An investigation into negative inductance circuit and its applications in power electronics

Abstract

In this thesis, a research study on the negative inductance circuit for power electronics systems is presented. Negative inductance exhibits the same reactance but reversed phase characteristics of normal inductance. With a 180o phase shift compared to normal inductance, it can be used to manipulate the impedance of a passive component. By connecting negative inductance circuit in series or parallel with a passive component, the overall impedance will be decreased or increased. Hence, its applications can provide impedance boosting or cancellation. The negative inductance can be constructed by a simple circuit named negative impedance converter (NIC) circuit. Operational-amplifiers and transistors are used to realize a NIC circuit and emulate a negative inductor. In this thesis, the electrical characteristics of negative inductance are studied based on the fundamental circuit theories. Two types of NIC circuits are investigated. The impacts of non-ideal components on the circuit performance are reported. The impedance characteristics and power consumptions of the NIC circuits are compared. A transformer-type negative inductance circuit is proposed to extend the impedance range of negative inductance. To ensure the proper operation of the negative inductance circuit, the operating regions and stability concerns are discussed. I-V curves are used to analyze the operations of NIC circuits. Meanwhile, the stability issue is investigated by conducting the transfer function analysis and time domain analysis. To demonstrate the benefit of impedance manipulation using negative inductance, a NIC circuit has been incorporated into an electromagnetic interference (EMI) filter to boost up the impedance of a common mode (CM) choke and obtain better CM noise suppression. The proposed NIC circuit is connected in parallel with the CM choke. An auxiliary winding is added to the core of the choke and connected to the NIC circuit. Without physically increasing the original inductance, the impedance of the CM choke is virtually boosted up to 4 times. This prototype is tested in a switched-mode power supply (SMPS). The CM noise measurement shows that this proposal can effectively improve the noise reduction performance, whereas power consumption of the additional circuit is not significant. To achieve both CM and differential mode (DM) impedance boosting and obtain a hybrid noise suppression effect, an asymmetrical three-winding EMI choke connecting with the negative inductance circuit is proposed. The equivalent CM and DM impedance of the choke is virtually increased by 4.1 and 3.2 times, respectively. Different from the design of the conventional EMI inductors which uses discrete CM and DM chokes, this proposal saves the cost and space of EMI filters.