Coordinated Optimal Operation Of Regional Integrated Energy System Considering Grid Voltage Regulation

In recent years,climate warming,environmental pollution and energy shortage are increasingly severe.In order to achieve “carbon neutrality” and “emission peak”,China is actively developing photovoltaics(PV)and other renewable energy generation.However,the active distribution network with high proportion of PV has changed the radial unidirectional power flow mode,which may lead to power quality problems such as voltage fluctuations and violations.The traditional distribution network that operates individually lacks the coordination between different energy systems and has limited flexibility.It cannot satisfy the requirements of the high proportion of PV consumption,which has a negative impact on operation security and economic benefits.With the wide application of distributed combined heat and power plants(DCHP),heat pumps,and thermal storage,the energy interactions and information exchange between power system and thermal system are increasingly deepened.As featured of multi-energy integration and complementary,the regional integrated energy system is gradually formed.It further expands the control boundary of the power system and improves flexibility,which provide an effective way to treat the renewable energy consumption.Therefore,this paper focuses on the decentralized community heating system with ground source heat pumps(GSHP)and the regional centralized heating system with DCHPs.Researches on system modeling and control methods are carried out.The main work and innovations are as follows:(1)A day-ahead optimization method of the district integrated energy system with GSHPs.For the decentralized community heating system with GSHPs,considering the lumped heat capacity,a simplified integrated model is first proposed to describe the sensitivity relationship between GSHP power and the average water temperature.GSHPs are modeled as a special flexible load with water temperature constraints.Then,a robust voltage optimization model is established considering the cooperative operation between GSHP,on load tap changer(OLTC),energy storage and other electrical control devices.We transform the original problem into a two-stage robust optimization problem.A verification subproblem of the AC power flow feasibility is added to eliminate the calculation error of the linear flow equation.Finally,a three-layer iterative framework is designed based on the column-and-constraint generation algorithm(C&CG)to solve the problem effectively.(2)An intraday optimization method of the district integrated energy system with GSHPs.Firstly,based on the thermal inertia of residential buildings and pipelines,an integrated thermal dynamic model of the community heating system is established.The optimal modeling time resolution for thermal dynamics is determined by error testing.Then,we formulate a multi-timescale optimization framework according to the time resolution.Based on the model predictive control(MPC)method,the intraday long-period rolling optimization and short-period feedback correction for district integrated energy systems are proposed.The water temperature and voltage are predicted based on the thermal dynamic model and the voltage sensitivity model,while the operation commands of prediction and control horizons are solved in the rolling optimization.The time scale of the feedback correction is based on the minimum interval of the thermodynamic control.The error between the actual water temperature or voltage and the predicted result is collected to revise the prediction model,which improves the stability of the system against uncertain factors.(3)Cluster partition method of regional integrated energy system with DCHPs.The heat for a large heating network comes from many combined heat and power(CHP)plants in different locations.A multi-dimensional cluster partition index system considering structure and function is proposed.For the structural property,the heat loss along the pipeline is calculated,and the modular index is applied to quantify the connection strength between the different two heat nodes.The indicators about supply-demand balance,adjustment capacity and cost are established in terms of functionality.We utilize the Louvain community detection algorithm to partition the power and heat systems into several initial single energy clusters,respectively.The electrothermal coupling degree is further investigated to match and combine the initial clusters by evaluating the cogeneration and actual consumption.(4)Multi-level optimization method of the regional integrated energy system with DCHPs.Based on the integrated energy cluster partition results,a cluster equivalent model of flexible capabilities is first established considering the overall adjustable power range,the cluster power-voltage sensitivity and the adjustment cost.Then,a two-layer distributed robust optimization model is established considering voltage security constraints.The upper layer is a multi-region complementary optimization model of the “system level”,while the lower layer is a cluster coordination robust optimization model of the “regional level”.We apply the alternating direction multiplier method(ADMM)to obtain the operation result of each integrated energy cluster.Finally,the active/reactive power allocation rules within the integrated energy cluster under the “economic operation scenario” and “security control scenario” are formulated respectively,according to the results from the two-layer optimization model.This method can realize the rapid response of various devices including DCHPs and ensure the reliability and economy of the multi-region integrated energy system.