CN116979793A - Double-active full-bridge DC-DC converter optimal control method - Google Patents
Double-active full-bridge DC-DC converter optimal control method Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/3353—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having at least two simultaneously operating switches on the input side, e.g. "double forward" or "double (switched) flyback" converter
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Abstract
The invention belongs to the technical field of direct current converter optimal control, and discloses a double-active full-bridge DC-DC converter optimal control method, which comprises the steps of firstly, carrying out working mode analysis on a double-active full-bridge DC-DC converter under extended phase-shifting modulation, and deducing a mathematical model of transmission power and reflux power; then the final internal phase shift D is obtained according to the improved Lagrangian function 1.end The inhibition effect on the reflux power is improved, and finally, a prediction equation of the output voltage is deduced according to an average equation of the state space of the output voltage to obtain the final external phase shift D 2.end Improving the dynamic response performance. The invention has the advantages of quick dynamic response, high efficiency, simple control process and the like, and has stronger practicability.
Description
Technical Field
The invention belongs to the technical field of direct current converter optimal control, and relates to a double-active full-bridge DC-DC converter optimal control method.
Background
With the aggravation of global energy crisis and environmental pollution, direct-current devices such as distributed renewable energy sources, energy storage power stations, electric automobiles and the like are rapidly developed, and the popularization and development of a direct-current power distribution network are greatly promoted. The double-active full-bridge (Dual Active Bridge, DAB) DC-DC converter has gradually become the most applied bidirectional DC-DC converter in a direct-current distribution network due to the characteristics of energy bidirectional flow, easy realization of soft switching, high power density and the like, and is also widely applied in the fields of electric automobile charging piles and the like. However, under the traditional control mode, the double-active full-bridge DC-DC converter can generate larger reflux power, the transmission efficiency of the converter is reduced, the dynamic characteristics are poor, and when the load suddenly changes, the response time of the converter is longer, so that the output voltage cannot be quickly restored to the rated value. Therefore, how to inhibit the backflow power generated by the double-active full-bridge DC-DC converter and improve the dynamic characteristics of the converter gradually becomes a hot spot of current research.
Currently, in the control of a dual active full-bridge DC-DC converter, phase-shift modulation is the most widely used control method, i.e. the magnitude and direction of the transmission power of the converter are adjusted by controlling the amount of phase shift between the individual switching transistors. Common Phase Shift modulation methods include single Phase Shift (Single Phase Shift, SPS) modulation, extended Phase Shift (Extended Phase Shift, EPS) modulation, double Phase Shift (DPS) modulation, and triple Phase Shift (Triple Phase Shift, TPS) modulation. In which the single phase shift modulation has only one control amount, so that it is difficult to effectively inhibit the return power, and in practical application, there is a large return power. The spread phase-shift modulation and the double phase-shift modulation have two control amounts, and although the inhibiting effect on the reflux power is obviously enhanced, larger reflux power still exists. The triple phase shift modulation has three control amounts, and although the effect of suppressing the reflux power is ideal, the control amounts are possibly combined in multiple ways, the analysis process is complex, and the triple phase shift modulation is difficult to apply in practical engineering. In addition, the existing phase shift optimization method needs to ensure power transmission by means of a PI controller, so that the dynamic characteristics are not ideal.
Disclosure of Invention
The invention aims to provide an optimal control method of a double-active full-bridge DC-DC converter, which aims to solve the problem of low transmission efficiency caused by high reflux power of the existing double-active full-bridge DC-DC converter.
The technical scheme adopted by the invention for realizing the purposes is as follows:
an optimized control method of a double-active full-bridge DC-DC converter comprises the following steps:
s1, carrying out working mode analysis on a double-active full-bridge DC-DC converter under extended phase-shift modulation, and constructing a state equation of inductance current of the double-active full-bridge DC-DC converter;
s2, deducing a mathematical model of transmission power and reflux power of the double-active full-bridge DC-DC converter after per unit treatment under the expansion phase-shift modulation according to a state equation of inductive current;
s3, combining the improved Lagrangian function and the per unit processed transmission power mathematical model, and calculating to obtain the final internal phase shift D 1.end ；
S4, under the condition of expanding phase-shifting modulation, constructing an output voltage state space average equation of the double-active full-bridge DC-DC converter, discretizing the output voltage state space average equation, calculating to obtain a prediction equation of the output voltage of the double-active full-bridge DC-DC converter, and obtaining a predicted value of the output voltage;
s5, outputting electricityThe predicted value of the voltage is equal to the reference value of the output voltage, and the final external phase shift D of the double-active full-bridge DC-DC converter under the expansion phase shift modulation is obtained by calculation 2.end 。
By way of limitation, in step S1, the method for constructing the state equation of the inductor current of the dual active full-bridge DC-DC converter is as follows:
the inductive current has symmetry, so that the working state of the double-active full-bridge DC-DC converter is divided into four stages in a half switching period, state equations of the inductive current are respectively established, and the inductive current value at each moment is obtained;
the four phases are t E [ t ] 0 ，t 1 ]、t∈[t 1 ，t 2 ]、t∈[t 2 ，t 3] and t∈[t3 ，t 4 ]；
t∈[t 0 ，t 1 ]The state equation of the inductor current in the phase is:
wherein ,iL (t) is the value of the current flowing through the inductor at time t, i L (t 0 ) At t 0 The current value flowing through the inductor at any time, n is the transformation ratio of the transformer, U o L is the energy storage inductance value for the output voltage;
t∈[t 1 ，t 2 ]the state equation of the inductor current in the phase is:
wherein ,iL (t 1 ) At t 1 Current value flowing through inductance at moment, U in Is the input voltage;
t∈[t 2 ，t 3 ]the state equation of the inductor current in the phase is:
wherein ,iL (t 2 ) At t 2 The current value flowing through the inductor at any moment;
t∈[t 3 ，t 4 ]the state equation of the inductor current in the phase is:
wherein ,iL (t 3 ) At t 3 The value of the current flowing through the inductor at the moment.
As a further limitation, in step S2, according to the state equation of the inductor current, the mathematical model of the transmission power of the dual-active full-bridge DC-DC converter under extended phase-shift modulation is:
wherein ,PEPS For transmitting power, T hs For half a switching period, u ab Is the primary side output voltage of a double-active full-bridge DC-DC converter, f s For switching frequency, D 1 To the internal phase shift, D 2 Is the external phase shift amount;
under the expansion phase-shifting modulation of the double-active full-bridge DC-DC converter, the mathematical model of the reflux power is as follows:
wherein ,QEPS For return power, k is the transformation ratio of the double-active full-bridge DC-DC converter, k=U in /nU o ；
Maximum transmission power P of double active full-bridge DC-DC converter under single phase shift modulation MAX As a reference value, the expression is:
carrying out per unit processing on the formula (5) and the formula (6) by utilizing the formula (7) to obtain a reflux power mathematical model of the transmission power of the double-active full-bridge DC-DC converter after per unit processing under the expansion phase-shifting modulation;
wherein ,pEPS The transmission power after per unit processing; q EPS The power is the per unit of the reflux power after the treatment.
As yet further defined, in step S3, the lagrangian function expression is:
E＝q EPS +λ(p EPS -p * ) (9)
wherein E is a lagrangian function, p is a given transmission power, and λ is a lagrangian multiplier;
bringing the formula (8) into the formula (9), and deriving the Lagrangian function:
the lambda in the formula (10) is eliminated to obtain an internal phase shift D 1 The expression of (2) is:
p in formula (8) EPS The result is given in equation (11):
in the formula ,
wherein ,Io Load current for the output;
solving the formula (12) to obtain the final internal phase shift D 1.end The method comprises the following steps:
in the formula ,
wherein ,
as yet further defined, in step S4, the output voltage state space average equation of the dual active full-bridge DC-DC converter is:
wherein ,Co The capacitor is a secondary side direct current voltage-stabilizing capacitor, and R is a load resistor;
discretizing the output voltage state space average equation according to a forward Euler method to obtain the discretized output voltage state space average equation:
wherein ,Uo (t i+1 ) At t i+1 Outputting a predicted value of the voltage at the moment, U o (t i ) At t i A time voltage output value;
bringing the formula (18) into the formula (17) to obtain a predictive equation of the output voltage of the double-active full-bridge DC-DC converter and obtain a predictive value U of the output voltage o (t i+1 )：
wherein ,Io (t i ) At t i Current flowing through the load at any time, U in (t i ) At t i The voltage is input at the moment.
As a further limitation, in step S5, the predicted value of the output voltage and the output voltage reference value are equalized, and the result is:
U o (t i+1 )＝U o.ref (20)
wherein ,Uo.ref Is an output voltage reference value;
bringing equation (20) into equation (19) to obtain the external phase shift D 2 The expression of (2) is:
wherein ,Uo.b U is the output voltage after per unit processing o.b ＝U o (t i )/U o.ref ；
Will output a voltage reference value U o.ref And output voltage U o The difference value of the phase difference is input into a PI controller to obtain a compensation voltage delta U, and then is brought into a formula (21) to obtain a final external phase shift D 2.end The method comprises the following steps:
compared with the prior art, the technical proposal adopted by the invention has the following technical progress: the method comprises the steps of firstly, carrying out working mode analysis on a double active full-bridge DC-DC converter under extended phase-shifting modulation, and deducing a mathematical model of transmission power and reflux power; then the final internal phase shift D is obtained according to the improved Lagrangian function 1.end The inhibiting effect on the reflux power is improved; finally according to the outputThe voltage state space average equation is used for obtaining a prediction equation of the output voltage, and obtaining the final external phase shift D 2.end Improving the dynamic response performance.
In conclusion, the method has the advantages of quick dynamic response, high efficiency, simple control process and the like, and has strong practicability.
Drawings
FIG. 1 is a schematic diagram of a topology of a dual active full bridge DC-DC converter according to an embodiment of the present invention;
FIG. 2 shows the working waveform of the dual-active full-bridge DC-DC converter under extended phase-shift modulation according to the embodiment of the invention;
FIG. 3 shows a dual active full bridge DC-DC converter at [ t ] according to an embodiment of the invention 0 ，t 1 ]Working modes under the stage;
FIG. 4 shows a dual active full bridge DC-DC converter at [ t ] according to an embodiment of the invention 1 ，t 2 ]Working modes under the stage;
FIG. 5 shows a dual active full bridge DC-DC converter at [ t ] according to an embodiment of the invention 2 ，t 3 ]Working modes under the stage;
FIG. 6 shows a dual active full bridge DC-DC converter at [ t ] according to an embodiment of the invention 3 ，t 4 ]Working modes under the stage;
FIG. 7 is a control block diagram of the dual active full-bridge DC-DC converter according to the embodiment of the invention under the optimized control method;
fig. 8 is a graph showing a change curve of the reflux power obtained when the dual-active full-bridge DC-DC converter adopts the conventional single phase shift modulation, the conventional extended phase shift modulation and the optimized control method according to the embodiment of the present invention, along with the transmission power after per unit processing;
fig. 9 is a waveform diagram of an output voltage obtained by adopting a conventional single phase-shift modulation, a conventional extended phase-shift modulation and an optimization control method of the embodiment when an output load of a dual-active full-bridge DC-DC converter is suddenly changed in the embodiment of the present invention.
Detailed Description
The invention will be better explained by the following detailed description of the embodiments with reference to the drawings.
Embodiment an optimized control method for double-active full-bridge DC-DC converter
The embodiment includes a method for optimally controlling a dual-active full-bridge DC-DC converter, as shown in FIG. 1, which is a topological structure diagram of the dual-active full-bridge DC-DC converter, wherein a primary full-bridge circuit HB 1 Direct current side of (2) and input voltage U in The alternating current side is connected with the primary side of the transformer T through an energy storage inductor L; secondary full-bridge circuit HB 2 The AC side of the transformer T is connected with the secondary side of the transformer T, and the DC side is connected with the output voltage U o And (5) connection.
Primary side full bridge circuit HB 1 Comprising the following steps: input capacitance C in First switching tube Q forming first full-bridge circuit 1 Second switch tube Q 2 Third switch tube Q 3 Fourth switching tube Q 4 And diode D correspondingly playing a role of freewheeling 1 Diode D 2 Diode D 3 Diode D 4 The method comprises the steps of carrying out a first treatment on the surface of the First full-bridge circuit and primary side direct current voltage stabilizing capacitor C in Parallel connection; secondary full-bridge circuit HB 2 Comprising the following steps: output capacitor C o Fifth switching tube Q forming second full-bridge circuit 5 Sixth switching tube Q 6 Seventh switch tube Q 7 Eighth switching tube Q 8 And diode D correspondingly playing a role of freewheeling 5 Diode D 6 Diode D 7 Diode D 8 The method comprises the steps of carrying out a first treatment on the surface of the Second full-bridge circuit and output capacitor C o And are connected in parallel. Wherein U is ab Outputting voltage for the primary full-bridge circuit; u (u) cd Is the secondary side voltage of the transformer, i L For inductor current, I o The output is loaded with current.
The extended phase-shift control of the double-active full-bridge DC-DC converter of the embodiment has two degrees of freedom of phase-shift control, namely the internal phase-shift D 1 And the amount of external phase shift D 2 . Wherein the internal phase shift amount D 1 Is a first switch tube Q 1 Lagging behind fourth switching tube Q 4 The amount of phase shift that is turned on; external phase shift D 2 Is a fifth switch tube Q 5 Lag behind the first switching tube Q 1 Opening upIs used for the phase shift of the optical fiber.
The embodiment comprises the following steps:
s1, carrying out working mode analysis on a double-active full-bridge DC-DC converter under extended phase-shift modulation, and constructing a state equation of inductance current of the double-active full-bridge DC-DC converter;
in the step, the method for constructing the state equation of the inductance current of the double-active full-bridge DC-DC converter comprises the following steps:
the inductive current has symmetry, so that only half switching period is analyzed, the working state of the double-active full-bridge DC-DC converter is divided into four stages, state equations of the inductive current are respectively established, and the inductive current value at each moment is obtained; as shown in FIG. 2, the working waveform of the double-active full-bridge DC-DC converter under the expansion phase-shift modulation is shown, and as can be seen from the waveform diagram of FIG. 2, t 0 -t 4 The four time periods add together to be a half switching period;
as shown in fig. 3 to 6, the working modes of the double-active full-bridge DC-DC converter in four stages are shown; the four stages are t E [ t ] 0 ，t 1 ]、t∈[t 1 ，t 2 ]、t∈[t 2 ，t 3] and t∈[t3 ，t 4 ]；
As shown in FIG. 3, t ε [ t ] 0 ，t 1 ]Stage: primary side full bridge circuit HB 1 Inner second switch tube Q 2 And a fourth switching tube Q 4 Conduction and secondary side full-bridge circuit HB 2 Inner sixth switch tube Q 6 And a seventh switching tube Q 7 On, but now the current i flowing through the energy storage inductance L L Is negative, so the primary side full bridge circuit HB 1 Internally pass through a second switch tube Q 2 And diode D 4 Follow current is carried out, and a secondary full-bridge circuit HB 2 Inner pass diode D 6 And diode D 7 Follow current can be deduced as t E [ t ] 0 ，t 1 ]The state equation of the inductor current in the phase is:
wherein ,iL (t) is the value of the current flowing through the inductor at time t, i L (t 0 ) At t 0 The current value flowing through the inductor at any time, n is the transformation ratio of the transformer, U o L is the energy storage inductance value for the output voltage;
as shown in FIG. 4, t ε [ t ] 1 ，t 2 ]Stage: primary side full bridge circuit HB 1 Inner first switch tube Q 1 And a fourth switching tube Q 4 Conduction and secondary side full-bridge circuit HB 2 Inner sixth switch tube Q 6 And a seventh switching tube Q 7 On, but now the current i flowing through the energy storage inductance L L Is still negative, so the primary side full bridge circuit HB 1 Inner pass diode D 1 And diode D 4 Follow current is carried out, and a secondary full-bridge circuit HB 2 Inner pass diode D 6 And diode D 7 Follow current can be deduced as t E [ t ] 1 ，t 2 ]The state equation of the inductor current in the phase is:
wherein ,iL (t 1 ) At t 1 Current value flowing through inductance at moment, U in Is the input voltage;
as shown in FIG. 5, t ε [ t ] 2 ，t 3 ]Stage: primary side full bridge circuit HB 1 Inner first switch tube Q 1 And a fourth switching tube Q 4 Conduction and secondary side full-bridge circuit HB 2 Inner sixth switch tube Q 6 And a seventh switching tube Q 7 On, at t 2 At the moment, the current i flowing through the energy storage inductance L L From negative to positive, so the primary side full bridge circuit HB 1 Internally pass through a first switch tube Q 1 And a fourth switching tube Q 4 Carry out transmission current, secondary side full bridge circuit HB 2 Inner through sixth switch tube Q 6 And a seventh switching tube Q 7 By transmitting current, t E t can be deduced 2 ，t 3 ]The state equation of the inductor current in the phase is:
wherein ,iL (t 2 ) At t 2 The current value flowing through the inductor at any moment;
as shown in FIG. 6, t ε [ t ] 3 ，t 4 ]Stage: primary side full bridge circuit HB 1 Inner first switch tube Q 1 And a fourth switching tube Q 4 Conduction and secondary side full-bridge circuit HB 2 Inner fifth switch tube Q 5 And an eighth switching tube Q 8 Conduction, current i flowing through energy storage inductance L L Positive, so the primary full-bridge circuit HB 1 Internally pass through a first switch tube Q 1 And a fourth switching tube Q 4 Carry out transmission current, secondary side full bridge circuit HB 2 Inner pass diode D 5 And diode D 8 Follow current can be deduced as t E [ t ] 3 ，t 4 ]The state equation of the inductor current in the phase is:
wherein ,iL (t 3 ) At t 3 The current value flowing through the inductor at any moment;
s2, deducing a mathematical model of transmission power and reflux power of the double-active full-bridge DC-DC converter after per unit treatment under the expansion phase-shift modulation according to a state equation of inductive current;
in the step, as the inductance current has symmetry, the mathematical model of the transmission power and the reflux power in one period can be deduced by the formulas (1) to (4);
therefore, according to the state equation of the inductive current, the mathematical model of the transmission power of the double-active full-bridge DC-DC converter under the expanding phase-shifting modulation is as follows:
wherein ,PEPS For transmitting power, T hs Is half of the switch cycleStage u ab Is the primary side output voltage of a double-active full-bridge DC-DC converter, f s For switching frequency, D 1 To the internal phase shift, D 2 Is the external phase shift amount;
under the expansion phase-shifting modulation of the double-active full-bridge DC-DC converter, the mathematical model of the reflux power is as follows:
wherein ,QEPS For return power, k is the transformation ratio of the double-active full-bridge DC-DC converter, k=U in /nU o ；
For easy analysis and calculation, the maximum transmission power P of the double active full-bridge DC-DC converter under single phase shift modulation is set MAX As a reference value, the expression is:
carrying out per unit processing on the formula (5) and the formula (6) by utilizing the formula (7) to obtain a transmission power reflux power mathematical model of the double-active full-bridge DC-DC converter after per unit processing under the expansion phase-shift modulation;
wherein ,pEPS The transmission power after per unit processing; q EPS The power is the reflux power after per unit treatment;
s3, ensuring transmission power while suppressing reflux power, and calculating to obtain final internal phase shift D by combining an improved Lagrange function and a per unit processed transmission power mathematical model 1.end ；
In this step, the Lagrangian function expression is:
E＝q EPS +λ(p EPS -p * ) (9)
wherein E is Lagrangian functionNumber, p * For a given transmission power, λ is the lagrange multiplier;
bringing the formula (8) into the formula (9), and deriving the Lagrangian function:
wherein, eta is the public part of two partial guide results;
in the traditional Lagrangian function solving process, eta and lambda in the formula (10) are simultaneously eliminated to obtain an internal phase shift D 1 With the external phase shift amount D 2 In the expression (2), lambda in the expression (10) is eliminated to obtain an internal phase shift D 1 The expression of (2) is:
p in formula (8) EPS The external phase shift D is eliminated by bringing the same into the formula (11) 2 Obtaining the internal phase shift D 1 The expression of (2) is:
in the formula ,
equation (12) is a standard of a unitary fourth-order equation, and the final internal phase shift D is obtained by solving equation (12) 1.end The method comprises the following steps:
in the formula ,
wherein ,
s4, under the condition of expanding phase-shifting modulation, constructing an output voltage state space average equation of the double-active full-bridge DC-DC converter, discretizing the output voltage state space average equation, calculating to obtain a prediction equation of the output voltage of the double-active full-bridge DC-DC converter, and obtaining a predicted value of the output voltage; in this step, the traditional PI control is replaced by model prediction, specifically:
under the expanding phase-shifting modulation, the output voltage state space average equation of the double-active full-bridge DC-DC converter is as follows:
wherein ,Co The capacitor is a secondary side direct current voltage-stabilizing capacitor, and R is a load resistor;
discretizing the output voltage state space average equation according to a forward Euler method to obtain the discretized output voltage state space average equation:
wherein ,Uo (t i+1 ) At t i+1 Outputting a predicted value of the voltage at the moment, U o (t i ) At t i A time voltage output value;
bringing the formula (18) into the formula (17) to obtain a predictive equation of the output voltage of the double-active full-bridge DC-DC converter and obtain a predictive value U of the output voltage o (t i+1 )：
wherein ,Io (t i ) At t i Current flowing through the load at any time, U in (t i ) At t i Inputting voltage at moment;
s5, in order to enable the output voltage to follow the output voltage reference value, enabling the predicted value of the output voltage to be equal to the output voltage reference value, and calculating to obtain the final external phase shift D of the double-active full-bridge DC-DC converter under the expansion phase shift modulation 2.end ；
Equalizing the predicted value of the output voltage with the reference value of the output voltage to obtain:
U o (t i+1 )＝U o.ref (20)
wherein ,Uo.ref Is an output voltage reference value;
bringing equation (20) into equation (19) to obtain the external phase shift D 2 The expression of (2) is:
wherein ,Uo.b U is the output voltage after per unit processing o.b ＝U o (t i )/U o.ref ；
Because the formula (21) is a mathematical model obtained under ideal conditions, the output voltage needs to be compensated in actual application, so that the output voltage can be stabilized at a reference value in a steady state; thus will output a voltage reference value U o.ref And output voltage U o The difference value of the phase difference is input into a PI controller to obtain a compensation voltage delta U, and then is brought into a formula (21) to obtain a final external phase shift D 2.end The method comprises the following steps:
as shown in fig. 7, the input voltage U of the double active full bridge DC-DC converter is sampled in Output voltage U o Output side load current I o Information by combining twoThe final internal phase shift D is solved by the transmission power mathematical model processed by the per unit of the active full-bridge DC-DC converter and the improved Lagrange multiplier method 1.end The predicted value of the output voltage in the next control period is obtained by combining the output voltage state space average equation of the double-active full-bridge DC-DC converter, so that the predicted value of the output voltage is equal to the output voltage reference value, and the final external phase shift D is obtained 2.end The final internal phase shift D obtained by the formula (14) 1.end And the final external phase shift D calculated by the formula (22) 2.end Input to the phase shift modulation module to control the first switch tube Q 1 Eighth switching tube Q 8 Conducting.
As shown in fig. 8, the dual-active full-bridge DC-DC converter adopts a conventional single phase shift (SPS in the figure), a conventional extended phase shift (EPS in the figure) and an optimized control method of the present embodiment (ML-EPS in the figure), so as to obtain a change curve of the reflux power along with the transmission power after per unit of the conversion treatment; the parameters set in fig. 8 are shown in table 1. As can be seen from the graph, the peak value of the reflux power under the conventional SPS modulation is maximum, and compared with the conventional SPS, the peak value of the reflux power under the conventional EPS modulation is obviously reduced, and the ML-EPS modulation of the embodiment has the most ideal effect of suppressing the reflux power, so that zero reflux power can be realized.
TABLE 1
As shown in FIG. 9, the per unit value p of the output power is shown when the output load of the double-active full-bridge DC-DC converter is suddenly changed EPS When the voltage is suddenly changed from 0.68 to 0.41, the waveform diagram of the output voltage obtained by adopting the traditional single phase shift modulation, the traditional extended phase shift modulation and the optimal control method of the embodiment can be seen from the diagram, the dynamic characteristics of the traditional SPS modulation and the EPS modulation are poor, and the dynamic characteristics of the ML-EPS modulation of the embodiment are ideal.
It should be noted that the foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, but the present invention is described in detail with reference to the foregoing embodiment, and it will be apparent to those skilled in the art that modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some of the technical features thereof. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. The double-active full-bridge DC-DC converter optimal control method is characterized by comprising the following steps of:
s1, carrying out working mode analysis on a double-active full-bridge DC-DC converter under extended phase-shift modulation, and constructing a state equation of inductance current of the double-active full-bridge DC-DC converter;
s2, deducing a mathematical model of transmission power and reflux power of the double-active full-bridge DC-DC converter after per unit treatment under the expansion phase-shift modulation according to a state equation of inductive current;
s3, combining the improved Lagrangian function and the per unit processed transmission power mathematical model, and calculating to obtain the final internal phase shift D 1.end ；
S4, under the condition of expanding phase-shifting modulation, constructing an output voltage state space average equation of the double-active full-bridge DC-DC converter, discretizing the output voltage state space average equation, calculating to obtain a prediction equation of the output voltage of the double-active full-bridge DC-DC converter, and obtaining a predicted value of the output voltage;
s5, enabling the predicted value of the output voltage to be equal to the reference value of the output voltage, and calculating to obtain the final external phase shift D of the double-active full-bridge DC-DC converter under the expansion phase shift modulation 2.end 。
2. The method for optimizing control of a dual active full-bridge DC-DC converter according to claim 1, wherein in step S1, the method for constructing an equation of state of an inductor current of the dual active full-bridge DC-DC converter is as follows:
the inductive current has symmetry, so that the working state of the double-active full-bridge DC-DC converter is divided into four stages in a half switching period, state equations of the inductive current are respectively established, and the inductive current value at each moment is obtained;
the four phases are t E [ t ] 0 ，t 1 ]、t∈[t 1 ，t 2 ]、t∈[t 2 ，t 3] and t∈[t3 ，t 4 ]；
t∈[t 0 ，t 1 ]The state equation of the inductor current in the phase is:
wherein ,iL (t) is the value of the current flowing through the inductor at time t, i L (t 0 ) At t 0 The current value flowing through the inductor at any time, n is the transformation ratio of the transformer, U o L is the energy storage inductance value for the output voltage;
t∈[t 1 ，t 2 ]the state equation of the inductor current in the phase is:
wherein ,iL (t 1 ) At t 1 Current value flowing through inductance at moment, U in Is the input voltage;
t∈[t 2 ，t 3 ]the state equation of the inductor current in the phase is:
wherein ,iL (t 2 ) At t 2 The current value flowing through the inductor at any moment;
t∈[t 3 ，t 4 ]the state equation of the inductor current in the phase is:
wherein ,iL (t 3 ) At t 3 The value of the current flowing through the inductor at the moment.
3. The method for optimizing control of a dual-active full-bridge DC-DC converter according to claim 2, wherein in step S2, according to a state equation of an inductor current, a mathematical model of transmission power of the dual-active full-bridge DC-DC converter under extended phase-shift modulation is:
wherein ,PEPS For transmitting power, T hs For half a switching period, u ab Is the primary side output voltage of a double-active full-bridge DC-DC converter, f s For switching frequency, D 1 To the internal phase shift, D 2 Is the external phase shift amount;
under the expansion phase-shifting modulation of the double-active full-bridge DC-DC converter, the mathematical model of the reflux power is as follows:
wherein ,QEPS For return power, k is the transformation ratio of the double-active full-bridge DC-DC converter, k=U in /nU o ；
Maximum transmission power P of double active full-bridge DC-DC converter under single phase shift modulation MAX As a reference value, the expression is:
carrying out per unit processing on the formula (5) and the formula (6) by utilizing the formula (7) to obtain a mathematical model of transmission power and reflux power of the double-active full-bridge DC-DC converter after per unit processing under the condition of expanding phase-shifting modulation;
wherein ,pEPS The transmission power after per unit processing; q EPS The power is the per unit of the reflux power after the treatment.
4. The method for optimizing control of a dual active full-bridge DC-DC converter according to claim 3, wherein in step S3, the lagrangian function expression is:
E＝q EPS +λ(p EPS -p * ) (9)
wherein E is a lagrangian function, p is a given transmission power, and λ is a lagrangian multiplier;
bringing the formula (8) into the formula (9), and deriving the Lagrangian function:
the lambda in the formula (10) is eliminated to obtain an internal phase shift D 1 The expression of (2) is:
p in formula (8) EPS The result is given in equation (11):
in the formula ,
wherein ,Io Load current for the output;
solving the formula (12) to obtain the final internal phase shift D 1.end The method comprises the following steps:
in the formula ,
wherein ,
5. the method for optimizing control of a dual active full-bridge DC-DC converter according to claim 4, wherein in step S4, the output voltage state space average equation of the dual active full-bridge DC-DC converter is:
wherein ,Co The capacitor is a secondary side direct current voltage-stabilizing capacitor, and R is a load resistor;
discretizing the output voltage state space average equation according to a forward Euler method to obtain the discretized output voltage state space average equation:
wherein ,Uo (t i+1 ) At t i+1 Outputting a predicted value of the voltage at the moment, U o (t i ) At t i A time voltage output value;
bringing the formula (18) into the formula (17) to obtain a predictive equation of the output voltage of the double-active full-bridge DC-DC converter and obtain a predictive value U of the output voltage o (t i+1 )：
wherein ,Io (t i ) At t i Current flowing through the load at any time, U in (t i ) At t i The voltage is input at the moment.
6. The method according to claim 5, wherein in step S5, the predicted value of the output voltage and the reference value of the output voltage are equalized to obtain:
U o (t i+1 )＝U o.ref (20)
wherein ,Uo.ref Is an output voltage reference value;
bringing equation (20) into equation (19) to obtain the external phase shift D 2 The expression of (2) is:
wherein ,Uo.b U is the output voltage after per unit processing o.b ＝U o (t i )/U o.ref ；
Will output a voltage reference value U o.ref And output voltage U o The difference value of the phase difference is input into a PI controller to obtain a compensation voltage delta U, and then is brought into a formula (21) to obtain a final external phase shift D 2.end The method comprises the following steps:
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