Power conversion method and power conversion device

Abstract

An electric-power conversion device (100) has a class-E electric-power conversion circuit (20). The class-E electric-power conversion circuit (20) has a class-E inverter circuit (30), and a rectifying circuit (40) that is connected to the class-E inverter circuit (30) and that rectifies high-frequency alternating current generated in the class-E inverter circuit (30) into DC or low-frequency AC voltage. The class-E inverter circuit (30) is provided with: an AC-voltage input section (10) into which AC voltage is inputted; a switch (32) that turns current on / off; an input choke inductor (31) connected to at least one end of the switch (32) and to the AC voltage input section (10); and an LC resonant circuit (34) connected to the rectifying circuit (40). The control unit (50) sets the duty-cycle "on time" of the switch (32) on the basis of output current or output power outputted from the class-E electric-power conversion circuit (20).

Description

[Technical Field]

[0001] The present invention relates to a power conversion method and a power conversion device. [Background technology]

[0002] An invention that allows a class E power conversion circuit to operate with high efficiency over a wide input range has been known (Patent Document 1). The invention described in Patent Document 1 allows the class E power conversion circuit to operate with high efficiency over a wide input range by arranging a voltage adjustment means for stabilizing the input voltage of the class E power conversion circuit between the class E power conversion circuit and the AC input voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-196271 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the invention described in Patent Document 1 requires the provision of an additional voltage adjustment means, which increases the size of the power conversion device.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a power conversion method and a power conversion device that can operate with high efficiency without increasing the size. [Means for solving the problem]

[0006] A power conversion method according to one aspect of the present invention sets the on-duty of a switch based on an output current or output power output from an E-class power conversion circuit. [Effects of the Invention]

[0007] According to the present invention, the power conversion device can operate with high efficiency without increasing in size. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a configuration diagram of a power conversion device 100 according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing the relationship between input voltage and switching frequency. [Figure 3] FIG. 3 is a graph showing the relationship between input voltage and switching frequency. [Figure 4] FIG. 4 is a configuration diagram of a power conversion device 100 according to a second embodiment of the present invention. [Figure 5] FIG. 5 is a configuration diagram of a power conversion device 100 according to a third embodiment of the present invention. [Figure 6] FIG. 6 is a map showing the feasibility of zero voltage switching. [Figure 7] FIG. 7 is a configuration diagram of a power conversion device 100 according to a fourth embodiment of the present invention. [Figure 8] FIG. 8 is a map showing the feasibility of zero voltage switching. [Figure 9] FIG. 9 is a configuration diagram of a power conversion device 100 according to a fifth embodiment of the present invention. [Figure 10] FIG. 10 is a map showing the feasibility of zero voltage switching. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same parts are designated by the same reference numerals and the description thereof will be omitted.

[0010] (First embodiment) The configuration of a power conversion device 100 according to the first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the power conversion device 100 includes an AC voltage input unit 10, an E-class power conversion circuit 20, a current sensor 60, and a control unit 50. A load 1 and an AC power source 2 are connected to the power conversion device 100. The E-class power conversion circuit 20 includes an E-class inverter circuit 30 and a rectifier circuit 40.

[0011] The class E inverter circuit 30 includes an input choke inductor 31, a switch 32, a shunt capacitor 33 connected in parallel to the switch 32, and an LC resonant circuit 34. The switch 32 generates a high-frequency AC current by repeatedly turning a high-frequency signal on and off. The switch 32 is configured with a semiconductor transistor such as a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). A capacitor may be disposed as a separate component as the shunt capacitor 33 connected in parallel to the switch 32. However, the shunt capacitor may not be disposed as a separate component by utilizing the parasitic capacitance of the MOSFET used as the switch.

[0012] The rectifier circuit 40 rectifies the high-frequency current generated by the class E inverter circuit 30. The rectifier circuit 40 has a diode, a rectifier-side shunt capacitor connected in parallel to the diode, and an output choke inductor. The rectifier circuit 40 may be a so-called class E rectifier. Alternatively, the rectifier circuit 40 may be a so-called class D rectifier consisting of four bridge-connected diodes.

[0013] It is generally known that the higher the operating frequency of the class E power conversion circuit 20, the smaller the inductance and capacitance values ​​required for the passive components used, such as inductors and capacitors. Utilizing this phenomenon makes it possible to reduce the size of the power conversion device 100. However, in order to operate the class E power conversion circuit 20 at a high frequency and with high efficiency, it is necessary to reduce the turn-on loss that occurs when the switch 32 is switched from off to on.

[0014] The turn-on loss in the class E power conversion circuit 20 occurs due to the following principle. When the switch 32 switches from off to on, the shunt capacitor 33 is short-circuited by the switch 32, causing the electrostatic energy stored in the shunt capacitor 33 to be converted into Joule heat by the switch 32. At this time, the switching loss Psw is expressed by Equation 1 using the capacitance Cs of the shunt capacitor 33 and the voltage Vton across the switch 32 at the moment the switch 32 switches from off to on.

[0015]

number

[0016] The class E power conversion circuit 20 performs so-called zero voltage switching (ZVS), which uses the current of the LC resonant circuit 34 to reduce the voltage across the switch 32 to zero when the switch 32 is off and then turns it on, thereby reducing turn-on loss to zero. This zero voltage switching makes it possible to reduce loss even when the operating frequency is increased, and enables the power conversion device 100 to be made smaller.

[0017] However, the zero-voltage switching operation of the class E power conversion circuit 20 is not unconditionally established; whether it is established or not depends on various conditions, such as the input voltage, output voltage, input current, output current, switching frequency, and on-duty of the switch 32. If zero-voltage switching is not established, the class E power conversion circuit 20 will experience large turn-on losses. For this reason, the class E power conversion circuit 20 has not been used in applications where input / output conditions fluctuate greatly. Furthermore, when it is used, a voltage adjustment means is installed to stabilize the input / output conditions, as in the prior art. However, as mentioned above, installing a voltage adjustment means leads to an increase in the size of the power conversion device.

[0018] Therefore, in this embodiment, the output current of the class E power conversion circuit 20 is detected, and the on-duty of the switch control signal is set based on the detected output current. As shown in FIG. 1, a current sensor 60 detects the output current of the class E power conversion circuit 20. A control unit 50 sets the on-duty of the switch control signal based on the output current detected by the current sensor 60. Specifically, the control unit 50 includes a command value generation unit 51, a comparison unit 52, an on-duty setting unit 53, and a signal generation unit 54. The command value generation unit 51, for example, sets the current value to be supplied to the load 1 as an output current command value and outputs it to the comparison unit 52. The signal generation unit 54 generates a control signal so that the measured value and the command value coincide with the output current command value and outputs it to the switch 32. Since each of these functions constitutes well-known feedback control, detailed description will be omitted. Note that the on-duty refers to the ratio of the on-period to the sum of the on-period and the off-period, i.e., the ratio of the on-period in one cycle.

[0019] Next, an example of the operation of the class E power conversion circuit 20 will be described with reference to Figures 2 and 3. In Figure 2, the horizontal axis represents the input voltage of the class E power conversion circuit 20, and the vertical axis represents the switching frequency of the class E power conversion circuit 20. In Figure 2, the values ​​on the horizontal axis range from 0 V to 283 V, representing the absolute value of the input voltage fluctuation range when the input voltage is 200 V AC. Note that, in a power conversion device that draws power from a general AC power system, it is required to control the input current to have as high a power factor as possible. Unless otherwise specified, the following description of the power conversion device 100 assumes that the power factor of the input current is controlled to have a high power factor. "Controlling the power factor to have a high power factor" means controlling the power factor so that it approaches unity. The graph shown in Figure 2 shows the operating locus of the class E power conversion circuit 20 when operated with an on-duty ratio of 0.55, superimposed on a contour plot of the turn-on loss when the input current power factor is unity, i.e., when the input current has a sinusoidal waveform similar to the input voltage.

[0020] Reference numeral 70 denotes the operating locus when the average output current is 2 A, reference numeral 71 denotes the operating locus when the average output current is 4 A, reference numeral 72 denotes the operating locus when the average output current is 6 A, and reference numeral 73 denotes the operating locus when the average output current is 8 A. The region indicated by reference numeral 80 is the region where zero voltage switching does not occur. The region indicated by reference numeral 81 indicates that the turn-on loss is zero, and is the region where zero voltage switching occurs under the condition that the voltage Vton across the switch 32 at turn-on is 0.

[0021] The graph in FIG. 2 reveals that as the average output current increases from 2 A (reference symbol 70), to 4 A (reference symbol 71), to 6 A (reference symbol 72), to 8 A (reference symbol 73), the switch drive frequency of the class E power conversion circuit 20 must be shifted downward. Under the condition of an on-duty ratio of 0.55, the operating locus for the average output currents of 8 A (reference symbol 73) and 6 A (reference symbol 72) passes through region 81 where zero voltage switching is possible throughout the entire voltage fluctuation range of AC 200 V, from 0 V to 283 V. This indicates that zero voltage switching is achieved over the entire range for AC voltage changes of 50 Hz and 60 Hz. On the other hand, the operating locus for the average output currents of 2 A (reference symbol 70) and 4 A (reference symbol 71) passes through region 80 where zero voltage switching is not achieved. Therefore, under the condition of an average output current of 2 A and 4 A, zero voltage switching is not achieved over the entire range for AC input voltage changes of 50 Hz and 60 Hz.

[0022] In Figure 3, the on-duty cycle is reduced compared to Figure 2. Specifically, in Figure 3, the on-duty cycle is set to 0.45. Under this on-duty cycle, a trajectory where the average output current is 8 A (reference numeral 73) cannot be traced. In other words, the class E power conversion circuit 20 cannot operate under conditions where the average output current is 8 A. As in Figure 2, Figure 3 also shows that as the average output current increases from 2 A (reference numeral 70), to 4 A (reference numeral 71), to 6 A (reference numeral 72), the switch drive frequency of the class E power conversion circuit 20 must be shifted toward lower frequencies. Comparing the zero-voltage switching region (region 81) in Figure 2 with the zero-voltage switching region (region 81) in Figure 3, it can be seen that changing the on-duty cycle from 0.55 to a smaller value of 0.45 shifts the zero-voltage switching region (region 81) toward higher frequencies. This effect was discovered by the inventors of the present invention. 3, part of the operating locus for an average output current of 6 A (reference symbol 72) passes through region 80 where zero voltage switching is not possible, and zero voltage switching cannot be achieved across the entire range for changes in AC voltage. In contrast, the operating locus for average output currents of 4 A (reference symbol 71) and 2 A (reference symbol 70) passes through region 81 where zero voltage switching is possible between 0 V and 283 V, and by lowering the on-duty cycle from 0.55 to 0.45, it becomes possible to achieve zero voltage switching across the entire range for changes in AC voltage, even for average output currents of 2 A and 4 A, where zero voltage switching could not be achieved across the entire range when the on-duty cycle was 0.55.

[0023] In the class E power conversion circuit 20 according to the first embodiment, when the average output current is 8 A, the on-duty is 0.55, and zero voltage switching is established over the entire AC voltage fluctuation range from 0 V to 283 V, the average output current is changed to 2 A. To reduce the average value of the output current, the drive frequency of the switch 32 is changed to a higher frequency. In this case, a new effect can be utilized: reducing the on-duty can shift the zero voltage switching region to a higher frequency. For example, reducing the on-duty from 0.55 to 0.45 enables zero voltage switching to be established over the entire AC voltage fluctuation range from 0 V to 283 V, even when the average output current is 2 A.

[0024] (Action and effect) As described above, the power conversion device 100 according to the first embodiment provides the following advantageous effects.

[0025] The class E power conversion circuit 20 includes a class E inverter circuit 30 and a rectifier circuit 40 connected to the class E inverter circuit 30 and rectifying a high-frequency AC current generated by the class E inverter circuit 30 into a DC or low-frequency AC voltage. The class E inverter circuit 30 includes an AC voltage input unit 10 to which an AC voltage is input, a switch 32 for switching the current on and off, an input choke inductor 31 connected to at least one end of the switch 32 and the AC voltage input unit 10, and an LC resonant circuit 34 connected to the rectifier circuit 40. A control unit 50 sets the on-duty of the switch 32 based on the output current or output power output from the class E power conversion circuit 20. When the class E power conversion circuit 20 connected to an AC voltage needs to output a larger power or current, such as when the output voltage drops due to fluctuations in the load 1 or when the control unit 50 receives an external command to supply a larger power, the control locus of the switch drive frequency of the class E power conversion circuit 20 tends to shift to a lower frequency. In the class E power conversion circuit 20 connected to an AC voltage, increasing the on-duty of the switch 32 shifts the region where zero voltage switching is achieved to the lower frequency side. Therefore, by detecting the magnitude of the output power or output current and increasing the on-duty of the switch 32 when the output power increases, it is possible to achieve zero voltage switching over a wide range of output current or output power and reduce losses.

[0026] Furthermore, the control unit 50 may set the on-duty based on a measured value of the output current or output power output from the class E power conversion circuit 20. In applications where the current drawn by the load 1 connected to the power conversion device 100 is determined independently of the state of the power conversion device 100, setting the on-duty based on a measured value of the output power or output current makes it possible to set an on-duty that is suitable for the actual operating conditions of the class E power conversion circuit 20 at that time. This makes it possible to maintain zero voltage switching even in a transient state where a fluctuation in the load current occurs, thereby reducing losses.

[0027] In the first embodiment, the output current is detected and the on-duty is set based on the detected output current, but the same effect can be obtained when the output voltage is detected separately and the on-duty is set based on the output power obtained by multiplying the output voltage and the output current.

[0028] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to Fig. 4. The second embodiment differs from the first embodiment in that an on-duty setting unit 53 sets an on-duty based on a command value (command value of output current) acquired from a command value generating unit 51. Configurations that overlap with those of the first embodiment will be referred to by reference numerals and will not be described again. The following description will focus on the differences.

[0029] In the second embodiment, the on-duty of the switch control signal of the class E power conversion circuit 20 is set based on the command value of the output current. For example, when the power conversion device 100 is used in an application such as a battery charger, a load 1 such as a battery with a very stable voltage is connected to the output of the power conversion device 100. In this case, the output voltage of the power conversion device 100 is predominantly determined by the state of the load 1, and the power conversion device 100 controls the output current or output power. For example, as shown in FIG. 4, when the power conversion device 100 controls the output current, the control unit 50 sets the current value to be supplied to the load 1 as the output current command value and generates a control signal so that the measured output current and the output current command value become equal to that value. However, in controlling the output current in an application such as a battery charger, the cutoff frequency of the current sensor 60 that detects the output current can be controlled at a frequency as low as, for example, 1 / 100 of the frequency of the switch control signal of the class E power conversion circuit 20. Since a cutoff frequency sufficiently higher than 100 Hz is sufficient, control is possible even with a cutoff frequency of about 10 kHz. When the class E power conversion circuit 20 is operated at, for example, 1 MHz, the relationship between these frequencies is about 1:100. However, when a current sensor with such a low cutoff frequency is used, the measured value will have a large delay relative to the current value of the output current. In the second embodiment, by setting the on-duty based on the output current command value, it becomes possible to achieve zero voltage switching without using an expensive current sensor and without being affected by delays in the measured value.

[0030] As described above, in the second embodiment, the control unit 50 sets the on-duty cycle based on the command value of the output current or output power. In applications such as a battery charger where the power conversion device 100 itself controls the current or power supplied to the load 1, setting the on-duty cycle based on the command value of the output current or output power makes it possible to control the output current or output power of the E-class power conversion circuit 20 to change the on-duty cycle in advance and set the on-duty cycle in advance. Zero-voltage switching can be maintained without being affected by delays in detection of the output current or output power, thereby reducing losses. Furthermore, there is no need to use a current sensor or voltage sensor capable of detecting up to high frequency bands to detect fluctuations in the output current or output power, which contributes to cost reduction.

[0031] (Third embodiment) Next, a third embodiment of the present invention will be described with reference to Figures 5 and 6. A power conversion device 100 according to the third embodiment has a voltage sensor 61 as shown in Figure 5. An on-duty setting unit 53 sets the on-duty of the switch control signal for the E-class power conversion circuit 20 based on the output power, which is the product of the output voltage of the E-class power conversion circuit 20 detected by the voltage sensor 61 and the output current of the E-class power conversion circuit 20 detected by the current sensor 60.

[0032] FIG. 6 is a map showing an evaluation of whether zero voltage switching is achieved across the entire range of AC input voltage fluctuations for the on-duty cycle value and the average output power in the class E power conversion circuit 20 according to the third embodiment. The power conversion device 100 according to the third embodiment references the map shown in FIG. 6 and sets the on-duty cycle so that zero voltage switching can be achieved at the average value of the current output power. This makes it possible to set an appropriate on-duty cycle that can reduce turn-on loss at the current average output power. The map shown in FIG. 6 will now be described. The average output powers are shown as 0.5 kW, 1 kW, 2 kW, and 3 kW. The on-duty cycle values ​​are shown as 0.35, 0.40, 0.45, 0.50, 0.55, and 0.60. The map shown in FIG. 6 is a map obtained by evaluating combinations of average output power and on-duty cycle. This evaluation is performed in advance. This evaluation makes it possible to set a more suitable on-duty by creating a map in advance by changing the average output power and on-duty in a wider range and with higher resolution within the range in which the power conversion device 100 may be used. Also, if the output power average value falls between the resolutions of the output power average value in the pre-evaluated map, it is possible to set an on-duty that is highly likely to establish zero voltage switching over the entire range of the AC input voltage fluctuation range by interpolating between the values.

[0033] As described above, in the third embodiment, the control unit 50 sets the on-duty cycle based on the relationship between the output current or output power and whether or not zero voltage switching can be achieved. Specifically, the control unit 50 sets the on-duty cycle value so that zero voltage switching can be achieved over the entire input voltage range under the output power conditions under which the class E power conversion circuit 20 is currently operating, based on the relationship obtained by previously evaluating whether or not zero voltage switching can be achieved for the average output power value and the on-duty cycle value. This makes it possible to maintain zero voltage switching over a wide range within the fluctuation range of the AC voltage, even if the output voltage of the class E power conversion circuit 20 changes, thereby reducing losses.

[0034] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described with reference to FIGS. 7 and 8. As shown in FIG. 7, the power conversion device 100 according to the fourth embodiment sets the on-duty of the switch control signal of the E-class power conversion circuit 20 based on the output power, which is the product of the output current and output voltage of the E-class power conversion circuit 20, and the output voltage of the E-class power conversion circuit 20. FIG. 8 shows a map evaluating whether zero voltage switching is achieved over the entire range of the AC input voltage fluctuations for the output DC voltage (Vout=260V, 340V, 420V), the on-duty value, and the output power average value in the E-class power conversion circuit 20 according to the fourth embodiment. As shown in FIG. 8, when the output voltage of the E-class power conversion circuit 20 fluctuates, the on-duty that can achieve zero voltage switching over the entire range of the AC input voltage fluctuations changes, even for the same output power average value. The power conversion device 100 according to the fourth embodiment sets the on-duty based on a map evaluating in advance the feasibility of zero voltage switching not only for the output current but also for the output voltage. This makes it possible to set an appropriate on-duty that can reduce turn-on loss at the current average output power even when the output voltage changes.

[0035] For example, if the output voltage Vout is 340V and the average output power is 0.5kW, setting the on-duty to 0.45 will establish zero-voltage switching throughout the entire range of the AC input voltage fluctuation. On the other hand, if the output voltage Vout is 260V and the average output power is 0.5kW, setting the on-duty to 0.45 will result in a range within the AC input voltage fluctuation where zero-voltage switching is not established. For example, if the on-duty is changed to 0.40 under the condition that the output voltage Vout is 260V, it will be possible to establish a zero-voltage switching region within the AC input voltage fluctuation range even in the operating trajectory where the average output power is 0.5kW.

[0036] FIG. 8 illustrates an example of a map for evaluating combinations of output voltage Vout (Vout: 260 V, 340 V, 420 V), average output power (Vout: 0.5 kW, 1 kW, 2 kW, 3 kW), and on-duty (Vout: 0.35, 0.40, 0.45, 0.50, 0.55, 0.60). This evaluation is performed in advance. This evaluation involves varying the average output power and on-duty over a wider range and with higher resolution within the range in which the power conversion device 100 may be used. By creating a map in advance, it becomes possible to set a more suitable on-duty. Furthermore, when the output voltage and average output power fall between the resolutions of the previously evaluated map, interpolating between the values ​​allows for setting an on-duty that is highly likely to achieve zero voltage switching across the entire range of the AC input voltage fluctuation.

[0037] As described above, in the fourth embodiment, the control unit 50 sets the on-duty based on the output voltage output from the class E power conversion circuit 20. When the zero voltage switching region and the control frequency locus change depending on the output voltage in the class E power conversion circuit 20 connected to an AC voltage, the control unit 50 sets the on-duty value based on the output voltage. This makes it possible to set an on-duty that is suitable for the current output voltage, and to maintain zero voltage switching even when the output voltage fluctuates, thereby reducing losses.

[0038] The control unit 50 may set the on-duty based on the relationship between the output voltage, the output current or the output power, and whether or not zero voltage switching can be achieved. This makes it possible to maintain zero voltage switching over a wide range within the fluctuation range of the AC voltage even if the output voltage and output power of the class E power conversion circuit 20 change, thereby reducing losses.

[0039] (Fifth embodiment) Next, a fifth embodiment of the present invention will be described with reference to Figures 9 and 10. The power conversion device 100 according to the fifth embodiment has a voltage sensor 61 and a voltage sensor 62, as shown in Figure 9. In the fifth embodiment, the on-duty of the switch control signal for the E-class power conversion circuit 20 is set taking into consideration not only the output current and output voltage of the E-class power conversion circuit 20 but also the AC input voltage of the E-class power conversion circuit 20.

[0040] FIG. 10 is a map evaluating whether zero voltage switching is established in the entire range of fluctuation of the AC input voltage for the AC input voltage (Vin=AC 200V, 240V), the output DC voltage (Vout=260V, 340V, 420V), the on-duty value, and the average output power in the E-class power conversion circuit 20 according to the fifth embodiment.

[0041] 10, when the AC input voltage of the class E power conversion circuit 20 fluctuates, the on-duty cycle that can establish zero voltage switching over the entire range of the AC input voltage fluctuation changes, even if the output voltage and average output power are the same. The power conversion device 100 of the fifth embodiment sets the on-duty cycle based on a map that evaluates in advance the feasibility of zero voltage switching not only for the output power and output voltage but also for the AC input voltage, so that it can set a suitable on-duty cycle that can reduce turn-on loss at the current average output power even when the output voltage changes.

[0042] For example, when connected to a power grid with an AC input voltage of Vin = 200V AC, setting the on-duty to 0.50 when the output voltage Vout is 340V and the average output power is 1kW will result in operation within the zero-voltage switching region throughout the entire range of the AC input voltage. In contrast, when connected to a power grid with an AC input voltage of Vin = 240V AC, setting the on-duty to 0.50 when the output voltage Vout is 340V and the average output power is 1kW will result in an area within the AC input voltage fluctuation range where zero-voltage switching is not achieved. Under these conditions of AC input voltage Vin = 240V AC and output voltage Vout = 340V, changing the on-duty to 0.45 will result in the zero-voltage switching region being established within the AC input voltage fluctuation range in the operating locus where the average output power is 1kW.

[0043] FIG. 10 illustrates an example of a map for evaluating combinations of AC input voltage Vin (200V, 240V, 260V, 340V, 420V), average output power (0.5kW, 1kW, 2kW, 3kW), and on-duty cycles (0.35, 0.40, 0.45, 0.50, 0.55, 0.60). This evaluation is performed in advance. This evaluation involves varying the average output power and on-duty cycle over a wider range and with higher resolution within the range in which the power conversion device 100 may be used. This allows for the creation of a map in advance, enabling the setting of a more suitable on-duty cycle. Furthermore, when the AC input voltage, output voltage, and average output power fall between the resolutions of the previously evaluated map, interpolating between the values ​​allows for the setting of an on-duty cycle that is highly likely to achieve zero voltage switching across the entire range of the AC input voltage fluctuation.

[0044] As described above, in the fifth embodiment, the control unit 50 sets the on-duty cycle based on the AC voltage value input to the AC voltage input unit 10. In the class E power conversion circuit 20 connected to an AC voltage, when the zero voltage switching region and the locus of the control frequency change depending on the value of the AC input voltage, the control unit 50 sets the on-duty cycle based on the AC input voltage. This makes it possible to set an on-duty cycle that is suitable for the current value of the AC input voltage. Even when connected to a different AC input voltage due to differences in country, region, etc., zero voltage switching can be achieved, thereby reducing losses.

[0045] The control unit 50 may set the on-duty based on the relationship between the AC voltage value input to the AC voltage input unit 10, the output current or output power, and whether or not zero voltage switching can be achieved. This allows zero voltage switching to be achieved over a wide range within the fluctuation range of the AC voltage, even if the AC input voltage of the class E power conversion circuit 20 changes, thereby reducing losses.

[0046] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. [Explanation of symbols]

[0047] 100 power conversion device, 10 AC voltage input section, 20 E-class power conversion circuit, 30 E-class inverter circuit, 31 input choke inductor, 32 switch, 33 shunt capacitor, 34 LC resonant circuit, 40 rectifier circuit, 50 control section

Claims

1. A power conversion method for a power conversion device having a class E power conversion circuit, comprising: the class E power conversion circuit includes an AC voltage input unit to which an AC voltage is input, a class E inverter circuit connected to the AC voltage input unit, and a rectifier circuit connected to the class E inverter circuit and rectifying a high-frequency AC current generated by the class E inverter circuit into a DC or low-frequency AC voltage; The class E inverter circuit comprises: A switch to turn the current on and off, an input choke inductor connected to at least one end of the switch and the AC voltage input; an LC resonant circuit connected to the rectifier circuit, The on-duty of the switch is set based on the relationship between the output current or output power output from the rectifier circuit and whether or not zero voltage switching can be achieved. A power conversion method comprising:

2. The larger the output current or the output power, the larger the on-duty.

2. The power conversion method according to claim 1.

3. The on-duty is set based on a measurement value of the output current or the output power.

3. The power conversion method according to claim 1 or 2.

4. The on-duty is set based on a command value of the output current or the output power.

3. The power conversion method according to claim 1 or 2.

5. The on-duty is set based on the output voltage output from the rectifier circuit.

5. The power conversion method according to claim 1, wherein the power conversion method is a power conversion method for converting a power from a power source to a power source.

6. The on-duty is set based on the relationship between the output voltage, the output current or the output power, and whether or not zero voltage switching can be achieved.

6. The power conversion method according to claim 5.

7. The on-duty is set based on the AC voltage value input to the AC voltage input unit.

7. The power conversion method according to claim 1, wherein:

8. The on-duty is set based on the relationship between the AC voltage value, the output current or the output power, and whether or not zero voltage switching can be achieved.

8. The power conversion method according to claim 7.

9. A power conversion device having a class E power conversion circuit, the class E power conversion circuit includes an AC voltage input unit to which an AC voltage is input, a class E inverter circuit connected to the AC voltage input unit, and a rectifier circuit connected to the class E inverter circuit and rectifying a high-frequency AC current generated by the class E inverter circuit into a DC or low-frequency AC voltage; The class E inverter circuit comprises: A switch to turn the current on and off, an input choke inductor connected to at least one end of the switch and the AC voltage input; an LC resonant circuit connected to the rectifier circuit, The class E power conversion circuit sets the on-duty of the switch based on the relationship between the output current or output power output from the rectifier circuit and whether or not zero voltage switching can be achieved. A power conversion device characterized by:

Images