CN109687537B - No-difference optimization control method for communication-free alternating current-direct current hybrid micro-grid - Google Patents

No-difference optimization control method for communication-free alternating current-direct current hybrid micro-grid Download PDF

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CN109687537B
CN109687537B CN201810857195.XA CN201810857195A CN109687537B CN 109687537 B CN109687537 B CN 109687537B CN 201810857195 A CN201810857195 A CN 201810857195A CN 109687537 B CN109687537 B CN 109687537B
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direct current
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CN109687537A (en
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米阳
宋根新
郝学智
何星瑭
韩云昊
苏向敬
李振坤
符杨
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Shanghai University of Electric Power
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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
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Abstract

The invention relates to a communication-free alternating current-direct current hybrid microgrid differential-free optimal control method, which comprises the following steps: step S1: establishing a droop control model of each controllable distributed power supply; step S2: building a combined droop control model of all controllable distributed power supplies of the overpass and the DC sub-microgrid; and step S3: determining the virtual standby capacity and the virtual maximum output power of the AC sub-microgrid and the DC sub-microgrid, and obtaining a sectional droop control model of the AC sub-microgrid and the DC sub-microgrid; and step S4: designing a sectional droop control model with secondary compensation control for the AC and DC sub-microgrid; step S5: and carrying out normalization processing on the alternating current frequency and the direct current voltage, and determining the exchange power between the alternating current sub-microgrid and the direct current sub-microgrid for control. Compared with the prior art, the invention can realize the no-difference operation of the system under the condition of no communication, improve the power quality of the system and simultaneously save the resources required by the communication line arrangement of the system.

Description

No-difference optimization control method for communication-free alternating current-direct current hybrid micro-grid
Technical Field
The invention relates to a method for controlling the error-free optimization of an alternating current-direct current hybrid micro-grid without communication.
Background
The AC/DC hybrid microgrid provides a more efficient solution for a large number of Distributed Generators (DGs) for wind power, photovoltaic power and the like to access a power distribution network, and is formed by respectively forming AC and DC sub-microgrids by AC and DC power supplies and loads and interconnecting the AC and DC sub-microgrids through an intermediate AC/DC bidirectional Interconnection Converter (IC). Meanwhile, the alternating current bus realizes the switching between grid connection and isolated island operation of the hybrid micro-grid and a power distribution network through a Static Transfer Switch (STS). The optimized operation in the alternating current and direct current sub-networks and the interconnection interaction between the sub-networks are very important for the safe and stable operation of the alternating current and direct current hybrid micro-grid.
The direct current bus voltage and the alternating current side frequency are key indexes for reflecting the balance of source load and power and the stability of the system in the hybrid micro-grid. The related literature provides an autonomous coordination control strategy based on droop control for an AC/DC/DS three-port system, autonomous operation of each sub-microgrid is realized through the droop control, and the autonomous coordination control among the sub-grids is realized by using the AC frequency and the DC voltage signals which are subjected to normalization processing. Although the whole control system does not need communication, the droop control can bring steady-state deviation to the frequency and the voltage of the system, and the power quality is affected. Related documents propose a hierarchical control strategy, which includes a primary distribution of power realized by a bottom-layer droop control; the intermediate layer realizes secondary recovery control of voltage and frequency; and the uppermost layer completes the power optimization distribution control. The provided control strategy respectively aims at the AC and DC micro-grid, and does not consider the power interconnection supporting function between the AC and DC micro-grid; meanwhile, when communication fails, the hierarchical control cannot acquire and provide signals, and great influence is brought to the optimization control of the system. The related literature aims at minimizing the power flow of the interconnected converters, establishes the relationship between interactive transmission power and direct current voltage and alternating current frequency, and realizes the optimal configuration of the power of the whole system. But the control strategy has better control effect only under the condition that only one microgrid is overloaded.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a no-difference optimization control method for a non-communication alternating current-direct current hybrid micro-grid.
The purpose of the invention can be realized by the following technical scheme:
a no-difference optimization control method for a communication-free alternating current-direct current hybrid micro-grid comprises the following steps:
step S1: establishing a droop control model of each controllable distributed power supply;
step S2: building a combined droop control model of all controllable distributed power supplies of the overpass and the DC sub-microgrid;
and step S3: determining the virtual standby capacity and the virtual maximum output power of the AC sub-microgrid and the DC sub-microgrid, and obtaining a sectional droop control model of the AC sub-microgrid and the DC sub-microgrid;
and step S4: designing a sectional droop control model with secondary compensation control for the AC and DC sub-microgrid;
step S5: and carrying out normalization processing on the alternating current frequency and the direct current voltage, and determining the exchange power between the alternating current sub-microgrid and the direct current sub-microgrid for control.
The step S3 includes:
step S31: determining the virtual standby capacity and the virtual maximum output power of the AC/DC sub-microgrid;
step S32: and obtaining the section droop control model of the AC/DC sub-microgrid.
The step S31 specifically includes: respectively designing corresponding virtual maximum output power P 'of the alternating-current sub-microgrid according to the capacity of the controllable distributed power supply of the alternating-current sub-microgrid and the direct-current sub-microgrid' amax Virtual spare capacity: delta P ac And DC sub-microgrid virtual maximum output power P' dmax Virtual spare capacity Δ P dc 。
The virtual spare capacity is specifically:
ΔP ac ＝P amax -P′ amax
wherein: p is amax Is the actual maximum output power of the AC sub-microgrid,
the virtual spare capacity is specifically:
ΔP dc ＝P dmax -P′ dmax
wherein: p is dmax The actual maximum output power of the direct current sub-microgrid is obtained.
The step S32 is specifically: and designing droop control sectional points at the virtual maximum output power positions of the AC and DC sub-microgrid to obtain a sectional droop control model of the system.
The step S4 specifically comprises the following steps: based on the obtained segmented droop control model, secondary compensation control of alternating current frequency and direct current voltage is introduced into the first segment droop control, and the segmented droop control model with the secondary compensation control in the alternating current and direct current sub-microgrid is determined to be respectively as follows:
Figure GDA0003655792680000021
Figure GDA0003655792680000031
M 1 ＝(f min -f max )/P′ amax
M 2 ＝(f min -f * )/(P amax -P′ amax )
Figure GDA0003655792680000032
Figure GDA0003655792680000033
wherein f is the AC system frequency, f min 、f max Respectively minimum and maximum values allowed by the frequency of the AC sub-network, f * Representing the nominal frequency, P, of the ac sub-microgrid ac The active power output by the whole controllable distributed power supply of the AC sub-microgrid is represented; direct-current voltage secondary compensation control signal:
Figure GDA0003655792680000034
k pV 、k iV for secondary compensation of the control parameter, V dc Which represents the dc-side bus voltage,
Figure GDA0003655792680000035
respectively the minimum value and the maximum value allowed by the voltage of the direct current sub-network,
Figure GDA0003655792680000036
representing the rated bus voltage, P, of the DC sub-microgrid dc And the power output by the controllable distributed power supply in the direct current sub-microgrid is integrally expressed.
In step S5, the normalization formula of the ac frequency and the dc voltage is as follows:
Figure GDA0003655792680000037
wherein: zeta is a value before normalization processing, and (ζ)' represents a value after the Zeta normalization processing and has a value range of [ -1,0 ]]，ζ * 、ζ min Representing the nominal and minimum values of ζ, respectively.
Compared with the prior art, the invention has the following beneficial effects:
1) The system can run without difference under the condition of no communication, the power quality of the system is improved, and resources required by the communication line arrangement of the system are saved.
2) The method provides an operation principle of self-governing in the microgrid and coordination among the microgrids aiming at the alternating current-direct current hybrid microgrid, is favorable for reducing power exchange loss among the microgrid sub-grids, and improves system efficiency.
3) The method provides a new thought and concept for the control of the micro-grid, the micro-grid group and the alternating current-direct current hybrid micro-grid, and is favorable for promoting the large-scale development and utilization of the distributed renewable energy.
Drawings
FIG. 1 is a schematic flow chart of the main steps of the method of the present invention;
FIG. 2 is a topological structure diagram of an island AC/DC hybrid micro-grid;
FIG. 3 is a conventional droop characteristic for a microgrid;
FIG. 4 is a power frequency static characteristic curve of a conventional power system;
fig. 5 is a section droop characteristic curve of the ac sub-microgrid;
fig. 6 is a section droop characteristic curve of the direct current sub microgrid;
fig. 7 is an ac microgrid segment droop control with secondary compensation;
fig. 8 shows the dc sub-microgrid segment droop control with the secondary compensation;
FIG. 9 control strategy for the interconnected inverters;
FIG. 10A-D hybrid microgrid simulation model;
FIG. 11 is a graph of DC bus voltage waveform at one operating condition;
FIG. 12 is a waveform diagram of AC frequency at one operating condition;
FIG. 13 is a voltage waveform diagram of the DC bus under the second operating condition;
FIG. 14 is a waveform diagram of AC frequency under the second operating condition;
fig. 15 illustrates power flowing out of the dc sub-microgrid under a second operating condition;
FIG. 16 illustrates DC bus voltage waveforms under the third operating condition;
FIG. 17 illustrates an AC frequency waveform under a third operating condition;
and in the working condition three of fig. 18, the power waveform flowing out of the direct current microgrid is shown.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
A method for controlling a wireless communication ac/dc hybrid microgrid differential-free optimization, as shown in fig. 1, includes:
step S1: establishing a droop control model of each controllable distributed power supply;
step S2: building a combined droop control model of all controllable distributed power supplies of the overpass and the DC sub-microgrid;
and step S3: determining the virtual standby capacity and the virtual maximum output power of the AC and DC sub-micro-grids, and obtaining a segmented droop control model of the AC and DC sub-micro-grids, wherein the step S3 comprises the following steps:
step S31: determining the virtual standby capacity and the virtual maximum output power of the AC and DC sub-microgrid;
step S31 specifically includes: respectively designing corresponding virtual maximum output power P 'of the alternating-current sub-microgrid according to the capacity of the controllable distributed power supply of the alternating-current sub-microgrid and the direct-current sub-microgrid' amax Virtual spare capacity: delta P ac And DC sub-microgrid virtual maximum output power P' dmax Virtual spare capacity Δ P dc 。
The virtual spare capacity is specifically:
ΔP ac ＝P amax -P′ amax
wherein: p is amax The actual maximum output power of the ac microgrid is,
the virtual spare capacity is specifically:
ΔP dc ＝P dmax -P′ dmax
wherein: p dmax The actual maximum output power of the direct current sub-microgrid is obtained.
Step S32: the method for obtaining the section droop control model of the AC/DC sub-microgrid specifically comprises the following steps: and designing droop control sectional points at the virtual maximum output power positions of the AC and DC sub-microgrid to obtain a sectional droop control model of the system.
And step S4: designing the section droop control model of the AC/DC sub-microgrid with secondary compensation control, which specifically comprises the following steps: based on the obtained segmented droop control model, secondary compensation control of alternating current frequency and direct current voltage is introduced into the first segment droop control, and the segmented droop control model with the secondary compensation control in the alternating current and direct current sub-microgrid is determined to be respectively as follows:
Figure GDA0003655792680000051
Figure GDA0003655792680000052
M 1 ＝(f min -f max )/P′ amax
M 2 ＝(f min -f * )/(P amax -P′ amax )
Figure GDA0003655792680000053
Figure GDA0003655792680000054
wherein f is the AC system frequency, f min 、f max Respectively minimum and maximum values allowed by the frequency of the AC sub-network, f * Representing the nominal frequency, P, of the ac sub-microgrid ac The active power output by the whole controllable distributed power supply of the AC sub-microgrid is represented; direct-current voltage secondary compensation control signal:
Figure GDA0003655792680000055
k pV 、k iV for quadratic compensation of the control parameter, V dc Which represents the dc-side bus voltage,
Figure GDA0003655792680000056
respectively the minimum and maximum allowed dc sub-network voltage,
Figure GDA0003655792680000057
representing the rated bus voltage, P, of the DC sub-microgrid dc And the power output by the controllable distributed power supply in the direct current sub-microgrid is expressed.
Step S5: carrying out normalization processing on the alternating current frequency and the direct current voltage, and determining the exchange power between the alternating current sub-microgrid and the direct current sub-microgrid for control, wherein the normalization formulas of the alternating current frequency and the direct current voltage are as follows:
Figure GDA0003655792680000058
wherein: zeta is a value before normalization processing, and (Zeta)' represents a value after the normalization processing and has a value range of [ -1,0 ]]，ζ * 、ζ min Representing the nominal and minimum values of ζ, respectively.
(1) Traditional droop control principle
Fig. 2 is a topology structure diagram of an island ac/dc hybrid microgrid, and droop control has been widely applied to ac and dc microgrids in order to realize distribution of output power between Controllable Distributed Generators (CDGs) according to their rated power. The P-f of the alternating current sub-microgrid and the P-v expression of the direct current sub-microgrid are as follows:
Figure GDA0003655792680000061
Figure GDA0003655792680000062
in the formula, P ac_x 、P dc_y The output power of the x-th alternating current controllable source and the output power of the y-th direct current controllable source are respectively; f. v dc_y The frequency of the alternating current system and the tail end voltage of the y direct current controllable source are respectively; m is a unit of x 、d y Droop coefficients of the x-th alternating current controllable source and the y-th direct current controllable source are respectively obtained; f. of min 、f max And
Figure GDA0003655792680000063
the minimum value and the maximum value allowed by the frequency of the alternating current sub-network and the minimum value and the maximum value allowed by the voltage of the direct current sub-network are respectively;
Figure GDA0003655792680000064
the maximum output power of the x-th alternating current controllable source and the y-th direct current controllable source are respectively.
Considering adverse effects on active power distribution of a direct current source caused by different impedances of various distributed power supply lines in a direct current sub-network, the following improved direct current voltage droop control strategy is applied:
Figure GDA0003655792680000065
in the formula i dc_y 、Z dc_y The output current and the output line resistance of the yth direct current controllable source are respectively.
By utilizing the droop characteristics of all controllable distributed power supplies, the combined droop control model of all the controllable distributed power supplies of the overpass and the direct current sub-microgrid is built as follows:
Figure GDA0003655792680000066
Figure GDA0003655792680000067
in the formula, M and D are combined droop coefficients of controllable distributed power supplies in the alternating current sub-microgrid and the direct current sub-microgrid respectively. The combined droop characteristics of the ac and dc sub-networks are shown in fig. 3, where f * 、
Figure GDA0003655792680000068
And the rated frequency of the alternating current sub-microgrid and the rated bus voltage of the direct current sub-microgrid are respectively represented.
(2) Segmented droop control with secondary compensation
Based on the power frequency static characteristic of a generator in a traditional power system, a segmented droop control strategy is provided, and the influence of the reserve capacity in the traditional generator on the active power regulation of the system is simulated. As can be seen from FIG. 4, when the output power of the generator is in the interval [0 GN ) When the generator has spare capacity, P-f is in a linear droop relation; when the output power of the generator reaches the upper limit P of the output power GN In time, the output power of the generator is constant, no spare capacity exists, and the system frequency reduction caused by the increase of the load is serious. Therefore, the active power reserve capacity in the conventional power system has the following two functions: 1) Providing active compensation for load fluctuations within a given range; 2) When the load in the system increases too much, resulting in insufficient active power backup, the system frequency will change rapidly with the load fluctuation, and the rapidly changing frequency can become an indication and reference signal of the system active power shortage.
The power frequency static characteristic of the traditional power system is applied to the controllable micro-source based on the droop control, the concept of 'virtual spare capacity' of the alternating-current sub-micro-grid is provided, the droop control of the alternating-current sub-micro-grid has the characteristic of segmentation, and a characteristic curve is shown in fig. 5. Wherein P' amax Virtual maximum output for AC sub-microgridOutput power ", P amax Is the actual maximum output power, delta P, of the AC sub-microgrid ac ＝P amax -P′ amax The virtual spare capacity of the AC sub-microgrid is obtained.
In order to overcome the adverse effect of the traditional droop control on the steady-state performance of the system, the sub-microgrid output power is 0,P' amax ]In the interval, the frequency of the system is adjusted without difference by applying secondary compensation control; when the output power is in (P' amax ,P amax ]In the interval, the mutual support of the alternating current micro-grid and the direct current micro-grid is realized through the interconnection converters, and the mutual support is mutually reserved. The section droop control of the alternating current sub-microgrid with the secondary compensation control is shown in fig. 7.
The section droop control with the secondary compensation in the ac microgrid can be expressed by the following formula:
Figure GDA0003655792680000071
δf＝k pf (f * -f)+k if ∫(f * -f)dt
in the formula, M 1 ＝(f min -f max )/P′ amax ，M 2 ＝(f min -f * )/(P amax -P′ amax )；
Figure GDA0003655792680000072
The active power output by the whole controllable micro-source of the AC sub-micro-grid is represented; δ f is a frequency quadratic compensation control signal; k is a radical of pf 、k if Is a quadratic compensation control parameter.
The power frequency characteristic of the generator is popularized to the direct-current sub-microgrid, and the droop characteristic similar to that in the alternating-current sub-microgrid can be obtained. Segment droop with secondary compensation control in DC sub-microgrid is shown in FIG. 8, wherein P' dmax Is the 'virtual maximum output power', P, of the DC sub-microgrid dmax Is the actual maximum output power, delta P, of the DC sub-microgrid dc ＝P dmax -P′ dmax The capacity is the 'virtual spare capacity' of the direct current sub-microgrid.
The segmented droop control with the secondary compensation in the direct current sub-microgrid can be represented by the following formula:
Figure GDA0003655792680000073
Figure GDA0003655792680000074
in the formula (I), the compound is shown in the specification,
Figure GDA0003655792680000075
the power output by the controllable micro source in the direct current sub-microgrid is represented;
Figure GDA0003655792680000076
δV dc compensating the control signal for the voltage twice; k is a radical of pV 、k iV Is a quadratic compensation control parameter.
(3) Coordination control between AC and DC sub-microgrid
Based on the sectional droop control strategy of the alternating current sub-microgrid and the direct current sub-microgrid, mutual support of power is achieved through interconnection converters when the output power reaches the virtual maximum output power of the sub-microgrid. The normalization formula of the alternating current frequency and the direct current voltage is as follows:
Figure GDA0003655792680000081
in the formula, ζ is f or V dc (ii) a (ζ)' represents a ζ normalization processing value having a value range of [ -1,0 ]]；ζ * 、ζ min Representing the nominal and minimum values of ζ, respectively.
From the above analysis, it was found that the output was [0,P' max ]Period (P' max Is P' amax Or P' dmax ) The sub-microgrid realizes the no-difference adjustment of the system through the secondary compensation control of each controllable distributed power supply, so that the value of (zeta)' is constantly 0; when the output power is in (P' max ,P max ]Interval time (P) max Is P amax Or P dmax ) And the value range of (zeta)' obtained by the droop characteristic of each sub-microgrid is [ -1, 0), and the interconnection converter senses the state change of the sub-microgrid by acquiring local signals so as to realize interconnection power transmission control.
In order to fully utilize the autonomous operation characteristic of each sub-microgrid and fully play the interactive supporting effect between alternating current sub-microgrid and direct current sub-microgrid, the application provides the operation principle of 'autonomous coordination' of the alternating current-direct current hybrid microgrid and analyzes the basic requirements of the power exchange of the interconnection converter:
1) When the output power of each sub-microgrid is within the virtual maximum output power, the sub-microgrid realizes the autonomous no-difference operation of the system through droop control with secondary compensation. At the same time, it should be satisfied that the switching power of the interconnection inverter is constantly 0 when the output power fluctuates within the virtual maximum output power.
2) When the output power of a certain sub-microgrid exceeds the virtual maximum output power of the sub-microgrid and the total output capacity of the hybrid microgrid does not exceed the sum of the virtual maximum output power of the system, power interaction is carried out through the interconnection converters, and the differential-free coordinated operation of the whole system is realized.
3) When the output power of the system exceeds the sum of the virtual maximum output power of the hybrid micro-grid, the whole system operates in the second droop control stage, and mutual support of power is achieved through the interconnected converters. However, such operating conditions can introduce steady state deviations into the system, which should be taken into account and avoided during system capacity design.
Assuming that the switching power transmitted from the dc microgrid to the ac microgrid by the interconnection converters is positive, the expression of the switching power P is:
Figure GDA0003655792680000082
the basic requirements of power exchange by interconnected converters may be to design power exchange management rules,
A：|(ζ τ )′|＞ζ g
B：|P|＞P g
wherein (ζ) is τ ) 'represents a value of (ζ)' after the lapse of time τ after occurrence of the power fluctuation; zeta g And P g Normal fluctuations at steady state (ζ)' and power losses of the interconnected converters are characterized, respectively, for normal numbers close to 0.
The expression of the switching power P with transmission power management is as follows:
Figure GDA0003655792680000091
in the formula, U and U are respectively logic OR and logic AND.
(4) Analysis of operating conditions
In order to verify the feasibility of the control strategy provided by the application, a simulation model of the alternating current-direct current hybrid microgrid shown in fig. 10 is built in an MATLAB/SIMULINK simulation platform.
Simulation verification is carried out according to different operation working conditions of the alternating current-direct current hybrid micro-grid, and the simulation verification mainly comprises three working conditions. Working condition 1 researches that when each sub-microgrid generates power fluctuation within the virtual maximum output power, the sub-microgrid is automatically operated without difference through secondary compensation control. And working condition 2 verifies the interaction coordination performance between the sub-micro grids. And the working condition 3 verifies the optimization effect of the strategy under the complex condition through the switching of a series of loads. The simulation is compared with the simulation before improvement, wherein the parameters of the alternating current sub-microgrid and the direct current sub-microgrid are the same, and the specific parameters are shown in table 1.
Table 1 simulation parameters of the system
Figure GDA0003655792680000092
Working condition 1:
in order to verify that when the output power of each sub-microgrid fluctuates within the virtual maximum output power, each sub-microgrid can realize autonomous non-differential operation through secondary compensation control on the controllable micro source, the following working conditions are designed.
When the system stably runs for 1s, the load of the AC sub-microgrid is suddenly increased from 2.8kW to 3.3kW; the load of the direct current sub-microgrid is increased from 2.33kW to 2.78kW at the time of 2 s; when the operation time reaches 3s, the load of the AC sub-microgrid is suddenly reduced from 3.3kW to 2.8kW; and when 4s, the active power demand of the AC sub-microgrid is increased by 0.4kW, the reactive power demand is increased from 0kVar to 1kVar, and the output power of the DC sub-microgrid is reduced to 2.41kW. The bus voltage of the dc subgrid and the voltage frequency waveform of the ac subgrid are shown in fig. 11 and 12.
Compared and analyzed by simulation results, 1) the frequency fluctuation is caused by the load fluctuation of the alternating-current sub-microgrid in 1s and 3s, but the control strategy provided by the application can quickly realize the secondary compensation of the frequency, so that the system no-difference running state is achieved; meanwhile, the power fluctuation of the alternating current sub-microgrid has no influence on the direct current voltage, which shows that no power flows between the alternating current sub-microgrid and the direct current sub-microgrid at the moment, and each microgrid can realize autonomous and no-difference operation. 2) And 2s, the strategy can realize the autonomous running without difference when the load of the direct current sub-microgrid suddenly changes. 3) When the reactive power demand of the AC sub-microgrid fluctuates, the strategy can realize the non-differential control of the voltage of the AC sub-microgrid.
In conclusion, when the output power of each sub-microgrid fluctuates in the spare capacity of the sub-microgrid, the control strategy provided by the application can realize the autonomous non-differential operation of the sub-microgrid, is beneficial to exerting the advantages of each sub-microgrid and simultaneously improves the electric energy quality.
Working condition 2:
in order to verify the power supporting effect of the strategy provided by the application on the AC and DC sub-microgrid during the coordinated operation of the hybrid microgrid, the following working conditions are designed.
When the time is 1s, the load of the AC sub-microgrid is increased from 3kW to 4.5kW; when 2.5s, the load power of the AC sub-microgrid is increased by 1kW; at 3.5s, an AC load of 1kW was removed. The load of the direct current sub-microgrid is constantly 2.41kW. The simulated waveforms are shown in fig. 13 to 15.
As can be seen from comparison of fig. 13 to fig. 15, 1) when the output power of the ac microgrid exceeds the virtual maximum output power thereof in 2.5s, the dc microgrid may be power-supported, and the system may be adjusted without difference through interactive coordination. 2) When 1s is needed, the load of the alternating current sub-microgrid is suddenly increased, but the output power is within the virtual maximum output power, the autonomous running of the system can be realized through the secondary compensation control of the sub-microgrid, but the prior art needs power exchange between the alternating current sub-microgrid and the direct current sub-microgrid. Meanwhile, as can be seen from fig. 15, the control strategy provided by the present application can reduce power exchange between the ac and dc sub-grids, which is beneficial to reducing power loss of the line.
According to the simulation analysis, the control strategy provided by the application has a good interaction coordination effect, and meanwhile, the autonomous regulation performance of each sub-microgrid can be fully exerted, and the power flow among the sub-microgrids is reduced.
Working condition 3:
the feasibility of the strategy in dealing with complex system conditions is verified through a series of power fluctuations. The working condition is designed as follows: the load of the alternating current microgrid is increased from 3kW to 4kW in 1s, and the load of the direct current microgrid keeps 2.41kW unchanged; the direct current load is increased to 4.81kW at 2 s; cutting off 1kW load of the AC sub-microgrid within 3 s; the DC load is reduced to 2.41kW at 4 s. The dc bus voltage, the ac frequency, and the power waveform flowing from the dc microgrid side are shown in fig. 16 to 18, respectively.
According to the simulation result of the working condition, the system can operate in a no-difference operation state through autonomous coordination no matter how the load of the alternating-current sub-microgrid in the hybrid microgrid fluctuates (such as 1s and 3 s) or the output power of the direct-current sub-microgrid fluctuates (such as 2s and 4 s), and the electric energy quality of the system is improved. Compared with the prior art, the control strategy provided by the application reduces the exchange power between the AC/DC sub-microgrid.

Claims (4)

1. A no-difference optimization control method for a non-communication alternating current-direct current hybrid micro-grid is characterized by comprising the following steps:
step S1: establishing a droop control model of each controllable distributed power supply;
step S2: building a combined droop control model of all controllable distributed power supplies of the interchange and the direct current sub-microgrid;
and step S3: determining the virtual standby capacity and the virtual maximum output power of the AC sub-microgrid and the DC sub-microgrid, and obtaining a sectional droop control model of the AC sub-microgrid and the DC sub-microgrid;
and step S4: designing a sectional droop control model containing secondary compensation control for the AC and DC sub-microgrid;
step S5: carrying out normalization processing on the alternating current frequency and the direct current voltage, and determining the exchange power between the alternating current sub-microgrid and the direct current sub-microgrid for control;
the process of obtaining the section droop control model of the ac and dc sub-microgrid in the step S3 specifically comprises: designing droop control sectional points at the virtual maximum output power of the AC/DC sub-microgrid to obtain a sectional droop control model of the system;
the step S4 specifically comprises the following steps: based on the obtained segmented droop control model, secondary compensation control of alternating current frequency and direct current voltage is introduced into the first-segment droop control, and the segmented droop control model of the alternating current sub-microgrid and the direct current sub-microgrid with the secondary compensation control is determined to be as follows:
Figure FDA0003742346860000011
Figure FDA0003742346860000012
M 1 ＝(f min -f max )/P′ amax
M 2 ＝(f min -f * )/(P amax -P′ amax )
Figure FDA0003742346860000013
Figure FDA0003742346860000014
wherein f is the AC system frequency, f min 、f max Respectively minimum and maximum values allowed by the frequency of the AC sub-network, f * Representing a communicatorNominal frequency, P, of the microgrid ac The active power output by the whole controllable distributed power supply of the AC sub-microgrid is represented; direct-current voltage secondary compensation control signal:
Figure FDA0003742346860000015
k pV 、k iV for quadratic compensation of the control parameter, V dc Which represents the dc-side bus voltage,
Figure FDA0003742346860000016
respectively the minimum value and the maximum value allowed by the voltage of the direct current sub-network,
Figure FDA0003742346860000017
representing the rated bus voltage, P, of the DC sub-microgrid dc And the power output by the controllable distributed power supply in the direct current sub-microgrid is expressed.
2. The method according to claim 1, wherein the step S3 of determining the virtual spare capacity and the virtual maximum output power of the ac/dc microgrid comprises: respectively designing corresponding virtual maximum output power P 'of the alternating-current sub-microgrid according to the capacity of the controllable distributed power supply of the alternating-current sub-microgrid and the direct-current sub-microgrid' amax Virtual spare capacity: delta P ac And virtual maximum output power P 'of the DC sub-microgrid' dmax Virtual spare capacity Δ P dc 。
3. The method for controlling the ac/dc hybrid microgrid with no communication according to claim 2, characterized in that the virtual spare capacity is specifically:
ΔP ac ＝P amax -P′ amax
wherein: p amax The actual maximum output power of the ac microgrid is,
the virtual spare capacity is specifically:
ΔP dc ＝P dmax -P′ dmax
wherein: p is dmax The actual maximum output power of the direct current sub-microgrid is obtained.
4. The method according to claim 1, wherein in step S5, the normalization formula of the ac frequency and the dc voltage is as follows:
Figure FDA0003742346860000021
wherein: zeta is a value before normalization processing, and (Zeta)' represents a value after the normalization processing and has a value range of [ -1,0 ]]，ζ * 、ζ min Representing the nominal and minimum values of ζ, respectively.
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