CN115276129A - AC/DC micro-grid stability control method considering energy storage charge state - Google Patents

AC/DC micro-grid stability control method considering energy storage charge state Download PDF

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CN115276129A
CN115276129A CN202210954250.3A CN202210954250A CN115276129A CN 115276129 A CN115276129 A CN 115276129A CN 202210954250 A CN202210954250 A CN 202210954250A CN 115276129 A CN115276129 A CN 115276129A
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energy storage
state
droop
frequency
voltage
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陈雨婷
张晓红
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Shanghai Dianji University
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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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • 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
    • 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
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
    • H02J7/0048—Detection of remaining charge capacity or state of charge [SOC]
    • 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
    • H02J7/0068—Battery or charger load switching, e.g. concurrent charging and load supply
    • 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
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • 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
    • H02J2300/28—The renewable source being wind energy

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  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention provides an alternating current-direct current microgrid stability control method considering an energy storage charge state, which comprises the following steps: s1: judging the energy storage running state according to the priority sequence of the voltage of the energy storage battery, the voltage of the bus and the state of charge; s2: grading the charge state and setting improved droop coefficients with continuous different variation trends; s3: for the AC side energy storage, multi-region frequency compensation droop control is adopted; s4: voltage compensation droop control is adopted for the direct current side energy storage; s5: adopting a normalized power outer loop control and current inner loop control strategy aiming at the interconnected converter; s6: and establishing an alternating current-direct current hybrid microgrid simulation model and verifying the effectiveness of the strategy. According to the alternating current-direct current microgrid stability control method considering the energy storage charge state, the response speed of the microgrid is increased and the dynamic performance of the microgrid is enhanced while the frequency and the voltage of the system are kept stable.

Description

AC/DC micro-grid stability control method considering energy storage charge state
Technical Field
The invention relates to the technical field of stability control of power systems, in particular to an alternating current-direct current micro-grid stability control method considering an energy storage charge state.
Background
At present, the research on an energy storage system in a single-side micro-grid is more, and the energy storage running state is controlled by the voltage or the charge state of a battery, wherein the alternating-current energy storage is mainly controlled by p-f droop, the direct-current energy storage is mainly controlled by U-I droop, and the setting of the energy storage droop coefficient is mostly adjusted by a fixed coefficient or a single function. The control of the interconnected converter mainly adopts the control of a voltage outer ring and a current inner ring so as to achieve the bidirectional flow of power.
The prior art has the following disadvantages:
1. the energy storage running state is controlled only through the voltage or the charge state of the battery, and the comprehensive influence of other environmental factors during the energy storage running is not considered.
2. For the adjustment of the energy storage droop coefficient, a fixed coefficient or a single function is mostly adopted for adjustment, and the change of different intervals of the energy storage SOC is not considered.
3. The micro-grid fluctuation problem caused by external conditions is not compensated by utilizing the flexible energy storage control characteristic.
4. The problem of response speed of the microgrid due to external environment change is not considered.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides the stability control method of the alternating current-direct current microgrid considering the energy storage charge state, so that when the conditions of output change, load change and incapability of working of single-side energy storage of a Distributed Generation (DG) are met, the response speed of the microgrid is increased and the dynamic performance of the microgrid is enhanced while the frequency and voltage of the system are kept stable.
In order to achieve the above object, the present invention provides an ac/dc microgrid stability control method considering energy storage state of charge, comprising the steps of:
s1: judging the energy storage running state through the priority sequence of the battery voltage, the bus voltage and the charge state of the energy storage of an alternating current-direct current hybrid micro-grid;
s2: grading the state of charge of the stored energy and setting improved droop coefficients with continuously different variation trends, wherein the improved droop coefficients are dynamically adjusted along with the state of charge;
s3: for the energy storage at the alternating current side, adopting multi-region frequency compensation droop control, and setting a frequency dead zone and frequency offset partition adjustment reference active power;
s4: voltage compensation droop control is adopted for the energy storage on the direct current side, and a voltage deviation amount is set to dynamically adjust the bus voltage;
s5: adopting a normalized power outer loop control and current inner loop control strategy aiming at the interconnected converter;
s6: and establishing an alternating current-direct current hybrid microgrid simulation model of a fan, a photovoltaic, an energy storage and a load under MATLAB and Simulink environments, and verifying the effectiveness of the strategy.
Preferably, in the step S2, the state of charge satisfies the formula:
Figure BDA0003790617800000021
Figure BDA0003790617800000022
wherein k is b_c And k is b_d The charging droop coefficient and the discharging droop coefficient of the ESS are respectively; SOC max 、SOC high 、SOC low 、SOC min Represents 90%,70%,40%,20% of said state of charge of said energy storage, respectively; here, a is a control coefficient, a =0.36; SOC represents the state of charge.
Preferably, in the step S3, the reference power of the stored energy and the frequency characteristic of the ac side are analyzed, and a frequency offset is added, where an expression of the frequency offset is:
Figure BDA0003790617800000031
wherein f is n Representing the frequency offset, f su_max Maximum frequency on the AC side, f su_min Is the minimum frequency on the ac side; f. of min And f max Representing microgrid systemAllowed minimum and maximum frequencies;
and combining the frequency offset with frequency compensation droop control to obtain a final ESS active power reference value formula containing SOC control:
Figure BDA0003790617800000032
wherein, P ref Representing the reference active power at the alternating current side, f representing the frequency of the microgrid system, k b Showing the improved energy storage droop control coefficient, delta f showing the frequency dead zone of the working of the energy storage function at the AC side, f 0 And the standard frequency of the normal work of the energy storage at the AC side is shown.
Preferably, in the step S4, a voltage compensation link is introduced to improve the voltage quality of the dc bus, and a difference between an actual value and a reference value of the dc bus voltage is subjected to PI adjustment and then added to a reference voltage of the droop controller, so as to obtain an expression of compensatory U-I droop control:
U dc ＝U dc_ref -I dc R droop_dc +dU
Figure BDA0003790617800000033
wherein, U dc_ref Is the dc side reference bus voltage; u shape dc Is the bus voltage; dU is the dc bus offset; I.C. A dc Is the output current of the ESS; r droop_dc Is the droop coefficient of the U-I droop control of the direct current side ESS; k is a radical of p And k is i Are the proportional and integral coefficients of the PI controller.
Preferably, in the step S5, a second-order ADRC controller is added to a feed-forward link of the current inner loop; the ADRC controller comprises a tracking differentiator, a nonlinear error feedback device and an extended state observer; through the combined action of a tracking differentiator, the nonlinear error feedback device and the extended state observer, a control object is obtained after a disturbance compensation link:
Figure BDA0003790617800000041
wherein, y * Representing the error output, u, of the ADRC controller 0 Representing the output control quantity, z, of the non-linear error feedback device 3 (t) represents a disturbance observed quantity, b 0 Indicates the control quantity u 0 The amplification factor of (1).
Preferably, the tracking differentiator is in the discrete form:
Figure BDA0003790617800000042
wherein v is 0 (i) Is the target value, h 0 For filtering factor, r is velocity factor, fh represents the function expression of tracking differentiator, v 1 (i) State variables, v, representing trace inputs 2 (i) State variable representing derivative of tracking input by changing h 0 And r adjusts the convergence rate of the target object.
Preferably, the mathematical model of the non-linear error feedback is:
u＝β n1 ·fal(e 1 ,α,δ)+β n2 ·fal(e 2 ,α,δ) (8)；
Figure BDA0003790617800000043
wherein, beta n1 、β n2 A feedback gain of two errors; e represents a tracking error, δ represents a filter constant, u represents an output control quantity of the nonlinear error feedback, and α is a nonlinear factor.
Preferably, the mathematical model of the extended state observer is:
Figure BDA0003790617800000044
wherein e represents a tracking error, z 1 、z 2 、z 3 Denotes the output quantity of the extended state observer, y denotes the feedback value of the d-axis current of the control object, i.e., the present invention, fe 1 Fal function, beta, representing different non-linear factors 1 、β 2 、β 3 Proportional coefficient representing observer, b 0 Denotes an amplification factor representing the control amount u, and h is a filter factor.
Preferably, in the step S5:
Figure BDA0003790617800000051
p MIC_ref ＝-k dc_MIC U dc_pu +k ac_ MICf pu (12)；
wherein f is pu 、U dc_pu For normalizing the processed frequency and DC bus voltage, f max 、f min For maximum and minimum values allowed for frequency, U max 、U min Maximum and minimum values, k, allowed for the DC bus voltage dc_MIC 、k ac_MIC Droop coefficient, p, for the DC side and the AC side MIC_ref A reference active power for the interconnected converters; when the load is switched randomly or the output of the distributed power supply changes, the alternating current-direct current hybrid micro-grid redistributes power through the interconnection converter, so that the frequency and the voltage reach a new balance state.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
the prior art is directed at a control method of an energy storage charging and discharging state, the charging and discharging state of the energy storage charging and discharging state is mainly judged through a battery voltage or a charge state, the judging method is relatively limited, and the battery voltage, the direct-current bus voltage and the charge state are judged through a priority ranking method.
In the prior art, when the energy storage is used for balancing the power of the microgrid, the compensation effect of the frequency and the voltage of the energy storage at the two sides of the alternating current and the direct current is not fully considered, but the frequency multi-region compensation droop control of the alternating current energy storage and the direct current side energy storage voltage compensation droop control are used, the characteristic of flexible adjustment of the energy storage is fully utilized, and the dynamic performance of the microgrid is enhanced.
In the prior art, a droop control or disturbance observer is mostly used independently in a control method for an interconnection converter, the application scene is ideal, the power generation state of a specific distributed power supply is not considered, and the practical applicability is low. The invention adopts outer ring power sharing control and feedforward inner ring second-order ADRC current control aiming at the interconnected converter, balances the power distribution of the AC side and the DC side under the output change of the photovoltaic side and the fan side, and accelerates the response speed of the system.
Drawings
Fig. 1 is a topological structure diagram of an ac/dc hybrid microgrid according to an embodiment of the present invention;
FIG. 2 is a flowchart illustrating the control of the energy storage operation state according to an embodiment of the present invention;
FIG. 3 is a graph of energy storage charge-discharge droop coefficient according to an embodiment of the present invention;
FIG. 4 is a diagram illustrating an ADRC controller model according to an embodiment of the present invention;
fig. 5 is a block diagram of an ADRC control strategy according to an embodiment of the present invention.
Detailed Description
The following description of the preferred embodiments of the present invention will be provided in conjunction with the accompanying drawings, which are set forth in the following drawings, and in the drawings, fig. 1-5, to provide a better understanding of the function and features of the present invention.
Referring to fig. 1 to 5, an ac/dc microgrid stability control method considering an energy storage state of charge according to an embodiment of the present invention includes the steps of:
s1: judging the running state of the energy storage 5 by the priority sequence of the battery voltage, the bus voltage and the charge state of the energy storage 5 of an alternating current-direct current hybrid micro-grid;
s2: grading the charge state of the energy storage 5 and setting improved droop coefficients with continuously different variation trends, wherein the improved droop coefficients are dynamically adjusted along with the charge state; the situation of overcharge and overdischarge can be effectively avoided, and the service life of the energy storage 5 is prolonged.
The specific control coefficient and the state of charge (SOC) satisfy the formula:
Figure BDA0003790617800000061
Figure BDA0003790617800000071
wherein k is b_c And k b_d The charging droop coefficient and the discharging droop coefficient of the ESS are respectively; SOC (system on chip) max 、SOC high 、SOC low 、SOC min Respectively represent 90%,70%,40% and 20% of the state of charge of the stored energy 5; here, a is a control coefficient, a =0.36; SOC represents the state of charge.
S3: for the AC side energy storage 5, multi-region frequency compensation droop control is adopted, and a frequency dead zone and a frequency offset are set to adjust reference active power in a partition mode;
the AC side energy storage 5 adopts multi-region frequency compensation droop control, the reference power of the energy storage 5 and the frequency characteristic of the AC side are analyzed, the frequency of the microgrid generates large fluctuation due to load change, and the maximum and minimum frequency of the AC side is changed into f su_max And f su_min Thereby establishing the ESS at a new operating point, it is necessary to add a frequency offset f to the above strategy n Frequency offset f n The expression of (a) is:
Figure BDA0003790617800000072
wherein f is n Denotes the frequency offset, f su_max Maximum frequency on the AC side, f su_min Is the minimum frequency on the ac side; f. of min And f max Representing the minimum and maximum frequencies allowed by the microgrid system;
and combining the frequency offset with frequency compensation droop control to obtain a final ESS active power reference value formula containing SOC control:
Figure BDA0003790617800000081
wherein, P ref Representing the reference active power at the alternating current side, f representing the frequency of the microgrid system, k b Showing the improved energy storage droop control coefficient, delta f showing the frequency dead zone of the working of the energy storage function at the AC side, f 0 And the standard frequency of the normal work of the energy storage at the AC side is shown.
S4: voltage compensation droop control is adopted for the direct current side energy storage 5, and a voltage deviation amount is set to dynamically adjust the bus voltage;
the U-I droop control achieves the purpose of correcting the voltage reference value of the direct current bus by introducing current feedback and a virtual resistor, but the voltage precision can be reduced, in order to solve the problem, a voltage compensation link is introduced to improve the voltage quality of the direct current bus, the difference between the actual value and the reference value of the direct current bus voltage is subjected to PI regulation and then added to the reference voltage of the droop controller, and the expression of the compensatory U-I droop control is obtained:
U dc ＝U dc_ref -I dc R droop_dc +dU
Figure BDA0003790617800000082
wherein, U dc_ref Is the dc side reference bus voltage; u shape dc Is the bus voltage; dU is the dc bus offset; i is dc Is the output current of the ESS; r droop_dc Is the droop coefficient of the U-I droop control of the direct current side ESS; k is a radical of p And k i Are the proportional and integral coefficients of the PI controller.
S5: adopting a normalized power outer loop control and current inner loop control strategy aiming at the interconnected converter;
wherein, a second-order ADRC controller is added in a feed-forward link of the current inner loop; the dynamic performance of the hybrid micro-grid is improved to a certain extent, and the hybrid micro-grid has stronger anti-jamming capability. The ADRC controller realizes control by comparing the magnitude and direction of errors of a desired signal and an actual signal so as to eliminate errors through errors, and comprises a tracking differentiator, a nonlinear error feedback device and an extended state observer;
wherein the discrete form of the tracking differentiator is:
Figure BDA0003790617800000091
wherein v is 0 (i) Is the target value, h 0 For filtering factor, r is velocity factor, fh represents the function expression of tracking differentiator, v 1 (i) State variable, v, representing trace input 2 (i) State variables representing derivatives of the tracking input by varying h 0 And r adjusts the convergence rate of the target object.
Wherein, the fhan function expression is:
u＝fhan(v 1 ,v 2 ,r,h):
Figure BDA0003790617800000092
the nonlinear error feedback device remarkably improves the feedback efficiency and precision, and the mathematical model is as follows:
u＝β n1 ·fal(e 1 ,α,δ)+β n2 ·fal(e 2 ,α,δ) (8)；
Figure BDA0003790617800000093
wherein, beta n1 、β n2 A feedback gain of two errors; e represents a tracking error, δ represents a filter constant, u represents an output control quantity of the nonlinear error feedback, and α is a nonlinear factor.
An Extended State Observer (ESO) is a key link of ADRC, and the observer can observe the running state of a system in real time under the condition that a system model and comprehensive interference are not clear, so that the observer is suitable for most control engineering problems. The mathematical model is as follows:
Figure BDA0003790617800000094
wherein e represents a tracking error, z 1 、z 2 、z 3 Denotes the output quantity of the extended state observer, y denotes the control target, i.e., the feedback value of the d-axis current of the present invention, fe 1 Fal function, beta, representing different non-linear factors 1 、β 2 、β 3 Representing the scale factor of the observer, b 0 Denotes an amplification factor representing the control amount u, and h is a filter factor.
Through the combined action of a tracking differentiator, a nonlinear error feedback device and an extended state observer, a control object is obtained after a disturbance compensation link:
Figure BDA0003790617800000101
wherein, y * Representing the error output, u, of the ADRC controller 0 Representing the output control quantity, z, of the non-linear error feedback 3 (t) represents a disturbance observed quantity, b 0 Indicates the control quantity u 0 The amplification factor of (2).
The power outer loop control adopts alternating current sub-network frequency and direct current sub-network voltage as droop variables, after normalization processing, obtained reference power is sent to ADRC with dq axis current after PI control, switching signals of a three-phase full-bridge inverter circuit are controlled by adopting SVPWM control technology, and are simultaneously fed back to frequency and voltage to be adjusted, so that active power flow is controlled, and the specific expression is as follows:
Figure BDA0003790617800000102
p MIC_ref ＝-k dc_MIC U dc_pu +k ac_MIC f pu (12)；
wherein f is pu 、U dc_pu For normalizing the processed frequency and DC bus voltage, f max 、f min For maximum and minimum values allowed for frequency, U max 、U min Maximum and minimum values, k, allowed for the DC bus voltage dc_MIC 、k ac_MIC Is the droop coefficient, p, on the DC side and on the AC side MIC_ref Is the reference active power of the interconnected converter; when the load is switched randomly or the output of the distributed power supply changes, the alternating current-direct current hybrid micro-grid redistributes the power through the interconnection converter, so that the frequency and the voltage reach a new balance state.
S6: and establishing an alternating current-direct current hybrid micro-grid simulation model of the fan 3, the photovoltaic 4, the energy storage 5 and the load in MATLAB and Simulink environments, and verifying the effectiveness of the strategy.
(1) And verifying the adaptability of the droop coefficient of the energy storage 5.
In order to verify the dynamic adjustment adaptability of the droop coefficient of the energy storage 5, the SOC of the energy storage 5 is charged from 20% to 90% through the output of a distributed power supply.
It can be known that, the time points corresponding to 20%,40%,70%, and 90% of the energy storage 5SOC are labeled in the SOC curve graph and the value of the SOC change rate corresponding to the time points is labeled in the SOC change rate curve graph, where KSOC is the SOC change rate. As can be seen from the SOC variation trend and the labeled data, the SOC variation rate decreases with the increase of the SOC of the energy storage 5, and the decreasing speed is slow and fast. Simulation results show that the provided energy storage 5 adaptive droop coefficient control strategy can better fit the running state of the energy storage 5, adaptively adjust the charging and discharging running capacity of the energy storage 5, and reduce the damage to an energy storage 5 system.
(2) And verifying the effectiveness of the BFVC-ADRC control strategy.
a. Simulation scenario 1: and 4, the energy storage 5 is switched between normal operation and an over-discharge state.
In order to verify that under the condition that the output of the fan 3, the photovoltaic 4 and the load changes, the energy storage 5 system can smoothly convert between a normal operation state and an over-discharge state, and the stability of alternating current frequency, direct current voltage, the working state of the energy storage 5 and MIC transmission power is maintained. The traditional control (TDC), the battery frequency only voltage compensation control (BFVC), and the battery frequency voltage compensation are compared with the combined control of the active disturbance rejection controller (BFVC-ADRC).
The initial SOC of the dc-side stored energy 5 is set to 20.02, and the initial SOC of the ac-side stored energy 5 is set to 20.12. At the initial moment, the load on the two sides of alternating current and direct current is maintained at 100KW, the photovoltaic 4 is increased from 80kW to 110kW at 0.5s, and then the load on the direct current side is increased to 130kW at 1 s; the fan 3 increased from 80kW to 110kW at 2s, followed by an increase in ac side load to 130kW at 2.5 s.
As a result, the operating states of the conventional control parts fluctuate greatly and are unstable, and therefore are not listed in detail; the BFVC control method has better performance in the aspect of maintaining frequency, but is disordered in the aspect of power distribution, and the energy storage 5 cannot smoothly switch the working state. When the power supply works, the strategy is obviously faster than the other two methods in the aspect of power response speed, and the energy storage 5 on the two sides of the alternating current and the direct current normally provides 20kW for the load. Then the DC side energy storage 5 stops running at 0.35s (SOC is less than or equal to 20%), and the AC side energy storage 5 provides about 35kW of power for the DC load 7, namely the MIC transmits 20kW of power to the DC sub-network. And when the time is 0.5s, the output of the photovoltaic 4 is increased to charge the direct-current side energy storage 5, and the MIC keeps a silent state. And when the time is 1s, the load on the direct current side is increased, the energy storage 5 on the direct current side is discharged again and reaches an over-discharge state (the SOC is less than or equal to 20%) in 1.4s, and at the moment, the energy storage 5 on the alternating current side and the MIC are transmitted power on the direct current side to maintain stable operation. Similarly, under the output variation of the fan 3 and the load on the alternating current side, the energy storage 5 on the alternating current side reaches an over-discharge state in 1.7s and 2.8s respectively, the energy storage 5 on the direct current side outputs 40kW (wherein 20kW is provided for the load on the direct current side), and the MIC transmits 20kW to the alternating current sub-network. The bus voltage and the system frequency slightly fluctuate when external conditions change, but are controlled within a stable operation range. The above results indicate that, in the conversion process between the normal operation and the over-discharge state of the energy storage 5, the BFVC-ADRC strategy provided herein reduces the response time while balancing the power distribution, and reduces the fluctuation range of the voltage and the frequency, so that the microgrid reaches the stable state faster.
b. Simulation scenario 2: and 4, the energy storage 5 is switched between normal operation and an overcharged state.
In order to verify the situation that the BFVC-ADRC strategy is switched between the normal operation and the overcharge state of the energy storage 5, the initial SOC of the direct-current side energy storage 5 is set to be 89.99, and the initial SOC of the alternating-current side energy storage 5 is set to be 89.93. At the initial moment, the photovoltaic 4 and the fan 3 are maintained at 150KW, and the loads on the two sides of alternating current and direct current are maintained at 100kW; the dc side load increased to 130kW at 0.5s, then the photovoltaic 4 decreased from 150kW to 110kW at 1.5 s; the AC side load is increased to 130kW at 2s, and then the fan 3 is reduced from 150kW to 110kW at 3 s.
As a result, at the beginning of operation, the power response speed of the proposed strategy in this simulation scenario is still significantly faster than that of the other two methods, where the ac side energy storage 5 is normal and each side DG provides 20kW for it. Then, under the change of DG and load output, the direct-current side energy storage 5 reaches an over-discharge state (SOC is more than or equal to 90%) in 0.2s and 1.3s respectively, the MIC transmits power to the alternating-current side by 20kW, and the alternating-current side energy storage 5 continues to be charged with power of 40 kW; the AC side energy storage 5 reaches an over-discharge state in 1.6s and 2.8s respectively, the MIC transmits power to the DC side by 20kW, and at the moment, the DC side energy storage 5 recovers to a normal charging state and is charged with power of 40 kW. The rest of the time period MIC remains silent. It is worth noting that the load consumption is reduced due to MIC transmission power imbalance by adopting the BFVC control method, and therefore the alternating-current side energy storage 5 enters the overcharging state earlier. Compared with the traditional method, the BFVC and BFVC-ADRC method has obvious effectiveness in maintaining the bus voltage and the system frequency stability.
Referring to fig. 1, fig. 1 is a topology structure of an ac/dc hybrid microgrid, including: the system comprises an alternating current bus 1, a direct current bus 2, a fan 3, a photovoltaic 4, an energy storage 5, an alternating current load 6 and a direct current load 7; the fan 3 is connected to the alternating current bus 1 by adopting a back-to-back power converter, the MPPT in the front-stage converter adopts an optimal power curve method, and the rear-stage converter adopts a control mode of a voltage/reactive power outer ring and a current inner ring to control the voltage stability of the direct current side. The photovoltaic 4 is connected to the DC bus through DC/DC, wherein the MPPT algorithm uses a perturbation and observation method to control the output power by controlling the port output voltage.
Referring to fig. 1 and 2, the first priority of the control method is the energy storage battery voltage U bat When 230V is less than or equal to U bat The voltage is less than or equal to 277V, and the energy storage 5 is in a charge-discharge free running state; when U is turned bat When the voltage is less than 230V, the energy storage 5 is in a power-off state(ii) a When U is turned bat When the voltage is larger than 277V, the energy storage 5 is in a full state. The second priority is bus voltage, the third level is energy storage state of charge (SOC), and the operation state of the energy storage 5 is judged by combining the three levels, so that the over-discharge and over-charge state is avoided, and the safe operation of the energy storage 5 system is ensured.
Referring to fig. 3, when the SOC shortage is larger, the decrease speed of the charge factor is slower than the increase speed of the SOC, which can reduce the voltage and frequency fluctuation of the system. When the SOC is between 0.7 and 0.9, the descending speed of the charging coefficient is faster than the ascending speed of the SOC, and the SOC is mainly maintained to be stable in the stage, so that the damage of the ESS caused by the fact that the charging speed is too fast is avoided.
Referring to fig. 4, the adrc controller model has better buffering compared to the PID controller under the condition of large power fluctuation.
Referring to fig. 5, an ADRC control strategy block diagram, a normalized power outer loop control and current inner loop control strategy is adopted for an interconnection converter (MIC), wherein a second-order ADRC controller is added to a current inner loop feedforward link, so that the dynamic performance of the hybrid microgrid is improved to a certain extent and the hybrid microgrid has stronger anti-jamming capability.
In this embodiment, system parameters of the ac/dc hybrid microgrid are shown in table 1:
TABLE 1 System parameter Table
Figure BDA0003790617800000131
While the present invention has been described in detail and with reference to the embodiments thereof as illustrated in the accompanying drawings, it will be apparent to one skilled in the art that various changes and modifications can be made therein. Therefore, certain details of the embodiments should not be construed as limitations of the invention, except insofar as the following claims are interpreted to cover the invention.

Claims (9)

1. An alternating current-direct current microgrid stability control method considering an energy storage charge state comprises the following steps:
s1: judging the energy storage running state through the priority sequence of the battery voltage, the bus voltage and the charge state of the energy storage of an alternating current-direct current hybrid micro-grid;
s2: grading the state of charge of the stored energy and setting improved droop coefficients with continuously different variation trends, wherein the improved droop coefficients are dynamically adjusted along with the state of charge;
s3: for the energy storage at the alternating current side, adopting multi-region frequency compensation droop control, and setting a frequency dead zone and frequency offset partition adjustment reference active power;
s4: voltage compensation droop control is adopted for the energy storage on the direct current side, and a voltage deviation amount is set to dynamically adjust the bus voltage;
s5: aiming at the interconnected converter, a normalized power outer loop control and current inner loop control strategy is adopted;
s6: and establishing an alternating current-direct current hybrid micro-grid simulation model of a fan, a photovoltaic, an energy storage and a load in MATLAB and Simulink environments, and verifying the effectiveness of the strategy.
2. The method for controlling the stability of the alternating current-direct current microgrid considering the energy storage state of charge according to claim 1, characterized in that in the step S2, the state of charge satisfies a formula:
Figure FDA0003790617790000011
Figure FDA0003790617790000021
wherein k is b_c And k is b_d The charging droop coefficient and the discharging droop coefficient of the ESS are respectively; SOC max 、SOC high 、SOC low 、SOC min Represents 90%,70%,40%,20% of said state of charge of said energy storage, respectively; here, a is a control coefficient, a =0.36; SOC represents the state of charge.
3. The method according to claim 2, wherein in the step S3, the reference power of the stored energy and the frequency characteristic of the ac side are analyzed, and a frequency offset is added, where the frequency offset is expressed as:
Figure FDA0003790617790000022
wherein, f n Representing the frequency offset, f su_max Maximum frequency on the AC side, f su_min Minimum frequency on the ac side; f. of min And f max Representing the minimum and maximum frequencies allowed by the microgrid system;
and combining the frequency offset with frequency compensation droop control to obtain a final ESS active power reference value formula containing SOC control:
Figure FDA0003790617790000031
wherein, P ref Representing the reference active power at the alternating current side, f representing the frequency of the microgrid system, k b Showing the improved energy storage droop control coefficient, delta f showing the frequency dead zone of the working of the energy storage function at the AC side, f 0 And the standard frequency of the normal work of the energy storage at the AC side is shown.
4. The method for controlling the stability of the alternating current-direct current microgrid considering the energy storage state of charge according to claim 3, wherein in the step S4, a voltage compensation link is introduced to improve the voltage quality of a direct current bus, the difference between the actual value and the reference value of the voltage of the direct current bus is subjected to PI regulation and then added to the reference voltage of a droop controller, and an expression of compensatory U-I droop control is obtained:
U dc ＝U dc_ref -I dc R droop_dc +dU
Figure FDA0003790617790000032
wherein, U dc_ref Is the dc side reference bus voltage; u shape dc Is the bus voltage; dU is the dc bus offset; i is dc Is the output current of the ESS; r is droop_dc Is the droop coefficient of the U-I droop control of the direct current side ESS; k is a radical of p And k is i Are the proportional and integral coefficients of the PI controller.
5. The method for controlling the stability of the AC/DC microgrid with the energy storage state of charge taken into consideration according to claim 4, characterized in that in the step S5, a second-order ADRC controller is added to a feed-forward link of the current inner loop; the ADRC controller comprises a tracking differentiator, a nonlinear error feedback device and an extended state observer; through the combined action of a tracking differentiator, the nonlinear error feedback device and the extended state observer, a control object is obtained after a disturbance compensation link:
Figure FDA0003790617790000033
wherein, y * Representing the error output, u, of the ADRC controller 0 Representing the output control quantity, z, of the non-linear error feedback 3 (t) represents a disturbance observed quantity, b 0 Represents the controlled variable u 0 The amplification factor of (2).
6. The method for controlling the stability of the AC/DC microgrid according to claim 5 and considering the state of charge of an energy storage, characterized in that the discrete form of the tracking differentiator is as follows:
Figure FDA0003790617790000041
wherein v is 0 (i) Is the target value, h 0 For the filter factor, r is the velocity factor, fh represents the function table of the tracking differentiatorFor short, v 1 (i) State variable, v, representing trace input 2 (i) State variables representing derivatives of the tracking input by varying h 0 And r adjusts the convergence rate of the target object.
7. The method for controlling the stability of the AC/DC microgrid according to the claim 6 and considering the state of charge of the stored energy is characterized in that the mathematical model of the nonlinear error feedback device is as follows:
u＝β n1 ·fal(e 1 ,α,δ)+β n2 ·fal(e 2 ,α,δ) (8)；
Figure FDA0003790617790000042
wherein, beta n1 、β n2 A feedback gain of two errors; e represents a tracking error, δ represents a filter constant, u represents an output control quantity of the nonlinear error feedback, and α is a nonlinear factor.
8. The method for controlling stability of the alternating current-direct current micro-grid considering the energy storage state of charge according to claim 7, wherein the mathematical model of the extended state observer is as follows:
Figure FDA0003790617790000043
wherein e represents a tracking error, z 1 、z 2 、z 3 Denotes the output quantity of the extended state observer, y denotes the control target, i.e., the feedback value of the d-axis current of the present invention, fe 1 Fal function, beta, representing different non-linear factors 1 、β 2 、β 3 Representing the scale factor of the observer, b 0 Denotes an amplification factor representing the control amount u, and h is a filter factor.
9. The method for controlling the stability of the ac/dc microgrid according to the energy storage state of charge of claim 8, wherein in the step S5:
Figure FDA0003790617790000051
p MIC_ref ＝-k dc_MIC U dc_pu +k ac_MIC f pu (12)；
wherein f is pu 、U dc_pu For normalizing the processed frequency and DC bus voltage, f max 、f min For maximum and minimum values allowed for frequency, U max 、U min Maximum and minimum values, k, allowed for the DC bus voltage dc_MIC 、k ac_MIC Is the droop coefficient, p, on the DC side and on the AC side MIC_ref Is the reference active power of the interconnected converter; when the load is switched randomly or the output of the distributed power supply changes, the alternating current-direct current hybrid micro-grid redistributes power through the interconnection converter, so that the frequency and the voltage reach a new balance state.
CN202210954250.3A 2022-08-10 2022-08-10 AC/DC micro-grid stability control method considering energy storage charge state Pending CN115276129A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116191516A (en) * 2023-04-03 2023-05-30 国网江苏省电力有限公司南通供电分公司 Multi-port energy hub multi-converter direct-current voltage/droop control method based on honeycomb active power distribution network

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116191516A (en) * 2023-04-03 2023-05-30 国网江苏省电力有限公司南通供电分公司 Multi-port energy hub multi-converter direct-current voltage/droop control method based on honeycomb active power distribution network
CN116191516B (en) * 2023-04-03 2024-03-15 国网江苏省电力有限公司南通供电分公司 DC voltage/power droop control method for multi-port energy hub multi-converter

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