Electric power converter

Abstract

The present invention provides an electric power converter capable of easily achieving high efficiency and low noise by performing soft switching, and realizes generation of an output pulse voltage having a constant rising speed and a constant falling speed without being affected by load and component variability. 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 with the load (2). One end of an inductor (L1) is connected to a connection point of the first and second switching elements (S1, S2). Capacitors and third and fourth switching elements (S3, S4) are connected such that the voltage on the other end side of the inductor (L1) lies at the middle (Vin / 2) of the voltage (Vin) of the direct-current power source DC. Then, a current is preliminarily passed through the inductor (L1) from before the first and second switching elements (S1, S2) become conductive.

Description

Power Converter

[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.

[0002] 1 and 2 show the circuit configuration and an example of operation in Patent Document 1. In Patent Document 1, a rectangular wave pulse voltage can be supplied to a load 2 by supplying energy to the load 2 via an inductor 1. At this time, soft switching is performed when the switching element is turned on, thereby reducing switching loss and easing stress on the switching element.

[0003] Japanese Patent Application Laid-Open No. 2022-7165

[0004] 1 and 2, hard switching occurs when the switching elements 3 and 4 are turned off, which increases noise due to surge voltages, etc. Furthermore, when a pulse voltage is supplied to the load 2 at a high frequency, there is a problem that switching loss increases.

[0005] Furthermore, since the rise and fall speeds of the voltage of the load 2 are determined depending on the load constant and the inductor constant of the inductor 1, there is a problem that the rise and fall speeds change due to variations in the constants.

[0006] Given the above, the challenge is to provide a power converter that can easily achieve high efficiency and low noise by performing soft switching, and to generate an output pulse voltage with constant rise and fall speeds without being affected by variations in the load or components.

[0007] The present invention has been devised in view of the above-mentioned problems in the related art, and one aspect thereof is a power converter that supplies power from a DC power supply to a load and is capable of returning the power of the load to the DC power supply, the power converter comprising: a first switching element connected between the DC power supply and the load; a second switching element connected in parallel to the load; an inductor 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 inductor is intermediate between the voltages of the DC power supply; and a current is preliminarily passed through the inductor before the first and second switching elements are rendered conductive.

[0008] In one aspect, the capacitor is a first and a second capacitor connected in series between a positive electrode and a negative electrode of the DC power supply, and includes: a second diode having an anode connected to a connection point between the first and second capacitors; the third switching element connected between a cathode of the second diode and the other end of the inductor; the third diode having a cathode connected to the connection point between the first and second capacitors; the fourth switching element connected between an anode of the third diode and the other end of the inductor; a first diode having an anode connected to the connection point between 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 between the third diode and the fourth switching element and an anode connected to the negative electrode of the DC power supply.

[0009] In one aspect, the capacitor is a first capacitor and a second capacitor connected in series between a positive electrode and a negative electrode of the DC power supply, and includes the third switching element having one end connected to a connection point between 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, the fourth switching element having one end connected to the connection point between 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 between 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 between the third diode and the fourth switching element and an anode connected to the negative electrode of the DC power supply.

[0010] 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, and includes 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.

[0011] 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, and the third and fourth switching elements are connected in anti-series between a 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] 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, and the third and fourth switching elements are connected in anti-series between a connection point of the first and second capacitors and the other end of the inductor, a fifth switching element is connected between the other end of the inductor and the positive electrode of the DC power supply, and a sixth switching element is connected between the other end of the inductor and the negative electrode of the DC power supply.

[0013] In one aspect, the power supply comprises 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 a connection point between the first diode and the third switching element and a connection point between the second diode and the fourth switching element.

[0014] In one aspect, the power supply comprises: a first diode having an anode connected to the other end of the inductor; the 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; the 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 a connection point of the first diode and the third switching element and a connection point of the second diode and the fourth switching element.

[0015] In one aspect, the power supply comprises the 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, the 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 a connection point between the fifth switching element and the third switching element and a connection point between the sixth switching element and the fourth switching element.

[0016] In one aspect, the inductor has an inductance that satisfies the condition of the following formula (9).

[0017]

[0018] L: inductance value of the inductor t ｃ＋ :Maximum target time set for load voltage rise time and fall time C ｍｉｎ : Minimum capacitance of the load.

[0019] In one aspect, a preliminary current flow period in which a current is preliminarily passed through the inductor before the first and second switching elements are turned on satisfies the condition of the following formula (5).

[0020]

[0021] T ＳＵ : Preliminary conduction period during which current is preliminarily passed through the inductor before the first and second switching elements are turned on. L: Inductance value of the inductor. C: Capacitance of the load. R Ｌ : Equivalent series resistance of the inductor.

[0022] In one aspect, the times set as the rise time and fall time of the load voltage satisfy the following formula (6).

[0023]

[0024] t ｃ: 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 A preliminary current conduction period in which a current is preliminarily passed through the inductor before the first and second switching elements are turned on.

[0025] In one aspect, a preliminary current conduction period in which a current is preliminarily conducted to the inductor before the first and second switching elements are turned on, and times set as the rise time and fall time of the load voltage satisfy the condition of the following formula (7).

[0026]

[0027] T ＳＵ t: A preliminary conduction period during which a current is preliminarily passed through the inductor before the first and second switching elements are turned on. ｃ : The time set as the load voltage rise time and fall time.

[0028] According to the present invention, a power converter that can easily achieve high efficiency and low noise by performing soft switching is provided, and it is possible to generate an output pulse voltage with constant rise and fall speeds without being affected by variations in the load or components.

[0029] FIG. 1 is a diagram showing a circuit configuration and an operation example of Patent Document 1 (Example 2). FIG. 2 is a diagram showing a circuit configuration and an operation example of Patent Document 1 (Example 1). FIG. 3 is a basic configuration diagram of an output pulse generation circuit (power converter) of embodiment 1. FIG. 4 is a basic operation diagram of the output pulse generation circuit (power converter) of embodiment 1. FIG. 5 is a diagram showing an operation example of soft switching. FIG. 6 is a basic configuration diagram of an output pulse generation circuit (power converter) of embodiment 2. FIG. 7 is a basic operation diagram of the output pulse generation circuit (power converter) of embodiment 2. FIG. 8 is a basic configuration diagram of an output pulse generation circuit (power converter) of embodiment 3. FIG. 9 is a diagram showing the basic operation of the output pulse generation circuit (power converter) of embodiment 3.

[0030] First to third embodiments of the power converter of the present invention will be described in detail below with reference to FIGS.

[0031] [Embodiment 1] Fig. 3 shows a basic circuit of a power converter (output pulse generating circuit) in this embodiment 1, and Fig. 4 shows basic operating waveforms of the power converter (output pulse generating circuit). Here, it is assumed that the load 2 is capacitive. Fig. 3 shows the load 2 schematically, but it may be, for example, 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 a direct-current power source DC to the load 2 and returns the power of the load 2 to the direct-current power source 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 a DC power supply DC. Furthermore, 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.

[0033] One end of the inductor L1 is connected to the connection point between the first and second switching elements S1 and S2. The anode of the second diode D2 is connected to the connection point between 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] 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 inductor L1.

[0035] 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 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 of the inductor L1 is Vin / 2, which is the intermediate voltage of the voltage Vin of the DC power supply DC.

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

[0037] The circuit of FIG. 3 charges and discharges the voltage of the load 2 using energy stored in the inductor L1, and maintains the voltage using the first and second switching elements S1 and S2, thereby realizing a rectangular waveform output voltage.

[0038] The amount of energy stored in inductor 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 the dv / dt of the output pulse voltage can be controlled.

[0039] Next, we will discuss the conditions under which soft switching is possible. The circuit in Figure 3 can achieve soft switching when the following conditions are met. If we assume that the load 2 is a pure capacitor with a capacitance of C, then the energy of the load is 1 / 2Cv ｏ ２ and the energy 1 / 2Li of the inductor L1 with inductance value L ｐｋ ２ From equation (1), the current flowing through the inductor L1 can be calculated as i ｐｋ By doing so, soft switching can be realized.

[0040]

[0041] In addition, taking into consideration the equivalent series resistance component of the inductor L1 in the circuit and the energy consumption of the resistance component of the load 2, it is preferable that the inequality in equation (1) has a larger difference than the range of the equality sign.

[0042] Here, if the charging time to the load 2 is sufficiently short, the current at the time of the rise of the load voltage becomes a peak current value, and the relationship of the formulas (2) and (3) is approximately satisfied.

[0043]

[0044]

[0045] t ＳＵ R: a period during which the third and fourth switching elements S3 and S4 are driven before the first and second switching elements S1 and S2 as an inductor preliminary conduction period Ｌ : Equivalent series resistance component of inductor L1.

[0046] Therefore, while assuming the current value of the load 2, the time t required for the rise / fall of the load 2 is calculated. Ｃ There is also a relationship between them expressed by the following equation (4): Note that equation (4) is based on the premise that the inductance value L is sufficiently large and is assumed to be a constant current source.

[0047]

[0048] Therefore, to more suitably implement the invention described in the first embodiment, the required relational expressions are as shown in expressions (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 period of time at least twice the time tc set as the rise time / fall time.

[0049]

[0050]

[0051]

[0052] Furthermore, in the case of Patent Document 1, the inductance value L of the inductor L1 is calculated based on the above relational expression as follows: Ｃ However, the time t Ｃ It is not possible to adjust the capacitance C, and if the capacitance C increases or decreases more than expected, it will be affected.

[0053] On the other hand, the invention described in the first embodiment is based on the assumption that the minimum value C of the capacitance C ｍｉｎ , time t Ｃ The target maximum value t Ｃ＋The lower limit of the inductance value L is determined from ＳＵ The minimum value of t ＳＵ－ , the maximum value of the capacitance C ｍａｘ The upper limit of the inductance value L is determined from the above equation (8).

[0054]

[0055] Here, the inductance preliminary conduction period t ＳＵ The minimum value of t ＳＵ－ is 2√(C ｍａｘ / C ｍｉｎ ) t ｃ＋ In this case, it is necessary to ｍａｘ / C ｍｉｎ )>1, so t ＳＵ >2 tons Ｃ＋ >2 tons Ｃ Also, even if there is a change in the capacitance C, the Ｃ is the inductance pre-current period t ＳＵ can be adjusted by

[0056] 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]

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

[0059] (1) Load voltage rise preparation period: The third switching element S3 is turned on while the second switching element S2 remains on, and energy is stored in the inductor L1. At this time, iL>0.

[0060] (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 inductor L1 causes a current to flow 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.

[0061] (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 inductor L1 at the connection point between the first and second switching elements S1 and S2, and the voltage Vin / 2 is applied to the inductor L1 at the connection point between the third and fourth switching elements S3 and S4, so that Vin / 2 is applied to the inductor L1 and the current decreases.

[0062] (4) Voltage holding period: The third switching element S3 is turned off while the first switching element S1 remains on. At this time, the current through the inductor L1 is zero, so the third switching element S3 performs zero-current switching.

[0063] (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 inductor L1. At this time, iL<0.

[0064] (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 inductor L1, causing the load voltage to fall.

[0065] (7) Voltage holding period: The second switching element S2 is turned ON while the fourth switching element S4 remains ON. The voltage on the inductor L1 side of the connection point between the first and second switching elements S1 and S2 is 0, and the voltage on the connection point between the inductor L1 and the third and fourth switching elements S3 and S4 is Vin / 2, so Vin / 2 is applied to the inductor L1 and the current decreases.

[0066] (8) Voltage holding period: The fourth switching element S4 is turned OFF while the second switching element S2 is kept ON. At this time, the current through the inductor L1 is 0, so the fourth switching element S4 performs zero-current switching.

[0067] 4, the slope changes discontinuously at the points where iL1 is maximum and minimum (the maximum and minimum points are angular), but when the capacitance of the load 2 is taken into account, the slope changes continuously (the maximum and minimum points are rounded). Furthermore, 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 zero, the first and second switching elements S1 and S2 are switched on. Therefore, the potential difference across the inductor L1 does not change suddenly due to the presence of the first and second capacitors C1 and C2, etc. Therefore, the slope of IL1 does not become discontinuous at the boundaries.

[0068] The rising and falling waveforms of the load voltage Vout are, strictly speaking, S-shaped rather than linear as shown in FIG. 4, but if ipk is set to be sufficiently large, they will be approximately linear.

[0069] The period (6) of the falling edge of the load voltage Vout is basically the discharge of the charged energy in the capacitive component of the load 2, so if the energy is reduced due to loss, it will be faster, and if there is no loss, it will remain the same. Therefore, regardless of the resistive component of the load 2, the periods (2) and (6) of the load voltage Vout are roughly equal, as shown in Figure 4.

[0070] Next, an example of soft switching operation 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 example of the operation of the first switching element S1 is shown in Figure 5(a). Because the first switching element S1 is connected in series with the load 2, the voltage applied to it is the voltage Vin of the direct-current 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 of 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.

[0072] 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.

[0073] An example of the operation of the second switching element S2 is shown in Figure 5(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 timing at which 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, at the timing at which the second switching element S2 turns off, the voltage applied to the second switching element S2 is 0, resulting in zero-voltage switching.

[0074] 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, at the timing when the second switching element S2 turns on, the voltage applied to the second switching element S2 is 0, resulting in zero-voltage switching.

[0075] An example of the operation of the third switching element S3 is shown in Figure 5(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 inductor 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 inductor 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 inductor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0076] 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 inductor 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 inductor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0077] An example of the operation of the fourth switching element S4 is shown in Figure 5(d). Because the fourth switching element S4 is an element 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 inductor 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 inductor 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 inductor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[0078] 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 inductor 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 inductor L1 is slower than the rate of change of the voltage of the switching element, resulting in zero-current switching.

[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) 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 inductor L1, so the neutral point voltage can also be controlled by controlling the average current value of inductor L1. The average current value of inductor L1 can be controlled by changing the ratio between period (1) and period (5). Theoretically, by controlling the average value to zero, fluctuations in the neutral point potential can be made zero.

[0080] If iL is positive and negative symmetrical, the neutral point potential will not fluctuate. However, if the load 2 includes a resistive component, the charging current and discharging current will not necessarily be positive and negative symmetrical. In this case, IL1 must be adjusted. If IL1 is positive, the neutral point potential will decrease, and if IL1 is negative, the neutral point potential will increase. This adjusts the voltages of the first capacitor C1 and the second capacitor C2, i.e., the neutral point potential.

[0081] The average current value when the first switching element S1 is ON is positive because it is supplied to the load 2. Furthermore, it shifts in the positive direction by the amount that increases the neutral point potential. The average current value when the second switching element S2 is ON is zero except for the amount that shifts in the positive direction as a decrease in the neutral point potential because no current is supplied to the load 2.

[0082] 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.

[0083] Although detailed description of the first embodiment will be omitted, the following configurations can also achieve the same operation as in Fig. 3. The orientation of the switching elements and diodes is the same as 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. Furthermore, by adjusting the on / off periods of each switching element, it is possible to control the rise and fall rates of the load voltage. Therefore, it is possible to generate output pulses with high efficiency and low noise, at constant rise and fall rates, without being affected by variations in the load or components. Maintaining constant rise and fall rates leads to improved accuracy of the output voltage of the power converter.

[0085] [Embodiment 2] Fig. 6 shows a basic circuit of a power converter (output pulse generating circuit) according to embodiment 2, and Fig. 7 shows basic operating waveforms of the power converter (output pulse generating circuit). Here, it is assumed that the load 2 is capacitive. Fig. 6 shows the load 2 schematically, but it may be, for example, 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 a direct-current power source DC to the load 2 and returns the power of the load 2 to the direct-current power source 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 a DC power supply DC. Furthermore, 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.

[0087] One end of the inductor L1 is connected to the connection point between the first and second switching elements. Third and fourth switching elements S3 and S4 are connected in anti-series between the connection point between the first and second capacitors C1 and C2 and the other end of the inductor L1. The anode of the 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 the DC power supply DC. The cathode of the 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 of the inductor L1 is Vin / 2, which is the intermediate voltage of the DC power supply DC voltage Vin.

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

[0089] The circuit of FIG. 6 charges and discharges the voltage of the load 2 using energy stored in the inductor L1, and maintains the voltage using the first and second switching elements S1 and S2, thereby realizing a rectangular wave output voltage.

[0090] The amount of 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 amount of this energy.

[0091] By adjusting the ON times of the third and fourth switching elements S3 and S4 according to variations in load and inductance, it is possible to control variations in dv / dt. In addition, since all switching elements are soft-switched even when turned 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.

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

[0094] (2) Load voltage rise period: The third switching element S3 remains ON while the second switching element S2 is turned OFF, and current flows through the third switching element S3 using the energy of the inductor L1 to raise the load voltage Vout. When the second switching element S2 is turned OFF, the load voltage Vout is zero, resulting in zero-voltage switching.

[0095] (3) Voltage holding period: The first switching element S1 is turned ON while the third switching element S3 remains ON. The connection point of the inductor L1 between the first and second switching elements S1 and S2 has a voltage Vin, and the voltage on the fourth switching element S4 side of the inductor L1 is Vin / 2, so Vin / 2 is applied to the inductor L1 and the current decreases.

[0096] (4) Voltage holding period: The third switching element S3 is turned OFF while the first switching element S1 remains ON. Since the current through the inductor L1 becomes 0, the third switching element S3 performs zero-current switching.

[0097] (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 inductor L1. At this time, iL<0.

[0098] (6) Load voltage fall period: The first switching element S1 is turned off while the fourth switching element S4 remains on, and the load voltage Vout falls due to the energy of the inductor L1.

[0099] (7) Voltage holding period: The second switching element S2 is turned ON while the fourth switching element S4 remains ON. The voltage on the connection point between the first and second switching elements S1 and S2 of the inductor L1 is 0, and the voltage on the fourth switching element S4 side of the inductor L1 is Vin / 2, so Vin / 2 is applied to the inductor L1 and the current decreases.

[0100] (8) Voltage holding period: The fourth switching element S4 is turned OFF while the second switching element S2 remains ON. Since the current through the inductor L1 becomes 0, the fourth switching element S4 performs zero-current switching.

[0101] The operation during soft switching is the same as in Fig. 5, and therefore a description thereof will be omitted. The voltages of the first capacitor C1 and the second capacitor C2 are also the same as in the first embodiment.

[0102] By operating in the above manner, it is possible to output an output pulse voltage with a constant dv / dt while performing soft switching of each switching element, without being affected by variations in components or loads. That is, the same effects as those of the first embodiment are achieved.

[0103] Although detailed description of the second embodiment will be omitted, the same operation as in Fig. 6 can also be achieved with the following configuration. The orientation of the switching elements is the same as in Fig. 6. A configuration in which the first and second diodes D1 and D2 are replaced with fifth and sixth switching elements.

[0104] [Embodiment 3] Fig. 8 shows a basic circuit of a power converter (output pulse generating circuit) according to embodiment 3, and Fig. 9 shows basic operating waveforms of the power converter (output pulse generating circuit). Here, it is assumed that the load 2 is capacitive. Fig. 8 shows the load 2 schematically, but it may be, for example, 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 a direct-current power source DC to the load 2 and returns the power of the load 2 to the direct-current power source DC.

[0105] As shown in Fig. 8, a first capacitor C1 is connected 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, 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.

[0106] One end of an inductor L1 is connected to the connection point between 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 direct-current power supply DC.

[0107] The other end of the inductor L1 is connected to the cathode of a second diode D2. The anode of the second diode D2 is connected to one end of a fourth switching element S4. The other end of the fourth switching element S4 is connected to the negative electrode of the direct-current 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 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 inductor L1 becomes Vin / 2, which is the intermediate voltage Vin of the direct-current power supply DC.

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

[0110] The circuit of FIG. 8 charges and discharges the voltage of the load 2 using energy stored in the inductor L1, and maintains the voltage using the first and second switching elements S1 and S2, thereby realizing a rectangular wave output voltage.

[0111] The amount of energy stored in inductor L1 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, variations in dv / dt can be controlled.

[0112] In addition, since all switching elements are soft-switched even when turned off, lower loss and noise can be achieved than in Patent Document 1.

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

[0114] (1) Load voltage rise preparation period: The third switching element S3 is turned on while the second switching element S2 remains on, and energy is stored in the inductor L1. At this time, iL>0.

[0115] (2) Load voltage rise period: The second switching element S2 is turned OFF while the third switching element S3 remains ON, and current flows through the third switching element S3 using the energy of the inductor L1 to raise the load voltage Vout. When the second switching element S2 is turned OFF, the load voltage Vout is zero, resulting in zero-voltage switching.

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

[0117] (4) Voltage holding period: The third switching element S3 is turned OFF while the first switching element S1 remains ON. Since the current through the inductor L1 becomes 0, the third switching element S3 performs zero-current switching.

[0118] (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 inductor L1. At this time, iL<0.

[0119] (6) Load voltage fall period: The fourth switching element S4 remains ON while the first switching element S1 is turned OFF, and the load voltage Vout falls due to the energy of the inductor L1.

[0120] (7) Voltage holding period: The second switching element S2 is turned ON while the fourth switching element S4 remains ON. The voltage on the connection point between the first and second switching elements S1 and S2 of the inductor L1 is 0, and the voltage on the third switching element S3 side of the inductor L1 is Vin / 2, so Vin / 2 is applied to the inductor L1 and the current decreases.

[0121] (8) Voltage holding period: The second switching element S2 remains ON while the fourth switching element S4 is turned OFF. When the fourth switching element S4 is turned OFF, the current through the inductor L1 becomes 0, and the fourth switching element S4 performs zero-current switching.

[0122] The operation during soft switching is the same as in FIG. 5 and will therefore be omitted.

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

[0124] By operating in the above manner, it is possible to output an output pulse voltage with a constant dv / dt while performing soft switching of each switching element, without being affected by variations in components or loads. That is, the same effects as those of the first and second embodiments are achieved.

[0125] Although detailed description of the third embodiment will be omitted, the same operation as in Fig. 8 can also be achieved with the following configurations. The orientation of the diodes and switching elements is the same as in Fig. 8. A configuration in which the third and fourth switching elements S3 and S4 are replaced with first and second diodes D1 and D2, and the first and second diodes D1 and D2 are replaced with third and fourth switching elements S3 and S4. A configuration in which the first and second diodes D1 and D2 are replaced with fifth and sixth switching elements.

[0126] 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.

[0127] DC... DC power supply C1, C2... First and second capacitors S1 to S4... First to fourth switching elements D1 to 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 capacitor and third and fourth switching elements connected such that the voltage on the other end side of the inductor is intermediate between the voltages of the DC power source, Characterized in that a current is preliminarily passed through the inductor before the first and second switching elements are turned on.

2. The capacitor is a first capacitor and a second capacitor connected in series between the positive and negative electrodes of the DC power source, A second diode having an anode connected to the connection point of the first and second capacitors; The 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; The 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 source; 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 source, The power converter according to claim 1, characterized by comprising the above.

3. 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, 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, The power converter according to claim 1, characterized by comprising.

4. 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, 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, The power converter according to claim 1, characterized by comprising.

5. 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 and a fourth switching element connected in reverse 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, 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, The power converter according to claim 1, characterized by comprising.

6. The capacitor is a first capacitor and a second capacitor connected in series between the positive and negative electrodes of the DC power supply, and the third and fourth switching elements reversely connected in 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. The power converter according to claim 1, characterized in that it comprises the above.

7. 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 supply, 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 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. The power converter according to claim 1, characterized in that it comprises the above.

8. 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. The power converter according to claim 1, characterized in that it comprises the above.

9. The third switching element having one end connected to the other end of the inductor; the 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; the sixth switching element having one end connected to the other end of the inductor; the 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. The power converter according to claim 1, characterized in that it comprises the above.

10. The power converter according to claim 1, wherein the inductor satisfies the condition of the following equation (9) for the inductance. 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 11. The power converter according to claim 1, wherein a preliminary current flowing period for preliminarily flowing a current through the inductor from before conduction of the first and second switching elements satisfies the condition of the following formula (5). T ＳＵ : The preliminary current flowing period for preliminarily flowing a current through the inductor from before conduction of the first and second switching elements. L: The inductance value of the inductor. C: The capacitance of the load. R Ｌ : The equivalent series resistance component of the inductor 12. The power converter according to claim 1, wherein the time set as the rise time and fall time of the load voltage satisfies the following formula (6). t ｃ : The time set as the rise time and fall time of the load voltage. L: The inductance value of the inductor. C: The capacitance of the load. T ＳＵ : The pre-conduction period for preliminarily passing a current through the inductor from before the conduction of the first and second switching elements.

13. The power converter according to claim 1, characterized in that a preliminary current flowing period for preliminarily passing a current through the inductor before conduction of the first and second switching elements, and a time set as the rise time and fall time of the load voltage satisfy the conditions of the following formula (7). T ＳＵ : The preliminary current flowing period t for preliminarily passing a current through the inductor before conduction of the first and second switching elements ｃ : The time set as the rise time and fall time of the load voltage

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