Power conversion device and its control method

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

Technical Field

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

Background Art

[0002] Conventionally, a power conversion device that performs power conversion using LC resonance by a switching element and an LC resonance circuit has been known. In the power conversion device of the conventional example described in Patent Document 1, for example, low-frequency AC power with an effective voltage of 200 V and a frequency of 50 Hz is converted into high-frequency AC power boosted by an E-class inverter circuit using LC resonance by a switching element and an LC resonance circuit, and the high-frequency AC power is rectified into DC power by an E-class rectifier circuit. Such a power conversion device of a conventional example can reduce the loss generated during switching by zero-voltage switching using LC resonance, and can also reduce the size of passive elements used in the power conversion device by increasing the switching operation frequency.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0005] The present invention aims to provide a power conversion device and a control method thereof that can suppress the peak voltage of AC power applied across the rectifier elements of a rectifier circuit. [Means for solving the problem]

[0006] One aspect of the present invention is a control method for a power converter comprising: an inverter circuit having a first switch and an LC resonant circuit that outputs AC power; a rectifier circuit having a first rectifier element and a choke inductor that converts AC power input from the inverter circuit into DC power and outputs it; a switching circuit having a second switch and a second rectifier element that is connected to the output of the rectifier circuit; and a control unit that controls the operation of the first switch and the second switch. The control unit operates the time ratio of the second switch based on the output voltage of the power converter. [Effects of the Invention]

[0007] According to one aspect of the present invention, the peak voltage of the AC power across the rectifier element of the rectifier circuit can be suppressed. [Brief explanation of the drawing]

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

[0009] Hereinafter, several embodiments of the power conversion device and its control method according to the present invention will be described in detail with reference to the drawings. In the drawings of the power conversion device and its control method according to each embodiment, the same or corresponding parts are denoted by the same reference numerals and their descriptions are omitted.

[0010] Figure 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 converter 1 shown in Figure 1 has an input terminal connected to a low-frequency AC power source Vi with an effective value of 200V and a frequency of 50Hz, and an output terminal connected to a DC load 10, such as a battery. The converter converts the AC power supplied from the AC power source Vi into DC power and supplies it to the DC load 10.

[0012] The power converter 1 comprises an inverter circuit 2, a rectifier circuit 3, a switching circuit 4, an output capacitor Co, and a control unit 8. The power converter 1 also includes, if necessary, a first current detection unit 6 for detecting the input current of the power converter 1, a voltage detection unit 7 for detecting the output voltage of the power converter 1, and a second current detection unit 9 for detecting the output current of the power converter 1. The control unit 8 controls the operation of the inverter circuit 2 and the switching circuit 4, and can also detect the detected 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 supply Vi.

[0013] 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. Inverter circuit 2 comprises a first choke inductor L1, a first switch Q1, a first shunt capacitor C1, and an LC resonant circuit 5. The control unit 8 turns the first switch Q1 on and off to generate a high-frequency AC current by increasing the frequency of the low-frequency AC input voltage from the AC power supply Vi. The first switch Q1 uses 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 to both ends of the AC power supply Vi. A first current detection unit 6 for detecting the input current of the power converter 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 to both ends of the first switch Q1. The connection end of 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 resonant capacitor Cr causes the voltage across switch Q1 to change 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 the input of the rectifier circuit 3, and a second choke inductor L2 at the output of the rectifier circuit 3. 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 the 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, consisting of a second switch Q2 and a second diode D2, is positioned between the rectifier circuit 3 and the DC load 10. The second switch Q2 uses 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 detection unit 7 for detecting the output voltage of the power converter 1 is connected between the cathode of the second diode and the other end of the second switch Q2 as needed. A second current detection unit 9 for detecting the output current of the power converter 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 switched on and off at a high frequency fr under the control of the control unit 8, a high-frequency AC current of 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 that 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 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, which is located after the rectifier circuit 3, when the second switch Q2 is on, current from the second choke inductor L2 flows through the second switch Q2, so the output voltage Vs of the rectifier circuit 3, which is the voltage at the connection point of the second switch Q2, the second diode D2, and the second choke inductor L2, becomes almost zero. Conversely, when the second switch Q2 is off, current from the second choke inductor L2 flows to the DC load 10 through 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) using the duty ratio Ds which is the ratio of the on-time in the operating cycle of the second switch Q2 of the switching circuit 4. And the peak voltage Vd1_peak of the voltage Vd1 across both ends of the first diode D1 is a value corresponding to the average voltage Vavg and is several times the average voltage Vavg. That is, as the average voltage Vavg is decreased, the peak voltage Vd1_peak of the voltage Vd1 across both ends of the first diode D1 can also be decreased. Note that the on / off, that is, the duty ratio Ds of the second switch Q2 of the switching circuit 4 is controlled by the control unit 8. Note that the output voltage Vo is maintained at a constant value by the output capacitor Co regardless of the fluctuation of 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 both ends of the first diode D1 of the rectifier circuit 3 in the first embodiment.

[0022] In a general usage method as the E-class rectifier circuit of the rectifier circuit 3, the output voltage Vs of the rectifier circuit 3 is usually a DC voltage with a constant value equal to the output voltage Vo of the power conversion device 1. And 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 both ends of 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 output voltage Vs of the rectifier circuit 3 is arbitrarily controlled by controlling the duty ratio Ds of the second switch Q2 of the switching circuit 4 by the control unit 8.

[0024] In the first embodiment, the power converter 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 converter 1 using the voltage detection unit 7 and, based on the detected output voltage Vo, operates the time 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 desired value set arbitrarily. For example, when the time ratio Ds is zero, the output voltage Vo of the power converter 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 converter 1 when the time ratio Ds is zero is higher than a predetermined value, it sets the time ratio Ds of the second switch Q2 to a predetermined value based on the output voltage Vo of the power converter 1 at that time. That is, the control unit turns the second switch Q2 on and off with a period Ts and a time ratio Ds of a predetermined value. As a result, the output voltage Vs of the rectifier circuit 3 becomes zero during the on period of Ts × Ds, as shown in Figure 2, and becomes a rectangular waveform 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 given by Vavg = Vo × (1-Ds). At this time, the peak voltage Vd1_peak of the first diode D1 is suppressed to a magnitude of Vavg / Vo = (1-Ds) compared to when the second switch Q2 is always off (Ds=0). The output voltage Vo is kept at a constant value by the output capacitor Co, regardless of fluctuations in the output voltage Vs of the rectifier circuit 3.

[0025] Thus, 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 time 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 the second embodiment, the power converter 1 controls the time ratio Ds of the second switch Q2 under specific output voltage Vo or output current Io conditions.

[0027] The peak voltage Vd1_peak of the first diode D1 in 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 converter 1. Therefore, even under the same average voltage Vavg conditions of the rectifier circuit 3, the peak voltage Vd1_peak of the first diode D1 becomes larger when the output current Io is large. Consequently, under conditions where the output voltage Vo or output current Io of the power converter 1 is low, the peak voltage Vd1_peak of the first diode D1 may not become excessively high even without switching the second switch Q2 of the switching circuit 4 to reduce the average voltage Vavg of the rectifier circuit 3.

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

[0029] 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, 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 set arbitrarily, and then switches the switching circuit 4 as in the first embodiment to suppress the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3.

[0030] Then, 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, the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is less than or equal to a arbitrarily set desired value, and operates the time ratio Ds of the second switch Q2 of the switching circuit 4 to zero to turn off the switching operation. Figure 3 shows the operation of the switching circuit 4 at this time and the waveform of the voltage across the first diode D1 of the rectifier circuit 3. As a result, when it is determined that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 exceeds the desired value, the switching circuit 4 is switched to suppress the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3, as in the first embodiment. When it is determined that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is less than or equal to the desired value, the switching operation of the switching circuit 4 is stopped. This improves the power conversion efficiency of the power converter 1.

[0031] (Third embodiment) In the third embodiment, the control unit 8 pre-acquires and stores the conditions for output voltage Vo and output current Io that result in high power conversion efficiency for the input voltage and input current of the power converter 1. Then, based on the pre-acquired conditions, the control unit 8 operates the time ratio Ds of the second switch Q2 so that the current values ​​of the input voltage, input current, output voltage Vo, and output current Io of the power converter 1 result in high power conversion efficiency.

[0032] In the third embodiment, the power converter 1 comprises 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, as well as 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] If 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 set arbitrarily, it switches the switching circuit 4 as in the first embodiment to suppress the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3.

[0034] Furthermore, in the power converter 1, if the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is less than or equal to a desired value set arbitrarily, there is no problem in controlling the average voltage Vavg of the rectifier circuit 3 to an arbitrary voltage by manipulating the time ratio Ds of the second switch Q2.

[0035] Utilizing this characteristic, the control unit 8 pre-acquires and stores the conditions for output voltage Vo and output current Io that maximize power conversion efficiency for the input voltage and input current of the power converter 1. Then, when the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is less than or equal to a arbitrarily set desired value, the control unit 8 operates the time ratio Ds of the second switch Q2 to maximize 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 converter 1 and the pre-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 an arbitrarily set desired value, 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 less than or equal to an arbitrarily set desired value, the power conversion efficiency of the power converter 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 converter 1 are detected, and the control unit 8 calculates the power conversion efficiency of the power converter 1 from the detected input voltage, input current, output voltage Vo, and output current Io.

[0038] Here, the control unit 8 assumes that when the time ratio Ds of the second switch Q2 of the switching circuit 4 is changed from a state where the average voltage Vavg1 is when the time ratio Ds1 is set to a state where the average voltage Vavg1 is set to a state where the time ratio Ds of the rectifier circuit 3 is set to a state where the time ratio Ds2 is set to a state where the average voltage Vavg2 is set to a state where the average voltage Vavg2 is set to a state where the time ratio of the switching circuit 4 is set to a state where the time ratio Ds of the second switch Q2 of the switching circuit 4 is set to a state where the average voltage Vavg2 is set to a state where the average voltage Vavg2 is set to a state where the time ratio Ds of the second switch Q2 of the switching circuit 4 is set to a state where the time ratio Ds is set to a state where the average voltage Vavg1 time ratio Ds of the second switch Q2 of the switching circuit 4 is set to a state where the time ratio Ds is set to a state where the average voltage Vavg1 is set to a state where the time ratio Ds of the second switch Q2 of the switching circuit 4 is set to a state where the time ratio Ds is set to a state where the time ratio Ds1 is set to a state where the average voltage Vavg1 is set to a state where the time ratio of the switching circuit 4 is set to a state where the time ratio Ds of the second switch Q2 of the switching circuit 4 is set to a state where the time ratio Ds1 is set to a state

[0039] In the fourth embodiment, the power converter 1 comprises 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, as well as 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 switches the switching circuit 4 as in the first embodiment to suppress the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3.

[0041] If the control unit 8 determines that the peak voltage Vd1_peak of the first diode D1 of the rectifier circuit 3 is less than or equal to a desired value, it calculates the power conversion efficiency of the power converter 1 based on the detected input and output voltages and currents for each operating condition when the time ratio Ds of the second switch Q2 is changed. Here, let η1 be the power conversion efficiency when the average output voltage of the rectifier circuit 3 is Vavg1, and η2 be the power conversion efficiency when it is Vavg2. If η1 > η2, it determines that the efficiency of the power converter 1 has decreased due to the change in the time ratio from Ds1 to Ds2, and changes the current time ratio Ds2 in a direction that brings it closer to Ds1. If η1 < η2, it determines that the power conversion efficiency of the power converter 1 has improved due to the change in the time ratio from Ds1 to Ds2, and changes the current time ratio Ds2 in a direction that moves it further away from Ds1. In this way, the next time ratio Ds is determined based on the power conversion efficiency when the time ratio Ds of the second switch Q2 of the switching circuit 4 is changed, and this process is repeated intermittently. This allows the power converter 1 to operate while maintaining a high power conversion efficiency.

[0042] In each embodiment of the power conversion device 1, an example configuration is given of 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. However, the present invention is not limited to such a configuration. For example, in power conversion devices having a current resonant inverter circuit, commonly called an LLC type, which generates high-frequency current using a resonant circuit, a bridge-type rectifier circuit with an output inductor, and a switching circuit arranged after the choke inductor of the rectifier circuit, the voltage applied to the rectifier of the rectifier circuit can be reduced by manipulating the time ratio of the switching circuit.

[0043] Furthermore, in each embodiment of the power conversion device 1, the input to the inverter circuit 2 was described as a low-frequency AC power supply Vi with an effective value of 200V and a frequency of 50Hz, but it is not limited to this, and it can operate similarly even if a DC power supply is used instead of an AC power supply Vi. [Industrial applicability]

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

[0045] 1. Power converter 2. Inverter Circuit 3 Rectifier circuit 4 Switching Circuits 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 resonant capacitor Co output capacitor D1 First Diode D2 Second Bypass 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, which outputs AC power, A rectifier circuit having a first rectifier element and a shunt capacitor connected in parallel to the input, and a choke inductor connected to the output, which converts the AC power input from the inverter circuit into DC power and outputs it, A switching circuit having a second switch and a second rectifier element, connected to the output of the rectifier circuit, A control unit that controls the operation of the first switch and the second switch. In a control method for a power conversion device, The control unit operates the time ratio of the second switch based on the output voltage of the power converter. A method for controlling a power converter.

2. The control unit, The output voltage of the power converter is detected, The time ratio of the second switch is operated based on the detected output voltage. A control method for a power converter according to claim 1.

3. The control unit, The output voltage and output current of the power converter are detected, The time ratio of the second switch is operated based on the detected output voltage and output current. A control method for a power converter according to claim 1.

4. The control unit, If it is determined that the peak voltage applied to the first rectifier element exceeds a predetermined value based on the detected output voltage and output current, the time ratio of the second switch is operated based on the output voltage of the power converter. If it is determined that the peak value of the voltage is less than or equal to a predetermined value based on the detected output voltage and output current, the time ratio of the second switch is operated to zero. A control method for a power converter according to claim 3.

5. The control unit, The conditions for the output voltage and output current that maximize the power conversion efficiency of the power converter for the input voltage and input current of the power converter are obtained in advance. The input voltage, input current, output voltage, and output current of the power converter are detected. If it is determined that the peak value of the voltage applied to the first rectifier element exceeds a predetermined value based on the detected input voltage, input current, output voltage, and output current, the time ratio of the second switch is operated based on the output voltage of the power converter. If it is determined that the peak value of the voltage is less than or equal to a predetermined value, the time ratio of the second switch is operated based on the previously acquired conditions and the detected input voltage, input current, output voltage, and output current, in order to increase the power conversion efficiency. A control method for a power converter according to claim 1.

6. The control unit, The input voltage, input current, output voltage, and output current of the power converter are detected. Based on the detected input voltage, input current, output voltage, and output current, the power conversion efficiency of the power converter is calculated. If it is determined that the peak value of the voltage applied to the first rectifier element exceeds a predetermined value based on the detected input voltage, input current, output voltage, and output current, the time ratio of the second switch is operated based on the output voltage of the power converter. If it is determined that the peak value of the voltage is below a predetermined value, the time ratio of the second switch is operated so that the power conversion efficiency is increased. A control method for a power converter according to claim 1.

7. An inverter circuit having a first switch and an LC resonant circuit, which outputs AC power, A rectifier circuit having a first rectifier element and a shunt capacitor connected in parallel to the input, and a choke inductor connected to the output, which converts the AC power input from the inverter circuit into DC power and outputs it, A switching circuit having a second switch and a second rectifier element, connected to the output of the rectifier circuit, A control unit that controls the operation of the first switch and the second switch. Equipped with, The control unit operates the time ratio of the second switch based on the output voltage of the power converter. Power converter.

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