阅读说明：本技术 三移相控制双有源桥变换器瞬态直流偏置的抑制方法 (Method for inhibiting transient direct current offset of three-phase-shift control double-active-bridge converter ) 是由 郭志强 骆勇 于 2021-06-09 设计创作，主要内容包括：本发明公开的三移相控制双有源桥变换器瞬态直流偏置的抑制方法,属于电力电子领域的储能用的双向DC-DC变换器领域。双有源桥DC-DC变换器(DAB),由串联电感和变压器、一次侧全桥、二次侧全桥组成,采用三移相控制,通过控制变换器一次侧和二次侧全桥的占空比和移相角实现双向功率流的控制。在稳态时,负载发生突变,变压器中的电流会产生较大的直流偏置,可能导致变压器过饱和,开关管过流,减少元器件寿命,降低变换器效率。本发明在三移相控制的电流峰值调制策略下,分析直流偏置产生的原因,通过控制切载时移相角消除直流偏置,从而提高双有源桥DC-DC变换器高效率的电能变换,实现变换器的稳定控制,提高变换器效率。(The invention discloses a method for inhibiting transient direct current bias of a three-phase-shift control double-active-bridge converter, belonging to the field of bidirectional DC-DC converters for energy storage in the field of power electronics. A double-active bridge DC-DC converter (DAB) is composed of a series inductor, a transformer, a primary side full bridge and a secondary side full bridge, adopts three-phase-shift control, and realizes the control of bidirectional power flow by controlling the duty ratio and phase shift angle of the primary side full bridge and the secondary side full bridge of the converter. In a steady state, the load suddenly changes, the current in the transformer generates a large direct current bias, the transformer is possibly supersaturated, the switch tube is subjected to overcurrent, the service life of components is shortened, and the efficiency of the converter is reduced. The invention analyzes the reason generated by DC bias under the current peak value modulation strategy of three phase shift control, and controls the phase shifting angle of load shedding The direct current bias is eliminated, so that the high-efficiency electric energy conversion of the double-active-bridge DC-DC converter is improved, the stable control of the converter is realized, and the efficiency of the converter is improved.)

1. The method for inhibiting the transient direct current offset of the three-phase-shift control double-active-bridge converter is characterized by comprising the following steps of: comprises the following steps of (a) carrying out,

the method comprises the following steps: by a voltage reference V_refAnd secondary side voltage feedback V_oThe voltage error obtained by subtraction is output as phase shift angle control quantity by an output voltage controllerWherein the phase shift angleDefining phase difference corresponding to neutral lines of square waves of full-bridge inversion of a primary side and a secondary side;

step two: defining equivalent voltage gain M ═ V_o/(nV_bat) N is the transformer transformation ratio, V_batIs the battery voltage, V_oIs the output voltage. According to the M value and the phase shift angleJudging the working mode of the circuit;

step three: definition D₁、D₂Primary side and secondary side full bridge voltage waveform duty ratio respectively; defining the neutral line of the negative voltage square wave of the primary side inversion in a steady state as T_skWherein k is 0,1,2, and the neutral line of the negative voltage square wave inverted in the next switching period is T_s(k+1)，T_skTo T_s(k+1)The neutral line of (a) is the neutral line of the switching cycle; defining the neutral line from the switching period to T_s(k+1)Has a phase shift angle and a duty cycle of D_1k，D_2k，From T_skPhase shift angle and duty cycle of full bridge to neutral of switching cycle is D_1kp，D_2kp，

Step four: when load shedding is carried out, parameters can be quickly obtained through feedforward control

Step five: in the three phase-shift modulation scheme taking the peak current in the converter as the optimization target, the method can obtainAnd D₁，D₂On the basis, the current and the phase shift angle control quantity at the neutral line of the primary side voltage square wave are obtainedThe relational expression of (1);

step six: current and phase shift angle control at neutral line of known primary voltage square waveUnder the condition of the relation of (1), obtainingAndusing the relational expression ofAndis calculated to obtain D_1k，D_2k，D_1kp，D_2kp；

Step seven: obtained by step fourStep six is to obtainAnd D_1k，D_2k，D_1kp，D_2kpObtaining an expression for generating a PWM signal; the PWM signals are used for driving eight switching tubes to work, the suppression of the direct current bias of the double-active-bridge DAB converter is realized, the saturation of a transformer and the overlarge current of the switching tubes are prevented, and the efficiency of the converter is improved.

2. The method for suppressing transient DC offset of a three-phase-shift-controlled dual-active-bridge converter according to claim 1, wherein: in the second step, the first step is carried out,

there are eight working modes, whenAnd M<1, the circuit works in a mode1 f; when in useAnd M<1, the circuit works in a mode2 f; when in useAnd M>1, the circuit works in a mode 3 f; when in use And M>1, the circuit works in a mode 4 f; when in useAnd M<1, the circuit works in a mode1 r; when in useAnd M<1, the circuit works in a mode2 r; when in useAnd M>1, the circuit works in a mode 3 r; when in useAnd M>1, the circuit works in a mode 4 r; the mode1f, the mode2f, the mode 3f and the mode 4f correspond to a forward power flow working mode, and the mode 1r, the mode 2r, the mode 3r and the mode 4r correspond to a reverse power flow working mode.

3. The method for suppressing transient DC offset of a three-phase-shift-controlled dual-active-bridge converter according to claim 2, wherein: in the fifth step, the first step is that,

deducing by a formula to obtain the current and phase shift angle control quantity at the neutral line of the primary voltage square waveThe relation of (A) is as follows:

4. the method for suppressing transient DC offset of a three-phase-shift-controlled dual-active-bridge converter according to claim 3, wherein: in the sixth step, the step of,

controlled quantity of current and phase shift angle at neutral line of square wave of primary voltageDerivation of the relational expression ofAndto obtain a relationship of

5. The method for suppressing transient DC offset of a three-phase-shift-controlled dual-active-bridge converter according to claim 4, wherein: in the seventh step, the process is carried out,

obtained by step fourStep six is to obtainAnd D_1k，D_2k，D_1kp，D_2kpThe expression for generating the PWM signal can be found as:

6. the method for suppressing transient DC offset of a three-phase-shift-controlled dual-active-bridge converter according to claim 5, wherein: the double-active converter consists of a series inductor, a transformer, a primary side full bridge and a secondary side full bridge; the converter is of a bidirectional topological structure, the primary side and the secondary side can be interchanged according to requirements, and any load can be connected.

Technical Field

The invention relates to a method for inhibiting transient direct current bias of a three-phase-shift control double-active-bridge converter, belonging to the field of bidirectional DC-DC converters for energy storage in the field of power electronics.

Background

Energy storage systems have become a major energy source for devices such as micro-grids and uninterruptible power supplies. The dual active bridge DC-DC converter has become the main circuit topology of the bidirectional DC-DC converter in the energy storage system. Fig. 1 shows a dual active bridge DC-DC converter circuit topology to which the present invention is directed. The energy storage DC-DC converter not only needs to realize high-efficiency electric energy conversion, but also needs not to have overlarge direct current bias during load shedding.

In order to solve the problem of direct Current bias generated by a Dual-Active-Bridge DC-DC Converter when load suddenly changes, 2020 in the article 'Deadbed Current Controller for Bidirectional Dual-Active-Bridge Converter Using Enhanced SPS Modulation Method' published by IEEE Transactions on Power Electronics journal, a dead-beat Current control is proposed, but the control strategy is only effective for SPS control and cannot be popularized to other control strategies. 2019 in IEEE Transactions on Power Electronics (Power Electronics journal), a text of "Transient DC Bias estimation of Dual-Active-Bridge DC-DC Converter With Improved Triple-Phase-Shift Control" is published, and in order to reduce Transient DC Bias current in a wide voltage range, an Improved TPS Control strategy is developed aiming at different working mode conversion. However, the control strategy needs to judge the working mode and the power change condition, and the control is complex. And the converter can not work in the global optimal modulation strategy in the steady state, so that the conduction loss is increased.

In order to well suppress the dc offset in the dual-active bridge converter in the global range, a global optimization control strategy based on three-phase shift control needs to be provided to realize suppression of the dc offset in the converter in the global range.

Disclosure of Invention

In order to solve the problem that the prior art method cannot completely inhibit the direct current bias in a double-active bridge (DAB) converter, the invention aims to provide a method for inhibiting the transient direct current bias of a three-phase-shift control double-active bridge converter, which can inhibit the direct current bias generated by sudden load change in the global range, prevent the saturation of a transformer and the overlarge current of a switching tube and improve the efficiency of the converter.

The purpose of the invention is realized by the following technical scheme.

The invention discloses a method for inhibiting transient direct current bias of a three-phase-shift control double-active-bridge converter, which is used for controlling the double-active-bridge DC-DC converter based on a three-phase-shift modulation strategy, wherein a primary side and a secondary side of a main circuit of the double-active-bridge DC-DC converter are full-bridge circuits, the two full bridges are connected together through a series inductor and a transformer, the primary side is connected with a storage battery, the secondary side can be connected with any load, the control of bidirectional power flow is realized by controlling internal phase shift angles of the full-bridge of the primary side and the secondary side of the converter and phase shift angles corresponding to voltage waveforms of the two full bridges, and the generation strategy of the driving of full-bridge duty ratio is adopted. The invention can inhibit the direct current bias in the Double Active Bridge (DAB) converter, improve the service life of components and reduce the loss.

The invention discloses a method for inhibiting transient direct current offset of a three-phase-shift control double-active-bridge converter, which comprises the following steps of:

step one, passing a voltage reference V_refThe voltage error obtained by subtracting the secondary side voltage feedback Vo is output as a phase shift angle control quantity by an output voltage controllerThe phase shift angle control quantityThe phase difference is corresponding to the neutral line of the square wave of the full-bridge inversion of the primary side and the secondary side.

Step two, defining equivalent voltage gain M as Vo/(nV)_bat) N is the transformer transformation ratio, V_batIs the battery voltage, Vo is the output voltage. According to the M value and the phase shift angle control quantity in the step oneAnd judging the working mode of the circuit.

There are eight working modes: when in useAnd M<1, the circuit works in a mode1 f; when in useAnd M<1, the circuit works in a mode2 f; when in useAnd M>1, the circuit works in a mode 3 f; when in use And M>1, the circuit works in a mode 4 f; when in useAnd M<1, the circuit works in a mode1 r; when in useAnd M<1, the circuit works in a mode2 r; when in useAnd M>1, the circuit works in a mode 3 r; when in useAnd M>1, the circuit operates in the mode 4 r.

The mode1f, the mode2f, the mode 3f and the mode 4f correspond to a forward power flow working mode, and the mode 1r, the mode 2r, the mode 3r and the mode 4r correspond to a reverse power flow working mode.

Step three, define D₁、D₂Primary and secondary side full bridge voltage waveform duty cycles, respectively. Defining the neutral line of the negative voltage square wave of the primary side inversion in a steady state as T_skWherein k is 0,1,2, and the neutral line of the negative voltage square wave inverted in the next switching period is T_s(k+1)，T_skTo T_s(k+1)Is the neutral line of the switching cycle. Defining slave switching cyclesLinear to T_s(k+1)Has a phase shift angle ofDuty ratio of D_1k，D_2k(ii) a From T_skThe phase shift angle of the full bridge to the neutral line of the switching cycle isDuty ratio of D_1kp，D_2kp。

Step four, when cutting the load, obtain the phase shift angle rapidly through feedforward control

Step five, obtaining the peak current in the converter as an optimization target through three-phase shift modulation optimizationAnd D₁，D₂On the basis, the current and the phase shift angle control quantity at the neutral line of the primary side voltage square wave are obtainedThe relational expression (c) of (c).

Deducing by a formula to obtain the current and phase shift angle control quantity at the neutral line of the primary voltage square waveThe relation of (A) is as follows:

wherein, T_sFor a switching period, L_rIs a series inductor.

Step six: current and phase shift angle control at neutral line of known primary voltage square waveUnder the condition of the relation of (1), obtainingAndusing the relational expression ofAndis calculated to obtain D_1k，D_2k，D_1kp，D_2kp。

Deducing from the formula (1) obtained in the fifth stepAndthe relation of (A) is as follows:

by usingAndis calculated to obtain D_1k，D_2k，D_1kp，D_2kp。

Step seven, the product obtained in step fourStep six is to obtainAnd D_1k，D_2k，D_1kp，D_2kpAn expression for generating the PWM signal is obtained. The PWM signals are used for driving eight switching tubes to work, the suppression of the direct current bias of the double-active-bridge DAB converter is realized, the saturation of a transformer and the overlarge current of the switching tubes are prevented, and the efficiency of the converter is improved.

The expression is:

wherein T is_dIs the cycle count value of the counter.

The double-active converter is composed of a series inductor, a transformer, a primary side full bridge and a secondary side full bridge. The converter is of a bidirectional topological structure, the primary side and the secondary side can be interchanged according to requirements, and any load can be connected.

Has the advantages that:

1. the invention discloses a method for inhibiting transient direct current bias of a three-phase-shift control double-active-bridge converter, which comprises the following steps of firstly controlling the transient direct current bias of the double-active-bridge converter according to an equivalent gain M and a phase shift angleThe size of the phase shift angle is divided into eight working modes, direct current bias generated by mode switching and mode-to-mode switching can be restrained by a method for controlling the phase shift angle, working modes and power conditions do not need to be judged, and the control is simple.

2. The invention discloses a method for inhibiting transient direct current offset of a three-phase-shift control double-active-bridge converter, and provides a control strategy of direct current offset in a double-active-bridge DAB converter according to the analysis method. During the cutting-loading process, by introducingTo eliminate the dc offset. At the time of the steady-state,during the process of cutting off the load,by controllingThe suppression of the DC offset in the dual-active bridge converter can be realized.

3. The method for inhibiting transient direct current offset of the three-phase-shift control double-active-bridge converter can inhibit direct current offset and prevent over saturation of a transformer and over current of a switch tube.

Drawings

FIG. 1 shows a Dual Active Bridge (DAB) converter circuit topology of the present embodiment;

FIG. 2 shows a closed loop control block diagram of the present invention;

FIG. 3 illustrates a waveform diagram of switching within Mode1f of the present invention;

FIG. 4 illustrates a waveform diagram of switching within Mode2f of the present invention;

FIG. 5 is a waveform diagram illustrating the Mode1f switching to Mode2 f;

FIG. 6 drive generation signals;

fig. 7 shows a flow chart of an implementation of the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and embodiments, and the technical problems and advantages solved by the technical solutions of the present invention are also described, it should be noted that the described embodiments are only intended to facilitate the understanding of the present invention, and do not limit the present invention in any way.

As shown in fig. 1, a circuit topology of a Dual Active Bridge (DAB) converter is shown, and the converter is composed of eight switching tubes, and the primary side and the secondary side are both composed of 4 switching tubes. The primary side full bridge comprises 4 switching tubes Q₁-Q₄. Switch tube Q₁And a switching tube Q₂Form a bridge arm, Q₂Drain electrode of (2) is connected to Q₁Of the substrate. Switch tube Q₃And a switching tube Q₄Form a bridge arm, Q₄Drain electrode of (2) is connected to Q₃Of the substrate. Switch tube Q₁Drain electrode of (1) and switching tube Q₃Are connected together, a switching tube Q₂And a switching tube Q₄Are connected together. Switch tube Q₁Is connected with a series inductor L_rOne end of (1) is connected in series with an inductor L_rThe other end of the primary side transformer winding is connected with the homonymous end of the primary side transformer winding, and the heteronymous end of the primary side transformer winding is connected with Q₃Of the substrate. The secondary side full bridge comprises 4 switching tubes Q₅-Q₈. Switch tube Q₅And a switching tube Q₆Form a bridge arm, Q₅Source electrode of (2) is connected to Q₆Of the substrate. Switch tube Q₇And a switching tube Q₈Form a bridge arm, Q₇Source electrode of (2) is connected to Q₈Of the substrate. Switch tube Q₅And Q₇The drains of the first and second capacitors are connected together and to the anode of the output capacitor as the output voltage anode. Switch tube Q₆And a switching tube Q₈Are connected together and connected to the negative pole of the output capacitor as the negative pole of the output voltage. Switch tube Q is connected to the end of the same name of the secondary side of the transformer₅The different name end of the secondary side winding of the transformer is connected with a switching tube Q₇Of the substrate. The node A and the node B are respectively the middle points of the two bridge arms of the primary side full bridge, and the node C and the node D are respectively the middle points of the two bridge arms of the secondary side full bridge. V_batAnd V_oThe equivalent voltage gain M of the converter is defined as Vo/(nV) for the primary side battery voltage and the secondary side output voltage respectively_bat)。

First switch tube Q in primary side full bridge₁And a second switching tube Q₂The driving signals of (1) are respectively the driving signals with the duty ratio of 0.5, and the first switch tube Q₁And a second switching tube Q₂The drive signals of (a) are complementary and there is a dead zone. Third switch tube Q₃And a fourth switching tube Q₄The driving signals of (1) are respectively the driving signals with the duty ratio of 0.5, and the third switching tube Q₃And a fourth switching tube Q₄The drive signals of (a) are complementary and there is a dead zone. The primary side full bridge controls the voltage difference of the middle points (namely the end points A and B) of the two bridge arms in a phase-shifting mode. Voltage V_ABCorresponding duty cycle of D₁。

Secondary side full bridge fifth switch tube Q₅And a sixth switching tube Q₆Respectively of duty ratio of0.5 driving signal, fifth switching tube Q₅And a sixth switching tube Q₆The drive signals of (a) are complementary and there is a dead zone. Seventh switch tube Q₇And an eighth switching tube Q₈The driving signals of (1) are respectively a driving signal with a duty ratio of 0.5, and a seventh switching tube Q₇And an eighth switching tube Q₈The drive signals of (a) are complementary and there is a dead zone. The primary side full bridge controls the voltage difference of the middle points (namely the end points C and D) of the two bridge arms in a phase-shifting mode. Voltage V_CDCorresponding duty cycle of D₂。

The method for suppressing the direct current offset in the dual-active bridge converter based on the three-phase shift modulation disclosed by the embodiment comprises the following specific control steps;

step one, passing a voltage reference V_refThe voltage error obtained by subtracting the secondary side voltage feedback Vo is output as a phase shift angle control quantity by an output voltage controllerWherein the phase shift angleThe phase difference corresponding to the neutral line of the square wave of the full-bridge inversion of the primary side and the secondary side is defined.

Step two, defining equivalent voltage gain M as Vo/(nV)_bat) N is the transformer transformation ratio, V_batIs the battery voltage, Vo is the output voltage. According to the M value and the phase shift angleAnd judging the working mode of the circuit.

There are eight working modes, whenAnd M<1, the circuit works in a mode1 f; when in useAnd M<1, the circuit works in a mode2 f; when in useAnd M>1, the circuit works in a mode 3 f; when in use And M>1, the circuit works in a mode 4 f; when in useAnd M<1, the circuit works in a mode1 r; when in useAnd M<1, the circuit works in a mode2 r; when in useAnd M>1, the circuit works in a mode 3 r; when in useAnd M>1, the circuit operates in the mode 4 r. The mode1f, the mode2f, the mode 3f and the mode 4f correspond to a forward power flow working mode, and the mode 1r, the mode 2r, the mode 3r and the mode 4r correspond to a reverse power flow working mode.

When the circuit works in the mode1f, the load is suddenly changed, and the circuit can work in the mode1f after sudden change, namely, the mode1f is switched, and the switching waveform in the mode1f is shown in fig. 3. When the circuit works in the mode2f, the load changes suddenly, and after the sudden change, the circuit works in the mode2f, namely the mode2f is switched, and the switching waveform in the mode2f is shown in fig. 4. When the circuit works in the mode1f, the load changes abruptly, but after the load changes abruptly, the circuit works in the mode2f, that is, the mode1f is switched to the mode2f, and the waveform of switching the mode1 to the mode2f is shown in fig. 5. Other modality switching is similar to the three cases described above.

Step three, define D₁、D₂Primary and secondary side full bridge voltage waveform duty cycles, respectively. Defining the neutral line of the negative voltage square wave of the primary side inversion in a steady state as T_skWherein k is 0,1,2, and the neutral line of the negative voltage square wave inverted in the next switching period is T_s(k+1)，T_skTo T_s(k+1)Is the neutral line of the switching cycle. Defining the neutral line from the switching period to T_s(k+1)Has a phase shift angle and a duty cycle of D_1k，D_2k，From T_skPhase shift angle and duty cycle of full bridge to neutral of switching cycle is D_1kp，D_2kp，In step three, the specific definitions of duty cycle and phase shift angle are shown in FIG. 3, from T_skTo T_s(k+1)Full bridge phase shift angle and duty cycle of the first half cycle are D_1kp，D_2kp，From T_skTo T_s(k+1)The phase shift angle and the duty ratio of the second half-cycle full bridge are D_1k，D_2k，In the digital controller, the driving signal of the switch tube is at T_skAnd (6) updating.

Step four, when load shedding is carried out, parameters can be quickly obtained through feedforward control

Step five, obtaining the peak current in the converter as the three phase shift modulation scheme of the optimization targetAnd D₁，D₂Is represented by the formula (3), wherein

Deducing by a formula to obtain the current and phase shift angle control quantity at the neutral line of the primary voltage square waveThe relation of (A) is as follows:

step six, controlling the current and the phase shift angle at the neutral line of the known primary side voltage square waveUnder the condition of the relation of (1), deducingAndthe relationship (2) of (c).

And D, obtaining the following expression according to the expression of the formula (4) obtained in the step five:

wherein, t_0mAnd t_4m、t_8mSee FIG. 3 for details, which can be derived from formula (5)Andis as in formula (6)

And isAndthe relation formula also satisfies the formula (3), i.e. D is obtained by calculation_1k，D_2k，D_1kp，D_2kp。

Step seven, the product obtained in step fourStep six is to obtainAnd D_1k，D_2k，D_1kp，D_2kpAn expression for generating the PWM signal is obtained. The corresponding drive signals are shown in fig. 6. The signal is used for driving eight switching tubes to work, and the suppression of the direct current bias of the double-active-bridge DAB converter is realized. The corresponding expression of the drive generation signal is as follows:

wherein T in FIG. 6_dIs the cycle count value of the counter. PWM1A corresponds to the rising edge of the Q1 driving signal and the falling edge of the Q2 driving signal; PWM1B corresponds to the falling edge of the Q1 driving signal and the rising edge of the Q2 driving signal; PWM2A corresponds to the rising edge of the Q4 drive signal and the falling edge of the Q3 drive signal; PWM2B corresponds to the falling edge of the Q4 drive signal and the rising edge of the Q3 drive signal; PWM3A corresponds to the rising edge of the Q5 driving signal and the falling edge of the Q6 driving signal; PWM3B corresponds to the falling edge of the Q5 driving signal and the rising edge of the Q6 driving signal; PWM4A corresponds to the rising edge of the Q8 drive signal and the falling edge of the Q7 drive signal; PWM4B corresponds to the falling edge of the Q8 drive signal and the rising edge of the Q7 drive signal;

the specific inhibition principle is as follows: take the mode of FIG. 3 as an exampleAnd in the loading process, the phase shift angle control quantity after load shedding is obtained through the step fourCalculated by the formula (6)And isAccording to the formula (4), i_r(t_4m)<i_r(t_8m) From the formula (3), D_1kp＜D_1kThen t is₁＝t₅-t_4mLess than t₂＝t₉-t_8mI.e. t₁＜t₂. Because of t₁And t₂In the period, the absolute value of the slope of the current is the same, and the absolute value of the current has the following relationship, | i_r(t₅)|<|i_r(t₉)|＝|i_r(t₁₃) If the system is stable, the DC bias is suppressed,the equation (6) is still true, so the modulation strategy proposed herein does not need to judge the working mode and power condition, the control is simple, the dc bias is completely suppressed, the control flow chart is shown in fig. 7, the working principle of other modes is similar, and details are not repeated here.

The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.