CN114285270B

CN114285270B - High-power density DC-DC converter

Info

Publication number: CN114285270B
Application number: CN202111656538.4A
Authority: CN
Inventors: 明鑫; 林治屹; 宫新策; 孙天一; 王卓; 张波
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2021-12-30
Filing date: 2021-12-30
Publication date: 2023-03-31
Anticipated expiration: 2041-12-30
Also published as: CN114285270A

Abstract

The invention belongs to the technical field of power management, and particularly relates to a high-power-density DC-DC converter. The structure of the invention can realize the voltage conversion ratio of 48-1V only by 4 power devices with voltage resistance of Vin/2 and 2 Vin/4 voltage resistance, 2 flying capacitors and output inductors, the actual duty ratio sensed by the output inductor end is about 8.3%, and the structure has the characteristics of ultra-low output ripple and quick transient response of a two-phase DC-DC converter, thereby achieving the purpose of realizing high transformation ratio by using minimum low-voltage devices and passive devices.

Description

High-power density DC-DC converter

Technical Field

The invention belongs to the technical field of power management, and particularly relates to a high-power-density DC-DC converter.

Background

With the rapid development of digital energy and digital economy in recent years, the requirement for energy consumption of an electric power system is higher and higher. Many power supply areas have developed increasing bus voltages to cope with the increasing load side power consumption. As data center dc power supply systems are evolving from traditional 12V bus to 48V bus, the load-oriented distribution network of new energy vehicles is transitioning from 12V power distribution systems to 48V systems. This change is caused by the increase in power consuming electronic drive functions and the advent of autonomous vehicles, which systems such as lidar, cameras and ultrasonic sensors place additional demands on the power distribution system. The voltage of the load end, such as the working voltage of a CPU, a microprocessor MCU and the like, is not increased, but the working voltage can be even reduced to be lower than 1V along with the development of advanced manufacturing processes. Therefore, in order to improve the energy consumption ratio and the power density of the whole power supply path, it becomes necessary to research a new one-stage conversion mode with high power density. However, the conventional DC-DC converter architecture is difficult to realize high voltage conversion ratio under the limitation of high frequency and high power density as shown in fig. 1. Therefore, the development of a novel high transformation ratio conversion structure is a common pursuit of both academic circles and industrial circles.

Disclosure of Invention

In view of the above problems, the present invention provides a high power density DC-DC converter.

The technical scheme of the invention is as follows:

a high-power density DC-DC converter is characterized by comprising a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a sixth switching tube, a first capacitor, a second capacitor, a first inductor and a second inductor; one end of the first switch tube is connected with an input power Vin, and the other end of the first switch tube is connected with one end of the first capacitor and one end of the second switch tube; the other end of the second switch tube is connected with one end of a third switch tube and one end of a second capacitor; the other end of the third switching tube is connected with the other end of the first capacitor and one end of the fourth switching tube; the other end of the fourth switching tube is connected with one end of the sixth switching tube and one end of the second inductor, and the other end of the sixth switching tube is grounded; the other end of the second capacitor is connected with one end of a fifth switching tube and one end of the first inductor, and the other end of the fifth switching tube is grounded; the other end of the first inductor is connected with the other end of the second inductor, and the connection point of the first inductor and the second inductor is an output end; the withstand voltage of the first switching tube, the second switching tube, the third switching tube and the fourth switching tube is Vin/2, and the withstand voltage of the fifth switching tube and the sixth switching tube is Vin/4.

Further, the converter includes eight operating states, which are:

a first working state: the first switch tube, the third switch tube and the sixth switch tube are closed, and the second switch tube, the fourth switch tube and the fifth switch tube are disconnected;

a second working state: the fourth switching tube, the fifth switching tube and the sixth switching tube are closed, and the first switching tube, the second switching tube and the third switching tube are disconnected;

a third working state: the third switch tube, the fourth switch tube and the fifth switch tube are closed, and the first switch tube, the second switch tube and the sixth switch tube are disconnected;

a fourth operating state: the fourth switching tube, the fifth switching tube and the sixth switching tube are closed, and the first switching tube, the second switching tube and the third switching tube are disconnected;

the fifth working state: the second switching tube, the fourth switching tube and the sixth switching tube are closed, and the first switching tube, the third switching tube and the fifth switching tube are disconnected;

a sixth working state: the fourth switching tube, the fifth switching tube and the sixth switching tube are closed, and the first switching tube, the second switching tube and the third switching tube are disconnected;

the seventh working state: the third switch tube, the fourth switch tube and the fifth switch tube are closed, and the first switch tube, the second switch tube and the sixth switch tube are disconnected;

an eighth working state: the fourth switching tube, the fifth switching tube and the sixth switching tube are closed, and the first switching tube, the second switching tube and the third switching tube are disconnected;

and the working time of the first working state, the third working state, the fifth working state and the seventh working state is equal.

The invention has the advantages that the structure of the invention can realize the voltage conversion ratio of 48-1V only by 4 power devices with voltage resistance of Vin/2 and 2 Vin/4 voltage resistance, 2 flying capacitors and output inductors, the actual duty ratio sensed by the output inductor end is about 8.3%, and the invention has the characteristics of ultra-low output ripple and quick transient response of the two-phase DC-DC converter, and achieves the purpose of realizing high conversion ratio by using minimum low-voltage devices and passive devices.

Drawings

FIG. 1 shows a conventional buck DC-DC converter

FIG. 2 is a diagram of the novel high power density DC-DC converter of the present invention

Fig. 3 is a front four-state mode diagram of the DC-DC converter of the present invention, wherein (a) is a first state, (b) is a second state, (c) is a third state, and (d) is a fourth state;

fig. 4 is a rear four-state mode diagram of the DC-DC converter of the present invention, wherein (e) is the fifth state, (f) is the sixth state, (g) is the seventh state, and (h) is the eighth state;

FIG. 5 is a waveform diagram of the switching state of the DC-DC converter according to the present invention

FIG. 6 is a graph of the output voltage waveform of the DC-DC converter of the present invention

FIG. 7 is a graph of the output voltage waveform of the load transient characteristic of the DC-DC converter according to the present invention

FIG. 8 is a diagram of the operating waveforms of the mismatch of the inductors of the DC-DC converter according to the present invention

FIG. 9 is a schematic diagram of a board-level area of a DC-DC converter according to the present invention

Description of the reference numerals: m is a group of _H 、M _L 、S ₁ 、S ₂ 、S ₃ 、S ₄ 、S ₅ 、S ₆ Is an ideal switching tube; c ₁ 、C ₂ 、C _o A capacitor device; l, L ₁ 、L ₂ Is an inductive device.

Detailed Description

The technical scheme of the invention is described in detail in the following with the accompanying drawings:

the active device of the novel high-power density DC-DC converter is composed of 4 low-voltage devices with voltage resistance of Vin/2: s. the ₁ 、S ₂ 、S ₃ 、S ₄ And 2 low-voltage devices S with voltage resistance of Vin/4 ₅ And S ₆ And (4) forming. The passive device is composed of two capacitors: c ₁ 、C ₂ And two inductors L ₁ And L ₂ And (4) forming. For the system to reach equilibrium, the normal operation mode is determined by eight states, see in particular fig. 3 and 4. FIG. 3 (a) shows a first state, which indicates that both capacitors are charged by the power supply and L ₁ Is also covered by C ₂ Charging, and L ₂ It is discharged to ground. (b) The state is that both output inductors are discharged to ground, and in order to reduce the overlap loss between state switching, (b) S in the state ₄ The switch needs to be kept closed to meet the action of the next state and set C ₁ The lower plate of the capacitor. The next state (C) is C ₂ Capacitor warp S ₆ 、S ₃ 、S ₄ And L ₂ Discharge to the output, so should be S during dead zone ₈ First open and then close S ₃ 。S ₄ Acting as a bridge connecting the two ends. (d) The state is also double-inductance discharge to ground, S ₄ Still need to be closed. Now the first four states have ended, but only the capacitor C ₂ Complete one charge and discharge, C ₁ Charged by the power supply only in state (a) without a discharge process, so figure 4 would beShow C ₁ The discharge process of (1).

The following four operating modes of the novel DC-DC converter of the present invention can be seen in fig. 4. Wherein state (e) is capacitance C ₁ Through S ₆ 、S ₄ 、S ₂ 、C ₂ And L ₁ Supply power to the output terminal, at this time L ₂ Naturally discharges to ground. At this time, the capacitance C ₁ Completing a charging and discharging process, and C ₂ Is also covered with C ₁ Once charged, it is therefore necessary to continue to complete the discharge to allow for equalization. State (f) is similar to state (b). FIG. 4- (g) is C ₂ Through L ₂ The output end is powered, and the charging and discharging processes of the two capacitors are indicated to be balanced after the process is completed. However, the inductance needs to satisfy volt-second balance, so the state (h) needs to be increased to discharge the double inductances simultaneously. By this, a total of 8 states are completed, and the capacitor and the inductor complete one or more energy cycles, one for the converter.

The working time of the four states (a), (c), (e) and (g) of the novel DC-DC converter is equal, otherwise, the system balance is gradually broken through time accumulation. In order to clearly describe the relationship between the capacitance and the inductance and the system parameters, the relationship in one cycle is listed for the capacitance and the inductance respectively. Capacitor C ₁ The charge conservation relation of (1) is as follows:

in the above formula i _L1 After the system is stabilized, the inductor current ramp-up phase is stable and constant. Thus C ₁ The charge-discharge balance of (c) can only be determined by the duty cycles of the states (a) and (e). Capacitor C ₂ The conservation of charge relation of (1):

note that the above formula for C ₂ In fact, it undergoes two complete charging and discharging processes, each of which should be balanced, i.e. it isΔ Q is zero. From this, the first two terms in D can be derived _a Is equal to D _c Under the premise of i _L1 And i _L2 And also must be equal, i.e., the average current of the dual inductors must be equal. The same applies to the inductor current of the latter two terms. If there is a large error in the duty cycles of the four states, i _L1 And i _L2 And the voltage is not equal any more, the system will deviate from the set state, so that the capacitor voltage is not the set value any more, and even the low-voltage device is damaged.

The inductance volt-second balance relational expression of the novel DC-DC converter is shown by the formula (3) and the formula (4). First on L ₁ For example, the volt-second relationship of the 8 states is:

for the same reason L ₂ A volt-second equilibrium description of the eight states was performed:

by simplifying equations (3) and (4), the input-output relationship and the relationship between the capacitor voltage and the input voltage are obtained. The expression is as follows:

VC ₂ ＝V _in /4 (5)

V _o ＝D*V _in /4 (6)

from the above formula, the capacitance C can be seen ₂ The voltage will be automatically balanced by the system at Vin/4 and the capacitor C ₁ Is cancelled in the volt-second relationship, which means that the capacitance C is ₁ The voltage can not be automatically balanced by the system, but the system can still maintain a stable working state. The main reason is C ₁ Only L1 is charged and L is not charged ₂ Charging, when the system is interfered, the inductive currents cannot be mutually corrected to form negative feedback to adjust C ₁ Of the charge of (c). And C is ₂ Is L ₁ And L ₂ Cross charging, when the capacitor voltage isWhen the balance is out of balance, the self-adaptive adjustment can be carried out through the volt-second balance of the inductive current, so that the balance state is recovered. Further, the duty ratio D is S ₅ And S ₆ Duty ratio of high level signal of switch node. Therefore, the structure realizes the pre-reduction of Vin/4 by using 6 switches, thereby realizing the conversion of 48-1V.

The simulation waveforms of the working principle of the novel DC-DC converter are shown in fig. 5 and 6. The input voltage is 48V and the output voltage is 1V. Wherein FIG. 5 shows a PWM waveform of 6 switching nodes, one can see S ₅ And S ₆ Is twice the switching frequency of the remaining switches. FIG. 6 shows six switches S _1-6 Working waveform diagram of voltage at two ends, only S can be seen ₅ And S ₆ The voltage difference is Vin/4, and the rest is Vin/2 voltage. Therefore, after considering the surge voltage, 4 power devices with the working voltage of 40V and two low-voltage devices with the withstand voltage of 30V can be selected as system implementation schemes.

The load transient characteristics of the novel DC-DC converter of the present invention are shown in fig. 7. Because the difference between the closed-loop control mode and the traditional two-phase Buck is not large, the converter can be subjected to closed-loop control by using a traditional two-phase peak current mode control circuit. When the input voltage is 48V, the output voltage is 1V, the output load is switched at the speed of 10ns by the load of 2-22A, the output capacitance is 320 muF, the output inductance is 500nH respectively, S ₅ And S ₆ The switching frequency of (2) is all 500KHz. As seen from FIG. 7, the drop of the output voltage is maximum 80mV, the overshoot voltage is maximum 120mV, and the transient characteristics are good. When there is a certain error in the output inductance, the inductance L shown in FIG. 8 ₁ Deviating by 25%, from 500nH to 600nH, the RMS value of the inductor current is almost constant and the ripple varies. This shows that the structure has current sharing capability for inductive current.

The power density and board level implementation of the novel DC-DC converter of the invention are shown in figure 9. Wherein S _1-4 The power device of (3) selects a 40V EPC device with the model number of EPC2014C, S _5-6 An EPC2023 device with a withstand voltage of 30V was selected. The rest part is output inductance and flying capacitor, and the power stage area is 770mm ² . The maximum current is 40A, so the power density is 5.19A/cm ² Realizes high power of 48-1VRate density.

The invention is characterized in that a unique capacitance and inductance mixed structure mode is adopted to realize the high transformation ratio from a 48V system to a load end, simultaneously improve the system efficiency and the power density and realize 5.19A/cm ² The power density of (a). In addition, the structure has the self-balancing function of an output inductor and a flying capacitor, and a novel high-power-density DC-DC converter with the voltage difference between two ends of the inductor being Vin/4 is realized by using minimum low-voltage devices and capacitors.

Claims

1. A high-power density DC-DC converter is characterized by comprising a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a first capacitor, a second capacitor, a first inductor and a second inductor; one end of the first switch tube is connected with an input power Vin, and the other end of the first switch tube is connected with one end of the first capacitor and one end of the second switch tube; the other end of the second switch tube is connected with one end of a third switch tube and one end of a second capacitor; the other end of the third switching tube is connected with the other end of the first capacitor and one end of the fourth switching tube; the other end of the fourth switching tube is connected with one end of the sixth switching tube and one end of the second inductor, and the other end of the sixth switching tube is grounded; the other end of the second capacitor is connected with one end of a fifth switching tube and one end of the first inductor, and the other end of the fifth switching tube is grounded; the other end of the first inductor is connected with the other end of the second inductor, and the connection point of the first inductor and the second inductor is an output end; the withstand voltage of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is Vin/2, and the withstand voltage of the fifth switch tube and the sixth switch tube is Vin/4.

2. A high power density DC-DC converter according to claim 1, characterized in that the converter comprises eight operating states, respectively:

the first working state: the first switching tube, the third switching tube and the sixth switching tube are closed, and the second switching tube, the fourth switching tube and the fifth switching tube are disconnected;

the fourth working state: the fourth switching tube, the fifth switching tube and the sixth switching tube are closed, and the first switching tube, the second switching tube and the third switching tube are disconnected;

the seventh working state: the third switching tube, the fourth switching tube and the fifth switching tube are closed, and the first switching tube, the second switching tube and the sixth switching tube are disconnected;

the eighth working state: the fourth switching tube, the fifth switching tube and the sixth switching tube are closed, and the first switching tube, the second switching tube and the third switching tube are disconnected;