POWER CONVERSION APPARATUS, CONTROL DEVICE FOR POWER CONVERSION APPARATUS, AND CONTROL METHOD

Abstract

To stop an occurrence of reverse flow even when there is a decrease in input voltage so that an output voltage is maintained at a prescribed voltage, in an electric power conversion device such as an insulated DC / DC converter.SOLUTION: An electric power conversion device includes: a first switching circuit provided on a primary side of a resonance transformer circuit, and a second switching circuit provided on a secondary side of the resonance transformer circuit. After DC input voltage is converted to AC voltage by the first switching circuit, the resultant voltage is sent to the second switching circuit via the resonance transformer circuit, and the converted AC voltage is converted to DC output voltage to be outputted. The electric power conversion device includes a control circuit that detects the output voltage and maintains the output voltage at a prescribed target value. When it is sensed that the input voltage is equal to or less than a prescribed reference value at which reverse flow occurs in the second switching circuit, the control circuit stops driving for the second switching circuit, thereby stopping the occurrence of reverse flow in the second switching circuit and maintaining the output voltage at the prescribed voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device, such as an isolated DC / DC converter device, and a control device and control method for the power conversion device. [Background technology]

[0002] Patent Document 1 discloses a general isolated DC / DC converter. The isolated DC / DC converter includes a switching circuit, which includes first and second half-bridge circuits connected in parallel to each other, a voltage divider circuit, and DC input power. Here, the first half-bridge circuit includes a first pair of switches connected in series, and the second half-bridge circuit includes a second pair of switches connected in series.

[0003] Patent Document 2 discloses a switching power supply device that can prevent reverse current flow in various operation modes and achieve a stable synchronous rectification function. (1) A switching power supply device in which an input DC voltage is applied to a series resonant circuit, a predetermined output voltage is generated via a transformer, and power is supplied to a load, (2) a series resonant circuit having a current resonant inductor and a current resonant capacitor; (3) a plurality of main switching elements or a group of main switching elements which are alternately turned on and off to switch the current path of the series resonant circuit; (4) a transformer that induces a current from the series resonant circuit to a secondary side by controlling on / off of the main switching element or a group of main switching elements on a primary side; (5) a plurality of synchronous rectification switch elements each having a built-in diode connected in parallel, the plurality of synchronous rectification switch elements being turned on and off in response to one of the plurality of main switch elements or the main switch element group to rectify a secondary current of the transformer; (6) a maximum on-width control circuit that instructs the synchronous rectifier switch element to start a maximum on-width in synchronization with an on-timing of the main switch element or the group of main switch elements and instructs the synchronous rectifier switch element to end the maximum on-width after a predetermined time has elapsed; (7) a synchronization control circuit that controls an on-period of the synchronous rectification switch element so as to turn on the synchronous rectification switch element in synchronization with a timing at which the maximum on-width control circuit instructs the start of the maximum on-width or a conduction timing of the built-in diode detected by a terminal voltage signal of the synchronous rectification switch element, whichever is later, and to turn off the synchronous rectification switch element in synchronization with an off-timing of the main switch element or a group of main switch elements or a timing at which the maximum on-width control circuit instructs the end of the maximum on-width, whichever is earlier; The present invention is characterized by the following features. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2018 / 006961 Brochure [Patent Document 2] JP 2010-098935 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Patent Document 1, there is a problem that when the input voltage is lowered, a reverse current flows to the power supply device.

[0006] In addition, in Patent Document 2, the drive pattern of the secondary side switching circuit is changed according to the output power, thereby making it possible to prevent the reverse flow of current. However, there is a problem in that the reverse flow cannot be suppressed when the input voltage drops.

[0007] An object of the present invention is to solve the above problems and to provide a power conversion device, such as an isolated DC / DC converter, that can stop the occurrence of backflow and maintain the output voltage at a predetermined voltage even when the input voltage drops, and a control device and control method for the power conversion device. [Means for solving the problem]

[0008] A power conversion device according to one aspect of the present invention includes: A power conversion device comprising a first switching circuit provided on a primary side of a resonant transformer circuit and a second switching circuit provided on a secondary side of the resonant transformer circuit, converting a DC input voltage into an AC voltage by the first switching circuit, sending the AC voltage to the second switching circuit via the resonant transformer circuit, and converting the converted AC voltage into a DC output voltage for output, a control circuit that detects the output voltage and maintains the output voltage at a predetermined target value; The control circuit includes: (1) detecting that the input voltage is equal to or lower than a predetermined reference value at which a backflow occurs in the second switching circuit; (2) detecting that an output current from the first switching circuit is equal to or smaller than a predetermined reference value at which a backflow occurs in the second switching circuit; (3) detecting that a phase of an output current relative to an output voltage from the first switching circuit is equal to or smaller than a predetermined reference value at which a reverse current occurs in the second switching circuit; (4) measuring a frequency of an output current from the first switching circuit and detecting that the measured frequency is equal to or lower than a predetermined reference frequency; When either (A) stopping the drive to the second switching circuit, or (B) shortening the time width of the drive signal for the second switching circuit compared to a normal time; The present invention is characterized in that the occurrence of a backflow in the second switching circuit is stopped and the output voltage is maintained at a predetermined voltage. Effect of the Invention

[0009] Therefore, according to the power conversion device of the present invention, in a power conversion device such as an isolated DC / DC converter, even when the input voltage drops, it is possible to stop the occurrence of backflow and maintain the output voltage at a predetermined voltage. [Brief description of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a configuration example of a power conversion device according to a first embodiment. [Diagram 2] 2 is a block diagram showing a configuration example of an isolated DC / DC converter 3 in FIG. 1. [Diagram 3] 3 is a timing chart showing the operation of gate control signals G1 to G12 in the switching circuits 21 and 22 in FIG. 2 under normal circumstances. [Figure 4] 2 is a timing chart of each voltage illustrating the problem and operation of the isolated DC / DC converter 3 of FIG. 1. [Diagram 5] FIG. 11 is a current waveform diagram when the input voltage drops in a conventional isolated DC / DC converter. [Figure 6] 4 is a current waveform diagram when the input voltage drops in the isolated DC / DC converter 3 according to the first embodiment. FIG. [Figure 7] 5 is a timing chart showing voltages and signals indicating the operation of an isolated DC / DC converter 3 according to a modified example of the first embodiment. [Figure 8] FIG. 11 is a block diagram showing an example of the configuration of an insulating DC / DC converter 3A of a power conversion device according to a second embodiment. [Figure 9] FIG. 11 is a block diagram showing an example of the configuration of an insulating DC / DC converter 3B of a power conversion device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the same or similar components are denoted by the same reference numerals.

[0012] (Embodiment 1) Fig. 1 is a block diagram showing a configuration example of a power conversion device according to a first embodiment. In Fig. 1, the power conversion device includes an AC / DC converter 2 with a PFC circuit and an isolated DC / DC converter 3. The AC / DC converter 2 with a PFC circuit converts an AC source The AC voltage from 1 is converted to a predetermined DC voltage while improving the power factor by the PFC circuit, and output to the isolated DC / DC converter 3. Next, the isolated DC / DC converter 3 has resonant transformer circuits 31, 32, and 33, which will be described in detail later with reference to FIG. 2, and converts the input DC voltage Vin into an AC voltage, and then converts the AC voltage obtained via the resonant transformer circuits 31, 32, and 33 into a predetermined DC voltage Vout and outputs it to the load 4.

[0013] Fig. 2 is a block diagram showing a configuration example of the isolated DC / DC converter 3 of Fig. 1. In Fig. 2, the isolated DC / DC converter 3 is configured to include a switching circuit 21, resonant transformer circuits 31, 32, and 33, a switching circuit 22, a smoothing capacitor 23, and a control circuit 10. Here, the control circuit 10 is configured, for example, by a digital computer or the like, and controls the overall operation of the isolated DC / DC converter 3, and specifically, is configured to include an error amplifier 11, a voltage controlled oscillator (VCO) 12, switching drive circuits 13 and 14, and a reverse current detection circuit 15.

[0014] FIG. 3 is a timing chart showing the operation of the gate control signals G1 to G12 having a period T0 in the switching circuits 21 and 22 in FIG. 2 under normal circumstances.

[0015] The switching circuit 21 is a so-called three-phase full-bridge inverter circuit that includes six switching elements Q1 to Q6, which are, for example, MOS field-effect transistors, and generates three high-frequency AC voltages V1, V2, and V3 by pulse-width modulating (PFM) the input DC voltage Vin with a three-phase shift in accordance with gate control signals (PFM control signals) G1 to G6 (see FIG. 3) from the switching drive circuit 13, and outputs these voltages to the switching circuit 22 via resonant transformer circuits 31, 32, and 33, respectively.

[0016] The resonant transformer circuit 31 includes an insulating transformer TR1, inductors L1 and L11, and a resonant capacitor Cr1, where the inductor L1 and the resonant capacitor Cr1 are connected in series with the primary winding of the transformer TR1, and the inductor L11 is connected in parallel with the primary winding of the transformer TR1. The resonant transformer circuit 32 includes an insulating transformer TR2, inductors L2 and L12, and a resonant capacitor Cr2, where the inductor L2 and the resonant capacitor Cr2 are connected in series with the primary winding of the transformer TR2, and the inductor L12 is connected in parallel with the primary winding of the transformer TR2. The resonant transformer circuit 33 includes an insulating transformer TR3, inductors L3 and L13, and a resonant capacitor Cr3, where the inductor L3 and the resonant capacitor Cr3 are connected in series with the primary winding of the transformer TR3, and the inductor L13 is connected in parallel with the primary winding of the transformer TR3. The other ends of the resonance capacitors Cr1, Cr2, and Cr3 are connected together.

[0017] The resonant transformer circuit 31 converts the input high-frequency AC voltage V1 into a high-frequency AC voltage V11 in a resonant state at a predetermined resonant frequency, and then outputs the voltage to the switching circuit 22. The resonant transformer circuit 32 converts the input high-frequency AC voltage V2 into a high-frequency AC voltage V12 in a resonant state at a predetermined resonant frequency, and then outputs the voltage to the switching circuit 22. The resonant transformer circuit 33 converts the input high-frequency AC voltage V3 into a high-frequency AC voltage V13 in a resonant state at a predetermined resonant frequency, and then outputs the voltage to the switching circuit 22.

[0018] The switching circuit 22 is a so-called three-phase full-bridge inverter circuit that includes six switching elements Q7 to Q12, which are, for example, MOS field-effect transistors, and performs PFM on the input DC voltage Vin with a three-phase shift in accordance with gate control signals (PFM control signals) G7 to G12 (see FIG. 3) from the switching drive circuit 14, thereby generating an AC voltage, which is converted into a predetermined DC output voltage Vout via a smoothing capacitor 23 and then output to the load 4.

[0019] An error amplifier 11 of a control circuit 10 compares a DC output voltage Vout with a predetermined target voltage Vtarget, and outputs an error voltage resulting from the comparison to a voltage controlled oscillator (VCO) 12. The voltage controlled oscillator 12 changes an oscillation frequency according to the input error voltage to generate an oscillation signal, and outputs the oscillation signal to switching drive circuits 13 and 14. Each switching drive circuit 13 and 14 changes the frequency of gate control signals G1 to G6 and G7 to G12 according to the input oscillation signal. Specifically, for example, if the DC output voltage Vout becomes higher than the target voltage Vtarget and the error voltage increases in the positive direction, the oscillation frequency of the oscillation signal is increased, and the frequencies of the gate control signals G1 to G6 and G7 to G12 are increased, whereas if the DC output voltage Vout becomes lower than the target voltage Vtarget and the error voltage increases in the negative direction, the oscillation frequency of the oscillation signal is decreased, and the frequencies of the gate control signals G1 to G6 and G7 to G12 are decreased.

[0020] The reverse current detection circuit 15 is a circuit characteristic of this embodiment, which detects the input voltage Vin, compares the input voltage Vin with a predetermined reference value Vref, and outputs a drive stop signal to the switching drive circuit 14 when it detects that the input voltage Vin is equal to or lower than the reference value Vref. The switching drive circuit 14 stops outputting the gate control signals G7 to G17 in response to the drive stop signal. The reference value Vref is set in advance by measuring the reference value of the input voltage Vin when reverse current occurs in an actually created power conversion device. According to a prototype created by the applicant, when the input voltage Vin in a normal state was 400V, the reference value Vref was 310V.

[0021] Next, the significance of the operation of the reverse current detection circuit 15 will be explained below.

[0022] Fig. 4 is a timing chart of each voltage showing the problems and operation of the isolated DC / DC converter 3 in Fig. 1, and Fig. 5 is an example of a current waveform diagram when the input voltage drops in the conventional isolated DC / DC converter. Also, Fig. 5 is an example of a current waveform diagram when the input voltage drops in the isolated DC / DC converter 3 according to the first embodiment.

[0023] If the power supply is interrupted due to an abnormality such as a power outage in the AC power source 1, the output voltage Vout of the isolated DC / DC converter 3, which is a power conversion device, must be maintained at a specified voltage. Maintaining the output voltage makes it possible to prevent malfunctions of the equipment of the load 4 connected in between and to back up the computer.

[0024] That is, for example, as shown in FIG. 4, when the input voltage Vin drops due to a power outage, the output voltage must be held for a certain period of time as shown in voltage Voutideal in FIG. 4. However, in reality, when the input voltage Vin drops due to an abnormality as shown in voltage Voutreal in FIG. 4, a backflow (see Iq in FIG. 5) occurs in the switching elements Q7 to Q12, the output voltage Vout drops due to this backflow, and the holding time Treal becomes shorter than the ideal time Tideal as shown in FIG. 4. In this embodiment, when the backflow occurrence condition "the input voltage Vin becomes equal to or lower than the reference value Vref," the switching drive circuit 22 stops driving the switching elements Q7 to Q12. As a result, no backflow occurs in the switching elements Q7 to Q12 (FIG. 6), and no backflow occurs even if the input voltage Vin drops.

[0025] As described above, according to this embodiment, the reverse current detection circuit 15 is provided which generates a drive stop signal Sstop when the input voltage Vin becomes equal to or lower than a predetermined reference value Vref to stop the drive of the switching drive circuit 14. Therefore, even if the power supply is stopped due to an abnormality such as a power outage of the AC power source 1, the output voltage Vout of the isolated DC / DC converter 3, which is a power conversion device, can be maintained at a predetermined voltage for a longer period of time than in the conventional example, and by maintaining the output voltage, it is possible to perform control to prevent malfunction of the equipment of the connected load 4 and back up the computer during this period.

[0026] (Modification of the first embodiment) FIG. 7 is a timing chart showing voltages and signals indicating the operation of the isolated DC / DC converter 3 according to the modified example of the first embodiment.

[0027] In the first embodiment, when the input voltage Vin becomes equal to or lower than a predetermined reference value Vref, a drive stop signal Sstop is generated to stop driving the switching drive circuit 14. The present invention is not limited to this, and may be configured such that when the input voltage Vin becomes equal to or lower than the predetermined reference value Vref, the on-time of the gate control signals G7 to G12 for the switching circuit 22 is made shorter than that during normal operation. This modification can be applied not only to the first embodiment, but also to the second to fourth embodiments described below.

[0028] Even in this case, even if the power supply is stopped due to an abnormality such as a power outage in the AC power source 1, the output voltage Vout of the isolated DC / DC converter 3, which is a power conversion device, can be maintained at a predetermined voltage for a longer period of time than in the conventional example, and by maintaining the output voltage, it is possible to prevent malfunction of the equipment of the connected load 4 and to back up the computer during this period.

[0029] (Embodiment 2) Fig. 8 is a block diagram showing a configuration example of an isolated DC / DC converter 3A of a power conversion device according to embodiment 2. The isolated DC / DC converter 3A according to embodiment 2 has the following differences compared to the isolated DC / DC converter 3 in Fig. 2. (1) Instead of detecting the input voltage Vin in FIG. 2, voltage detectors CS1, CS2, CS3 are provided which detect high frequency currents I1, I2, I3 flowing due to high frequency AC voltages V1, V2, V3 output from the switching circuit 21. (2) A reverse current detection circuit 15A is provided instead of the reverse current detection circuit 15 in Fig. 2. The reverse current detection circuit 15A measures the frequencies of the currents I1, I2, and I3 detected by the voltage detectors CS1, CS2, and CS3, respectively, using a built-in frequency counter, and outputs a drive stop signal Sstop to the switching drive circuit 14 when at least one of the measured frequency f1 of the current I1, the frequency f2 of the current I2, and the frequency f3 of the current I3 becomes equal to or lower than a predetermined reference frequency fref.

[0030] According to a prototype created by the applicant, when the normal frequencies f1, f2, and f3 were 100 kHz, the reference value fref was 72 kHz.

[0031] According to the second embodiment configured as above, by including the backflow detection circuit 15A, the same effects as those of the first embodiment are achieved.

[0032] (Embodiment 3) Fig. 9 is a block diagram showing a configuration example of an isolated DC / DC converter 3B of a power conversion device according to embodiment 3. The isolated DC / DC converter 3B according to embodiment 3 has the following differences compared to the isolated DC / DC converter 3 in Fig. 2. (1) Instead of detecting the input voltage Vin in FIG. 2, a voltage detector CS is provided that detects a high-frequency current I3 that flows due to a high-frequency AC voltage V3 output from a switching circuit 21. (2) A reverse current detection circuit 15B is provided instead of the reverse current detection circuit 15 in Fig. 2. The reverse current detection circuit 15B detects the phase of the current I3 detected by the voltage detector CS relative to the high frequency AC voltage V3, and outputs a drive stop signal Sstop to the switching drive circuit 14 when the detected phase becomes equal to or smaller than a predetermined reference value θRef.

[0033] The current and high frequency AC voltage to be detected may be the current and voltage related to the voltage V1 or V2. According to a prototype created by the applicant, when the normal phase is 45°, the reference value θref is 30°.

[0034] According to the third embodiment configured as above, by including the backflow detection circuit 15B, the same effects as those of the first embodiment are achieved.

[0035] (Modification) In the above embodiment, the current is detected using the current detectors CS, CS1 to CS3, but the present invention is not limited to this, and the current may be detected using a current sensor or a current detection IC. [Industrial Applicability]

[0036] As described above in detail, according to the present invention, by providing the reverse current detection circuits 15, 15A to 15C, even when the input voltage drops in a power conversion device such as an isolated DC / DC converter, the occurrence of a reverse current can be stopped and the output voltage can be maintained at a predetermined voltage. [Explanation of symbols]

[0037] 1 AC power supply 2 AC / DC converter with PFC circuit 3,3A,3B,3C Isolated DC / DC Converter 4. Load 10, 10A, 10B, 10C Control circuit 11 Error Amplifier 12 Voltage Controlled Oscillator (VCO) 13, 14, 14C Switching drive circuit 15, 15A, 15B, Reverse current detection circuit 21,22 Switching circuits 23 Smoothing capacitor 31-33 Resonant transformer circuit Cr1~Cr3 Resonant capacitors CS,CS1~CS3 Current detector G1~G12 Gate control signals L1~L13 Inductors Q1~Q12 Switching elements TR1~TR3 Isolation transformer

Claims

1. A power conversion device comprising: a first switching circuit provided on a primary side of a resonant transformer circuit; and a second switching circuit provided on a secondary side of the resonant transformer circuit, wherein a DC input voltage is converted into an AC voltage by the first switching circuit, and then the converted AC voltage is sent to the second switching circuit via the resonant transformer circuit, and the converted AC voltage is converted into a DC output voltage and output, a control circuit that detects the output voltage and maintains the output voltage at a predetermined target value; The control circuit includes: (1) detecting that a phase of an output current with respect to an output voltage from the first switching circuit is equal to or smaller than a predetermined reference value at which a reverse current occurs in the second switching circuit; (2) measuring a frequency of an output current from the first switching circuit and detecting that the measured frequency is equal to or lower than a predetermined reference frequency; When either (A) stopping the drive to the second switching circuit, or (B) shortening the time width of the drive signal for the second switching circuit compared to a normal time; a second switching circuit that switches the output of the power converter from a first switching circuit to a second switching circuit;

2. A control circuit for a power conversion device comprising: a first switching circuit provided on a primary side of a resonant transformer circuit; and a second switching circuit provided on a secondary side of the resonant transformer circuit, the control circuit converting a DC input voltage into an AC voltage by the first switching circuit, sending the AC voltage to the second switching circuit via the resonant transformer circuit, and converting the converted AC voltage into a DC output voltage for output; The control circuit detects the output voltage and maintains the output voltage at a predetermined target value; The control circuit includes: (1) detecting that a phase of an output current with respect to an output voltage from the first switching circuit is equal to or smaller than a predetermined reference value at which a reverse current occurs in the second switching circuit; (2) measuring a frequency of an output current from the first switching circuit and detecting that the measured frequency is equal to or lower than a predetermined reference frequency; When either (A) stopping the drive to the second switching circuit, or (B) shortening the time width of the drive signal for the second switching circuit compared to a normal time; A control circuit for a power conversion device, characterized in that it stops occurrence of a backflow in said second switching circuit and maintains an output voltage at a predetermined voltage.

3. A control method for a power conversion device comprising a first switching circuit provided on a primary side of a resonant transformer circuit and a second switching circuit provided on a secondary side of the resonant transformer circuit, converting a DC input voltage into an AC voltage by the first switching circuit, sending the AC voltage to the second switching circuit via the resonant transformer circuit, and converting the converted AC voltage into a DC output voltage for output, comprising: The power conversion device includes a control circuit that detects the output voltage and maintains the output voltage at a predetermined target value, The control method includes the control circuit: (1) detecting that a phase of an output current relative to an output voltage from the first switching circuit is equal to or smaller than a predetermined reference value at which a reverse current occurs in the second switching circuit; (2) measuring a frequency of an output current from the first switching circuit and detecting that the measured frequency is equal to or lower than a predetermined reference frequency; When either (A) stopping the drive to the second switching circuit, or (B) shortening the time width of the drive signal for the second switching circuit compared to a normal time; A method for controlling a power conversion device, comprising the steps of: stopping generation of a backflow in the second switching circuit and maintaining an output voltage at a predetermined voltage.

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