Topology study for an inductive power transmitter in cordless kitchen system

Abstract

In a cordless kitchen system, the appliances do not make use of a power cord. The system consists of a power channel and a communication channel. There are various resonant topologies which can be implemented in the power channel[9]. The chosen topology should meet the functional as well as non-functional equirements of the system. Presently, a series resonant topology is used in the system. The topology is easy to understand, to implement and could meet the functional requirements like the amount of power and high efficiency of the system easily. But, it is difficult to meet the non-functional requirements like overvoltage protection, EMI and simple control of the system. This master’s thesis is mainly focused on design and realization an inductive power transmitter which addresses the following research questions:
• EMI: The present inductive power transmitter is based on a series resonant inverter which has a disadvantage of high dV/dt’s across the inverter bridge and the transmitter coil. Furthermore, ZVS of the power switches can be lost at low duty cycles or low loads. Both mechanisms causes high dV/dt’s in the system, which results in increase in common mode noise problems.
• Overvoltage: The present series resonant topology with the calculated circuit components and given load conditions (coupling factor (k) and load resistance (RL)), is observed to be operating in the capacitive mode of operation, when the load is disconnected/removed. Therefore, disconnection of the load causes overvoltage on the transmitter as well as the receiver coil. The overvoltage, in the absence of ’expensive’ protective means, can damage the system components and the system may fail to operate.
• Simple control: The present system is a 4th order system. Due to weak coupling between the transmitter and the receiver coils, there exists multiple operating points where the voltage gain is the same. Therefore, it is difficult to find an optimal operating point for the control loop. Also, as mentioned in previous point, the load disconnection results in capacitive mode of operation of the system. To protect the system the control loop should take care that the system operates in the desired inductive mode of operation, as fast as possible and without causing significant losses.
The report proceeds with an introduction about the cordless kitchen project. It is followed by the description and the analysis of the present system. Next, the detailed analysis of other possible topologies and selection of the alternative topology is described. It is followed by the description about the new proposed model. The report concludes with the conclusion and a paper publication. The paper is published during the Wireless Power Congress arranged by WEKA FACHMEDIEN GmbH in July-2017.