CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a U.S. patent application filed herewith which claims the priority of China patent application No. 201811444435.X entitled “Method and Apparatus for Smoothing Link-line Power of Electrothermal Microgrid Using Thermal Storage Heat Pump” and filed on Nov. 29, 2018 to the State Intellectual Property Office of the People's Republic of China, which is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to the technical field of electrical power and thermal power and more particular relates to an electrothermal microgrid technique, which includes a method and apparatus for smoothing a link-line power of an electrothermal microgrid using a thermal storage heat pump cluster.

BACKGROUND

An electrothermal microgrid is a type of ultimate integrated energy supply facility composed of a distributed energy source, an energy storage device, an electrothermal device, and a control based on the electric and thermal requirements of an ultimate consumer. The electrothermal microgrid can comprehensively utilize two different energy forms of electricity and heat to improve the reliability and the economy of regional ultimate energy supply. As a large number of distributed renewable energy sources are accessing the microgrid, the intermittence and volatility of renewable energy power generation bring challenges to the stable operation of the microgrid. The electrothermal microgrid adopts key electrothermal conversion technologies such as heat generation using electricity to take the advantages of a quick response of electric energy and ease of thermal energy storage thereby improving the control flexibility and reliability of the operation of the microgrid. The electrothermal microgrid has become scholars' focus of attention.

At present, a large number of researches have proposed battery energy storage for smoothing power fluctuations of the microgrid, including document “A Control Strategy of Hybrid Energy Storage System Capable of Suppressing Output Fluctuation of Photovoltaic Generation System” (WANG Haibo, YANG Xiu, ZHANG Meixia. Power System Technology. 2013 (09). Volume 37)”; document “Hybrid Energy Storage Scheduling based Microgrid Energy Optimization Under Different Time Scales” (LIU Fang, YANG Xiu, SHI Shansan, ZHANG Meixia, DENG Hong, GUO Pengchao. Power System Technology. 2014 (11)); patent application “Micro-grid energy management method based on hybrid energy storage and electric automobiles” (CN107769235A) and patent application “Method for micro-grid system coordinated control based on multi-element composite energy storage” (CN104022528A). They all use the hybrid energy storage made up of power type energy storage and energy type energy storage as a control object to achieve output optimization by different control methods. However, the high costs of battery storage limit the technical economy of its application.

In the electrothermal microgrid, a thermal controlled load (TCL) with a good controlled characteristic such as an air conditioner and an electric heat pump can effectively smooth the power fluctuations. Document “A Hierarchical and Distributed Control Strategy of Thermostatically Controlled Appliances for City Park based on Load model Prediction” (WEI Wenting, WANG Dan, JIA Hongjie, WANG Ran, GUO Bingqing, QU Bo, FAN Menghua. Proceedings of the CSEE. 2016 (08)) provides a control strategy for thermostatically controlled appliances based on the load model prediction in which power of a heat pump cluster is controlled through a variable temperature control strategy to match the fluctuations of renewable energy, but the coordination with battery energy storage is not considered. Document “A Coordination Control Strategy of Battery and Virtual Energy Storage to Smooth the Micro-grid Link-line Power Fluctuations” (WANG Ran, WANG Dan, JIA Hongjie, YANG Zhaoyong, QI Yebai, FAN Menghua, SHENG Wanxing, HOU Lirui, Proceedings of the CSEE. 2015 (20)) provides an index priority list (IPL) to construct a heat pump model and sets a heat pump start-stop condition to avoid repeated start-stop. However, the control of the heat pump is monotonous and the overall start-stop frequency of the heat pump cluster is not optimized. Document “A Link-line Power Smoothing Method for Microgrid Using Residential Thermostatically-controlled Loads” (WANG Chengshan, LIU Meng, LU Ning. Proceedings of the CSEE. 2012 (25)) coordinates hybrid energy storage and the output of the heat pump cluster based on an algorithm for controlling the heat pump cluster. However, residential buildings are used as virtual thermal energy storage, which imposes a great limitation on the control of the heat pump cluster. Patent application “Group control heat pump-based power fluctuation smoothing method and system for micro-grid link line(CN106849132A) smooths power fluctuations taking into account the power regulation of the heat pump, but the power regulation and control model is simplistic and the coordination with the output of a storage battery is not considered.

SUMMARY

An object and a problem to be solved of the present disclosure are described below.

(1) In view of the high operation costs of battery energy storage, electric energy and thermal energy are coupled in a microgrid, and partial electric energy storage is replaced with distributed thermal energy storage to implement an economical operation of the microgrid. There is thus a need to propose a corresponding microgrid control method.

(2) In view of the lack of a thorough research on the control of an electrothermal coupling device and the lack of a mature control model in the existing art, the present disclosure deeply analyzes the characteristics of a thermal storage heat pump, fully considers operational characteristics of the heat pump and thermal storage characteristics of a thermal storage water tank matching the heat pump, and establishes a thermal storage heat pump control model.

(3) The traditional cluster control algorithm has inconsistent heat pump losses due to differentiated conditions of thermal storage heat pumps participating in power regulation and control, such as different rated powers of the heat pumps, different volumes of matching water tanks and different thermal loads of users, enthusiasm and fairness of the users are difficult to ensure. The object of the present disclosure is to achieve consistent adjustment of losses of a heat pump cluster and reduce strategy implementation costs.

(4) In a traditional method, control of the heat pump cluster and control of an output of a storage battery are difficult to coordinate with each other due to different response time characteristics. The present disclosure establishes a heat pump cluster power adjustment model, this enabling the heat pump cluster to smooth medium frequency fluctuations, and assists the storage battery in reducing battery losses.

The technical scheme of the present disclosure is as follows: a method for smoothing a link-line power of an electrothermal microgrid using a thermal storage heat pump cluster, the method including determining a link-line power control target of the microgrid, a heat pump cluster start-stop control layer, a heat pump cluster power adjustment layer, and a storage battery smoothing adjustment. A link-line power control cycle is divided into a number of TDtime points, let k denote discrete time, where k∈[1, TD] then each control cycle includes the following steps.

(1) A current link-line power control target PTar[k] is determined based on an original link-line power PTLO[k] and an energy storage state SOCall[k−1] of the storage battery and the heat pump cluster at a last time point, link-line fluctuating power Pflu[k] is obtained based on PTar[k] in conjunction with the original link-line power PTLO[k], and the fluctuating power is then subjected to low-pass filtering before a smoothing task Pfl_HP[k] is pre-distributed to the heat pump cluster based on the energy storage state of the storage battery and the heat pump cluster.

(2) A heat pump start-stop control layer cluster makes a heat pump cluster start-stop scheme, and a start-stop state si[k] of the heat pump cluster and a heat pump cluster start-stop smoothing component PHP_sw[k] are determined according to Pfl_HP[k], where i is a reference number of the heat pump.

(3) A remaining fluctuating power Pflu_rem[k] is obtained based on the link line fluctuating power Pflu[k] and the heat pump cluster start-stop smoothing component PHP_sw[k], the heat pump cluster power adjustment layer smooths some medium and low frequency components and determines a heat pump cluster power adjustment smoothing component PHP_adj[k] for a storage battery output optimization target based on Pflu_rem[k], the heat pump cluster start-stop smoothing component PHP_sw[k] and the heat pump cluster power adjustment smoothing component PHP_adj[k] are combined and entered into the heat pump cluster to output a heat pump cluster smoothing component PHP_f[k].

(4) The storage battery simultaneously undertakes a smoothing task of the remaining fluctuating power, the heat pump cluster start-stop smoothing component PHP_sw[k] and the heat pump cluster power adjustment smoothing component PHP_adj[k] are combined with the link-line fluctuating power Pflu[k] and then entered into the storage battery to output a storage battery smoothing component Pess[k] to complete the smoothing of the fluctuating power in the control cycle.

The present disclosure further provides an apparatus for implementing the foregoing method for smoothing a link-line power of an electrothermal microgrid using a thermal storage heat pump cluster. The apparatus includes a strategy information collection module, a heat pump cluster start-stop control strategy module, a heat pump cluster power adjustment strategy module, and a storage battery power adjustment strategy module. These modules are computer storage media, configured to store a computer program which, when executed, implements the method described below.

The strategy information collection module acquires an input signal required by the smoothing method from a microgrid energy management system, where the input signal includes an original link-line power and an energy storage state of the storage battery and the heat pump cluster at a last time point, thus implementing the above-described step (1).

The heat pump cluster start-stop control strategy module implements step (2).

The heat pump cluster power adjustment strategy module implements step (3).

The storage battery power adjustment strategy module implements step (4).

Output information of the heat pump cluster start-stop control strategy module, the heat pump cluster power adjustment strategy module and the storage battery power adjustment strategy module is entered into the microgrid energy management system for the electrothermal microgrid to control the storage battery and the heat pump cluster so as to smooth the link-line power.

The present disclosure has the following beneficial effects:

(1) The present disclosure fully considers a heat pump and a matching thermal storage water tank, establishes a control model based on the thermal storage heat pump for the first time, and performs cluster control by use of the distributed heat pump cluster and thermal storage cluster to coordinate with the storage battery to smooth link-line power fluctuations of the microgrid.

(2) The present disclosure designs a strategy structure of fluctuating power distribution and smoothing using the storage battery coordinating with the thermal storage of the heat pump cluster, and replaces the partial battery energy storage with the existing distributed thermal storage in the electrothermal microgrid, greatly reducing costs of the microgrid on the fluctuating power smoothing.

3) Based on a greedy algorithm, the present disclosure designs a method for quickly making a heat pump cluster smoothing control strategy, which has no limit on the characteristics of the heat pump and the thermal storage characteristics participating in the power adjustment thereby providing strong practicability. Meanwhile, the present disclosure further solves the problems of initiative and enthusiasm of the heat pump cluster to actively participate in the smoothing, achieves consistency of losses of the heat pump cluster by designing a simulated annealing optimization algorithm, which is beneficial to overall maintenance and fairness of the heat pump cluster in the microgrid. The control strategy in the method of the present disclosure fully considers differentiated factors of the rated powers of the heat pumps, the volumes of water tanks, the thermal loads of the users and the like, combines the greedy algorithm with the simulated annealing algorithm, thereby achieving more effective optimization and control of the heat pump cluster with different characteristics while providing superior robustness.

(4) In view of simplification of communication, the heat pump start-stop states as well as other conditions, the present disclosure adopts a more refined heat pump cluster power adjustment control method and the heat pump cluster power adjustment closely cooperates with the output of the storage battery to optimize the output of the storage battery. The control strategy in which the power adjustment of the heat pump cluster closely cooperates with the output of the storage battery designed by the present disclosure fully considers power adjustment characteristics of the heat pump and assists the storage battery in reducing charge-discharge conversion cycles, thus reducing operation costs of the microgrid.

(5) In a practical test of the apparatus, the present disclosure achieves consistency of losses of the heat pumps with different characteristics while the link-line power fluctuations are effectively smoothed, thereby effectively reducing the charge-discharge conversion cycles of the storage battery, and reducing the operation costs.

