Wireless power transfer: control algorithm to transfer the maximum power
Rojas Urbano, Javier Arturo
- Publisher: Madrid / Universidad Politécnica de Madrid
ELECTRÓNICA DIGITAL | ELECTRÓNICA ANALÓGICA | AUTOMATIZACIÓN | TRANSMISIÓN INALÁMBRICA DE ENERGÍA | ALGORITMO DE CONTROL | WITRICIDAD
This job is developed as part of “Health aware enhanced range wireless power transfer systems", known as ETHER. It is a cooperation project where Universidad Politécnica de Madrid (UPM) and Universidad Politécnica de Cataluña (UPC) research groups are mainly involved. ETHER objective is to develop a wireless power transfer system for medical applications, specifically a pacemaker charger to improve patient’s
lifestyle decreasing the number of required operations to replace pacemaker battery. This job was developed in Centro de Electrónica Industrial (CEI) from UPM together with Carlos Terciado, who works on his final grade job.
Wireless power transmission refers to energy transmission from a source to a receiver located at a determined distance without the use of cables or conductors, it is useful where the use of conducting cables is not possible or not preferred, and it provides mobility and flexibility for consumer electronics. It could deliver power to rotating and highly mobile industrial equipment, mission critical systems in wet or dirty environments.
WPT isn’t a new concept, in 1893, Nikola Tesla demonstrated the illumination of vacuum bulbs without using wires at the World Columbian Exposition in Chicago. In 2007, a team at the Massachusetts Institute of Technology (MIT) was successful in transferring the power wirelessly at a mid-range. They lit a bulb of 60 W at a range of 2m. In 2014, the Korea Advanced Institute of Science and Technology (KAIST) scientists
had transferred power wirelessly using dipole coil resonant system. The Volvo Group is working on the possibility of developing a dynamic charging solution for city buses. The wireless transmission of power can be achieved using electromagnetic radiation, magnetic coupling and electric field coupling. The magnetic coupling mode is mainly used for short-range. It is produced when two coils are in close proximity to each
other, magnetic flux caused by current flowing through one coil links itself with the other.
This induces a voltage in the other coil, by the phenomenon known as mutual induction.
Magnetic coupling WPT technologies that are based on two coupled magnetic
resonators to transfer power over distance are knowledge as Resonant Inductive Coupling
(RIC). RIC system has the advantage of obtaining high currents and producing more
magnetic coupling field, increasing the energy transmission distance between the two
coils, which ranged from a few centimeters to over 2.5 Previous jobs on ETHER project like  and  had determined operational
parameters and circuit topology. The WPT system determined is a RIC system that consist
of several parts, it includes a high frequency Inverter, the magnetic coupling system,
including primary and secondary coils and resonant capacitors, high frequency active
Rectifier and a DC-DC converter as a voltage regulation module. An additional proposal
includes a third resonant tank that acts as a bridge increasing WPT separation distance,
general concept of these topologies are represented. This job looks for determining the active power behavior in a RIC system and
propose an adequate control algorithm to achieve the maximum active power transfer in
any perturbation condition to obtain a fast battery charge, it considers as principal
perturbations the resonant components change, because degradation or tolerance, and
coils separation distance variation, because mobility application parameters, they affect
the inductive coupling and vary induced voltage and transferred power.
An equivalent model is determined to analyze the resonant coupling circuit and
determine adequate control variables, a voltage source and an impedance represent the
induced voltage, and the active rectifier and DC-DC converter are represented by a
voltage source. To analyze the circuit, the first harmonic approximation is valid because
it is operating at resonance frequency, Active power behavior is analyzed and control
variables are determined and its influence is explored in Chapter 2. Adequate control
variables expressions to determine the maximum active power operation point are
acquired and graphically analyzed with Matlab. A Simulink simulation includes the active
rectifier as a first validation. Chapter 3 describes the control variables and active power behavior validation through simulations that include the effect of the inverter and active rectifier switching. 3 commercial coils set from Würth Elektronik are characterized to obtain proper and mutual inductances required for the model’s application. The complete circuit scheme is simulated in SIMPLIS to acquire a more realistic active power’s behavior, the variation of the control variables is implemented to obtain different results and determine the absolute maximum power operation point. These results are compared with theoretical behavior and optimal control values determined with equations acquired in Chapter 2.
Additionally an experimental setup is designed, components’ sizing and selection criteria are described. The experimental results and its analysis with respect to simulation results are shown to obtain a practical validation. The experimental process is developed with the coils’ set 2 because its current’s limits and maximum active power achievable.
In Chapter 4 the control algorithm proposal is described, the control actions are determined according to the control variables influence analysis. The algorithm control concept is based on a derivative calculus criteria to find the absolute maximum in a function. Flux diagram is shown and the algorithm is tested with simulations in Matlab because it allows to simulate power and control stage together.
Finally, Chapter 5 shows the conclusions extracted from each job step and suggest some future lines that can be implemented as a job continuation or recommendations to obtain better results in new implementations.