JP4274364B2 - DC-DC converter - Google Patents

Description

  The present invention relates to a DC-DC converter, and more particularly, to an insulated DC-DC converter that enables step-up / step-down that is not limited by the winding ratio of a primary side winding and a secondary side winding of a voltage conversion transformer. .

  In an insulation type DC-DC converter that interposes a voltage conversion transformer, voltage conversion is performed by on / off control of switching means provided on the primary side of the voltage conversion transformer. The output voltage that can be output at that time is governed by the turn ratio of the primary side winding and the secondary side winding of the voltage converting transformer.

  FIG. 6 is a circuit diagram showing a DC-DC converter previously proposed by the present applicant. This DC-DC converter has a voltage conversion transformer (hereinafter simply referred to as a transformer) 1 including a primary winding 1-1 and a secondary winding 1-2.

  The switching means 2 configured by connecting the switching elements 2-1 to 2-4 in a bridge manner is provided on the primary side of the transformer 1, and the rectifying elements 3-1 to 3-4 are configured in a bridge connection on the secondary side. The bridge type rectifier circuit 3 is provided. A secondary side of the transformer 1 is further provided with a resonance circuit 4 including a resonance reactor and a resonance capacitor.

  The switching elements 2-1 to 2-4 are composed of, for example, FETs, and rectifying elements 5-1 to 5-4 such as parasitic diodes are attached to the switching elements 2-1 to 2-4. Capacitors 6 and 7 are smoothing capacitors connected to the input terminal and the output extraction terminal.

  When the pair of switching elements 2-1, 2-3, 2-2 and 2-4 are alternately turned on / off at the resonance frequency of the resonance circuit 4, the input voltage is at a frequency according to the on / off drive frequency. The voltage is increased or decreased via the transformer 1.

  The resonance frequency f of the resonance circuit 4 is expressed by f = 1 / 2π√LC, where L is the inductance of the reactor in the resonance circuit 4 and C is the capacitance of the capacitor. For example, L = 130 μH and C = 0.47 μF. Then, f≈20.4 KHz.

Here, if the input voltage is V1, and the winding ratio of the primary side winding 1-1 and the secondary side winding 1-2 of the voltage converting transformer is N1: N2, the switching means 2 is turned on / off. The output voltage V2 that can be output by controlling is expressed by the following equation. However, losses such as switching loss are ignored.
V2 ≦ (N2 / N1) V1

Patent Document 1 below proposes a bidirectional DC-DC converter capable of boosting a voltage more than the winding ratio of the primary side winding and the secondary side winding of the voltage conversion transformer. This is because the four switching elements of the secondary side switching circuit that acts as a rectifier circuit during step-down of forward power transmission are all turned on first at the time of step-up of reverse power transmission, and then part of the switching elements are turned off. The on / off control is repeated to repeatedly store and release the magnetic energy in the choke coil so as to obtain a voltage conversion ratio larger than the winding ratio of the voltage conversion transformer.
JP 2002-165448 A

  When the voltage conversion ratio is restricted by the turn ratio of the primary side winding and the secondary side winding of the voltage conversion transformer as in the above-described conventional technology, the lower limit (or upper limit) of the required output voltage is restricted. If there is, the lower limit (or upper limit) of the input voltage is 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.

  For example, in an engine-driven generator used as a power supply device, when the engine generator supplies power to the load and charges the battery, if the engine speed is 4000 rpm and the power generation output voltage is 260 V during normal load operation, In order to charge the 12V battery by stepping down the generated output voltage 260V, it is necessary to secure a charging voltage of about 13V using a voltage conversion transformer having a winding ratio of 20: 1.

  Here, if the engine speed is controlled according to the load amount, and the engine speed is 2500 rpm and the power generation output voltage is 180 V during light load operation, the voltage applied to the battery at this time is 9 V, The voltage to be charged is insufficient. In this example, considering only the charging of the battery, the winding ratio of the voltage conversion transformer is set to 14: 1, for example, so that the voltage of 12.8V can be given to the battery even if the power generation output voltage becomes 180V. In this case, however, an overvoltage of 18.6 V is applied to the battery during normal load operation, and it is necessary to limit the applied voltage.

  In addition, when the DC-DC converter is configured as a bidirectional DC-DC inverter and a battery is used for assisting power supply to the load, the voltage obtained by boosting the battery voltage is 128 V (12 V × 14). Since the power generation output voltage is not limited to 180V, power cannot be supplied from the battery to the load even if the voltage is boosted.

  Further, in the bidirectional DC-DC converter proposed in Patent Document 1, on / off control is repeated by first turning on all four switching elements of the switching circuit and then turning off the pair of switching elements. Since voltage conversion is performed and all or a pair of switching elements are turned on / off at the same time, there is a problem in that switching loss is likely to occur due to a difference in on / off timing. In addition, it is difficult to vary the voltage conversion ratio in various ways. Furthermore, it is difficult to set the on / off timing to a current value near zero, and there is a problem in that switching loss occurs due to a deviation in the timing.

  The present invention solves the above-described problems and provides a DC-DC converter capable of step-up / step-down with high conversion efficiency regardless of the winding ratio of the primary side winding and the secondary side winding of the voltage conversion transformer. The purpose is to do.

In order to solve the above problems, the present invention includes a transformer voltage conversion, provided on the primary side of the voltage conversion transformer, and a switching means for turning on and off the input voltage, the prior SL-voltage conversion transformer 2 In a DC-DC converter having a rectifier circuit and an output extraction terminal provided on the secondary side, and a driving means for turning on and off the switching means, the switching means is constituted by a bridge type switching circuit, and the voltage conversion transformer A reactor is provided in series with the secondary winding, the rectifier circuit is configured as a bridge-type rectifier circuit , a short-circuit switch is provided in parallel with the rectifier element forming the bridge-type rectifier circuit, and the on-duty of the short-circuit switch is The current flowing in the bridge type rectifier circuit controlled in synchronization with the ON timing of the switching means There is first characterized in that the changeable constructed up ratio by causing a portion on-operation of the short-circuit switch ring flowed to the reactor.

  The second feature of the present invention is that the secondary output voltage of the voltage conversion transformer is detected and the on-duty of the short-circuit switch is controlled so that the secondary output voltage becomes a predetermined value. is there.

  Further, the present invention has a third feature in that a resonance capacitor that constitutes an LC resonance circuit together with the reactor is provided, and the driving means turns on and off the switching means at a resonance frequency of the LC resonance circuit.

Furthermore, the present invention, by a Turkey respectively provided rectifying elements in parallel to the switching elements constituting the switching means, there is a fourth feature in that the DC-DC converter function of the bi-directional is provided.

  According to the first aspect of the present invention, the winding of the voltage converting transformer is driven by driving the secondary short-circuit switch in synchronization with the primary-side switching means and controlling the on-duty during the driving. Various output voltages boosted exceeding the ratio limitation can be obtained. Further, since the short-circuit switch may be driven by one instead of a pair, occurrence of switching loss can be suppressed.

  Further, according to the second feature, the output voltage boosted beyond the limitation by the winding ratio of the voltage converting transformer can be easily set as the target voltage.

  Further, according to the third feature, since the current waveform by switching can be made sinusoidal, it is easy to set the timing at which the switching element is turned off near the zero cross point of the current value. Further, it is not necessary to increase the dead time or shorten the driving time in order to prevent a short circuit of the switching element due to a transmission delay of the transformer. This makes it possible to increase the conversion efficiency.

  Furthermore, according to the fourth feature, it is possible to easily charge the battery from the high voltage side and to assist the power supply to the load using this battery, and the step-up ratio and step-down ratio at that time can be freely and easily set. Can be controlled.

  The present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a DC-DC converter according to the present invention, and the same or equivalent parts as in FIG. FIG. 1 differs from FIG. 6 in that a switching element 8-1 that functions as a short-circuit switch in parallel with each of the rectifying elements 3-1 to 3-4 of the bridge type rectifier circuit 3 provided on the secondary side of the transformer 1. 8-4 are connected, and the on-duty of these short-circuit switches 8-1 to 8-4 is controlled in synchronization with the on-timing of the switching elements 2-1 to 2-4 of the switching means 2. The switching elements 8-1 to 8-4 are made of FETs, for example.

  Next, the operation of this embodiment will be described. First, a normal operation for performing voltage conversion at a winding ratio N1: N2 or less of the transformer 1 will be described with reference to FIG. In the normal operation, the switching means 2 is driven on / off at a resonance frequency based on the element constant of the circuit element of the resonance circuit 4. That is, the pairs of switching elements 2-1 and 2-3, 2-2 and 2-4 are alternately turned on / off. At this time, the secondary side switching elements 8-1 to 8-4 are kept off.

  The time chart of FIG. 3A shows the on / off timing SW1 of the switching elements 2-1 and 2-3, the on / off timing SW2 of the switching elements 2-2 and 2-4, and the switching elements 8-1 to 8--. 4 shows the on / off timing SW3. SW1 and SW2 alternately turn on and off, and SW3 remains off. Note that the on-duty of SW1 and SW2 can be changed according to the required output voltage as long as it is less than the winding ratio.

  A current I-1 indicated by a solid line and a current I-2 indicated by a broken line in FIG. 1 alternately flow on the primary side of the transformer 1, and thereby, a current I-3 and a current I-4 flow on the secondary side of the transformer 1. Flowing. The currents I-3 and I-4 are rectified by pairs of rectifying elements 3-1 and 3-3, 3-2 and 3-4, respectively. As a result, DC-DC conversion from the primary side to the secondary side is performed at a winding ratio N1: N2 or less of the transformer 1.

  Next, an operation when voltage conversion is performed at a ratio exceeding the winding ratio N1: N2 of the transformer 1 will be described with reference to FIG. The point that the switching means 2 is driven on and off at the resonance frequency based on the element constant of the circuit element of the resonance circuit 4 is the same as described above.

  In this case, the switching element 8-2 or 8-4 is turned on during a part of the ON period of the switching elements 2-1 and 2-3, and the switching is performed during a part of the ON period of the switching elements 2-2 and 2-4. The element 8-1 or 8-3 is turned on.

  FIG. 2 is a diagram showing the operation at this time, and the current I flowing to the primary side of the transformer 1 when the switching element 8-2 is turned on during a part of the ON period of the switching elements 2-1 and 2-3. -1 and the path of the current I-5 flowing to the secondary side is shown.

  As apparent from the path of the current I-5 flowing on the secondary side, when the switching element 8-4 is turned on, the output side is short-circuited across the transformer 1 when viewed from the input side. Energy is stored in the reactor of the resonance circuit 4 during this short-circuit state.

  Next, when the switching element 8-4 is turned off to open the short circuit state, the energy stored in the reactor in the short circuit state is added to the voltage boosted by the winding ratio of the transformer 1 and appears in the output. As a result, voltage conversion at a winding ratio N1: N2 or more of the transformer 1 becomes possible.

  The time chart of FIG. 3B shows the on / off timing SW1 of the switching elements 2-1 and 2-3, the on / off timing SW2 of the switching elements 2-2 and 2-4, the switching element 8-2 or 8- 4 shows an on / off timing SW3-1, and an on / off timing SW3-2 of the switching element 8-1 or 8-3. In FIG. 3B, the switching elements 8-2 or 8-4 are turned on during a part (short circuit period) t1 of the ON periods of the switching elements 2-1 and 2-3, and the switching elements 2-2 and 2-4 are turned on. In this example, the switching element 8-1 or 8-3 is turned on during part of the on-period (short-circuit period) t2. The short circuit period t1 and the short circuit period t2 are normally set to be the same. Further, by changing the short-circuit period t1, t2, various output voltages can be output by changing the voltage conversion ratio.

  FIG. 4 is a block diagram showing an embodiment of the present invention including a control system. In this embodiment, the secondary output voltage of the transformer 1 is detected, and the switching elements 2-1 to 2-4 and 8-1 to 8-4 are turned on so that the secondary output voltage becomes the target voltage value.・ Control off. For example, if the target voltage value is a value that can be sufficiently converted by the winding ratio of the transformer 1, the target voltage value is achieved by controlling on / off the switching elements 2-1 to 2-4 on the primary side. Is a high value that cannot be obtained by the winding ratio of the transformer 1, the switching elements 8-1 to 8-4 are further turned on / off as described above to achieve the target voltage.

  Specifically, the control system includes output voltage detection means 9 that detects the secondary output voltage of the transformer 1. The output voltage detection means 9 gives a detection output to the control unit 10. If the target voltage value is a value that can be sufficiently converted by the winding ratio of the transformer 1, the control unit 10 gives a control signal only to the driver 11 of the switching means 2, and the switching elements 2-1 and 2- 3. The on-duty is controlled so that the pair of 2-2, 2-4 alternately becomes the set output voltage within 50% of the on-duty.

  Further, if the target voltage value is a high value that cannot be obtained by the winding ratio of the transformer 1, a control signal is further given to the drivers 12 of the switching elements 8-1 to 8-4. At this time, the driver 11 alternately drives the pair of switching elements 2-1, 2-3, 2-2 and 2-4 of the switching means 2, for example, with an on-duty of 50%. The ON period (short-circuit period t1, t2) of the switching element 8-2 or 8-4 and the switching element 8-1 or 8-3 is controlled within 50% so that the difference in the detection output of the detection means 9 is eliminated.

  FIG. 5 is a circuit diagram showing an application example of the present invention. This application example is an example in which the DC-DC converter of FIG. 1 is applied to a system in which electric power is interchanged by a DC power source including a generator 13 and a battery 14 to supply electric power to a load. The generator 13 is, for example, an engine-driven three-phase multipolar magnet generator.

  First, when the engine is started, the pair of switching elements 8-1 and 8-3 and 8-2 and 8-4 of the low-voltage side switching means 8 of the DC-DC converter 100 are alternately turned on, and the battery 14 boosted thereby. Is applied to the drive inverter (rectifier circuit) 15. The drive inverter 15 converts the applied DC voltage into a three-phase AC voltage and applies it to the generator 13 to start it as an engine starting motor.

  When the engine is started, the generator 13 is driven by the engine, and the switching operation of the drive inverter 15 is stopped. The output of the generator 13 is rectified by a rectifier circuit (drive inverter) 15, adjusted by a regulator 16, further converted into AC power having a predetermined frequency by an inverter 17, and supplied to a load.

  When the voltage of the battery 14 drops, the rectifier circuit 15 can be obtained by alternately turning on the pair of switching elements 2-1, 2-3, 2-2 and 2-4 of the high-voltage side switching means 2 of the DC-DC converter 100. Can be stepped down by the DC-DC converter 100 and the battery 14 can be charged with the stepped down voltage.

  When the output of the generator 13 decreases and a sufficient battery charge voltage cannot be obtained, the switching elements 8-1 to 8-4 of the low-voltage side switching means 8 are turned on / off as described above to generate a short-circuit period. By doing so, a sufficient battery charging voltage can be obtained.

  Further, when the battery 14 is used for assisting power supply to the load, it is sufficient to drive the switching elements 2-1 to 2-4 of the high voltage side switching means 2 in the same manner to generate a short circuit period. Power can be supplied to the load at the boost ratio.

  In addition, although this application example is an example which assists the direct-current power source which consists of an engine drive type generator with a battery, this invention is not restricted to this, A battery, a normal generator, solar power generation, wind power generation, fuel The present invention can also be applied when combining with an appropriate DC power supply system such as a battery. For example, it can also be applied when power is exchanged between a traveling power system and a safety electrical system in a hybrid vehicle.

1 is a circuit diagram showing an embodiment of a DC-DC converter according to the present invention. It is operation | movement explanatory drawing in the case of performing pressure | voltage rise with the voltage conversion ratio more than the winding ratio of a transformer. It is a time chart for operation | movement description of a DC-DC converter. It is a block diagram which shows embodiment of this invention also including a control system. It is a circuit diagram which shows the example of application of this invention. It is a circuit diagram which shows the DC-DC converter proposed previously.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transformer, 1-1 ... Low voltage side winding, 1-2 ... High voltage side winding, 2 ... Switching means, 2-1 to 2-4, 8-1 to 8-4 ... Switching element, 3 ... Bridge type rectifier circuit, 3-1 to 3-4, 5-1 to 5-4 ... Rectifier element, 4 ... LC resonance circuit, 6,7 ... Smoothing capacitor, 9 ... output voltage detecting means, 10 ... control unit (CPU), 11, 12 ... driver, 13 ... generator, 14 ... battery, 15 ... for driving Inverter (rectifier circuit), 16 ... regulator, 17 ... inverter, 100 ... DC-DC converter

Claims (4)

A transformer voltage conversion, the provided on the primary side of the voltage conversion transformer, and a switching means for turning on and off the input voltage, the rectifier circuit provided on the secondary side of the front SL voltage conversion transformer and the output extraction terminals And a DC-DC converter having driving means for turning on and off the switching means,
The switching means is constituted by a bridge type switching circuit, a reactor is provided in series with the secondary winding of the voltage conversion transformer, the rectifier circuit is constituted as a bridge type rectifier circuit, and the bridge type rectifier circuit is constituted. Provide a short-circuit switch in parallel with the rectifier element,
The step-up ratio is changed by controlling the on-duty of the short-circuit switch in synchronization with the on-timing of the switching means, and circulating a part of the current flowing through the bridge type rectifier circuit to the reactor by the on-operation of the short-circuit switch. A DC-DC converter characterized by being configured. 2. The DC− according to claim 1, wherein a secondary output voltage of the voltage conversion transformer is detected, and an on-duty of the short-circuit switch is controlled so that the secondary output voltage becomes a predetermined value. DC converter. 2. The DC-DC converter according to claim 1, further comprising a resonance capacitor that forms an LC resonance circuit together with the reactor, wherein the driving unit turns on and off the switching unit at a resonance frequency of the LC resonance circuit. . Wherein the a Turkey respectively provided rectifying elements in parallel to the switching elements constituting the switching means, a DC-DC converter according to claim 1, characterized in that the DC-DC converter function bidirectional is provided.

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