Non-isolated DC / DC converter

Abstract

An object of the present invention is to provide a high-efficiency and low-noise non-insulated DC / DC converter while suppressing an increase in cost and size. 【Means for Solving the Problem】The present invention is an H-bridge type DC / DC converter that connects a primary circuit in which two primary-side devices are connected in series and a secondary circuit in which two secondary-side devices are connected in series with a choke coil L1, and includes a primary-side capacitor Ca connected in parallel to one or each of the primary-side devices, and a secondary-side capacitor Cb connected in parallel to one or each of the secondary-side devices. Each of the primary-side devices and the secondary-side device on the low-potential side is a switching device, the secondary-side device on the high-potential side is a diode D4, and the total capacitance C of the primary circuit in , the total capacitance C of the secondary circuit out , the relationship between the maximum value Vimax of the input DC voltage of the primary circuit and the minimum value Vomin of the output DC voltage of the secondary circuit is Vimax 2 ·C in < Vomin 2 ·C out is characterized by this.

Description

Technical Field

[0001] The present disclosure relates to a buck-boost non-insulated DC / DC converter.

Background Art

[0002] As a buck-boost non-insulated DC / DC converter that can perform buck-boost and whose output voltage polarity does not reverse, there exists a buck-boost DC / DC converter circuit that combines a buck chopper and a boost chopper (see, for example, Patent Document 1). This circuit can handle even a wide input-output voltage range and is a circuit capable of bidirectional operation by making all semiconductor elements into switch elements.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A general non-insulated buck-boost DC / DC converter as shown in FIG. 1 has hard switching, so there are problems such as large switching losses and noise, and the need for a snubber circuit to suppress surge voltage. As methods for solving that problem, various soft switching methods have been devised. However, in order to execute that soft switching method, it is necessary to add many components, and there is a problem that it is difficult to reduce cost and size. Furthermore, when that soft switching method is executed, the switching loss during light load becomes large, so there is also a problem that it is difficult to improve efficiency.

[0005] Therefore, an object of the present invention is to provide a high-efficiency and low-noise non-insulated DC / DC converter while suppressing an increase in cost and size in order to solve the above problems.

Means for Solving the Problems

[0006] To achieve the above objective, the 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. In this specification, the DC input side of a DC / DC converter will be referred to as the "primary side" or "primary," and the DC output side of a DC / DC converter will be referred to as the "secondary side" or "secondary."

[0007] Specifically, the DC / DC converter according to the present invention is A primary circuit in which two primary-side devices are connected in series between a pair of primary terminals to which DC is input, A secondary circuit in which two secondary devices are connected in series between a pair of secondary terminals that output DC, A choke coil connects the connection point of the two primary devices to the connection point of the two secondary devices, An H-bridge type DC / DC converter equipped with, The system further comprises a primary capacitor connected in parallel to one or each of the primary devices, and a secondary capacitor connected in parallel to one or each of the secondary devices. Each of the primary side devices and the secondary side device on the low-potential side are switching devices composed of a switching element consisting of a parasitic capacitance and a parallel diode with the high-potential side as the cathode. The secondary device on the high-potential side is a diode with the high-potential side as the cathode, and Total capacitance C of the primary circuit in and the total capacitance C of the secondary circuit out Relationship Vimax 2 ·C in < Vomin 2 ·C out Being It is characterized by the following. However, Vimax is the maximum value of the DC voltage Vi input to the primary terminal pair, and Vomin is the minimum value of the DC voltage Vo output from the secondary terminal pair.

[0008] This DC / DC converter is a buck-boost DC / DC converter circuit that combines a buck chopper and a boost chopper. This DC / DC converter uses the parasitic capacitance of the switching element in the secondary circuit and the discharge current of the capacitor connected in parallel with it to reverse the current of the choke coil, and this current (hereinafter sometimes referred to as "reversing choke coil current") discharges the parasitic capacitance of the switching element in the primary circuit and the charge of the capacitor connected in parallel with it. As a result, zero-voltage switching when the switching element in the primary circuit is on can be achieved.

[0009] Furthermore, this 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 DC / DC converter can achieve zero voltage switching when each switching element is ON, thereby reducing switching losses and improving efficiency.

[0010] Furthermore, this DC / DC converter requires fewer components than a typical non-isolated DC / DC converter circuit. Therefore, this DC / DC converter can minimize increases in cost and size. Therefore, the present invention can provide a highly efficient and low-noise non-isolated DC / DC converter while suppressing increases in cost and size. [Effects of the Invention]

[0011] This invention can provide a highly efficient and low-noise non-isolated DC / DC converter while keeping costs and size increases to a minimum. [Brief explanation of the drawing]

[0012] [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 DC / DC converter according to the present invention. [Figure 3] This diagram illustrates the operation of the DC / DC converter according to the present invention. [Figure 4] This diagram illustrates the operation of the DC / DC converter according to the present invention. The arrows indicate the flow of current. [Figure 5] This diagram illustrates the operation of the DC / DC converter according to the present invention. [Figure 6] This diagram illustrates the operation of the DC / DC converter according to the present invention. The arrows indicate the flow of current. [Figure 7] This diagram illustrates the circuit of the DC / DC converter according to the present invention. [Modes for carrying out the invention]

[0013] 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.

[0014] Figure 2 is a diagram illustrating the circuit of the DC / DC converter of this embodiment. This DC / DC converter is A primary circuit 10 is formed by connecting two primary-side devices in series between the primary terminal to which DC (voltage Vi) is input and Ter1, A secondary circuit 20 is formed by connecting two secondary devices in series between the secondary terminal where DC (voltage Vo) is output and Ter2, A choke coil L1 connects the connection points of the two primary devices and the connection points of the two secondary devices, An H-bridge type DC / DC converter equipped with, A primary capacitor Ca connected in parallel to one or each of the primary-side devices, and a secondary capacitor Cb connected in parallel to one or each of the secondary-side devices are further provided. Each of the primary-side devices and the secondary-side device on the low-potential side is a switching device composed of a switch element in parallel with a parasitic capacitance and a parallel diode with the high-potential side as the cathode. The secondary-side device on the high-potential side is a diode D4 with the high-potential side as the cathode, and The total capacitance C of the primary circuit 10 in and the total capacitance C of the secondary circuit 20 out The relationship between Vimax 2 ·C in < Vomin 2 ·C out is characterized by. However, Vimax is the maximum value of the DC voltage Vi input to the primary terminal pair Ter1, and Vomin is the minimum value of the DC voltage Vo output from the secondary terminal pair Ter2. Further, this DC / DC converter further includes a control device 30 that turns on / off the switching devices (S1 to S3) by controlling each switch element (Q1 to Q3). Capacitors C4 and C5 are connected for smoothing the input / output voltage.

[0015] In this specification, the ground wire GND side in FIG. 2 is described as the "low-potential side", and the opposite side is described as the "high-potential side". That is, the primary-side device on the high-potential side of the primary circuit 10 is the switching device S1. And the switching device S1 is configured such that a parasitic capacitance C1 and a parallel diode D1 with the high-potential side as the cathode are in parallel with the switch element Q1. The primary-side device on the low-potential side (directly connected to the ground wire GND) of the primary circuit 10 is the switching device S2, and is configured such that a parasitic capacitance C2 and a parallel diode D2 with the high-potential side as the cathode are in parallel with the switch element Q2. The secondary device on the low-potential side of the secondary circuit 20 (directly connected to the ground wire GND) is a switching device S3, which consists of a switching element Q3, a parasitic capacitance C3, and a parallel diode D3 with the high-potential side as the cathode. Furthermore, the secondary device on the high-potential side of the secondary circuit 20 is a diode D4 with the high-potential side as the cathode.

[0016] In this embodiment, the primary capacitor Ca is connected in parallel with the switching device S2, but as will be described later, it may also be connected in parallel with the switching device S1, or in parallel with both the switching device S1 and the switching device S2. In this embodiment, the secondary capacitor Cb is connected in parallel with the switching device S3, but as will be described later, it may be connected in parallel with the diode D4, or in parallel with both the switching device S3 and the diode D4. In either configuration, the total capacitance C of the primary circuit 10 in The total capacitance C of the secondary circuit 20 out Relationship Vimax 2 ·C in < Vomin 2 ·C out Let's leave it at that. However, total capacity C in =C1+C2+Ca, total capacity C out =C3+Cb, where Vimax is the maximum value of the DC voltage Vi input to the primary terminal pair Ter1, and Vomin is the minimum value of the DC voltage Vo output from the secondary terminal pair Ter2. By satisfying the above relationship, it is possible to secure a sufficient value for the inverting choke coil current required for zero-volt switching. In the following, the total capacitance C of the capacitors on the secondary circuit side of the above relationship will be considered. out The total capacitance C of the capacitors on the primary circuit side. in The case where the value is greater will be explained, but the present invention is established when the above relationship is satisfied.

[0017] [Basic operation] The control device 30 is The switching devices (S1, S2) of the primary circuit 10 are turned on alternately. After turning off the high-potential switching device S1 of the primary circuit 10, and after a predetermined time Td has elapsed, the low-potential switching device S2 of the primary circuit 10 is turned on, thereby reversing the current of the choke coil L1 using the discharge current of the secondary capacitor Cb. By turning off the switching device S2 on the low-potential side of the primary circuit 10 while the current in the choke coil L1 is reversed, charge is discharged from the parasitic capacitance C1 of the switching device S1 on the high-potential side of the primary circuit 10, and if a primary-side capacitor is connected to the switching device S1, charge is also discharged from that primary-side capacitor, and Zero-volt switching is achieved by turning on the switching device S1 on the high-potential side of the primary circuit 10 after a predetermined time Td has elapsed, following the turning off of the switching device S2 on the low-potential side of the primary circuit 10. It is characterized by the following.

[0018] The predetermined time Td is set to approximately 1 / 4 of the resonant period between the parasitic capacitances (C1, C2) and the primary capacitor Ca, and the choke coil L1. Specifically, the predetermined time Td is calculated and determined using the following formula.

number

[0019] [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 device S3 on the low-potential side of the secondary circuit 20 permanently off.

[0020] Figure 3 shows the drive signals (Sg) that turn the switch elements (Q1, Q2) on and off during the step-down operation. Q1 Sg Q2 ), the current value I flowing through the choke coil L1 L , the voltage across each switching element (Q1~Q3) (V Q1 ~V Q3 Figure 4 is a time chart explaining the operation. Figure 4 is a diagram illustrating the current flow during each period (a to h). Figures 3 and 4 are used to explain the step-down operation of this DC / DC converter.

[0021] (Period a) The period a 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, is 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, the secondary capacitor Cb added in parallel to the switching device S3 is charged, and the voltage V of the switching element Q3 is increased. Q3 It will rise. (period b) When the parasitic capacitance C3 and the secondary capacitor Cb are charged to the output voltage Vo, the 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 the switch element Q1 is turned off. When the switch element Q1 is turned off, the parasitic capacitance C1 is charged and at the same time the parasitic capacitance C2 and the primary capacitor Ca are discharged. Since the capacitance of the primary capacitor Ca is larger than that of the parasitic capacitance C2, the voltage does not drop easily even when this discharge occurs, and the voltage V of the switch element Q1 Q1The rise in the difference voltage between the input voltage Vi and the voltage across the primary 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 the primary 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 period of time between when the switch element Q1 starts to turn off and when the current flowing through the switch element 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-volt switching). (Period e) If the inductance of the choke coil L1 is sufficiently small, the current I L The current I reaches zero. L When it reaches zero, the current I L The current flows through the already-on switch element Q2, reversing the flow in the choke coil L1 (generating a reversing choke coil current), which discharges the parasitic capacitance C3 and the secondary capacitor Cb. (period f) When the parasitic capacitance C3 and secondary 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 I L The value remains constant. The reason for adding the secondary capacitor Cb is the reversed current I at this time. L This is to increase the value of the (reverse choke coil current). (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 are charged, while the parasitic capacitance C1 is discharged. (period h) The capacitance of the secondary capacitor Cb is sufficiently large, causing the current I to reverse. L If sufficient (inverting choke coil current) is secured, 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.

[0022] [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 by turning on the switching device S3 on the low-potential side of the secondary circuit 20 during the period when the switching device S2 on the low-potential side of the primary circuit 10 is on, and turning off the switching device S1 on the high-potential side of the primary circuit 10 during the period when it is on.

[0023] Figure 5 shows the drive signals (Sg) that turn the switch elements (Q1~Q3) on and off during the boost operation. Q1 ~Sg Q3 ), the current value I flowing through the choke coil L1 L , the voltage across each switching element (Q1~Q3) (V Q1 ~V Q3 Figure 6 is a time chart explaining the operation. Figure 6 is a diagram illustrating the current flow during each period (a to h). The boost operation of this DC / DC converter will be explained using Figures 5 and 6.

[0024] (Period a) The period a 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, is 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 b) Period b begins when the switch element Q3 turns off. After the switch element Q3 turns off, when the parasitic capacitance C3 and the secondary capacitor Cb are charged to the output voltage Vo, the diode D4 conducts, and current I L The voltage decreases. Since a secondary capacitor Cb is added in parallel to the switching element Q3, the voltage V of the switching element Q3 decreases. Q3 The rise becomes more gradual, and switching losses during the off state decrease. [Supplement 2] There is a short period of time between when the switch element Q3 starts to turn off and when the current flowing through the switch element Q3 becomes zero and it completely turns off. The voltage V during that time is V. Q3 By slowing down the rise in voltage, switching losses are reduced. [End of supplement 2] (period c) Period c begins when the switch element Q1 is turned off. When the switch element Q1 is turned off, the parasitic capacitance C1 is charged and at the same time the parasitic capacitance C2 and the primary capacitor Ca are discharged. Since the capacitance of the primary capacitor Ca is larger than that of the parasitic capacitance C2, the voltage does not drop easily even when this discharge occurs, and the voltage V of the switch element Q1 Q1 The rise in the difference voltage (between the input voltage Vi and the voltage across the primary capacitor Ca) becomes more gradual, reducing switching losses when the switch element Q1 is turned off (see Supplement 1 above). Furthermore, by turning off the switch element Q1 while current is flowing through it, the current I of the choke L1 at that time can be determined. L This is used to discharge the charge from the parasitic capacitance C2 and the primary capacitor Ca, and the voltage across the switching element Q2 V Q2 It can be reduced to zero. (Period d) When the parasitic capacitance C2 and the primary capacitor Ca are discharged to zero voltage, the parallel diode D2 conducts, and the current I in the choke coil L1 flows through it. L It decreases at an even steeper slope. (Period e) While the parallel diode D2 is conducting, the voltage across the switch element Q2 is V Q2Since it is zero, the switch element Q2 can be turned on with zero voltage (zero-volt switching). Then the current I L When it reaches zero, the current I L The current flows through the already-on switch element Q2, reversing the flow through the choke coil L1 (reversing choke coil current), which discharges the parasitic capacitance C3 and the secondary capacitor Cb. (period f) When the parasitic capacitance C3 and secondary 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 I L The value remains constant. The reason for adding the secondary capacitor Cb is the reversed current I at this time. L This is to increase the value of the (reverse choke coil current). (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 are charged, while the parasitic capacitance C1 is discharged. (period h) The capacitance of the secondary 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.

[0025] (Other embodiments) Figures 2 to 6 show an example of the DC / DC converter circuit according to the present invention. The DC / DC converter according to the present invention has a variation circuit shown in Figure 7, depending on the position of the primary capacitor Ca and the secondary capacitor Cb. In any variation circuit, the switching timing and current flow are the same as described in Figures 2 to 6.

[0026] Figure 7(1) shows the DC / DC converter circuit described in Figures 2 to 6. In the variation circuits shown in Figures 7(2) to 7(9), only the positions of the primary capacitor Ca and the secondary capacitor Cb are indicated by their symbols (the choke coil and switching devices are the same as in Figure 7(1)). Furthermore, when primary capacitors are connected to both switching devices S1 and S2, they are designated as Ca1 and Ca2, respectively. When secondary capacitors are connected to both switching device S3 and diode D4, they are designated as Cb1 and Cb2, respectively. The capacitance of the primary capacitor Ca is the sum of the capacitances of Ca1 and Ca2, and the capacitance of the secondary capacitor Cb is the sum of the capacitances of Cb1 and Cb2.

[0027] Furthermore, the above inventions can be combined as much as possible.

[0028] (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, making it possible to realize a low-loss, low-noise step-up / step-down DC / DC converter without increasing cost or size. [Explanation of symbols]

[0029] 10: Primary circuit 20: Secondary circuit 30: Control device

Claims

1. A primary circuit in which two primary-side devices are connected in series between a pair of primary terminals to which DC is input, A secondary circuit in which two secondary devices are connected in series between a pair of secondary terminals that output DC, A choke coil connects the connection point of the two primary devices to the connection point of the two secondary devices, An H-bridge type DC / DC converter comprising, The system further comprises a primary capacitor connected in parallel to one or each of the primary devices, and a secondary capacitor connected in parallel to one or each of the secondary devices. Each of the primary devices and the secondary device on the low-potential side are switching devices composed of a switching element consisting of a parasitic capacitance and a parallel diode with the high-potential side as the cathode. The secondary device on the high-potential side is a diode with the high-potential side as the cathode, and Total capacitance C of the primary circuit ｉｎ and the total capacitance C of the secondary circuit ｏｕｔ Relationship Vimax ２ ・C ｉｎ < Vomin ２ ・C ｏｕｔ Being A DC / DC converter characterized by the following features. However, Vimax is the maximum value of the DC voltage Vi input to the primary terminal pair, and Vomin is the minimum value of the DC voltage Vo output from the secondary terminal pair.

2. The device further comprises a control device that turns the switching device on or off by controlling the switch element, The control device is The switching device of the primary circuit is turned on alternately. After turning off the switching device on the high-potential side of the primary circuit, and after a predetermined time has elapsed, the switching device on the low-potential side of the primary circuit is turned on, thereby reversing the current of the choke coil using the discharge current of the secondary capacitor. By turning off the switching device on the low-potential side of the primary circuit while the current in the choke coil is reversed, charge is discharged from the parasitic capacitance of the switching device on the high-potential side of the primary circuit, and if the primary-side capacitor is connected to the switching device, charge is also discharged from the primary-side capacitor, and Zero-volt switching is achieved by turning off the switching device on the low-potential side of the primary circuit, and then turning on the switching device on the high-potential side of the primary circuit after a predetermined time has elapsed. The DC / DC converter according to claim 1, characterized by the following:

3. The control device is The DC / DC converter according to claim 2, characterized in that the switching device on the low-potential side of the secondary circuit is kept off at all times.

4. The control device is The DC / DC converter according to claim 2, characterized in that the switching device on the low-potential side of the secondary circuit is turned on during the period when the switching device on the low-potential side of the primary circuit is turned on, and is turned off during the period when the switching device on the high-potential side of the primary circuit is turned on.

5. The DC / DC converter according to claim 2, characterized in that the predetermined time is the time calculated by formula 1. [Math 1] Here, Td is the predetermined time (sec), L1 is the inductance of the choke coil (H), C1 is the parasitic capacitance of the switching device on the high-potential side of the primary circuit (F), C2 is the parasitic capacitance of the switching device on the low-potential side of the primary circuit (F), and Ca is the total capacitance of the primary side capacitor (F).

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