Abstract
The inherently different dynamics of a DC-DC converter while operating in both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) necessitate an advanced controller to control the inductor current. A conventional PI controller cannot be used across both modes since it does not guarantee a smooth transition between both modes. Furthermore, in time-varying input-output voltage applications of the four-quadrant converter such as in battery charging applications, the location of the boundary between the CCM and the DCM changes dynamically, creating an uncertainty. Therefore, a robust controller is required to accurately track the inductor current in the presence of uncertainties. Thus, an adaptive controller is proposed in this work, which is based on the general inverse model of the four-quadrant converter in both modes. Moreover, gain scheduling is used to switch the parameters of the controller as the converter transits between the DCM and the CCM. The adaptability and effectiveness of the controller in ensuring a smooth transition is validated by numerical simulations conducted on various converter topologies. Experimental results are also presented for a buck converter.
Highlights
Research on DC-DC converters has traditionally focused on the topology with a voltage source as the input and a load at the output [1,2,3,4]
The converter can operate in two different modes, namely discontinuous conduction mode (DCM) and continuous conduction mode (CCM)
Once the transition is made into CCM, the controller is able to perfectly track the reference current. These results prove that a single PI cannot simultaneously achieve good tracking in both the DCM and CCM operation of the converter
Summary
Research on DC-DC converters has traditionally focused on the topology with a voltage source as the input and a load at the output [1,2,3,4]. Energies 2020, 13, 4187 discharge period than it gains during the charge period In this topology, the operation of the converter in either CCM or DCM is determined by the duty cycle. The relationship between the duty cycle and the inductor current changes radically as the converter transits from the DCM region to the CCM region This nonlinear behavior of the converter with a source at both ends implies that a linear inductor current regulator—such as the PID controller—cannot be used over its entire range of operation. For battery charging applications, this boundary is not fixed in the constant current charging stage since the battery voltage changes with the state of charge This calls for an advanced controller that is able to cope with the transition between the different modes of operation.
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