This paper presents a novel contactless field excitation~(CFE) system based on wireless power transfer~(WPT), which utilizes the existing voltage source inverter~(VSI) of the motor drive for electrically excited synchronous motors~(EESMs). In conventional CFE systems, an extra high-frequency converter is required to excite the field winding.  In this paper, it is proposed to utilize existing voltage switching harmonics of the VSI for exciting the field winding while the low-frequency modulated component is used to drive the motor. In the proposed system, a novel variable carrier phase shift method~(VCPSM) is developed to achieve constant input excitation voltage for the WPT part independently from the motor operation. In addition, a hybrid frequency detuning control method is introduced to adjust the field current.  For experimental validation, a small-scale prototype with 100~V DC-link and 60~kHz switching frequency is established. It is observed that the field current could be kept almost constant at 5~A under different motor driving conditions operations regarding modulation index and fundamental frequency.  Also, it is shown that the field current could be reduced by detuning the switching frequency. In brief, without an additional active converter and only with a software update, a cost-effective CFE system for EESMs can be easily implemented.

The aim of this paper is to design a modular, fault tolerant multi transmitter(Tx) -multi receiver(Rx) parallel connected common DC bus inductive power transfer(IPT) system to replace slip rings in wind turbines or brushless exciters. In parallel connected common DC bus systems, current unbalance is a major issue which results in thermal stresses and over current or voltages. In this paper, two different new current balancing methods are proposed: Cross-coupled Rx modules and intentional miss-tuning of Rx side resonant frequency. These methods are investigated both analytically and experimentally for a single Tx and two Rx system for a 500 W prototype. The proposed methods are tested independently, and then the combined current balancing method is also investigated. For the same missalignment case cross-coupled/de-tuned has a 55.8% current balancing improvement compared to de-coupled/fullytuned topology.