JP2012200122A - Power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion device that implements improved power efficiency, fewer components and a compact size while having a DC/DC conversion section and a DC/AC conversion section.SOLUTION: The power conversion device includes a DC/DC conversion section 1 for stepping up or down a DC voltage Vdc1 from a DC power supply E1 by open loop control, and a DC/AC conversion section 2 for converting a DC voltage Vdc2 output from the DC/DC conversion section 1 to an AC voltage Vac1 by feedback control. The DC/AC conversion section 2 includes a detection section 23 for detecting the AC voltage Vac1, and a control circuit 24 for feedback-controlling the AC voltage Vac1 in a direction to match the detection value of the AC voltage Vac1 to a predetermined desired value.

Description

  The present invention relates to a power conversion device.

  2. Description of the Related Art Conventionally, there is a power conversion device that converts a DC voltage into an AC voltage. Generally, a DC / DC converter that boosts or lowers a DC voltage, and a DC / DC that converts a DC voltage output from the DC / DC converter into an AC voltage. An AC converter (see, for example, Patent Document 1).

  For example, the power conversion device B illustrated in FIG. 6 includes a DC / DC conversion unit 101 and a DC / AC conversion unit 102.

  The DC / DC conversion unit 101 includes a switching circuit 1011, a high-frequency transformer Tr 101, a rectifier circuit 1012, a detection unit 1013, and a control circuit 1014.

  The switching circuit 1011 receives the DC voltage Vdc101 of the DC power supply E100 and drives a switching element (not shown) on and off to periodically invert the polarity of the current supplied from the DC power supply E100 and Supply to the primary winding. An induced voltage is generated in the secondary winding of the high-frequency transformer Tr101 and is rectified by the rectifier circuit 1012. A DC voltage Vdc102 is generated between the output terminals of the rectifier circuit 1012. The DC voltage Vdc102 is a voltage obtained by stepping up or down the DC voltage Vdc101.

  The detection unit 1013 detects the DC voltage Vdc102, and the control circuit 1014 performs switching control of the switching circuit 1011 so that the detected value of the DC voltage Vdc102 matches the target voltage. That is, the control circuit 1014 performs feedback control of the DC voltage Vdc102 to the target voltage.

  Next, the DC / AC conversion unit 102 includes a switching circuit 1021, a filter circuit 1022, a detection unit 1023, and a control circuit 1024.

  The switching circuit 1021 receives the DC voltage Vdc102 as an input, and converts the DC voltage Vdc102 into an AC voltage by driving a switching element (not shown) on and off. Then, the AC voltage output from the switching circuit 1021 passes through the filter circuit 1022, and the AC voltage Vac101 in which an unnecessary frequency band is attenuated is output from the filter circuit 1022.

  The detecting unit 1023 detects the AC voltage Vac101, and the control circuit 1024 performs switching control of the switching circuit 1021 so that the detected value of the AC voltage Vac101 matches the target voltage. That is, the control circuit 1024 performs feedback control of the AC voltage Vac101 to the target voltage.

  As described above, the power conversion apparatus B includes detection units 1013 and 1023 that detect outputs of the DC / DC conversion unit 101 and the DC / AC conversion unit 102, and control circuits 1014 and 1024 that perform feedback control based on the detection results. And.

JP 2010-44979 A

  As described above, in a power conversion device including a DC / DC conversion unit and a DC / AC conversion unit, improvement in power efficiency, reduction in the number of components, and downsizing are required.

  The present invention has been made in view of the above reasons, and an object thereof is to provide a DC / DC conversion unit and a DC / AC conversion unit to improve power efficiency, reduce the number of parts, and reduce the size. It is in providing the power converter device which can do.

  The power conversion device of the present invention converts a DC voltage from a DC power source into a DC / DC converter that boosts or steps down a DC voltage by open loop control, and converts a DC voltage output from the DC / DC converter into an AC voltage by feedback control. A DC / AC converter, wherein the DC / AC converter includes a first output detector that detects the AC voltage, and the AC voltage in a direction in which the detected value of the AC voltage matches a predetermined target value. And a control circuit that feedback-controls.

  In the present invention, the DC / DC converter includes a series resonance circuit in which an inductor, a primary winding of a transformer, and a capacitor are connected in series, and a switching operation that periodically inverts a resonance current flowing from the DC power source to the series resonance circuit. It is preferable to provide a switching element for performing the above.

  In the present invention, the switching element is connected in series to the series resonance circuit, and a resonance period from when the switching element is turned on to when the resonance current flowing through the switching element increases and falls below a predetermined current is the switching element. It is preferable that the period is set to be shorter than the ON period of the element.

  In the present invention, the resonance period is preferably set to be equal to or greater than a value obtained by multiplying an ON period of the switching element by 0.7.

  As described above, the present invention includes the DC / DC conversion unit and the DC / AC conversion unit, and has an effect of improving power efficiency, reducing the number of parts, and reducing the size.

It is a block block diagram which shows the power converter device of embodiment. It is a circuit block diagram which shows a DC / DC conversion part same as the above. It is a wave form diagram which shows the voltage and electric current in a diode. It is a wave form diagram which shows the voltage and electric current in the diode of embodiment. It is a wave form diagram which shows a resonance current same as the above. It is a block block diagram which shows the conventional power converter device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 shows a block configuration of a power conversion device A1 (DC / AC converter) of the present embodiment. The power conversion device A1 includes a DC / DC conversion unit 1 and a DC / AC conversion unit 2. Yes.

  The DC / DC converter 1 includes a switching circuit 11, a high frequency transformer Tr1, and a rectifier circuit 12. FIG. 2 shows a circuit configuration of the DC / DC converter 1.

  The switching circuit 11 includes a parallel circuit of switching elements Q1 and Q2 connected in series and switching elements Q3 and Q4 connected in series, and capacitors C1 to C4 connected in parallel to each of the switching elements Q1 to Q4. A DC power supply E1 is connected between both ends of each series circuit of the switching elements Q1, Q2 and the switching elements Q3, Q4. Then, the drive circuit K1 drives the switching elements Q1, Q4 and the switching elements Q2, Q3 alternately on and off. Further, a series resonance circuit K2 is connected between the connection midpoints of switching elements Q1, Q2 and switching elements Q3, Q4. In the series resonant circuit K2, an inductor Ls, a capacitor Cs, and a primary winding N1 of the high frequency transformer Tr1 are connected in series, and the switching circuit 11 constitutes an LLC resonant converter.

  The rectifier circuit 12 includes full-bridge connected diodes D1 to D4 and a capacitor C5 connected between the output terminals. The induced voltage generated in the secondary winding N2 of the high-frequency transformer Tr1 is full-wave rectified by the diodes D1 to D4, and this rectified voltage is applied across the capacitor C5.

  The DC / DC converter 1 configured as described above periodically turns on and off the switching elements Q1 and Q4 and the switching elements Q2 and Q3, thereby periodically supplying the current supplied from the DC power supply E1. The polarity is inverted and supplied to the primary winding N1 of the high-frequency transformer Tr1. An induced voltage is generated in the secondary winding N2 of the high-frequency transformer Tr1, and is rectified by the rectifier circuit 12. A DC voltage Vdc2 is generated between the output terminals of the rectifier circuit 12. The DC voltage Vdc2 is a voltage obtained by stepping up or stepping down the DC voltage Vdc1 input to the DC / DC converter 1 from the DC power supply E1.

  Here, the drive circuit K1 has a predetermined switching frequency (ON) related to each value of the DC voltage Vdc1 input to the DC / DC converter 1 and the DC voltage Vdc2 output from the DC / DC converter 1. The switching elements Q1 to Q4 are turned on / off in the period and the off period). That is, the DC / DC converter 1 generates a DC voltage Vdc2 obtained by boosting or stepping down the DC voltage Vdc1 by open loop control. Therefore, a detection unit for detecting the input / output state of the DC / DC conversion unit 1 and a control circuit for feedback control of the DC voltage Vdc2 are not required, improving power efficiency by reducing power consumption, reducing the number of components, and downsizing. Can be achieved.

  Next, the DC / AC conversion unit 2 includes a switching circuit 21, a filter circuit 22, a detection unit 23 (first output detection unit), and a control circuit 24.

  The switching circuit 21 receives the DC voltage Vdc2 as input and drives the switching element (not shown) on and off to convert the DC voltage Vdc2 into an AC voltage. The AC voltage output from the switching circuit 21 passes through the filter circuit 22 and outputs from the filter circuit 22 an AC voltage Vac1 with an unnecessary frequency band attenuated.

  The detection unit 23 detects the AC voltage Vac1, and the control circuit 24 performs switching control of the switching circuit 21 so that the detected value of the AC voltage Vac1 matches the target voltage. That is, the control circuit 24 performs feedback control of the AC voltage Vac1 to the target voltage.

  As described above, in the power conversion device A1, the DC / DC conversion unit 1 performs open loop control, and the DC / AC conversion unit 2 performs feedback control. Therefore, even when the DC voltage Vdc2 output from the DC / DC converter 1 that performs open loop control varies, the DC / AC converter 2 that performs feedback control may match the output AC voltage Vac1 to the target voltage. it can. That is, the power conversion device A1 can ensure the accuracy of the output voltage while improving power efficiency by reducing power consumption, reducing the number of parts, and reducing the size.

  Further, the DC / DC conversion unit 1 is configured by an LLC resonance type converter using the series resonance circuit K2, and can reduce the switching loss of the switching elements Q1 to Q4, thereby further improving the efficiency. it can.

  Next, the relationship between the switching period of the switching elements Q1 to Q4 of the DC / DC converter 1 and the resonance current of the series resonance circuit K2 will be described.

  3 shows the voltage waveform Y1 of the cathode-anode voltage Vk and the current waveform of the forward current If in the diodes D1 to D4 of the rectifier circuit 12 (hereinafter referred to as the diode DA when the diodes D1 to D4 are not distinguished). Y2 is shown. Note that the resonance current of the series resonance circuit K2 flows through the switching elements Q1 to Q4 (hereinafter referred to as the switching element QA when the switching elements Q1 to Q4 are not distinguished), and the waveform of the resonance current is represented by the forward current If. Is substantially the same as the current waveform Y2.

  After the switching element QA is turned on, the resonance current of the series resonance circuit K2 flows (see current waveform Y2 in FIG. 3). When the switching element QA is turned off while the resonance current is flowing, the current flowing through the diode DA also decreases rapidly, and the reverse recovery current Ir flows through the diode DA (see FIG. 3). In the diode DA, the reverse recovery current Ir causes power loss.

  Therefore, in this embodiment, the relationship between each switching period of the switching element QA and the resonance current is set as shown in FIG. FIG. 4 shows a voltage waveform Y3 of the cathode-anode voltage Vk and a current waveform Y4 of the forward current If in the diode DA. When the switching element QA is turned on, the resonance current flowing through the switching element QA increases. It will decline later. When the period from when the switching element QA is turned on until the resonance current falls below a predetermined current near “0” is defined as the resonance period To, the resonance period To is set to be equal to or less than the on period Ts of the switching element QA. The That is, by adjusting the constants of the inductor Ls and the capacitor Cs of the series resonance circuit K2, the relationship between the resonance period To of the resonance current and the ON period Ts of the switching element QA is set to [To ≦ Ts] in advance. .

  Therefore, when the switching element QA is turned off, the current flowing through the diode DA becomes substantially 0, and the reverse recovery current Ir generated in the diode DA is suppressed, so that the power loss in the rectifier circuit 12 is reduced and the power efficiency is reduced. Further improvement can be achieved.

  FIG. 5 shows current waveforms Y5 and Y6 of the resonance current. The current waveform Y5 is a current waveform when the resonance frequency of the resonance current is increased and set to a short resonance period To1, and the current waveform Y6. These are current waveforms when the resonance frequency of the resonance current is lowered and set to the long resonance period To2. The peak value of the current waveform Y5 corresponding to the short resonance period To1 is higher than the peak value of the current waveform Y6 corresponding to the long resonance period To2, and the power due to the on-resistance of the switching element QA becomes shorter as the resonance period To becomes shorter. Loss increases.

  Therefore, the relationship between the resonance period To and the ON period Ts of the switching element QA is set to [0.7 · Ts ≦ To ≦ Ts]. In this case, the power loss due to the on-resistance of the switching element QA can be suppressed, and the power efficiency can be further improved.

A1 power converter 1 DC / DC converter 11 switching circuit 12 rectifier circuit Tr1 high frequency transformer 2 DC / AC converter 21 switching circuit 22 filter circuit 23 detector (first output detector)
24 Control circuit E1 DC power supply

Claims (4)

A DC / DC converter that steps up or steps down a DC voltage from a DC power supply by open loop control;
A DC / AC converter that converts the DC voltage output from the DC / DC converter into an AC voltage by feedback control;
The DC / AC conversion unit includes a first output detection unit that detects the AC voltage, and a control circuit that feedback-controls the AC voltage in a direction in which a detection value of the AC voltage matches a predetermined target value. The power converter characterized by doing.   The DC / DC converter includes a series resonance circuit in which an inductor, a primary winding of a transformer, and a capacitor are connected in series, and a switching element that performs a switching operation for periodically inverting a resonance current flowing from the DC power source to the series resonance circuit. The power conversion device according to claim 1, further comprising:   The switching element is connected in series to the series resonance circuit, and a resonance period from when the switching element is turned on to when the resonance current flowing through the switching element increases to below a predetermined current is an on period of the switching element. The power converter according to claim 2, wherein the power converter is set as follows.   The power converter according to claim 3, wherein the resonance period is set to be equal to or greater than a value obtained by multiplying an ON period of the switching element by 0.7.

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