CN110752627A - Microgrid autonomous cooperative control system considering energy complementation - Google Patents

Abstract

The invention discloses a microgrid self-discipline cooperative control system considering energy complementation, comprising several DC microgrids and AC microgrids with a common DC bus, wherein the DC microgrids and the AC microgrids include a relaxation unit and a power unit. Each of the DC microgrids and AC microgrids corresponds to a local controller, and each local controller is used for autonomous control in the corresponding DC microgrid or AC microgrid; it also includes an upper-layer centralized controller, the upper-layer centralized controller Coordinated control between DC microgrids and AC microgrids is carried out through the Internet. The purpose of the present invention is to provide a microgrid self-discipline cooperative control system considering energy complementation, so as to solve the problem that the capacity constraints and power supply stability of a single microgrid in the prior art are difficult to meet the increasing electricity load, and realize efficient and flexible acceptance. AC and DC renewable energy and load, while enhancing the power supply reliability and operation stability of the system.

Description

A Microgrid Autonomous Coordinated Control System Considering Energy Complementarity

technical field

The invention relates to the field of microgrids, in particular to a microgrid autonomous cooperative control system considering energy complementation.

Background technique

Microgrid refers to a small power generation and distribution system composed of distributed power sources, energy storage devices, loads, monitoring and protection devices, etc., which can efficiently accommodate distributed power sources and improve the utilization efficiency of renewable energy (photovoltaic, wind power, etc.). , improve power supply reliability and power quality. The microgrid can work in grid-connected mode and island operation mode. When working in the island operation mode, it can provide independent power supply for remote areas or islands.

In a single AC microgrid, the DC source and DC load need to be connected through the corresponding DC/AC converter; similarly, in a single DC microgrid, the AC element and the AC load need to be connected through the corresponding AC/DC converter . Compared with a single AC (DC) microgrid, the AC/DC hybrid microgrid can flexibly and efficiently receive AC (DC) sources and loads, reduce intermediate conversion steps, improve energy utilization, and reduce costs. With the increasing electricity load in the microgrid, the capacity constraints and power supply stability of a single microgrid are more prominent.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a microgrid self-discipline cooperative control system considering energy complementation, so as to solve the problem that the capacity constraints and power supply stability of a single microgrid in the prior art are difficult to meet the increasing electricity load, and realize efficient and flexible acceptance. AC and DC renewable energy and load, while enhancing the power supply reliability and operation stability of the system.

The present invention is achieved through the following technical solutions:

A microgrid autonomous cooperative control system considering energy complementarity, comprising several DC microgrids and AC microgrids with a common DC bus, wherein said DC microgrids and AC microgrids include relaxation units and power units, and each DC microgrid Each of the AC microgrids corresponds to a local controller, and each local controller is used for autonomous control in the corresponding DC microgrid or AC microgrid; it also includes an upper-layer centralized controller, which performs various functions through the Internet. Collaborative control between DC microgrids and AC microgrids.

In view of the problem that the capacity constraints and power supply stability of a single microgrid in the prior art are difficult to meet the increasing electricity load, the inventor believes that if the adjacent AC and DC microgrids are flexibly interconnected in the form of clusters, the AC and DC microgrids can be efficiently and flexibly accommodated. , DC renewable energy and load, while enhancing the power supply reliability and operation stability of the system. In the present application, the AC and DC areas are connected to the public DC bus through the power electronic interface device in parallel mode, which can efficiently and flexibly accommodate distributed generation units and energy storage units, and provide high-reliability power supply for local loads. The invention maintains power balance and common DC bus voltage stability through the coordinated self-discipline control of each DC microgrid and AC microgrid, and realizes flexible DC bus voltage control.

Further, the relaxation units are distributed energy storage devices, and one or more of the relaxation units are ice cold storage devices. Ice storage uses ice as the energy storage medium, which enables large air-conditioning units to store energy during low power consumption periods and supply cooling loads during peak power supply periods of the power grid. It has the following advantages: 1) Relieve the load during the peak period of electricity consumption, achieve peak shifting effect, and use the peak-valley electricity price implemented in different regions to obtain energy-saving costs; 2) Use the regional peak-valley electricity price difference to achieve energy saving; 3) Refrigeration equipment in the system The proportion of full-load operation is increased, the state is stable, and the equipment utilization rate is improved. In this application, ice storage is incorporated into the multi-energy microgrid control framework, and the multi-energy complementarity is used to fully tap the user's controllable potential and increase the user's energy flexibility.

Further, in the energy storage stage: each slack unit absorbs electric energy according to its rated capacity, and each local controller controls the actual energy storage power of the corresponding slack unit to reasonably undertake according to its rated capacity ratio;

In the energy release stage: the ice storage device is given priority, and the rest of the equivalent electrical load of the cooling load and the electrical load are borne by other distributed energy storage devices according to the rated capacity ratio. In this scheme, when electricity is abundant, distributed energy is generated, or electricity prices are low, and when electricity is purchased from the Internet, ice storage and storage batteries and other energy storage devices absorb electricity according to their rated capacity, and reasonably undertake energy storage; According to the principle of cold storage device, priority should be given to the ice cold storage device, and the rest of the equivalent electrical load of the cooling load and the electrical load should be reasonably borne by other energy storage devices according to their rated capacity ratios.

Further, the local controller adopts constant power control for the control of the DC microgrid and the AC microgrid.

Preferably, the constant power control method for the AC microgrid by the local controller is as follows: the outer loop controls the active power-frequency droop and reactive power-voltage droop to generate the instantaneous value of the inner loop voltage and the voltage reference value of the closed-loop control system. Phase signal, voltage amplitude signal, and then through the inner loop voltage control to complete the final control target.

Preferably, the constant power control method of the local controller for the DC microgrid is as follows: the outer loop generates the inner loop voltage reference value through active power-voltage droop control, and then completes the final control target through the inner loop voltage or current control.

Further, the cooperative control of the AC microgrid by the upper-layer centralized controller includes interconnected power control, virtual synchronization control, and voltage instantaneous value closed-loop control;

The cooperative control of the upper-layer centralized controller to the DC microgrid includes interconnection power control and phase shift control.

Further, the method for interconnecting power control includes the following steps:

(1) Assuming that there is a virtual slack unit at the common DC bus, construct a virtual DC voltage droop control curve:

U _dc =U _dcref -P _dc /k _dc ; where U _dc is the common DC bus voltage; U _dcref is the set value of the DC voltage in the virtual DC voltage droop control, P _dc is the power injected into the DC system by the virtual energy storage unit; k _dc is the sag coefficient;

(2) Define the power error;

(3) The power error is corrected according to the droop control curve, and the interconnected power control system is obtained.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. The present invention is a microgrid self-discipline cooperative control system that considers energy complementation, maintains power balance and common DC bus voltage stability through the coordinated self-discipline control of each DC microgrid and AC microgrid, and realizes flexible DC bus voltage control.

2. The present invention is a micro-grid self-discipline collaborative control system considering energy complementation, and a multi-energy micro-grid considering ice storage, which can efficiently and flexibly accommodate distributed generation units and energy storage units, provide high-reliability power supply for local loads, and at the same time To achieve multi-energy complementarity, energy saving and environmental protection.

3. The present invention is a micro-grid self-discipline collaborative control system that considers energy complementation. When the electric energy is abundant, the ice storage, storage battery and other devices absorb electric energy according to their rated capacity, and reasonably undertake the energy storage; when the load peaks, the ice storage device is given priority, The remaining cooling load equivalent electrical load and electrical load shall be reasonably borne by other energy storage devices according to their rated capacity ratios. The utilization rate of the energy storage device is effectively improved and the service life of the equipment is prolonged.

Description of drawings

The accompanying drawings described herein are used to provide further understanding of the embodiments of the present invention, and constitute a part of the present application, and do not constitute limitations to the embodiments of the present invention. In the attached image:

1 is a schematic structural diagram of a multi-energy microgrid according to a specific embodiment of the present invention;

2 is an equivalent model of a multi-energy microgrid system according to a specific embodiment of the present invention;

3 is a multi-energy microgrid control framework according to a specific embodiment of the present invention;

4 is a control block diagram of an AC microgrid relaxation unit in a specific embodiment of the present invention;

5 is a control block diagram of a DC microgrid relaxation unit in a specific embodiment of the present invention;

FIG. 6a is a schematic diagram of the interconnection control of the communication micro-grid in a specific embodiment of the present invention;

FIG. 6b is a schematic diagram of interconnection control of a DC microgrid in a specific embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and the accompanying drawings. as a limitation of the present invention.

The structure of the multi-energy microgrid system shown in FIG. 1 is equivalent to the model shown in FIG. 2 . As shown in FIG. 2 , this embodiment includes one AC microgrid and two DC microgrids. Each microgrid contains relaxation units (such as energy conversion devices, energy storage devices such as batteries, controllable distributed power sources, etc.) and power units (such as new energy generation, loads, etc.). Among them, relaxation units (such as energy-based energy storage devices, controllable distributed power sources, etc.) are used as main power sources to control voltage/frequency (AC region) and DC region (DC sub-network) stability in the system. Renewable energy distributed generation units using maximum power control or energy storage units and loads in power scheduling mode can be regarded as power units. The AC and DC microgrids are respectively connected to the common DC bus through corresponding interconnection devices (DC-AC or DC-DC).

In order to realize the stable control of the multi-energy microgrid shown in FIG. 2 , the present embodiment proposes a basic framework of the autonomous cooperative control strategy of the multi-energy microgrid as shown in FIG. 3 . In this embodiment, through the self-discipline cooperative control of the multi-energy microgrid, it is expected to realize the following main temporary and steady-state operation control functions:

1) The physical level of the multi-energy microgrid shown in Figure 3 includes the distributed area of the DC microgrid and the flexible interconnection of the AC microgrid. The AC microgrid and the DC microgrid are respectively controlled by the corresponding local controller and the upper-level centralized controller. Each microgrid achieves the goal of self-discipline control within the microgrid through the corresponding local controller, and the cooperative control between microgrids is completed by the upper-layer centralized controller.

2) The micro-grids in the multi-energy micro-grid are interconnected through interconnecting devices, which can be controlled and dispatched by the upper-level centralized controller. The multi-energy complementarity is used to fully tap the user's controllable potential and achieve the corresponding optimal operation goal of the whole system.

The control objectives to be achieved in this embodiment are as follows:

Energy storage stage: when electricity is abundant, distributed energy is generated, or the price of electricity is low, when purchasing electricity from the Internet, distributed energy storage devices such as ice storage and storage batteries absorb electricity according to their rated capacity and reasonably undertake energy storage. As shown in Figure 2, the output power of the power units in the three microgrids (that is, the net power output by the load and other new energy power generation units, with the injection into the corresponding bus as the positive direction) are respectively P _p,A , P _p,B and P _p,C . It is assumed that the rated capacities of the slack cells in AC microgrid A, DC microgrid B and DC microgrid C are _Pos,A , _Pos,B and _Pos,C , and their capacity ratios satisfy _Pos,A : _Pos,B : _Pos,C =a:b:1. When the multi-energy microgrid is running normally, the self-discipline cooperative control strategy ensures that the actual energy storage powers P _s,A , P _s,B and P _{s of the relaxation units in AC microgrid A, DC microgrid B and DC microgrid C, C} can be reasonably borne according to its rated capacity ratio (ie a:b:1) to improve the utilization efficiency of the relaxation unit in the multi-energy microgrid.

Energy release stage: For example, when the load is peak, the principle of using ice cold storage device is followed, and the ice cold storage device is given priority, and the rest of the equivalent electrical load of the cooling load and the electrical load are reasonably borne by other distributed energy storage devices according to their rated capacity ratios.

The control strategy of the AC microgrid relaxation unit:

As shown in Figure 2, the power unit in AC microgrid #A adopts a constant power control strategy; the relaxation unit control strategy is shown in Figure 4. Through active power-frequency droop (Pf) control and reactive power-voltage (QV) droop control, the outer loop generates the phase signal θ _A and the voltage amplitude signal V _ref of the voltage reference value of the inner loop voltage instantaneous value closed-loop control system, respectively. _{, A} , and then complete the final control goal through the voltage inner loop control system. In order to reduce the steady-state error and improve the dynamic response of the control system, the voltage inner loop usually adopts PR control.

It can be seen from Figure 4 that the output active power and frequency of the relaxation unit in the AC microgrid A will have the following steady-state droop characteristics:

ω _A = ω _set,A -P _s,A /k _p,A (1)

In the formula, ω _A , ω _set,A and P _s,A respectively represent the bus frequency of the AC microgrid A, the AC frequency set value of the droop control characteristic curve and the actual output active power of the balance unit; k _p,A represents the active power / The droop factor of the frequency droop control system.

DC microgrid relaxation unit control strategy:

As shown in Figure 2, the power unit in the DC microgrid i (i=B, C) adopts a constant power control strategy; the relaxation unit control strategy is shown in Figure 5. The outer loop generates the inner loop voltage reference value u _ref ,i through active power-voltage droop (PV) control, and then completes the final control goal through the inner loop voltage/current control.

When the DC microgrid i adopts the DC voltage droop control strategy as shown in Figure 5, the droop control characteristics shown in the following formula (2) can be used to describe the relationship between the DC microgrid bus voltage and the output power of the balance unit in the system:

u _i =u _set,i -P _s,i /k _p,i (2)

In the formula, u _i and P _s,i represent the DC microgrid #i busbar voltage and the output power of the balance unit respectively; u _{set,i and} ki are the DC voltage setting value and the droop coefficient in the droop control, respectively.

In this embodiment, the multi-energy micro-grid interconnection control strategy is the key to achieve the above control goal. Based on the droop characteristics of the slack cell in the AC/DC microgrid obtained above, a multi-energy microgrid interconnection control strategy is proposed, as shown in Fig. 6(a) and (b), respectively. AC microgrid interconnection control includes interconnection power control, virtual synchronization control and voltage instantaneous value closed-loop control; DC microgrid interconnection device includes interconnection power control and phase shift control.

The design of the interconnected power control system is the key to realize the coordinated control of multi-energy microgrid power. The core design ideas are as follows:

First, it is assumed that there is a virtual relaxation unit at the common DC bus of the multi-energy microgrid shown in Figure 2, and the following virtual DC voltage droop control curve is constructed:

U _dc =U _dcref -P _dc /k _dc (3)

In the formula, U _dc is the common DC bus voltage; U _dcref and P _dc represent the DC voltage setting value in the virtual DC voltage droop control and the power injected by the virtual energy storage unit into the DC system respectively; k _dc is the droop coefficient.

The power error is defined as follows:

In addition, since the actual output power of the slack unit in each AC and DC microgrid and the injected power of the virtual energy storage unit at the common DC bus have the drooping operation characteristics of equations (1) to (3), respectively, each power in equation (4) The error can be further expressed as:

On the basis of formula (5), the interconnected power control system shown in Figures 6a and 6b can be designed, which can be expressed as follows:

In the formula, P _refA , _{P refB} and P _refC respectively represent the output results of the corresponding microgrid interconnection power control system in Figures 6a and 6b, that is, the actual active power reference value of the corresponding microgrid interface interconnection device; G _ICB (s) and G _ICC (s) are respectively the controllers of the corresponding interconnected power control system, which are both used as PI controllers in this embodiment.

The specific embodiments described above further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (8)

1. A microgrid autonomous cooperative control system considering energy complementation comprises a plurality of direct-current microgrids and alternating-current microgrids with a common direct-current bus, wherein each of the direct-current microgrids and the alternating-current microgrids comprises a relaxation unit and a power unit; the system further comprises an upper-layer integrated controller, and the upper-layer integrated controller performs cooperative control among the direct-current micro-grids and the alternating-current micro-grids through the Internet.

2. The microgrid autonomous cooperative control system considering energy complementation is characterized in that the relaxation units are distributed energy storage devices, and one or more of the relaxation units are ice cold storage devices.

3. The microgrid autonomous cooperative control system considering energy complementation is characterized in that,

in the energy storage stage: each relaxation unit absorbs electric energy according to the rated capacity of the relaxation unit, and each local controller controls the actual energy storage power of the corresponding relaxation unit to be reasonably borne according to the rated capacity ratio of the relaxation unit;

in the energy release stage: and preferentially putting the ice storage device, and bearing the equivalent electric load of the rest cold loads and the electric load by other distributed energy storage devices according to the rated capacity ratio.

4. The microgrid autonomous cooperative control system considering energy complementation is characterized in that the local controller adopts constant power control for controlling the direct current microgrid and the alternating current microgrid.

5. The microgrid autonomous cooperative control system considering energy complementation is characterized in that a constant power control method of an local controller for an alternating current microgrid comprises the following steps: the outer ring generates an inner ring voltage instantaneous value, a phase signal of a voltage reference value of a closed-loop control system and a voltage amplitude signal through active power-frequency droop and reactive power-voltage droop control, and then the final control target is completed through inner ring voltage control.

6. The microgrid autonomous cooperative control system considering energy complementation is characterized in that a constant power control method of a local controller for a direct current microgrid is as follows: the outer ring generates an inner ring voltage reference value through active power-voltage droop control, and then the final control target is completed through inner ring voltage or current control.

7. The microgrid autonomous cooperative control system considering energy complementation is characterized in that,

the cooperative control of the upper-layer integrated controller on the alternating-current micro-grid comprises interconnection power control, virtual synchronous control and voltage instantaneous value closed-loop control;

the cooperative control of the upper-layer integrated controller on the direct-current micro-grid comprises interconnection power control and phase-shifting control.

8. The microgrid autonomous cooperative control system considering energy complementation, as claimed in claim 7, wherein the method for controlling interconnection power comprises the following steps:

(1) assuming that a virtual relaxation unit is contained at the position of the common direct current bus, a virtual direct current voltage droop control curve is constructed:

U_dc＝U_dcref-P_dc/k_dc(ii) a Wherein U is_dcIs the common dc bus voltage; u shape_dcrefIndicating the DC voltage set-point, P, in the virtual DC voltage droop control_dcRepresenting the virtual energy storage unit to inject the direct current system power; k is a radical of_dcIs the sag factor;

(2) defining a power error;

(3) and correcting the power error according to the droop control curve to obtain the interconnected power control system.

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