CN116565870A - Island AC/DC hybrid micro-grid control method considering power constraint - Google Patents
Island AC/DC hybrid micro-grid control method considering power constraint Download PDFInfo
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- CN116565870A CN116565870A CN202310670543.3A CN202310670543A CN116565870A CN 116565870 A CN116565870 A CN 116565870A CN 202310670543 A CN202310670543 A CN 202310670543A CN 116565870 A CN116565870 A CN 116565870A
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Classifications
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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
- H02J3/02—Circuit arrangements for ac mains or ac distribution networks using a single network for simultaneous distribution of power at different frequencies; using a single network for simultaneous distribution of ac power and of dc power
Abstract
The invention discloses an island AC/DC hybrid micro-grid control method considering power constraint, which comprises the following steps: s100, PI droop coordination control is adopted for an alternating current sub-network; s200, adopting distributed droop coordination control on the direct current sub-network; s300, adopting self-adaptive droop control for the interconnection converter in the island mode; s400, voltage and current double closed-loop control is realized through abc/dq0 coordinate conversion and decoupling, and control of the bidirectional converter is realized through PWM modulation. The invention can realize the power sharing of the hybrid micro-grid.
Description
Technical Field
The invention relates to a micro-grid control method, in particular to an island AC/DC hybrid micro-grid control method considering power constraint.
Background
The micro-grid is a small power generation and distribution system formed by integrating a distributed power supply, an energy storage device, an energy conversion device, related loads and a monitoring and protecting device. The power supply in the micro-grid is mostly a distributed power supply with smaller capacity, namely a small-sized unit with a power electronic interface, and the power supply comprises a micro gas turbine, a fuel cell, a photovoltaic cell, a small wind power generator set, an energy storage device such as a super capacitor, a flywheel and a storage battery. They are connected to the user side and have the features of low cost, low voltage, less pollution, etc.
The micro-grid can be divided into an alternating current micro-grid, a direct current micro-grid and an alternating current-direct current hybrid micro-grid according to grid-connected type, distributed power supply and load type. The AC/DC hybrid micro-grid is used as the latest form of the micro-grid, combines the advantages of a single micro-grid, optimizes the network structure of the micro-grid, can reduce the loss caused by multi-stage electric energy conversion, and can avoid unstable operation caused by overload of a single-side sub-grid load. The two sub-networks of the AC/DC hybrid micro-grid are connected through the interconnection converter, the two sub-networks can be operated independently or in an interconnected mode, the whole hybrid micro-grid system can be in an island mode or in a grid-connected mode, and a proper control strategy is a precondition for ensuring the stable and reliable operation of the system.
Compared with a grid-connected mode, in the island mode, the island adjusting capability is weakened due to low system capacity, the power distribution among all subsystems becomes more important, and the adjusting capability and the adaptability of the island system can be greatly improved through reasonable power distribution. However, for a hybrid micro-grid island system containing an alternating current sub-network and a direct current sub-network, unlike the traditional schedulable power source, the storage battery has the constraints of rated power, SOC and the like, and even distribution of power in the island is difficult to realize. In the existing AC/DC hybrid structure, the average division of the active power cannot be accurately realized under the condition of considering the power constraint of the storage battery.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides an island AC/DC hybrid micro-grid control method considering power constraint.
An island AC/DC hybrid micro-grid control method considering power constraint comprises the following steps: s100, PI droop coordination control is adopted for an alternating current sub-network; s200, adopting distributed droop coordination control on the direct current sub-network; s300, adopting self-adaptive droop control for the interconnection converter in the island mode; s400, voltage and current double closed-loop control is realized through abc/dq0 coordinate conversion and decoupling, and control of the bidirectional converter is realized through PWM modulation.
Optionally, the step S100 includes: the storage batteries in different running states are coordinated under the per unit framework, and the per unit calculation expression is:
wherein x is ω, V, P, Q
x real Is the actual value of the system variable, x * For the rated value of the system variable, the power constraint of the storage battery is realized by utilizing frequency control, and the control expression is as follows:
V i,pu ＝1-nQ i,pu
m p 、m i the active sagging proportional coefficient and the integral coefficient of the storage battery are respectively; when the normalized power 1 is exceeded, the integral droop control is activated, enabling signal en i Turning from 0 to 1.
In the step S200, the dc subnet distributed droop coordination control expression is:
V dci,pu ＝1-k(P i,pu -1)+δV
V dci,pu and P i,pu The per unit values of the output voltage and the output power of the ith direct current sub-network storage battery are respectively, and k is the droop coefficient of V-P.
In the step S300, the adaptive droop control expression of the interconnection transformer is:
ω ic ＝ω n -m p (P ic.pu -1)+δω
k p,ic1 andthe self-adaptive droop control proportion and integral coefficients of the interconnection converter; m is m p Is the proportional coefficient of AC PI sagging, V dc,pu And f pu The measured and calculated DC voltage and AC frequency per unit values for the interconnected converters.
In the step S400, the calculation formula of the active power and the reactive power obtained in the three-phase ac system under the synchronous rotation dq coordinate system is as follows:
the current decoupling is:
k p3 、k i3 the proportional and integral coefficients of the inner loop of the current are respectively;
the voltage decoupling is:
k p4 、k i4 the proportional and integral coefficients of the outer ring of the voltage, respectively.
The beneficial effects of the invention are as follows: when the power constraint of the storage battery is considered, the traditional droop control cannot realize accurate power sharing, so that the efficiency of the distributed power supply is difficult to develop, and even the distributed power supply is overloaded; the invention provides PI droop coordination control of the alternating current sub-network, distributed droop coordination control of the direct current sub-network and interconnection converter control strategy in island mode on the basis of considering the power constraint of the storage battery, thereby realizing accurate power sharing.
Drawings
FIG. 1 is a block diagram of an island AC/DC hybrid micro-grid control system;
fig. 2 is a graph of coordinated control of PI droop in an ac subnetwork;
FIG. 3 is a DC subnet communication architecture;
FIG. 4 is a block diagram of an interconnection inverter adaptive droop control;
FIG. 5 is a dual closed loop control block diagram;
fig. 6 is a decoupling schematic.
Detailed Description
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the invention, as illustrated in the accompanying drawings. Like reference numerals refer to like parts throughout the several views of the drawings. The drawings are not intended to be drawn to scale, emphasis instead being placed upon illustrating the principles of the invention.
As shown in fig. 1, the island ac-dc hybrid micro-grid system taking power constraint into consideration of the present invention is composed of a dc sub-network, an interconnection converter and an ac sub-network, wherein the dc sub-network is connected with the ac sub-network through the interconnection converter. The interconnection converter may be, for example, an AC/DC bi-directional converter, through which the mutual flow of electrical energy between the DC sub-network and the AC sub-network may be achieved.
In the invention, in the operation of the island AC/DC hybrid micro-grid taking power constraint into consideration, an AC sub-network adopts PI droop coordination control of the AC sub-network; the direct current sub-network adopts distributed droop coordination control of the direct current sub-network; the interconnection converter adopts self-adaptive droop control in an island mode. The method comprises the following steps: s100, performing PI droop coordination control on the alternating current sub-network; s200, distributed droop coordination control of a direct current sub-network; s300, self-adaptive droop control of the interconnection converter in the island mode; s400, voltage and current double closed-loop control is realized through abc/dq0 coordinate conversion and decoupling, and control of the bidirectional converter is realized through PWM modulation.
S100, performing PI droop coordination control on the alternating current sub-network.
Unlike conventional dispatchable power sources, batteries have constraints such as rated power, SOC, etc., and therefore, constraint control of the batteries cannot be achieved based on conventional PI droop control. The invention adopts PI sagging control considering power constraint to realize coordination of storage batteries with different rated capacities and working conditions.
Firstly, the storage batteries with different charge states have different rated output powers, and the storage batteries with different running states are coordinated under the per unit frame.
The per unit calculation expression is:
wherein x is ω, V, P, Q
x real Is the actual value of the system variable, x * Is the nominal value of the system variable.
After per unit, the invention improves the per unit PI droop control and utilizes frequency control to realize the power constraint of the storage battery. The control expression is as follows
V i,pu ＝1-nQ i,pu
m p 、m i The active droop proportion coefficient and the integral coefficient of the storage battery are respectively. When the normalized power 1 is exceeded, the integral droop control is activated, enabling signal en i Turning from 0 to 1, the sag curve is shown in fig. 2. By integrating the droop control, power constraint of the battery can be achieved.
S200, direct current sub-network distributed droop coordination control.
Since the voltage in the dc sub-network is not a common variable of the system, droop control cannot achieve accurate power sharing under conditions of line impedance mismatch. The power constraint of the battery cannot be realized by means of the decentralized droop control alone. Thus, these objectives are achieved with distributed control of low bandwidth communications.
The distributed communication network is shown in fig. 3. The diagram (a) in fig. 3 is a conventional redundant communication structure, and the communication "voltage", "output power" with a plurality of power supply nodes is high in communication cost and large in communication delay τ. (b) The annular communication structure of the invention only communicates with the adjacent two power supply nodes with low cost and low redundancy. In the figure, DG i Representing the ith distributed power supply
The design of the communication network structure requires consideration of its reliability and cost. The invention adopts a bidirectional sparse low-bandwidth communication network structure, as shown in a (b) diagram in fig. 3. The ring communication network is considered to be a reliable structure, has enough redundancy, and can avoid the problem of unstable system caused by single-point communication failure of the system. Based on the ring communication network topology, the output voltage of each storage battery is constructed as a common variable of the direct current sub-network.
Distributed droop coordination control of direct current sub-network
V dci,pu ＝1-k(P i,pu -1)+δV
V dci,pu And P i,pu The per unit values of the output voltage and the output power of the ith direct current sub-network storage battery are respectively, and k is the droop coefficient of V-P. Adding a distributed control term V in the V-P droop control, wherein the distributed control term comprises a power average term and a power constraint term, and an enable signal EN is set at the same time i When the output power of the storage battery is greater than 1 per unit rating, the enable signal EN i From 1 to 0, a power constraint mode is entered. k (k) p1 、k i1 The proportional coefficient and the integral coefficient of the power equipartition controller are respectively; k (k) p2 、k i2 The proportional coefficient and the integral coefficient of the power constraint controller respectively.
Through the design of the distributed droop controller of the direct current sub-network, the direct current sub-network achieves the following two aims: (1) when the output power of the storage battery is in a normal range, accurate power sharing is realized among the direct-current energy storage power supplies; (2) when the stored energy reaches the power limit, the power constraint mode is switched to seamlessly so that the output power is controlled to be at the limit value
S300, self-adaptive droop control of the interconnection converter in the island mode.
In hybrid micro-grids, the internal impedance of the micro-grid is generally high, and is considered as a weak grid, due to the small capacity and low voltage level of each partial sub-grid. The traditional current control strategy does not have the power grid supporting capability, and serious current distortion can occur under the conditions of load fluctuation and line switching, so that the unstable condition of the system is caused. Therefore, the invention provides the self-adaptive droop control with the power grid supporting capability, which can reduce active power fluctuation and reduce the distortion rate of output current when global active power equalization is carried out.
The control block diagram of the adaptive droop control is shown in fig. 4, and the adaptive droop control expression of the interconnection transformer is:
ω ic ＝ω n -m p (P ic.pu -1)+δω
k p,ic1 and k i,ic,1 The self-adaptive droop control proportion and integral coefficients of the interconnection converter; m is m p Is the proportionality coefficient of AC PI droop. V (V) dc,pu And f pu The measured and calculated DC voltage and AC frequency per unit values for the interconnected converters.
The scaling factor λ per unit depends on the power class and droop factor of the ac-dc hybrid microgrid.
Its calculation expression can be written as
Under steady state operation, the voltage standard value of the direct current sub-network is the same as the frequency standard value of the alternating current sub-network, which indicates that the power levels of the alternating current sub-network are consistent, and the global active power equipartition of the hybrid micro-grid is realized. The essence of the adaptive droop control is a voltage source control mode, and the phase reference of the voltage is given by active loop control; the voltage amplitude may be obtained by a voltage-reactive droop loop.
S400, voltage and current double closed-loop control is realized through abc/dq0 coordinate conversion and decoupling, and control of the bidirectional converter is realized through PWM modulation.
And voltage and current double closed-loop control is realized through abc/dq0 coordinate conversion and decoupling, and finally, the control of the bidirectional converter is realized through PWM modulation.
The calculation formula of the active power and the reactive power obtained in the three-phase alternating current system under the synchronous rotation dq coordinate system is as follows:
current decoupling:
k p3 、k i3 the proportional and integral coefficients of the inner loop of the current are respectively;
voltage decoupling:
k p4 、k i4 the proportional and integral coefficients of the outer ring of the voltage, respectively.
In the above description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The foregoing description is only of a preferred embodiment of the invention, which can be practiced in many other ways than as described herein, so that the invention is not limited to the specific implementations disclosed above. While the foregoing disclosure has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention without departing from the technical solution of the present invention still falls within the scope of the technical solution of the present invention.
Claims (10)
1. The island AC/DC hybrid micro-grid control method considering power constraint is characterized by comprising the following steps of:
s100, PI droop coordination control is adopted for an alternating current sub-network;
s200, adopting distributed droop coordination control on the direct current sub-network;
s300, adopting self-adaptive droop control for the interconnection converter in the island mode;
s400, voltage and current double closed-loop control is realized through abc/dq0 coordinate conversion and decoupling, and control of the bidirectional converter is realized through PWM modulation.
2. The control method according to claim 1, characterized in that said step S100 includes: the storage batteries in different running states are coordinated under the per unit framework, and the per unit calculation expression is:
wherein x is ω, V, P, Q
x real Is the actual value of the system variable, x * Is the nominal value of the system variable.
3. The control method according to claim 2, characterized in that the power constraint of the battery is achieved by frequency control, the control expression of which is as follows:
V i,pu ＝1-nQ i,pu
m p 、m i the active sagging proportional coefficient and the integral coefficient of the storage battery are respectively; when the normalized power 1 is exceeded, the integral droop control is activated, enabling signal en i Turning from 0 to 1.
4. The control method according to claim 1, characterized in that said step S200 includes: a bidirectional sparse low-bandwidth communication ring network structure is adopted.
5. The control method according to claim 4, wherein the direct current subnet distributed droop coordination control expression is:
V dci,pu ＝1-k(P i,pu -1)+δV
V dci,pu and P i,pu The per unit values of the output voltage and the output power of the ith direct current sub-network storage battery are respectively, and k is the droop coefficient of V-P.
6. The control method according to claim 1, wherein the interconnection inverter adaptive droop control expression in step S300 is:
ω ic ＝ω n -m p (P ic.pu -1)+δω
k p,ic1 andthe self-adaptive droop control proportion and integral coefficients of the interconnection converter; m is m p Is the proportional coefficient of AC PI sagging, V dc,pu And f pu The measured and calculated DC voltage and AC frequency per unit values for the interconnected converters.
7. The control method according to claim 6, wherein the scaling factor λ per unit depends on the power class and droop factor of the ac/dc hybrid micro-grid, and the calculation expression is:
8. the control method according to claim 7, characterized in that in steady state operation the voltage per-value of the dc sub-network is the same as the frequency per-value of the ac sub-network.
9. The control method according to claim 1, wherein the calculation formula of the active power and the reactive power obtained in the three-phase ac system in step S400 under the synchronous rotation dq coordinate system is:
10. the control method according to claim 9, wherein the current decoupling is:
k p3 、k i3 the proportional and integral coefficients of the inner loop of the current are respectively;
the voltage decoupling is:
k p4 、k i4 the proportional and integral coefficients of the outer ring of the voltage, respectively.
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