CN111277141A - Bidirectional DC/DC converter optimization control method - Google Patents

Bidirectional DC/DC converter optimization control method Download PDF

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CN111277141A
CN111277141A CN202010132057.2A CN202010132057A CN111277141A CN 111277141 A CN111277141 A CN 111277141A CN 202010132057 A CN202010132057 A CN 202010132057A CN 111277141 A CN111277141 A CN 111277141A
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firework
mode
current
converter
formula
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陈启宏
文雅钦
章子祎
张立炎
周克亮
肖朋
刘莉
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Wuhan University of Technology WUT
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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
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L50/00—Electric propulsion with power supplied within the vehicle
    • B60L50/40—Electric propulsion with power supplied within the vehicle using propulsion power supplied by capacitors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L50/00—Electric propulsion with power supplied within the vehicle
    • B60L50/50—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells
    • B60L50/60—Electric propulsion with power supplied within the vehicle using propulsion power supplied by batteries or fuel cells using power supplied by batteries
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L2210/00—Converter types
    • B60L2210/10—DC to DC converters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L2260/00—Operating Modes
    • B60L2260/10—Temporary overload
    • B60L2260/16—Temporary overload of electrical drive trains
    • B60L2260/162—Temporary overload of electrical drive trains of electrical cells or capacitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/72—Electric energy management in electromobility

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention relates to the technical field of DC/DC converters, in particular to a bidirectional DC/DC converter optimization control method, which comprises the following steps: calculating to obtain a transfer function from the duty ratio of each mode to the inductive current according to equivalent circuits of the DC/DC converter in different modes; discrete change is carried out on the transfer function from the duty ratio of each mode to the inductive current, and a corresponding time domain expression is obtained; obtaining a corresponding inductive current prediction equation according to the time domain expression from the duty ratio of each mode to the inductive current; combining the inductive current prediction equation of each mode with a value function and a constraint condition, and calculating by adopting a firework algorithm to obtain an optimal duty ratio in each mode; and optimally controlling the power circuit of the DC/DC converter by using the corresponding duty ratio for each mode. The invention can smoothly and quickly track the target value and provides better dynamic and steady-state performance.

Description

Bidirectional DC/DC converter optimization control method
Technical Field
The invention relates to the technical field of DC/DC converters, in particular to an optimization control method of a bidirectional DC/DC converter.
Background
With the development of the automobile industry and the improvement of the living standard of people, the demand of automobiles is increasing day by day, and the emission of automobile exhaust gradually brings more and more harm to the living environment of people. The problems of environmental pollution, heavy use of petroleum and the like are gradually paid attention to by people and are two major problems which need to be solved urgently in the modern society. The driving principle of an Electric Vehicle (EV) is that the original mode of using gasoline as the only energy source is replaced by electric energy, so that the environmental pollution caused by gasoline combustion can be well reduced, the petroleum consumption is saved, and the energy utilization efficiency is high. The automobile fuel can solve the problems of the traditional fuel automobile and bring benefits to the development of the society.
Various electric automobiles have high requirements on power systems, and the development of the electric automobiles is limited by the problems of insufficient power batteries, insufficient starting or accelerating power, waste of braking energy, limited service life and the like. The new energy hybrid electric vehicle has a wide application prospect, and the bidirectional DC/DC converter is a key component in the new energy hybrid electric vehicle and is one of the research hotspots in the field at present. In such a hybrid power supply, a bidirectional DC/DC converter is a key to its energy management. When the electric automobile accelerates, the super capacitor provides required instantaneous power for the automobile, and energy can be fed back to the super capacitor through the bidirectional DC/DC converter for storage during deceleration, so that the driving capability of an electric automobile power system is improved to a great extent, and the driving distance of single charging of the automobile is increased. For such a key device which needs to have high real-time performance, high reliability and high stability, more and more researchers and scientific research laboratories have successively started to discuss and research the implementation technology thereof.
At present, both the topology structure of the bidirectional DC/DC converter and the modulation technology of the power switching tube have been implemented in a very complete way, so in order to meet the application requirements of the bidirectional DC/DC converter in the electric vehicle, selecting an appropriate optimal control algorithm is the key to achieve good control performance of the bidirectional DC/DC converter.
Disclosure of Invention
The bidirectional DC/DC converter optimization control method provided by the invention can smoothly and quickly track the target value and provides better dynamic and steady-state performance.
The invention provides a bidirectional DC/DC converter optimization control method, which comprises the following steps:
calculating to obtain a transfer function from the duty ratio of each mode to the inductive current according to equivalent circuits of the DC/DC converter in different modes;
discrete change is carried out on the transfer function from the duty ratio of each mode to the inductive current, and a corresponding time domain expression is obtained;
obtaining a corresponding inductive current prediction equation according to the time domain expression from the duty ratio of each mode to the inductive current;
combining the inductive current prediction equation of each mode with a value function and a constraint condition, and calculating by adopting a firework algorithm to obtain an optimal duty ratio in each mode;
and optimally controlling the power circuit of the DC/DC converter by using the corresponding duty ratio for each mode.
Further, the calculating, according to equivalent circuits of the DC/DC converter in different modes, a transfer function from a duty ratio of each mode to an inductor current includes:
for the current mode:
obtaining an average value expression of corresponding inductive voltage according to the inductive voltage expression of the power circuit in different time periods;
acquiring a state space average equation of the inductive current of the power circuit;
sorting an average value expression of the inductive voltage of the power circuit and a state space average equation of the inductive current to obtain a small signal model in the current mode;
and performing Laplace transformation on the small signal model to obtain a transfer function from the duty ratio of the current mode to the inductive current.
Still further, the modes include: buck mode and boost mode;
the buck mode represents that energy in the DC/DC converter flows from the lithium battery side to the super capacitor side;
the boost mode indicates that energy flows from the supercapacitor side to the lithium battery side in the DC/DC converter.
Still further, the transfer function from the duty cycle of the buck mode to the inductor current is:
Figure BDA0002396052640000021
in the formula, RERepresenting equivalent series resistance, V, at the supercapacitor sidebatThe voltage of the lithium battery terminal, C represents the equivalent capacitance value of a super capacitor in the power circuit, and L represents the inductance value, wherein the inductance value of a first inductor (L1) in the power circuit is equal to that of a second inductor (L2) in the power circuit;
the transfer function of the duty cycle of the boost mode to the inductor current is:
Figure BDA0002396052640000022
in the formula, RESRRepresents the equivalent internal resistance of the lithium battery side, V0Is the output voltage in boost mode, C1Representing the capacitance value of a filter capacitor in the power circuit.
Still further, the inductor current prediction equation of the buck mode is as follows:
Figure BDA0002396052640000031
in the formula iL1(k + p | k) and iL2(k + p | k) represents the predicted values of the two-phase inductor current at the time k to the time (k + p), and b0，b1，a1，a2Inputting and outputting coefficients for the DC/DC converter;
the inductor current prediction equation of the boost mode is as follows:
Figure BDA0002396052640000032
in the formula iL1(k + p | k) and iL2(k + p | k) represents the predicted values of the two-phase inductor current at the time k to the time (k + p), and b2，b3，a3，a4The input and output coefficients of the DC/DC converter.
In the above technical solution, the expression of the cost function and the constraint condition is:
Figure BDA0002396052640000033
wherein q is an output deviation weight coefficient of the DC/DC converter, r is a control weight coefficient of the DC/DC converter, iL(k + i) denotes the reference value of the inductor current at the moment k + iLThe (k + i | k) represents a predicted value of the inductor current at the time k to the time k + i, and the Δ d (k + i) represents an increment of the duty ratio of the switching tube in the DC/DC converter.
In the above technical solution, the calculating to obtain the optimal duty ratio in each mode by using the firework algorithm specifically includes:
obtaining a preset number of duty ratios as initial fireworks to perform current iteration:
calculating the fitness value of each initial firework through a constraint condition;
calculating the number of sparks which can be generated by each initial firework and the explosion range through the fitness value of each initial firework;
after each initial firework explodes, calculating the displacement of each spark in each initial firework population according to the corresponding spark number and the explosion range;
aiming at each initial firework population:
keeping the individual with the minimum fitness value; the individuals include fireworks and sparks;
the distance between any two bodies;
selecting next generation individuals except the individuals with the minimum fitness value according to the distance between any two individuals;
taking the next generation of individuals selected from each initial firework population as initial fireworks of the next iteration process;
until the error between the inductance current corresponding to the individual with the minimum reserved fitness value and the given inductance current reaches a preset threshold value, or the iteration times reach preset times;
the optimal duty cycle is the spark corresponding to the individual with the minimum fitness value.
Further, the calculation formula of the number of sparks generated by each initial firework is as follows:
Figure BDA0002396052640000041
in the formula, Si is the number of sparks generated by the ith firework, m is a constant and used for limiting the total number of the generated sparks, and Ymax is the fitness value of the individual with the worst fitness value in the current firework population; f (x)i) Is an individual xiF () is a cost function, and epsilon is a minimal constant;
in order to limit the number of sparks which can be generated by each initial firework, a firework limiting formula is set:
Figure BDA0002396052640000042
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000043
the number of sparks that can be generated for the ith firework; round () is a rounding function; a and b are given constants;
the calculation formula of the explosion range of each initial firework is as follows:
Figure BDA0002396052640000044
in the formula, Ai is the explosion range of the ith firework, namely, the spark generated by the current firework explosion will randomly generate displacement within the range, but cannot exceed the range;
Figure BDA0002396052640000045
and the constant value represents the maximum explosion amplitude, and Ymin is the fitness value of the individual with the minimum fitness value in the current firework population.
Further, the displacement of the spark is calculated by the formula:
Figure BDA0002396052640000046
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000047
indicating the location in the k dimension of the ith spark in the current firework population, round (0, A)i) Representing a uniform random number, i.e. a random solution, generated within the corresponding explosion range;
in order to ensure that the sparks generated by each firework are in a feasible domain, a modular operation mapping rule is introduced:
Figure BDA0002396052640000048
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000049
and
Figure BDA00023960526400000410
respectively, the upper and lower boundaries of the boundary in the k-th dimension,% represents the modulo operation.
Still further, the calculation formula of the distance between two individuals in the initial firework population is as follows:
Figure BDA00023960526400000411
in the formula, d (x)i,xj) Representing any two individuals xiAnd xjJ e K represents that the j-th position belongs to a set K, and the set K is a set of positions of sparks in the current firework population.
In the invention, the firework algorithm is used for the first time in the research field of the bidirectional DC/DC converter. The firework algorithm adopts a distributed information sharing mechanism, determines the explosion intensity and the radiation amplitude according to the fitness values of fireworks distributed in different areas, and simultaneously maintains an optimal firework in the whole iteration process, and adopts an elite strategy. The method combines an inductive current prediction equation, a constraint condition and a value function, then adopts a firework algorithm to obtain the optimal duty ratio, and optimally controls the bidirectional DC/DC converter through the optimal duty ratio, thereby providing better dynamic and steady-state performance.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method in an embodiment of the present invention;
FIG. 2 is a control schematic diagram of buck mode according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating the control of the boost mode in an embodiment of the present invention;
FIG. 4 is a flow chart of a firework algorithm according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the method for optimally controlling a bidirectional DC/DC converter provided by this embodiment includes:
101. calculating to obtain a transfer function from the duty ratio of each mode to the inductive current according to equivalent circuits of the DC/DC converter in different modes;
102. discrete change is carried out on the transfer function from the duty ratio of each mode to the inductive current, and a corresponding time domain expression is obtained;
103. obtaining a corresponding inductive current prediction equation according to the time domain expression from the duty ratio of each mode to the inductive current;
104. combining the inductive current prediction equation of each mode with a value function and a constraint condition, and calculating by adopting a firework algorithm to obtain an optimal duty ratio in each mode;
105. and optimally controlling the power circuit of the DC/DC converter by using the corresponding duty ratio for each mode.
In the embodiment, the firework algorithm is used for the first time in the research field of the bidirectional DC/DC converter. The firework algorithm adopts a distributed information sharing mechanism, determines the explosion intensity and the radiation amplitude according to the fitness values of fireworks distributed in different areas, and simultaneously maintains an optimal firework in the whole iteration process, and adopts an elite strategy. The method combines an inductive current prediction equation, a constraint condition and a value function, then adopts a firework algorithm to obtain the optimal duty ratio, and optimally controls the bidirectional DC/DC converter through the optimal duty ratio, thereby providing better dynamic and steady-state performance.
Example one
As shown in FIG. 2, when the setting circuit works in Buck mode, the energy in the system flows from the lithium battery side to the super capacitor side, and at this time, Q on the arm a is connected3And Q on the b arm4Keep off, Q on arm a1And Q on the b arm2The input phases differ by a control duty cycle of one half cycle.
The 101 specifically includes:
for the current mode:
1011. obtaining an average value expression of corresponding inductive voltage according to the inductive voltage expression of the power circuit in different time periods;
1012. acquiring a state space average equation of the inductive current of the power circuit;
1013. sorting an average value expression of the inductive voltage of the power circuit and a state space average equation of the inductive current to obtain a small signal model in the current mode;
in this embodiment, since it is assumed that the inductance is large, the inductor current is continuous, and then a state space average equation of the inductor current can be obtained by adding a small disturbance amount to the duty ratio and the input voltage near the steady-state operating point, and finally, a small signal model in the Buck mode can be obtained after sorting:
Figure BDA0002396052640000061
in the formula, L1Is the inductance value of the first inductor L1, L2Is the inductance value of the second inductor L2, L1＝L2＝L，VbatIs the voltage of the lithium battery terminal, Vc is the voltage of the two ends of the super capacitor C, iL1Is the current i on the first inductor L1L2Is the current, R, in the second inductor L2ERepresenting the equivalent series resistance at the side of the super capacitor, C is the capacitance value of the super capacitor,
Figure BDA0002396052640000062
in order to disturb the amount of disturbance of the switching tube Q1,
Figure BDA0002396052640000071
for the disturbance amount of the switching tube Q2, D1 is the duty ratio of the switching tube Q1 in the steady state, and D2 is the duty ratio of the switching tube Q2 in the steady state.
1014. Performing Laplace transformation on the small signal model to obtain a transfer function from the duty ratio of the current mode to the inductive current;
the transfer function from the duty ratio of the buck mode to the inductive current obtained by performing the Laplace conversion on the formula (1) is as follows:
Figure BDA0002396052640000072
in the formula, RERepresenting equivalent series resistance, V, at the supercapacitor sidebatThe voltage of the lithium battery terminal, C represents the equivalent capacitance value of a super capacitor in the power circuit, and L represents the inductance value, wherein the inductance value of a first inductor L1 in the power circuit is equal to that of a second inductor L2 in the power circuit;
the 102 specifically includes:
the discretization model can be obtained by performing Z transformation on the formula (3):
Figure BDA0002396052640000073
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000074
Figure BDA0002396052640000075
the time domain expression of equation (4) is:
iL(k)＝-a1iL(k-1)-a2iL(k-2)+b0d(k)+b1d(k-1) (5)
in the formula, b0，b1，a1，a2Inputting and outputting coefficients for the DC/DC converter;
the step 103 specifically includes:
in conclusion, a prediction equation of the two-phase inductor current at the time k + p, namely an inductor current prediction equation in the buck mode, is obtained:
Figure BDA0002396052640000076
in the formula iL1(k + p | k) and iL2(k + p | k) represents time k to time (k + p), respectivelyAnd (3) a predicted value of the two-phase inductive current, wherein the duty ratio of the switching tube is a system control variable, and the inductive current is a system output variable.
The step 104 specifically includes:
1041. obtaining a preset number of duty ratios as initial fireworks to perform current iteration:
in the embodiment, in the range of (0,1), 5 values are randomly given as initial fireworks (duty ratio), and the fitness value corresponding to each fireworks is calculated through a value function j (k);
the expression of the cost function and the constraint condition is as follows:
Figure BDA0002396052640000081
wherein q is an output deviation weight coefficient of the DC/DC converter, r is a control weight coefficient of the DC/DC converter, iL(k + i) denotes the reference value of the inductor current at the moment k + iL(k + i | k) represents a predicted value of the inductive current at the k moment to the k + i moment, and delta d (k + i) represents the duty ratio increment of a switching tube in the DC/DC converter;
1042. calculating the fitness value of each initial firework through a constraint condition;
1043. calculating the number of sparks which can be generated by each initial firework and the explosion range through the fitness value of each initial firework;
the calculation formula of the number of sparks generated by each initial firework is as follows:
Figure BDA0002396052640000082
in the formula, Si is the number of sparks generated by the ith firework, m is a constant and used for limiting the total number of the generated sparks, and Ymax is the fitness value of the individual with the worst fitness value in the current firework population; f (x)i) Is an individual xiF () is a cost function, and epsilon is a minimal constant;
the function of epsilon is to avoid the situation that the denominator is zero;
in order to limit the number of sparks which can be generated by each initial firework to be too large or too small, a firework limiting formula is set:
Figure BDA0002396052640000083
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000084
the number of sparks that can be generated for the ith firework; round () is a rounding function; a and b are given constants; taking a as 0.8 and b as 0.04;
the calculation formula of the explosion range of each initial firework is as follows:
Figure BDA0002396052640000085
in the formula, Ai is the explosion range of the ith firework, namely, the spark generated by the current firework explosion will randomly generate displacement within the range, but cannot exceed the range;
Figure BDA0002396052640000086
and the constant value represents the maximum explosion amplitude, and Ymin is the fitness value of the individual with the minimum fitness value in the current firework population.
1043. After each initial firework explodes, calculating the displacement of each spark in each initial firework population according to the corresponding spark number and the explosion range;
the formula for calculating the displacement of the spark is:
Figure BDA0002396052640000091
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000092
indicating the location in the k dimension of the ith spark in the current firework population, round (0, A)i) Representing a uniform random number, i.e. a random solution, generated within the corresponding explosion range;
in order to ensure that the sparks generated by each firework are in a feasible domain, a modular operation mapping rule is introduced:
Figure BDA0002396052640000093
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000094
and
Figure BDA0002396052640000095
respectively representing the upper and lower boundaries of the boundary on the k dimension,% represents the modular operation;
in the present embodiment, it is preferred that,
Figure BDA0002396052640000096
as shown in fig. 4, for each initial firework population:
1044. keeping the individual with the minimum fitness value; the individuals include fireworks and sparks;
1045. the distance between any two bodies;
the calculation formula of the distance between the two individuals in the initial firework population is as follows:
Figure BDA0002396052640000097
in the formula, d (x)i,xj) Representing any two individuals xiAnd xjJ e K represents that the j-th position belongs to a set K, and the set K is a set of positions of sparks in the current firework population.
1046. Selecting next generation individuals except the individuals with the minimum fitness value according to the distance between any two individuals;
selecting next generation individuals by roulette among the rest N-1 individuals on the premise of keeping the optimal value of each generation of individuals, wherein the probability of each individual being selected is p (x)i) Represents:
Figure BDA0002396052640000098
1047. taking the next generation of individuals selected from each initial firework population as initial fireworks of the next iteration process;
1048. until the error between the inductor current corresponding to the individual with the minimum reserved fitness value and the given inductor current reaches a preset threshold value, or the iteration number reaches a preset number. At this time, the "spark" corresponding to the individual with the minimum fitness value is the optimal duty ratio.
In the present embodiment, an expression of an average value of the inductor voltage is column-written according to an expression of the inductor voltage over different time periods; the method comprises the steps that as the inductance is assumed to be large, the inductance current is continuous, then a state space average equation of the inductance current can be obtained by adding a small disturbance quantity to the duty ratio near a steady-state working point and the input voltage, and finally a small signal model in a Buck mode can be obtained after arrangement; obtaining a transfer function from the duty ratio to the inductive current in the Buck mode after the Laplace conversion; discretizing the obtained transfer function from the duty ratio to the inductive current to obtain a time domain expression between the inductive current and the duty ratio, and finally obtaining a prediction equation of the inductive current; and solving by adopting a firework algorithm according to the defined value function and the constraint condition to obtain the optimal duty ratio acting on the switching tube at the next moment, thereby realizing the optimal control of the DC/DC converter.
Example two
As shown in fig. 3, when the setting circuit operates in the Boost mode, energy in the system flows from the supercapacitor side to the lithium battery side, at this time, Q1 on the a-arm and Q2 on the b-arm are kept off, Q3 on the a-arm and Q4 on the b-arm input control duty ratios with a phase difference of half a cycle, and an average value expression of the inductor voltage is listed according to expressions of the inductor voltage at different time periods; because the inductance is supposed to be large, the inductance current is continuous, then a state space average equation of the inductance current can be obtained by adding a small disturbance quantity to the duty ratio near the steady-state working point and the input voltage, and finally a small signal model in a Boost mode can be obtained after arrangement; obtaining a transfer function from the duty ratio to the inductive current in a Boost mode after Ralsberg transformation; discretizing the obtained transfer function from the duty ratio to the inductive current to obtain a time domain expression between the inductive current and the duty ratio, and finally obtaining a prediction equation of the inductive current; and solving by adopting a firework algorithm according to the defined value function and the constraint condition to obtain the optimal duty ratio acting on the switching tube at the next moment, thereby realizing the optimal control of the DC/DC converter.
When the small signal model works in a Boost mode, a small signal model in the Boost working state is obtained by a disturbance method:
Figure BDA0002396052640000101
in the formula, L1Is the inductance value of the first inductor L1, L2Is the inductance value of the second inductor L2, L1＝L2＝L，VbatIs the voltage of the lithium battery terminal, Vc is the voltage of the two ends of the super capacitor C, iL1Is the current i on the first inductor L1L2Is the current, R, in the second inductor L2ERepresents the equivalent series resistance on the super capacitor side,
Figure BDA0002396052640000102
in order to disturb the amount of disturbance of the switching tube Q3,
Figure BDA0002396052640000103
for the disturbance amount of the switching tube Q4, D3 is the duty ratio of the switching tube Q3 in the steady state, and D4 is the duty ratio of the switching tube Q4 in the steady state.
The formula (15) is subjected to Laplace transformation to obtain:
Figure BDA0002396052640000104
bring the above assumed values into order
Figure BDA0002396052640000105
Obtaining a transfer function from the duty ratio to the inductive current in a Boost mode:
Figure BDA0002396052640000106
in the formula, RESRRepresents the equivalent internal resistance of the lithium battery side, V0Is the output voltage in boost mode, C1Representing the capacitance value of a filter capacitor in the power circuit.
The discretization model can be obtained by performing Z transformation on the formula (17):
Figure BDA0002396052640000111
in the formula (I), the compound is shown in the specification,
Figure BDA0002396052640000112
Figure BDA0002396052640000113
then, the time domain expression of equation (18) is:
iL(k)＝-a3iL(k-1)-a4iL(k-2)+b2d(k)+b3d(k-1) (19)
then obtaining an inductance current prediction equation of the boost mode as follows:
Figure BDA0002396052640000114
in the formula iL1(k + p | k) and iL2(k + p | k) represents the predicted values of the two-phase inductor current at the time k to the time (k + p), and b2，b3，a3，a4Inputting and outputting coefficients for the DC/DC converter;
the duty ratio of the switching tube is a system control variable, and the inductive current is a system output variable.
The remaining algorithms and functions achieved in the second embodiment are the same as those in the first embodiment, and are not described herein again.
Compared with the particle swarm algorithm adopted in the prior art, the firework algorithm adopted by the invention has a different information sharing mechanism. In the particle swarm optimization, only the global optimal particles and other particles give information, which is a single item of information flow, and the whole searching and updating process is a process following the current optimal solution. The firework algorithm adopts a distributed information sharing mechanism, determines the explosion intensity and the radiation amplitude according to the fitness values of fireworks distributed in different areas, and simultaneously maintains an optimal firework in the whole iteration process, and adopts an elite strategy.
It should be understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented.
In the foregoing detailed description, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the subject matter require more features than are expressly recited in each claim. Rather, as the following claims reflect, invention lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. To those skilled in the art; various modifications to these embodiments will be readily apparent, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, but one of ordinary skill in the art may recognize that many further combinations and permutations of various embodiments are possible. Accordingly, the embodiments described herein are intended to embrace all such alterations, modifications and variations that fall within the scope of the appended claims. Furthermore, to the extent that the term "includes" is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term "comprising" as "comprising" is interpreted when employed as a transitional word in a claim. Furthermore, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A bidirectional DC/DC converter optimization control method is characterized by comprising the following steps:
calculating to obtain a transfer function from the duty ratio of each mode to the inductive current according to equivalent circuits of the DC/DC converter in different modes;
discrete change is carried out on the transfer function from the duty ratio of each mode to the inductive current, and a corresponding time domain expression is obtained;
obtaining a corresponding inductive current prediction equation according to the time domain expression from the duty ratio of each mode to the inductive current;
combining the inductive current prediction equation of each mode with a value function and a constraint condition, and calculating by adopting a firework algorithm to obtain an optimal duty ratio in each mode;
and optimally controlling the power circuit of the DC/DC converter by using the corresponding duty ratio for each mode.
2. The method according to claim 1, wherein the step of obtaining the transfer function from the duty ratio of each mode to the inductor current by calculating according to the equivalent circuit of the DC/DC converter in different modes specifically comprises:
for the current mode:
obtaining an average value expression of corresponding inductive voltage according to the inductive voltage expression of the power circuit in different time periods;
acquiring a state space average equation of the inductive current of the power circuit;
sorting an average value expression of the inductive voltage of the power circuit and a state space average equation of the inductive current to obtain a small signal model in the current mode;
and performing Laplace transformation on the small signal model to obtain a transfer function from the duty ratio of the current mode to the inductive current.
3. The method of claim 2, wherein the modes include: buck mode and boost mode;
the buck mode represents that energy in the DC/DC converter flows from the lithium battery side to the super capacitor side;
the boost mode indicates that energy flows from the supercapacitor side to the lithium battery side in the DC/DC converter.
4. The method of claim 3, wherein the transfer function of the buck mode duty cycle to inductor current is:
Figure FDA0002396052630000011
in the formula, RERepresenting equivalent series resistance, V, at the supercapacitor sidebatIs the terminal voltage of the lithium battery, C represents the equivalent capacitance value of a super capacitor in the power circuit, L represents the inductance value, wherein, the first inductance (L1) in the power circuitThe inductance value equals the second inductance (L2) equals L;
the transfer function of the duty cycle of the boost mode to the inductor current is:
Figure FDA0002396052630000021
in the formula, RESRRepresents the equivalent internal resistance of the lithium battery side, V0Is the output voltage in boost mode, C1Representing the capacitance value of a filter capacitor in the power circuit.
5. The optimal control method for the bidirectional DC/DC converter according to claim 4, wherein the inductor current prediction equation in buck mode is as follows:
Figure FDA0002396052630000022
in the formula iL1(k + p | k) and iL2(k + p | k) represents the predicted values of the two-phase inductor current at the time k to the time (k + p), and b0，b1，a1，a2Inputting and outputting coefficients for the DC/DC converter;
the inductor current prediction equation of the boost mode is as follows:
Figure FDA0002396052630000023
in the formula iL1(k + p | k) and iL2(k + p | k) represents the predicted values of the two-phase inductor current at the time k to the time (k + p), and b2，b3，a3，a4The input and output coefficients of the DC/DC converter.
6. The method of claim 1, wherein the cost function and the constraint are expressed as:
Figure FDA0002396052630000024
wherein q is an output deviation weight coefficient of the DC/DC converter, r is a control weight coefficient of the DC/DC converter, iL(k + i) denotes the reference value of the inductor current at the moment k + iLThe (k + i | k) represents a predicted value of the inductor current at the time k to the time k + i, and the Δ d (k + i) represents an increment of the duty ratio of the switching tube in the DC/DC converter.
7. The method for optimizing and controlling the bidirectional DC/DC converter according to claim 1, wherein the optimal duty ratio under each mode is obtained by calculation through a firework algorithm, and the method specifically comprises the following steps:
obtaining a preset number of duty ratios as initial fireworks to perform current iteration:
calculating the fitness value of each initial firework through a constraint condition;
calculating the number of sparks which can be generated by each initial firework and the explosion range through the fitness value of each initial firework;
after each initial firework explodes, calculating the displacement of each spark in each initial firework population according to the corresponding spark number and the explosion range;
aiming at each initial firework population:
keeping the individual with the minimum fitness value; the individuals include fireworks and sparks;
the distance between any two bodies;
selecting next generation individuals except the individuals with the minimum fitness value according to the distance between any two individuals;
taking the next generation of individuals selected from each initial firework population as initial fireworks of the next iteration process;
until the error between the inductance current corresponding to the individual with the minimum reserved fitness value and the given inductance current reaches a preset threshold value, or the iteration times reach preset times;
the optimal duty cycle is the spark corresponding to the individual with the minimum fitness value.
8. The method for optimizing and controlling the bidirectional DC/DC converter according to claim 7, wherein the calculation formula of the number of sparks generated by each initial firework is as follows:
Figure FDA0002396052630000031
in the formula, Si is the number of sparks generated by the ith firework, m is a constant and used for limiting the total number of the generated sparks, and Ymax is the fitness value of the individual with the worst fitness value in the current firework population; f (x)i) Is an individual xiF () is a cost function, and epsilon is a minimal constant;
in order to limit the number of sparks which can be generated by each initial firework, a firework limiting formula is set:
Figure FDA0002396052630000032
in the formula (I), the compound is shown in the specification,
Figure FDA0002396052630000033
the number of sparks that can be generated for the ith firework; round () is a rounding function; a and b are given constants;
the calculation formula of the explosion range of each initial firework is as follows:
Figure FDA0002396052630000034
in the formula, Ai is the explosion range of the ith firework, namely, the spark generated by the current firework explosion will randomly generate displacement within the range, but cannot exceed the range;
Figure FDA0002396052630000035
and the constant value represents the maximum explosion amplitude, and Ymin is the fitness value of the individual with the minimum fitness value in the current firework population.
9. The method of claim 8, wherein the displacement of the spark is calculated by the formula:
Figure FDA0002396052630000041
in the formula (I), the compound is shown in the specification,
Figure FDA0002396052630000042
indicating the location in the k dimension of the ith spark in the current firework population, round (0, A)i) Representing a uniform random number, i.e. a random solution, generated within the corresponding explosion range;
in order to ensure that the sparks generated by each firework are in a feasible domain, a modular operation mapping rule is introduced:
Figure FDA0002396052630000043
in the formula (I), the compound is shown in the specification,
Figure FDA0002396052630000044
and
Figure FDA0002396052630000045
respectively, the upper and lower boundaries of the boundary in the k-th dimension,% represents the modulo operation.
10. The method of claim 9, wherein the distance between two individuals in the initial firework population is calculated by the formula:
Figure FDA0002396052630000046
in the formula, d (x)i,xj) Representing any two individuals xiAnd xjJ e K represents that the j-th position belongs to a set K, and the set K is a set of positions of sparks in the current firework population.
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