Accurate modeling techniques for power delivery

“Power delivery is essential in electronic systems to provide reliable power from voltage sources to load devices. Driven by the ambitious user demands and technology evolutions, the power delivery design is posed serious challenges. In this work, we focus on modeling two types of power delivery paths: the power distribution network (PDN) and the wireless power transfer (WPT) system. For the modeling of PDN, a novel pattern-based analytical method is proposed for PCB-level PDN impedance calculations, which constructs an equivalent circuit with one-to-one correspondences to the PCB’s physical structure. A practical modeling methodology is also introduced to optimize the PDN design. In addition, a topology-based behavior model is developed for the current-mode voltage regulator module (VRM). This model includes all the critical components in the power stage, the voltage control loop, and the current control loop of a VRM device. A novel method is also proposed to unify the modeling of the continuous and discontinuous conduction modes for transient load responses. Cascading the proposed VRM model with the PCB-level PDN model enables a combined PDN analysis, which is much needed for modern PDN designs. For the modeling of WPT system, a system-level model is developed for both efficiency and power loss of all the blocks in WPT systems. A rectifier characterization method is also proposed to obtain the accurate load impedance. This model is capable of deriving the power capabilities for both the fundamental and higher order harmonics. Based on the system model, a practical design methodology is introduced to simultaneously optimize multiple system parameters, which greatly accelerates the design process”--Abstract, page iv

Midrange Magnetically-Coupled Resonant Circuit Wireless Power Transfer

Recent years have seen numerous efforts to make wireless power transfer (WPT) feasible for application in diverse fields, from low-power domestic applications and medical applications to high-power industrial applications and electrical vehicles (EVs). As a result, it has been found that WPT by means of non-radiative magnetically-coupled resonant circuits is an optimum method for mid-range applications where the separation of source and receiver is in the range of 1-2m.This thesis investigates various aspects of the design of magnetically-coupled resonant circuits for non-radiative WPT. Firstly, a basic four-coil network for a mid-range (1-2m gap) WPT system with a single power source and single resistive load was developed and simulated. The system was then constructed and experimental results were obtained for comparison with theoretical expectations. Methodologies were developed for empirical measurement of flux-coupling coefficients (k) among the coupled resonator coils and measurement of resonator parameters (inductance, capacitance, and equivalent-series resistance). Secondly, a structure called a universal resonator is proposed to permit design of WPT networks of arbitrary complexity with multiple power sources (transmitters) and multiple loads (receivers). An Excel simulation tool has been developed to analyze designs involving up to eight resonators. Designs with five resonators (including one power source and two loads) and six resonators (with two power sources and two loads) with separation of 1m between transmitting and receiving resonators have been analyzed, constructed, and subjected to experimental validation. The measured outputs numerical were found to be in good agreement with the predicted models. Conclusions and suggestions for future work are provided

Bidirectional Electric Vehicles Service Integration in Smart Power Grid with Renewable Energy Resources

As electric vehicles (EVs) become more popular, the utility companies are forced to increase power generations in the grid. However, these EVs are capable of providing power to the grid to deliver different grid ancillary services in a concept known as vehicle-to-grid (V2G) and grid-to-vehicle (G2V), in which the EV can serve as a load or source at the same time. These services can provide more benefits when they are integrated with Photovoltaic (PV) generation. The proper modeling, design and control for the power conversion systems that provide the optimum integration among the EVs, PV generations and grid are investigated in this thesis. The coupling between the PV generation and integration bus is accomplished through a unidirectional converter. Precise dynamic and small-signal models for the grid-connected PV power system are developed and utilized to predict the system’s performance during the different operating conditions. An advanced intelligent maximum power point tracker based on fuzzy logic control is developed and designed using a mix between the analytical model and genetic algorithm optimization. The EV is connected to the integration bus through a bidirectional inductive wireless power transfer system (BIWPTS), which allows the EV to be charged and discharged wirelessly during the long-term parking, transient stops and movement. Accurate analytical and physics-based models for the BIWPTS are developed and utilized to forecast its performance, and novel practical limitations for the active and reactive power-flow during G2V and V2G operations are stated. A comparative and assessment analysis for the different compensation topologies in the symmetrical BIWPTS was performed based on analytical, simulation and experimental data. Also, a magnetic design optimization for the double-D power pad based on finite-element analysis is achieved. The nonlinearities in the BIWPTS due to the magnetic material and the high-frequency components are investigated rely on a physics-based co-simulation platform. Also, a novel two-layer predictive power-flow controller that manages the bidirectional power-flow between the EV and grid is developed, implemented and tested. In addition, the feasibility of deploying the quasi-dynamic wireless power transfer technology on the road to charge the EV during the transient stops at the traffic signals is proven

Network Methods for Analysis and Design of Resonant Wireless Power Transfer Systems

In this chapter we illustrate networks methods for the analysis an design of Wireless Power Transfer (WPT) systems. We begin with an introduction which compares the alternatives available for transfering electromagnetic power. In particular, we illustrate the advantages and disadvantages of the various possibilities: transmission lines, antennas, and mid-range reactive field couplings. Then, in the introduction, we also illustrate practical applications for WPT and discuss relevant papers published so far. In the second section, after introducing a basic structure for realizing WPT (see Fig.1), we discuss the relevant theory for WPT by considering a very simple network which, nevertheless, contains all the relevant phenomenology. We derive formulas for maximizing the efficiency of power transfer and we show the necessity of introducing matching networks. Several possible realizations of matching networks are then illustrated. In the next section we introduce appropriate methods, based on the ABCD matrix, for the narrow-band analysis of WPT systems including matching networks. An example of such a network is reported in Fig. 2. A section will be devoted to the input and output coupling design where we will provide new formulas for the design of the matching networks. In particular we show that, for a given type of resonators with a given quality factor Q and a given value of the coupling between the two resonators, we can find the optimal coupling coefficients which maximize the efficiency. An example of the results achievable when optimizing the input/output coupling is reported in Fig. 3. Having derived a procedure for attaining maximum efficiency, it is also possible to establish the theoretical limits that can be achieved for a given value of coupling and for specified values of the resonators Q. A section will be also devoted to the case of multiple transmitting and multiple receiving resonators. For this arrangement, which has practical relevance and is illustrated in Fig 5, we also introduce a rigorous general network model for its analysis. Several different types of resonators will be investigated and compared. Closed form formulas relevant to the resonators' design will be introduced and also fullwave analysis of resonators well be exploited. Theoretical results will be compared with measured ones and measurement methods will be discussed. One of the problems of WPT, i.e. the frequency shift occurring when resonators are placed at different distances, will be discussed and the solution will be outlined. This is very important in practice because allows to realize systems without the need of complex sources or difficult tracking mechanisms. Finally, we will also illustrate how to analyze, both in frequency and time domain, the network representations used for WPT

Design of Power Receiving Units for 6.78MHz Wireless Power Transfer Systems

In the last decade, the wireless power transfer (WPT) technology has been a popular topic in power electronics research and increasingly adopted by consumers. The AirFuel WPT standard utilizes resonant coils to transfer energy at 6.78 MHz, introducing many benefits such as longer charging distance, multi-device charging, and high tolerance of the coil misalignment. However, variations in coil coupling due to the change in receiving coil positions alter the equivalent load reactance, degrading efficiency. In recent studies, active full-bridge rectifiers are employed on WPT receivers because of their superior efficiency, controllability, and ability to compensate for detuned WPT networks. In order to take advantage of those characteristics, the rectifier switching actions must be synchronized with the magnetic field. In the literature, existing solutions for synchronizing the active rectifier in WPT systems are mostly not reliable and bulky, which is not suitable for small receivers. Therefore, a frequency synchronous rectifier with compact on-board control is proposed in this thesis. The rectifier power stage is designed to deliver 40 W to the load while achieving full zero-voltage switching to minimize the loss. The inherent feedback from the power stage dynamics to the sensed signal is analyzed to design stable and robust synchronization control, even at a low power of 0.02 W. The control system is accomplished using commercial components, including a low-cost microcontroller, which eliminates the need for bulky control and external sensing hardware. This high power density design allows the receiver to be integrated into daily consumer electronics such as laptops and monitors. Finally, a wide-range and high v resolution control scheme of the rectifier input phase is proposed to enable the dynamic impedance matching capability, maintaining high system efficiency over wide loading conditions. In addition, to increase the WPT technology adoption to low-power consumer electronics, a small wireless receiver replacing conventional AA batteries is developed. This receiver can supply power to existing AA battery-powered devices while providing the benefit of WPT technologies to consumers

Multi-Frequency Modulation and Control for DC/AC and AC/DC Resonant Converters

Harmonic content is inherent in switched-mode power supplies. Since the undesired harmonics interfere with the operation of other sensitive electronics, the reduction of harmonic content is essential for power electronics design. Conventional approaches to attenuate the harmonic content include passive/active filter and wave-shaping in modulation. However, those approaches are not suitable for resonant converters due to bulky passive volumes and excessive switching losses. This dissertation focuses on eliminating the undesired harmonics from generation by intelligently manipulating the spectrum of switching waveforms, considering practical needs for functionality.To generate multiple ac outputs while eliminating the low-order harmonics from a single inverter, a multi-frequency programmed pulse width modulation is investigated. The proposed modulation schemes enable multi-frequency generation and independent output regulation. In this method, the fundamental and certain harmonics are independently controlled for each of the outputs, allowing individual power regulations. Also, undesired harmonics in between output frequencies are easily eliminated from generation, which prevents potential hazards caused by the harmonic content and bulky filters. Finally, the proposed modulation schemes are applicable to a variety of DC/AC topologies.Two applications of dc/ac resonant inverters, i.e. an electrosurgical generator and a dual-mode WPT transmitter, are demonstrated using the proposed MFPWM schemes. From the experimental results of two hardware prototypes, the MFPWM alleviates the challenges of designing a complicated passive filter for the low-order harmonics. In addition, the MFPWM facilitates combines functionalities using less hardware compared to the state-of-the-art. The prototypes demonstrate a comparable efficiency while achieving multiple ac outputs using a single inverter.To overcome the low-efficiency, low power-density problems in conventional wireless fast charging, a multi-level switched-capacitor ac/dc rectifier is investigated. This new WPT receiver takes advantage of a high power-density switched-capacitor circuit, the low harmonic content of the multilevel MFPWMs, and output regulation ability to improve the system efficiency. A detailed topology evaluation regarding the regulation scheme, system efficiency, current THD and volume estimation is demonstrated, and experimental results from a 20 W prototype prove that the multi-level switched-capacitor rectifier is an excellent candidate for high-efficiency, high power density design of wireless fast charging receiver

High Efficiency and High Sensitivity Wireless Power Transfer and Wireless Power Harvesting Systems.

In this dissertation, several approaches to improve the efficiency and sensitivity of wireless power transfer and wireless power harvesting systems, and to enhance their performance in fluctuant and unpredictable circumstances are described. Firstly, a nonlinear resonance circuit described by second-order differential equation with cubic-order nonlinearities (the Duffing equation) is developed. The Duffing nonlinear resonance circuit has significantly wider bandwidth as compared to conventional linear resonators, while achieving a similar level of amplitude. The Duffing resonator is successfully applied to the design of WPT systems to improve their tolerance to coupling factor variations stemming from changes of transmission distance and alignment of coupled coils. Subsequently, a high sensitivity wireless power harvester which collects RF energy from AM broadcast stations for powering the wireless sensors in structural health monitoring systems is introduced. The harvester demonstrates the capability of providing net RF power within 6 miles away from a local 50 kW AM station. The aforementioned Duffing resonator is also used in the design of WPH systems to improve their tolerance to frequency misalignment resulting from component aging, coupling to surrounding objects or variations of environmental conditions (temperature, humidity, etc.). At last, a rectifier array circuit with an adaptive power distribution method for wide dynamic range operation is developed. Adaptive power distribution is achieved through impedance transformation of the rectifiers’ nonlinear impedance with a passive network. The rectifier array achieves high RF-to-DC efficiency within a wide range of input power levels, and is useful in both WPT and WPH applications where levels of the RF power collected by the receiver are subject to unpredictable fluctuations.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133338/1/tinyfish_1.pd

Omnidirectional WPT and data communication for electric air vehicles: feasibility study

This paper investigates the feasibility of using the three dimensional omnidirectional inductive channel for power transfer and as a power line communication PLC for ground-based vehicle, electric air vehicle or space applications, the simulation results is performed by the advanced design system software using lumped equivalent circuit model. The power transfer efficiency determined based on multiport scattering (S)-parameters numerical simulation results while the theoretical channel capacity is calculated based on Matlab software as a function of the coupling coefficient considering an additive white Gaussian noise . Furthermore, the magnetic field distribution is evaluated as function of the misalignment angle θ between the receiver and the three orthogonal transmitters coils