CN114050590A - 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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CN114050590A
CN114050590A CN202111396727.2A CN202111396727A CN114050590A CN 114050590 A CN114050590 A CN 114050590A CN 202111396727 A CN202111396727 A CN 202111396727A CN 114050590 A CN114050590 A CN 114050590A
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power
energy storage
storage system
hybrid energy
voltage
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CN114050590B (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

Abstract

The invention discloses a converter control parameter design method of a hybrid energy storage system, which comprises the steps of firstly designing a control strategy of the hybrid energy storage system based on constant power load power regulation; establishing a nonlinear energy function model of the hybrid energy storage system; based on the established nonlinear energy function model, a system large signal stability criterion is obtained by combining the control strategy derivation of the hybrid energy storage system; according to the obtained system large signal stability criterion, a power outer loop proportion coefficient k of a super capacitor DC-DC link control unit is givenp1And the voltage outer ring proportionality coefficient k of the storage battery DC-DC link control unitp2The maximum value range of the hybrid energy storage system is obtained, and the design of the converter control parameters of the hybrid energy storage system is realized. The method can effectively compensate the negative impedance characteristic of the constant power load, and solves the problem of large disturbance of the micro-grid systemThe system instability and even breakdown caused by dynamic phenomena enhance 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 converter control parameters of a hybrid energy storage system.
Background
The large amount of renewable energy can effectively relieve the current coal crisis, greatly reduce the emission of pollutants and obtain better energy-saving and emission-reducing 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 guaranteed, and the renewable energy power generation system, the distributed power supply, the energy storage system and the load form a micro-grid system together. The types of the energy storage systems are various, and can be divided into an energy type and a 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, superconducting 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 state requirement of a system; on the other hand, the super capacitor is internally physically changed during charging and discharging, the power density is high, large power can be provided in a short time, but the energy density is low, and the system cannot be supplied with energy for a long time. Therefore, the hybrid energy storage system consisting of 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 and steady-state performance.
Hybrid energy storage systems have become an important component of micro-grid systems, and in addition, a large number of closed-loop controlled loads exist in the micro-grid systems, which can be regarded as constant-power loads. Under the conditions of grid-on and off-grid switching, micro-source removal, large load change, system faults and the like of a micro-grid, a constant-power load presents a negative impedance characteristic, a disturbance signal is amplified, and the phenomenon of bus voltage oscillation and even breakdown can occur, so that how to efficiently design the converter control parameters of the hybrid energy storage system and enhance the stability of the micro-grid system becomes a technical problem which needs to be solved urgently.
Disclosure of Invention
The invention aims to provide a method for designing the 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 problem of system instability and even breakdown of a micro-grid system due to a large disturbance phenomenon and enhance the stability of the micro-grid system.
The purpose of the invention is realized by 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 regulation;
step 2, establishing a nonlinear energy function model of the hybrid energy storage system;
step 3, based on the established nonlinear energy function model, combining a control strategy of the hybrid energy storage system to deduce and obtain a system large signal stability criterion;
step 4, according to the obtained system large signal stability criterion, a power outer loop proportion coefficient k of the super capacitor DC-DC link control unit is givenp1And the voltage outer ring proportionality coefficient k of the storage battery DC-DC link control unitp2The maximum value range of the hybrid energy storage system is obtained, and the design of the converter control parameters of the hybrid energy storage system is realized.
According to the technical scheme provided by the invention, the method can effectively compensate the negative impedance characteristic of the constant-power load, solve the problem of system instability and even breakdown of the micro-grid system due to a large disturbance phenomenon, and enhance the stability of the micro-grid system.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic flow chart of a method for designing converter control parameters of a hybrid energy storage system according to an embodiment of the present invention;
fig. 2 is a schematic view of a topology of a hybrid energy storage system according to an embodiment of the present invention;
FIG. 3 is a control block diagram of the low pass filter according to the embodiment of the present invention;
FIG. 4 is a control block diagram of a battery converter 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 model diagram of a hybrid energy storage system according to an embodiment of the present invention;
FIG. 7 is an equivalent simulation model of a hybrid energy storage system in accordance with an exemplary embodiment of the present invention;
FIG. 8 is a schematic diagram of a constant power load power step waveform for set A parameters in accordance with an exemplary embodiment of the present invention;
FIG. 9 is a schematic diagram of a DC bus voltage waveform illustrating group A parameters according to an exemplary embodiment of the present invention;
FIG. 10 is a schematic diagram of a battery power waveform illustrating group A parameters of an exemplary embodiment of the present invention;
FIG. 11 is a diagram illustrating exemplary super capacitor power waveforms for set A parameters;
FIG. 12 is a schematic diagram of a set B parameter constant power load power step waveform in accordance with an exemplary embodiment of the present invention;
FIG. 13 is a schematic diagram of a DC bus voltage waveform illustrating group B parameters in accordance with an exemplary embodiment of the present invention;
FIG. 14 is a schematic diagram of a battery power waveform illustrating group B parameters of an exemplary embodiment of the present invention;
FIG. 15 is a diagram of super capacitor power waveforms illustrating group B parameters according to an exemplary embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, not all embodiments, and this does not limit the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic flow chart of a method for designing converter control parameters 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 regulation;
in this step, the process of specifically designing the control strategy is as follows:
as shown in fig. 2, which is a schematic diagram of a topological structure of a hybrid energy storage system according to an embodiment of the present invention, for a hybrid energy storage system based on constant power load power regulation, a storage battery and a super capacitor are respectively connected to a dc bus through a bidirectional Buck-Boost converter, and then are connected to a constant power load after being filtered through an LC filter; 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 a low-pass filter, specifically, a low-frequency part of power is used as target stabilizing power of the storage battery, and a high-frequency part of the power is used as target stabilizing 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, and as shown in fig. 3, which is a control block diagram of the low-pass filter according to the embodiment of the present invention, the relationship between the unit powers is as shown in formula (1):
PDG-Pload＝Pbat-ref+Psc-ref (1)
wherein, PDGGenerating power for the micro source; ploadIs the load power; pbat-refA target power for the battery; psc-refIs the target power of the 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:
Figure BDA0003370160430000031
wherein T is a filtering time constant; s is the complex frequency;
PHESSfor the total power needed to be stabilized by the hybrid energy storage system, the target stabilizing power of the storage battery is derived as follows:
Figure BDA0003370160430000041
the target stabilizing power of the super capacitor is:
Figure BDA0003370160430000042
after the difference of the formula (3) is obtained, discretization is carried out, and the following can be obtained:
Figure BDA0003370160430000043
Figure BDA0003370160430000044
the final transformation of formula (3) is:
Figure BDA0003370160430000045
wherein, TsThe value is a fixed value in the filtering process for calculating the period;
after differentiating the equation (4), discretizing it can be inferred as:
Figure BDA0003370160430000046
Figure BDA0003370160430000047
the final transformation of formula (4) is:
Figure BDA0003370160430000048
let P in formula (10)HESS(k+1)-PHESS(k)＝ΔPHESSThen, obtaining:
Figure BDA0003370160430000049
when designing control strategy, the influence of power fluctuation to system stability should be considered, consequently change the filtering time constant according to power fluctuation to change the power distribution of super capacitor and battery, let the hybrid energy storage system guarantee system stability when stabilizing power, specifically:
dividing 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 region (1Hz and above), a medium-frequency region (0.01-1 Hz) and a low-frequency region (0.01Hz and below), respectively selecting a filtering time constant T meeting stability requirements, and changing the filtering time constant T of a low-pass filter in real time in the process of constant power load power change so as to change the target stabilizing power of a super capacitor and a storage battery, namely fully considering the influence of constant power load power on system stability in the process of super capacitor and storage battery power distribution, thereby compensating the negative impedance characteristic of the constant power load;
as shown in fig. 4, which is a control block diagram of the battery converter according to the embodiment of the present invention, the battery serves as a voltage stabilizing unit of the hybrid energy storage system to maintain the voltage of the dc bus, so that a control method of a dc bus voltage outer loop and an inductive current inner loop is adopted to maintain the voltage of the dc bus constant, and to implement automatic switching of charging and discharging of the battery;
as shown in fig. 5, which is a control block diagram of the super capacitor converter according to the embodiment of the present invention, a high frequency portion of a difference between electric energy generated by a distributed power source and electric energy consumed by a constant power load is used as a target stabilizing power of a super capacitor, an outer loop of power and an inner loop of current are used to control actual charge and discharge power of the super capacitor to be equal to the target stabilizing power, a filtering time constant T of a low pass filter changes 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 the function model is established, the hybrid energy storage system is simplified, as shown in fig. 6, which is a simplified model schematic diagram of the hybrid energy storage system according to the embodiment of the present invention, the distributed power source is equivalent to a current source with power PDG，CeIs a voltage stabilizing capacitor on a direct current bus, and the voltage at two ends of the capacitor is Ve(ii) a The storage battery and the super capacitor are controlled by the DC-DC link, so the storage battery and the super capacitor are integrally equivalent to a controlled current source with the power of PbatAnd Psc；R1、L1Respectively a circuit equivalent resistance and an inductance; l iss、RsRespectively a filter inductor and an equivalent resistor thereof; the current flowing through the filter inductor is ie；CsIs a filter capacitor with voltage V at both endss；PloadAnd (3) writing a voltage potential function to the distributed power supply and the hybrid energy storage column for constant power load power:
Figure BDA0003370160430000051
write current potential function to resistive columns:
Figure BDA0003370160430000052
write voltage potential function for constant power load column:
Figure BDA0003370160430000053
the energy stored on the filter capacitor is:
Figure BDA0003370160430000054
and finally, expressing the nonlinear energy function model of the hybrid energy storage system as follows:
Figure BDA0003370160430000055
the obtained nonlinear energy function model is further checked:
Figure BDA0003370160430000061
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, based on the established nonlinear energy function model, combining a control strategy of the hybrid energy storage system to deduce and obtain a system large signal stability criterion;
in the step, firstly, according to a nonlinear energy function model formula (16) of the hybrid energy storage system, a current potential function a (i) and a voltage potential function b (v) of the system are obtained as follows:
Figure BDA0003370160430000062
Figure BDA0003370160430000063
by performing the second partial derivation on the equations (18) and (19), respectively:
Figure BDA0003370160430000064
Figure BDA0003370160430000065
according to the control strategy and the power conservation principle of the storage battery converter, the following steps are known:
iL2＝iBref＝kp2(veref-ve)+ki2(veref-ve)dt (22)
ibatve＝iBvB (23)
wherein k isp2、ki2Controlling parameters of a proportional link and an integral link of a direct-current voltage outer ring of a DC-DC link control unit of the storage battery pack; v. ofeThe voltage of two ends of a voltage stabilizing capacitor on a direct current bus is obtained; i.e. ibatOutputting current for the storage battery DC/DC converter; v. ofB、iBVoltage and current on the storage battery side of the DC/DC converter; i.e. iL2Is the inductive current in the DC/DC converter of the storage battery;
further obtaining:
Figure BDA0003370160430000071
according to the control strategy and the power conservation principle of the super capacitor converter, the following steps are known:
iL1＝iSCref＝kp1(Pscref-iscve)+ki1(Pscref-iscve)dt (25)
iscve＝iSCvSC (26)
wherein k isp1、ki1Controlling parameters of a proportional link and an integral link of a power outer loop of a super capacitor DC-DC link control unit; v. ofSC、iSCVoltage and current on the super capacitor side of the DC/DC converter; i.e. iL1The current is the inductive current in the super capacitor DC/DC converter;
further obtaining:
Figure BDA0003370160430000072
then, solving the minimum characteristic root of the system energy function according to the equations (20), (21), (24) and (27), so as to obtain:
Figure BDA0003370160430000073
Figure BDA0003370160430000074
wherein, the formula (28) is a current energy function, and the formula (29) is a voltage energy function;
further, by bringing formula (11) into formula (29), it is possible to obtain:
Figure BDA0003370160430000075
finally, the design constraint conditions for deriving the control parameters of the converter of the hybrid energy storage system are as follows:
Figure BDA0003370160430000081
and the formula (31) is the criterion of the stability of the system large signal.
Step 4, according to the obtained system large signal stability criterion, a power outer loop proportion coefficient k of the super capacitor DC-DC link control unit is givenp1And the voltage outer ring proportionality coefficient k of the storage battery DC-DC link control unitp2The maximum value range of the hybrid energy storage system is obtained, and the design of the converter control parameters 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 signal, a power outer loop proportion coefficient k of the super-capacitor DC-DC link control unit is obtained by a formula (31)p1And the voltage outer ring proportionality coefficient k of the storage battery DC-DC link control unitp2The maximum value range of (a).
Wherein, the value range of the control parameter of the converterAnd constant power load power PloadAccumulator and supercapacitor power PbatAnd PscEquivalent resistance and inductance R of circuit1And L1Filter inductor and its equivalent resistance LsAnd RsFilter capacitor CsAnd its voltage V acrosssDC bus voltage-stabilizing capacitor CeAnd a voltage V across iteAnd the filter time constant T of the low-pass filter.
It is noted that those skilled in the art will recognize that embodiments of the present invention are not described in detail herein.
The process and accuracy of the parameter design method are verified by using a specific example, in the example, Matlab software is firstly applied to build an equivalent simulation model of the hybrid energy storage system shown in fig. 7, and the parameters of the topology of the hybrid energy storage system are shown in the following table 1:
TABLE 1 System simulation parameters
Figure BDA0003370160430000082
The converter control parameters 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 power of the constant power load fluctuates.
Simulation verification is performed as follows:
two sets of control parameters were designed, respectively, as shown in table 2 below. Group a parameters satisfy formula (31), group B parameters do not satisfy formula (31):
TABLE 2 hybrid energy storage System converter control parameters
Figure BDA0003370160430000091
When t is 2s, the constant power load power is stepped from 2kw to 12kw, and whether stable operation of the system can be ensured after power step of two groups of parameters can be obtained.
The parameter of group A is the external ring ratio of DC voltage of the DC-DC converterIntegral parameter k p12, a proportional integral parameter k of a direct current voltage outer ring of a super capacitor unit DC-DC link control unitp1Fig. 8 is a schematic diagram of a power step waveform of a group a parameter constant power load according to an example of the present invention, fig. 9 is a schematic diagram of a voltage waveform of a group a parameter dc bus, fig. 10 is a schematic diagram of a power waveform of a group a parameter storage battery, fig. 11 is a schematic diagram of a power waveform of a group a parameter super capacitor, and as can be seen from fig. 8 to 11, a dc bus voltage of a microgrid system is still maintained at 400V after a power step, power waveforms of the storage battery and the super capacitor are normal, and a hybrid energy storage system can stably operate.
The B group of parameters are direct-current voltage outer ring proportional integral parameters k of the storage battery DC-DC converterp110, the proportion integral parameter k of the direct current voltage outer ring of the super capacitor unit DC-DC link control unitp1Fig. 12 is a schematic diagram of a power step waveform of a group B parameter constant power load according to an example of the present invention, fig. 13 is a schematic diagram of a voltage waveform of a group B parameter dc bus, fig. 14 is a schematic diagram of a power waveform of a group B parameter storage battery, fig. 15 is a schematic diagram of a power waveform of a group B parameter super capacitor, and fig. 12 to 15 show that a dc bus voltage of a microgrid system cannot be maintained at 400V after a power step, so that power waveforms of the storage battery and the super capacitor are unstable. Therefore, when the control parameter of the energy storage converter does not meet the criterion formula (31), the hybrid energy storage system cannot stably operate when the load power is stepped.
The comparison of the simulation results of the group A control parameters and the group B control parameters shows that under the same power step condition, the group A control parameters enable the system to continue to stably run after the system is subjected to large disturbance of constant power load step; the group B control parameters cause the system not to keep stable operation after the system is subjected to large disturbance of constant power load step. Therefore, the constraint conditions of the control parameters of the energy storage converter shown in the formula (31) are verified to be correct.
In summary, the embodiment of the invention can suppress the influence of the constant power load in the system on the stability of the system by optimally designing the control parameters of the energy storage converter in the hybrid energy storage system, and provides a basis for optimally designing the system parameters.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims (5)

1. A method for designing converter control parameters of a hybrid energy storage system is characterized by comprising the following steps:
step 1, designing a control strategy of a hybrid energy storage system based on constant-power load power regulation;
step 2, establishing a nonlinear energy function model of the hybrid energy storage system;
step 3, based on the established nonlinear energy function model, combining a control strategy of the hybrid energy storage system to deduce and obtain a system large signal stability criterion;
step 4, according to the obtained system large signal stability criterion, a power outer loop proportion coefficient k of the super capacitor DC-DC link control unit is givenp1And the voltage outer ring proportionality coefficient k of the storage battery DC-DC link control unitp2The maximum value range of the hybrid energy storage system is obtained, and the design of the converter control parameters of the hybrid energy storage system is realized.
2. The method for designing the converter control parameters of the hybrid energy storage system according to claim 1, wherein the process of the step 1 specifically comprises the following steps:
aiming at a hybrid energy storage system based on constant power load power regulation, a storage battery and a super capacitor are respectively connected to a direct current bus through a bidirectional Buck-Boost converter, and 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 a low-pass filter, specifically, a low-frequency part of power is used as target stabilizing power of the storage battery, and a high-frequency part of the power is used as target stabilizing 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, and the relationship between the unit powers is shown as formula (1):
PDG-Pload＝Pbat-ref+Psc-ref (1)
wherein, PDGGenerating power for the micro source; ploadIs the load power; pbat-refA target power for the battery; psc-refIs the target power of the 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:
Figure FDA0003370160420000011
wherein T is a filter time constant, and s is a complex frequency;
PHESSfor the total power needed to be stabilized by the hybrid energy storage system, the target stabilizing power of the storage battery is derived as follows:
Figure FDA0003370160420000012
the target stabilizing power of the super capacitor is:
Figure FDA0003370160420000021
after the difference of the formula (3) is obtained, discretization is carried out, and the following can be obtained:
Figure FDA0003370160420000022
Figure FDA0003370160420000023
the final transformation of formula (3) is:
Figure FDA0003370160420000024
wherein, TsThe value is a fixed value in the filtering process for calculating the period;
after differentiating the equation (4), discretizing it can be inferred as:
Figure FDA0003370160420000025
Figure FDA0003370160420000026
the final transformation of formula (4) is:
Figure FDA0003370160420000027
let P in formula (10)HESS(k+1)-PHESS(k)＝ΔPHESSThen, obtaining:
Figure FDA0003370160420000028
when designing control strategy, the influence of power fluctuation to system stability should be considered, consequently change the filtering time constant according to power fluctuation to change the power distribution of super capacitor and battery, let the hybrid energy storage system guarantee system stability when stabilizing power, specifically:
dividing 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 stability requirements, and changing the filtering time constant T of a low-pass filter in real time in the process of constant power load power change so as to change the target stabilizing 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 and plays a role in maintaining the voltage of the direct current bus, so that the voltage of the direct current bus is maintained to be constant by adopting a control method of a direct current bus voltage outer ring and an inductive current inner ring, and the automatic charge-discharge switching of the battery is realized;
the high-frequency part of the difference between the electric energy generated by the distributed power supply and the electric energy consumed by the constant-power load is used as the target stabilizing power of the super capacitor, the actual charging and discharging power of the super capacitor is controlled to be equal to the target stabilizing power by the power outer loop and the current inner loop, the filtering time constant T of the low-pass filter can change in real time, and the changed filtering time constant T is input in real time.
3. The method for designing the converter control parameters of the hybrid energy storage system according to claim 2, wherein 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 with power of PDG，CeIs a voltage stabilizing capacitor on a direct current bus, and the voltage at two ends of the capacitor is Ve(ii) a The storage battery and the super capacitor are controlled by the DC-DC link, so the storage battery and the super capacitor are integrally equivalent to a controlled current source with the power of PbatAnd Psc；R1、L1Respectively a circuit equivalent resistance and an inductance; l iss、RsRespectively a filter inductor and an equivalent resistor thereof; the current flowing through the filter inductor is ie；CsIs a filter capacitor with voltage V at both endss；PloadIs of constant powerAnd (3) writing a voltage potential function to the distributed power supply and the hybrid energy storage column by using the load power:
Figure FDA0003370160420000031
write current potential function to resistive columns:
Figure FDA0003370160420000032
write voltage potential function for constant power load column:
Figure FDA0003370160420000033
the energy stored on the filter capacitor is:
Figure FDA0003370160420000034
and finally, expressing the nonlinear energy function model of the hybrid energy storage system as follows:
Figure FDA0003370160420000035
the obtained nonlinear energy function model is further checked:
Figure FDA0003370160420000036
it can be seen that the nonlinear energy function model obtained by equation (16) is correct.
4. The method for designing the converter control parameters of the hybrid energy storage system according to claim 3, wherein the process of the step 3 is specifically as follows:
firstly, according to a nonlinear energy function model formula (16) of the hybrid energy storage system, a current potential function A (i) and a voltage potential function B (v) are obtained and respectively:
Figure FDA0003370160420000041
Figure FDA0003370160420000042
by performing the second partial derivation on the equations (18) and (19), respectively:
Figure FDA0003370160420000043
Figure FDA0003370160420000044
according to the control strategy and the power conservation principle of the storage battery converter, the following steps are known:
iL2＝iBref＝kp2(veref-ve)+ki2(veref-ve)dt (22)
ibatve＝iBvB (23)
wherein k isp2、ki2Controlling parameters of a proportional link and an integral link of a direct-current voltage outer ring of a DC-DC link control unit of the storage battery pack; v. ofeThe voltage of two ends of a voltage stabilizing capacitor on a direct current bus is obtained; i.e. ibatOutputting current for the storage battery DC/DC converter; v. ofB、iBVoltage and current on the storage battery side of the DC/DC converter; i.e. iL2Is the inductive current in the DC/DC converter of the storage battery;
further obtaining:
Figure FDA0003370160420000045
according to the control strategy and the power conservation principle of the super capacitor converter, the following steps are known:
iL1＝iSCref＝kp1(Pscref-iscve)+ki1(Pscref-iscve)dt (25)
iscve＝iSCvSC (26)
wherein k isp1、ki1Controlling parameters of a proportional link and an integral link of a power outer loop of a super capacitor DC-DC link control unit; v. ofSC、iSCVoltage and current on the super capacitor side of the DC/DC converter; i.e. iL1The current is the inductive current in the super capacitor DC/DC converter;
further obtaining:
Figure FDA0003370160420000051
then, solving the minimum characteristic root of the system energy function according to the equations (20), (21), (24) and (27), so as to obtain:
Figure FDA0003370160420000052
Figure FDA0003370160420000053
wherein, the formula (28) is a current energy function, and the formula (29) is a voltage energy function;
further, by bringing formula (11) into formula (29), it is possible to obtain:
Figure FDA0003370160420000054
finally, the design constraint conditions for deriving the control parameters of the converter of the hybrid energy storage system are as follows:
Figure FDA0003370160420000055
and the formula (31) is the criterion of the stability of the system large signal.
5. The method for designing the converter control parameters of the hybrid energy storage system according to claim 1, wherein in step 4, the value range of the converter control parameters and the constant power load power PloadAccumulator and supercapacitor power PbatAnd PscEquivalent resistance and inductance R of circuit1And L1Filter inductor and its equivalent resistance LsAnd RsFilter capacitor CsAnd its voltage V acrosssDC bus voltage-stabilizing capacitor CeAnd a voltage V across iteAnd the filter time constant T of the low-pass filter.
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