CN215580910U - DC-DC bidirectional converter - Google Patents

Abstract

The utility model relates to a DC-DC bidirectional converter, which is characterized in that an intermediate capacitor is added at an inductor common end, so that the midpoint voltage of a bridge arm is controllable, and the voltage of an output end and the voltage of the intermediate capacitor are controlled at the same time to keep stable, thereby solving the problems that the voltage stress on a power switch device is overlarge and the device is even damaged due to unstable voltage control in the DCDC conversion process, and simultaneously, because the intermediate capacitor exists, the currents on L1 and L3 are mutually independent, the loop at the input side and the loop at the output side can be independently controlled, the modulation complexity is greatly reduced, and the modulation modes at two ends are simpler and more stable.

Description

DC-DC bidirectional converter

Technical Field

The utility model relates to a transformation technology, in particular to a DC-DC bidirectional converter.

Background

A dc-dc converter, referred to as DCDC converter for short, is a converter that converts a dc voltage source into dc power sources of different voltage classes through a voltage boosting or reducing circuit. The method is widely applied to the fields of photovoltaic power generation, battery chargers, fuel cells, electric automobiles and the like. With the gradual rise of the battery voltage, a novel topology of the voltage-type DCDC capable of being increased and decreased is provided for adapting to different voltage inputs of the battery. The corresponding topological structures are proposed in documents [1] and [2], and the logic sequence and the control method of the switch tube are described in detail. The voltage on the side of the middle inductor is uncontrollable, so that the stress of the switching tube is larger. According to the utility model, through the topology design of the bidirectional liftable profiling DCDC controller, the intermediate capacitor is added at the common end of the inductor, so that the midpoint voltage of the bridge arm is controllable, and the voltage of the output end and the intermediate capacitor is controlled to keep stable, thereby solving the problems that the voltage stress on a power switch device is overlarge and the system loss is increased due to unstable voltage control in the DCDC conversion process. Meanwhile, after the voltage of the intermediate capacitor is controllable, the size of the inductive current can be controlled, and through reasonable design, the loss on the inductor can be reduced, and the efficiency is further improved. After the intermediate capacitor is added, the loop of the input side and the loop of the output side can be independently controlled, the complex logic time sequence of the switching tube does not need to be considered, and the debugging difficulty is greatly reduced.

Document [1] Huang Zhanjiang Yong, Wu Qing Bin, Lianhai power A control method of a DCDC bidirectional converter [ P ] Chinese patent No. CN107959417A.2018-04-24.

The literature [2] Wangchang, Shenzhi, bidirectional DCDC conversion circuit, energy storage converter and charge-discharge control method [ P ] Chinese patent No. CN111525815A.2020-8-11.

Disclosure of Invention

The DC-DC bidirectional converter is provided, through the topology design of a bidirectional liftable profiling DCDC controller, an intermediate capacitor is added at an inductance common end, so that the midpoint voltage of a bridge arm is controllable, and meanwhile, the voltage of an output end and the intermediate capacitor is controlled to keep stable, and the voltage stress of a switching tube is reduced.

The technical scheme of the utility model is as follows: a DC-DC bidirectional converter comprises four groups of upper and lower bridge arms S with input and output_xjAnd a capacitor C connected in parallel with each group of bridge arms_xFree-wheeling inductance L_xAnd an intermediate capacitor C_n(ii) a Each group of bridge arms comprises an integral multiple of 2 switching tubes connected in series, x is a group number, and x is 1,2,3 and 4; j is the number of switching tubes in each group; the first and second groups of bridge arms are upper and lower input end bridge arms, and the third and fourth groups of bridge arms are upper and lower output end bridge arms; the common end of the two serially connected switching tubes of each group of bridge arms is Px, and the common end P of the first group of bridge arms₁Sequentially passes through the first inductor L₁And a third inductor L₃Common terminal P with third set of legs₃Connected, common terminal P of the second set of legs₂Sequentially passes through the second inductor L₂And a fourth inductance L₄Common terminal P with fourth set of legs₄Connected to a first inductor L₁And a third inductor L₃Is P_n1Second inductance L₂And a fourth inductor L₄Is P_n2Said intermediate capacitance C_nIs connected across P_n1And P_n2In the meantime.

Preferably, the first inductor L₁And a third inductor L₃Second inductance L₂And a fourth inductance L₄All adopt the tapped inductance.

Preferably, the first inductor L₁And a third inductor L₃The two inductors are independent inductors, or two inductors obtained by extending two ends of a tapped inductor.

Preferably, the intermediate capacitor C_nAnd a small capacitance value capacitor without absorbing harmonic waves is adopted.

Preferably, the four groups of bridge arm switching tubes are selected from IGBTs or MOSFETs.

The utility model has the beneficial effects that: according to the DC-DC bidirectional converter, the intermediate capacitor is added at the common end of the inductor, so that the bridge arm at the input side and the bridge arm at the output side are independently controlled, the complex logic time sequence of the switching tube does not need to be considered, the debugging difficulty is greatly reduced, the control of the switching tube is simplified, meanwhile, the voltage stress of the switching tube is reduced by controlling the voltage on the intermediate capacitor to be stabilized in a certain range, the loss of the inductor can be reduced through reasonable design, and the efficiency is further improved.

Drawings

FIG. 1 is a schematic diagram of a DC-DC bidirectional converter according to the present invention;

fig. 2 is a schematic diagram of the control of the DC-DC bidirectional converter of the present invention.

Detailed Description

The utility model is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

As shown in fig. 1, the DC-DC bidirectional converter includes four sets of arms (S) with input and output_xjX is the number of groups, each group has two switching tubes connected in series, x is 1,2,3, 4; j ═ 1, 2) and a capacitor C connected in parallel to each set of arms_xFree-wheeling inductance L_xAnd an intermediate capacitor C_nEach group of bridge arms comprises two first switching tubes S connected in series_x1And a second switching tube S_x2The common end of the two serially connected switching tubes of each group of bridge arms is Px, and the common end P of the first group of bridge arms₁Sequentially passes through the first inductor L₁And a third inductor L₃Common terminal P with third set of legs₃Connected, common terminal P of the second set of legs₂Sequentially passes through the second inductor L₂And a fourth inductance L₄Common terminal P with fourth set of legs₄Connected to a first inductor L₁And a third inductor L₃Is P_n1Second inductance L₂And a fourth inductor L₄Is P_n2Said intermediate capacitance C_nIs connected across P_n1And P_n2In the meantime.

As shown in fig. 2, the control scheme of the DC-DC bidirectional converter includes:

step 1: sampling the current input voltage V_inA first inductor current iL1, a third inductor current iL3, and an intermediate capacitor C_nVoltage V_midVoltage V at output terminal_out(ii) a Due to the intermediate capacitance C_nSo iL1 is not equal to iL3, so the input and output sides can be broken down into two separate loops.

Step 2: by means of a voltage C to the intermediate capacitor_nVoltage V_midControl is performed to obtain the current reference value iL1Ref of the first inductor current value iL 1. The control method comprises the following steps: intermediate capacitor voltage set value V_midRef(taking the efficiency of the whole system and the voltage stress borne by the switch tube into consideration, taking a compromise value) and the intermediate capacitor C_nVoltage V_midAfter the difference is made, the difference sequentially passes through a low-pass filter, a PI regulator and an amplitude limiter to obtain iL1Ref, and the specific formula is as follows:

wherein, tau₁Representing the voltage loop low-pass filter time constant, K_p1Indicating the proportional gain, K, of the intermediate capacitor voltage loop PI regulator_i1Representing the intermediate capacitor voltage loop PI regulator integral gain.

And step 3: according to the iL1Ref obtained in the step 2 and the sampled first inductance current value iL1, the difference between the two current values is sequentially subjected to input-side low-pass filter, PI regulator and carrier coefficient conversion adjustment, and then is superposed with feed-forward voltage to output the front-stage DCDC duty ratio D_Presat1，D_Presat1And then outputs the PWM1 driving waveform through amplitude limiting. D_Presat1The calculation formula is as follows:

wherein, tau₂Represents the input-side current loop low-pass filter time constant, K_p2Proportional gain, K, of the input-side current loop PI regulator_i2To representInput side current loop PI regulator integral gain, K_carr1For PWM1 carrier coefficients, D_FedFraw1Is a feed-forward voltage of a front stage,

V_inthe input voltage of the DC-DC bidirectional converter is obtained.

And 4, step 4: the input voltage is controlled by the following two formulas, and the current amplitude limiting value corresponding to the output side is calculated.

Wherein, tau₃Representing the voltage loop low-pass filter time constant, K_p3Indicating the proportional gain, K, of the input-side voltage loop PI regulator_i3Indicating the input side voltage loop PI regulator integral gain, V_ChargeHighUpper limit of charge for input, V_DisChargeLowFor the lower limit of the input end discharge, after the control of the PI regulator, I can be obtained_OutLimHigh、I_OutLimLowI.e. the upper and lower limits of the output current limit value on the output side. When the battery works normally, the control loop is in a saturated state, and when the voltage of the battery approaches the upper limit of the charging voltage or the lower limit of the discharging voltage, the corresponding output current is limited to be close to 0. Note that the output-side current limit value may also be obtained from the SOC of the battery.

And 5: the output side output voltage is controlled by the following formula, and iL3Ref is calculated.

Wherein, tau₄Representing the voltage loop low-pass filter time constant, K_p4Indicating the proportional gain, K, of the output side voltage loop PI regulator_i4Indicating output side voltage loopIntegral gain, V, of PI regulator_BusRefFor the given value of the output voltage, iL3Ref1 is the result obtained by controlling iL3 through a PI regulator, then the current amplitude limit is carried out to obtain the current reference value iL3Ref of iL3, the upper limit and the lower limit of the amplitude limit value are the results obtained in the step 4, namely when iL3Ref1 is more than I_outLimLowWhen iL3Ref is equal to I_outLimLowWhen iL3Ref1 > I_outLimHighWhen iL3Ref is equal to I_outLimHighIn other cases, iL3Ref is iL3Ref 1.

Step 6: obtaining the subsequent DCDC duty ratio D according to the iL3Ref obtained in the step 5 and the iL3 obtained by sampling_Presat2，

Wherein, tau₅Represents the current loop low-pass filter time constant, K_p5Indicating the proportional gain, K, of the output side current loop PI regulator_i5Represents the integral gain, K, of the output side current loop PI regulator_carr2For PWM2 carrier coefficients, D_FedFraw2In order to feed forward the voltage at the later stage,

V_outfor DC-DC bidirectional converter output voltage, output D_Presat2And PWM2 driving waveforms can be output after amplitude limiting, and PWM2 is used for controlling the on-off of switching tubes S31, S32, S41 and S42.

According to the utility model, through skillful design of a DCDC controller topology, the intermediate capacitor is added at the common end of the inductor, so that the midpoint voltage (the midpoint voltage is the voltage between P1 and P2 and the voltage between P3 and P4 in the figure 1) of a bridge arm is controllable, and the voltage of the output end and the voltage of the intermediate capacitor are controlled at the same time, so that the bridge arm is kept stable, and the problems that the voltage stress borne by a power switch device is overlarge and the device is even damaged due to unstable voltage control in the DCDC conversion process are solved, and meanwhile, due to the existence of the intermediate capacitor, the currents on L1 and L3 are mutually independent, so that the loop at the input side and the loop at the output side can be independently controlled, the modulation complexity is greatly reduced, and the modulation modes at two ends are enabled to be independentIs simpler and more stable. In addition, the inductors L1 and L3, L2 and L4 can adopt tapped inductors, the cost of a hardware topology can be reduced, and simultaneously, the intermediate capacitor C has a hard requirement only on the harmonic waves of the input side and the output side, but the harmonic wave of the intermediate capacitor side has no clear requirement, so that the intermediate capacitor C has a simple structure, is convenient to use, and has a high efficiency, and the cost is low_nAnd a capacitor with a smaller capacitance value can be adopted to reduce the hardware cost.

It should be finally noted that the above embodiment is only used to illustrate the technical solution of the present method, and not to limit the protection range of the present method, for example, the power device in the hardware topology may be an IGBT or a MOSFET, the inductors L1 and L3 may be two independent inductors, or two inductors obtained by extending two ends of one tap inductor, the feed-forward current is increased in steps 3 and 6, the feed-forward current is not increased in steps 2 and 5, the feed-forward current is not increased and does not affect the final result, and the output-end current limit value obtained in step 4 is obtained by controlling the input-end voltage, and if the output-end current limit value is obtained by the SOC of the battery, the final result is not affected. Although the present method has been described in detail with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present method.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the utility model. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (5)

1. The DC-DC bidirectional converter is characterized by comprising four groups of upper and lower bridge arms S with input and output_xjAnd a capacitor C connected in parallel with each group of bridge arms_xFree-wheeling inductance L_xAnd an intermediate capacitor C_n(ii) a Each group of bridge arms comprises an integral multiple of 2 switching tubes connected in series, x is a group number, x is 1,2 and 3,4; j is the number of switching tubes in each group; the first and second groups of bridge arms are upper and lower input end bridge arms, and the third and fourth groups of bridge arms are upper and lower output end bridge arms; the common end of the two serially connected switching tubes of each group of bridge arms is Px, and the common end P of the first group of bridge arms₁Sequentially passes through the first inductor L₁And a third inductor L₃Common terminal P with third set of legs₃Connected, common terminal P of the second set of legs₂Sequentially passes through the second inductor L₂And a fourth inductance L₄Common terminal P with fourth set of legs₄Connected to a first inductor L₁And a third inductor L₃Is P_n1Second inductance L₂And a fourth inductor L₄Is P_n2Said intermediate capacitance C_nIs connected across P_n1And P_n2In the meantime.

2. The DC-DC bidirectional converter according to claim 1, wherein the first inductor L₁And a third inductor L₃Second inductance L₂And a fourth inductance L₄All adopt the tapped inductance.

3. The DC-DC bidirectional converter according to claim 1 or 2, wherein the first inductor L₁And a third inductor L₃The two inductors are independent inductors, or two inductors obtained by extending two ends of a tapped inductor.

4. The DC-DC bidirectional converter according to claim 1, wherein the intermediate capacitor C_nAnd a small capacitance value capacitor without absorbing harmonic waves is adopted.

5. The DC-DC bidirectional converter according to claim 1, wherein the four sets of bridge arm switching tubes are selected from IGBT or MOSFET.

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