A large amount of wind power has to be curtailed due to the inflexibility of the combined heat and power (CHP) system in the heating season in northern China. The power-to-gas (P2G) technology, which uses electricity to produce hydrogen or synthetic natural gas, has become a promising energy conversion option for the utilization of surplus power energy. In this paper, an integrated natural gas, heat, and power dispatch (INGHPD) model which balances natural gas, heat, and power demand considering wind power and a P2G unit, is proposed. A natural gas network and P2G are modeled and integrated into the dispatch model. To demonstrate the effectiveness of the proposed model, an integrated energy system consisting of a six-bus power system, a six-node natural gas system, and a district heating system is simulated. The benefits of P2G are investigated in terms of reducing wind power curtailment, as well as system operation cost and CO 2 emissions. The results in the deterministic model show that with the introduction of 40 MW P2G, the wind power curtailment rate decreases from 24.0% to 9.7%. The daily wind power energy consumed by P2G reaches 256 MWh and the daily CO 2 emissions reduction reaches 46,080 kg. Additionally, the impact of the power and heat demand on the gas production of P2G and of the P2G capacity on the wind power curtailment are also investigated. P2G tends to generate more natural gas when the power demand is low and the heat demand is high.

To realise the accurate and real-time compensation of the harmonics of a power system, this study proposes a novel control strategy for shunt active power filter (SAPF), adopting the composite strategy of neural network proportional-integral (PI) control and dual-repetitive controller (DRC). In DRC, one repetitive controller is used to ensure current tracking accuracy and the other one is used to enhance dynamic response. The neural network PI control is adopted to improve response speed by turning the PI parameters adaptively and setting optimisation parameters online. Through the optimisation of this approach and the rational configuration of the hardware and software systems, the SAPF could achieve rapid dynamic response with high tracking accuracy and excellent compensation performance. A 100 kVA industrial prototype active power filter has been developed by using this control strategy. System compensation could effectively reduce the total harmonic distortion values from 26 to 27.7%, 27.6 to 4.25% and 4.57 to 4.35% for each phase of the current. The full response time of the system is < 10 ms.

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Wind power has achieved great development in Northern China, but abundant wind power is dissipated, rather than utilized, due to inflexible electricity production of combined heat and power (CHP) units. In this paper, an integrated CHP system consisting of CHP units, wind power plants, and condensing power plants is investigated to decouple the power and heat production on both the power supply side and heat supply side, by incorporating electrical energy storage (EES) and thermal energy storage (TES). Then the integrated CHP system dispatch (ICHPSD) model is formulated to reach the target of reducing wind power curtailment and primary energy consumption. Finally, the feasibility and effectiveness of the proposed ICHPSD model are verified by the six-bus system, and the simulation results show that EES has a better effect on wind power integration than TES. The annual net benefits by incorporating EES and TES increase with increasing wind penetration, but they gradually approach saturation. Introducing both EES and TES can largely increase the amount of wind power integration and improve the operation efficiency of the system. Energies 2016, 9, 474 2 of 17 technologies which are suitable for large-scale applications, conventional battery storage is efficient but the investment would be very high. Pumped hydro is fit for large-scale applications but it is applicable only in certain locations [11]. Nowadays, hydrogen storage is emerging as a promising alternative due to high energy density, clean fuel, and relatively low capital cost [12,13]. Adding hydrogen storage to a CHP system could improve the accommodation of wind power, as well as primary energy saving, since the wind energy curtailed in off-peak hours could be used to split water into hydrogen and oxygen. Hydrogen would be stored and then transformed to electrical energy, when necessary, by various ways.Thermal energy storage (TES) is another attractive option for wind energy integration. Although thermal storage is not directly related with electrical energy production, introducing TES is an efficient solution to relieve the mismatch between heat/power demand and supply, by decoupling the generation of electricity and heat [14]. The surplus thermal energy is stored during the operating periods for a later use when electrical demand is low, leading to a decrease in heat production of CHP plants, along with a reduction in electricity production, as a result, wind power would be better integrated. Under the influence of real-time electricity pricing, a large number of TES units have been installed in European countries which have a large percentage of wind power [15]. For example, in Denmark, TES systems have been an important part of its 100% renewable energy system plan [16].Many studies have been involved in the flexible operation of integrated CHP systems recently. In [17], heat pumps and thermal inertia of buildings and thermal comfort of end users are considered to increase the wind power integration. In [18], electric boilers and heat storage tanks are...

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