Power converter and control method for power converter

Abstract

To provide a power converter in which the efficiency can be increased and noise can be reduced by soft switching.SOLUTION: A power converter is capable of supplying power from a DC power source DC to a load 2, and returning power in the load 2 to the DC power source DC. A first switching element S1 is connected between the DC power source DC and the load 2. A second switching element S2 is connected in parallel with the load 2. One end of a reactor L1 is connected to a connection point between the first and second switching elements S1 and S2. First capacitors C1, C2 and third and fourth switching elements S3, S4 are connected in such a way that a voltage at the other end side of the reactor L1 is at midpoint of a DC voltage Vin of the DC power source DC. An auxiliary winding L2 is magnetically coupled to the reactor L1. An AC side of an auxiliary inverter 3 is connected to both ends of the auxiliary winding L2.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a low-loss, low-noise power converter capable of supplying a pulse voltage at high voltage and high frequency. [Background technology]

[0002] Patent Document 1 discloses a technology that can supply a square-wave pulse voltage to a load by supplying energy to the load via a reactor. Patent Document 1 also discloses that soft switching is performed when the switching element is turned on, thereby reducing switching loss and easing stress on the switching element. However, Patent Document 1 also discloses a switching element that undergoes hard switching when turned off.

[0003] An example of a power converter that improves on Patent Document 1 is shown in Figure 1. Figure 2 shows the basic operating waveforms of an output pulse generation circuit. Here, the load 2 is assumed to be capacitive. The circuit in Figure 1 charges and discharges the voltage of the load 2 using energy stored in the reactor L1, and maintains the voltage using the first and second switching elements S1 and S2, thereby achieving a rectangular waveform output voltage.

[0004] The amount of energy stored in reactor L1 (peak current value) can be controlled by the ON time of third and fourth switching elements S3 and S4, and the dv / dt of the output pulse voltage is controlled by the amount of this energy. By adjusting the ON time of third and fourth switching elements S3 and S4 in accordance with variations in load 2 and inductance and controlling the amount of energy (peak current value), variations in dv / dt can be controlled.

[0005] Next, we will discuss the conditions under which soft switching is possible. The circuit in Figure 1 can achieve soft switching when the condition in the following equation (1) is met. If we consider the load 2 to be a pure capacitor with capacitance C, then the energy of the load 2 is 1 / 2Cv o 2 and the energy 1 / 2Li of the reactor with inductance L pk2 From equation (1), soft switching can be achieved by setting the current flowing through reactor L1 to ipk or more.

[0006]

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[0007] In addition, when the equivalent series resistance component of the reactor in the circuit and the energy consumption of the resistance component of the load are also taken into consideration, it is preferable that the inequality in equation (1) has a larger difference than the range of the equality sign.

[0008] The operation sequence can be divided into the following eight steps as shown in Figure 2.

[0009] (1) Load voltage rise preparation period: The third switching element S3 is turned on while the second switching element S2 is kept on, and energy is stored in the reactor L1. At this time, iL>0.

[0010] (2) Load voltage rise period: The second switching element S2 is turned OFF while the third switching element S3 remains ON, and the energy of the reactor L1 is used to flow current through the third switching element S3, causing the load voltage to rise. When the second switching element S2 is turned OFF, the load voltage is zero, so the second switching element S2 is in zero-voltage switching mode.

[0011] (3) Voltage holding period: The first switching element S1 is turned ON while the third switching element S3 remains ON. The voltage Vin is applied to the reactor L1 at the connection point between the first and second switching elements S1 and S2, and the voltage Vin / 2 is applied to the reactor L1 at the connection point between the third and fourth switching elements S3 and S4, so Vin / 2 is applied to the reactor L1 and the current decreases.

[0012] (4) Voltage holding period: The third switching element S3 is turned OFF while the first switching element S1 is kept ON. At this time, the current in the reactor L1 is 0, so the third switching element S3 performs zero-current switching.

[0013] (5) Load voltage fall preparation period: The fourth switching element S4 is turned on while the first switching element S1 is kept on, and reverse energy is stored in the reactor L1. At this time, iL<0.

[0014] (6) Load voltage fall period: The first switching element S1 is turned off while the fourth switching element S4 remains on, and current flows through the fourth switching element S4 using the energy of the reactor L1, causing the load voltage to fall.

[0015] (7) Voltage holding period: The second switching element S2 is turned ON while the fourth switching element S4 remains ON. The voltage on the reactor L1's side of the connection point between the first and second switching elements S1 and S2 is 0, and the voltage on the reactor L1's side of the connection point between the third and fourth switching elements S3 and S4 is Vin / 2, so Vin / 2 is applied to the reactor L1 and the current decreases.

[0016] (8) Voltage holding period: The fourth switching element S4 is turned OFF while the second switching element S2 remains ON. At this time, the current in the reactor L1 is 0, so the fourth switching element S4 performs zero-current switching.

[0017] Next, an example of soft switching operation is shown in Fig. 3. In Fig. 3, the voltages Vds_s1 to Vds_s4 of the first to fourth switching elements S1 to S4 are shown by solid lines, and the currents ids_s1 to ids_s4 are shown by dashed lines. Vout is the load voltage.

[0018] An example of the operation of the first switching element S1 is shown in Figure 3(a). Because the first switching element S1 is connected in series with the load 2, the voltage applied to it is the DC voltage Vin of the DC power supply DC minus the load voltage Vout. The timing at which the first switching element S1 turns on is the moment when steps (2) and (3) above switch places, and the load voltage Vout has risen to Vin. Therefore, when the first switching element S1 turns on, the applied voltage to the first switching element S1 is 0, and the rate of change of the voltage of the load 2 is slower than the rate at which the switching element cuts off the current, resulting in zero-voltage switching.

[0019] On the other hand, the timing when the first switching element S1 turns off is the moment when the above steps (5) and (6) are switched over, and the load voltage Vout is Vin. Therefore, when the first switching element S1 turns off, the applied voltage to the first switching element S1 is 0, and the voltage change rate of the load 2 is slower than the current interruption rate of the switching element, resulting in zero voltage switching.

[0020] An example of the operation of the second switching element S2 is shown in Figure 3(b). Because the second switching element S2 is connected in parallel with the load 2, the voltage applied to it is the same as the load voltage Vout. The moment the second switching element S2 turns off is the moment when steps (1) and (2) above are switched over, and the load voltage is 0. Therefore, when the second switching element S2 turns off, the applied voltage to the second switching element S2 is 0, resulting in zero-voltage switching.

[0021] On the other hand, the timing when the second switching element S2 turns on is the moment when the above steps (6) and (7) are switched over, and the load voltage Vout is 0. Therefore, when the second switching element S2 turns on, the applied voltage to the second switching element S2 is 0, resulting in zero-voltage switching.

[0022] An example of the operation of the third switching element S3 is shown in Figure 3(c). Because the third switching element S3 is connected to the neutral point (the intermediate potential of the DC power supply DC), Vin / 2 is applied, and a portion of the current IL1 passing through the reactor L1 (IL1>0) flows. The timing when the third switching element S3 turns on is the moment when steps (8) and (1) in the above are switched over, and the current IL1 passing through the reactor L1 is 0. Therefore, the current is 0 when the third switching element S3 turns on, and the rate of change of the voltage of the reactor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0023] The timing at which the third switching element S3 turns off is the moment when the above steps (3) and (4) are switched over, and the current IL1 passing through the reactor L1 is 0. Therefore, the current is 0 when the third switching element S3 turns off, and the rate of change of the voltage of the reactor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0024] An example of the operation of the fourth switching element S4 is shown in Figure 3(d). Because the fourth switching element S4 is connected to the neutral point (the intermediate potential of the direct-current power supply DC), Vin / 2 is applied, and a portion of the current IL1 passing through the reactor L1 (IL1<0) flows. The timing when the fourth switching element S4 turns on is the moment when steps (4) and (5) above are switched over, and the current IL1 passing through the reactor L1 is 0. Therefore, the current is 0 when the fourth switching element S4 turns on, and the rate of change of the voltage of the reactor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0025] The timing at which the fourth switching element S4 turns off is the moment when the above steps (7) and (8) are switched over, and the current IL1 passing through the reactor L1 is 0. Therefore, the current is 0 when the fourth switching element S4 turns off, and the rate of change of the voltage of the reactor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0026] The voltages of the first capacitor C1 and the second capacitor C2 can be controlled by the average value of the current flowing in and out of the connection point (neutral point) between the first capacitor C1 and the second capacitor C2. Under conditions where soft switching is possible, all of the current flowing into the neutral point flows through the reactor L1, so the neutral point voltage can also be controlled by controlling the average current value of the reactor L1. The average current value of the reactor L1 can be controlled by changing the ratio between the periods (1) and (5). Theoretically, by controlling the average value to zero, fluctuations in the neutral point potential can be made zero.

[0027] By operating in the above manner, it becomes possible to output an output pulse voltage with a constant dv / dt without being affected by variations in parts or loads while performing soft switching operations on the first to fourth switching elements S1 to S4.

[0028] The following configuration can also achieve the same operation as in Figure 3. The orientation of the switching elements and diodes is the same as in Figure 3. The third and fourth switching elements S3 and S4 are replaced with second and third diodes D2 and D3, and the second and third diodes D2 and D3 are replaced with third and fourth switching elements S3 and S4. The first to fourth diodes D1 to D4 are replaced with fifth to eighth switching elements. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] Japanese Patent Publication No. 2022-7165 Summary of the Invention [Problem to be solved by the invention]

[0030] In the circuit shown in Figure 1, zero-current switching occurs when the third switching element S3 and the fourth switching element S4 are turned on. However, there are cases where voltage is applied across both ends of the third and fourth switching elements S3 and S4, in which case losses occur due to parasitic capacitance. Therefore, as the switching frequency increases, there is the issue of increased losses and noise. This is particularly noticeable when a high voltage is applied and switching is performed at a high frequency.

[0031] In view of the above, it is necessary to provide a power converter that can easily achieve high efficiency and low noise by performing soft switching. [Means for solving the problem]

[0032] The present invention has been devised in view of the above-mentioned problems in the related art, and one aspect of the present invention is a power converter that supplies power from a DC power supply to a load and returns the power of the load to the DC power supply, and is characterized by comprising: a first switching element connected between the DC power supply and the load; a second switching element connected in parallel to the load; a reactor having one end connected to a connection point between the first and second switching elements; a capacitor and third and fourth switching elements connected so that the voltage on the other end of the reactor is intermediate the voltage of the DC power supply; an auxiliary winding magnetically coupled to the reactor; and an auxiliary inverter having an AC side connected to both ends of the auxiliary winding.

[0033] In one embodiment, a voltage matching transformer is connected between the auxiliary winding and the auxiliary inverter.

[0034] In one aspect, the number of turns of the reactor, the number of turns of the auxiliary winding, the DC voltage of the DC power supply, and the DC voltage of the auxiliary inverter satisfy the condition of the following formula (2).

[0035]

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[0036] N1: Number of turns of reactor N2: Number of turns of auxiliary winding Vin: DC voltage of the DC power supply Vsub: DC voltage of the auxiliary inverter.

[0037] In one aspect, the number of turns of the reactor, the number of turns of the auxiliary winding, the number of turns of the primary winding of the voltage matching transformer, the number of turns of the secondary winding of the voltage matching transformer, the DC voltage of the DC power supply, and the DC voltage of the auxiliary inverter satisfy the condition of the following formula (3).

[0038]

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[0039] N1: Number of turns of reactor N2: Number of turns of auxiliary winding N3: Number of turns of the primary winding of the voltage matching transformer N4: Number of turns of the secondary winding of the voltage matching transformer Vin: DC voltage of the DC power supply Vsub: DC voltage of the auxiliary inverter.

[0040] In one embodiment, an auxiliary power supply is connected to the DC side of the auxiliary inverter.

[0041] In one embodiment, an auxiliary capacitor is connected to the DC side of the auxiliary inverter.

[0042] In one aspect, the present invention provides a power supply including a first switching element connected between a DC power source and a load, a second switching element connected in parallel to the load, a reactor having one end connected to a connection point between the first and second switching elements, first and second capacitors connected in series between a positive electrode and a negative electrode of the DC power source, a second diode having an anode connected to the connection point between the first and second capacitors, a third switching element connected between the cathode of the second diode and the other end of the reactor, a third diode having a cathode connected to the connection point between the first and second capacitors, a fourth switching element connected between the anode of the third diode and the other end of the reactor, and a fourth switching element having an anode connected to the connection point between the second diode and the third switching element. a first diode connected to a node between the third diode and the fourth switching element and having its cathode connected to the positive electrode of the DC power supply; a fourth diode connected to a node between the third diode and the fourth switching element and having its anode connected to the negative electrode of the DC power supply; an auxiliary winding magnetically coupled to the reactor; and an auxiliary inverter connected to an AC side of both ends of the auxiliary winding, the power converter being capable of supplying power from the DC power supply to the load and returning the power of the load to the DC power supply, the method comprising: controlling the auxiliary inverter so that a current flows in a negative direction through the reactor before the third switching element is turned on; and controlling the auxiliary inverter so that a current flows in a positive direction through the reactor before the fourth switching element is turned on. [Effects of the Invention]

[0043] According to the present invention, it is possible to provide a power converter that is highly efficient and easy to reduce noise by performing soft switching. [Brief explanation of the drawings]

[0044] [Figure 1] FIG. 1 is a basic configuration diagram of a conventional output pulse generation circuit (power converter). [Figure 2] FIG. 1 is a diagram illustrating the basic operation of a conventional output pulse generating circuit (power converter). [Figure 3]FIG. 10 is a diagram showing an example of soft switching operation. [Figure 4] FIG. 1 is a basic configuration diagram of an output pulse generating circuit (power converter) according to a first embodiment. [Figure 5] FIG. 2 is a diagram showing a configuration example of a reactor according to the first embodiment. [Figure 6] FIG. 2 is a diagram illustrating the basic operation of the output pulse generating circuit (power converter) according to the first embodiment. [Figure 7] FIG. 10 is a basic configuration diagram of an output pulse generating circuit (power converter) according to a second embodiment. [Figure 8] FIG. 10 is a diagram showing a configuration example of a reactor according to a second embodiment. [Figure 9] FIG. 10 is a basic configuration diagram of an output pulse generating circuit (power converter) according to a third embodiment. [Figure 10] FIG. 10 is a diagram showing a configuration example of a reactor according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0045] Hereinafter, first to third embodiments of the power converter of the present invention will be described in detail with reference to FIGS.

[0046] [Embodiment 1] Fig. 4 shows an example circuit of the power converter (output pulse generating circuit) in this embodiment 1. Fig. 5 shows an example configuration of the reactor L1 and auxiliary winding L2. In this embodiment 1, an auxiliary winding L2 is provided that is magnetically coupled to the current control reactor L1, and when the third and fourth switching elements S3 and S4 are turned on, a voltage is applied between A and B of the auxiliary winding L2, causing a current to flow through the reactor L1, thereby reducing the voltage applied to the third and fourth switching elements S3 and S4 to zero, thereby achieving zero voltage switching of the third and fourth switching elements S3 and S4.

[0047] 4, a first capacitor C1 and a second capacitor C2 are connected in series between the positive and negative electrodes of a direct-current power supply DC. A first switching element S1 and a second switching element S2 are connected in series between the positive and negative electrodes of the direct-current power supply DC. A load 2 is connected between the connection point of the first and second switching elements S1 and S2 and the negative electrode of the direct-current power supply DC. That is, the first switching element S1 is connected between the direct-current power supply DC and the load 2, and the second switching element S2 is connected in parallel to the load 2.

[0048] One end of a reactor L1 is connected to the connection point between the first and second switching elements S1 and S2. The anode of a second diode D2 is connected to the connection point between the first and second capacitors C1 and C2. A third switching element S3 is connected between the cathode of the second diode D2 and the other end of the reactor L1.

[0049] The cathode of a third diode D3 is connected to the connection point between the first and second capacitors C1 and C2. A fourth switching element S4 is connected between the anode of the third diode D3 and the other end of the reactor L1.

[0050] The anode of the first diode D1 is connected to the connection point between the second diode D2 and the third switching element S3. The cathode of the first diode D1 is connected to the positive electrode of the DC power supply DC. The cathode of the fourth diode D4 is connected to the connection point between the third diode D3 and the fourth switching element S4. The anode of the fourth diode D4 is connected to the negative electrode of the DC power supply DC. In this manner, the first and second capacitors C1 and C2 and the third and fourth switching elements S3 and S4 are connected so that the voltage on the other end of the reactor L1 is Vin / 2, which is the intermediate voltage Vin of the DC power supply DC. In addition, in the first embodiment, an auxiliary winding L2 is provided which is magnetically coupled to the reactor L1.

[0051] An auxiliary inverter 3 having an auxiliary power supply DCsub is connected to the auxiliary winding L2. A fifth switching element Sa and a sixth switching element Sb are connected in series between the positive and negative electrodes of the auxiliary power supply DCsub. Furthermore, a seventh switching element Sc and an eighth switching element Sd are connected in series between the positive and negative electrodes of the auxiliary power supply DCsub. The connection point between the fifth switching element Sa and the sixth switching element Sb is connected to A of the auxiliary winding L2. The connection point between the seventh switching element Sc and the eighth switching element Sd is connected to B of the auxiliary winding L2. In this way, both ends of the auxiliary winding L2 are connected to the AC side of the auxiliary inverter 3.

[0052] The voltage of the DC power supply DC is Vin, the voltage of the first and second capacitors C1 and C2 is Vin / 2, the current flowing through the reactor L1 is IL1, and the DC voltage of the auxiliary power supply DCsub is Vsub.

[0053] This auxiliary inverter 3 applies a voltage between A and B of the auxiliary winding L2. The auxiliary inverter 3 can be implemented at a low voltage by increasing the turns ratio of the reactor L1 and the auxiliary winding L2, so it can be implemented in a small size, at low cost, and with low power consumption.

[0054] 5, assuming that the number of turns of the reactor L1 is N1 and the number of turns of the auxiliary winding L2 is N2, the following conditional expression (2) is established between the turns ratio of the reactor L1 and the auxiliary winding L2 and the voltage. When the following expression (2) is established, a voltage equal to or greater than the DC voltage Vin of the DC power supply DC is applied to the reactor L1 due to the output voltage from the auxiliary inverter 3, and therefore the voltages of the third and fourth switching elements S3 and S4 can be discharged to 0.

[0055]

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[0056] A detailed operation pattern is shown in Fig. 6. As shown in Fig. 6, by providing a period for setting the voltage Vds of the third and fourth switching elements S3 and S4 to 0 before the third and fourth switching elements S3 and S4 are turned on, zero voltage switching of the third and fourth switching elements S3 and S4 is achieved.

[0057] Since it is necessary to control the voltage of the auxiliary inverter 3 so as not to affect the output, the auxiliary inverter 3 is operated at least during the period when the first switching element S1 or the second switching element S2 is ON and the output voltage is constant.

[0058] For example, when the voltage Vds of the third switching element S3 is set to 0 (between (8) and (1)), the fifth and eighth switching elements Sa and Sd are made conductive. As a result, by passing a current in the negative direction (from the load 2 to the DC power supply DC) through the reactor L1, a current flows through the parasitic capacitance of the third switching element S3 and the first diode D1, and the voltage Vds of the third switching element S3 becomes 0.

[0059] When the voltage Vds of the fourth switching element S4 is set to 0 (4), the sixth and seventh switching elements Sb and Sc are made conductive. As a result, by passing a current in the forward direction (from the direct-current power supply DC to the load 2) through the reactor L1, a current flows through the parasitic capacitance of the fourth switching element S4 and the fourth diode D4, and Vds of the fourth switching element S4 becomes 0.

[0060] This reduces losses that occur due to discharge (spike current) caused by parasitic capacitance in the third switching element S3 or the fourth switching element S4 when the switching elements are turned on. The parasitic capacitance charge at turn-on is released to the auxiliary inverter 3 side via the reactor L1, reducing heat concentration in the third and fourth switching elements S3 and S4. At the same time, energy is regenerated on the auxiliary power supply DCsub side, reducing total losses.

[0061] As described above, according to the first embodiment, zero voltage switching can be achieved in all switching elements, including the third and fourth switching elements S3 and S4, by using the auxiliary winding L2 and the auxiliary inverter 3. This makes it possible to realize a low-noise, highly efficient power conversion device for high-voltage, high-frequency applications.

[0062] A known configuration of a power converter (output pulse generating circuit) is one in which switching elements are connected in series for use at high voltages, and a capacitor is connected in parallel to each switching element to balance the voltage. This configuration offers a more pronounced effect. Specifically, the larger the capacitance of each switching element connected in parallel, the greater the loss when consuming the capacitance's energy. In this case, even if the current is zero and zero-current switching (ZCS) occurs during turn-on, the loss becomes significant. In this first embodiment, the third switching element S3 and the fourth switching element S4 are zero-voltage switching (ZVS) during turn-on, enabling low-noise, high-efficiency operation even at high voltages and high frequencies.

[0063] [Embodiment 2] An example circuit of the power converter (output pulse generating circuit) in the second embodiment is shown in Fig. 7. An example configuration of the reactor L1 and auxiliary winding L2 is shown in Fig. 8. When the current and voltage flowing from the power converter are large and high, there are cases where the number of turns is reduced in order to reduce the winding amount of the reactor L1 and auxiliary winding L2. In such a case, a sufficient transformation ratio cannot be ensured, and the DC voltage Vsub of the auxiliary inverter 3 becomes large, which may result in the auxiliary inverter 3 becoming larger and more expensive.

[0064] In the second embodiment, the above problem is solved by connecting a voltage matching transformer Tr. Connecting the voltage matching transformer Tr makes it possible to design the DC voltage Vsub of the auxiliary inverter 3 regardless of the number of turns of the reactor L1 and the auxiliary winding L2, thereby enabling the auxiliary inverter 3 to be manufactured compact and inexpensively. It is assumed that the following equation (3) holds between the number of turns N1 of the reactor L1, the number of turns N2 of the auxiliary winding L2, the number of turns N3 of the primary winding L3 of the voltage matching transformer Tr, the number of turns N4 of the secondary winding L4, the DC voltage Vin of the DC power supply DC, and the DC voltage Vsub of the auxiliary inverter (auxiliary power supply DCsub).

[0065]

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[0066] The operation is the same as in the first embodiment, so a description thereof will be omitted.

[0067] As described above, according to the second embodiment, the same effects as those of the first embodiment can be achieved. Furthermore, by providing the voltage matching transformer Tr, the auxiliary inverter 3 can be manufactured compactly and inexpensively, improving design flexibility. Furthermore, by connecting the voltage matching transformer Tr, it becomes easier to improve the insulation between the auxiliary inverter 3 and the power converter, and to design insulation and sharing.

[0068] [Embodiment 3] In the first and second embodiments, an independent DC power supply (auxiliary power supply DCsub) is provided as a DC input for the auxiliary inverter 3, but this poses a problem in that the number of components increases.

[0069] In the third embodiment, a circuit configuration and a method for obtaining a required DC voltage by rectifying the voltage applied to the reactor L1 will be described.

[0070] An example circuit of the power converter (output pulse generating circuit) in the third embodiment is shown in Fig. 9. An example configuration of the reactor L1 and the auxiliary winding L2 is shown in Fig. 10. The difference from Fig. 7 (second embodiment) is that an auxiliary capacitor CSub is used instead of the auxiliary power supply (battery, etc.) DCSub of the auxiliary inverter 3.

[0071] It is assumed that the following equation (4) holds true between the number of turns N1 of the reactor L1, the number of turns N2 of the auxiliary winding L2, the number of turns N3 of the primary winding L3 of the voltage matching transformer Tr, the number of turns N4 of the secondary winding L4, the DC voltage Vin of the DC power supply DC, and the DC voltage Vsub of the auxiliary inverter (auxiliary capacitor Csub).

[0072]

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[0073] The DC voltage Vsub of the auxiliary capacitor CSub is controlled to a desired value by the switching operations of the fifth to eighth switching elements Sa to Sd.

[0074] When the above conditions are met, the power required for the auxiliary inverter 3 can be supplied from the DC voltage Vin of the DC power supply DC via the reactor L1 and the auxiliary winding L2, so that the same effects as in the first and second embodiments can be obtained even without an independent DC power supply.

[0075] The operation is omitted here because it is the same as that of the first embodiment. Note that the third embodiment is applicable not only to the second embodiment but also to the first embodiment.

[0076] As described above, according to the third embodiment, the same effects as those of the first and second embodiments can be achieved. In addition, it is possible to omit an independent DC power supply. Furthermore, there are cases where the circuit configuration is such that the DC voltage Vin of the DC power supply DC is variable. In such cases, the auxiliary capacitor CSub can be used to accommodate this, and the required DC voltage Vsub can be charged to the auxiliary capacitor CSub.

[0077] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the scope of the technical concept of the present invention, and it is natural that such modifications and variations fall within the scope of the claims. [Explanation of symbols]

[0078] DC…DC power supply Vin: DC voltage of DC power supply C1, C2: First and second capacitors D1 to D4: 1st to 4th diodes S1 to S4: First to fourth switching elements L1...Reactor 2. Load L2: Auxiliary winding 3...Auxiliary inverter Sa to Sd: 5th to 8th switching elements DCsub...Auxiliary power supply Vsub: DC voltage of the auxiliary inverter (auxiliary power supply, auxiliary capacitor) Tr: Transformer for voltage matching L3...Primary winding L4...Secondary winding Csub: Auxiliary capacitor

Claims

1. A power converter capable of supplying power from a DC power source to a load and returning the power of the load to the DC power source, a first switching element connected between the DC power supply and the load; a second switching element connected in parallel to the load; a reactor having one end connected to a connection point between the first and second switching elements; a capacitor and third and fourth switching elements connected so that the voltage on the other end of the reactor is intermediate between the voltage of the positive electrode and the voltage of the negative electrode of the DC power supply; an auxiliary winding magnetically coupled to the reactor; an auxiliary inverter having an AC side connected to both ends of the auxiliary winding; Equipped with a power converter configured to control the auxiliary inverter so that a current flows through the reactor from one end to the other end before the third switching element is turned on, and to control the auxiliary inverter so that a current flows through the reactor from the other end to one end before the fourth switching element is turned on.

2. 2. The power converter according to claim 1, further comprising a voltage matching transformer connected between said auxiliary winding and said auxiliary inverter.

3. 2. The power converter according to claim 1, wherein the number of turns of the reactor, the number of turns of the auxiliary winding, the DC voltage of the DC power supply, and the DC voltage of the auxiliary inverter satisfy the condition of the following formula (2): [Equation 2] N1: Number of turns of reactor N2: Number of turns of auxiliary winding Vin: DC voltage of DC power supply Vsub: DC voltage of auxiliary inverter

4. 3. The power converter according to claim 2, wherein the number of turns of the reactor, the number of turns of the auxiliary winding, the number of turns of the primary winding of the voltage matching transformer, the number of turns of the secondary winding of the voltage matching transformer, the DC voltage of the DC power supply, and the DC voltage of the auxiliary inverter satisfy the condition of the following formula (3): [Equation 3] N1: Number of turns of reactor N2: Number of turns of auxiliary winding N3: Number of turns of the primary winding of the voltage matching transformer N4: Number of turns of the secondary winding of the voltage matching transformer Vin: DC voltage of DC power supply Vsub: DC voltage of auxiliary inverter

5. 2. The power converter according to claim 1, wherein an auxiliary power supply is connected to the DC side of the auxiliary inverter.

6. 2. The power converter according to claim 1, wherein an auxiliary capacitor is connected to the DC side of the auxiliary inverter.

7. a first switching element connected between the DC power supply and the load; a second switching element connected in parallel to the load; a reactor having one end connected to a connection point between the first and second switching elements; first and second capacitors connected in series between the positive and negative electrodes of the DC power supply; a second diode having an anode connected to the connection point of the first and second capacitors; a third switching element connected between the cathode of the second diode and the other end of the reactor; a third diode having a cathode connected to the connection point of the first and second capacitors; a fourth switching element connected between the anode of the third diode and the other end of the reactor; a first diode having an anode connected to a connection point between the second diode and the third switching element and a cathode connected to a positive electrode of the DC power supply; a fourth diode having a cathode connected to a connection point between the third diode and the fourth switching element and an anode connected to a negative electrode of the DC power supply; an auxiliary winding magnetically coupled to the reactor; an auxiliary inverter having an AC side connected to both ends of the auxiliary winding; a control method for a power converter capable of supplying power from the DC power supply to the load and returning power of the load to the DC power supply, a control method for a power converter, comprising: controlling the auxiliary inverter so that a current flows through the reactor from one end to the other end before the third switching element is turned on; and controlling the auxiliary inverter so that a current flows through the reactor from the other end to one end before the fourth switching element is turned on.

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