CN113809733A

CN113809733A - Direct-current bus voltage and super capacitor charge management control method of light storage system

Info

Publication number: CN113809733A
Application number: CN202111078029.8A
Authority: CN
Inventors: 刘海涛; 马丙泰; 郝思鹏; 黄铖; 张匡翼
Original assignee: Nanjing Institute of Technology
Current assignee: Nanjing Institute of Technology
Priority date: 2021-09-15
Filing date: 2021-09-15
Publication date: 2021-12-17
Anticipated expiration: 2041-09-15
Also published as: CN113809733B

Abstract

A method for managing and controlling the DC bus voltage and supercapacitor charge of an optical storage system, including a photovoltaic grid-connected hybrid energy storage system, adding a control coefficient to the PI control of the VSC unit of the system, so that the VSC unit can optimize the voltage and power balance unit of the common DC bus to the common DC bus. No static voltage control; the hybrid energy storage system includes super capacitors and batteries, and the working modes of the super capacitors are divided; according to the different modes of the super capacitors, the primary power distribution of the batteries and the super capacitors through the power distribution unit or the mixed energy storage power The secondary distribution control unit performs optimal control on the hybrid energy storage charging and discharging pulse triggering control unit, so that the hybrid energy storage charging and discharging pulse triggering control unit controls the charging or discharging of the supercapacitor and the battery, so that the supercapacitor power and the battery power are secondary distribute. Through the above improvements, the DC bus voltage is more stable, the reliability of the energy storage device is enhanced, and the life of the super capacitor is prolonged.

Description

Direct-current bus voltage and super capacitor charge management control method of light storage system

Technical Field

The invention relates to the technical field of photovoltaic energy storage, in particular to a direct-current bus voltage and super capacitor charge management control method of an optical storage system.

Background

In recent years, with the rapid rise of new energy power generation such as wind/light, the remarkable improvement of the performance of a power converter and the continuous progress of novel materials, the energy storage technology shows unprecedented development prospects with flexible power regulation capability and good controllability. Hybrid energy storage systems have attracted attention because of their dual attributes of high energy density and high power density. Due to the volatility and the randomness, the large-scale grid connection of the wind and light renewable energy sources has great influence on a power grid, and the consumption of the renewable energy sources and the system stability can be improved by utilizing the hybrid energy storage. Some documents propose a Photovoltaic (PV) maximum power tracking working point control and Hybrid Energy Storage System (HESS) coordination stabilization photovoltaic grid-connected power fluctuation strategy, and PV grid-connected power fluctuation can be effectively suppressed within an acceptable range of a power grid through close cooperation between PV and HESS. Stability of a grid-connected Voltage Source Converter (VSC) system is one of the most important issues in the stability research of the current power electronic power system, which is most concerned and has the most practical application significance. Some documents coordinate and integrate a constant power control strategy and a direct current bus voltage non-static tracking control strategy of a power converter in a photovoltaic-energy storage micro grid system, so that the photovoltaic-energy storage micro grid system is ensured to provide required active power and reactive power for a large grid, and the stable operation of the micro grid system is effectively maintained. Classical proportional-integral (PI) control parameters are difficult to set, the anti-interference capability is weak, and good control performance is difficult to maintain under complex working conditions; some documents adopt an improved PI control model to improve the steady-state precision and response speed of the voltage of the direct-current bus; some documents propose a direct-current voltage control method based on deep reinforcement learning, which fuses a deep learning neural network and a determination strategy gradient to realize continuous action search and adaptively adjust a voltage control strategy. Compared with the traditional proportional-integral (PI) control method, the method has better dynamic and static performances, effectively improves the control precision of the direct current voltage, reduces the direct current voltage fluctuation and power overshoot under disturbance, and shortens the recovery stabilization time of the direct current voltage and power; some documents propose a variable-argument-domain fuzzy PI adaptive control strategy, and a better control effect is obtained by adjusting a fuzzy argument domain in real time according to the magnitude of an input error. In consideration of the characteristic that energy type and power type hybrid energy storage bear power components respectively, some documents provide a hybrid energy storage double-layer optimization configuration method based on a meta-model optimization algorithm aiming at the configuration problem of the hybrid energy storage in wind power stabilization. The inner layer of the method is a hybrid energy storage power optimization allocation strategy; the outer layer takes minimum capacity and minimum power as constraint conditions, and takes the minimum annual average cost of the whole life cycle of the hybrid energy storage as an objective function. The optimized configuration method can effectively avoid frequent charging and discharging of the storage battery while keeping the optimal economy of hybrid energy storage, thereby prolonging the service life of the storage battery. Some documents decompose a second-order high-frequency filtering link into a response filtering link and a compensation filtering link, analyze the frequency characteristics of the response filtering link and the compensation filtering link, clarify the selection principle of the handover frequency, and distribute the hybrid energy storage power, so that the wind power fluctuation is suppressed more efficiently while the charge state of the power type energy storage equipment is considered. Some documents provide a distributed energy storage system load power distribution hierarchical control strategy based on a discrete consistency algorithm, wherein the lower layer performs power distribution once, and the upper layer performs power control again by using a current correction generated by the consistency algorithm. Some documents perform variable mode decomposition on photovoltaic original power in a self-adaptive manner, so as to realize primary power distribution; secondly, the charge state of the super capacitor is monitored in the energy storage system, the primary power of the energy storage element is corrected secondarily through fuzzy control, and the result shows that the primary power is corrected optimally based on the fuzzy control, so that the energy storage element works in a charge State (SOC) safety range, and the economic life of the energy storage element is greatly prolonged. In the stabilizing power fluctuation mode, the wavelet packet decomposition is utilized to carry out primary distribution on the internal power of the energy storage system, and the primary power is corrected by combining the charge state information of the energy storage device, so that secondary power distribution is realized. Some documents adopt a management strategy based on a super capacitor charge state limit value aiming at a photovoltaic direct-current micro-grid hybrid energy storage system to limit the super capacitor from being overcharged and overdischarged; but the fluctuation amplitude of the direct current bus voltage is large during the operation, and the control effect is not ideal. Some documents propose a variational modal decomposition-fuzzy control strategy to stabilize wind power fluctuation. The result shows that the control strategy can not only meet the maximum output power change rate limit requirement of the wind power plant, but also keep the SOC in a reasonable range and avoid the occurrence of overcharge and overdischarge. Some documents discuss feasibility and implementation methods of soft switching implementation technologies of non-isolated photovoltaic grid-connected inverters, and lay a foundation for next-generation high-power-density non-isolated photovoltaic grid-connected inverters. Decomposing power outside a target domain into high-frequency and low-frequency components based on spectrum analysis, realizing the purpose of power distribution, switching the states of the charging/discharging battery packs according to charging/discharging reference power, realizing primary control of compensating prediction errors under different working conditions and secondary control of stabilizing fluctuation, and finishing the control of the charging/discharging priority of mixed energy storage.

In conclusion, the stability of the direct-current bus voltage can be further improved based on the prior art, so that the whole photovoltaic grid-connected power generation system is more stable, and in addition, the SOC of the super capacitor can be optimally controlled, so that the working state of the super capacitor is optimized, and the service life of the super capacitor is prolonged.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a direct current bus voltage and super capacitor charge management control method for a photovoltaic grid-connected hybrid energy storage system, and provides improved PI control for optimizing the common direct current bus voltage without static error control aiming at a grid-connected voltage type converter (VSC) of the photovoltaic grid-connected hybrid energy storage system, so that the common direct current bus voltage is maintained to be stable at a reference value after grid connection. Aiming at a photovoltaic grid-connected power generation system, a secondary power distribution control strategy of a hybrid energy storage system based on interactive control and limit management is provided, the reliability of an energy storage device is enhanced, and the service life of a super capacitor is prolonged.

In order to achieve the purpose, the invention adopts the following technical scheme:

the direct-current bus voltage and super capacitor charge management control method of the light storage system comprises the following steps:

a photovoltaic grid-connected hybrid energy storage system; the photovoltaic grid-connected hybrid energy storage system comprises a VSC unit, a hybrid energy storage charge-discharge pulse trigger control unit, a hybrid energy storage system, a common direct current bus voltage power balancing unit, a power distribution unit and a hybrid energy storage power secondary distribution control unit;

a plurality of control coefficients are added in the outer loop PI control of the VSC unit, so that the voltage outer loop control in the VSC unit is optimized, the current inner loop is controlled, and finally the static error-free control on the voltage of the common direct current bus is indirectly realized;

the hybrid energy storage system comprises a super capacitor and a storage battery, and the working modes of the super capacitor are divided;

according to different working modes divided by the super capacitor, the power distribution unit is used for carrying out primary power distribution on the storage battery and the super capacitor or the hybrid energy storage power secondary distribution control unit is used for carrying out optimization control on the hybrid energy storage charge-discharge pulse trigger control unit, so that the hybrid energy storage charge-discharge pulse trigger control unit controls the charging or discharging of the super capacitor and the storage battery, and the power of the super capacitor and the power of the storage battery are subjected to secondary distribution.

Further, the plurality of control coefficients includes: control coefficient c1, control coefficient c2, control coefficient p 3; PI control outputs a VSC unit inner ring control input reference current I after being optimized by a plurality of control coefficients_{d_ref}Through the control of the inner ring current of the VSC unit, the voltage of the common direct current bus is indirectly controlled without static error;

the control coefficient c1 is:

in the formula, maxU represents U_{dc_ref}-U_dcMin represents U_{dc_ref}-U_dcMinimum difference of (1), wherein U_{dc_ref}Representing the common DC bus voltage reference, U_dcRepresenting the actual measured value of the voltage of the common direct current bus;

the control coefficient c2 is:

in the formula, | maxU' | represents U_{dc_ref}-U_dcMaximum value in the first derivative of the difference value, and taking the amplitude result, | minU' | represents U_{dc_ref}-U_dcThe minimum value in the first derivative of the difference value and taking the amplitude result;

the control coefficient p3 is:

in the formula of U_dcmaxRepresents the maximum value of the voltage of the common direct current bus;

said I_{d_ref}The current is as follows:

in the formula, K_p0、K_i0Indicating the initial parameter value, U, of the PI controller_eRepresents U_{dc_ref}-U_dcDifference of (d), dU_eDt represents U_{dc_ref}-U_dcThe first derivative of the difference.

Further, the specific content of dividing the working mode of the super capacitor is as follows:

setting a limit management alarm value a1 and a critical discharge alarm value a within the 0-50% state period of the state of charge SOCsc of the super capacitor, wherein a1 is less than a; setting a limit management alarm value b1 and a critical charging alarm value b in the charge state of the super capacitor within the period of 50-100%, wherein b is less than b 1;

normal operating state interval: a & ltnoc & gt & ltb & gt;

the critical charging and discharging state interval comprises a critical charging interval: b < SOCsc < b1, critical discharge interval: a1 < SOCsc < a;

the limit value management limit charging and discharging state interval comprises a limit value management limit discharging interval: 0 < SOCsc < ═ a1, limit management limit charging interval: b1 & lt, SOCsc & lt, 100%.

Further, when the state of charge SOCsc of the super capacitor is in a normal operation state, i.e. a < ═ SOCsc < ═ b;

the low-pass filtering LPF in the power distribution unit is used for carrying out primary power distribution on the storage battery and the super capacitor, so that the photovoltaic grid-connected hybrid energy storage system (model) is kept stable.

Further, when the state of charge SOCsc of the super capacitor is in the critical charging interval: b < SOCsc < b1, critical discharge interval: a1 < SOCsc < a, limit management limit discharge interval: 0 < SOCsc < ═ a1, limit management limit charging interval: b1 & lt ═ SOCsc & lt 100%;

according to different intervals, the super capacitor SOC control module in the hybrid energy storage power secondary distribution control unit correspondingly processes and calculates partial parameters in the photovoltaic grid-connected hybrid energy storage system to obtain virtual correction current I in the corresponding interval_vir(ii) a The hybrid energy storage power secondary distribution control unit performs virtual correction current I in a corresponding interval_virOptimally controlling the hybrid energy storage charge-discharge pulse trigger control unit to obtain the virtual corrected current I in the corresponding interval_virControlled power P of super capacitor_{sc_ref_1}Further obtain the power P of the storage battery under the corresponding interval_{b_ref_1}，P_{b_ref_1}And P_{sc_ref_1}The feedback is transmitted to the super capacitor SOC control module through closed loop, and the super capacitor SOC control module is combined with P_{b_ref_1}、P_{sc_ref_1}And processing and calculating partial parameters to obtain reference current I of the super capacitor in the corresponding interval_{sc_ref_1}And a reference current I of the storage battery in a corresponding interval_{b_ref_1}；

The hybrid energy storage power secondary distribution control unit enables the reference current I of the super capacitor in the corresponding interval_{sc_ref_1}And a battery reference current I_{b_ref_1}Input into the mixed energy storage charge-discharge pulse trigger control unit to charge and discharge through the mixed energy storageThe electric pulse trigger control unit controls the storage battery and the super capacitor to carry out adaptive charging or discharging, so that power distribution between the storage battery and the super capacitor is realized, and the charge state of the super capacitor is changed towards a stable direction.

Further, the partial parameters comprise super capacitor state of charge reference value SOC_refAnd the real-time state of charge (SOC) value of the super capacitor_(t)Reference power P of the accumulator_{b_ref}Reference power P of super capacitor_{sc_ref}One or more of a limit value management alert value a1, a critical discharging alert value a, a limit value management alert value b1, a critical charging alert value b, and an interaction rate factor k.

Further, when the state of charge SOCsc of the super capacitor is in the critical discharge interval, i.e. a1 < SOCsc < a, and is in the continuous discharge state, i.e. P_{sc_ref}>When equal to 0, I_vir＝-|K*(SOC_(t)-SOC_ref)|、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

When the SOC SOCsc is in the critical discharge interval, i.e. a1 < SOCsc < a, and in the continuous charging state, i.e. P_{sc_ref}<0，I_vir＝0、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

When the SOC SOCsc is in the critical charging interval, i.e. b < SOCsc < b1, and is in the continuous charging state, i.e. P_{sc_ref}<0，I_vir＝|K*(SOC_(t)-SOC_ref)|、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

When the SOC SOCsc is in the critical charging interval, i.e. b < SOCsc < b1, and is in the continuous discharging state, i.e. P_{sc_ref}>＝0，I_vir＝0、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}。

Further, when the state of charge socc of the super capacitor is in the limit management limit discharge interval, i.e. 0 < socc < a1, and is in the continuous discharge state, i.e. P_{sc_ref}>When equal to 0；I_vir＝0、P_{sc_ref_1}＝0、P_{b_ref_1}＝P_{b_ref}+P_{sc_ref}；

When the SOC SOCsc is in the limit management limit discharge interval, i.e. 0 < SOCsc < ═ a1, and is in the continuous charging state, i.e. P_{sc_ref}<At 0; i is_vir＝0、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

When the SOC SOCsc is in the limit management limit charging interval, i.e. b1 < ═ SOCsc < 100%, and is in the continuous discharging state, i.e. P_{sc_ref}>When the value is 0; i is_vir＝0、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

When the state of charge SOCsc of the super capacitor is in the limit value management limit charging interval, namely b1 < ═ SOCsc < 100%, and is in the continuous charging state, namely P_{sc_ref}<At 0; i is_vir＝0、P_{sc_ref_1}＝0、P_{b_ref_1}＝P_{b_ref}+P_{sc_ref}。

Further, I_{b_ref_1}＝P_{b_ref_1}/U_bat；

I_{sc_ref_1}＝P_{sc_ref_1}/U_sc；

In the formula of U_batRepresenting the battery voltage, U_scRepresenting the supercapacitor voltage.

The invention has the beneficial effects that:

1. aiming at a grid-connected voltage type converter (VSC) in a photovoltaic grid-connected hybrid energy storage system, improved PI control optimization common direct-current bus voltage non-static control is provided, and compared with the traditional PI control, the common direct-current bus voltage can be better maintained near a reference voltage.

2. Aiming at the critical charging and discharging interval of the super capacitor, a concept of virtual correction current is introduced, the magnitude of the virtual correction current is determined according to the positive and negative of the distributed power of the super capacitor and an interaction rate factor, and the charge state of the super capacitor is changed towards a stable direction. The working state of the super capacitor is optimized, and the service life of the super capacitor is prolonged.

3. On the basis of the existing research, the application provides improved PI control for a VSC system in a photovoltaic grid-connected system; and considering the power distribution problem of the hybrid energy storage system, a secondary power distribution control strategy based on interactive control and limit management is provided. The control strategy maintains the voltage of the direct current bus to be stable at a reference value by optimizing the common direct current bus voltage non-static-error control; the trend of the super capacitor SOC can be stably changed through secondary power distribution of the hybrid energy storage system. And dividing the working state of the system into three working modes by taking the SOC of the super capacitor as a reference. When the SOC is in a working mode of a normal operation interval, performing primary power distribution by adopting low-pass filtering; under a critical charging and discharging mode, introducing a concept of virtual correction current, and controlling the SOC of the super capacitor to trend to a normal operation interval by controlling the power alternation between the energy storage elements through the virtual correction current when a control condition is reached; and under the limit charging and discharging mode, limit management is adopted for the super capacitor, and overcharge and overdischarge of the super capacitor are avoided. The control strategy can realize the voltage stabilization of the photovoltaic grid-connected direct-current bus and the reasonable operation of the super capacitor SOC. By building a photovoltaic grid-connected hybrid energy storage system (model), simulation comparison analysis is carried out on a VSC system under the traditional PI control and the improved PI control; and meanwhile, simulation is carried out in three operation ranges of normal operation, critical charge and discharge and limit charge and discharge, and the correctness and the effectiveness of the provided control strategy are verified.

Drawings

Fig. 1 is a schematic structural diagram of a photovoltaic grid-connected hybrid energy storage system or model of the invention.

Fig. 2 is a block diagram of the dc bus voltage non-static tracking control in the prior art.

Fig. 3 is a schematic diagram of the dc bus voltage non-dead-center tracking control of the improved PI control of the present invention.

FIG. 4 is a schematic diagram of the super capacitor SOC partition of the present invention.

FIG. 5 shows a reference power P of a battery according to the prior art_{b_ref}And reference power P of super capacitor_{sc_ref}A schematic was obtained.

Fig. 6 is a schematic diagram of a hybrid energy storage charge-discharge pulse trigger control unit controlling a storage battery charge-discharge trigger pulse in the prior art.

Fig. 7 is a schematic diagram of a hybrid energy storage charge-discharge pulse trigger control unit controlling a charge-discharge trigger pulse of a super capacitor in the prior art.

FIG. 8 is a schematic diagram of the super capacitor SOC control module processing calculations according to the present invention.

FIG. 9 is a diagram of the present invention based on an introduced virtual correction current I_virAnd a reference current I of the super capacitor_{sc_ref_1}And the trigger pulse schematic diagram controls the charging and discharging of the super capacitor through the hybrid energy storage charging and discharging pulse trigger control unit.

FIG. 10 is a battery reference current I according to the present invention_{b_ref_1}And the schematic diagram is that the mixed energy storage charge-discharge pulse trigger control unit controls the charge-discharge trigger pulse of the storage battery.

Fig. 11 is a schematic diagram of the hybrid energy storage secondary power distribution and interactive control process according to the present invention.

Fig. 12 is a comparison of dc bus voltage curves of the present invention.

FIG. 13 is a comparative plot of the change in state of charge (critical charge) of the supercapacitor of the present invention.

FIG. 14 is a graph comparing the charging and discharging current curves of the battery of the present invention.

FIG. 15 is a comparative plot of the change in state of charge (critical discharge) of the supercapacitor of the present invention.

Fig. 16 is a graph comparing the charging and discharging current curves of the secondary battery of the present invention.

FIG. 17 is a comparison of the change in state of charge (limit charge management) for a supercapacitor according to the present invention.

FIG. 18 is a schematic diagram of critical charging power of super capacitor under the control method of the present invention.

FIG. 19 is a schematic diagram of the power assumed by the ultracapacitor under the condition of the invention not adopting the control condition.

FIG. 20 is a schematic diagram of the critical discharge super capacitor power under the control method of the present invention.

FIG. 21 shows the power carried by the super capacitor without the control method of the present invention.

Detailed Description

The present invention will now be described in further detail with reference to the accompanying drawings.

The invention discloses a direct current bus voltage and super capacitor charge management control method of a photovoltaic grid-connected hybrid energy storage system, and provides improved PI control optimization common direct current bus voltage non-static control aiming at a grid-connected voltage type converter (VSC) of the photovoltaic grid-connected hybrid energy storage system, so that the direct current bus voltage is maintained to be stable at a reference value. For the problem of power distribution of an energy storage device in a microgrid containing random and intermittent renewable energy sources, a secondary power distribution control strategy of a hybrid energy storage system based on interactive control and limit management is provided. And dividing system working modes according to the charge state of the super capacitor, and analyzing a coordination control method in each working mode. In a normal charging and discharging mode, low-pass filtering is adopted to distribute power, and the mixed energy storage respectively bears corresponding power components; under a critical charging and discharging mode, introducing a concept of virtual correction current, and determining the magnitude of the virtual correction current according to the positive and negative of the distributed power of the super capacitor and an interaction rate factor to ensure that the charge state of the super capacitor changes towards a stable direction; when the system reaches a limit charge-discharge mode, the charge state of the super capacitor is limited and managed, and the phenomenon of overcharge and overdischarge is avoided. And finally, verification is carried out in the built photovoltaic grid-connected simulation model, and the result shows that the provided control strategy can ensure the voltage stability of the direct-current bus, enhance the reliability of the energy storage device and prolong the service life of the super capacitor.

The invention is realized by adopting the following technical scheme.

1. Research on secondary power distribution and control strategies of the photovoltaic grid-connected hybrid energy storage system:

step 1, building a photovoltaic grid-connected hybrid energy storage system (model) according to the invention requirement;

step 2, designing and improving PI control optimization common direct current bus voltage quiet-error-free control according to the invention requirement;

step 3, dividing the working modes of the super capacitor according to the invention requirements;

step 4, controlling the charge state of the super capacitor in different working modes according to the requirements of the invention, and introducing virtual current to control the charge and discharge of the super capacitor;

and 5, running and debugging in the photovoltaic grid-connected model according to the invention requirements, and performing simulation verification analysis.

2. In the step 1, an existing photovoltaic grid-connected hybrid energy storage system model is built according to the invention requirement, and partial units are improved. As shown in fig. 1.

The method specifically comprises the following steps: the system comprises a photovoltaic power generation unit, a large power grid unit, a VSC unit, an alternating current and direct current load unit, a hybrid energy storage (charge and discharge) pulse trigger control unit, a hybrid energy storage system, a public direct current bus voltage and power balancing unit, a power distribution unit and a hybrid energy storage power secondary distribution control unit.

A photovoltaic power generation unit: the method comprises photovoltaic maximum power tracking and BOOST control, and provides photovoltaic power for the system;

a large power grid unit: providing grid power to the system;

VSC unit: the grid-connected voltage type converter is connected with a photovoltaic power generation and power grid system;

AC/DC load unit: consuming system power;

the hybrid energy storage charge-discharge pulse trigger control unit comprises: the device comprises a storage battery pulse trigger control unit, a storage battery charging and discharging unit, a super capacitor charging and discharging control unit and a super capacitor pulse trigger control unit; generating corresponding charge-discharge trigger pulses through PWM control according to the mixed energy storage current index parameters, and controlling the on-off of a power MOSFET of a mixed energy storage charge-discharge control switch to realize the function of mixed energy storage charge-discharge;

a hybrid energy storage system: the device comprises a storage battery and a super capacitor;

public direct current bus voltage power balancing unit: the voltage of the common direct current bus is maintained to be stable;

a power distribution unit: primarily distributing the hybrid energy storage power;

the hybrid energy storage power secondary distribution control unit comprises: and by combining the charge state change condition of the super capacitor and related index parameters, introducing virtual correction current and interaction rate factors, so that the charge state of the super capacitor changes towards a stable direction, and the charge state of the super capacitor is optimally controlled.

3. In step 2, the PI control is designed and improved to optimize the common direct current bus voltage non-static control according to the invention requirement.

The VSC is a core component of the photovoltaic power generation unit and realizes conversion from direct current to alternating current. In order to improve the active and reactive control performance, the controller usually adopts a double-ring control structure under a dq0 coordinate system; the outer loop controller realizes the control of direct current voltage, reactive power or alternating current voltage and outputs the target current value of the inner loop current decoupling controller. The inner ring adopts direct current vector control, and the VSC outer ring control adopts simplified constant power control and constant direct current bus voltage constant reactive power control. Fig. 2 is a block diagram of conventional dc bus voltage non-static tracking control. U in FIG. 2_dcFor actual measurement of the common DC bus voltage, U_{dc_ref}Is a DC bus voltage reference value. In order to better stabilize the voltage of the common direct current bus, the traditional control method is improved and the traditional PI control is optimized based on the relevant theory of fuzzy PI control; an improved PI method is proposed for control, and a block diagram thereof is shown in fig. 3.

Wherein, du/dt in FIG. 3 means: to (U)_{dc_ref}-U_dc) Performing first-order derivation on the difference value; the function F1 produces a control coefficient c1, the value of which is related to the error; the function F2 produces a control coefficient c2, the value of which is related to the rate of change of the error; the function F3 produces a scaling factor p3, which is related to U_dcCorrelation; the specific calculation formula is as follows:

in the formula, | maxU' | represents U_{dc_ref}-U_dcMaximum value in the first derivative of the difference, and taking the absolute result, | minU' | represents U_{dc_ref}-U_dcThe minimum value in the first derivative of the difference value and taking the absolute value result;

in the formula of U_dcmaxRepresenting the maximum value of the common dc bus voltage.

4. In step 3, the supercapacitor operation modes are divided according to the invention requirements.

The change speed of the energy storage charge state of the super capacitor is considered to be high, and the phenomenon of overcharge and overdischarge is easy to occur. In order to enable the energy storage unit to operate effectively, the normal operating range of the state of charge of the energy storage unit needs to be set. The state of charge of the super capacitor is divided as shown in fig. 4. In fig. 4, a1 and b1 are guard values of the limit management mode; and a and b are critical charging and discharging alarm values. The 4 warning values divide the charge state of the super capacitor into 3 states, namely a normal operation state, a critical charge-discharge state and a limit value management limit charge-discharge state.

5. In step 4, controlling the charge state of the super capacitor in different working modes according to the invention requirements, and introducing virtual current to control the charge and discharge of the super capacitor;

control of the hybrid energy storage system can be divided into the following three operating states according to fig. 4, where socc represents the state of charge of the supercapacitor:

(1) and (3) a normal operation interval: a & ltnocsc & gt & ltb & gt

In the interval, the charge state of the super capacitor is in a normal operation state, and the hybrid energy storage is subjected to preliminary power distribution through low-pass filtering to maintain the stability of the system.

(2) Critical charging and discharging interval: b < SOCsc < b1 (critical charging interval) or a1 < SOCsc < a (critical discharging interval).

Control of critical charging and discharging intervalAs shown in fig. 5, 8-10. In FIGS. 5, 8-10, I_{b_ref}、I_{sc_ref}Current distribution of accumulators, supercapacitors for primary power, I_{b_ref_1}、I_{sc_ref_1}Distributing the current of the hybrid energy storage for secondary power; i is_{sc_refn}The current of the super capacitor after the secondary distribution of the virtual correction current is increased in a critical charging and discharging interval; i is_virFor virtually correcting the current, I_{sc_refn}＝I_{sc_ref}+I_virTherefore, the power exchange amount of the super capacitor is changed, the purpose of power redistribution is achieved, and the charge state of the super capacitor is optimized. The specific contents compared with the traditional method are as follows:

the conventional hybrid energy storage charging and discharging pulse signal generation method is shown in fig. 5 to 7. Firstly, the residual power P_hessDecomposed by Low Pass Filtering (LPF) (residual power includes P)_LD(DC load Power), P_LS(AC load Power), P_dc(maintaining DC bus voltage for stable power), P_pv(photovoltaic power), P_sys(large grid power)), obtaining the storage battery reference power P respectively_{b_ref}And reference power P of super capacitor_{sc_ref}. Secondly, P is added_{b_ref}And the voltage U of the storage battery_batCalculating and obtaining the reference current I of the storage battery by quotient_{b_ref}And a current I flowing through the battery_batMaking a difference; and then the difference value is subjected to PI control, amplitude limiting, PWM and judgment comparison (switch) links to generate storage battery charging and discharging trigger pulse control signals G1 and G2. P_{sc_ref}And super capacitor voltage U_scCalculating and obtaining the reference current I of the super capacitor by quotient_{sc_ref}And with the current I flowing through the super capacitor_scMaking a difference; and then the difference value is subjected to PI control, amplitude limiting, PWM and judgment comparison (switch) links to generate super capacitor charging and discharging trigger pulse control signals G3 and G4.

In the invention, the traditional content is improved, and the same part of parameters are not described again. As shown in fig. 5 and 8-10, the hybrid energy storage power is secondarily distributed by forming a virtual current and limiting management control based on the super capacitor SOC. In the super capacitor SOC control module part in FIG. 8, the left dotted line frame is the main input parameter, which is super-processedThe stage capacitor SOC control module outputs corresponding control parameters, and the part mainly realizes the functions as follows: during critical charging and discharging period, a virtual current (I) is generated_vir) Slowing down the change trend of the super capacitor SOC, I_virAct on I_{sc_ref}Further controlling the charging and discharging trigger pulse signals G3 and G4 of the super capacitor to achieve the purpose of power redistribution, considering the closed-loop control of the whole system, and further the power of the super capacitor and the storage battery is not P any more_{sc_ref}、P_{b_ref}To become P_{sc_ref_1}，P_{b_ref_1}Obtaining respective reference current I by respectively making quotient with respective voltage_{sc_ref_1}，I_{b_ref_1}And (5) controlling.

In the third case, when 0 < SOCsc < a1 in the limit value management limit charging/discharging state, the discharging state is continued, i.e. P_{sc_ref}>When equal to 0, P_{sc_ref_1}＝0，P_{b_ref_1}＝P_{b_ref}+P_{sc_ref}(ii) a Or when b1 & lt ═ SOCsc & lt 100%, and is in a state of continued charge, i.e., P_{sc_ref}<At 0, P_{sc_ref_1}＝0，P_{b_ref_1}＝P_{b_ref}+P_{sc_ref}. (i.e. the super capacitor bears all the residual power, still belongs to the secondary power distribution, and the index still uses P_{sc_ref_1}，P_{b_ref_1}，I_{sc_ref_1}，I_{b_ref_1}During the period I_virNo effect occurs).

Wherein: virtual correction current I_virThe calculation formula is as follows:

in the formula: k is an interaction rate factor, and K is more than 0; SOC_refIs a super capacitor charge state reference value; SOC_(t)Representing the real-time state of charge value of the super capacitor; the virtual current correction depends on the super capacitor state of charge offset (SOC)_(t)－SOC_ref) And an interaction rate factor K. From the above formula, it can be seen that: when the charge state of the super capacitor is in the discharge critical interval and still needs to be discharged continuously, I_virTaking the negative value of the reaction mixture,reducing the discharge current of the super capacitor (the discharge current is positive), wherein the current of the storage battery relatively changes, and the discharge current is increased; within the interval P_{sc_ref}<At 0, indicating that charging is imminent, the state of charge rises, leaving the discharge critical region, and the virtual current is 0. When the charge state of the super capacitor is in the charge critical interval and the charging is still required to be continued, I_virTaking a positive value, reducing the charging current (the charging current is negative) of the super capacitor, I_virThe size (positive and negative) determines the change amplitude (trend) of the SOC under the control method provided by the invention, at the moment, the current of the storage battery relatively changes, and the charging current increases; within the interval P_{sc_ref}>When 0, it indicates that discharge is imminent, the state of charge decreases, the state of charge leaves the critical charging region, and the virtual current is 0.

In the hybrid energy storage control unit, an interaction rate factor K is used for interacting a correction current I_virThe effect of (b) is also of great importance. The larger K is, the larger the interaction current and power is, and the faster the interaction speed is, and the smaller K can cause the virtual correction current to be smaller, and the conversion time to be longer. The K value is limited by the current of the super capacitor, and the proper K value is selected to enable I to be larger than the current of the super capacitor_virThe current amplitude of the super capacitor is maintained to be about 0.3-0.6 times.

(3) Limit management interval: 0 < SOCsc < ═ a1 or b1 < ═ SOCsc < 100%

In order to avoid the situation that the super capacitor is discharged to the limit and still needs to be discharged or is charged to the limit and still needs to be charged, a limit value management control strategy is adopted for the charge state of the super capacitor in the situation, so that the storage battery bears the residual power change in the situation, and when the charging or discharging situation opposite to the limit situation occurs, the SOCsc returns to the mode (2) to continue to operate.

The secondary power distribution and interactive control flow of the hybrid energy storage system is shown in fig. 11. As can be seen from fig. 11, the required operation index parameters of the microgrid system are collected first, so as to determine the mode of the system at this time, and then power redistribution is performed according to different control methods, so as to obtain the control current of the energy storage unit to generate the PWM signal to control the charging and discharging of the energy storage element. Meanwhile, the power distribution result in different intervals and states can be more intuitively seen by combining with a chart, as shown in table 1:

TABLE 1 Interactive control and Limit management hybrid energy storage System Secondary Power distribution

6: in step 5, designing to run and debug in the photovoltaic grid-connected model according to the requirements of the invention, and carrying out simulation verification analysis;

in order to verify the effectiveness of the improved PI control and the secondary power distribution control strategy of the hybrid energy storage system based on interactive control and limit management, a photovoltaic grid-connected model shown in FIG. 1 is built on a Matlab/Simulink simulation platform. The light intensity was 1000W/m2 at an ambient temperature of 25 ℃, and the DC load was varied for 0.8 seconds, 1.5 seconds, and the AC load was varied for 1.4 seconds. The rated voltage of the storage battery is 120V, the rated capacity is 50 A.h, in order to accelerate the SOC change of the super capacitor, the capacity of the super capacitor is set to be small during the simulation verification period, and the storage battery is supposed to be in a reasonable running state in the simulation process. Setting SOC_ref0.5, 0.25 for a1, 0.3 for a, 0.7 for b1, 0.8 for b 1. Namely, the super capacitor SOC range in the normal operation state is as follows: [0.3,0.7](ii) a The range of the critical discharge and charge interval is as follows: [0.25,0.3]And [0.7, 0.8 ]](ii) a Limit discharge and charge interval range: [0,0.25]And [0.8, 1 ]](ii) a K has a value interval of [800,1100 ]]。

The invention has the innovation point that in the step 2, aiming at a grid-connected voltage type converter (VSC) in a photovoltaic grid-connected hybrid energy storage system, improved PI control optimization common direct-current bus voltage non-static-error control is provided, and compared with the traditional PI control, the common direct-current bus voltage can be better maintained near a reference voltage.

The innovation point of the method is that in the step 4, a concept of virtual correction current is introduced for the critical charging and discharging interval of the super capacitor, and the magnitude of the virtual correction current is determined according to the positive and negative of the distributed power of the super capacitor and an interaction rate factor, so that the charge state of the super capacitor changes towards a stable direction. The working state of the super capacitor is optimized, and the service life of the super capacitor is prolonged.

II, secondly: next, an analysis description is made from the experimental simulation results. According to the invention, matlab/simulink is used for modeling analysis. The details are as follows.

1. Traditional PI control and improved PI control common DC bus voltage control

Under the same simulation model and conditions, the corresponding control parameters are shown in table 2. Comparative simulation is carried out on common direct-current bus voltage no-static-error control in VSC control, and voltage results are shown in FIG. 12, wherein it can be seen that a system voltage reference value is 700V (U)_dcref) System voltage (U) under traditional PI control_dc) The voltage is basically maintained at about 680V, and the voltage stabilizing effect of the common direct current bus is poor; improving PI control so that the voltage (improving U)_dc) Well maintained around the reference voltage value, indicating the effectiveness of the improved method.

TABLE 2 control parameters

2. Control of super capacitor working in normal operation interval and critical charging interval

When the super capacitor operates in a normal operation interval, the residual power is subjected to low-pass filtering to perform primary power distribution. When the soccs is in the critical charging interval, as shown in fig. 13 and 14, during normal operation before the region a (region 1), the conventional low-pass filtering initial power control method (without considering the soccs control condition) and the method proposed by the present invention keep the super capacitor SOC curve consistent with the battery current curve; in region a, when the super capacitor is charged to the critical region, I_virStarting to act, reducing the charging current of the super capacitor, increasing the charging current of the storage battery (area 1), increasing the charging electric quantity of the storage battery, and relieving the charging state of the super capacitor; at 0.8 second, the super capacitor is switched to a discharge state, and the charge state and the current curve of the storage battery of the two methods start to change in the same trend. In region b (region 2), when the super capacitor continues to charge and the residual power is still maintained, the super capacitor is chargedWhen long-term charging is carried out, the SOCsc continuously rises to be close to the limit charging state in the traditional method, and the SOC controlled by the method of the invention is subjected to I after reaching the critical charging interval_virOnset of action decreases (I)_virThe larger the numerical value is, the stronger the action trend is), the charging capacity of the super capacitor is reduced, the charging current of the storage battery is increased, and the charging state of the super capacitor is relieved, so that the SOCsc is changed to a normal operation area. Original source SOC and original source I in the figure_batShowing simulation curves, new control SOC and new control I under the condition of not adding other control_batShows the curves under the control method of the present invention. Fig. 18-19 show graphs of the change of the power borne by the super capacitor. As can be seen from fig. 18-19, when the super capacitor SOC is in the critical charging state, the charging power component borne by the super capacitor is reduced, and the continuous charging energy of the super capacitor is reduced, so as to meet the control requirement.

3. Control of super capacitor working in critical discharge and limit discharge interval

As can be seen from fig. 15-16, the socc is lower than the lower limit of critical discharge without other control methods, that is, the super capacitor still continues to discharge when discharging to the management area of the limit value, and the super capacitor has an overdischarge phenomenon; when the method of the present invention is used, it can be seen from the region c that when the critical discharge region is approached, I_virStarting to act, reducing the discharge current of the super capacitor, and enabling the SOCsc to change towards a normal interval, so that the discharge current of the storage battery is increased (shown in an area 3), the discharge electric quantity of the storage battery is increased, and the discharge state of the super capacitor is relieved; when the SOCsc reaches the limit management alert value, the limited management curve is saved unchanged (25%). Original source SOC and original source I in the figure_batShowing simulation curves, new control SOC and new control I under the condition of not adding other control_batShows the curves under the control method of the present invention. 20-21 show the curves of the change of the power born by the super capacitor, and it can be seen from FIGS. 20-21 that the discharge power component born by the super capacitor is reduced between 0.1 s and 0.2s, so that the continuous discharge energy of the super capacitor is reduced, and the control requirement is met.

4. Control of super capacitor working in limit management interval

When the critical charging and discharging control method cannot well control the SOCsc, a state of reaching a limit charging and discharging state can occur, in the state, the limitation management is adopted to restrain the SOC of the super capacitor, the charging and discharging of the super capacitor are limited, and the storage battery bears all the residual power. In order to verify the feasibility of the method, the invention carries out limit management analysis on the limit charging state, as shown in a region 4 of fig. 17, a limit management schematic diagram is given, and it can be seen that after limit management, the SOC of the super capacitor is kept unchanged by 90% in a continuous charging state, so that the service life of the super capacitor is prevented from being damaged by an overcharge phenomenon; meanwhile, the effect of limiting management in the limiting discharge state is reflected in the area c of fig. 15, and the limiting management curve is kept unchanged (25%), so that the over-discharge phenomenon is avoided. The original SOC represents the SOC curve without other controls, and the limit SOC represents the SOC curve after the limit management is adopted.

Through simulation verification, the following conclusions can be drawn:

1. the improved PI control optimizes the common direct-current bus voltage under the photovoltaic grid-connected model without static error control, and maintains the voltage stability of the direct-current bus.

2. In consideration of the characteristic of high charging and discharging speed of the super capacitor, a control method based on interactive control and limit management is provided to correct the charge state of the super capacitor so as to keep the charge state in a better working interval. Under the critical charging and discharging state of the hybrid energy storage system, the power redistribution among the energy storage elements is controlled by introducing the concept of virtual correction current, and the working state of the super capacitor is optimized. And under the limit charge-discharge state of the hybrid energy storage system, limit value management is adopted to limit the charge-discharge of the super capacitor and avoid the overcharge and overdischarge phenomena.

It should be noted that the terms "upper", "lower", "left", "right", "front", "back", etc. used in the present invention are for clarity of description only, and are not intended to limit the scope of the present invention, and the relative relationship between the terms and the terms is not limited by the technical contents of the essential changes.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.

Claims

1. The direct-current bus voltage and super capacitor charge management control method of the optical storage system is characterized by comprising the following steps:

adding a plurality of control coefficients in PI control of the VSC unit to enable the VSC unit to optimize a common direct-current bus voltage power balancing unit to carry out no-static-error control on the common direct-current bus voltage;

2. The method for managing and controlling the direct-current bus voltage and the super capacitor charge of the light storage system according to claim 1, wherein the plurality of control coefficients comprise: control coefficient c1, control coefficient c2, control coefficient p 3; PI control outputs a VSC unit inner ring control input reference current I after being optimized by a plurality of control coefficients_{d_ref}And the voltage is transmitted to a public direct current bus voltage power balancing unit after being processed by the VSC unit, so that the static error-free control of the public direct current bus voltage is optimized;

the control coefficient c1 is:

in the formula, max U represents U_{dc_ref}-U_dcMin represents U_{dc_ref}-U_dcMinimum difference of (1), wherein U_{dc_ref}Representing the common DC bus voltage reference, U_dcRepresenting the actual measured value of the voltage of the common direct current bus;

the control coefficient c2 is:

in the formula, | max U' | represents U_{dc_ref}-U_dcMaximum value in the first derivative of the difference value, and taking the amplitude result, | minU' | represents U_{dc_ref}-U_dcThe minimum value in the first derivative of the difference value and taking the amplitude result;

the control coefficient p3 is:

said I_{d_ref}The current is as follows:

3. The method for managing and controlling the direct-current bus voltage and the super capacitor charge of the optical storage system according to claim 1, wherein the specific content for dividing the working mode of the super capacitor is as follows:

normal operating state interval: a & ltnoc & gt & ltb & gt;

4. The method for controlling the direct-current bus voltage and super-capacitor charge management of the light storage system according to claim 3, wherein when the super-capacitor state of charge (SOCsc) is in a normal operation state, that is, a < ═ SOCsc < ═ b;

and performing primary power distribution on the storage battery and the super capacitor through a low-pass filter LPF in the power distribution unit, so that the photovoltaic grid-connected hybrid energy storage system is kept stable.

5. The method for managing and controlling the direct-current bus voltage and the super capacitor charge of the optical storage system according to claim 3, wherein when the super capacitor charge state SOCsc is in a critical charging interval: b < SOCsc < b1, critical discharge interval: a1 < SOCsc < a, limit management limit discharge interval: 0 < SOCsc < ═ a1, limit management limit charging interval: b1 & lt ═ SOCsc & lt 100%;

according to different intervals, the super capacitor SOC control module in the hybrid energy storage power secondary distribution control unit correspondingly processes and calculates partial parameters in the photovoltaic grid-connected hybrid energy storage system to obtain virtual correction current I in the corresponding interval_vir(ii) a The hybrid energy storage power secondary distribution control unit performs virtual correction current I in a corresponding interval_virOptimally controlling the hybrid energy storage charge-discharge pulse trigger control unit to obtain the virtual corrected current in the corresponding intervalI_virControlled power P of super capacitor_{sc_ref_1}Further obtain the power P of the storage battery under the corresponding interval_{b_ref_1}，P_{b_ref_1}And P_{sc_ref_1}The feedback is transmitted to the super capacitor SOC control module through closed loop, and the super capacitor SOC control module is combined with P_{b_ref_1}、P_{sc_ref_1}And processing and calculating partial parameters to obtain reference current I of the super capacitor in the corresponding interval_{sc_ref_1}And a reference current I of the storage battery in a corresponding interval_{b_ref_1}；

The hybrid energy storage power secondary distribution control unit enables the reference current I of the super capacitor in the corresponding interval_{sc_ref_1}And a battery reference current I_{b_ref_1}The energy storage device is input into the hybrid energy storage charge-discharge pulse trigger control unit, and the hybrid energy storage charge-discharge pulse trigger control unit controls the storage battery and the super capacitor to carry out adaptive charge or discharge, so that the power distribution between the storage battery and the super capacitor is realized, and the charge state of the super capacitor is changed towards a stable direction.

6. The method for controlling management of direct current bus voltage and super capacitor charge of light storage system according to claim 5, wherein the partial parameters comprise super capacitor state of charge reference value SOC_refAnd the real-time state of charge (SOC) value of the super capacitor_(t)Reference power P of the accumulator_{b_ref}Reference power P of super capacitor_{sc_ref}One or more of a limit value management alert value a1, a critical discharging alert value a, a limit value management alert value b1, a critical charging alert value b, and an interaction rate factor k.

7. The light storage system direct current bus voltage and super capacitor charge management control method according to claim 6,

when the SOC SOCsc is in the critical discharge interval, i.e. a1 < SOCsc < a, and in the continuous discharge state, i.e. P_{sc_ref}>When equal to 0, I_vir＝-|K*(SOC_(t)-SOC_ref)|、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

When the SOC SOCsc is in the critical charging interval, i.e. b < SOCsc < b1, and in the continuous charging state, i.e. P_{sc_ref}<0，I_vir＝|K*(SOC_(t)-SOC_ref)|、P_{sc_ref_1}＝P_{sc_ref}、P_{b_ref_1}＝P_{b_ref}；

8. The light storage system direct current bus voltage and super capacitor charge management control method according to claim 6,

when the SOC SOCsc is in the limit management limit discharge interval, i.e. 0 < SOCsc < ═ a1, and is in the continuous discharge state, i.e. P_{sc_ref}>When the value is 0; i is_vir＝0、P_{sc_ref_1}＝0、P_{b_ref_1}＝P_{b_ref}+P_{sc_ref}；

When the state of charge of the super capacitorThe SOCsc is in the limit management limit charging interval, i.e. b1 < ═ SOCsc < 100%, and in the state of continued charge, i.e. P_{sc_ref}<At 0; i is_vir＝0、P_{sc_ref_1}＝0、P_{b_ref_1}＝P_{b_ref}+P_{sc_ref}。

9. The light storage system direct current bus voltage and super capacitor charge management control method according to claim 7 or 8,

I_{b_ref_1}＝P_{b_ref_1}/U_bat；

I_{sc_ref_1}＝P_{sc_ref_1}/U_sc；