Integration of high volume (high penetration) of photovoltaic (PV) generation with power grids consequently leads to some technical challenges that are mainly due to the intermittent nature of solar energy, the volume of data involved in the smart grid architecture, and the impact power electronic-based smart inverters. These challenges include reverse power flow, voltage fluctuations, power quality issues, dynamic stability, big data challenges and others. This paper investigates the existing challenges with the current level of PV penetration and looks into the challenges with high PV penetration in future scenarios such as smart cities, transactive energy, proliferation of plug-in hybrid electric vehicles (PHEVs), possible eclipse events, big data issues and environmental impacts. Within the context of these future scenarios, this paper reviewed the existing solutions and provides insights to new and future solutions that could be explored to ultimately address these issues and improve the smart grid’s security, reliability and resiliency.

A direct three-phase ac-ac matrix converter for inductive power transfer (IPT) systems with soft-switching operation is introduced. The proposed topology is expected to have a high reliability and extended lifetime due to the soft-switching operation and elimination of short-life electrolytic capacitors. The soft-switching operation will also reduce switching stress, switching loss, and electromagnetic interference of the converter. A variable-frequency control strategy based on the energy-injection and free-oscillation technique is used to regulate the resonant current, the resonant voltage, and the output power. With the use of reverse-blocking switches, the proposed converter can be built with a reduced number of switches (only seven), which will consequently increase the reliability and efficiency and reduce the cost of the converter. The converter operates in eight modes, which are described in detail. With the use of the proposed converter as the primary converter, simulation analysis and experimental implementations on a case study IPT system show that the current regulation control method can fully regulate the output current and output power around user-defined reference values, thus making it suitable for dynamic IPT applications, where the system has inherent variations.

A direct soft-switched single-phase ac-ac matrix converter (MC) for bidirectional inductive power transfer (IPT) systems is proposed. Quantum energy injection/regeneration principle is used to design a simplified digital power controller that enables the converter to establish bidirectional power transfer between the IPT system and single-phase ac mains at a desired power level. The simplified controller can be implemented using basic logic circuit components, without the need for digital signal processor/field programmable gate array platforms, thereby reducing the complexity and the implementation cost. The converter benefits from resonance frequency tracking capability for the synchronization of switching operations of the converter with the resonant current, which makes it ideal for dynamic IPT systems. Also, it benefits from soft-switching operations to achieve an enhanced efficiency and low electromagnetic interference. The converter is specifically suitable for establishing grid-to-vehicle and vehicle-to-grid connections through inductive electric vehicle charging/discharging systems. The proposed converter is analyzed theoretically, is simulated in MATLAB/Simulink, and finally is verified experimentally at low power on a case study IPT system. The results show that the proposed MC can effectively establish bidirectional power transfer at different power levels with soft-switching operation and resonance frequency tracking capability.

A foreign object detection (FOD) method for inductive charging systems is introduced in this article. The proposed FOD only requires primary side measurements, i.e., primary resonant current and resonance frequency deviation. The proposed FOD incorporates a mechanism for effective discrimination of foreign object intrusion, horizontal and vertical alignment variations of the transmitter and receiver magnetic pads. Alignment variations of primary and secondary magnetic pads as well as intrusion of conductive/magnetic foreign object both impact electromagnetic characteristics, consequently the resonant frequency. FOD for large size objects works properly based on resonance frequency deviation, however, there is the need for discrimination between the FOD for small objects and misalignment. Thereby, both disturbances can be detected by online monitoring of the resonance frequency deviation, and be discriminated from each other by real-time measurement of the primary current. The proposed FOD technique can be added as a protection scheme to the self-tuning controllers of inductive power transfer (IPT) systems operating off its resonance frequency. Finite element analysis along with theoretical formulation of the studied IPT circuit is presented using the proposed method. Conductive FOD method based on frequency deviation and discrimination method using primary resonance current are implemented on an IPT setup, and the experimental results verify its effectiveness in both standby and full-power modes. The test results show that the frequency deviation based FOD method has a high speed in detection of even small scale objects such as a coin.

The power transfer efficiency and performance of solid-state transformers (SST) highly depends on the design of its High-frequency transformers (HFTs) which is required to provide galvanic isolation between the primary and secondary side converters. Therefore, to achieve a highly efficient SST regardless of its topology, the design optimization of the HFTs becomes imperative. Also, high power density of SSTs are desirable which largely depends on the power density of the HFT. In this paper, a multi-physics-based design and multi-objective optimization of HFTs for SST applications is proposed. The proposed algorithm (based on time-harmonic electromagnetic, thermal and fluid physics model coupling) minimizes the volume of the HFT (consequently maximizes its power density), total cost as well maximizes its efficiency (by minimizing its total power loss). A case study of 20kW, 10 kHz investigated and its Pareto solutions presented. The simulation results show the various dependencies of the design variables on the proposed objectives function which verifies effectiveness of the proposed algorithm. The Pareto-optimal solutions show that efficiencies above 99\% can be achieved with appropriate selection of the design variables. From the Pareto solutions, two case studies of the HFTs (referred to as HFT1 and HFT2 using AMCC-100 and AMCC-250 amorphous cores respectively) are further investigated based on multi-physics numerical models and presented. An experimental implementation of the optimized HFTs (HFT1 and HFT2) and a self-tuned dual active bridge converter are carried out to validate the performance of the HFT based on the optimized simulation parameters. The experimental measurements from the HFTs are in very good agreement with the optimization results.

The use of a horizontal arrangement of wall shunts is proposed in this paper as a cost-effective way to reduce the stray losses in power transformers. This paper compares the performance of horizontal wall shunts with the available alternative (vertical shunts). A 3-D finite-element analysis (FEA) is used for the calculation of stray losses in tank walls, and other structural parts. A novel hybrid numerical/analytical method is proposed for the calculation of stray losses inside the magnetic shunts. The proposed method is based on the double Fourier series expansions of the magnetic field distribution at the surface of the shunts, which is determined using 3-D FEA. A 200 MVA power transformer is investigated as a case study where the stray losses are calculated with and without the vertical and horizontal shunts. A parametric FEA is carried out to find the optimal placement of the horizontal shunts on the tank walls. Results show that the proposed horizontal magnetic shunts arrangement are as effective as the conventional vertical shunts in reducing the stray losses while reducing the weight of the shields, therefore providing a cost-effective method for magnetic shielding of the transformer tank walls.