1.

2) Mode 2 section

The section is a dead time section in which all of the switches of the high voltage circuit are turned off. When the third switch S3 is turned off in the Mode 1 section, the interior of the third switch S3 and the fourth switch S4 is turned off. The capacitors respectively charge and discharge, and when the internal capacitors of the switches complete charging and discharging, current flows to the internal diode of the fourth switch S4.

In this case, a gate voltage is applied to the fourth switch S4.

3) Mode 3 section

When the gate voltage is applied to the fourth switch S4 in the mode 2 section, the current flowing through the internal diode of the fourth switch S4 flows in the reverse direction of the switch channel, and the fourth switch S4 naturally switches zero voltage. (ZVS) is achieved and turned on.

Meanwhile, the controller terminates Mode 3 by turning off the first switch S1 after maintaining the main duty D of the first switch S1. In the present embodiment, as described above, the first switch S1 is terminated. ) Is set equal to the main duty (D) of the third switch (S3).

4) Mode 4 section

The section is a dead time section in which all the switches of the low voltage side circuit are turned off. When the first switch S1 is turned off in the Mode 3 section, the internal capacitors of the first switch S1 and the second switch S2 are turned off. Respectively charge and discharge, and when the internal capacitors of the switches complete charging and discharging, current flows to the internal diode of the second switch S2.

At this time, a gate voltage is applied to the second switch S2.

5) Mode 5 section

When the gate voltage is applied to the second switch S2 in the Mode 4 section, the current flowing through the internal diode of the second switch S2 flows in the reverse direction of the switch channel, and the second switch S2 naturally switches to zero voltage. (ZVS) is achieved and turned on. At this time, the current direction of the second inductor L ₂ is also reversed.

On the other hand, the controller terminates Mode 5 by turning off the fourth switch S4 when the duty 1 -D of the fourth switch S4 is completed.

6) Mode 6 section

The section is a dead time section in which all of the switches of the high-voltage circuit are turned off. When the fourth switch S4 is turned off in the mode 5 section, the third switch S3 and the fourth switch S4 are inside. The capacitors respectively charge and discharge, and when the internal capacitors of the switches complete charging and discharging, current flows to the internal diode of the third switch S3.

At this time, a gate voltage is applied to the third switch S3.

7) Mode 7 section

When the gate voltage is applied to the third switch S3 in the Mode 6 section, current flowing through the internal diode of the third switch S3 flows in the reverse direction of the switch channel, and the third switch S3 naturally switches to zero voltage. (ZVS) is achieved and turned on.

Thereafter, the control unit turns off the second switch S2 at the time when the duty 1-D of the second switch S2 is completed, thereby ending Mode 7. As a result, one cycle ends.

Subsequently, the first switch S1 is turned on by zero voltage switching in the dead time period in which all the switches of the low voltage side circuit are turned off by the same method as described above, and is repeated from Mode 1.

As shown in FIG. 7 and FIG. 9, the bidirectional non-isolated DC-DC converter according to the present invention operates as a CCM continuously flowing current to the first inductor L ₁ of the low voltage side circuit during charging or discharging. The current ripple can be lowered in power applications, which allows the use of devices with lower current ratings and the capacity of capacitor filters.

In addition, the bidirectional non-isolated DC-DC converter according to the present invention has an advantage of reducing heat generation by reducing iron loss of the first inductor L ₁ due to the CCM operation as described above.

In addition, the bidirectional non-isolated DC-DC converter according to the present invention improves the overall efficiency of the converter by reducing switching loss since each switch performs zero voltage switching naturally by charging and discharging of an internal capacitor during charging or discharging. There is an advantage that it can.

1 is a system configuration of a hybrid vehicle according to the prior art,

2 is a circuit diagram of a conventional bidirectional buck-boost DC-DC converter,

3 is a circuit diagram of a bidirectional non-isolated DC-DC converter according to an embodiment of the present invention;

4 is a circuit diagram illustrating a switching scheme of the DC-DC converter of FIG. 3;

5 is an equivalent circuit diagram for the DC-DC converter of FIG.

FIG. 6 is a diagram showing voltage and current waveforms applied to a high voltage side inductor of the DC-DC converter of FIG. 3; FIG.

FIG. 7 is a view showing main waveforms of a boost operation of the DC-DC converter of FIG. 3; FIG.

FIG. 8 is a circuit diagram illustrating an operation principle of each section for explaining a boost operation of the DC-DC converter of FIG.

FIG. 9 shows main waveforms for the step-down operation of the DC-DC converter of FIG. 3; and

FIG. 10 is a circuit diagram illustrating an operation principle of each section for explaining the step-down operation of the DC-DC converter of FIG. 3.

Claims (5)

A bidirectional non-isolated DC-DC converter having a low voltage power supply and a high voltage power supply, Branched at a first contact between the first inductor, the first switch and the first capacitor, and the first inductor and the first switch sequentially connected to the low voltage power supply and connected in parallel to the first switch and the first capacitor A low voltage side circuit having a second switch; A second capacitor connected in series to the high voltage power source, a third switch and a fourth switch connected in parallel to the second capacitor and connected in series with each other, and a second contact point between the third switch and the fourth switch and the first switch; A high voltage side circuit having a second inductor for connecting the contacts; And And a controller for controlling the operation of the first to fourth switches such that the converter is operated in CCM and each switch is turned on by zero voltage switching. The method of claim 1, And a voltage detector detecting voltages of the low voltage power supply and the high voltage power supply. The control unit controls the duty of the first switch to the fourth switch using the output of the voltage detector, bidirectional non-isolated DC-DC converter. The method of claim 2, The control unit, the bi-directional non-isolated DC-DC converter characterized in that the first switch and the third switch to control the second switch and the fourth switch to have a duty by complementary switching, respectively. The method of claim 3, The control unit, the bi-directional non-isolated DC-DC converter, characterized in that for controlling so that the duty of the second switch and the fourth switch equal. The method according to any one of claims 1 to 4, The first switch to the fourth switch is a bidirectional non-isolated DC-DC converter, characterized in that the MOSFET or IGBT.

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