阅读说明：本技术 一种基于v2g的两级式双向变换器分数阶控制方法 (Fractional order control method of two-stage bidirectional converter based on V2G ) 是由 董海鹰 黄云帆 张凯 李国胜 于 2021-08-26 设计创作，主要内容包括：本发明公开了一种基于V2G的两级式双向变换器分数阶控制方法,该方法包括:对两级式一体化拓扑结构进行小信号建模,以得到两级式一体化拓扑结构的小信号模型；对小信号模型进行分数阶控制,以对两级式一体化拓扑结构的两级同时进行控制；用粒子群算法对分数阶控制器的控制参数进行联合优化,同时对两级参数寻优。本发明采用分数阶控制,分数阶PI既保留了整数PI控制器的结构简单、鲁棒性强的特点,又增加了一个可调参数,进一步提高了系统的控制性能。采用控制参数联合优化,兼顾变换器的前级和后级的系统偏差以及前级、后级和联络母线的指标要求,保证系统的一致性和稳定性。(The invention discloses a V2G-based two-stage bidirectional converter fractional order control method, which comprises the steps of carrying out small signal modeling on a two-stage integrated topological structure to obtain a small signal model of the two-stage integrated topological structure; performing fractional order control on the small signal model to simultaneously control two stages of the two-stage integrated topological structure; and performing combined optimization on the control parameters of the fractional order controller by using a particle swarm algorithm, and optimizing the two-stage parameters. The invention adopts fractional order control, the fractional order PI not only keeps the characteristics of simple structure and strong robustness of an integer PI controller, but also adds an adjustable parameter, and further improves the control performance of the system. And the control parameters are jointly optimized, the system deviation of the front stage and the rear stage of the converter and the index requirements of the front stage, the rear stage and the interconnection bus are considered, and the consistency and the stability of the system are ensured.)

1. An integrated topology of a two-stage bidirectional converter, comprising:

the bidirectional totem-pole bridgeless PFC circuit comprises a bidirectional totem-pole bridgeless PFC circuit and a bidirectional resonant CLLC circuit;

the bidirectional totem-pole bridgeless PFC circuit forms a first stage of the topological structure, and the bidirectional resonant CLLC circuit forms a second stage of the topological structure;

the alternating current side of the bidirectional totem-pole bridgeless PFC circuit is connected to a power grid, the direct current side of the bidirectional totem-pole bridgeless PFC circuit is connected to one side of the bidirectional resonance CLLC circuit, and the other side of the bidirectional resonance CLLC circuit is connected to a storage battery of a vehicle.

2. The integrated topology structure of the two-stage bidirectional converter according to claim 1, wherein the topology structure is in an AC/DC rectification state during a charging process of the storage battery, the first stage is an AC-DC rectification circuit, and the second stage is a DC-DC conversion circuit;

when the storage battery is in a discharging process, the topological structure is in a DC/AC inversion state, the second stage is a DC-DC conversion circuit, and the first stage is a DC-AC inversion circuit.

3. A two-stage bidirectional converter based on V2G, comprising: the device comprises a main circuit, a central processing unit, an analog signal detection and conditioning unit and a driving unit;

wherein the main circuit comprises an integrated topology of the two-stage bidirectional converter of any of claims 1 or 2;

the output end of the analog signal detection and conditioning unit is connected with the input end of the central processing unit, the output end of the central processing unit is connected with the driving unit, the output end of the driving unit is connected with the input end of the main circuit, and two ends of the main circuit are respectively connected with a power grid and a storage battery.

4. The V2G-based two-stage bidirectional converter according to claim 3, wherein the central processing unit comprises a DSP and peripheral circuits, the analog signal detection and conditioning unit detects and conditions voltage and current signals in the main circuit, and the driving unit isolates and amplifies PWM signals output by the DSP to generate driving signals for driving the main circuit.

5. A fractional order control method of a two-stage bidirectional converter based on V2G, which is used for the two-stage bidirectional converter based on V2G of any one of claims 3 or 4, and comprises the following steps:

carrying out small signal modeling on a two-stage integrated topological structure to obtain a small signal model of the two-stage integrated topological structure;

based on the small signal model, performing fractional order control of the converter to control two stages of the two-stage integrated topology separately and simultaneously.

6. The V2G-based two-stage bidirectional converter fractional order control method of claim 5, wherein the step of small-signal modeling the two-stage unified topology to obtain a small-signal model of the two-stage unified topology comprises:

establishing a small-signal equivalent model for the bidirectional totem-pole bridgeless PFC circuit by adopting an average current injection method;

applying disturbance to the bidirectional totem-pole bridgeless PFC circuit, and separating the disturbance to obtain a linearized equation;

the transfer function is obtained by using a pull-type variation method.

7. The V2G-based two-stage bidirectional converter fractional order control method according to claim 6, wherein the perturbation is applied to the bidirectional totem-pole bridgeless PFC circuit by using the following formula:

wherein, T_on，V_m，V_oAnd I_oRespectively as the steady state values of the turn-on time, the peak value of the input voltage, the output voltage and the output current,small signal perturbations added near the steady state value,disturbances caused around the steady state value.

8. The V2G-based two-stage bidirectional converter fractional order control method according to claim 7, comprising:

circuit on timeAnd the output voltageThe transfer function expression between is:

input voltageAnd the output voltageThe transfer function expression between is:

wherein the content of the first and second substances,

9. the V2G-based two-stage bidirectional converter fractional order control method of claim 8, wherein the gain characteristic equation of the forward mode of the bidirectional resonant CLLC circuit is as follows:

wherein: c₁Is a primary side resonance capacitor, C₂Is a secondary side resonance capacitor, R_aIs the resistance, R, of the load equivalent to the output side of the resonant cavity_aAnd C₂Converting to the primary side of the transformer to obtain R_eAnd C_2eN is transformer transformation ratio, L_mFor transformer excitation inductance, omega_s＝2πf_sAngular frequency, f, of the switching frequency_sIs the switching frequency of operation;

the voltage gain characteristic equation of the reverse mode of the bidirectional resonant CLLC circuit is as follows:

wherein: omega_s＝2πf_sAngular frequency, f, of the switching frequency_sFor operating switching frequency, AC equivalent loadR_LIs an equivalent load resistance, L₁Is the high-voltage side inductor of the transformer.

10. The V2G-based two-stage bidirectional converter fractional order control method of claim 5, wherein the step of performing fractional order control of the converter to individually and simultaneously control two stages of the two-stage unified topology based on the small signal model comprises:

for the input signal f (t), the G-L fractional calculus is defined as follows:

where t, a is the upper and lower bounds of the product of the operator, α is the order of the calculus, h is the step length, [ (t-a)/h]For rounding operations, it represents the time [ a, t ]]The number of sampling points in the system, namely the summation times;is a binomial coefficient, and is replaced by a Gamma function:

in order to avoid the D component from introducing peak-like disturbance in individual sampling period and omit the D component, fractional order PI is adopted^λA controller:

wherein k is_p，k_iProportional gain and integral gain are respectively, and lambda is an integral term fractional order factor;

respectively carrying out fractional order PI of optimal order in charging/discharging mode in matlab by adopting particle swarm algorithm^λSetting the parameters of the controller to obtain a corresponding controller;

the converter works in two working modes, namely a rectification mode and an inversion mode, system control parameters in the two modes need to be optimized respectively, the control parameters of the front stage and the rear stage of the converter are optimized in a combined manner, the optimization of 6 parameters of the front stage and the rear stage of the converter is completed at one time, the system deviation of the front stage and the rear stage of the converter and the index requirements of the front stage, the rear stage and a connection bus are considered, and the consistency and the stability of a system are ensured;

in the rectification mode, in order to control the large deviation and shorten the regulation time, according to the time-squared error integral criterion, the objective function is set as ITSE, and the optimization is performed with the objective of the minimum maximum ripple voltage ripple, as shown in the following formula, where U is_rms1Representing maximum ripple of DC bus end at front stage of converterVoltage, U_rms2Representing the maximum ripple voltage of the DC battery end at the rear stage of the converter;

in an inversion mode, in order to minimize system regulation time, according to a time-absolute error integral criterion, an objective function is set as ITAE, namely, an absolute value of system frequency deviation in t time is multiplied by integral of time t, so that an optimization model of an inversion mode parameter of a bidirectional converter is established;

the load effect is considered, and the load regulation rate of the alternating current output ends of the bus and the converter is minimized, as shown in the following formula, wherein delta U₁Representing the load regulation, Δ U, of the AC side of the converter at the preceding stage₂Representing the load regulation rate of a rear-stage DC bus end of the converter;

setting an effective working range for setting parameters to be optimized according to the limitation of the battery characteristics of the electric automobile, the load frequency control characteristics and the index requirements of the junctor of the front stage and the back stage, wherein the constraint conditions in the established optimization model are as follows:

in the formula, k_pmax、k_imax、k_λmaxAre respectively 1-8 groups of fractional order controllers k_p、k_i、k_λMaximum value of, k_pmin、k_imin、k_λminAre respectively 1-8 groups of fractional order controllers k_p、k_i、k_λMinimum value of (d);

two PI^λThe controller respectively controls the first stage and the second stage of the integrated topological structure of the two-stage bidirectional converter, and the control is carried out simultaneously.

Technical Field

The invention relates to the technical field of V2G, in particular to an integrated topological structure of a two-stage bidirectional converter, the two-stage bidirectional converter based on V2G and a fractional order control method of the two-stage bidirectional converter based on V2G.

Background

In real life, the efficiency of the power grid is not high. Because the electric energy has the characteristic of being incapable of being stored in large quantity, a large part of capacity is vacant during power generation. Daily fluctuations in load demand and the need for voltage and frequency regulation of the grid are also among the reasons for the above problems. Urban and rural power utilization has time fluctuation like a peak period and a valley period, and also has space unreasonable like unbalanced power utilization demand and uneven power utilization load.

During peak periods of electricity usage, the power grid tends to run at an overload, with the demand exceeding the capacity of the power plant. At the moment, the peak shaving power plant is put into operation, an additional generator set is started to meet the requirement, and a rotary standby power plant can be started when necessary. When the demand of the power grid is low, the power consumption is lower than the output of the base load power plant, and the redundant power is lost in the circuit. In summary, voltage and frequency regulation of the power grid increases the operating cost of the power grid to a great extent.

With the large-scale access of renewable energy sources (such as solar energy, wind energy and the like) to a power system, the discontinuity and the fluctuation of the renewable energy sources can cause the instability of the power generation system, so that other energy sources (such as battery energy storage equipment) are needed for compensation, the grid frequency is stabilized, and the voltage rise caused by reverse power flow is restrained.

The concept of V2G is proposed to solve the above problem. The core idea is to use a large number of storage batteries of the electric automobile to form an energy storage system to provide peak-shaving frequency-modulation service for a power grid. When the load of the power grid is too high, the energy storage of the electric automobile feeds power to the power grid; when the load of the power grid is low, the storage battery of the electric automobile can store the surplus power generation of the power grid, and the power consumption is reduced. Through the mode, the owner of the electric automobile can buy electricity during the valley electricity and sell electricity during the peak electricity, the obtained profit is larger than the reduction of the service life of the storage battery of the electric automobile caused by charging and discharging, and certain social benefit is obtained while the economic benefit is ensured.

With the large-scale application of pure electric vehicles and plug-in hybrid electric vehicles, the theory of V2G is more feasible. In real life, a large number of automobiles are in a stop state for a large part of time every day, and during the time, an idle resource, namely a large-capacity battery of the electric automobile, can be regarded as an energy storage system, so that the idle resource can provide energy buffering for a regional power grid when the electric automobile is parked. If the number of the grid-connected electric vehicles is large enough, the total capacity of the storage battery is considerable, so that the requirement of power grid buffering can be completely met, and frequency modulation and voltage regulation services are provided for the power grid.

However, the electric vehicle cannot be directly incorporated into the power grid, which has extremely high requirements on the real-time monitoring and communication technology of the power grid, and needs to meet the requirements of both the power grid and the electric vehicle. This is because if the grid is at peak load, large-scale charging requirements will necessarily severely impact grid performance; from the perspective of an electric vehicle owner, the electric vehicle can accept frequency modulation and voltage regulation for a power grid when the electric vehicle owner does not need the electric vehicle owner, but daily travel of the electric vehicle owner cannot be influenced by the frequency modulation and voltage regulation for the power grid. Therefore, when the electric automobile feeds power to the power grid, the lower charging limit of the power battery in the feeding mode must be set reasonably so as not to influence normal use. In combination with the two aspects, it is very necessary to research the electric vehicle V2G to coordinate the charging and discharging between the vehicle and the power grid, so that the operation of the power grid is not affected, and the normal use of the vehicle is not limited.

The current research combined with the existing vehicle-mounted converter and the control strategy thereof mainly has the following problems:

(1) the single full-bridge topology is adopted, the on and off of the switch tube are controlled by hard switches, the efficiency of a power supply processing unit is influenced in high-power application occasions, and the heat dissipation difficulty is increased.

(2) Although the resonant DC/DC bidirectional AC/DC converter can realize Zero Voltage (ZVS) soft switching in a full load range, the introduction of elements such as an inductor and a capacitor can increase the quality of a power supply, and the control is more complicated.

(3) The two-stage design of the bidirectional AC/DC converter occupies a large space, influences the vehicle-mounted application of the converter, and increases the production cost.

(4) Control methods such as neural network PID/PI, hysteresis voltage control, single closed loop PID/PI control and the like are adopted, and the methods have various characteristics but are difficult to combine good steady-state output, fast dynamic response and good robustness.

Disclosure of Invention

The technical problem to be solved by the invention is to provide an integrated topological structure, a converter and a control method of a two-stage bidirectional converter, wherein the two-stage bidirectional converter based on V2G is subjected to fractional order control, so that the control performance of the two-stage bidirectional converter based on V2G is further improved.

In order to solve the above technical problem, according to an aspect of the present invention, there is provided an integrated topology of a two-stage bidirectional converter, including:

the bidirectional totem-pole bridgeless PFC circuit comprises a bidirectional totem-pole bridgeless PFC circuit and a bidirectional resonant CLLC circuit;

the bidirectional totem-pole bridgeless PFC circuit forms a first stage of the topological structure, and the bidirectional resonant CLLC circuit forms a second stage of the topological structure;

the alternating current side of the bidirectional totem-pole bridgeless PFC circuit is connected to a power grid, the direct current side of the bidirectional totem-pole bridgeless PFC circuit is connected to one side of the bidirectional resonance CLLC circuit, and the other side of the bidirectional resonance CLLC circuit is connected to a storage battery of a vehicle.

Further, when the storage battery is charged, the topological structure is in an AC/DC rectification state, the first stage is an AC-DC rectification circuit, and the second stage is a DC-DC conversion circuit;

when the storage battery is in a discharging process, the topological structure is in a DC/AC inversion state, the second stage is a DC-DC conversion circuit, and the first stage is a DC-AC inversion circuit.

According to another aspect of the invention, the two-stage bidirectional converter based on V2G comprises a main circuit, a central processing unit, an analog signal detection and conditioning unit and a driving unit;

the main circuit comprises an integrated topological structure of the two-stage bidirectional converter;

the output end of the analog signal detection and conditioning unit is connected with the input end of the central processing unit, the output end of the central processing unit is connected with the driving unit, the output end of the driving unit is connected with the input end of the main circuit, and two ends of the main circuit are respectively connected with a power grid and a storage battery.

Furthermore, the central processing unit comprises a DSP and a peripheral circuit, the analog signal detecting and conditioning unit detects and conditions voltage and current signals in the main circuit, and the driving unit isolates and amplifies a PWM signal output by the DSP to generate a driving signal for driving the main circuit.

According to the invention, the invention provides a fractional order control method of the V2G-based two-stage bidirectional converter, which is used for any one of the V2G-based two-stage bidirectional converters, and comprises the following steps:

carrying out small signal modeling on a two-stage integrated topological structure to obtain a small signal model of the two-stage integrated topological structure;

based on the small signal model, performing fractional order control of the converter to control two stages of the two-stage integrated topology separately and simultaneously.

Further, the step of performing small-signal modeling on the two-stage integrated topology structure to obtain a small-signal model of the two-stage integrated topology structure includes:

establishing a small-signal equivalent model for the bidirectional totem-pole bridgeless PFC circuit by adopting an average current injection method;

applying disturbance to the bidirectional totem-pole bridgeless PFC circuit, and separating the disturbance to obtain a linearized equation;

the transfer function is obtained by using a pull-type variation method.

Further, applying disturbance to the bidirectional totem-pole bridgeless PFC circuit by adopting the following formula:

wherein, T_on，V_m，V_oAnd I_oRespectively as the steady state values of the turn-on time, the peak value of the input voltage, the output voltage and the output current,small signal perturbations added near the steady state value,disturbances caused around the steady state value.

Further, comprising:

circuit on timeAnd the output voltageThe transfer function expression between is:

input voltageAnd the output voltageThe transfer function expression between is:

wherein the content of the first and second substances,

further, the gain characteristic equation of the forward mode of the bidirectional resonant CLLC circuit is as follows:

wherein: c₁Is a primary side resonance capacitor, C₂Is a secondary side resonance capacitor, R_aIs the resistance of the load equivalent to the output side of the resonator. R_aAnd C₂Converting to the primary side of the transformer to obtain R_eAnd C_2eN is transformer transformation ratio, L_mFor transformer excitation inductance, omega_s＝2πf_sAngular frequency, f, of the switching frequency_sThe switching frequency of operation.

The voltage gain characteristic equation of the reverse mode of the bidirectional resonant CLLC circuit is as follows:

wherein: omega_s＝2πf_sAngular frequency, f, of the switching frequency_sFor operating switching frequency, AC equivalent loadR_LIs an equivalent load resistance, L₁Is the high-voltage side inductor of the transformer.

Further, the step of performing fractional order control of the converter to individually and simultaneously control two stages of the two-stage integrated topology based on the small signal model comprises:

for the input signal f (t), the G-L fractional calculus is defined as follows:

where t, a is the upper and lower bounds of the product of the operator, and α is the order of the calculusH is the step size, [ (t-a)/h]For rounding operations, it represents the time [ a, t ]]The number of sampling points in the system, namely the summation times;is a binomial coefficient, and is replaced by a Gamma function:

in order to avoid the D component from introducing peak-like disturbance in individual sampling period and omit the D component, fractional order PI is adopted^λA controller:

wherein k is_p，k_iRespectively proportional gain and integral gain, and lambda is an integral term fractional order factor.

Respectively carrying out fractional order PI of optimal order in charging/discharging mode in matlab by adopting particle swarm algorithm^λAnd setting the parameters of the controller to obtain the corresponding controller.

The converter works in a rectification mode and an inversion mode, system control parameters in the two modes need to be optimized respectively, and the optimization of 6 parameters of a front-stage controller and a rear-stage controller is completed at one time by jointly optimizing the control parameters of the front-stage controller and the rear-stage controller. Based on the system deviation of the front stage and the rear stage of the converter and the index requirements of the front stage, the rear stage and the contact bus, the consistency and the stability of the system are ensured;

in the rectification mode, to control large deviation and shorten regulation time, a time-multiplied-square error integral criterion is applied, an objective function is set as ITSE, and optimization is performed with the objective of minimum maximum ripple voltage ripple as shown in the following formula, wherein U is_rms1Represents the maximum ripple voltage of the DC bus end at the front stage of the converter, U_rms2Representing the maximum ripple voltage of the DC battery end at the rear stage of the converter;

in an inversion mode, in order to minimize system regulation time, according to a time-absolute error integral criterion, an objective function is set as ITAE, namely, an absolute value of system frequency deviation in t time is multiplied by integral of time t, so that an optimization model of an inversion mode parameter of a bidirectional converter is established;

the Load Regulation rate (Load Regulation) of the AC output terminals of the bus and the converter is minimized by considering the Load effect, as shown in the following formula, wherein, the Load Regulation rate is Δ U₁Representing the load regulation, Δ U, of the AC side of the converter at the preceding stage₂Representing the load regulation rate of a rear-stage DC bus end of the converter;

according to the limitation of the battery characteristics of the electric automobile (such as charging and discharging rate and the like), the load frequency control characteristics and the index requirements of the junctor (bus) of the front stage and the rear stage, the parameter to be optimized (fractional order control parameter k) is set_p、k_iAnd lambda) setting an effective working range, wherein the constraint conditions in the established optimization model are as follows:

in the formula, k_pmax、k_imax、k_λmaxAre respectively 1-8 groups of fractional order controllers k_p、k_i、k_λMaximum value of, k_pmin、k_imin、k_λminAre respectively 1-8 groups of fractional order controllers k_p、k_i、k_λIs measured.

Each particle in the particle Swarm represents a possible solution of a problem, and the intelligence of problem solution is realized through the simple behavior of individual particles and the information interaction in the Swarm. Because the PSO is simple to operate and high in convergence speed, the PSO is adopted to optimize the objective function.

Two PI^λThe controller respectively controls the first stage and the second stage of the integrated topological structure of the two-stage bidirectional converter, and the control is carried out simultaneously.

Compared with the prior art, the invention has obvious advantages and beneficial effects. By means of the technical scheme, the integrated topological structure of the two-stage bidirectional converter, the two-stage bidirectional converter based on V2G and the fractional-stage control method of the two-stage bidirectional converter based on V2G can achieve considerable technical progress and practicability, have industrial wide utilization value and at least have the following advantages:

the topological structure of the two-stage bidirectional converter is integrally designed, so that the vehicle-mounted application of the two-stage bidirectional converter can be effectively optimized, the occupied space of equipment is reduced, and the production cost is reduced.

According to the invention, the fractional order PI is adopted to control the two-stage bidirectional converter based on V2G, so that the characteristics of simple structure and strong robustness of the integral order PI controller are maintained, an adjustable parameter is added, and the controllability is effectively improved.

And thirdly, the invention adopts a method of controlling parameter joint optimization, optimizes 6 parameters of the two controllers simultaneously, comprehensively considers the system deviation of the converter and the index requirements of the junctor (bus) of the front stage, the rear stage and the front stage and the rear stage, and effectively improves the system stability.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.

Drawings

Fig. 1 is a schematic diagram illustrating an integrated topology of a two-stage bidirectional converter according to an embodiment of the present invention;

fig. 2 is a schematic diagram illustrating a topology of a bidirectional totem-pole bridgeless PFC circuit according to an embodiment of the present invention;

FIG. 3 shows a schematic diagram of a bidirectional resonant CLLC circuit topology according to an embodiment of the present invention;

FIG. 4 is a schematic block diagram of a two-stage bidirectional converter based on V2G according to an embodiment of the present invention;

FIG. 5 is a flow chart illustrating a fractional order control method of a two-stage bidirectional converter based on V2G according to an embodiment of the invention;

FIG. 6 shows a fractional order PI of an embodiment of the present invention^λA unit feedback control system of the controller;

FIG. 7 illustrates a dual closed loop control system for the AC/DC stage in a charging mode in accordance with an embodiment of the present invention;

FIG. 8 illustrates a dual closed-loop control system for the DC/DC stage in a charging mode in accordance with an embodiment of the present invention;

FIG. 9 illustrates a dual closed-loop control system for the DC/DC stage in the discharging mode in accordance with an embodiment of the present invention;

FIG. 10 illustrates a dual closed-loop control system for the DC/AC stage in a discharging mode in accordance with an embodiment of the present invention;

fig. 11 shows a flow chart of the particle swarm optimization algorithm according to an embodiment of the present invention.

Detailed Description

To further illustrate the technical means and effects of the present invention for achieving the predetermined objects, the following detailed description of the integrated topology of the two-stage bidirectional converter, the two-stage bidirectional converter based on V2G and the fractional-stage control method of the two-stage bidirectional converter based on V2G and the effects thereof will be made with reference to the accompanying drawings and the preferred embodiments.

The embodiment of the invention provides an integrated topological structure of a two-stage bidirectional converter, which comprises a bidirectional totem-pole bridgeless PFC circuit and a bidirectional resonant CLLC circuit, as shown in figure 1.

The bidirectional totem-pole bridgeless PFC circuit forms a first stage of a topological structure, and the bidirectional resonant CLLC circuit forms a second stage of the topological structure; the alternating current side of the bidirectional totem-pole bridgeless PFC circuit is connected to a power grid, the direct current side of the bidirectional totem-pole bridgeless PFC circuit is connected to one side of the bidirectional resonance CLLC circuit, and the other side of the bidirectional resonance CLLC circuit is connected to a storage battery of a vehicle.

Specifically, the charging process and the discharging process can be divided according to the charging and discharging state of the storage battery of the electric automobile, the converter is in an AC/DC rectification state during charging, the first stage is an AC-DC converter, and the second stage is a DC-DC converter; when feeding, the converter is in a DC/AC inversion state, the second stage is a bidirectional DC-DC converter, and the first stage is a DC-AC converter.

Analyzing the working mode:

the converter adopts a two-stage integrated topology, so that the occupied space of equipment can be effectively reduced, and the high-power miniaturization target can be realized. The two-stage design can meet the requirement of bidirectional operation of the converter, the switching of the working modes is determined by the vehicle-mounted control center, and when the electric vehicle runs in a grid-connected mode, the system can be switched between the two modes at will through options of a driver on the operation panel.

By adopting a two-stage integrated topological structure, the electric energy loss can be effectively reduced, and the problem that the traditional vehicle-mounted converter cannot supply power bidirectionally can be solved. According to the technical requirement of a vehicle-mounted converter at V2G, a dual-mode control strategy combining two control modes is adopted, when the electric vehicle is in a charging mode, the converter is in an AC/DC rectification state, the first stage is an AC-DC converter, and the second stage is a bidirectional DC-DC converter; when the electric automobile feeds power to the power grid, the converter is in a DC/AC inversion state, the second stage is a bidirectional DC-DC converter, and the first stage is a DC-AC converter.

Fig. 2 shows a topology diagram of a bidirectional totem-pole bridgeless PFC circuit.

As shown in fig. 2, the bidirectional totem-pole bridgeless PFC circuit topology is used as a front-stage circuit of the two-stage bidirectional AC/DC converter to connect the power grid side and the rear-stage bidirectional DC/DC circuit side, and not only can realize the forward charging PFC function and the reverse discharging grid-connected inversion function, but also can control the quality of the grid-side current to prevent harmonic pollution, and can provide a relatively stable DC bus voltage for the rear-stage circuit. The main circuit structure of the power factor correction circuit is the same as the full-bridge circuit topology structure, two fly-wheel diodes are replaced by two power switching devices on the basis of the traditional totem-pole type bridgeless PFC, so that bidirectional flow of energy can be realized, a synchronous rectification strategy can be realized by effectively controlling the newly added switching devices, and the loss is further reduced.

Fig. 3 shows a bidirectional resonant CLLC circuit topology.

As shown in fig. 3, the resonant bidirectional CLLC circuit is composed of two sets of full-bridge switching device units, a resonant inductor, a resonant capacitor, an isolation high-frequency transformer, and the like. The double active bridge circuit and the CLLC circuit realize electrical isolation due to the self-contained high-frequency transformer, and can realize soft switching, thereby obtaining higher efficiency and realizing wide-range voltage input and output.

An embodiment of the present invention provides a two-stage bidirectional converter based on V2G, as shown in fig. 4, including: the device comprises a main circuit, a central processing unit, an analog signal detection and conditioning unit and a driving unit;

the main circuit comprises an integrated topological structure of the two-stage bidirectional converter in any one of the embodiments;

the output end of the analog signal detection and conditioning unit is connected with the input end of the central processing unit, the output end of the central processing unit is connected with the driving unit, the output end of the driving unit is connected with the input end of the main circuit, and the two ends of the main circuit are respectively connected with the power grid and the storage battery.

Specifically, the central processing unit comprises a DSP and a peripheral circuit, analog signals are detected in voltage and current signals in the multi-main circuit of the conditioning unit for detection and conditioning, and the driving unit isolates and amplifies PWM signals output by the DSP to generate driving signals for driving the main circuit.

In one embodiment, the central processing unit is composed of a DSP and peripheral circuits such as a crystal oscillator, a reset and a memory expansion which are necessary for forming a digital control system; the analog signal detection and conditioning unit completes the detection of voltage and current signals in the main circuit and the post-conditioning function of the signals; the driving unit is responsible for isolating and amplifying the PWM signal output by the DSP to generate a driving signal for driving the MOS tube.

The embodiment of the invention provides a fractional-stage control method of a two-stage bidirectional converter based on V2G, which is used for the two-stage bidirectional converter based on V2G in any one of the embodiments. The two fractional order controllers respectively control one stage of the two-stage bidirectional converter based on the V2G, the control is carried out simultaneously, and further fractional solution control of the two-stage bidirectional converter based on the V2G is achieved.

The two-stage bidirectional converter based on the V2G works in two modes, namely an AC/DC rectification mode and a DC/AC inversion mode, so that the storage battery can work in two states of charging and feeding power to a power grid.

As shown in fig. 5, the method includes:

and step S50, carrying out small signal modeling on the two-stage integrated topological structure to obtain a small signal model of the two-stage integrated topological structure.

In one embodiment, a small-signal equivalent model is established for the bidirectional totem-pole bridgeless PFC circuit by adopting an average current injection method; applying disturbance to the bidirectional totem-pole bridgeless PFC circuit, and separating the disturbance to obtain a linearized equation; the transfer function is obtained by using a pull-type variation method.

Specifically, a main power switch tube and an auxiliary switch tube in the converter are assumed to be ideal components; the passive elements in the converter are linear time invariant; after the output voltage is filtered by the electrolytic capacitor, the ripple voltage is small enough. The method comprises the steps of establishing a small-signal equivalent model for the bidirectional totem-pole bridgeless PFC circuit by adopting an average current injection method, applying disturbance to the small-signal equivalent model, separating the disturbance to obtain a linearized equation, and finally obtaining a transfer function by utilizing a Laplace transform method.

Further, the following formula is adopted to apply disturbance to the bidirectional totem-pole bridgeless PFC circuit:

wherein, T_on，V_m，V_oAnd I_oRespectively as the steady state values of the turn-on time, the peak value of the input voltage, the output voltage and the output current,small signal perturbations added near the steady state value,disturbances caused around the steady state value.

Circuit on timeAnd the output voltageThe transfer function expression between is:

input voltageAnd the output voltageThe transfer function expression between is:

wherein the content of the first and second substances,

the gain characteristic equation of the forward mode of the bidirectional resonant CLLC circuit is as follows:

wherein: c₁Is a primary side resonance capacitor, C₂Is a secondary side resonance capacitor, R_aIs a loadEquivalent to the resistance of the resonator output side. R_aAnd C₂Converting to the primary side of the transformer to obtain R_eAnd C_2eN is transformer transformation ratio, L_mFor transformer excitation inductance, omega_s＝2πf_sAngular frequency, f, of the switching frequency_sThe switching frequency of operation.

The voltage gain characteristic equation of the reverse mode of the bidirectional resonant CLLC circuit is as follows:

wherein: omega_s＝2πf_sAngular frequency, f, of the switching frequency_sFor operating switching frequency, AC equivalent loadR_LIs an equivalent load resistance, L₁Is the high-voltage side inductor of the transformer.

And step S51, based on the small signal model, performing fractional order control on the converter so as to independently and simultaneously control two stages of the two-stage integrated topological structure.

In particular, Grumwald-Letnikov is one of the most widely used definitions in the development of fractional calculus theory. For the input signal f (t), the G-L fractional calculus is defined as follows:

where t, a is the upper and lower bounds of the product of the operator, α is the order of the calculus, h is the step length, [ (t-a)/h]For rounding operations, it represents the time [ a, t ]]The number of sampling points in the inner, i.e. the number of summations.Is a binomial coefficient, which can be replaced by a Gamma function, and is:

in order to avoid the D component introducing the peak-like disturbance in the individual sampling period, the D component is omitted, and as shown in FIG. 6, fractional order PI is adopted^λA controller:

wherein k is_p，k_iRespectively proportional gain and integral gain, and lambda is an integral term fractional order factor. For fractional order PI^λParameter setting to obtain PI^λAnd a controller.

As shown in fig. 7, 8, 9 and 10, in the charging and discharging modes, the AC/DC and the DC/DC adopt double closed-loop control, and the current inner loop and the voltage outer loop both adopt fractional order PI^λAnd a controller. V_{_ref}Representing the voltage ring reference voltage, i_{_ref}Denotes the reference current of the current loop, H_{_}i denotes the closed-loop feedback coefficient of the current loop, H_{_v}Representing the closed-loop feedback coefficient, G, of the voltage loop_cRepresenting fractional order controls, G_idRepresenting the transfer function of the output current to the control, G_viRepresenting the transfer function of the output voltage to the output current, i.e. the open loop output impedance.

Fractional order PI^λK of two parameters of the controller_p，K_iThe two parameters are consistent with those of the integral-order PI controller, and the functions of the two controllers are approximately the same; and fractional order PI^λAnother parameter in the controller, the integration order λ, whose magnitude determines the strength of the integration element of the controller. λ mainly affects the steady state accuracy of the system. Current fractional order PI^λWhen the parameter of the controller is changed in a small range, the control effect is basically unchanged, and the fractional order PI is reflected^λThe controller has strong robustness.

Respectively carrying out fractional order PI of optimal order in charging/discharging mode in matlab by adopting particle swarm algorithm^λAnd setting the parameters of the controller to obtain the corresponding controller.

Because the system works in two working modes of rectification and inversion, the system control parameters in the two modes need to be optimized respectively. The invention jointly optimizes the control parameters of the front stage and the rear stage, and completes optimization of 6 parameters of the front stage converter and the rear stage converter at one time. The system deviation of the front and rear stages and the index requirements of the front stage, the rear stage and the contact bus are considered, and the consistency and the stability of the system are guaranteed.

In the rectification mode, in order to control large deviation and shorten the regulation time, the objective function is set to ITSE according to the time-multiplied square error integration criterion. The optimization is performed with the goal of minimizing the maximum ripple voltage ripple, as shown in the following formula, where U_rms1Represents the maximum ripple voltage of the DC bus end at the front stage of the converter, U_rms2And represents the maximum ripple voltage of the DC battery end of the rear stage of the converter.

In the inversion mode, in order to minimize the system regulation time, according to the time-absolute error integration criterion, the objective function is set as ITAE, that is, the absolute value of the system frequency deviation in the time t is multiplied by the integral of the time t, so as to establish an optimization model of the inversion mode parameters of the bidirectional converter.

The Load Regulation rate (Load Regulation) of the ac output terminals of the bus and the converter is minimized in consideration of the Load effect, as shown in the following formula. Wherein Δ U₁Representing the load regulation, Δ U, of the AC side of the converter at the preceding stage₂And the load regulation rate of the DC bus end of the rear stage of the converter is shown.

In practical applications, considering the limitations of battery characteristics of the electric vehicle (such as charging and discharging rate), load frequency control characteristics, and index requirements of the front-stage and rear-stage interconnections (buses), the parameters to be optimized (fractional order control parameter k) need to be considered_p、k_iAnd λ) The effective working range is set, so the constraint conditions in the optimization model established by the invention are as follows:

in the formula, k_pmax、k_imax、k_λmaxAre respectively 1-8 groups of fractional order controllers k_p、k_i、k_λMaximum value of, k_pmin、k_imin、k_λminAre respectively 1-8 groups of fractional order controllers k_p、k_i、k_λIs measured.

Each particle in the particle Swarm represents a possible solution of a problem, and the intelligence of problem solution is realized through the simple behavior of individual particles and the information interaction in the Swarm. Because the PSO is simple to operate and high in convergence speed, the PSO is adopted to optimize the objective function.

The work flow of the whole optimization algorithm is shown in fig. 11, and comprises the following steps:

step S110, randomly initializing a particle population;

step S111, calculating individual adaptive values of particles;

step S112, updating population optimal individuals and particle optimal individuals;

and step S113, judging whether the maximum iteration times is reached, if so, finishing particle swarm optimization, and if not, executing step S111.

The two fractional order controllers respectively control the first stage of the bidirectional converter, the control is carried out simultaneously, and then the control effect is analyzed through simulation.

In a specific embodiment, the main circuit can realize two working modes of rectification and inversion and can realize the working requirement of soft switching aiming at the design of a 3kW switching power supply, and the TMS320F28335 is selected as the main control chip. The indexes are shown in table 1:

TABLE 1

Generally, the voltage-stabilizing output of the power bidirectional AC/DC converter is mainly based on the PID algorithm, however, with the increasing requirements of high precision and high robustness on the quality of electric energy, the traditional PID algorithm is more laborious, and the control is more flexible due to the fractional order control strategy, so the practical application effect of the fractional order controller with higher robustness in the field of converters needs to be researched. The invention aims to overcome the defects of the prior control technology, provides a V2G-based two-stage bidirectional converter fractional order control method, realizes the stable operation of the converter in different working modes, effectively solves the problem of ensuring the quality of input and output electric energy when realizing the bidirectional flow of energy, and finally realizes the goals of peak clipping, valley filling, voltage regulation, frequency modulation and the like of a power grid.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.