Power conversion device and method for controlling same

Abstract

The present invention provides a method for controlling a power conversion device (1) comprising: an inverter circuit (2) which has a first switch (Q1) and an LC resonant circuit (5) and which outputs AC power; a rectifier circuit (3) which has a first rectifier element (D1) and a choke inductor (L2) and which converts AC power input from the inverter circuit (2) into DC power for output; a switching circuit (4) which has a second switch (Q2) and a second rectifier element (D2) and which is connected to the output of the rectifier circuit (3); and a control unit (8) that controls the operations of the first switch (Q1) and the second switch (Q2). The control unit (8) manipulates the time ratio of the second switch (Q2) on the basis of the output voltage of the power conversion device (1).

Description

Power conversion device and control method thereof

[0001] The present invention relates to a power conversion device and a control method thereof.

[0002] Power conversion devices that perform power conversion using LC resonance with switching elements and an LC resonant circuit have been known for some time. The conventional power conversion device described in Patent Document 1 converts low-frequency AC power, for example, with an effective voltage of 200 V and a frequency of 50 Hz, into high-frequency AC power boosted by a class E inverter circuit that utilizes LC resonance with switching elements and an LC resonant circuit, and then rectifies the high-frequency AC power into DC power using a class E rectifier circuit. This conventional power conversion device is a so-called class E^2 power conversion device. Zero-voltage switching using LC resonance reduces losses that occur during switching, and increasing the frequency of the switching operation allows for the miniaturization of passive elements used in the power conversion device.

[0003] JP 2021-145433 A

[0004] In the conventional power conversion device described in Patent Document 1, the class E rectifier circuit has at least a rectifier element such as a diode connected in parallel to the output of the class E inverter circuit and a choke inductor connected in series to the rectifier element, and rectifies the boosted high-frequency AC power from the inverter circuit into DC power. This conventional power conversion device has a problem in that the peak voltage of the high-frequency AC power applied across the rectifier element of the class E rectifier circuit is several times the voltage of the DC power output by the class E rectifier circuit.

[0005] An object of the present invention is to provide a power conversion device and a control method thereof that can suppress the peak voltage of AC power applied across a rectifying element of a rectifying circuit.

[0006] One aspect of the present invention is a control method for a power conversion device including: an inverter circuit having a first switch and an LC resonant circuit and outputting AC power; a rectifier circuit having a first rectifier element and a choke inductor and converting AC power input from the inverter circuit into DC power and outputting the DC power; a switching circuit having a second switch and a second rectifier element and connected to the output of the rectifier circuit; and a controller that controls the operation of the first switch and the second switch. The controller operates the duty ratio of the second switch based on the output voltage of the power conversion device.

[0007] According to one aspect of the present invention, it is possible to suppress the peak voltage of AC power applied across a rectifying element of a rectifier circuit.

[0008] Fig. 1 is a circuit diagram showing the configuration of a power conversion device according to each embodiment. Fig. 2 shows the operation of a switching circuit and the waveform of a voltage across a first diode of a rectifier circuit in a power conversion device according to a first embodiment. Fig. 3 shows the operation of a switching circuit and the waveform of a voltage across a first diode of a rectifier circuit in a power conversion device according to a second embodiment.

[0009] Hereinafter, a power conversion device and a control method thereof according to several embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings of the power conversion device and the control method according to each embodiment will be assigned the same reference numerals and their description will be omitted.

[0010] FIG. 1 is a circuit diagram showing the configuration of a power conversion device 1 according to each embodiment of the present invention.

[0011] The power conversion device 1 shown in FIG. 1 has an input terminal connected to a low-frequency AC power source Vi having an effective value of 200 V and a frequency of 50 Hz, and an output terminal connected to a DC load 10 such as a battery. The power conversion device 1 converts AC power supplied from the AC power source Vi into DC power and supplies it to the DC load 10.

[0012] The power conversion device 1 includes an inverter circuit 2, a rectifier circuit 3, a switching circuit 4, an output capacitor Co, and a control unit 8. The power conversion device 1 also includes, as necessary, a first current detection unit 6 that detects an input current to the power conversion device 1, a voltage detection unit 7 that detects an output voltage of the power conversion device 1, and a second current detection unit 9 that detects an output current of the power conversion device 1. The control unit 8 controls the operations of the inverter circuit 2 and the switching circuit 4, and can detect the detection values ​​of the first current detection unit 6, the voltage detection unit 7, and the second current detection unit 9, as well as the voltage of the AC power source Vi.

[0013] The inverter circuit 2 is a class E inverter circuit capable of high-frequency switching by achieving low-loss switching using resonance by an LC resonant circuit 5. The inverter circuit 2 includes a first choke inductor L1, a first switch Q1, a first shunt capacitor C1, and the LC resonant circuit 5, and generates a high-frequency AC current by turning on and off the first switch Q1 using a control unit 8. The first switch Q1 is, for example, a semiconductor switching element such as an N-channel MOSFET.

[0014] A series circuit of a first choke inductor L1 and a first switch Q1 is connected across the AC power supply Vi. A first current detector 6 for detecting the input current of the power conversion device 1 is connected to the series circuit of the first choke inductor L1 and the first switch Q1 as needed. A first shunt capacitor C1 is connected in parallel across the first switch Q1. The connection end between the first choke inductor L1 and the switch Q1 is connected to an LC resonant circuit 5.

[0015] The LC resonant circuit 5 is a series resonant circuit in which a resonant inductor Lr and a resonant capacitor Cr are connected in series. When the first switch Q1 is off, the resonant frequency of the series resonant circuit of the resonant inductor Lr and the resonant capacitor Cr changes the voltage across the switch Q1 into a high-frequency sinusoidal wave.

[0016] The rectifier circuit 3 is a class E rectifier circuit having a first diode D1 and a second shunt capacitor C2 connected in parallel to its input and a second choke inductor L2 connected to its output. It rectifies the high-frequency AC current from the LC resonant circuit 5 and outputs the resulting DC voltage or low-frequency AC voltage as an output voltage. The cathode of the first diode D1 is connected to one end of the resonant capacitor Cr. The anode of the first diode D1 is connected to one end of the first shunt capacitor C1. The second shunt capacitor C2 is connected in parallel to the first diode D1. One end of the second choke inductor L2 is connected to the cathode of the first diode D1 and one end of the second shunt capacitor C2.

[0017] A switching circuit 4 including a second switch Q2 and a second diode D2 is disposed between the rectifier circuit 3 and the DC load 10. The second switch Q2 is, for example, a semiconductor switching element such as an N-channel MOSFET. One end of the second switch Q2 is connected to the other end of the second choke inductor L2. The other end of the second switch Q2 is connected to the other end of the second shunt capacitor C2. The anode of the second diode D2 is connected to the other end of the second shunt capacitor C2 and one end of the second switch Q2. The DC load 10 is connected between the cathode of the second diode and the other end of the second switch Q2 via an output capacitor Co. A voltage detector 7 for detecting the output voltage of the power conversion device 1 is connected between the cathode of the second diode and the other end of the second switch Q2 as needed. A second current detector 9 for detecting the output current of the power conversion device 1 is connected between the cathode of the second diode and the DC load 10 as needed.

[0018] When the first switch Q1 of the inverter circuit 2 is repeatedly turned on and off at the high frequency fr under the control of the control unit 8, a high-frequency AC current of the frequency fr is generated in the LC resonant circuit 5. The rectifier circuit 3 rectifies the high-frequency AC current of the LC resonant circuit 5. At this time, the voltage across the first diode D1 of the rectifier circuit 3 becomes a positive AC voltage obtained by half-wave rectifying the applied AC current of the frequency fr, and this positive AC voltage is smoothed by the second shunt capacitor C2 to produce a DC voltage that supplies power to the second choke inductor L2.

[0019] In the switching circuit 4 arranged downstream of the rectifier circuit 3, when the second switch Q2 is on, the current from the second choke inductor L2 flows through the second switch Q2, and the output voltage Vs of the rectifier circuit 3, which is the voltage at the connection point between the second switch Q2, the second diode D2, and the second choke inductor L2, becomes almost zero. On the other hand, when the second switch Q2 is off, the current from the second choke inductor L2 flows to the DC load 10 via the second diode D2, and the output voltage Vs of the rectifier circuit 3 becomes almost equal to the output voltage Vo applied to the DC load 10.

[0020] Here, the average voltage Vavg of the output voltage Vs of the rectifier circuit 3 can be expressed as Vavg = Vo × (1 - Ds), where Ds is the ratio of the on-time of the second switch Q2 of the switching circuit 4 in the operating cycle. The peak voltage Vd1_peak of the voltage Vd1 across the first diode D1 is a value corresponding to the average voltage Vavg and is several times the average voltage Vavg. In other words, the peak voltage Vd1_peak of the voltage Vd1 across the first diode D1 can be reduced by reducing the average voltage Vavg. The on / off state of the second switch Q2 of the switching circuit 4, i.e., the duty ratio Ds, is controlled by the control unit 8. The output voltage Vo is maintained at a constant value by the output capacitor Co, regardless of fluctuations in the output voltage Vs of the rectifier circuit 3.

[0021] First Embodiment FIG. 2 shows the operation of the switching circuit 4 of the power conversion device 1 and the waveform of the voltage Vd1 across the first diode D1 of the rectifier circuit 3 in the first embodiment.

[0022] When the rectifier circuit 3 is generally used as a class E rectifier circuit, the output voltage Vs of the rectifier circuit 3 is usually a constant DC voltage equal to the output voltage Vo of the power conversion device 1. A half-wave rectified high-frequency AC voltage with a peak voltage Vd1_peak several times the output voltage Vs of the rectifier circuit 3 is applied as the voltage Vd1 across the first diode D1 of the rectifier circuit 3 at a period of 1 / fr.

[0023] On the other hand, in the first embodiment, the control unit 8 controls the duty ratio Ds of the second switch Q2 of the switching circuit 4, thereby arbitrarily controlling the output voltage Vs of the rectifier circuit 3.

[0024] In the first embodiment, the power conversion device 1 includes a voltage detection unit 7 that detects the output voltage Vo. The control unit 8 detects the output voltage Vo of the power conversion device 1 using the voltage detection unit 7 and, based on the detected output voltage Vo, controls the duty ratio Ds of the second switch Q2 so that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 does not exceed a predetermined value. For example, when the duty ratio Ds is zero, the output voltage Vo of the power conversion device 1 is equal to the output voltage Vs of the rectifier circuit 3. When the control unit 8 determines that the output voltage Vo of the power conversion device 1 when the duty ratio Ds is zero is higher than a predetermined value, the control unit 8 sets the duty ratio Ds of the second switch Q2 to a predetermined value based on the output voltage Vo of the power conversion device 1 at that time. That is, the control unit turns the second switch Q2 on and off at a period Ts and a predetermined value of the duty ratio Ds. As a result, as shown in FIG. 2 , the output voltage Vs of the rectifier circuit 3 becomes zero during the on-period of Ts × Ds and has a rectangular waveform that is equal to the output voltage Vo during the off-period of Ts × (1 - Ds). The average voltage Vavg of the output voltage Vs of the rectifier circuit 3 is Vavg = Vo × (1 - Ds). At this time, the peak voltage Vd1_peak of the first diode D1 is suppressed to a value of Vavg / Vo = (1 - Ds), compared to when the second switch Q2 is always off (Ds = 0). The output voltage Vo is maintained at a constant value by the output capacitor Co, regardless of fluctuations in the output voltage Vs of the rectifier circuit 3.

[0025] In this way, in the first embodiment, the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 can be suppressed by manipulating the duty ratio Ds of the second switch Q2 to reduce the average voltage Vavg of the output voltage Vs of the rectifier circuit 3.

[0026] Second Embodiment In a second embodiment, in the power conversion device 1, the duty ratio Ds of the second switch Q2 is controlled under the condition of a specific output voltage Vo or output current Io.

[0027] The peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is several times the average voltage Vavg of the rectifier circuit 3. Furthermore, the peak voltage Vd1_peak, which is the peak value of the voltage applied to the first diode D1, also depends on the output current Io of the power conversion device 1. Therefore, even under the same average voltage Vavg of the rectifier circuit 3, the peak voltage Vd1_peak of the first diode D1 becomes larger when the output current Io is large. Therefore, under the condition that the output voltage Vo or the output current Io of the power conversion device 1 is low, the peak voltage Vd1_peak of the first diode D1 may not become excessively high even if the switching operation of the second switch Q2 of the switching circuit 4 is not performed to reduce the average voltage Vavg of the rectifier circuit 3.

[0028] In the second embodiment, the power conversion device 1 includes a voltage detection unit 7 that detects the output voltage Vo of the power conversion device 1 and a second current detection unit 9 that detects the output current Io.

[0029] When the control unit 8 determines, based on the output voltage Vo detected by the voltage detection unit 7 and the output current Io detected by the second current detection unit 9, that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 exceeds a desired value that has been arbitrarily set, it causes the switching circuit 4 to perform switching operation as in the first embodiment, thereby suppressing the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3.

[0030] When the control unit 8 determines, based on the output voltage Vo detected by the voltage detection unit 7 and the output current Io detected by the second current detection unit 9, that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is equal to or lower than a predetermined desired value, the control unit 8 sets the duty ratio Ds of the second switch Q2 of the switching circuit 4 to zero to turn off the switching operation. FIG. 3 shows the operation of the switching circuit 4 and the waveform of the voltage across the first diode D1 of the rectifier circuit 3 at this time. As a result, when the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 exceeds the desired value, the control unit 8 causes the switching circuit 4 to perform switching operation to suppress the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3, as in the first embodiment. When the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is equal to or lower than the desired value, the control unit 8 stops the switching operation of the switching circuit 4. This improves the power conversion efficiency of the power conversion device 1.

[0031] Third Embodiment In a third embodiment, the conditions of the output voltage Vo and the output current Io that result in high power conversion efficiency for the input voltage and the input current of the power conversion device 1 are acquired in advance and stored in the control unit 8. Then, based on the previously acquired conditions, the control unit 8 operates the duty ratio Ds of the second switch Q2 to achieve the conditions that result in high power conversion efficiency for the current values ​​of the input voltage, input current, output voltage Vo, and output current Io of the power conversion device 1.

[0032] In the third embodiment, the power conversion device 1 includes a first current detection unit 6, a voltage detection unit 7, and a second current detection unit 9. The control unit 8 detects the current values ​​detected by the first current detection unit 6, the voltage detection unit 7, and the second current detection unit 9 and the current value of the AC voltage of the AC power supply Vi, and estimates the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 based on these detected current values.

[0033] When the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 exceeds a desired value that has been arbitrarily set, it causes the switching circuit 4 to perform switching operation as in the first embodiment, thereby suppressing the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3.

[0034] In the power conversion device 1, when the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is equal to or lower than a desired value that has been arbitrarily set, there is no problem in manipulating the duty ratio Ds of the second switch Q2 to control the average voltage Vavg of the rectifier circuit 3 to an arbitrary voltage.

[0035] Using this characteristic, the conditions for the output voltage Vo and output current Io that result in high power conversion efficiency for the input voltage and input current of the power conversion device 1 are acquired and stored in advance in the control unit 8. Then, when the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is equal to or lower than a desired value that has been arbitrarily set, the control unit 8 operates the duty ratio Ds of the second switch Q2 so as to increase the power conversion efficiency, based on the detected current values ​​of the input voltage, input current, output voltage Vo, and output current Io of the power conversion device 1 and the previously acquired conditions.

[0036] As a result, in the third embodiment, when the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 exceeds a desired value that has been arbitrarily set, the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 can be suppressed, and when the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is equal to or lower than the desired value that has been arbitrarily set, the power conversion efficiency of the power conversion device 1 can be improved.

[0037] (Fourth embodiment) In the fourth embodiment, the input voltage, input current, output voltage Vo, and output current Io of the power conversion device 1 are detected, and the control unit 8 calculates the power conversion efficiency of the power conversion device 1 from the detected input voltage, input current, output voltage Vo, and output current Io.

[0038] Here, it is assumed that the average voltage of the rectifier circuit 3 changes from Vavg1 when the duty ratio Ds of the second switch Q2 of the switching circuit 4 is Ds1 to Ds2 when the control unit 8 changes the duty ratio of the switching circuit 4 to Vavg2. Then, the average voltages Vavg1 and Vavg2 are expressed as Vavg1=Vo×(1−Ds1) and Vavg2=Vo×(1−Ds2), respectively.

[0039] In the fourth embodiment, the power conversion device 1 includes a first current detection unit 6, a voltage detection unit 7, and a second current detection unit 9. The control unit 8 detects the values ​​detected by the first current detection unit 6, the voltage detection unit 7, and the second current detection unit 9, and the value of the AC voltage of the AC power supply Vi.

[0040] When the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 exceeds a desired value, the control unit 8 causes the switching circuit 4 to perform switching operation as in the first embodiment, thereby suppressing the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3.

[0041] When the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is equal to or lower than the desired value, it calculates the power conversion efficiency of the power conversion device 1 based on the detected input and output voltages and currents under each operating condition when the duty ratio Ds of the second switch Q2 is changed. Here, the power conversion efficiency when the average output voltage of the rectifier circuit 3 is Vavg1 is defined as η1, and the power conversion efficiency when the average output voltage is Vavg2 is defined as η2. If η1 > η2, it is determined that the efficiency of the power conversion device 1 has decreased due to the change in the duty ratio from Ds1 to Ds2, and the control unit 8 changes the current duty ratio Ds2 in a direction toward Ds1. Furthermore, if η1 < η2, it is determined that the power conversion efficiency of the power conversion device 1 has improved due to the change in the duty ratio from Ds1 to Ds2, and the control unit 8 changes the current duty ratio Ds2 in a direction away from Ds1. In this way, the next duty ratio Ds is determined intermittently and repeatedly based on the power conversion efficiency when the duty ratio Ds of the second switch Q2 of the switching circuit 4 is changed, thereby allowing the power conversion device 1 to operate while maintaining a high power conversion efficiency.

[0042] Although the power conversion device 1 according to each embodiment is exemplified by a configuration including a class E inverter circuit 2, a class E rectifier circuit 3 having a choke inductor L2 on the output side, and a switching circuit 4 arranged between the class E rectifier circuit 3 and the DC load 10, the present invention is not limited to such a configuration. For example, even in a current resonant inverter circuit, generally called an LLC type, which uses a resonant circuit to generate high-frequency current, a bridge-type rectifier circuit having an output inductor, or a power conversion device having a switching circuit arranged downstream of the choke inductor of the rectifier circuit, the voltage applied to the rectifier of the rectifier circuit can be reduced by manipulating the duty ratio of the switching circuit.

[0043] Furthermore, in the power conversion device 1 according to each embodiment, the input of the inverter circuit 2 has been described as an AC power source Vi having an effective value of 200 V and a low frequency of 50 Hz or the like at the input terminal, but this is not limited to this, and the device can operate in the same way even if a DC power source is used instead of the AC power source Vi.

[0044] The power conversion device 1 of the present invention is applicable to charging a storage battery from AC power and external power supply from an electric vehicle.

[0045] REFERENCE SIGNS LIST 1 Power conversion device 2 Inverter circuit 3 Rectifier circuit 4 Switching circuit 5 LC resonant circuit 6 First current detection unit 7 Voltage detection unit 8 Control unit 9 Second current detection unit 10 DC load 10 C1 First shunt capacitor C2 Second shunt capacitor Cr Resonance capacitor Co Output capacitor D1 First diode D2 Second diode Io Output current L1 First choke inductor L2 Second choke inductor Q1 First switch Q2 Second switch Vi AC power supply Vo Output voltage

Claims

1. an inverter circuit having a first switch and an LC resonant circuit and outputting AC power; a rectifier circuit including a first rectifier element and a shunt capacitor connected in parallel to an input and a choke inductor connected to an output, which converts the AC power input from the inverter circuit into DC power and outputs the DC power; a switching circuit having a second switch and a second rectifying element, the switching circuit being connected to the output of the rectifying circuit; a control unit that controls the operations of the first switch and the second switch; A control method for a power conversion device comprising: The control unit controls the duty ratio of the second switch based on the output voltage of the power conversion device. A method for controlling a power conversion device.

2. The control unit Detecting an output voltage of the power conversion device; The duty ratio of the second switch is controlled based on the detected output voltage. The method for controlling a power conversion device according to claim 1 .

3. The control unit Detecting an output voltage and an output current of the power conversion device; The duty ratio of the second switch is controlled based on the detected output voltage and output current. The method for controlling a power conversion device according to claim 1 .

4. The control unit when it is determined that the peak value of the voltage applied to the first rectifier element exceeds a predetermined value based on the detected output voltage and output current, the duty ratio of the second switch is controlled based on the output voltage of the power conversion device; When it is determined that the peak value of the voltage is equal to or less than a predetermined value based on the detected output voltage and output current, the duty ratio of the second switch is set to zero. The method for controlling a power conversion device according to claim 3 .

5. The control unit acquiring in advance conditions of an output voltage and an output current that result in a high power conversion efficiency of the power conversion device relative to an input voltage and an input current of the power conversion device; Detecting an input voltage, an input current, an output voltage, and an output current of the power conversion device; when it is determined that a peak value of the voltage applied to the first rectifier element exceeds a predetermined value based on the detected input voltage, the input current, the output voltage, and the output current, the duty ratio of the second switch is controlled based on the output voltage of the power conversion device; When it is determined that the peak value of the voltage is equal to or less than a predetermined value, the duty ratio of the second switch is controlled based on the previously acquired condition and the detected input voltage, input current, output voltage, and output current so that the power conversion efficiency is increased. The method for controlling a power conversion device according to claim 1 .

6. The control unit Detecting an input voltage, an input current, an output voltage, and an output current of the power conversion device; calculating a power conversion efficiency of the power conversion device based on the detected input voltage, input current, output voltage, and output current; when it is determined that a peak value of the voltage applied to the first rectifier element exceeds a predetermined value based on the detected input voltage, the input current, the output voltage, and the output current, the duty ratio of the second switch is controlled based on the output voltage of the power conversion device; When it is determined that the peak value of the voltage is equal to or less than a predetermined value, the duty ratio of the second switch is controlled so as to increase the power conversion efficiency. The method for controlling a power conversion device according to claim 1 .

7. an inverter circuit having a first switch and an LC resonant circuit and outputting AC power; a rectifier circuit including a first rectifier element and a shunt capacitor connected in parallel to an input and a choke inductor connected to an output, which converts the AC power input from the inverter circuit into DC power and outputs the DC power; a switching circuit having a second switch and a second rectifying element, the switching circuit being connected to the output of the rectifying circuit; a control unit that controls the operations of the first switch and the second switch; Equipped with The control unit controls the duty ratio of the second switch based on the output voltage of the power conversion device. Power conversion device.