CN114050590B - Converter control parameter design method of hybrid energy storage system - Google Patents

Converter control parameter design method of hybrid energy storage system Download PDF

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CN114050590B
CN114050590B CN202111396727.2A CN202111396727A CN114050590B CN 114050590 B CN114050590 B CN 114050590B CN 202111396727 A CN202111396727 A CN 202111396727A CN 114050590 B CN114050590 B CN 114050590B
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power
energy storage
voltage
storage system
super capacitor
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CN114050590A (en
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刘欣博
刘宁
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North China University of Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/345—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering using capacitors as storage or buffering devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention is disclosed inThe design method of the control parameters of the converter of the hybrid energy storage system is provided, and firstly, a control strategy of the hybrid energy storage system based on constant-power load power adjustment is designed; establishing a nonlinear energy function model of the hybrid energy storage system; based on the established nonlinear energy function model, deriving a system large signal stability criterion by combining a control strategy of the hybrid energy storage system; according to the obtained system large signal stability criterion, a power outer loop proportionality coefficient k of the super capacitor DC-DC link control unit is given p1 And the voltage outer loop scaling factor k of the battery DC-DC link control unit p2 The maximum value range of the hybrid energy storage system is realized. The method can effectively compensate the negative impedance characteristic of the constant power load, solves the problems of system instability and even collapse of the micro-grid system caused by the large disturbance phenomenon, and enhances the stability of the micro-grid system.

Description

Converter control parameter design method of hybrid energy storage system
Technical Field
The invention relates to the technical field of hybrid energy storage systems, in particular to a method for designing control parameters of a converter of a hybrid energy storage system.
Background
The mass utilization of renewable energy sources can effectively relieve the current coal crisis, simultaneously can greatly reduce the emission of pollutants, and achieves better energy conservation and emission reduction benefits. However, the renewable energy power generation system has the problems of randomness and uncertainty, so that the generated energy is unstable, the energy storage system is indispensable, the stability and the reliability of power supply are ensured, and the renewable energy power generation system, the energy storage system and the load form a micro-grid system together. The energy storage system has various types and can be divided into energy type and power type according to the characteristics of the energy storage technology, wherein the energy storage technology comprises battery energy storage, compressed air energy storage, water pumping energy storage and the like; the power type energy storage technology mainly comprises super capacitor energy storage, flywheel energy storage, superconductive energy storage and the like. The storage battery is widely applied to energy storage equipment, has high energy density, meets the requirement of distributed power generation on the energy density, is limited by electrochemical reaction rate, has low power density, cannot quickly absorb or release target power when load power suddenly changes, and is difficult to meet the transient requirement of a system; on the other hand, the super capacitor is physically changed in charge and discharge, has high power density, can provide larger power in a short time, but has lower energy density, and cannot supply energy for a system for a long time. Therefore, the hybrid energy storage system formed by the super capacitor and the storage battery can fully exert the advantages of high energy density of the storage battery and high power density of the super capacitor, so that the energy storage system obtains better transient steady-state performance.
Hybrid energy storage systems have become an important component of micro-grid systems, and in addition there are a large number of closed-loop controlled loads in micro-grid systems, which can be considered constant power loads. Under the conditions of micro-grid parallel-off switching, micro-source cutting, large load change, system fault and the like, a constant-power load presents negative impedance characteristics, disturbance signals can be amplified, bus voltage oscillation and even breakdown can occur, so that how to efficiently design the control parameters of the converter of the hybrid energy storage system, and the stability of the micro-grid system is enhanced, and the technical problem to be solved urgently becomes.
Disclosure of Invention
The invention aims to provide a design method of control parameters of a converter of a hybrid energy storage system, which can effectively compensate the negative impedance characteristic of a constant power load, solve the problems of instability and even collapse of a micro-grid system caused by a large disturbance phenomenon, and strengthen the stability of the micro-grid system.
The invention aims at realizing the following technical scheme:
a method of designing converter control parameters for a hybrid energy storage system, the method comprising:
step 1, designing a control strategy of a hybrid energy storage system based on constant-power load power adjustment;
step 2, establishing a nonlinear energy function model of the hybrid energy storage system;
step 3, deriving a system large signal stability criterion based on the established nonlinear energy function model and combining a control strategy of the hybrid energy storage system;
step 4, according to the obtained system large signal stability criterion, giving out the power outer loop proportionality coefficient k of the super capacitor DC-DC link control unit p1 And a battery DC-DC link control unitVoltage outer loop scaling factor k of element p2 The maximum value range of the hybrid energy storage system is realized.
According to the technical scheme provided by the invention, the negative impedance characteristic of the constant power load can be effectively compensated, the problems of instability and even collapse of the micro-grid system caused by a large disturbance phenomenon are solved, and the stability of the micro-grid system is enhanced.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic flow chart of a method for designing control parameters of a converter of a hybrid energy storage system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a hybrid energy storage system according to an embodiment of the present invention;
FIG. 3 is a control block diagram of a low pass filter according to an embodiment of the present invention;
FIG. 4 is a control block diagram of a battery inverter according to an embodiment of the present invention;
FIG. 5 is a control block diagram of a super capacitor converter according to an embodiment of the present invention;
FIG. 6 is a simplified schematic diagram of a hybrid energy storage system according to an embodiment of the present invention;
FIG. 7 is an equivalent simulation model of an exemplary hybrid energy storage system of the present invention;
FIG. 8 is a schematic diagram of a group A parametric constant power load power step waveform according to an example of the present invention;
FIG. 9 is a schematic diagram of a voltage waveform of a DC bus with group A parameters according to an example of the present invention;
FIG. 10 is a schematic diagram of a power waveform of a battery with group A parameters according to an example of the present invention;
FIG. 11 is a schematic diagram of a power waveform of a super capacitor with group A parameters according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of an example group B parametric constant power load power step waveform of the present invention;
FIG. 13 is a schematic diagram of a voltage waveform of a DC bus with group B parameters according to an example of the present invention;
FIG. 14 is a schematic diagram of a battery power waveform for example B-set parameters according to the present invention;
FIG. 15 is a schematic diagram of a power waveform of a group B parametric supercapacitor according to an example of the present invention.
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments of the present invention, and this is not limiting to the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to fall within the scope of the invention.
Fig. 1 is a schematic flow chart of a method for designing control parameters of a current transformer of a hybrid energy storage system according to an embodiment of the present invention, where the method includes:
step 1, designing a control strategy of a hybrid energy storage system based on constant-power load power adjustment;
in this step, the process of specifically designing the control strategy is:
fig. 2 is a schematic diagram of a topological structure of a hybrid energy storage system according to an embodiment of the present invention, and for the hybrid energy storage system based on constant power load power adjustment, a storage battery and a super capacitor are connected to a dc bus through a bidirectional Buck-Boost converter respectively, and then filtered by an LC filter to connect with a constant power load; the photovoltaic micro source provides electric energy for the system and is connected to the direct current bus;
the power shortage of the distributed power supply and the constant power load is distributed to the storage battery and the super capacitor through the low-pass filter, specifically, the low-frequency part of the power is used as the target stabilized power of the storage battery, and the high-frequency part of the power is used as the target stabilized power of the super capacitor; the filtering time constant of the low-pass filter can be dynamically adjusted by the power difference between the distributed power supply and the constant power load, as shown in fig. 3, which is a control block diagram of the low-pass filter according to the embodiment of the invention, and the relation between the powers of the units is shown in formula (1):
P DG -P load ＝P bat-ref +P sc-ref (1)
wherein P is DG Generating power for the micro source; p (P) load Is the load power; p (P) bat-ref Target power for the battery; p (P) sc-ref The target power is super capacitor;
the power difference between the distributed power supply and the constant power load is the sum of target stabilizing power of the storage battery and the super capacitor, a first-order low-pass filter LPF is adopted to realize a low-pass filtering function, and the corresponding transfer function is as follows:
wherein T is a filtering time constant; s is complex frequency;
P HESS the total power required to be stabilized for the hybrid energy storage system is obtained by deducting the target stabilized power of the storage battery as follows:
the target stabilized power of the super capacitor is as follows:
then, after the difference of the formula (3), discretizing the difference to obtain the following formula:
then formula (3) is finally converted into:
wherein T is s For calculating the period, the period is a fixed value in the filtering process;
after differentiating the formula (4), discretizing the formula to obtain the following formula:
then formula (4) is finally converted into:
let P in (10) HESS (k+1)-P HESS (k)＝ΔP HESS Then the following steps are obtained:
when a control strategy is designed, the influence of power fluctuation on the stability of the system is considered, so that the filtering time constant is changed according to the power fluctuation, the power distribution of the super capacitor and the storage battery is changed, the hybrid energy storage system ensures the stability of the system while stabilizing the power, and specifically:
dividing the power fluctuation of a distributed power supply and a constant power load into a plurality of ranges according to frequency, wherein each range corresponds to different power fluctuation intervals, namely a high-frequency area (1 Hz and above), a medium-frequency area (0.01-1 Hz) and a low-frequency area (0.01 Hz and below), respectively selecting a filtering time constant T meeting the stability requirement, and changing the filtering time constant T of a low-pass filter in real time in the process of changing the constant power load power so as to change the target stabilized power of a super capacitor and a storage battery, namely fully considering the influence of the constant power load power on the system stability in the process of distributing the power of the super capacitor and the storage battery, thereby compensating the negative impedance characteristic of the constant power load;
as shown in fig. 4, the control block diagram of the battery converter according to the embodiment of the invention is shown, and the battery is used as a voltage stabilizing unit of the hybrid energy storage system to maintain the voltage of the dc bus, so that the control method of the outer ring of the voltage of the dc bus and the inner ring of the inductance current is adopted to maintain the voltage of the dc bus constant and realize automatic switching of charging and discharging of the battery;
fig. 5 is a control block diagram of the super capacitor converter according to the embodiment of the present invention, wherein a high frequency part of a difference between electric energy generated by a distributed power supply and electric energy consumed by a constant power load is used as a target stabilizing power of a super capacitor, an actual charging and discharging power of the super capacitor is controlled to be equal to the target stabilizing power by using an outer loop and an inner loop of the power, a filtering time constant T of a low pass filter is changed in real time, and the changed filtering time constant T is input in real time.
Step 2, establishing a nonlinear energy function model of the hybrid energy storage system;
in this step, before building the function model, the hybrid energy storage system is first simplified, as shown in fig. 6, which is a simplified model diagram of the hybrid energy storage system according to the embodiment of the present invention, and the distributed power source is equivalent to a current source, whose power is P DG ，C e Is a voltage stabilizing capacitor on the direct current bus, and the voltage at two ends of the voltage stabilizing capacitor is V e The method comprises the steps of carrying out a first treatment on the surface of the The storage battery and the super capacitor are controlled by the DC-DC link, so that the storage battery and the super capacitor are integrally equivalent to a controlled current source, and the power of the controlled current source is P respectively bat And P sc ；R 1 、L 1 The equivalent resistance and inductance of the circuit are respectively; l (L) s 、R s The filter inductance and the equivalent resistance are respectively; the current flowing through the filter inductance is i e ；C s Is a filter capacitor, the voltage at two ends of the filter capacitor is V s ；P load For constant power load power, the distributed power supply and the hybrid energy storage column write voltage potential function:
write current potential function to resistive column:
write voltage potential function for constant power load column:
the energy stored on the filter capacitor is:
the nonlinear energy function model of the hybrid energy storage system is finally obtained and expressed as:
further checking the obtained nonlinear energy function model:
it can be seen that the nonlinear energy function model obtained by equation (16) is correct for the simplified model shown in fig. 6.
Step 3, deriving a system large signal stability criterion based on the established nonlinear energy function model and combining a control strategy of the hybrid energy storage system;
in the step, firstly, according to a nonlinear energy function model type (16) of the hybrid energy storage system, a current potential function A (i) and a voltage potential function B (v) of the system are respectively obtained as follows:
the secondary bias is carried out on the formulas (18) and (19) respectively to obtain:
the control strategy and the principle of conservation of power of the storage battery converter are as follows:
i L2 ＝i Bref ＝k p2 (v eref -v e )+k i2 (v eref -v e )dt (22)
i bat v e ＝i B v B (23)
wherein k is p2 、k i2 The control parameters of the proportional link and the integral link of the direct-current voltage outer ring of the DC-DC link control unit of the storage battery pack are obtained; v e The voltage of two ends of the voltage stabilizing capacitor on the direct current bus is the voltage of two ends of the voltage stabilizing capacitor on the direct current bus; i.e bat Outputting current to a storage battery DC/DC converter; v B 、i B Voltage and current on the battery side of the DC/DC converter; i.e L2 An inductor current in the battery DC/DC converter;
the method further comprises the following steps:
the control strategy and the principle of power conservation of the super capacitor converter can be known:
i L1 ＝i SCref ＝k p1 (P scref -i sc v e )+k i1 (P scref -i sc v e )dt (25)
i sc v e ＝i SC v SC (26)
wherein k is p1 、k i1 The control parameters of the proportional link and the integral link of the power outer loop of the super capacitor DC-DC link control unit are obtained; v SC 、i SC The voltage and the current of the super capacitor side of the DC/DC converter are obtained; i.e L1 The inductor current in the super capacitor DC/DC converter;
the method further comprises the following steps:
then solving the minimum feature root of the system energy function according to equations (20), (21), (24) and (27), it is possible to obtain:
wherein equation (28) is a current energy function and equation (29) is a voltage energy function;
bringing formula (11) into formula (29) yields:
finally, the design constraint conditions of the control parameters of the hybrid energy storage system converter are obtained by deduction:
equation (31) is the system large signal stability criterion.
Step 4, according to the obtained system large signal stability criterion, giving out the power outer loop proportionality coefficient k of the super capacitor DC-DC link control unit p1 And the voltage outer loop scaling factor k of the battery DC-DC link control unit p2 The maximum value range of the hybrid energy storage system is realized.
In the step, in order to compensate the negative impedance characteristic of the constant power load and ensure the safe and stable operation of the direct current micro-grid system under the condition of large signals, the power outer loop proportionality coefficient k of the super capacitor DC-DC link control unit is obtained by a formula (31) p1 And the voltage outer loop scaling factor k of the battery DC-DC link control unit p2 Is a maximum value range of (a).
Wherein, the value range of the control parameter of the converter and the constant power load power P load Storage battery and super capacitor power P bat And P sc Line equivalent resistance, inductance R 1 And L 1 Filtering inductance and equivalent resistance L thereof s And R is s Filter capacitor C s Voltage V across it s DC bus voltage stabilizing capacitor C e And the voltage V across it e And the filtering time constant T of the low-pass filter.
It is noted that what is not described in detail in the embodiments of the present invention belongs to the prior art known to those skilled in the art.
The process and accuracy of the above-mentioned parameter design method are verified by a specific example, in this example, matlab software is first applied to build an equivalent simulation model of the hybrid energy storage system shown in fig. 7, and the parameters of the hybrid energy storage system topology are shown in the following table 1:
table 1 system simulation parameters
The control parameters of the converter designed according to the formula (31) can inhibit the influence of the constant power load on the stability of the system, and the system still keeps stable when the system is subjected to the fluctuation of the constant power load power.
Simulation verification is performed as follows:
two sets of control parameters were separately designed as shown in table 2 below. Group a parameters satisfy formula (31), and group B parameters do not satisfy formula (31):
table 2 hybrid energy storage system converter control parameters
When t=2s, the constant power load power is stepped from 2kw to 12kw, and whether the system can stably run after the power step can be ensured by two groups of parameters.
The A group parameter is the direct-current voltage outer ring proportional integral parameter k of the storage battery DC-DC converter p1 2, the proportional integral parameter k of the DC-DC link control unit DC voltage outer ring of the super capacitor unit p1 Fig. 8 shows a schematic diagram of a power step of the constant power load with parameter a of the example of the present invention, fig. 9 shows a schematic diagram of a voltage waveform of the dc bus with parameter a, fig. 10 shows a schematic diagram of a power waveform of the battery with parameter a, fig. 11 shows a schematic diagram of a power waveform of the super capacitor with parameter a, as can be seen from fig. 8-11, the voltage of the dc bus of the micro grid system is still maintained at 400V after the power step, the power waveforms of the battery and the super capacitor are normal, and the hybrid energy storage system can stably operate.
The B group parameter is the direct-current voltage outer ring proportional integral parameter k of the storage battery DC-DC converter p1 10, the proportional integral parameter k of the DC-DC link control unit DC voltage outer ring of the super capacitor unit p1 0.1, as shown in FIG. 12, which is a schematic diagram of a B-group parameter constant power load power step waveform, as shown in FIG. 13, which is a schematic diagram of a B-group parameter DC bus voltage waveform, as shown in FIG. 14, which is a schematic diagram of a B-group parameter battery power waveformFig. 15 is a schematic diagram of a power waveform of a super capacitor with B-group parameters, and fig. 12-15 show that the voltage of the dc bus of the micro grid system cannot be maintained at 400V after the power step, so that the power waveforms of the storage battery and the super capacitor are unstable. It follows that the hybrid energy storage system cannot operate stably during load power steps when the energy storage converter control parameters do not meet criterion (31).
As can be seen from comparison of simulation results of the control parameters of the group A and the group B, under the same power step condition, the control parameters of the group A enable the system to continue to run stably after undergoing large disturbance of constant power load step; the group B control parameters make the system unable to maintain stable operation after experiencing large disturbances of the constant power load step. Thereby, it is verified that the energy storage converter control parameter constraint condition shown in the formula (31) is correct.
In summary, according to the embodiment of the invention, the control parameters of the energy storage converter in the hybrid energy storage system are optimally designed, so that the influence of the constant power load in the system on the stability of the system can be restrained, and a basis is provided for the optimal design of the system parameters.
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the scope of the present invention should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims. The information disclosed in the background section herein is only for enhancement of understanding of the general background of the invention and is not to be taken as an admission or any form of suggestion that this information forms the prior art already known to those of ordinary skill in the art.

Claims (4)

1. A method for designing control parameters of a converter of a hybrid energy storage system, the method comprising:
step 1, designing a control strategy of a hybrid energy storage system based on constant-power load power adjustment;
step 2, establishing a nonlinear energy function model of the hybrid energy storage system;
the process of the step 2 specifically comprises the following steps:
firstly, simplifying a hybrid energy storage system, and enabling a distributed power supply to be equivalent to a current source, wherein the power of the distributed power supply is P DG ，C e Is a voltage stabilizing capacitor on the direct current bus, and the voltage at two ends of the voltage stabilizing capacitor is V e The method comprises the steps of carrying out a first treatment on the surface of the The storage battery and the super capacitor are controlled by the DC-DC link, so that the storage battery and the super capacitor are integrally equivalent to a controlled current source, and the power of the controlled current source is P respectively bat And P sc ；R 1 、L 1 The equivalent resistance and inductance of the circuit are respectively; l (L) s 、R s The filter inductance and the equivalent resistance are respectively; the current flowing through the filter inductance is i e ；C s Is a filter capacitor, the voltage at two ends of the filter capacitor is V s ；P load For constant power load power, the distributed power supply and the hybrid energy storage column write voltage potential function:
write current potential function to resistive column:
write voltage potential function for constant power load column:
the energy stored on the filter capacitor is:
the nonlinear energy function model of the hybrid energy storage system is finally obtained and expressed as:
further checking the obtained nonlinear energy function model:
it follows that the nonlinear energy function model obtained by equation (16) is correct;
step 3, deriving a system large signal stability criterion based on the established nonlinear energy function model and combining a control strategy of the hybrid energy storage system;
step 4, according to the obtained system large signal stability criterion, giving out the power outer loop proportionality coefficient k of the super capacitor DC-DC link control unit p1 And the voltage outer loop scaling factor k of the battery DC-DC link control unit p2 The maximum value range of the hybrid energy storage system is realized.
2. The method for designing parameters of current transformer control of hybrid energy storage system according to claim 1, wherein the process of step 1 specifically comprises:
aiming at a hybrid energy storage system based on constant power load power adjustment, a storage battery and a super capacitor are respectively connected into a direct current bus through a bidirectional Buck-Boost converter, and then are connected with a constant power load after being filtered through an LC filter;
the power shortage of the distributed power supply and the constant power load is distributed to the storage battery and the super capacitor through the low-pass filter, specifically, the low-frequency part of the power is used as the target stabilized power of the storage battery, and the high-frequency part of the power is used as the target stabilized power of the super capacitor; the filtering time constant of the low-pass filter can be dynamically adjusted by the power difference of the distributed power supply and the constant power load, and the relation among the unit powers is shown as the following formula (1):
P DG -P load ＝P bat-ref +P sc-ref (1)
wherein P is DG Generating power for the micro source; p (P) load Is the load power; p (P) bat-ref Target power for the battery; p (P) sc-ref The target power is super capacitor;
the power difference between the distributed power supply and the constant power load is the sum of target stabilizing power of the storage battery and the super capacitor, a first-order low-pass filter LPF is adopted to realize a low-pass filtering function, and the corresponding transfer function is as follows:
wherein T is a filtering time constant, s is complex frequency;
P HESS the total power required to be stabilized for the hybrid energy storage system is obtained by deducting the target stabilized power of the storage battery as follows:
the target stabilized power of the super capacitor is as follows:
then, after the difference of the formula (3), discretizing the difference to obtain the following formula:
then formula (3) is finally converted into:
wherein T is s For calculating the period, the period is a fixed value in the filtering process;
after differentiating the formula (4), discretizing the formula to obtain the following formula:
then formula (4) is finally converted into:
let P in (10) HESS (k+1)-P HESS (k)＝ΔP HESS Then the following steps are obtained:
when a control strategy is designed, the influence of power fluctuation on the stability of the system is considered, so that the filtering time constant is changed according to the power fluctuation, the power distribution of the super capacitor and the storage battery is changed, the hybrid energy storage system ensures the stability of the system while stabilizing the power, and specifically:
dividing the power fluctuation of a distributed power supply and a constant power load into a plurality of ranges according to frequency, wherein each range corresponds to different power fluctuation intervals, namely a high-frequency area, a medium-frequency area and a low-frequency area, respectively selecting a filtering time constant T meeting the stability requirement, and changing the filtering time constant T of a low-pass filter in real time in the process of changing the power of the constant power load so as to change the target stabilized power of a super capacitor and a storage battery;
the storage battery is used as a voltage stabilizing unit of the hybrid energy storage system to play a role in maintaining the voltage of the direct-current bus, so that a control method of an outer ring of the voltage of the direct-current bus and an inner ring of the inductance current is adopted to maintain the voltage of the direct-current bus constant and realize automatic switching of charging and discharging of the battery;
and taking a high-frequency part of the difference between the electric energy emitted by the distributed power supply and the electric energy consumed by the constant power load as the target stabilizing power of the super capacitor, controlling the actual charging and discharging power of the super capacitor to be equal to the target stabilizing power by using the power outer loop and the current inner loop, wherein the filtering time constant T of the low-pass filter can be changed in real time, and the changed filtering time constant T is input in real time.
3. The method for designing parameters of current transformer control of hybrid energy storage system according to claim 1, wherein the process of step 3 specifically comprises:
firstly, according to a nonlinear energy function model type (16) of the hybrid energy storage system, a current potential function A (i) and a voltage potential function B (v) are respectively obtained as follows:
the secondary bias is carried out on the formulas (18) and (19) respectively to obtain:
the control strategy and the principle of conservation of power of the storage battery converter are as follows:
i L2 ＝i Bref ＝k p2 (v eref -v e )+k i2 (v eref -v e )dt (22)
i bat v e ＝i B v B (23)
wherein k is p2 、k i2 The control parameters of the proportional link and the integral link of the direct-current voltage outer ring of the DC-DC link control unit of the storage battery pack are obtained; v e The voltage of two ends of the voltage stabilizing capacitor on the direct current bus is the voltage of two ends of the voltage stabilizing capacitor on the direct current bus; i.e bat Outputting current to a storage battery DC/DC converter; v B 、i B Voltage and current on the battery side of the DC/DC converter; i.e L2 An inductor current in the battery DC/DC converter;
the method further comprises the following steps:
the control strategy and the principle of power conservation of the super capacitor converter can be known:
i L1 ＝i SCref ＝k p1 (P sc-ref -i sc v e )+k i1 (P sc-ref -i sc v e )dt (25)
i sc v e ＝i SC v SC (26)
wherein k is p1 、k i1 The control parameters of the proportional link and the integral link of the power outer loop of the super capacitor DC-DC link control unit are obtained; v SC 、i SC The voltage and the current of the super capacitor side of the DC/DC converter are obtained; i.e L1 The inductor current in the super capacitor DC/DC converter;
the method further comprises the following steps:
then solving the minimum feature root of the system energy function according to equations (20), (21), (24) and (27), it is possible to obtain:
wherein equation (28) is a current energy function and equation (29) is a voltage energy function;
bringing formula (11) into formula (29) yields:
finally, the design constraint conditions of the control parameters of the hybrid energy storage system converter are obtained by deduction:
equation (31) is the system large signal stability criterion.
4. The method of claim 1, wherein in step 4, the range of values of the converter control parameters and the constant power load power P are set load Storage battery and super capacitor power P bat And P sc Line equivalent resistance, inductance R 1 And L 1 Filtering inductance and equivalent resistance L thereof s And R is s Filter capacitor C s Voltage V across it s DC bus voltage stabilizing capacitor C e And the voltage V across it e And the filtering time constant T of the low-pass filter.
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