This paper presents a unit commitment problem with uncertain loads and wind power. A chance-constrained two-stage stochastic program programming formulation is proposed for the stochastic day-ahead ...scheduling. The loss of load probability (LOLP) and the probability of wind power utilization less than certain level, referred to as loss of wind probability (LOWP), and transmission line overloading probability (TLOP) are modeled as chance constraints, to provide high reliability of power supply and to ensure the high utilization of wind generation. The chance-constrained stochastic programming formulation is converted into an equivalent deterministic formulation by a sequence of approximations and verification. Correlations between loads at different buses and correlations between wind power at different buses are also considered by the proposed approach. Numerical tests are performed on a six-bus system and a modified IEEE 118-bus system. Results validate the viability of the proposed algorithm formulation for the day-ahead stochastic scheduling. The impact of different levels of LOLP and LOWP on the required up/down spinning reserves are also presented in this paper.
When the digital hysteresis current control (DHCC) strategy is applied to control the uninterruptible power supply (UPS) inverter, here are some issues such as large hysteresis tracking error caused ...by sampling interval and severe switching frequency swing caused by rapid change rate of inductor current. To address these issues, this paper presents a digital control strategy based on the hybrid digital hysteresis current control (HDHCC) of variable opening time (VOT) and variable falling time (VFT) for UPS inverter. Firstly, the HDHCC structure is established and the working principle of the inverter system is described in detail. Then, the tracking error and switching frequency error of the DHCC are derived. Based on the performance requirement of quasi-constant frequency control of UPS inverter, VOT and VFT control criteria without the dependency of circuit parameters are given. The experimental results demonstrate that the hybrid digital hysteresis control strategy based on VOT and VFT has the advantages of high current tracking accuracy, accurate switching frequency control, small output voltage waveform distortion, and simple implementation.
In a modular multilevel converter‐based high‐voltage direct current (MMC‐HVDC) system, the dc fault ride through (FRT) control is an effective way to deal with a dc‐side pole‐to‐ground (PTG) fault. ...However, the setting of FRT duration brings potential hazards: 1) MMC will face the risk of “secondary short circuit” if FRT duration is short; 2) ac grid may have power angle stability issue if FRT duration is long. To avoid these hazards and provide theoretical guidance for the FRT duration setting, transient behaviour of dc fault current during the PTG FRT stage is explored in this work. Firstly, challenges of the transient analysis are summarised as non‐linearity and high‐order issues. In light of this, numerical and Hilbert‐Huang Transformation methods are introduced to evaluate the non‐linearity issue. It is found that the path of MMC from dc current to dc internal voltage is weakly non‐linear. Hence, a linear transient model is built to analyse the dc fault current. By participation factor analysis, the order of the proposed model is further reduced, so that an analytical expression of the dc fault current is approximately derived. Based on the analytical expression, regularities and mechanism of dc fault current are fully revealed. Application of the transient analysis to the setting of FRT duration is elaborated in detail. Finally, the PSCAD/EMTDC simulation verifies the validity of the proposed model and analytical expression.
With the increasing concerns about railway energy efficiency, two typical driving strategies have been used in actual train operation. One includes a sequence of full power traction, cruising, ...coasting, and full braking (CC). The other uses coasting–remotoring (CR) to replace cruising in CC. However, energy‐saving performance by CC and CR, which can be affected by route parameters of gradients and speed limits, has not been fully compared and studied. This paper analyses the energy distribution of CC and CR considering various route parameters and proposes an improved strategy for different gradients and speed limits. The detailed energy flow of CC and CR is analysed by Cauchy–Bunyakovsky–Schwarz inequality and the generalised Hölder's inequality, and then, a novel driving strategy CC_CR is designed. To verify the theoretical results and the effectiveness of the proposed strategy, three simulators with CC, CR, and CC_CR driving modes have been developed and implemented into case studies of four scenarios as well as a real‐world metro line. Simulation results demonstrate that CR can only outperform CC on routes with steep downhill and CC_CR is always the best strategy. The energy savings of CC_CR can be as much as 15% more than CR and 42% greater than CC.
This paper analysed the energy distribution of driving strategies considering various route parameters and proposed a novel driving strategy that can minimise the energy consumption of a train on different routes.
Development and utilization of renewable energy is an effective way to deal with global warming. In this context, integrated electricity–heat–gas energy system (IEHGES) provides a new way for the ...efficient use of renewable energy. Existing IEHGES planning methods focus on the improvement of cost and energy efficiency, while not designing a capacity configuration scheme for high renewable energy penetration scenarios. Here, a coordinated planning method for IEHGES considering renewable energy consumption is proposed. Firstly, electricity/gas/heat storage, electric boiler and power to gas are co‐configured to realize heat‐electricity decoupling operation of combined heat and power, providing flexible and controllable electricity supply for the system. Then, coordinated planning method of IEHGES is proposed which takes into account the coordination of multi‐energy and the coordination between optimal planning and optimal operation. The spare capacity factors are included in the planning and cost of environmental penalty and renewable energy generation subsidy are included in operation cost. In view of the uncertainties, complementary characteristics between electricity, gas and heat supply systems in IEHGES are combined with k‐means to obtain optimal schemes of coordinated planning. Finally, the correctness and validity of the proposed method are verified by three indexes in a case study.
Considering high penetration of renewable energy, a coordinated planning method for integrated electricity‐heat‐gas energy system (IEHGES) is proposed. A coordinated optimal model for IEHGES is established that include the coordination among multi‐energy flows and the coordination between the optimal planning and the optimal operation. In view of the uncertainties of both renewable energy and energy demands, the model is modified by a scenario‐based clustering approach to obtain schemes of optimal planning and those of optimal operation
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This paper presents an analytical model of a dual‐stator spoke‐type permanent magnet (DSSTPM) synchronous machines accounting for tooth‐tips. Based on the two‐dimensional (2‐D) subdomain technique, ...the field domain of DSSTPM machine is divided into seven sub‐regions, that is, permanent magnet (PM), outer/inner air gaps, slots and slot openings. The magnetic field distribution and electromagnetic performance can be calculated via solving the governing functions based on boundary and interface conditions. The analytical predictions for DSSTPM machine under both open‐circuit and on‐load conditions are calculated and compared by the finite element (FE) method.
Modular multilevel converter (MMC) based fault ride through (FRT) control is a promising solution to deal with the pole-to-ground (PTG) fault in high voltage direct current (HVDC) system. However, ...when MMC switches to the FRT control, capacitor voltage imbalance between upper and lower arms will occur, resulting in the deterioration of FRT performance. This letter provides a comprehensive analysis for the imbalance issue from the perspective of fundamental frequency circulating current (FFCC). It is found the imbalance during FRT stage will not expand continuously, but converge to a certain value gradually. The specific imbalance degree is closely associated with the amplitude of FFCC. In order to solve the imbalance issue, an open-loop balancing control is proposed. By introducing a fundamental frequency feedforward item to the inherent circulating current control, the proposed method can not only balance the capacitor voltages, but also minimize the amplitude of FFCC, and consequently the power loss of MMC during FRT process can be reduced. Finally, simulation results of PSCAD/ EMTDC verify the validity of theoretical analysis.
To improve the motion distortion caused by LiDAR data at low and medium frame rates when moving, this paper proposes an improved algorithm for scanning matching of estimated velocity that combines an ...IMU and odometer. First, the information of the IMU and the odometer is fused, and the pose of the LiDAR is obtained using the linear interpolation method. The ICP method is used to scan and match the LiDAR data. The data fused by the IMU and the odometer provide the optimal initial value for the ICP. The estimated speed of the LiDAR is introduced as the termination condition of the ICP method iteration to realize the compensation of the LiDAR data. The experimental comparative analysis shows that the algorithm is better than the ICP algorithm and the VICP algorithm in matching accuracy.
The Gallium Nitride high electron mobility transistor (GaN HEMT) has been considered as a potential power semiconductor device for high switching speed and high power density application since its ...commercialization. Compared with the traditional Si transistors, GaN HEMT has faster switching speed and lower on-off loss. As a result, it is more sensitive to the nonlinear parameters due to the fast switching speed. The subsequent voltage and current overshooting will affect the efficiency and safety of the GaN HEMT and power electronic systems. In this paper, an accurate switching transient analytical model for GaN HEMT is proposed, which considers the effects of parasitic inductances, nonlinear junction capacitances and nonlinear transconductance. The model characteristic of turn-ON process and turn-OFF process is illustrated in detail, and the equivalent circuits are derived for each switching transition. The accuracy of the proposed model can be verified by comparing the predicted switching waveform and switching loss with that of the experimental results based on the double pulse test (DPT) circuit. Compared with the conventional model, the proposed model is more accurate and matches better with the experimental results than the conventional model. Finally, this model can be used for analyzing the influences of gate resistance, nonlinear junction capacitances, and parasitic inductances on switching transient waveform and refining calculation switching loss.
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