JP2006081263A - Bidirectional dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bidirectional DC-DC converter that can transform a voltage to a prescribed output voltage in a wide range of an input voltage. <P>SOLUTION: When stepping up a voltage for feeding power to a high-voltage side from a low-voltage side, a pair of FETs 4-1, 4-4 and a pair of FETs 4-2, 4-3 at a low-voltage side switch 4 are alternately turned on and off. When stepping down a voltage for feeding power to the low-voltage side from the high-voltage side, a pair of FETs 5-1, 5-4 and a pair of FETs 5-2, 5-3 at a high-voltage side switch 5 are alternately turned on and off. A current flowing at this time forms a sine wave due to the existence of an LC resonance circuit 6. A voltage ratio exceeding a winding ratio of a transformer 3 can be obtained by controlling conduction angles of the FETs 5-1 to 5-4 of the high-voltage side switch 5 or FETs 4-1 to 4-4 of the low-voltage side switch 4 in a control zone of almost 50%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a bidirectional DC-DC converter, and more particularly to a bidirectional DC-DC converter that enables transformation (step-down or step-up) to a predetermined output voltage over a wide input voltage range.

  Some vehicles have two power supply systems of batteries having different voltage values. When power is interchanged between two DC power supply systems having different voltage values, generally, a configuration is adopted in which a DC booster circuit and a DC stepdown circuit are arranged in parallel between the DC power supply systems and used appropriately. Has been.

  It has also been proposed to use a bidirectional DC-DC converter in order to obtain a sufficiently high DC voltage in a small circuit when power is interchanged in a DC power supply system.

For example, the following Patent Document 1 has bidirectional orthogonal transform units on both sides of the transformer, and in particular, the secondary-side orthogonal transform unit is forward power transmission (step-down power transmission from the first DC terminal to the second DC terminal). Sometimes, a choke coil that operates as a smoothing coil is used as a choke coil for a choke circuit type chopper circuit type inverter, and a switching / rectifying unit between the choke coil and a secondary coil of the transformer functions as a rectifier during forward power transmission, A bidirectional DC-DC converter is described that functions as a chopper circuit during reverse power transmission (step-up power transmission from the second DC terminal to the first DC terminal).
Japanese Patent Laid-Open No. 2002-165448

  However, in a configuration in which a DC booster circuit and a DC stepdown circuit are arranged in parallel between two DC power supply systems, the circuit scale becomes large, and sufficient performance can be obtained due to voltage loss inside the circuit when operated simultaneously. There is a problem that cannot be done.

  In the bidirectional DC-DC converter as described in Patent Document 1, when the voltage conversion ratio is restricted by the winding ratio of the primary side winding and the secondary side winding of the voltage conversion transformer. If the required lower limit (or upper limit) of the output voltage is restricted, the lower limit (or upper limit) of the input voltage is also restricted accordingly. For this reason, when it is assumed that the input voltage fluctuates greatly, there is a problem that the winding ratio of the voltage conversion transformer must be set sufficiently large.

  An object of the present invention is to provide a bidirectional DC-DC converter that solves the above-described problems and enables transformation to a predetermined output voltage in a wide input voltage range.

  In order to solve the above problems, the present invention provides a low voltage side terminal, a high voltage side terminal, a transformer including a low voltage side coil and a high voltage side coil, and the low voltage side terminal and the low voltage side coil. The inserted low voltage side switching unit, the high voltage side switching unit inserted between the high voltage side terminal and the high voltage side winding, and the low voltage side rectifying element connected in parallel to each switching element of the low voltage side switching unit And a high voltage side rectifying element connected in parallel to each switching element of the high voltage side switching unit, and a control circuit that controls the switching element of the low voltage side switching unit and the switching element of the high voltage side switching unit. In the DC-DC converter, L between the high-voltage side winding and the high-voltage side switching unit or between the low-voltage side winding and the low-voltage side switching unit. Provided with a resonant circuit, there is first characterized in that performing the step-down control by controlling the switching elements of the high voltage side switching unit in the control zone of the conduction angle 0 of approximately 50% of the range.

  The present invention also provides a low voltage side terminal, a high voltage side terminal, a transformer including a low voltage side coil and a high voltage side coil, and a low voltage side switching inserted between the low voltage side terminal and the low voltage side coil. A high-voltage side switching unit inserted between the high-voltage side terminal and the high-voltage side winding, a low-voltage side rectifying element connected in parallel to each switching element of the low-voltage side switching unit, and the high-voltage side switching In a bidirectional DC-DC converter, comprising: a high-voltage side rectifying element connected in parallel to each switching element of the unit; and a control circuit that controls the switching element of the low-voltage side switching unit and the switching element of the high-voltage side switching unit. When an LC resonance circuit is provided between the high-voltage side winding and the high-voltage side switching unit or between the low-voltage side winding and the low-voltage side switching unit In, there is a second feature that performs control to boost control the switching elements of the low voltage side switching unit conduction angle of 100% or almost 50% of the control zone in accordance with the input voltage to the low-voltage side terminal.

  The third feature of the present invention is that the LC resonance circuit is provided between the high-voltage side winding and the high-voltage side switching unit.

  In addition, the present invention has a fourth feature in that both the low voltage side switching unit and the high voltage side switching unit have a bridge connection configuration including four switching elements.

  Furthermore, the present invention has a fifth feature in that a battery is connected to the low voltage side terminal and a generator output is connected to the high voltage side terminal.

  According to the first feature of the present invention, the current waveform due to switching is made sinusoidal in the LC resonance circuit, and the switching element of the high-voltage side switching unit is controlled in the control zone in the range of conduction angle 0 to approximately 50%, A predetermined output voltage can be obtained in a wider input voltage range.

  Further, according to the second feature, the current waveform due to switching is made sinusoidal by an LC resonance circuit, and the switching element of the low-voltage side switching unit is controlled in a control zone with a conduction angle of 100% or almost 50% according to the input voltage. Thus, a predetermined output voltage can be obtained in a wider input voltage range.

  Further, according to the third feature, by providing the LC resonance circuit on the high voltage side where the current value is small, the loss in the LC resonance circuit can be reduced compared to the case where the LC resonance circuit is provided on the low voltage side. .

  Further, according to the fourth feature, since both the low-voltage side switching unit and the high-voltage side switching unit are bridge-type single-phase inverters, the structure of the transformer connected thereto can be simplified.

  Furthermore, according to the fifth feature, it is possible to stably charge the battery even when the output of the generator such as an engine generator, a fuel cell, or a solar generator has a large fluctuation in generated voltage.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a bidirectional DC-DC converter according to the present invention. The bidirectional DC-DC converter according to the present embodiment includes a transformer between a DC power source connected to the low voltage side terminals 1-1 and 1-2 and a DC power source connected to the high voltage side terminals 2-1 and 2-1. 3 is used to perform voltage conversion.

  The transformer 3 includes a low voltage side winding 3-1 and a high voltage side winding 3-2. The low-voltage side switching unit 4 is inserted between the low-voltage side terminals 1-1 and 1-2 and the low-voltage side winding 3-1, and the high-voltage side terminals 2-1 and 2-2 and the high-voltage side winding 3-2 The high voltage side switching unit 5 is inserted in between.

  The low voltage side switching unit 4 can be configured by bridge-connecting four switching elements (hereinafter referred to as FETs) 4-1 to 4-4 such as FETs, and the high voltage side switching unit 5 includes four FETs 5. -1 to 5-4 can be configured by bridge connection.

  A rectifying element such as a diode is connected in parallel to each of the FETs 4-1 to 4-4 and 5-1 to 5-4. These rectifying elements may be FET parasitic diodes or junction diodes connected separately. If the rectifying elements connected in parallel are combined, the low-voltage side switching unit 4 and the high-voltage side switching unit 5 can be considered as switching / rectifying units, respectively. The LC resonance circuit 6 is inserted between the high-voltage side terminals 2-1 and 2-2 and the high-voltage side winding 3-2.

  The voltage on the low voltage side and the voltage on the high voltage side are detected by the voltage detectors 7 and 8, respectively, and the detected voltage is input to the control circuit 9 comprising a CPU or the like. The control circuit 9 performs switching control of the FETs 4-1 to 4-4 of the low-voltage side switching unit 4 and the FETs 5-1 to 5-4 of the high-voltage side switching unit 5 via the drivers 10 and 11. The capacitors 12 and 13 connected between the low voltage side terminals 1-1 and 1-2 and between the high voltage side terminals 2-1 and 2-2 are output smoothing capacitors.

  Next, the operation of FIG. 1 will be described. When boosting power from the low voltage side to the high voltage side, the FET4-1 and 4-4 pairs and the FET4-2 and 4-3 pairs of the low voltage side switching unit 4 are alternately turned on and off. At this time, when the input voltage to the low-voltage terminals 1-1 and 1-2 has a predetermined voltage value, this on / off operation is performed at the full conduction angle. At this time, as will be described later, voltage conversion is performed at a voltage ratio close to the winding ratio A / B of the transformer 3. In addition, since the FETs 4-1 to 4-4 can be turned on and off near the zero cross point of the current waveform that has been made sinusoidal by the resonance circuit 6, switching loss can be suppressed even at a large current.

  Further, when the input voltage to the low-voltage side terminals 1-1 and 1-2 is lower than a predetermined voltage value, the FETs 4-1 to 4- are used as control zones with an ON / OFF conduction angle of approximately 50%. 4 is controlled. At this time, as will be described later, voltage conversion can be performed at a voltage ratio exceeding the winding ratio A / B of the transformer 3.

  The current accompanying this on / off flows to the low-voltage side winding 3-1 of the transformer 3. The current induced in the high-voltage side winding 3-2 is input to the high-voltage side switching unit 5 through the LC resonance circuit 6, rectified by a rectifying element connected in parallel to the FETs 5-1 to 5-4, and Smoothed and output. At this time, the current flowing to the low voltage side and the high voltage side becomes sinusoidal due to the presence of the LC resonance circuit 6.

  When the power is supplied from the high voltage side to the low voltage side, the FET 5-1 and 5-4 pairs and the FET 5-2 and 5-3 pairs of the high voltage side switching unit 5 are alternately turned on at a predetermined conduction angle described later. Turn off. The current accompanying this on / off flows to the high-voltage side winding 3-2 of the transformer 3. When the FETs 5-1 to 5-4 are turned on and off, the current flowing to the high voltage side and the low voltage side changes in a sine wave shape due to the presence of the LC resonance circuit 6.

  The current induced in the low-voltage side winding 3-1 is input to the low-voltage side switching unit 4, rectified by the rectifying element connected in parallel to the FETs 4-1 to 4-4, smoothed by the smoothing capacitor 12, and output. The

  Next, the principle of the present invention will be described. In the following, the case where the high voltage applied to the high voltage side terminals 2-1 and 2-1 is stepped down and output to the low voltage side terminals 1-1 and 1-2 will be described as an example. The present invention can also be applied to boosting from the 1-1, 1-2 side to the high-voltage side terminals 2-1, 2-1 side.

  FIG. 2 shows a transformer when the FET5-1, 5-4 pair and the FET5-2, 5-3 pair of the high-voltage side switching unit 5 are alternately turned on and off at the full conduction angle (duty ratio 100%). 3 is a diagram showing a current flowing through the high-voltage side winding 3-2 or the low-voltage side winding 3-1. This current becomes sinusoidal due to the presence of the LC resonance circuit 6.

  FIG. 3 is a characteristic diagram showing a voltage ratio between the high-voltage side voltage and the low-voltage side voltage obtained when the FETs 5-1 to 5-4 are controlled by changing the duty ratio to 0 to 100%. As shown in the figure, when the FETs 5-1 to 5-4 are turned off in the vicinity of a duty ratio of 50%, the voltage ratio exceeding the winding ratio A / B of the transformer 3 is obtained. This is because the energy stored in the winding of the transformer 3 and the choke coil of the LC resonance circuit 6 is released by turning off near the maximum current. When the duty ratio exceeds 50%, the voltage ratio returns to a value close to the winding ratio A / B of the transformer 3. This is because when the duty exceeds 50%, the induced energies cancel each other out due to continuous on and off.

  The present invention pays attention to the fact that a voltage ratio exceeding the winding ratio A / B of the transformer can be obtained when turning off at a duty ratio of around 50%, and enables voltage transformation control in a wider input voltage range. It is.

  For example, when stepping down, the FETs 5-1 to 5-4 of the high-voltage side switching unit 5 are set as control zones in the range of the conduction angle 0 to almost 50%, and when the high-voltage side voltage is high, the FETs 5-1 to 5-5 The conduction angle of -4 is narrowed down, and when it is low, the conduction angle is approximately 50%, so that the step-down control can be performed in a wider high-voltage side voltage range without being restricted by the winding ratio of the transformer 3. The control zone in the present invention is shown in FIG.

FIG. 4 is a diagram showing a comparison between the voltage conversion characteristic (a) according to the present invention and the voltage conversion characteristic (b) according to the prior art. As shown in the figure, in the prior art, when the low voltage side voltages Vl _{1 to} Vl ₂ in a predetermined range are to be obtained, the conversion characteristics are restricted by the winding ratio A / B of the transformer 3, and the high voltage side voltage is Vh. ₁ must be in the range of ~Vh _2.

That is, when the high voltage side voltage exceeds Vh ₂ , the low voltage side voltage exceeds Vl ₂ , and when the high voltage side voltage becomes less than Vh ₁ , the low voltage side voltage becomes less than Vl ₁ . For this reason, for example, when a battery is connected to the low-voltage side and charged, it is necessary to limit the high-voltage side voltage to a range of Vh ₁ to Vh ₂ in order to prevent overcharging or insufficient charging of the battery.

On the other hand, in the present invention, when the output voltages Vl _{1 to} Vl ₂ in a predetermined range are to be obtained, the conversion characteristics are not restricted by the winding ratio A / B of the transformer ₃ , and the high-voltage side voltage is Vh ₃ ( Since Vh ₃ <Vh ₁ ) or more, step-down control in a wider high-voltage side voltage range is possible. Since the linear relationship between the voltage control and the conduction angle is maintained, a predetermined low-voltage side voltage can be obtained stably and easily by the conduction angle control even if the high-voltage side voltage fluctuates.

  FIG. 5 is a circuit diagram showing an application example of the present invention, in which an electric power is exchanged between a direct current power source including a generator 51 and a battery 52 using a bidirectional DC-DC converter 50 according to the present invention. It is. The generator 51 is, for example, an engine-driven three-phase multipolar magnet generator. When the engine is started, the low-voltage side switching unit of the bidirectional DC-DC converter 50 is driven, and the DC voltage of the battery 52 boosted thereby is applied to the drive inverter (rectifier circuit) 53. The drive inverter 53 converts the applied DC voltage into a three-phase AC voltage and applies it to the generator 51, which is activated as an engine starter motor.

  When the engine is started, the generator 51 is driven by the engine, and the switching operation of the drive inverter 53 is stopped. The output of the generator 51 is rectified by a rectifier circuit (drive inverter) 53, adjusted by a regulator 54, and further converted into AC power of a predetermined frequency by an inverter 55 and output.

  If the high voltage side switching unit of the bidirectional DC-DC converter 50 is driven when the voltage of the battery 52 decreases, the output of the rectifier circuit 53 is stepped down by the bidirectional DC-DC converter 50, and the battery 52 is charged by this voltage. can do.

  Although the embodiments have been described above, the present invention can be variously modified. For example, the LC resonance circuit can be provided not on the step-down side but on the low-pressure side. In this case, an LC resonance circuit may be inserted between the low voltage side switching unit and the low voltage side winding of the transformer.

  The present invention is not limited to between batteries or between a DC power source consisting of an engine-driven generator and a battery, but to allow power to be exchanged with an appropriate DC power source system such as a normal generator, solar power generation, wind power generation, or fuel cell. For example, power can be exchanged between a traveling power system and a safety electrical system in a hybrid vehicle or the like.

1 is a circuit diagram showing an embodiment of a bidirectional DC-DC converter according to the present invention. It is a wave form diagram for explanation of operation of a bidirectional DC-DC converter. It is a characteristic view which shows the relationship between a duty ratio and a voltage ratio. It is a characteristic view which shows the voltage conversion characteristic of this invention, and the voltage conversion characteristic of a prior art. It is a circuit diagram which shows the example of application of this invention.

Explanation of symbols

1-1, 1-2 ... low voltage side terminal, 2-1, 2-2 ... high voltage side terminal, 3 ... transformer, 3-1 ... low voltage side winding, 3-2 ...・ High voltage side winding, 4 ... Low voltage side switching part, 4-4 ~ 4-4,5-1 ~ 5-4 ... FET, 5 ... High voltage side switching part, 6 ... LC resonance Circuit, 7, 8 ... Voltage detection unit, 9 ... Control unit, 10, 11 ... Driver, 12, 13 ... Smoothing capacitor, 50 ... Bidirectional DC-DC converter, 51 ... -Generator, 52 ... Battery, 53 ... Drive inverter (rectifier circuit), 54 ... Regulator, 55 ... Inverter

Claims (5)

A low-voltage side terminal; a high-voltage side terminal; a transformer including a low-voltage side winding and a high-voltage side winding; a low-voltage side switching unit inserted between the low-voltage side terminal and the low-voltage side winding; A high-voltage side switching unit inserted between a terminal and the high-voltage side winding; a low-voltage side rectifying element connected in parallel to each switching element of the low-voltage side switching unit; and each switching element of the high-voltage side switching unit In a bidirectional DC-DC converter comprising a high voltage side rectifying element connected in parallel, and a control circuit for controlling the switching element of the low voltage side switching unit and the switching element of the high voltage side switching unit,
An LC resonance circuit is provided between the high-voltage side winding and the high-voltage side switching unit or between the low-voltage side winding and the low-voltage side switching unit, and the switching element of the high-voltage side switching unit has a conduction angle of 0 to 0. A bidirectional DC-DC converter that performs step-down control by controlling in a control zone in a range of approximately 50%. A low-voltage side terminal; a high-voltage side terminal; a transformer including a low-voltage side winding and a high-voltage side winding; a low-voltage side switching unit inserted between the low-voltage side terminal and the low-voltage side winding; A high-voltage side switching unit inserted between a terminal and the high-voltage side winding; a low-voltage side rectifying element connected in parallel to each switching element of the low-voltage side switching unit; and each switching element of the high-voltage side switching unit In a bidirectional DC-DC converter comprising a high-voltage side rectifying element connected in parallel, and a control circuit for controlling the switching element of the low-voltage side switching unit and the switching element of the high-voltage side switching unit,
An LC resonance circuit is provided between the high-voltage side winding and the high-voltage side switching unit or between the low-voltage side winding and the low-voltage side switching unit, and the low-voltage side according to the input voltage to the low-voltage side terminal A bidirectional DC-DC converter that performs step-up control by controlling a switching element of a side switching unit in a control zone having a conduction angle of 100% or almost 50%. The bidirectional DC-DC converter according to claim 1 or 2, wherein the LC resonance circuit is provided between the high-voltage side winding and the high-voltage side switching unit. The bidirectional DC-DC converter according to claim 1 or 2, wherein each of the low-voltage side switching unit and the high-voltage side switching unit has a bridge connection configuration including four switching elements. The bidirectional DC-DC converter according to claim 1 or 2, wherein a battery is connected to the low-voltage side terminal, and a generator output is connected to the high-voltage side terminal.

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