Power converter

Abstract

To provide a power converter that easily achieves high efficiency and low noise by performing soft switching to generate an output pulse voltage at constant rising speed and falling speed without being affected by variations in a load and a component.SOLUTION: A first switching element S1 is connected between a DC power source DC and a load 2. A second switching element S2 is connected in parallel to the load 2. One end of an inductor L1 is connected to a connection point of the first and second switching elements S1, S2. A capacitor and a third and a fourth switching elements S3, S4 are connected so that a voltage on the other end side of the inductor L1 becomes an intermediate Vin / 2 of a voltage Vin of the DC power source DC. Then, a current is preliminarily passed through the inductor L1 before conduction of the first and second switching elements S1, S2.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a power converter with low loss and low noise that can supply a pulsed voltage at high voltage and high frequency.

Background Art

[0002] Figs. 1 and 2 show the circuit configuration and operation example in Patent Document 1. In Patent Document 1, a rectangular wave pulsed voltage can be supplied to the load 2 by supplying energy to the load 2 via the inductor 1. At this time, by performing a soft switching operation when the switching element is turned on, the switching loss is reduced and the stress on the switching element is alleviated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the circuits of Figs. 1 and 2, hard switching occurs when the switching elements 3 and 4 are turned off, so noise due to surge voltage and the like increases. Furthermore, when supplying a pulsed voltage to the load 2 at high frequency, there arises a problem that the switching loss increases.

[0005] In addition, since the rising speed and falling speed of the voltage of the load 2 are determined depending on the load constant and the inductance constant of the inductor 1, there arises a problem that the rising speed and falling speed change due to variations in the constants.

[0006] From the above, it is an issue to provide a power converter that can achieve high efficiency and low noise by performing soft switching, and to realize the generation of an output pulse voltage with a constant rise speed and fall speed without being affected by variations in the load and components.

Means for Solving the Problem

[0007] The present invention has been devised in view of the above conventional problems, and one aspect thereof is a power converter capable of supplying power from a DC power supply to a load and returning the power of the load to the DC power supply, comprising: a first switching element connected between the DC power supply and the load; a second switching element connected in parallel with the load; an inductor having one end connected to the connection point of the first and second switching elements; and a capacitor and third and fourth switching elements connected such that the voltage on the other end side of the inductor becomes the middle of the voltage of the DC power supply, characterized in that a current is preliminarily passed through the inductor before the first and second switching elements are turned on.

[0008] Also, as one aspect, the capacitor is 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 inductor, 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 inductor, a first diode having an anode connected to the connection point of the second diode and the third switching element and a cathode connected to the positive electrode of the DC power supply, and a fourth diode having a cathode connected to the connection point of the third diode and the fourth switching element and an anode connected to the negative electrode of the DC power supply. It is characterized by comprising the above.

[0009] Also, in one aspect, the capacitor is a first capacitor and a second capacitor connected in series between the positive electrode and the negative electrode of the DC power supply, a third switching element having one end connected to the connection point of the first and second capacitors, a second diode having an anode connected to the other end of the third switching element and a cathode connected to the other end of the inductor, a fourth switching element having one end connected to the connection point of the first and second capacitors, a third diode having a cathode connected to the other end of the fourth switching element and an anode connected to the other end of the inductor, a first diode having an anode connected to the connection point of the second diode and the third switching element and a cathode connected to the positive electrode of the DC power supply, and a fourth diode having a cathode connected to the connection point of the third diode and the fourth switching element and an anode connected to the negative electrode of the DC power supply, and is characterized by including these components.

[0010] Also, in one aspect, the capacitor is a first capacitor and a second capacitor connected in series between the positive electrode and the negative electrode of the DC power supply, a sixth switching element and the third switching element connected between the connection point of the first and second capacitors and the other end of the inductor, a seventh switching element and the fourth switching element connected between the connection point of the first and second capacitors and the other end of the inductor, a fifth switching element connected between the connection point of the sixth switching element and the third switching element and the positive electrode of the DC power supply, and an eighth switching element connected between the connection point of the seventh switching element and the fourth switching element and the negative electrode of the DC power supply, and is characterized by including these components.

[0011] Also, as one aspect, the capacitor is a first capacitor and a second capacitor connected in series between the positive electrode and the negative electrode of the DC power supply, and the third and fourth switching elements connected in anti-series between the connection point of the first and second capacitors and the other end of the inductor, a first diode having an anode connected to the other end of the inductor and a cathode connected to the positive electrode of the DC power supply, and a second diode having a cathode connected to the other end of the inductor and an anode connected to the negative electrode of the DC power supply.

[0012] Also, as one aspect, the capacitor is a first capacitor and a second capacitor connected in series between the positive electrode and the negative electrode of the DC power supply, and the third and fourth switching elements connected in anti-series between the connection point of the first and second capacitors and the other end of the inductor, a fifth switching element connected between the other end of the inductor and the positive electrode of the DC power supply, and a sixth switching element connected between the other end of the inductor and the negative electrode of the DC power supply.

[0013] Also, as one aspect, the third switching element having one end connected to the other end of the inductor, a first diode having an anode connected to the other end of the third switching element and a cathode connected to the positive electrode of the DC power supply, a second diode having a cathode connected to the other end of the inductor, the fourth switching element having one end connected to the anode of the second diode and the other end connected to the negative electrode of the DC power supply, and a second capacitor connected between the connection point of the first diode and the third switching element and the connection point of the second diode and the fourth switching element.

[0014] Also, as one aspect, a first diode having an anode connected to the other end of the inductor, a third switching element having one end connected to the cathode of the first diode and the other end connected to the positive electrode of the DC power supply, a fourth switching element having one end connected to the other end of the inductor, a second diode having a cathode connected to the other end of the fourth switching element and an anode connected to the negative electrode of the DC power supply, and a second capacitor connected between the connection point of the first diode and the third switching element and the connection point of the second diode and the fourth switching element.

[0015] Also, as one aspect, a third switching element having one end connected to the other end of the inductor, a fifth switching element having one end connected to the other end of the third switching element and the other end connected to the positive electrode of the DC power supply, a sixth switching element having one end connected to the other end of the inductor, a fourth switching element having one end connected to the other end of the sixth switching element and the other end connected to the negative electrode of the DC power supply, and a second capacitor connected between the connection point of the fifth switching element and the third switching element and the connection point of the sixth switching element and the fourth switching element.

[0016] Also, as one aspect, the inductor is characterized in that the inductance satisfies the conditions of the following equation (9).

[0017]

Equation

[0018] L: Inductance value of the inductor t c+ : Target maximum value of the time set as the rise time and fall time of the load voltage C min : Minimum value of the capacitance of the load.

[0019] Also, as one aspect, a preliminary current flowing period for preliminarily flowing a current through the inductor before conduction of the first and second switching elements is characterized by satisfying the condition of the following formula (5).

[0020]

Number

[0021] T SU : The preliminary current flowing period for preliminarily flowing a current through the inductor before conduction of the first and second switching elements L: Inductance value of the inductor C: Capacitance of the load R L : Equivalent series resistance component of the inductor

[0022] Also, as one aspect, the time set as the rise time and fall time of the load voltage is characterized by satisfying the following formula (6).

[0023]

Number

[0024] t c : The time set as the rise time and fall time of the load voltage L: Inductance value of the inductor C: Capacitance of the load T SU : The preliminary current flowing period for preliminarily flowing a current through the inductor before conduction of the first and second switching elements

[0025] Also, as one aspect, the preliminary current flowing period for preliminarily flowing a current through the inductor before conduction of the first and second switching elements, and the time set as the rise time and fall time of the load voltage are characterized by satisfying the condition of the following formula (7).

[0026]

Number

[0027] T SU : A preliminary current flowing period for preliminarily flowing a current through an inductor before conduction of the first and second switching elements. t c : A time set as the rise time and fall time of the load voltage.

Advantages of the Invention

[0028] According to the present invention, a power converter capable of high efficiency and low noise by performing soft switching is provided, and it is possible to realize the generation of an output pulse voltage with a constant rise speed and fall speed without being affected by variations in loads and components.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0030] Hereinafter, Embodiments 1 to 3 of the power converter according to the present invention will be described in detail with reference to FIGS. 3 to 9.

[0031] [Embodiment 1] FIG. 3 shows the basic circuit of the power converter (output pulse generation circuit) in the first embodiment, and FIG. 4 shows the basic operation waveforms of the power converter (output pulse generation circuit). Here, it is assumed that the load 2 is capacitive. Although the load 2 is schematically shown in FIG. 3, for example, it is a CR series circuit or a CR parallel circuit including a resistive component and a capacitive component. The circuit in FIG. 3 supplies power from the DC power supply DC to the load 2 and returns the power of the load 2 to the DC power supply DC.

[0032] As shown in FIG. 3, a first capacitor C1 and a second capacitor C2 are connected in series between the positive and negative electrodes of the DC power supply DC. Also, a first switching element S1 and a second switching element S2 are connected in series between the positive and negative electrodes of the DC 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 DC power supply DC. That is, the first switching element S1 is connected between the DC power supply DC and the load 2, and the second switching element S2 is connected in parallel with the load 2.

[0033] One end of an inductor L1 is connected to the connection point of the first and second switching elements S1 and S2. The anode of a second diode D2 is connected to the connection point of the first and second capacitors C1 and C2. A third switching element is connected between the cathode of the second diode D2 and the other end of the inductor L1.

[0034] Also, the cathode of a third diode D3 is connected to the connection point of 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 inductor L1.

[0035] The anode of the first diode D1 is connected to the connection point of 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 of 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 way, the first and second capacitors C1, C2 and the third and fourth switching elements S3, S4 are connected so that the voltage on the other end side of the inductor L1 becomes the middle value Vin / 2 of the voltage Vin of the DC power supply DC.

[0036] Let the voltage of the DC power supply DC be Vin, the voltages of the first and second capacitors C1, C2 be Vin / 2, and the current flowing through the inductor L1 be IL1.

[0037] The circuit in Fig. 3 charges and discharges the voltage of load 2 by the energy stored in the inductor L1, and realizes a rectangular-wave output voltage by holding the voltage with the first and second switching elements S1, S2.

[0038] The magnitude of the energy (current peak value) stored in the inductor L1 can be controlled by the ON time of the third and fourth switching elements S3, S4, and the dv / dt of the output pulse voltage is controlled by the magnitude of this energy. By adjusting the ON time of the third and fourth switching elements S3, S4 according to the variations in load 2 and inductance and controlling the magnitude of the energy (current peak value), the variation in dv / dt of the output pulse voltage can be controlled.

[0039] Next, the conditions for soft switching to occur will be described. The circuit in Fig. 3 can achieve soft switching when the following conditions are met. Assuming that load 2 is a pure capacitor with capacitance C, the energy of the load 1 / 2Cv o 2 and the energy 1 / 2Li of the inductor L1 with inductance value L pk 2 can be derived from the relational expression. From equation (1), the current flowing through the inductor L1 is i pkBy doing the above, soft switching can be achieved.

[0040]

Number

[0041] In addition, considering the equivalent series resistance component in the inductor L1 on the circuit and the energy consumption in the resistance component of the load 2, the inequality sign in equation (1) is preferably larger than the equal sign range.

[0042] Here, when the charging time to the load 2 is sufficiently short, the current at the time of the load voltage rise becomes the peak current value, and generally, there is a relationship as shown in equations (2) and (3).

[0043]

Number

[0044]

Number

[0045] t SU : As the inductor pre - current - flowing period, the period during which the third and fourth switching elements S3 and S4 are driven before the first and second switching elements S1 and S2 R L : The equivalent series resistance component of the inductor L1.

[0046] Therefore, while assuming the current value of the load 2, furthermore, there is generally a relationship as shown in equation (4) between the time t C obtained for the rise / fall of the load 2. Note that equation (4) is based on the premise that the inductance value L is sufficiently large and assumes a constant - current source.

[0047]

Number

[0048] Therefore, when implementing the invention described in Embodiment 1 more preferably, the required relational expressions are as shown in equations (5) to (7). That is, before the first switching element S1 or the second switching element S2 is turned on, the third switching element S3 or the fourth switching element S4 needs to be turned on for a length that is at least twice the time tc set as the rise time / fall time.

[0049]

Number

[0050]

Number

[0051]

Number

[0052] Also, the inductance value L of the inductor L1 is determined from the target value of the time t with respect to the assumed capacitance C in the case of Patent Document 1 according to the above relational expression. However, the time t C cannot be adjusted, and if the capacitance C increases or decreases from the assumption, it will be dragged along. C

[0053] On the other hand, in the invention described in Embodiment 1, the lower limit of the inductance value L is determined from the minimum value C min of the assumed capacitance C and the target maximum value t C of the time t C+ , and the upper limit of the inductance value L is determined from the minimum value t SU of the set inductance preliminary current-carrying period t SU- and the maximum value C max of the capacitance C. That is, it is as shown in equation (8).

[0054]

Number

[0055] Here, the minimum value t of the inductance preliminary current flowing period t SU should be greater than 2√(C SU- / C max )t min . In this case, since √(C c+ / C max ) > 1, t min > 2t SU > 2t C+ > 2t C also holds and conforms to equation (7). And even if there is a fluctuation in the capacitance C, the time t C can be adjusted by the inductance preliminary current flowing period t SU .

[0056] Note that although equation (8) shows the upper and lower limits of the inductance value L of the inductor L1, an inductor L1 that satisfies the condition of equation (9) showing only the lower limit of the inductance value L may be selected.

[0057]

Number

[0058] The operation sequence can be divided into the following 8 steps (1) to (8) as shown in Fig. 4.

[0059] (1) Load voltage rising preparation period: With the second switching element S2 in the on state, turn on the third switching element S3 to accumulate energy in the inductor L1. At this time, iL > 0.

[0060] (2) Load voltage rising period: With the third switching element S3 in the on state, turn off the second switching element S2, and use the energy of the inductor L1 to pass a current through the third switching element S3 to raise the load voltage. When turning off the second switching element S2, since the load voltage is zero, the second switching element S2 performs zero-voltage switching.

[0061] (3) Voltage holding period: With the third switching element S3 in the ON state, turn on the first switching element S1. Since the connection point side of the first and second switching elements S1 and S2 of the inductor L1 becomes the voltage Vin, and the connection point side of the third and fourth switching elements S3 and S4 of the inductor L1 becomes the voltage Vin / 2, Vin / 2 is applied to the inductor L1 and the current decreases.

[0062] (4) Voltage holding period: With the first switching element S1 in the ON state, turn off the third switching element S3. At this time, since the current of the inductor L1 is 0, the third switching element S3 performs zero-current switching.

[0063] (5) Preparation period for the load voltage to fall: With the first switching element S1 in the ON state, turn on the fourth switching element S4 to accumulate energy in the opposite direction in the inductor L1. At this time, iL < 0.

[0064] (6) Load voltage falling period: With the fourth switching element S4 in the ON state, turn off the first switching element S1, and let the current flow through the fourth switching element S4 by the energy of the inductor L1 to lower the load voltage.

[0065] (7) Voltage holding period: With the fourth switching element S4 in the ON state, turn on the second switching element S2. Since the connection point side of the first and second switching elements S1 and S2 of the inductor L1 becomes the voltage 0, and the connection point of the third and fourth switching elements S3 and S4 of the inductor L1 becomes the voltage Vin / 2, Vin / 2 is applied to the inductor L1 and the current decreases.

[0066] (8) Voltage holding period: With the second switching element S2 in the ON state, turn off the fourth switching element S4. At this time, since the current of the inductor L1 is 0, the fourth switching element S4 performs zero-current switching.

[0067] In Fig. 4, the slope changes discontinuously at the point where iL1 is maximum and the point where it is minimum (the maximum and minimum points are angular). However, when considering the capacitance of load 2, the slope changes continuously (the maximum and minimum points become rounded). Also, when the third and fourth switching elements S3 and S4 are ON and the potential difference between the first and second switching elements S1 and S2 is 0, the first and second switching elements S1 and S2 switch. Therefore, the potential difference across inductor L1 does not change abruptly due to the presence of the first and second capacitors C1 and C2, etc. Thus, the slope of IL1 does not become discontinuous at the boundary either.

[0068] Regarding the rising waveform and falling waveform of the load voltage Vout, rather than being linear as shown in Fig. 4, it is actually an S-shaped waveform. However, if ipk is set to be sufficiently large, it will be approximately linear.

[0069] The period (6) of the fall of the load voltage Vout basically discharges the charging energy in the capacitive component of load 2. So, if the energy decreases due to losses, it will be faster, and if there are no losses, it will remain as it is. Therefore, the periods (2) and (6) of the load voltage Vout are approximately equal as shown in Fig. 4, regardless of the resistive component of load 2.

[0070] Next, an operation example of soft switching is shown in Fig. 5. In Fig. 5, 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.

[0071] An operating example of the first switching element S1 is shown in Fig. 5(a). Since the first switching element S1 is connected in series with the load 2, the voltage applied thereto is the voltage obtained by subtracting the load voltage Vout from the voltage Vin of the DC power supply DC. The timing at which the first switching element S1 turns on is the moment when steps (2) and (3) of the above steps are interchanged, and the load voltage Vout has risen to Vin. Therefore, at the timing when the first switching element S1 turns on, the voltage applied to the first switching element S1 is 0, and since the rate of change of the voltage of the load 2 is slower than the current interruption rate of the switching element, zero voltage switching occurs.

[0072] On the other hand, the timing at which the first switching element S1 turns off is the moment when steps (5) and (6) of the above steps are interchanged, and the load voltage Vout is Vin. Therefore, at the timing when the first switching element S1 turns off, the voltage applied to the first switching element S1 is 0, and since the rate of change of the voltage of the load 2 is slower than the current interruption rate of the switching element, zero voltage switching occurs.

[0073] An operating example of the second switching element S2 is shown in Fig. 5(b). Since the second switching element S2 is connected in parallel with the load 2, the voltage applied thereto is the same value as the load voltage Vout. The timing at which the second switching element S2 turns off is the moment when steps (1) and (2) of the above steps are interchanged, and the load voltage is 0. Therefore, at the timing when the second switching element S2 turns off, the voltage applied to the second switching element S2 is 0, and zero voltage switching occurs.

[0074] On the other hand, the timing at which the second switching element S2 turns on is the moment when steps (6) and (7) of the above steps are interchanged and the load voltage Vout is 0. Therefore, at the timing when the second switching element S2 turns on, the voltage applied to the second switching element S2 is 0, and zero voltage switching occurs.

[0075] An operating example of the third switching element S3 is shown in Fig. 5(c). Since the third switching element S3 is an element connected to the neutral point (the intermediate potential of the DC power supply DC), Vin / 2 is applied, and a part of the current IL1 passing through the inductor L1 (IL1 > 0) flows. The timing at which the third switching element S3 turns on is the moment when (8) and (1) of the above steps are interchanged, and the current IL1 passing through the inductor L1 is 0. Therefore, the current at the timing when the third switching element S3 turns on is 0, and since the voltage change rate of the inductor L1 is slower than the voltage change rate of the switching element, zero-current switching occurs.

[0076] The timing at which the third switching element S3 turns off is the moment when (3) and (4) of the above steps are interchanged, and the current IL1 passing through the inductor L1 is 0. Therefore, the current at the timing when the third switching element S3 turns off is 0, and since the voltage change rate of the inductor L1 is slower than the voltage change rate of the switching element, zero-current switching occurs.

[0077] An operating example of the fourth switching element S4 is shown in Fig. 5(d). Since the fourth switching element S4 is an element connected to the neutral point (the intermediate potential of the DC power supply DC), Vin / 2 is applied, and a part of the current IL1 passing through the inductor L1 (IL1 < 0) flows. The timing at which the fourth switching element S4 turns on is the moment when (4) and (5) of the above steps are interchanged, and the current IL1 passing through the inductor L1 is 0. Therefore, the current at the timing when the fourth switching element S4 turns on is 0, and since the voltage change rate of the inductor L1 is slower than the voltage change rate of the switching element, zero-current switching occurs.

[0078] The timing at which the fourth switching element S4 turns off is the moment when (7) and (8) of the above steps are interchanged, and the current IL1 passing through the inductor L1 is 0. Therefore, the current at the timing when the fourth switching element S4 turns off is 0, and since the voltage change rate of the inductor L1 is slower than the voltage change rate of the switching element, zero-current switching occurs.

[0079] 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) of the first capacitor C1 and the second capacitor C2. Under the condition where soft switching is established, since all the current flowing through the neutral point flows through the inductor L1, the neutral point voltage can also be controlled by controlling the average value of the current of the inductor L1. The average value of the current of the inductor L1 can be controlled by changing the ratio between the period of (1) and the period of (5). Theoretically, by controlling the average value to 0, the fluctuation of the neutral point potential can be made 0.

[0080] If iL is positive-negative symmetric, the neutral point potential does not fluctuate. However, when the load 2 includes a resistive component, the charging current and the discharging current are not necessarily positive-negative symmetric. In that case, IL1 must be adjusted. When IL1 is positive, the neutral point potential drops, and when IL1 is negative, the neutral point potential rises. Thereby, the voltages of the first capacitor C1 and the second capacitor C2, that is, the neutral point potential are adjusted.

[0081] Note that the average value of the current when the first switching element S1 is ON takes a positive value for the portion supplied to the load 2. Further, it shifts in the positive direction for the portion that raises the neutral point potential. The average value of the current when the second switching element S2 is ON becomes 0 except for the portion that shifts in the positive direction as the portion that decreases the neutral point potential since no supply is made to the load 2.

[0082] By operating as described above, it becomes possible to output an output pulse voltage with a constant dv / dt without being affected by variations in components and loads while the first to fourth switching elements S1 to S4 perform soft switching operation.

[0083] Although the detailed description in the first embodiment is omitted, the following configuration can also realize the same operation as that in FIG. 3. Note that the directions of the switching elements and the diodes are the same as those in FIG. 3. ·A configuration in which the third and fourth switching elements S3 and S4 are replaced with the second and third diodes D2 and D3, and the second and third diodes D2 and D3 are replaced with the third and fourth switching elements S3 and S4. ·A configuration in which the first to fourth diodes D1 to D4 are replaced with the fifth to eighth switching elements.

[0084] As described above, according to the first embodiment, hard switching is not performed. Further, by adjusting the on-off periods of the respective switching elements, it is possible to control the rise speed and fall speed of the load voltage. Therefore, with high efficiency and low noise, an output pulse can be generated with a constant rise speed and fall speed without being affected by variations in the load and components. Making the rise speed and fall speed constant leads to an improvement in the output voltage accuracy of the power converter.

[0085] [Embodiment 2] FIG. 6 shows the basic circuit of the power converter (output pulse generation circuit) in the second embodiment, and FIG. 7 shows the basic operation waveforms of the power converter (output pulse generation circuit). Here, it is assumed that the load 2 is capacitive. Although the load 2 is schematically shown in FIG. 6, for example, it is a CR series circuit or a CR parallel circuit including a resistive component and a capacitive component. The circuit in FIG. 6 supplies power from the DC power supply DC to the load 2 and returns the power of the load 2 to the DC power supply DC.

[0086] As shown in FIG. 6, a first capacitor C1 and a second capacitor C2 are connected in series between the positive and negative electrodes of the DC power supply DC. Also, a first switching element S1 and a second switching element S2 are connected in series between the positive and negative electrodes of the DC 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 DC power supply DC. That is, the first switching element S1 is connected between the DC power supply DC and the load 2, and the second switching element S2 is connected in parallel to the load 2.

[0087] One end of an inductor L1 is connected to the connection point of the first and second switching elements. Third and fourth switching elements S3 and S4 are connected in reverse series between the connection point of the first and second capacitors C1 and C2 and the other end of the inductor L1. The anode of a first diode D1 is connected to the other end of the inductor L1. The cathode of the first diode D1 is connected to the positive electrode of a DC power supply DC. The cathode of a second diode D2 is connected to the other end of the inductor L1. The anode of the second diode D2 is connected to the negative electrode of the DC power supply DC. In this way, 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 side of the inductor L1 becomes the middle value Vin / 2 of the voltage Vin of the DC power supply DC.

[0088] Let the voltage of the DC power supply DC be Vin, the voltages of the first and second capacitors C1 and C2 be Vin / 2, and the current flowing through the inductor L1 be IL1.

[0089] The circuit in FIG. 6 charges and discharges the voltage of the load 2 with the energy stored in the inductor L1, and realizes the output voltage on the rectangular wave by holding the voltage with the first and second switching elements S1 and S2.

[0090] The magnitude of the energy stored in the inductor L1 can be controlled by the ON time of the third and fourth switching elements S3 and S4, and the dv / dt of the output pulse voltage is controlled by the magnitude of this energy.

[0091] The variation of dv / dt can be controlled by adjusting the ON time of the third and fourth switching elements S3 and S4 according to the variations of the load and the inductance. In addition, since all the switching elements perform soft switching even at turn-off, it is possible to achieve lower loss and lower noise than in Patent Document 1.

[0092] The operation sequence can be divided into the following eight steps (1) to (8) as shown in FIG. 7.

[0093] (1) Load voltage rising preparation period: With the second switching element S2 remaining in the on state, the third switching element S3 is turned on to store energy in the inductor L1. At this time, iL > 0.

[0094] (2) Load voltage rising period: With the third switching element S3 remaining in the on state, the second switching element S2 is turned off, and the energy of the inductor L1 is used to pass a current through the third switching element S3 to raise the load voltage Vout. When the second switching element S2 is turned off, since the load voltage Vout is zero, zero-voltage switching occurs.

[0095] (3) Voltage holding period: With the third switching element S3 remaining in the on state, the first switching element S1 is turned on. The connection point of the first and second switching elements S1 and S2 of the inductor L1 becomes the voltage Vin, and the fourth switching element S4 side of the inductor L1 becomes the voltage Vin / 2. Therefore, Vin / 2 is applied to the inductor L1 and the current decreases.

[0096] (4) Voltage holding period: With the first switching element S1 remaining in the on state, the third switching element S3 is turned off. Since the current of the inductor L1 becomes zero, the third switching element S3 performs zero-current switching.

[0097] (5) Load voltage falling preparation period: With the first switching element S1 remaining in the on state, the fourth switching element S4 is turned on to store reverse energy in the inductor L1. At this time, iL < 0.

[0098] (6) Load voltage falling period: With the fourth switching element S4 remaining in the on state, the first switching element S1 is turned off, and the energy of the inductor L1 is used to lower the load voltage Vout.

[0099] (7) Voltage holding period: With the fourth switching element S4 in the ON state, turn on the second switching element S2. Since the connection point side of the first and second switching elements S1 and S2 of the inductor L1 becomes voltage 0 and the fourth switching element S4 side of the inductor L1 becomes voltage Vin / 2, Vin / 2 is applied to the inductor L1 and the current decreases.

[0100] (8) Voltage holding period: With the second switching element S2 in the ON state, turn off the fourth switching element S4. Since the current of the inductor L1 becomes 0, the fourth switching element S4 performs zero-current switching.

[0101] Since the operation during soft switching is the same as that in FIG. 5, the description is omitted. The voltages of the first capacitor C1 and the second capacitor C2 are also the same as those in Embodiment 1.

[0102] By operating as described above, it is possible to output an output pulse voltage with a constant dv / dt without being affected by variations in components and loads while performing soft switching operation on each switching element. That is, the same operational effects as in Embodiment 1 are achieved.

[0103] Although the detailed description of this Embodiment 2 is omitted, the same operation as in FIG. 6 can be realized with the following configuration. The directions of the switching elements are the same as in FIG. 6. · A configuration in which the first and second diodes D1 and D2 are replaced with the fifth and sixth switching elements.

[0104] [Embodiment 3] FIG. 8 shows the basic circuit of the power converter (output pulse generation circuit) in this Embodiment 3, and FIG. 9 shows the basic operation waveforms of the power converter (output pulse generation circuit). Here, it is assumed that the load 2 is capacitive. Although the load 2 is schematically shown in FIG. 8, for example, it is a CR series circuit or a CR parallel circuit including a resistive component and a capacitive component. The circuit in FIG. 8 supplies power from the DC power supply DC to the load 2 and returns the power of the load 2 to the DC power supply DC.

[0105] As shown in Fig. 8, a first capacitor C1 is connected between the positive and negative electrodes of a DC power supply DC. Also, a first switching element S1 and a second switching element S2 are connected in series between the positive and negative electrodes of the DC power supply DC. A load 2 is connected between the connection point of the first and second switching elements S1, S2 and the negative electrode of the DC power supply DC. That is, the first switching element S1 is connected between the DC power supply DC and the load 2, and the second switching element S2 is connected in parallel to the load 2.

[0106] One end of an inductor L1 is connected to the connection point of the first and second switching elements. The other end of the inductor L1 is connected to one end of a third switching element S3. The other end of the third switching element S3 is connected to the anode of a first diode D1. The cathode of the first diode D1 is connected to the positive electrode of the DC power supply DC.

[0107] The cathode of a second diode D2 is connected to the other end of the inductor L1. One end of a fourth switching element S4 is connected to the anode of the second diode D2. The other end of the fourth switching element S4 is connected to the negative electrode of the DC power supply DC.

[0108] A second capacitor (flying capacitor) C2 is connected between the connection point of the first diode D1 and the third switching element S3 and the connection point of the second diode D2 and the fourth switching element S4. In this way, the first and second capacitors C1, C2 and the third and fourth switching elements S3, S4 are connected so that the voltage on the other end side of the inductor L1 becomes the middle Vin / 2 of the voltage Vin of the DC power supply DC.

[0109] Let the voltage of the DC power supply DC be Vin, the voltage of the first capacitor C1 be Vin, the voltage of the second capacitor (flying capacitor) C2 be Vin / 2, and the current flowing through the inductor L1 be IL1.

[0110] The circuit in Fig. 8 charges and discharges the voltage of the load 2 by the energy stored in the inductor L1, and realizes the output voltage on the rectangular wave by holding the voltage with the first and second switching elements S1, S2.

[0111] The magnitude of the energy stored in the inductor L1 can be controlled by the ON times of the third and fourth switching elements S3 and S4, and the dv / dt of the output pulse voltage is controlled by the magnitude of this energy. By adjusting the ON times of the third and fourth switching elements S3 and S4 according to the variations in the load 2 and inductance, the variations in dv / dt can be controlled.

[0112] In addition, since all the switching elements perform soft switching even during turn-off, it is possible to achieve lower loss and lower noise than in Patent Document 1.

[0113] The operation sequence can be divided into the following eight steps (1) to (8) as shown in FIG. 9.

[0114] (1) Load voltage rising preparation period: With the second switching element S2 in the ON state, the third switching element S3 is turned ON to accumulate energy in the inductor L1. At this time, iL > 0.

[0115] (2) Load voltage rising period: With the third switching element S3 in the ON state, the second switching element S2 is turned OFF, and the energy of the inductor L1 is used to pass a current through the third switching element S3 to raise the load voltage Vout. When the second switching element S2 is turned OFF, since the load voltage Vout is zero, zero-voltage switching occurs.

[0116] (3) Voltage holding period: With the third switching element S3 in the ON state, the first switching element S1 is turned ON. The voltage on the connection point side of the first and second switching elements S1 and S2 of the inductor L1 becomes Vin, and the voltage on the third switching element S3 side of the inductor L1 becomes Vin / 2. Therefore, Vin / 2 is applied to the inductor L1 and the current decreases.

[0117] (4) Voltage holding period: With the first switching element S1 in the ON state, the third switching element S3 is turned OFF. Since the current of the inductor L1 becomes zero, the third switching element S3 performs zero-current switching.

[0118] (5) Preparation period for the load voltage to fall: With the first switching element S1 in the ON state, the fourth switching element S4 is turned ON, and energy in the reverse direction is stored in the inductor L1. At this time, iL < 0.

[0119] (6) Load voltage falling period: With the fourth switching element S4 in the ON state, the first switching element S1 is turned OFF, and the load voltage Vout is lowered by the energy of the inductor L1.

[0120] (7) Voltage holding period: With the fourth switching element S4 in the ON state, the second switching element S2 is turned ON. Since the voltage on the connection point side of the first and second switching elements S1 and S2 of the inductor L1 becomes zero and the voltage on the third switching element S3 side of the inductor L1 becomes Vin / 2, Vin / 2 is applied to the inductor L1 and the current decreases.

[0121] (8) Voltage holding period: With the second switching element S2 in the ON state, the fourth switching element S4 is turned OFF. When the fourth switching element S4 is turned OFF, since the current of the inductor L1 becomes zero, the fourth switching element S4 performs zero-current switching.

[0122] The operation during soft switching is the same as that in Fig. 5, so it is omitted.

[0123] The voltage of the second capacitor (flying capacitor) C2 can be controlled by the average value of the current of the inductor L1. The average value of the current of the inductor L1 is the same as in Embodiments 1 and 2.

[0124] By operating as described above, it becomes possible to output an output pulse voltage with a constant dv / dt without being affected by variations in components and loads while causing each switching element to perform soft switching operation. That is, it exhibits the same operational effects as those of Embodiments 1 and 2.

[0125] Although the detailed description of this Embodiment 3 is omitted, the same operation as that in FIG. 8 can also be realized with the following configuration. The directions of the diodes and the switching elements shall be the same as those in FIG. 8. · A configuration in which the third and fourth switching elements S3 and S4 are replaced with the first and second diodes D1 and D2, and the first and second diodes D1 and D2 are replaced with the third and fourth switching elements S3 and S4. · A configuration in which the first and second diodes D1 and D2 are replaced with the fifth and sixth switching elements.

[0126] As described above, in the present invention, although detailed description has been made only for the specific examples described, it is obvious to those skilled in the art that various modifications and corrections are possible within the scope of the technical idea of the present invention, and it is natural that such modifications and corrections belong to the scope of the claims.

Explanation of Reference Numerals

[0127] DC... DC power supply C1, C2... First and second capacitors S1~S4... First to fourth switching elements D1~D4... First to fourth diodes L1... Inductor 2... Load

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, comprising: a first switching element connected between the DC power source and the load; a second switching element connected in parallel with the load; an inductor having one end connected to the connection point of the first and second switching elements; a first capacitor connected between the positive and negative electrodes of the DC power source; a third switching element having one end connected to the other end of the inductor; a first diode having an anode connected to the other end of the third switching element and a cathode connected to the positive electrode of the DC power source; a second diode having a cathode connected to the other end of the inductor; a fourth switching element having one end connected to the anode of the second diode and the other end connected to the negative electrode of the DC power source; a second capacitor connected between the connection point of the first diode and the third switching element and the connection point of the second diode and the fourth switching element; wherein the first and second capacitors and the third and fourth switching elements are connected such that the voltage on the other end side of the inductor is intermediate between the voltage of the DC power source; the power converter is characterized in that a current is preliminarily passed through the inductor before the first and second switching elements are turned on.

2. 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, comprising: a first switching element connected between the DC power source and the load; a second switching element connected in parallel with the load; an inductor having one end connected to the connection point of the first and second switching elements; a first capacitor connected between the positive and negative electrodes of the DC power source; a first diode having an anode connected to the other end of the inductor; a third switching element having one end connected to the cathode of the first diode and the other end connected to the positive electrode of the DC power source; a fourth switching element having one end connected to the other end of the inductor; a second diode having a cathode connected to the other end of the fourth switching element and an anode connected to the negative electrode of the DC power source; a second capacitor connected between the connection point of the first diode and the third switching element and the connection point of the second diode and the fourth switching element; wherein The first and second capacitors and the third and fourth switching elements are connected such that the voltage at the other end of the inductor is intermediate between the voltage of the DC power supply. A power converter characterized by preliminarily passing a current through the inductor before conduction of the first and second switching elements. **Claim 3** A power converter capable of supplying power from a DC power supply to a load and returning the power of the load to the DC power supply, a first switching element connected between the DC power supply and the load, a second switching element connected in parallel with the load, an inductor having one end connected to the connection point of the first and second switching elements, a first capacitor connected between the positive and negative electrodes of the DC power supply, a third switching element having one end connected to the other end of the inductor, a fifth switching element having one end connected to the other end of the third switching element and the other end connected to the positive electrode of the DC power supply, a sixth switching element having one end connected to the other end of the inductor, a fourth switching element having one end connected to the other end of the sixth switching element and the other end connected to the negative electrode of the DC power supply, a second capacitor connected between the connection point of the fifth switching element and the third switching element and the connection point of the sixth switching element and the fourth switching element, comprising: The first and second capacitors and the third and fourth switching elements are connected such that the voltage at the other end of the inductor is intermediate between the voltage of the DC power supply. A power converter characterized by preliminarily passing a current through the inductor before conduction of the first and second switching elements. **Claim 4** The inductor is characterized in that the inductance satisfies the condition of the following formula (9) in any one of Claims 1 to 3. 【Number 9】 L: Inductance value of the inductor t ｃ＋ : The target maximum value of the time set as the rise time and fall time of the load voltage C ｍｉｎ : Minimum value of the load capacitance **Claim 5** The pre-conduction period for preliminarily passing a current through the inductor before conduction of the first and second switching elements satisfies the condition of the following formula (5) in any one of Claims 1 to 3. 【Number 5】 T ＳＵ : Pre-conduction period for preliminarily passing a current through the inductor before conduction of the first and second switching elements L: Inductance value of the inductor C: Capacitance of the load R Ｌ : Equivalent series resistance component of the inductor **Claim 6** The time set as the rise time and fall time of the load voltage satisfies the following formula (6) in any one of Claims 1 to 3. 【Number 6】 t ｃ : The time set as the rise time and fall time of the load voltage L: Inductance value of the inductor C: Capacitance of the load T ＳＵ : Pre-conduction period for preliminarily passing a current through the inductor before conduction of the first and second switching elements **Claim 7** The pre-conduction period for preliminarily passing a current through the inductor before conduction of the first and second switching elements, and the time set as the rise time and fall time of the load voltage satisfy the conditions of the following formula (7), and the power converter according to any one of claims 1 to 3 is characterized in that. 【Number 7】 T ＳＵ : A preliminary current flowing period for preliminarily flowing a current through an inductor before conduction of the first and second switching elements t ｃ : The time set as the rise time and fall time of the load voltage

Images