Model predictive control (MPC) methods are popularly employed in modular multilevel converters (MMCs) due to their fast dynamic response and multi-objective control capability. However, they present some inherent problems, such as computational complexity, variable switching frequency, poor steady-state performance and tedious weighting factor selection. This paper develops a deadbeat predictive current control method for MMCs. This method can realize the reference tracking of ac current and circulating current in one sampling period without error, and thus provide a fast dynamic response as conventional MPC methods. Besides, switching state or voltage level evaluation, cost function calculation as well as weighting factor selection are not required. Therefore, it has a very low calculation burden, which is independent of the number of submodules (SMs). Since a modulation stage is utilized, a fixed switching frequency and consequently a satisfactory steady-state performance are obtained. The effects of time delay, parameter mismatch and SM capacitor voltage ripple on the control algorithm are discussed. Also, the corresponding improvement measures are provided to further enhance the steady-state performance and system stability of MMCs. The effectiveness and performance of the developed control algorithm are verified by experimental results.

Owing to a higher energy supply efficiency and operational flexibility, integrated energy system (IES), including power, heating and gas systems, will be the primary form of energy supply in the future. However, with the increase of large-scale stochastic wind power integrated, the IES planning will face a significant challenge as traditional power system. Therefore, a probability-interval based IES planning considering wind power integrated is proposed in this paper. Firstly, a conditional value-at-risk (CVaR) based probability-interval method is developed to describe the uncertain wind power. Secondly, besides traditional facilities, electricity storage system (ESS) is introduced to improve the flexibility of IES. Then, an expansion planning model for IES is established to minimize the total cost including investment, operation, CVaR cost and unserved energy cost. Moreover, the piecewise linearization method is used to deal with the nonlinear integral terms of the proposed model to improve the solution efficiency. Finally, IEEE14-NGS14 and IEEE118-NGS40 systems are constructed and the planning model is solved by GAMS/CPLEX. The numerical results illustrate the correctness and effectiveness of the proposed method.

This paper proposes a method for fault-tolerant operation of medium voltage modular multilevel converters (MMCs) with phase-shifted carrier (PSC) modulation. The existing methods need to recalculate and reconfigure all the carriers every time a submodule (SM) fails. However, the proposed method combines the sorting voltage balancing control and the PSC modulation to avoid breaking the symmetry and balance of the carriers. Therefore, the modulation stage in the proposed method can be kept the same and the output voltage of the MMC can remain unchanged without causing voltage mismatch. Moreover, considering both the modulation margin and the physical redundancy configuration, two fault SM replacing strategies, i.e., optimal dynamic performance and optimal electrical stress are proposed as well as their respective control structures. Compared with the normal operation of the MMC, the proposed fault-tolerant operation method has only slightly changed the control system and thus the added calculation burden and control complexity can be ignored, which is extremely beneficial for the practical implementation. The effectiveness and performance of the proposed operation method are carefully verified by both simulation and experimental results.

A multi-bus MG normally bridge multiple DC buses via a complex line impedance network. This intricate configuration together with tickling constant power loads (CPLs) may cause severe stability issues. For system stability improvement, a novel uniform nonsmooth control scheme (UNCS) is proposed. UNCS has the following four-fold advantages. 1) UNCS helps to express commonly used DC/DC converters, boost, buck and buck-boost, into a uniform model. The model substantially facilitates a uniform stabilizer design that accommodate the preceding three converters despite their typology differences. 2) UNCS assigns each converter based distributed generator (DG) with a composite large signal stabilizer comprising a nonsmooth observer and a nonsmooth controller. 3) The stabilizer also provides an additional control degree of freedom, a fine-tuning factor, to refine DG dynamic responses to meet high requirements for voltage and power qualities. 4) When numerous DGs with the proposed stabilizer assembles to build a multi-bus MG, the overall system large signal stabilization is autonomously attained without communication links, which is mathematically justified by Lyapunov stability analyses. As such, DGs are allowed to randomly plug in/out without worrying about vitiating system level stability. Experiments show that UNCS will stabilize the multi-bus MG in a large operation range.