Search

Stealthy zero-dynamics attacks are a subset of false data injection attacks (FDIAs) that are especially dangerous, as they are designed to be undetectable by any intrusion detection mechanisms. This paper shows that stealthy attacks can be more destructive on power electronic dominated grids (PEDGs) than traditional power systems, by taking advantage of the low inertia property of PEDGs. The low inertia of these power grids causes the system to be prone to frequency instability when disturbances occur, meaning that an attacker can cause more harm to a system in a shorter amount of time. Another advantage to the attacker is an increased amount of telecommunication devices in PEDGs which provides the attacker with a larger attack surface. It is thus critical that we strive to design PEDGs in such a manner that we minimize their susceptibility to stealthy attacks. We provide a small signal model for a PEDG system, along with the the state space representation of the low-inertia part of the system, and we show that even without the state-space model of the whole system, a stealthy zero-dynamics attack can be constructed and can be successful on a PEDG. Results are also provided to show that strategically choosing model parameters in the design phase of the system can prevent the existence of stealthy zero-dynamics attacks.

The hierarchical control structure was introduced to allow the integration of power-electronics-based distributed generation into the microgrid in a smart and flexible manner. The main aim of the primary controller in such a structure is to achieve accurate active and reactive power sharing, whereas the secondary control aims to ensure voltage and frequency (V/f) stability. Generally, converter-level secondary controllers utilize classical nested loop control that suffer from a slow dynamic response and cumbersome parameter tuning. The existing-model-based and estimation-based secondary controllers are fast, but require complex design methodology, high communication bandwidth, and, consequently, higher data analysis and computational burden. This article presents a simple predictive-based secondary control for the ac microgrid that is fast and robust and has a low design complexity, low communication bandwidth, and no parameter tuning requirement in the secondary control layer. The proposed predictive control optimally restores voltage and frequency in the microgrid by predicting their trajectory deviations and leveraging the droop characteristic curves. Experimental tests performed with three parallel-connected grid-forming inverters in an islanded operation validate that the controller can accurately maintain V/f stability, while ensuring active and reactive power sharing.

This article presents an intrusion detection system (IDS) for a multi-layer-controlled power electronics-dominated grid (PEDG). This IDS improves the situational awareness of PEDG against malicious set-points from a compromised upper control layer. Firstly, a mathematical theory is developed for deriving a safe operation region. This mathematical theory extends the stability margins inferred from $P-V$ curves to the abstract concept of morphisms. Particularly, there are two morphisms for each point of common coupling (PCC) bus when operating in the safe operation region: (Morphism 1) PCC bus voltage mapped to network set-points, and (Morphism 2) network set-points mapped to PCC bus voltage. Morphism 1 is used for anomaly detection. Explicitly, observation of a non-zero imaginary-part in the PCC voltage $L_{2}$ norm is evidence of an anomaly. Morphism 2 is utilized for independent decision making at the primary layer of the dispersed energy generator (DEG) during intrusion scenarios. Morphism 2 is an alternative for the secondary layer when the dispatched set-points are not trusted. The theoretical analysis is verified by several case studies to substantiate the situational awareness against malicious set-points and consequently enhancing the cybersecurity aspects of the PEDG.

This paper proposes a control scheme to force homogeneity for heterogenous network of the grid-forming (GFM) inverters in power electronics dominated grid (PEDG) to enable their aggregation and coherent dynamic interaction. Increased penetration of the renewable energy in distributed generation (DG) fashion is moving traditional power system to a highly disperse and complex heterogenous system i.e., PEDG with fleet of grid-forming and grid-following inverters. Optimal coordination, stability assessment, and situational awareness of PEDG is challenging due to numerous heterogenous inverters operating at the grid-edge that is outside the traditional utility centric power generation boundaries. Aggregation of these inverters will not be insightful due to their heterogenous characteristics. The proposed control scheme to force enclaved homogeneity (FEH) enables an insightful aggregation of GFM that can fully mimic the given physical system dynamics. The proposed FEH scheme enables coherent and homogenized dynamic interaction of GFM inverters that enhances the PEDG resiliency. Moreover, different cluster of GFM can be merged into single cluster with minimal synchronization time and frequency fluctuations. Accurate reference models can be achieved that enables effective dynamic assessment and optimal coordination which results in resilient PEDG. Several case studies provided to validate the effectiveness of proposed FEH in network of GFM. Then, GFMs aggregation and developed reference model for the PEDG system is validated via multiple comparative case studies.

The grid integration of a photovoltaic solar system operating with maximum power point tracking is being presented in this paper. The system uses a dc-dc converter for power tracking while employing finite control set model predictive control (FCS-MPC) to govern the dc-ac inverter. An effective control scheme that employs only FCS-MPC in the entirety of its control layer is proposed, where three control objectives; the regulation of the dc-link voltage, the injection of active power, and the injection of reactive power to the main grid have been achieved within a single cost function. The controller avoids translating dc-link voltage deviations to the active power reference and controls all variables directly in the cost function. The controller’s feasibility has been evaluated through experiments where experimental testing using OPAL-RT has been carried out to prove the concept. The results show that all three control objectives can be achieved efficiently using the proposed method, with minimal error in the controlled variables. Furthermore, the controller shows high robustness against parameter mismatch and grid inductance variations.

This paper presents a method for improving the reliability of DC nanogrids by decreasing the input capacitance requirement. The nanogrid DC bus capacitance requirement is reduced by utilizing the zero-sequence operation mode of the solid state converter (SSC). This SSC is often considered as the main DC nanogrid energy control unit that is linking the nanogrid with the main utility AC grid and managing the nanogrid elements. The proposed method injects a zero-sequence voltage in the SSC AC filter capacitors to compensate the low frequency power ripples that are imposed on the DC bus. The proposed method compensates power ripple due to non-linear loads, linear loads, distorted grids, and load variations. Moreover, the compensation method does not require additional components that are commonly used with the existing power ripple compensators. Furthermore, practical considerations of the proposed control are discussed in the paper regarding stabilization of the nanogrid in case of lack of critical damping. The analysis and results demonstrated that a 50 μF total capacitance is sufficient at the DC bus for 500V/5kW DC nanogrid to achieve negligible DC bus voltage ripple. Thereby, with such small DC nanogrid input capacitance, the DC link capacitor can be a film type capacitor to enhance the reliability of the nanogrid.

Low-inertia power generation units make nanogrids vulnerable to the voltage and power fluctuations caused by pulse loads and abnormal grid conditions. The conversion of critical loads to smart loads is a potential solution for improving the stability and power quality in nanogrids. This paper investigates the effects of utilizing smart loads on the performance of nanogrids. A smart load can compensate for sudden deviations between supply and demand and therefore can mitigate voltage and power oscillations in low-inertia nanogrids. The conversion of critical loads to smart loads can reduce the stress on the energy storage units and minimize the required battery banks in nanogrids. In this paper, several case studies are considered to verify the stability and power quality improvement of nanogrids when some loads are converted to smart loads.

This paper presents a decoupled active and reactive power control scheme for grid-tied quasi-impedance source cascaded multilevel inverter (qZS-CMI). For photovoltaic (PV) applications, the proposed control scheme is based on an enhanced finite-set model predictive control (MPC) to harvest the desired active power from the PV modules with the ability to provide the ancillary services for the grid. The proposed control scheme has two modes of operation: normal grid mode and low voltage ride through (LVRT) mode. In normal grid mode, the controller commands the qZS-CMI to operate at the global maximum power point (MPP). The proposed technique regulates the impedance network's current and voltage according to the MPP of PV strings and grid current/voltage requirements. In LVRT mode, the controller commands the qZS-CMI to provide the required reactive power to the grid during voltage sags as an ancillary service from the inverter as imposed by the grid codes. The main features of the proposed system include the global MPP operation during normal grid condition, LVRT capability during a grid voltage sag, mitigation of the PV modules mismatch effect on overall energy harvesting, seamless transition between a normal grid and LVRT modes of operation, and an efficient predictive controller that exploits the model redundancies in the control objectives. Several real-time experiments are conducted to verify the system performance with transients in both the solar irradiance and the grid voltage.

In this paper, an ultrafast active rectifier is presented for variable-frequency applications. Three-phase ac-dc converters (rectifiers) are extensively implemented in motor-drives, wind turbines, electric vehicles, and aircraft's power systems. In some technologies, e.g., more electric aircraft and drones, power systems may employ variable-frequency generators for higher efficiency and reliability indices. The proposed ultrafast rectifier is equipped by a step-ahead predictive control scheme, an instantaneous phase-locked loop (PLL), and a module of six SiC MOSFETs. The control scheme regulates the dc voltage and maintains unity power factor with an extremely low total harmonic distortion in the input currents. The instantaneous PLL, applicable only for three-phase systems, is integrated to the proposed variable-frequency control scheme in order to minimize the error in the power factor. The step-ahead predictive scheme and instantaneous PLL combination provides fast and smooth dynamic responses under rapid frequency transients. Experimental results are presented using a laboratory-scale SiC-based MOSFET 115VLL/270Vdc rectifier, and the performance of the proposed controller is compared with a classical power factor correction controller in the presence of frequency ramp and step changes. The experimental results demonstrate a superior dynamic performance of the proposed ultrafast active rectifier.

Mobile platforms cover a broad range of applications from small portable electric devices, drones, and robots to electric transportation, which influence the quality of modern life. The end-to-end energy systems of these platforms are moving toward more electrification. Despite their wide range of power ratings and diverse applications, the electrification of these systems shares several technical requirements. Electrified mobile energy systems have minimal or no access to the power grid, and thus, to achieve long operating time, ultrafast charging or charging during motion as well as advanced battery technologies are needed. Mobile platforms are space-, shape-, and weight-constrained, and therefore, their onboard energy technologies such as the power electronic converters and magnetic components must be compact and lightweight. These systems should also demonstrate improved efficiency and cost-effectiveness compared to traditional designs. This paper discusses some technical challenges that the industry currently faces moving toward more electrification of energy conversion systems in mobile platforms, herein referred to as E-Mobility, and reviews the recent advancements reported in literature.