TW202226732A - Electric power conversion device, and device and method for controlling electric power conversion device - Google Patents

Abstract

According to the present invention, in an electric power conversion device such as an insulated DC/DC converter, the occurrence of reverse flow is stopped even when there is a decrease in input voltage, and the output voltage is maintained at a prescribed voltage. This electric power conversion device comprises a first switching circuit provided on the primary side of a resonance transformer circuit, and a second switching circuit provided on the 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 and outputted. The electric power conversion device comprises 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.

Description

Power conversion device, control device for power conversion device, and control method

The present invention relates to a power conversion device such as an insulated direct current (DC)/DC converter device, and a control device and control method of the power conversion device.

In Patent Document 1, a general isolated DC/DC converter is disclosed. The isolated DC/DC converter includes a switching circuit composed of first and second half-bridge circuits connected in parallel with each other, a voltage divider circuit, and DC input power. Here, it is characterized in that 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.

In addition, Patent Document 2 discloses a switching power supply device capable of realizing a stable synchronous rectification function by preventing reverse current flow in various operation modes. The characteristics of the switching power supply device are: (1) It applies an input DC voltage to a series resonant circuit, generates a specified output voltage through a transformer, and supplies power to a load, including: (2) A series resonance circuit, including a current resonance inductor and a current resonance capacitor (condenser); (3) A plurality of main switching elements or groups of main switching elements are alternately switched to switch the current path of the series resonant circuit; (4) a transformer, which switches and controls the main switching element or main switching element group on the primary side, thereby inducing a current from the series resonant circuit to the secondary side; (5) A plurality of switching elements for synchronous rectification, in which built-in diodes are connected in parallel, and switches corresponding to any one of the plurality of main switching elements or main switching element groups, respectively, rectify the secondary current of the transformer ; (6) A maximum on-time control circuit for instructing the start of the maximum on-time with respect to the switching element for synchronous rectification in synchronization with the on-time point of the main switching element or the main switching element group, and at a predetermined time after indicating the end of said maximum on-time; and (7) A synchronous control circuit, and the maximum on-time control circuit instructs the start of the maximum on-time, or the built-in two detected by the voltage signal between the terminals of the switching element for synchronous rectification. The switching element for synchronous rectification is turned on in synchronization with any later one of the on-time points of the pole body, and the off-time point of the main switching element or main switching element group, or the maximum on-time of the main switching element or the main switching element group. The time control circuit turns off the synchronous rectification switching element synchronously at any earlier time point instructing the end of the maximum on-time to turn on the synchronous rectification switching element in the manner described above. control during. [Prior Art Literature] [Patent Literature]

[Patent Document 1] International Publication No. 2018/006961 [Patent Document 2] Japanese Patent Laid-Open No. 2010-098935

[The problem to be solved by the invention]

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

In addition, in Patent Document 2, by changing the drive mode of the secondary-side switching circuit according to the output power, the reverse flow of the current can be prevented. However, there is a problem that the reverse current cannot be suppressed when the input voltage is lowered.

An object of the present invention is to solve the above problems, and to provide a power conversion device, which is a power conversion device such as an isolated DC/DC converter, and a control device and control method of the power conversion device, even if When the input voltage drops, the generation of reverse current can also be stopped, and the output voltage can be maintained at the specified voltage. [Means of Solving Problems]

A power conversion device according to an aspect of the present invention It includes a first switching circuit arranged on the primary side of the resonant transformer circuit, and a second switching circuit arranged on the secondary side of the resonant transformer circuit, and the first switching circuit converts the DC input voltage into After the AC voltage is sent to the second switching circuit through the resonant transformer circuit, the converted AC voltage is converted into a DC output voltage for output, and the power conversion device includes: a control circuit that detects the output voltage and keeps the output voltage at a predetermined target value, The control circuit is (1) It is detected that the input voltage is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (2) It is detected that the output current from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (3) It is detected that the phase of the output current with respect to the output voltage from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (4) Measure the frequency of the output current from the first switching circuit, and detect that the measured frequency is below a predetermined reference frequency In either case, by (A) stop driving of said second switching circuit, or (B) shortening the time range of the driving signal for the second switching circuit from the normal time, Then, the generation of the reverse current in the second switching circuit is stopped, and the output voltage is maintained at a predetermined voltage. [Effect of invention]

Therefore, according to the power conversion device of the present invention, even when the input voltage drops, in a power conversion device such as an isolated DC/DC converter, the generation of reverse current can be stopped, and the output voltage can be maintained at a predetermined voltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same symbol is attached|subjected to the same or the same structural element.

(Embodiment 1) FIG. 1 is a block diagram showing an example of the configuration of a power conversion device according to Embodiment 1. As shown in FIG. In FIG. 1 , the power conversion device includes an AC (Alternating Current, alternating current)/DC (Direct Current, direct current) converter 2 with a power factor correction (power factor correction, PFC) circuit, and an isolated DC/DC converter 3 and constitute. The AC/DC converter 2 with a PFC circuit improves the power factor of the AC voltage from the AC power source 1 by the PFC circuit, converts it into a predetermined DC voltage, and outputs it to the isolated DC/DC converter 3 . Next, as described in detail below with reference to FIG. 2 , the isolated DC/DC converter 3 includes a resonance transformer circuit 31 , a resonance transformer circuit 32 , and a resonance transformer circuit 33 , and after converting the input DC voltage Vin into an AC voltage , the AC voltage obtained via the resonance transformer circuit 31 , the resonance transformer circuit 32 , and the resonance transformer circuit 33 is converted into a predetermined DC voltage Vout and output to the load 4 .

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 includes a switching circuit 21 , a resonance transformer circuit 31 , a resonance transformer circuit 32 , a resonance transformer circuit 33 , a switching circuit 22 , a capacitor 23 , and a control circuit 10 . . Here, the control circuit 10 includes, for example, a digital computer or the like, and controls the entire operation of the isolated DC/DC converter 3 , and specifically includes an error amplifier 11 , a voltage controlled oscillator (VCO) 12 , The switching drive circuit 13 , the switching drive circuit 14 , and the reverse current detection circuit 15 are constituted.

FIG. 3 is a timing chart showing the operations of the gate control signal G1 to the gate control signal G12 having a period T0 in the switching circuit 21 and the switching circuit 22 in the normal time of FIG. 2 .

The switching circuit 21 includes, for example, six switching elements Q1 to Q6 that are metal-oxide-semiconductor (MOS) field-effect transistors, and are so-called three-phase full-bridge inverter circuits. The pole control signal (pulse frequency modulation (PFM) control signal) G1 ~ the gate control signal G6 (refer to Figure 3), use the three-phase phase shift to pulse width modulation (PFM) the input DC voltage Vin , thereby generating three high-frequency AC voltages V1 , V2 and V3 , which are respectively output to the switching circuit 22 via the resonance transformer circuit 31 , the resonance transformer circuit 32 , and the resonance transformer circuit 33 .

The resonant transformer circuit 31 includes an insulating transformer TR1, an inductor L1, an inductor L11, and a resonant capacitor Cr1. Here, the inductor L1 and the resonant capacitor Cr1 are connected in series with the primary winding of the transformer TR1. 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, an inductor L2, an inductor L12, and a resonant capacitor Cr2. Here, the inductor L2 and the resonant capacitor Cr2 are connected in series with the primary winding of the transformer TR2. connected, the inductor L12 is connected in parallel with the primary winding of the transformer TR2. Further, the resonant transformer circuit 33 includes an insulating transformer TR3 , an inductor L3 , an inductor L13 , and a resonant capacitor Cr3 . Here, the inductor L3 and the resonant capacitor Cr3 are connected in series with the primary winding of the transformer TR3 connected, the inductor L13 is connected in parallel with the primary winding of the transformer TR3. Furthermore, the other ends of each of the resonant capacitors Cr1, the resonant capacitors Cr2, and the resonant capacitors Cr3 are connected together.

The resonant transformer circuit 31 converts the input high-frequency AC voltage V1 into a high-frequency AC voltage V11 in a resonance state at a predetermined resonance frequency, and outputs the converted high-frequency AC voltage V11 to the switching circuit 22 . In addition, the resonance transformer circuit 32 converts the input high-frequency AC voltage V2 into a high-frequency AC voltage V12 in a resonance state of a predetermined resonance frequency, and outputs it to the switching circuit 22 . Furthermore, the resonance transformer circuit 33 converts the input high-frequency AC voltage V3 into a high-frequency AC voltage V13 in a resonance state of a predetermined resonance frequency, and outputs the converted high-frequency AC voltage V13 to the switching circuit 22 .

The switching circuit 22 includes, for example, six switching elements Q7 to Q12 which are MOS field effect transistors, and is a so-called three-phase full-bridge frequency conversion circuit. The control signal G12 (refer to FIG. 3 ) uses the three-phase phase shift to perform PFM on the input DC voltage Vin, thereby generating an AC voltage, which is converted into a predetermined DC output voltage Vout through a smoothing capacitor (capacitor) 23, and then output to the load. 4.

The error amplifier 11 of the control circuit 10 compares the DC output voltage Vout with a predetermined target voltage Vtarget, and outputs the error voltage resulting from the comparison to a voltage controlled oscillator (VCO) 12 . The voltage controlled oscillator 12 changes the oscillation frequency according to the input error voltage, and generates an oscillation signal, which is output to the switching driving circuit 13 and the switching driving circuit 14 . The switching driving circuit 13 and the switching driving circuit 14 change the frequencies of the gate control signal G1 - the gate control signal G6 and the gate control signal G7 - the gate control signal G12 according to the input oscillation signal. Specifically, for example, if the DC output voltage Vout is greater 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 gate control signal G1-gate control signal G6 and the gate control signal G7 are increased. ~ the frequency of the gate control signal G12, on the other hand, if the DC output voltage Vout is lower than the target voltage Vtarget, the error voltage becomes larger in the negative direction, the oscillation frequency of the oscillation signal will be reduced, and the gate control signal G1 ~ gate The frequency of the pole control signal G6, the gate control signal G7 ~ the gate control signal G12.

The reverse current detection circuit 15 is a characteristic circuit of the present embodiment, and detects the input voltage Vin, compares the input voltage Vin with a predetermined reference value Vref, and drives when the input voltage Vin is detected to be equal to or less than the reference value Vref. The stop signal is output to the switching driving circuit 14 . The switching driving circuit 14 stops the output of the gate control signal G7 - the gate control signal G12 in response to the driving stop signal. In addition, the reference value Vref is set in advance by measuring the reference value of the input voltage Vin at the time of reverse flow in the power conversion device actually produced. Furthermore, according to the prototype machine made by the applicant, when the input voltage Vin is 400V in normal state, the reference value Vref is 310V.

Next, the significance of the operation of the backflow detection circuit 15 will be described below.

FIG. 4 is a timing chart showing the problems in the isolated DC/DC converter 3 of FIG. 1 and the respective voltages in operation, and FIG. 5 is a current waveform diagram when the input voltage is lowered in the isolated DC/DC converter of the conventional example. An example. In addition, it is an example of a current waveform diagram when the input voltage drops in the isolated DC/DC converter 3 of the first embodiment.

When the power supply is stopped due to an abnormality such as a power failure of the AC power supply 1, it is necessary to maintain the output voltage Vout of the isolated DC/DC converter 3 as a power conversion device at a predetermined voltage. The malfunction prevention control of the equipment of the connected load 4 or the backup of the computer is performed.

That is, for example, as shown in FIG. 4 , when the input voltage Vin decreases due to a power failure, the output voltage must be maintained at the voltage Voutideal in FIG. 4 for a certain period of time, but in fact, the input voltage Vin is abnormal when the voltage Voutreal in FIG. 4 is abnormal. When decreasing, the switching element Q7 - the switching element Q12 generate a reverse current (refer to Iq in FIG. 5 ), the reverse current causes the output voltage Vout to decrease, and as shown in FIG. 4 , the holding time Treal becomes shorter than the ideal time Tideal. In the present embodiment, when the input voltage Vin, which is the condition for generating the reverse current, becomes equal to or lower than the reference value Vref, the driving of the switching element Q7 to the switching element Q12 by the switching drive circuit 22 is stopped. Thereby, a reverse current does not occur in the switching element Q7 - the switching element Q12 ( FIG. 6 ), and the reverse current does not occur even if the input voltage Vin decreases.

As described above, according to the present embodiment, the reverse current detection circuit 15 is included. When the input voltage Vin becomes equal to or lower than the predetermined reference value Vref, the reverse current detection circuit 15 generates the drive stop signal Sstop and stops the switching of the drive circuit 14. drive. Therefore, even when the power supply is stopped due to an abnormality such as a power failure of the AC power supply 1, the output voltage Vout of the isolated DC/DC converter 3 serving as the power conversion device can be maintained at a time period longer than that in the conventional example. By keeping the output voltage at a predetermined voltage, it is possible to prevent malfunction of the equipment of the connected load 4 and back up the computer.

(Variation of Embodiment 1) 7 is a timing chart of voltages and signals showing the operation of the isolated DC/DC converter 3 according to the modification of the first embodiment.

In the first embodiment, when the input voltage Vin becomes equal to or lower than the predetermined reference value Vref, the drive stop signal Sstop is generated, and the drive of the switching drive circuit 14 is stopped. The present invention is not limited to this, and may be configured as follows: when the input voltage Vin is equal to or less than the predetermined reference value Vref The action is relatively short. The modified example can be applied not only to Embodiment 1 but also to Embodiments 2 to 4 described below.

In this case, even when the power supply is stopped due to an abnormality such as a power failure of the AC power source 1, the output voltage Vout of the isolated DC/DC converter 3 as the power conversion device can be made longer than that in the conventional example. A predetermined voltage is maintained for a certain period of time, and by maintaining the output voltage, malfunction prevention control of the equipment of the connected load 4 or backup of the computer can be performed during the period.

(Embodiment 2) FIG. 8 is a block diagram showing an example of the configuration of the isolated DC/DC converter 3A of the power conversion device according to the second embodiment. The isolated DC/DC converter 3A of the second embodiment is different from the isolated DC/DC converter 3 of FIG. 2 in the following points. (1) In place of the voltage detection of the input voltage Vin shown in FIG. 2 , a voltage detector CS1 , a voltage detector CS2 , and a voltage detector CS3 are included to detect the high-frequency AC voltage V1 and the high-frequency AC voltage output by the self-switching circuit 21 . The high-frequency current I1, the high-frequency current I2, and the high-frequency current I3 flowing from V2 and the high-frequency AC voltage V3 are detected. (2) Instead of the reverse current detection circuit 15 in FIG. 2 , a reverse current detection circuit 15A is included. The reverse current detection circuit 15A uses a built-in frequency counter to measure the respective frequencies of the current I1 , the current I2 , and the current I3 detected by the voltage detector CS1 , the voltage detector CS2 , and the voltage detector CS3 . When at least one of the frequency f1 of the current I2 , the frequency f2 of the current I2 , and the frequency f3 of the current I3 is equal to or lower than the predetermined reference frequency fref, the drive stop signal Sstop is output to the switching drive circuit 14 .

According to the prototype machine produced by the applicant, when the normal frequency f1, frequency f2, and frequency f3 are 100 kHz, the reference value fref is 72 kHz.

According to the second embodiment configured as described above, by including the backflow detection circuit 15A, the same functions and effects as those of the first embodiment can be obtained.

(Embodiment 3) 9 is a block diagram showing an example of the configuration of an isolated DC/DC converter 3B of the power conversion apparatus according to the third embodiment. The isolated DC/DC converter 3B of the third embodiment is different from the isolated DC/DC converter 3 of FIG. 2 in the following points. (1) In place of the voltage detection of the input voltage Vin in FIG. 2 , a voltage detector CS is included to detect the high-frequency current I3 flowing by the high-frequency AC voltage V3 output from the switching circuit 21 . (2) Instead of the reverse current detection circuit 15 in FIG. 2 , a reverse current detection circuit 15B is included. The reverse current detection circuit 15B detects the phase of the current I3 detected by the voltage detector CS with respect to the high-frequency AC voltage V3, and when the detected phase is equal to or less than a predetermined reference value θRef, switches to the drive circuit 14 Output drive stop signal Sstop.

Furthermore, the detected current and the high-frequency AC voltage can also be the current and voltage related to the voltage V1 or the voltage V2. According to the prototype machine made by the applicant, when the normal phase is 45º, the reference value θref is 30º.

According to the third embodiment configured as described above, by including the backflow detection circuit 15B, the same functions and effects as those of the first embodiment can be obtained.

(Variation) In the above embodiment, the current is detected by using the current detector CS, the current detector CS1 to the current detector CS3, but the present invention is not limited to this, and a current sensor or a current detection integrated circuit (IC) may also be used. ) to detect the current. [Industrial Availability]

As described in detail above, according to the present invention, by including the reverse current detection circuit 15 , the reverse current detection circuit 15A to the reverse current detection circuit 15B, in a power conversion device such as an isolated DC/DC converter, the When the input voltage drops, the generation of reverse current can also be stopped, and the output voltage can be maintained at the specified voltage.

1: AC power supply 2: AC/DC converter with PFC circuit 3, 3A, 3B: isolated DC/DC converter 4: load 10, 10A, 10B: Control circuit 11: Error amplifier 12: Voltage Controlled Oscillator (VCO) 13, 14: Switch the drive circuit 15, 15A, 15B: reverse current detection circuit 21, 22: Switching circuit 23: smoothing capacitor (capacitor) 31～33: Resonant transformer circuit Cr1～Cr3: resonant capacitor (capacitor) CS, CS1 to CS3: Current detector G1～G12: Gate control signal I1～I3: High frequency current L1～L13: Sensor Q1～Q12: switching element TR1～TR3: Insulation transformer V1～V3, V11～V13: high frequency AC voltage

FIG. 1 is a block diagram showing an example of the configuration of a power conversion device according to Embodiment 1. As shown in FIG. FIG. 2 is a block diagram showing a configuration example of the isolated DC/DC converter 3 of FIG. 1 . FIG. 3 is a timing chart showing operations of the gate control signal G1 to the gate control signal G12 in the switching circuit 21 and the switching circuit 22 in the normal time of FIG. 2 . FIG. 4 is a timing chart showing the problems in the isolated DC/DC converter 3 of FIG. 1 and the respective voltages that operate. FIG. 5 is a current waveform diagram when the input voltage is lowered in the isolated DC/DC converter of the conventional example. FIG. 6 is a current waveform diagram when the input voltage decreases in the isolated DC/DC converter 3 according to the first embodiment. 7 is a timing chart of voltages and signals showing the operation of the isolated DC/DC converter 3 according to the modification of the first embodiment. FIG. 8 is a block diagram showing an example of the configuration of the isolated DC/DC converter 3A of the power conversion device according to the second embodiment. 9 is a block diagram showing an example of the configuration of an isolated DC/DC converter 3B of the power conversion apparatus according to the third embodiment.

1: AC power supply

2: AC/DC converter with PFC circuit

3: Isolated DC/DC converter

4: load

Claims (3)

A power conversion device, comprising: a first switching circuit arranged on the primary side of a resonant transformer circuit; and a second switching circuit arranged on the secondary side of the resonant transformer circuit, After the DC input voltage is converted into an AC voltage, it is sent to the second switching circuit through the resonant transformer circuit, and the converted AC voltage is converted into a DC output voltage for output, The power conversion device includes: a control circuit that detects the output voltage and keeps the output voltage at a predetermined target value, The control circuit is (1) It is detected that the input voltage is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (2) It is detected that the output current from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (3) It is detected that the phase of the output current with respect to the output voltage from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (4) Measure the frequency of the output current from the first switching circuit, and detect that the measured frequency is below a predetermined reference frequency In either case, by (A) stop driving of said second switching circuit, or (B) shortening the time range of the driving signal for the second switching circuit from the normal time, Then, the generation of the reverse current in the second switching circuit is stopped, and the output voltage is maintained at a predetermined voltage. A control circuit of a power conversion device, the power conversion device comprises: a first switching circuit, which is arranged on the primary side of a resonant transformer circuit; and a second switching circuit, which is arranged on the secondary side of the resonant transformer circuit, and is After the first switching circuit converts the DC input voltage into an AC voltage, it is sent to the second switching circuit through the resonant transformer circuit, and the converted AC voltage is converted into a DC output voltage for output, The control circuit detects the output voltage and keeps the output voltage at a predetermined target value, The control circuit is (1) It is detected that the input voltage is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (2) It is detected that the output current from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (3) It is detected that the phase of the output current with respect to the output voltage from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (4) The frequency of the output current from the first switching circuit is measured, and it is detected that the measured frequency is below a predetermined reference frequency In either case, by (A) stop driving of said second switching circuit, or (B) shortening the time range of the driving signal for the second switching circuit from the normal time, Then, the generation of the reverse current in the second switching circuit is stopped, and the output voltage is maintained at a predetermined voltage. A control method for a power conversion device, the power conversion device comprising: a first switching circuit arranged on a primary side of a resonant transformer circuit; and a second switching circuit arranged on a secondary side of the resonant transformer circuit, After the first switching circuit converts the DC input voltage into an AC voltage, it is sent to the second switching circuit through the resonant transformer circuit, and the converted AC voltage is converted into a DC output voltage for output, The power conversion device includes a control circuit that detects the output voltage and keeps the output voltage at a predetermined target value, The control method includes the following steps: the control circuit is (1) It is detected that the input voltage is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (2) It is detected that the output current from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (3) It is detected that the phase of the output current with respect to the output voltage from the first switching circuit is equal to or less than a predetermined reference value at which a reverse current occurs in the second switching circuit, (4) Measure the frequency of the output current from the first switching circuit, and detect that the measured frequency is below a predetermined reference frequency In either case, by (A) stop driving of said second switching circuit, or (B) shortening the time range of the driving signal for the second switching circuit from the normal time, Then, the generation of the reverse current in the second switching circuit is stopped, and the output voltage is maintained at a predetermined voltage.

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