Transportation electrification involves the wide utilization of power electronics based DC distribution networks and the integration of a large amount of power electronic loads. These power electronic loads, when tightly controlled, behave as constant power loads (CPLs) and may cause system instability when interacting with their source converters. In this paper, a composite nonlinear controller is proposed for stabilizing DC/DC boost converter feeding CPLs by integrating a nonlinear disturbance observer (NDO) based feedforward compensation with backstepping design algorithm. First, the model is transformed into the Brunovsky’s canonical form using the exact feedback linearization technique, to handle the nonlinearity introduced by the CPL. Second, the NDO technique is adopted to estimate the load power variation within a fast dynamic response, serving as a feedforward compensation to increase the accuracy of output voltage regulation. Then a nonlinear controller is developed by following the step-by-step backstepping algorithm with strictly guaranteed large signal stability. The proposed controller not only ensures global stability under large variation of the CPL, but also features fast dynamic response with accurate tracking over wide operating range. Both simulations and experiments are conducted to verify the proposed strategy.

Permanent magnet synchronous motors are extensively used in high-performance industrial applications. However, plenty of practical factors (cogging torques, load torques, friction torques, measurement error effects, dead-time effects, mechanical/electrical parameter perturbations, etc.) in the closed-loop servo system inevitably bring barriers to the high-performance speed regulation. All these factors can be regarded as generalized disturbances. Most approaches only focus on dealing with one single kind of disturbances. In practical cases, the servo system is affected by multiple sources of disturbances simultaneously, and these disturbances enter the system via different channels.To this end, this paper systematically analyzes several representative disturbances (particularly including their features and distribution in the practical servo system), and then, specifically puts forward a novel disturbance rejection framework based on the non-cascade structure. In this framework, a comprehensive disturbance observer is proposed to simultaneously and accurately estimate multiple disturbances so that the composite controller can have a corresponding part to compensate for multiple disturbances. Rigorous analysis of stability is established. Comparative experimental results demonstrate that the proposed method achieves a better speed dynamic response and a higher precision tracking performance in the presence of multiple disturbances.

The high penetration of power electronic converters into DC microgrids may cause the constant power load stability issues, which could lead to large voltage oscillations or even system collapse. On the other hand, dynamic performance should be satisfied in the control of power electronic converter systems with small overshoot, less oscillations and smooth transient performance, etc. This paper proposes an offset-free model predictive controller for a DC/DC buck converter feeding constant power loads with guaranteed dynamic performance and stability. First, a receding horizon optimization problem is formulated for optimal voltage tracking. To deal with the unknown load variation and system uncertainties, a higher-order sliding mode observer (HOSMO) is designed and integrated into the optimization problem. Then an explict closed-loop solution is obtained by solving the receding horizon optimization problem offline. A rigorous stability analysis is performed to ensure the system large signal stability. The proposed controller achieves optimized transient dynamics and accurate tracking with simple implementation. The effectiveness of the proposed controller is validated by simulation and experimental results.

For a hybrid ac/dc microgrid (MG), bidirectional interlinking converters (BICs) enable flexible power interactions between ac and dc subgrids. In each subgrid, power sharing among diversified sources has been effectively realized by droop controllers. These power sharing concepts can also be extended to BIC applications. This paper proposes a distributed power management strategy (DPMS) for multi-paralleled BICs in the hybrid MG to avoid the overstress of a single BIC. In this strategy, each BIC is assigned with a well-devised localized distributed controller (LDC) which generates the respective power reference for the BIC. By using the LDC, BICs are allowed to exchange information with one another in the distributed communication graph. The power interactions between ac and dc subgrids can be proportionally allocated to BICs based on their different power ratings in a full distributed manner. Then the system reliability and scalability are significantly improved. Meanwhile, accurate global power sharing among all ac and dc sources in the MG would be accordingly attained. Considering the communication time delay involved in BICs, a small signal model is derived to predict the maximum tolerable delay of the studied system. The validities of the proposed DPMS and delay stability analyses are verified by a controller hardware-in-loop experimental platform.

With the penetration of renewable generation and tightly regulated power electronic loads, the power quality and stability of modern DC microgrids are greatly challenged. To solve this problem, energy storage systems (ESSs) are widely proposed. Unfortunately, most of the existing control methods for ESSs can only ensure the stability of DC microgrids with small signal disturbances, which may not be satisfying for realtime applications where large signal disturbances exist. Moreover, they are usually designed for low boost ratio and low power converters, negating their suitability for grid-scale applications. To ensure the large signal stability of DC microgrids using high boost ratio interleaved converter interfaced ESSs, this paper proposes a new backstepping control strategy with finite-time disturbance observers. Its effectiveness is verified by simulation and experiments carried out on an interleaved double dual boost converter (IDDBC).

Hybrid energy storage system (HESS) is an attractive solution to compensate power balance issues caused by intermittent renewable generations and pulsed power load in DC microgrids. The purpose of HESS is to ensure optimal usage of heterogeneous storage systems with different characteristics. In this context, power allocation for different energy storage units is a major concern. At the same time, the wide integration of power electronic converters in DC microgrids would possibly cause the constant power load instability issue. This paper proposes a composite model predictive control based decentralized dynamic power sharing strategy for HESS. First, a composite model predictive controller (MPC) is proposed for a system with a single ESS and constant power loads (CPLs). It consists of a baseline MPC for optimized transient performance and a sliding mode observer to estimate system disturbances. Then, a coordinated scheme is developed for HESS by using the proposed composite MPC with a virtual resistance droop controller for the battery system and with a virtual capacitance droop controller for the supercapacitor (SC) system. With the proposed scheme, the battery only supplies smooth power at steady state, while the SC compensates all the fast fluctuations. The proposed scheme achieves a decentralized dynamic power sharing and optimized transient performance under large variation of sources and loads. The proposed approach is verified by simulations and experiments.