Non-isolated bidirectional DC / DC converter

Abstract

The objective is to provide a highly efficient and low-noise non-isolated bidirectional DC / DC converter while keeping costs and size increases to a minimum. [Solution] The present invention is an H-bridge type bidirectional DC / DC converter comprising a switching circuit 10 connected in series with two switching devices, a switching circuit 20 connected in series with two switching devices, and a choke coil L1 connecting the connection points of switching devices (S1, S2) and the connection points of switching devices (S3, S4), further comprising a capacitor Ca connected in parallel with switching device S2 of switching circuit 10, a capacitor Cb connected in parallel with switching device S3 of switching circuit 20, and a capacitance addition means for increasing the total capacitance of the capacitors of the switching circuit on the side where DC is output for any period of time by an additional capacitance.

Description

[Technical Field]

[0001] This disclosure relates to a step-up / step-down, non-isolated, bidirectional DC / DC converter. [Background technology]

[0002] As a non-isolated DC / DC converter that can boost or buck the voltage and does not reverse the polarity of the output voltage, there is a boost-buck DC / DC converter circuit that combines a buck chopper and a boost chopper (see, for example, Patent Document 1). This circuit can handle a wide input / output voltage range and is capable of bidirectional operation by using all semiconductor elements as switching elements. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2007-274778 [Overview of the project] [Problems that the invention aims to solve]

[0004] Typical non-isolated buck-boost DC / DC converters, like the one shown in Figure 1, employ hard switching, resulting in high switching losses and noise, as well as the need for a snubber circuit to suppress surge voltages. Various soft-switching methods have been devised to address these issues. However, implementing these soft-switching methods requires the addition of many components, making it difficult to reduce costs and size. Furthermore, implementing soft-switching methods increases switching losses under light loads, making efficiency improvements difficult.

[0005] Therefore, the present invention aims to provide a highly efficient and low-noise non-isolated bidirectional DC / DC converter while suppressing increases in cost and size, in order to solve the aforementioned problems. [Means for solving the problem]

[0006] To achieve the above objective, the bidirectional DC / DC converter according to the present invention adds a capacitor in parallel with the switching device and controls the switching timing to achieve zero-volt switching. Furthermore, the bidirectional DC / DC converter according to the present invention enables bidirectional operation by adjusting the capacitance of the capacitor added to one side and the capacitor added to the other side relative to the choke coil.

[0007] Specifically, the bidirectional DC / DC converter according to the present invention is: Two switching circuits, in which two switching devices are connected in series between pairs of input / output terminals that receive DC input and output, A choke coil connecting the connection points of the two switching devices in both of the aforementioned switching circuits, An H-bridge type bidirectional DC / DC converter comprising, In each of the switching circuits, a capacitor is connected in parallel to one or each of the switching devices, and Capacitance addition means for increasing the total capacitance of the capacitor in the switching circuit on the side where DC is output during any period by an additional capacitance. It is further characterized by having the following features.

[0008] This bidirectional DC / DC converter is a buck-boost DC / DC converter circuit that combines a buck chopper and a boost chopper. This bidirectional DC / DC converter uses the parasitic capacitance of the switching element of the switching circuit on the power output side and the discharge current of the capacitor connected in parallel with it to reverse the current of the choke coil, and this current discharges the parasitic capacitance of the switching element of the switching circuit on the power input side and the charge of the capacitor connected in parallel with it. As a result, zero-voltage switching when the power is on can be achieved for the switching element of the switching circuit on the power input side.

[0009] Furthermore, this bidirectional DC / DC converter adds a capacitance enhancement mechanism, consisting of a switch element and a capacitor connected in series, to each switch circuit. By controlling this capacitance enhancement mechanism, it is possible to prevent the current used for ON-zero voltage switching (inverted current) from becoming excessively large, thereby preventing an increase in circuit losses.

[0010] Furthermore, this bidirectional DC / DC converter can also be turned on while the built-in diode is conducting in other switching elements, enabling zero-voltage switching when each switching element is on. As described above, this bidirectional DC / DC converter can achieve zero voltage switching when each switching element is ON, thereby reducing switching losses and improving efficiency.

[0011] Furthermore, this bidirectional DC / DC converter requires fewer components than a typical non-isolated bidirectional DC / DC converter circuit. Therefore, this bidirectional DC / DC converter can minimize cost and size increases. Therefore, the present invention can provide a highly efficient and low-noise non-isolated bidirectional DC / DC converter while suppressing increases in cost and size. [Effects of the Invention]

[0012] This invention can provide a highly efficient and low-noise non-isolated bidirectional DC / DC converter while keeping costs and size increases to a minimum. [Brief explanation of the drawing]

[0013] [Figure 1] This diagram illustrates the circuit (A) and switching timing charts (B, C) of a typical non-isolated DC / DC converter. [Figure 2] This diagram illustrates the circuit of the bidirectional DC / DC converter according to the present invention. [Figure 3] This diagram illustrates the operation of the bidirectional DC / DC converter according to the present invention. [Figure 4] This diagram illustrates the operation of the bidirectional DC / DC converter according to the present invention. [Figure 5] This diagram illustrates the operation of the bidirectional DC / DC converter according to the present invention. [Figure 6] This diagram illustrates the operation of the bidirectional DC / DC converter according to the present invention. [Figure 7] This diagram illustrates the circuit of the bidirectional DC / DC converter according to the present invention. [Figure 8] This diagram illustrates the circuit of the bidirectional DC / DC converter according to the present invention. [Figure 9] This diagram illustrates the circuit of the bidirectional DC / DC converter according to the present invention. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described with reference to the attached drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to these embodiments. In this specification and in the drawings, components with the same reference numerals refer to the same components. Furthermore, although the following embodiment will be described using the case where power is transferred from input / output terminal pair Ter1 to input / output terminal pair Ter2 (power is transferred from left to right in Figure 2; this direction is considered the forward direction), since this DC / DC converter operates bidirectionally, the same operation will occur even when power is transferred from input / output terminal pair Ter2 to input / output terminal pair Ter1 (power is transferred from right to left in Figure 2; this direction is considered the reverse direction).

[0015] Figure 2 is a diagram illustrating the circuit of the bidirectional DC / DC converter of this embodiment. This bidirectional DC / DC converter is A switching circuit 10 is formed by connecting two switching devices (S1, S2) in series between the input / output terminals and Ter1, A switching circuit 20 is formed by connecting two switching devices (S3, S4) in series between the input / output terminals and Ter2, A choke coil L1 connecting between the connection points of two switching devices (S1, S2) and the connection points of two switching devices (S3, S4), is a H-bridge type bidirectional DC / DC converter comprising: A capacitor Ca connected in parallel with the switching device S2 of the switching circuit 10, a capacitor Cb connected in parallel with the switching device S3 of the switching circuit 20, and a capacitance adding means for increasing the capacitance of the capacitor Cb by an additional capacitance Cy or increasing the capacitance of the capacitor Ca by an additional capacitance Cx during an arbitrary period.

[0016] Here, the capacitance adding means is a series circuit of a switching device S5 connected in parallel with the switching device S2 and an additional capacitance Cx, and a series circuit of a switching device S6 connected in parallel with the switching device S3 and an additional capacitance Cy.

[0017] When DC is input from the input / output terminal pair Ter1 and DC is output from the input / output terminal pair Ter2, the additional capacitance Cy (F) is: Vi max 2 ×C in <Vo min 2 ×(C out +Cy) and satisfies the capacitance. However, Vi max is the maximum value of the input DC voltage Vi (V), Vo min is the minimum value of the output DC voltage Vo (V), C in (F) is the total capacitance of the capacitors of the switching circuit 10 on the side where DC is input (that is, C in =C1 + C2 + Ca), C out (F) is the total capacitance of the capacitors of the switching circuit 20 on the side where DC is output (that is, C out =C3 + C4 + Cb) and is as follows. In the reverse direction, the additional capacitance Cx (F) is: Vimax 2 ×C in <Vo min 2 ×(C out +Cx) The capacity should satisfy the following conditions.

[0018] Furthermore, this bidirectional DC / DC converter is equipped with a control device 30 that controls each switching device (S1 to S6) to turn the switching elements (Q1 to Q6) of the switching devices (S1 to S6) on or off. Capacitors C7 and C8 are connected to smooth the input and output voltages.

[0019] The high-potential switching device S1 of the switching circuit 10 has a configuration in which a parasitic capacitance C1 and a parallel diode D1 with the high-potential side as the cathode are connected in parallel to the switching element Q1. The switching device S2 on the low-potential side of the switching circuit 10 has a configuration in which a parasitic capacitance C2 and a parallel diode D2 with the high-potential side as the cathode are connected in parallel to the switching element Q2. The switching device S5, which is a means for adding capacitance to the switching circuit 10, has a configuration in which a parasitic capacitance C5 and a parallel diode D5 with the high-potential side as the cathode are connected in parallel to the switching element Q5.

[0020] The high-potential switching device S4 of the switching circuit 20 has a configuration in which a parasitic capacitance C4 and a parallel diode D4 with the high-potential side as the cathode are connected in parallel to the switching element Q4. The switching device S3 on the low-potential side of the switching circuit 20 has a configuration in which a parasitic capacitance C3 and a parallel diode D3 with the high-potential side as the cathode are connected in parallel to the switching element Q3. The switching device S6 of the capacitance addition means for the switching circuit 20 has a configuration in which a parasitic capacitance C6 and a parallel diode D6 with the high-potential side as the cathode are connected in parallel to the switching element Q6.

[0021] By switching element Q5 on or off, it is possible to select whether or not the additional capacitance Cx is connected in parallel with capacitor Ca, thereby adjusting the capacitance of the capacitor connected in parallel with switch device S2. Similarly, by switching element Q6 on or off, it is possible to select whether or not the additional capacitance Cy is connected in parallel with capacitor Cb, thereby adjusting the capacitance of the capacitor connected in parallel with switch device S3.

[0022] In this embodiment, capacitor Ca is connected in parallel with switching device S2 in the switching circuit 10, but as will be described later, it may also be connected in parallel with switching device S1, or in parallel with both switching device S1 and switching device S2. In this embodiment, the capacitor Cb in the switching circuit 20 is connected in parallel with the switching device S3, but as will be described later, it may also be connected in parallel with the switching device S4, or in parallel with both the switching device S3 and the switching device S4. In either configuration, the total capacitance of the capacitors included in the switching circuit on the output side is temporarily increased by the amount of the additional capacitance (Cy or Cx) for any given period.

[0023] [Basic operation] The control device 30 is In the switching circuit 10 on the side where DC is input, the switching elements (Q1, Q2) of the switching devices (S1, S2) are turned on alternately. In the switching circuit 10 on the DC input side, after turning off the switch element Q1 of the high-potential switching device S1, and after a predetermined time Td has elapsed, the switch element Q2 of the low-potential switching device S2 is turned on, thereby in the switching circuit 20 on the DC output side, the discharge current of the parasitic capacitance C3 of the low-potential switching device S3, and, if a capacitor Cb is in parallel, the discharge current of the capacitor Cb, are used to reverse the current of the choke coil L1. In the switching circuit 10 on the DC input side, by turning off the switching element Q2 of the switching device S2 on the low-potential side while the current in the choke coil L1 is reversed, the charge of the parasitic capacitance C1 of the switching device S1 on the high-potential side, and the charge of capacitor Ca if capacitor Ca is connected to the switching device S1, are discharged. In the switching circuit 10 on the DC input side, zero-volt switching is achieved by turning on the switch element Q1 of the high-potential switching device S1 after a predetermined time Td has elapsed since turning off the switch element Q2 of the low-potential switching device S2, and The aforementioned arbitrary period is from any timing during the period when the current in the choke coil L1 is reversed to any timing during the period when the switching element Q1 of the switching device S1 on the high-potential side, which is the side to which DC is input, is turned on. It is characterized by the following.

[0024] The predetermined time Td is set to approximately 1 / 4 of the resonant period between the parasitic capacitances (C1, C2) and capacitor Ca, and the choke coil L1. Specifically, the predetermined time Td is determined by calculating it using the following formula.

number

[0025] This bidirectional DC / DC converter realizes zero-voltage switching in the forward direction by discharging the charge of the parasitic capacitance C1 of the switch element Q1 using the discharge currents of capacitors C3 and Cb and the charging current of capacitor C4, and simultaneously charging capacitors C2 and Ca. Here, when the input voltage Vi is higher than the output voltage Vo (in the case of step-down operation), there is a problem that the discharge currents of capacitors C3 and Cb and the charging current of capacitor C4 cannot obtain a current value sufficient for zero-voltage switching of the switch element Q1. To solve this problem, the capacitance of capacitor Cb may be increased (Ca < Cb). However, when configured in this way, zero-voltage switching of the switch element Q4 becomes difficult in the reverse direction.

[0026] Therefore, this bidirectional DC / DC converter connects an additional capacitance Cy in parallel with capacitor Cb and an additional capacitance Cx in parallel with capacitor Ca. When the input voltage Vi is higher than the output voltage Vo (in the case of forward step-down operation), switch element Q6 is turned on to increase the capacitance of capacitor Cb (that is, the capacitor capacitance is set to Cb + Cy), thereby ensuring the current required for zero-voltage switching of switch element Q1. On the other hand, in the reverse direction, similar to the forward direction, switch element Q5 is turned on to increase the capacitance of capacitor Ca (that is, the capacitor capacitance is set to Ca + Cx), thereby ensuring the current required for zero-voltage switching of switch element Q4.

[0027] Also, when the input voltage Vi is higher than the output voltage Vo (in the case of forward step-down operation), if the capacitance of the additional capacitance Cy is set to a relatively large value, zero-voltage switching is possible even at a low output voltage Vo. However, when the output voltage Vo becomes a relatively high voltage, if switch element Q6 is always on, the discharge current from the additional capacitance Cy becomes excessive, and the conduction loss of each part of the circuit increases. Therefore, by controlling the on-time of Q6 to limit the charging time of the additional capacitance Cy, it is possible to ensure the current required for zero-voltage switching while setting the current discharged from the additional capacitance Cy to an appropriate value. The same applies to the reverse direction.

[0028] Describe the method for setting the value of the specific additional capacitance Cy (in the forward direction). During the period when the switch element Q3 is off, the output voltage Vo is applied to the capacitors C3, C4, and Cb. At this time, the energy J2 stored in the capacitors (C3, C4, and Cb) included in the switching circuit 20 is expressed by the following equation. J2 = 0.5Vo 2 (C3 + C4 + Cb)

[0029] The current I of the choke coil L1 L After decreasing to zero, the current I L reverses, the capacitors C3 and Cb are discharged, and the current I L increases in the negative direction. At this time, the energy stored in the capacitors C3 and Cb moves to L1.

[0030] After that, when the switch element Q2 turns off, the current I of the choke coil L1 L charges the capacitors C2 and Ca and discharges the capacitor C1 at the same time. At this time, the energy J1 required to charge the voltages of the capacitors C2 and Ca from zero to Vi and discharge the voltage of the capacitor C1 from Vi to zero is expressed by the following equation. J1 = 0.5Vi 2 (C1 + C2 + Ca)

[0031] Since this energy is supplied from J2 stored in the choke coil L1, the condition for discharging the voltage of the switch element Q1 to zero and achieving ZVS is J1 < J2, so it is expressed by the following equation. Vi 2 (C1 + C2 + Ca) < Vo 2 (C3 + C4 + Cb)

[0032] Here, the condition for enabling ZVS in the entire range of Vi and Vo is Vi max 2 (C1 + C2 + Ca) < Vo min 2 (C3 + C4 + Cb) (Vimax :Maximum value of Vi, Vo min (Minimum value of Vo) That is the case.

[0033] However, since the capacitance of each capacitor is fixed, setting the capacitance under forward conditions makes it impossible to achieve ZVS in the reverse direction. Therefore, in this embodiment, additional capacitances Cx and Cy are added to switching circuits 10 and 20, respectively, and the total capacitance of each switching circuit (10, 20) can be temporarily increased using switching devices S5 and S6, respectively. In other words, if the direction is forward, the additional capacity Cy(F) is, Vi max 2 ×C in <Vo min 2 ×(C out +Cy) This satisfies the following conditions. Also, in the reverse direction, the additional capacity Cx(F) is: Vi max 2 ×C in <Vo min 2 ×(C out +Cx) It satisfies the condition.

[0034] [Step-down operation] In the case of step-down operation where the output voltage Vo is less than the input voltage Vi, the control device 30 is characterized by keeping the switching element Q3 of the switching device S3 on the side where DC is output and on the low-potential side permanently off.

[0035] Figure 3 shows the drive signals (Sg) that turn the switch elements (Q1, Q2, Q6) on and off during the step-down operation. Q1 Sg Q2 Sg Q6 ), the current value I flowing through the choke coil L1 L , the voltage across each switching element (Q1~Q3) (V Q1 ~V Q3Figure 4 is a time chart explaining the operation. Figure 4 is a diagram illustrating the current flow during each period (a1 to h). Figures 3 and 4 are used to explain the step-down operation of this bidirectional DC / DC converter.

[0036] (Period a1) The period a1 begins when the switch element Q1 is turned on. The voltage V of the switch element Q1 during the period h, which will be explained later. Q1 Since it is zero, the switch element Q1 can be turned on with zero voltage (zero-volt switching). When the switch element Q1 is turned on, the current I of the choke L1 L As the voltage increases in the forward direction, the discharge of capacitor C4 and the charging of additional capacitance Cy via parasitic capacitance C3, capacitor Cb, and the switched element Q6 begin. Therefore, the voltage V of the switched element Q3 Q3 It will rise. (period a2) Period a2 begins when the switch element Q6 is turned off before the charging of the additional capacitor Cy is complete. During period a2, charging of the additional capacitor Cy stops. Meanwhile, charging of the parasitic capacitor C3 and capacitor Cb, and discharging of capacitor C4 continue until the voltages of the parasitic capacitor C3 and capacitor Cb reach Vo. (period b) When the parasitic capacitance C3 and capacitor Cb are charged to the output voltage Vo, the parallel diode D4 conducts, and the voltage V Q3 The rise stops. Current I of choke L1 L The number will continue to increase. (period c) Period c begins when switch element Q1 is turned off. When switch element Q1 is turned off, parasitic capacitance C1 is charged, and at the same time, parasitic capacitance C2 and capacitor Ca, as well as parasitic capacitance C5 and additional capacitance Cx, are discharged. Since the capacitance of capacitor Ca is larger than that of parasitic capacitance C2, the voltage does not drop easily even when this discharge occurs, and the voltage of switch element Q1 V Q1The rise in the difference voltage between the input voltage Vi and the voltage across capacitor Ca becomes gradual, reducing switching losses when the switch element Q1 is off (see Supplement 1 below). Subsequently, when the voltage between the parasitic capacitance C2 and capacitor Ca becomes zero, the parallel diode D2 conducts, and the current I of the choke L1 flows. L It begins to decrease. [Supplement 1] There is a short time between when the switch element Q1 starts to turn off and when the current in Q1 becomes zero and it completely turns off. The voltage V during that time is V. Q1 By slowing down the rise in voltage, switching losses are reduced. [End of Supplement 1] (Period d) While the parallel diode D2 is conducting, the voltage across the switch element Q2 is V Q2 Since it is zero, the switch element Q2 can be turned on with zero voltage (zero-voltage switching). (Period e1) If the inductance of the choke coil L1 is sufficiently small, the current I L The current I of the choke coil L1 reaches zero. L After it drops to zero, current I L The current flows through the already-on switch element Q2, reversing the flow through the choke coil L1, initiating the discharge of parasitic capacitance C3 and capacitor Cb, and the charging of capacitor C4. Since the voltage across the additional capacitance Cy is lower than the voltage across parasitic capacitance C3 and capacitor Cb, the parallel diode D6 does not conduct, and the additional capacitance Cy does not discharge. (Period e2) When the voltage across parasitic capacitance C3 and capacitor Cb falls below the voltage across additional capacitance Cy, the parallel diode D6 conducts, and the discharge of additional capacitance Cy begins. Furthermore, by turning on the switch element Q6 between the time the parallel diode D6 conducts and the time when charging of parasitic capacitance C3 and capacitor Cb begins, the device is turned on by zero-voltage switching. (period f) When the parasitic capacitance C3 and capacitor Cb discharge and the voltage becomes zero, the parallel diode D3 conducts. At this time, the voltage applied to the choke coil L1 becomes zero, and the current I L The slope becomes zero and the current IL The current remains constant. The additional capacitance Cy is the reversed current I at this time. L It has the function of increasing the value of [the capacitor]. Capacitor Cb has the same function as capacitor Ca (reduction of switching loss) when operating in the reverse direction. (Period g) Period g begins when the switch element Q2 turns off. When the switch element Q2 turns off, current I L As a result, the parasitic capacitance C2 and capacitor Ca, as well as the parasitic capacitance C5 and additional capacitance Cx, are charged, while the parasitic capacitance C1 is discharged. (period h) The capacitance of capacitor Cb is sufficiently large, causing the current I to reverse. L If sufficient power is ensured, the parasitic capacitance C1 can be completely discharged, and the voltage across the switching element Q1 V Q1 The voltage becomes zero, and the parallel diode D1 conducts. The voltage across the switching element Q1 is V Q1 Since it is zero, the switch element Q1 can be turned on at zero volts at the start of the next period a.

[0037] [Boost operation] In the case of a boost operation in which the output voltage Vo is made greater than the input voltage Vi, the control device 30 is characterized in that it turns on the switch element Q3 of the switching device S3 on the side where DC is output and on the low potential side during the period when the switch element Q2 of the switching device S2 on the side where DC is input and on the low potential side is on, and turns off the switch element Q1 of the switching device S1 on the high potential side during the period when it is on.

[0038] Figure 5 shows the drive signals (Sg) that turn the switch elements (Q1~Q3, Q6) on and off during the boost operation. Q1 ~Sg Q3 Sg Q6 ), the current value I flowing through the choke coil L1 L , the voltage across each switching element (Q1~Q3) (V Q1 ~V Q3Figure 6 is a time chart explaining the operation. Figure 6 is a diagram illustrating the current flow during each period (a0 to h). The boost operation of this bidirectional DC / DC converter will be explained using Figures 5 and 6.

[0039] (Period a0) The period a0 begins when the switch element Q1 is turned on. The voltage V of the switch element Q1 during the period h, which will be explained later. Q1 Since it is zero, the switch element Q1 can be turned on with zero voltage (zero-volt switching). When the switch element Q1 is turned on, the current I in the choke coil L1 passes through the switch element Q3 which is already on. L A current flows. Also, since the input voltage Vi is applied to the choke coil L1, the current I L It increases. (Period a1) Here, when the switch element Q3 is turned off, current I L This causes the discharge of capacitor C4 and the charging of the additional capacitance Cy via parasitic capacitance C3, capacitor Cb, and the switched element Q6. Therefore, the voltage V of the switched element Q3 Q3 It will rise. (period a2) Period a2 begins when the switch element Q6 is turned off before the charging of the additional capacitor Cy is complete. During period a2, charging of the additional capacitor Cy stops. Meanwhile, charging of the parasitic capacitor C3 and capacitor Cb, and discharging of capacitor C4 continue until the voltages of the parasitic capacitor C3 and capacitor Cb reach Vo. (period b) When the parasitic capacitance C3 and capacitor Cb are charged to the output voltage Vo, the parallel diode D4 conducts, and the voltage V Q3 The rise stops. This operation is a boost operation, so the voltage V between the parasitic capacitance C3 and capacitor Cb after charging is complete. Q3 Since Vo (>Vi) is applied, a reverse voltage is applied to the choke coil L1. Therefore, the current I in the choke L1 L It will gradually decrease. (period c) Period c begins when switch element Q1 is turned off. When switch element Q1 is turned off, parasitic capacitance C1 is charged, and at the same time, parasitic capacitance C2 and capacitor Ca, as well as parasitic capacitance C5 and additional capacitance Cx, are discharged. Since the capacitance of capacitor Ca is larger than that of parasitic capacitance C2, the voltage does not drop easily even when this discharge occurs, and the voltage of switch element Q1 V Q1 The rise in the difference voltage between the input voltage Vi and the voltage across capacitor Ca becomes gradual, reducing switching losses when the switch element Q1 is off (see Supplement 1 above). Subsequently, when the voltage between the parasitic capacitance C2 and capacitor Ca becomes zero, the parallel diode D2 conducts, and the current I of the choke L1 flows. L The decrease begins to become significant. (Period d) While the parallel diode D2 is conducting, the voltage across the switch element Q2 is V Q2 Since it is zero, the switch element Q2 can be turned on with zero voltage (zero-voltage switching). (Period e1) If the inductance of the choke coil L1 is sufficiently small, the current I L The current I of the choke coil L1 reaches zero. L After it drops to zero, current I L The current flows through the already-on switch element Q2, reversing the flow through the choke coil L1, initiating the discharge of parasitic capacitance C3 and capacitor Cb, and the charging of capacitor C4. Since the voltage across the additional capacitance Cy is lower than the voltage across parasitic capacitance C3 and capacitor Cb, the parallel diode D6 does not conduct, and the additional capacitance Cy does not discharge. (Period e2) When the voltage across parasitic capacitance C3 and capacitor Cb falls below the voltage across additional capacitance Cy, the parallel diode D6 conducts, and the discharge of additional capacitance Cy begins. Furthermore, by turning on the switch element Q6 between the time the parallel diode D6 conducts and the time when charging of parasitic capacitance C3 and capacitor Cb begins, the device is turned on by zero-voltage switching. (period f) When the parasitic capacitance C3 and capacitor Cb discharge and the voltage becomes zero, the parallel diode D3 conducts. At this time, the voltage applied to the choke coil L1 becomes zero, and the current IL has a slope of zero and the current I L becomes constant. The additional capacitance Cy has the function of increasing the value of the reversed current I L at this time. The capacitor Cb has the same function as the capacitor Ca (reduction of switching loss) during reverse operation. (Period g1) The period g1 starts when the switching element Q3 turns on. While the parallel diode D3 is conducting, the voltage V Q3 across the switching element Q3 is 0V, so the switching element Q3 can be turned on with zero-voltage switching during this period. (Period g2) The period g2 starts when the switching element Q2 turns off. When the switching element Q2 turns off, the current I L charges the parasitic capacitance C2 and the capacitor Ca, as well as the parasitic capacitance C5 and the additional capacitance Cx, and at the same time discharges the parasitic capacitance C1. (Period h) Since the current I L reversed by the additional capacitance Cy is sufficiently ensured, the parasitic capacitance Cx can be completely discharged, and the voltage V Q1 across the switching element Q1 becomes zero and the parallel diode D1 conducts. Since the voltage V Q1 across the switching element Q1 is zero, the switching element Q1 can be turned on at zero volts at the start of the next period a0.

[0040] (Other embodiments) [Positions of capacitors Ca and Cb] Figures 2 to 6 are examples of the circuit of the bidirectional DC / DC converter according to the present invention. The bidirectional DC / DC converter according to the present invention has a variation circuit in FIG. 7 depending on the positions of the capacitors Ca and Cb. In any of the variation circuits, the switching timing and the current flow are the same as those described in FIGS. 2 to 6.

[0041] Figure 7(1) shows the circuit of the bidirectional DC / DC converter described in Figures 2 to 6. In the variation circuits shown in Figures 7(2) to 7(9), only the positions of capacitors Ca and Cb are indicated by their symbols (the choke coil and switching devices are the same as in Figure 7(1)). Furthermore, if capacitors are connected to both switching devices S1 and S2, they are designated as Ca1 and Ca2, respectively. If capacitors are connected to both switching devices S3 and S4, they are designated as Cb1 and Cb2, respectively. The "total capacitance of capacitor Ca" is the sum of the capacitances of Ca1 and Ca2, and the "total capacitance of capacitor Cb" is the sum of the capacitances of Cb1 and Cb2.

[0042] [Location of capacity expansion mechanism] The bidirectional DC / DC converter according to the present invention has the variation circuit shown in Figure 8, depending on the position of the capacitance addition means. In any variation circuit, the switching timing and current flow are the same as described in Figures 2 to 6.

[0043] Figure 8(1) shows the circuit of the bidirectional DC / DC converter described in Figures 2 to 6. In the variation circuits shown in Figures 8(2) to 8(9), only the positions of the additional capacitors Cx and Cy of the capacitance addition means are indicated by their symbols (the choke coil and switching devices are the same as in Figure 8(1)). When two capacitance addition means are connected to one switching circuit, the capacitors of the capacitance addition means in switching circuit 10 are designated as Cx1 and Cx2, and the capacitors of the capacitance addition means in switching circuit 20 are designated as Cy1 and Cy2. Furthermore, each variation circuit has variations in the positions of capacitors Ca and Cb, as explained in Figure 7. In other words, the total number of variations in Figure 8, considering Figure 7, is 81.

[0044] [Orientation of parallel diodes] In the bidirectional DC / DC converters described in Figures 2 to 8, the switching devices of the capacitance addition means were all arranged with the cathode of the parallel diode facing the choke coil side. However, the orientation of the switching devices of the capacitance addition means is not limited to this, and variations exist as shown in Figure 9.

[0045] Figure 9(1) shows the circuit of the bidirectional DC / DC converter described in Figures 2 to 6. Figures 9(2) to 9(9) illustrate variation circuits in which the orientation of the switching device of the capacitance addition means is reversed from that in Figure 8 (the choke coil and switching device are the same as in Figure 9(1)). Note that the orientation of each switching device of the capacitance addition means is not limited to uniformity (the cathode of the parallel diode is on the choke coil side, or vice versa). The orientation may differ for each switching device of the capacitance addition means. Furthermore, each variation circuit has variations in the positions of capacitors Ca and Cb as described in Figure 7. In other words, the total number of variations in Figure 9, considering Figures 7 and 8, is 729.

[0046] Furthermore, the above inventions can be combined as much as possible.

[0047] (effect) The present invention enables zero-voltage switching of all switching elements with fewer additional components than a basic step-up / step-down DC / DC converter like the one shown in Figure 1, and can realize a low-loss, low-noise bidirectional DC / DC converter without increasing cost or size. [Explanation of symbols]

[0048] 10, 20: Switching circuits 30: Control device

Claims

1. Two switching circuits are formed by connecting two switching devices in series between pairs of input / output terminals that receive DC input and output, A choke coil connects the connection points of the two switching devices in both of the aforementioned switching circuits, An H-bridge type bidirectional DC / DC converter comprising, In each of the switching circuits, a capacitor is connected in parallel to one or each of the switching devices, and Capacitance addition means for increasing the total capacitance of the capacitor in the switching circuit on the side where DC is output during any period by an additional capacitance. A bidirectional DC / DC converter further characterized by having the following features.

2. The aforementioned additional capacity Cy(F) is Vi ｍａｘ ２ ×C ｉｎ <Vo ｍｉｎ ２ ×(C ｏｕｔ +Cy) The bidirectional DC / DC converter according to claim 1, characterized in that it satisfies the requirements. However, Vi ｍａｘ This is the maximum value of the input DC voltage Vi (V). Vo ｍｉｎ This is the minimum value of the output DC voltage Vo (V). C ｉｎ (F) is the total capacitance of the capacitors of the switching circuit on the side where direct current is input, C ｏｕｔ (F) is the total capacitance of the capacitors in the switching circuit on the side where DC is output. That is the case.

3. The control device further comprises a control device that controls the switching device to turn the switching elements of the switching device on and off. The control device is In the switching circuit on the side to which DC is input, the switching elements of the switching device are turned on alternately. In the switching circuit on the DC input side, after turning off the switch element of the switching device on the high-potential side and waiting for a predetermined time to elapse, the switch element of the switching device on the low-potential side is turned on, thereby in the switching circuit on the DC output side, the discharge current of the parasitic capacitance of the switching device on the low-potential side, and, if the capacitors are in parallel, the discharge current of the capacitors are used to reverse the current of the choke coil. In the switching circuit on the side to which DC is input, by turning off the switching element of the switching device on the low-potential side while the current in the choke coil is reversed, the charge of the parasitic capacitance of the switching device on the high-potential side, and the charge of the capacitor if the capacitor is connected to the switching device, are discharged. In the switching circuit on the side to which DC is input, zero-volt switching is achieved by turning on the switch element of the switching device on the high-potential side after a predetermined time has elapsed since turning off the switch element of the switching device on the low-potential side, and The aforementioned arbitrary period is from any timing during the period when the current in the choke coil is reversed to any timing during the period when the switching element of the switching device on the high-potential side of the DC input is turned on. A bidirectional DC / DC converter according to claim 2, characterized in that

4. The control device is The bidirectional DC / DC converter according to claim 3, characterized in that the switching element of the switching device on the side where DC is output and on the low-potential side is kept off at all times.

5. The control device is The bidirectional DC / DC converter according to claim 3, characterized in that the switch element of the switching device on the side where DC is output and is on the low-potential side is turned on during the period when the switch element of the switching device on the side where DC is input and is on, and is turned off during the period when the switch element of the switching device on the high-potential side is on.

6. The bidirectional DC / DC converter according to claim 3, characterized in that the predetermined time is the time calculated by formula 1. [Math 1] Here, Cin is the combined capacitance on the input side, Td (sec) is the predetermined time, L1 (H) is the inductance of the choke coil, C5 (F) is the parasitic capacitance of the switching device provided in the capacitance addition means on the side to which DC is input, and Cx (F) is the additional capacitance on the side to which DC is input.

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