Antonio Ginart

Safety and efficiency of the wireless charging of electric vehicles

Wireless power transfer is a promising method to address the concerns over charging an electric vehicle. Since wireless charging stations operate without large cables or above-ground stations, they can be conveniently installed in public locations without the risk of vandalism or weather-inflicted damage, improving the lifespan of the electric vehicle charging station. In order for wireless charging stations to become widespread, possible health effects regarding exposure to the strong electromagnetic fields present during wireless power transfer must be investigated. This work examines, first, the potential human safety hazards, second, the electronic device interference, and, third, the thermal heating effects of wireless charging systems. A 3.3 kW wireless power transfer prototype was built in order to examine these effects. Changes in the wireless power transfer efficiency due to the coil misalignment were also investigated using an automated three-axis platform. Design considerations for electric vehicle wireless charging systems and safety recommendations are presented.

Residential Battery Storage: Is the Timing Right?

In the last two decades, there has been a strong interest in diversifying the energy generation portfolio by reexamining the role of renewable energy. The focus on renewables has gained momentum recently. This renewed focus, backed by the rapid development of more efficient and affordable technology, has created the right conditions for an industry to solidly establish itself (U.S. Energy Information Administration, 2014).

Uniform-gain frequency tracking of wireless EV charging for improving alignment flexibility

Wireless power transfer is a promising alternative option for electric vehicle charging due to its non-contact operation. However, the magnetic coupling variation caused by misaligned coils limits its practical application. The output voltage can significantly drop due to the coupling change, lowering the power transfer capability. A uniform-gain frequency tracking control is proposed to keep the output voltage stable within a large misalignment. The uniform-gain control is achieved through voltage gain and impedance analysis across the frequency domain. Experimental results demonstrate that the voltage variation of uniform gain control is within 3.3% across the misalignment range of 200mm, while it is 57.2% for the same misalignment range under fixed frequency control.

Misalignment effect on efficiency of wireless power transfer for electric vehicles

In order to consistently provide efficient EV wireless charging, changes in efficiency caused by coil misalignment should be investigated. This body of work uses a vector network analyzer to record the power transmission coefficients then calculate the efficiency and coupling factors. An automated 3-axis platform was built for coil motion control. The test result shows that the efficiency can remain at 90% as long as the misalignment ratio is within 0.5 and the air gap ratio is from 0 to 0.25.

Observer Based Sensor Fault Tolerant for Grid Tied - Solar Inverters

Grid-tied Solar Inverters rely heavily on the current sensor information to fulfill all the complex tasks associated to deliver appropriate power to the energy system with low distortion. Sensing voltage and current are an essential part of the feedback current control loop for any grid tied-solar inverter. When the sensed signal is lost, the inverter output could become unstable thus having, as a consequence, over-current situations, and other undesired power generation conditions that could lead to the catastrophic failure of the inverter. To overcome this issue, a fault-tolerant system is proposed using an observer structure designed as a way to make a 3 phase inverter current control system immune to any fault or lost of its sensing capabilities. The sensor verification is made by a smart control capable of monitoring the physical sensor operation and switch to the synthetics sensors in case of physical damage of the equipment. The proposed technique is verified by inserting a sensor fault in the system. Under this condition a good performance of the proposed fault tolerant structure is observed. The fault tolerant scheme is able to follow and determine the sensing signal lost or corrupted and seemliness continue the operation of the inverter, notified of the fault situation and wait planned shutdown is scheduled.

Partial 5/3 Level Topology for Solar Grid-tie Inverters

Solar inverters are designed specifically to handle photovoltaic (PV) panels, to efficiently extract the most amount of power, and to transform it properly so that it can be injected into the grid. The singularities of the application allow for opportunities that can be exploited for better performance. Inverters for PV applications are designed to operate at very low voltage variations, almost at a fixed frequency, and with a power factor usually greater than 0.8. While keeping these inverter-specific characteristics in mind, a new topology is proposed. In this work, such new topology provides operational characteristics close to a 5-level topology. This achievement is accomplished by adding just a few more power-electronic components required for a 3-level topology. A complete 3-phase system is designed and simulated. Its good performance is demonstrated, and its benefits and limitations are pointed out. Furthermore the feasibility of this new topology is also explored and verified by implementing a low-power inverter system with the proposed topology.

3-D Coil Positioning Based on Magnetic Sensing for Wireless EV Charging

Wireless power transfer (WPT) via magnetic resonance coupling is considered a promising outlet for electric vehicle (EV) charging due to the noncontact method. Unlike a traditional transformer, with WPT, the relative spacing and lateral distance between the primary and secondary coils are highly variable, which can affect the wireless power delivery and lower the efficiency. A magnetic positioning approach that shares the wireless charging structure is proposed to solve the misalignment issue associated with wireless EV charging. The proposed alignment sensing system employs multiple auxiliary minor coils on the secondary side to position the charging pad. The positioning principle and equivalent circuit were analyzed. The 108 samples were tested and they were distributed throughout the detection range of 70 cm. The experimental results demonstrate that >92% of those samples have positioning errors of <2 cm and 98% of them have positioning errors of <3 cm.

An online LiFePO 4 battery impedance estimation method for grid-tied residential energy storage systems

There has recently been a significant interest directed towards residential battery storage systems mainly motivated by high penetration of renewables, the low cost and high efficiency of power electronic devices, and the advancements in the safety and energy density of the batteries, especially Lithium-Ion (Li-Ion) batteries. Furthermore, the possibility for the end user to become a utility-independent entity with the capacity to overcome power outages and tariff rises is even further propelling this fast growing industry. Lithium iron phosphate (LiFePO4) battery is one of those technologies chosen to take the lead in residential battery storage due to its intrinsic safe performance, good energy density and price. This paper describes an online method for estimating the impedance of LiFePO4 batteries when they are used in residential single phase energy storage systems. Single phase power systems have the intrinsic characteristics of delivering power at twice the frequency of the grid; by energy conservation principle, this pulsating characteristics is transferred directly to the current in the DC stage of the battery storage system. The proposed method takes advantage of this phenomenon and, without interrupting the energy conversion process or adding any external perturbation to the system, is able to characterize, in situ, the AC impedance behavior of the battery. Experimental results are provided to validate the proposed method and simulations show the potential applicability of this method in the assessment of the actual battery aging state.