The paper presents a topological overview of hybrid powertrains for battery-powered vehicles reinforced by range extenders. First, tradeoffs of employing high energy versus high power battery are revealed. Then, different topologies of battery-ultracapacitor hybrids are discussed, highlighting pros and cons of each configuration. The superiority of fully active hybrids is indicated, obtained at the expense of increase of power electronic circuitry, control effort, and efficiency. The second part of the paper focuses on two types of range extenders: renewable energy and fuel-based units. The operation strategy is shown to be different for each range extender type. The renewable-energy-based range extender should be operated employing either passive or active maximum power point tracking strategy and hence not be involved in the powertrain energy balancing. It is shown that such a strategy allows the rest of system to perceive the renewable energy range extender (RERE) as a part of the load and act accordingly. Solar array is given as an example of a RERE and the possible connection topologies are discussed. On the other hand, the fuel-based range extender (FBRE) should be operated near the lowest specific fuel consumption point employing maximum efficiency point tracking strategy. Fuel cells and internal combustion engines are specified as examples of FBREs. The complete powertrain is shown to resemble a dc microgrid with source, storage, and load units connected through power management circuitry to a common dc link.

Design of a battery-ultracapacitor semiactive hybrid for powering pulsed current loads is presented in this paper. The semiactive hybrid energy source consists of an ultracapacitor assisted Li-Ion battery, connected to the load via a dc-dc converter. The system is controlled such that the battery is supplying a near-constant current to satisfy the average load demand while the ultracapacitor supplies the dynamic component of the load current. The control algorithm is based on a well-known capacitance-emulating approach. As a result, a high-energy battery can be used despite the high-power load demand spikes. In addition, the battery-load voltage matching is not required and the control algorithm does not require load current sensing. It is shown that the proposed system performance is equivalent to the performance of a passive hybrid, employing a very high nonfeasible capacitance. Moreover, it is revealed that the battery current is independent of the capacitor size, which affects the load voltage ripple only. Extended simulation and experimental results are presented to demonstrate the feasibility of the approach.

A pulse-width modulation modulator for a noninverting bidirectional buck-boost converter is analyzed and a corresponding average-mode current controller design is revealed. The main feature of the modulator is the ability to create switching sequences for both converter legs without requiring any information regarding either operation mode or the direction of power flow. The modulator receives a control signal generated by the current controller, and a triangular carrier and generates driving signals with two different duty cycles, allowing tight control of the inductor current throughout the entire operating range. The underlying circuitry is thus relatively simple; moreover, the proposed method greatly simplifies the outer loop controller design. The revealed findings are supported by simulations and experiments.

In this paper, instantaneous power and energy capabilities of supercapacitor (SC) connected to a power element are derived for an arbitrary power profile, given either in analytical or statistical distribution form. A class of applications is considered where the device is used as deeply cycled energy storage with significant capacity, absorbing/supplying the whole power flow or its significant component rather than shaving low-energy high-frequency peaks. The analytical derivation of SC behavior is based on simple RC model with parameters taken from a manufacturer datasheet. It is shown that the commonly adopted “state-of-charge” indication based on terminal voltage only is insufficient to reflect the energy balance for both charging and discharging; hence an alternative definition of “state-of-energy” is proposed for each direction of energy flow, depending on both instantaneous power and terminal voltage. A simplified quick noniterative sizing procedure is proposed at the expense of a slightly oversized SC. Comprehensive example is provided in order to reinforce the proposed method of analyzing SC performance and demonstrate sizing procedure.

Analytical description of a constant power fed supercapacitor behavior is revealed in the paper. The derivation is based on a simple RC model with parameters taken from a manufacturer datasheet. Different power and energy-related figures of merit are obtained using the derived expressions. It is shown that some of the performance figures used in datasheets are strictly theoretical and cannot be achieved in practice. The process of Ragone plot construction based on the proposed method is described as well. Moreover, it is shown that the upper limit of a supercapacitor voltage imposes certain limits on power and energy capabilities of the device. Extended simulation and experimental results are provided in order to reinforce the proposed method and justify the selected model for describing supercapacitor performance. Appropriate comparison of simulations and experiments shows that the simple first-order model may be utilized to predict supercapacitor behavior with reasonable accuracy to perform an initial design.