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The need for reconfigurable, high power density, and low-cost configurations of DC-DC power electronic converters (PEC) in areas such as the transport electrification and the use of renewable energy has spread out the requirement to incorporate in a single circuit several topologies, which generally result in an increment of complexity about the modeling, control, and stability analyses. In this paper, a reconfigurable topology is presented which can be applied in alterative/changing power conversion scenarios and consists of a reconfigurable Buck, Boost, and Buck-Boost DC-DC converter (RBBC). A unified averaged model of the RBBC is obtained, a robust controller is designed through a polytopic representation, and a Lyapunov based switched stability analysis of the closed-loop system is presented. The reported RBBC provides a wide range of voltage operation, theoretically from

It is widely known that the main goal of power electronic converters (PEC) is to convert energy from one stage to another in the most efficient way [

In particular, examples of integrated PEC can be found in a wide range of different applications. For instance, in [

Actually, the integration of various PEC in a single circuitry (reconfigurable PEC or RPEC) is preferred because it has several advantages such as low cost, portability, modularity, an increment of power density, and a wide operation region [

Few studies have investigated the development of RPEC and even of integrated PEC considering them as a class of polytopic switched system (PSS) [

In this paper a reconfigurable Buck, Boost, and Buck-Boost DC-DC converter (RBBC), unified/generalized-averaged PSS model of the RBBC, a robust voltage-mode controller, and a Lyapunov stability proof in closed-loop are proposed in order to advance our knowledge of integrated PEC and RPEC from a PSS perspective. This RPEC was developed to provide a unique, low-cost, and stable solution to several problems arising in Electric Vehicles and smart grid scenarios. For example, in an Electric Vehicle, a single solution to driving the power from the battery to the main motor is desirable in a wide range of speed forward direction and in low speed reverse direction while several parameters are dynamic. The model, controller, and stability proof presented can be used for any combination of the aforementioned converters, even in an on-the-fly reconfigurable scheme. Numerical data for a demonstrative Proportional-Derivative (PD) controller, implemented in an experimental testbed, are presented.

This paper is organized as follows. The unified Buck, Boost DC-DC converter (UBBC) and the methodology for the modeling are described in Section

In this section, the schematic and the operating modes of the RBBC are presented; later a polytopic representation of the RBBC is obtained. Such polytopic representation is used to demonstrate the closed-loop stability of the RBBC, despite parametric uncertainty.

In order to explain the functioning of the aforementioned RBBC consider the circuit shown in Figure

S1, S2 closed, S3, M2 open, and PWM switching on M1, Buck

M1, S2 closed, S1, S3 open, and PWM switching on M2, Boost

M2, S3 closed, S1, S2 open, and PWM switching on M1, Buck-Boost.

Proposed RBBC.

A nonpolarized capacitor

Consider Mode 1; the equivalent circuit idealized as the well-known noninverting Buck converter is shown in Figure

Mode 1 of the proposed RBBC.

The MOSFET M1 is modeled as a variable resistance

Idealized Mode 1 of the proposed RBBC.

In such idealization, the voltage supplied to the

Idealized Mode I schematic.

Consider Mode 2; the equivalent circuit can be idealized as the well-known noninverting Boost converter shown in Figure

Mode 2 of the proposed RBBC.

In a similar way, Mode 3 shows the well-known inverting Buck-Boost converter shown in the Figure

Mode 3 of the proposed RBBC.

By considering smooth transitions (allowing discharge of

Mode 1:

Mode 2:

Mode 3:

Note that the theoretical output voltage

Consider the following voltage PD control law:

In the following analysis, model (

The converter components selection depends on application specifications as maximum voltage or current ripple, input voltage, and load current among others. In this work, an insight into their selection is presented and depends on the maximum inductor current ripple, switching frequency, source voltage, and output voltage [

Semiconductor manufacturers recommend using low ESR capacitors to minimize the ripple on the output voltage, and the minimum value of

The control objective is to design a controller for the RBBC, such that stability of the trajectories of system (

Without loss of generality, the origin is considered the equilibrium point; note that a variable change calculated from an operating point can be performed in order to achieve it. Stability of a polytopic system can be ensured by the following result.

Quadratic stability of system (

In other words, it is enough to prove that all of the systems built with each vertex (in the following, vertex is used to identify the system built with the

In this section, representative simulations of the RBBC are presented. Simulations are performed in PSIM with a switching frequency of 10 kHz and an integration time of 1

Sine reference response.

In order to show the benefits of the proposed control strategy, in Figure

Sliding mode versus robust PD comparison for an abrupt load change.

In this section some of the relevant experimental results obtained by the implementation of the RBBC are presented.

Figure

Experimental work bench.

In Figure

Buck mode parameter change response in closed-loop.

In Figure

Boost mode parameter change response in closed-loop.

The simulations and experimental data shown in the previous sections allow confirming that the proposed reconfigurable topology has benefit for a wide range of applications, such as vehicular one since the reversible power flow is possible with a simple reconfiguration. A new unified modeling technique is proposed and allows the use of a wide range of control techniques, even those that do not consider the switching reconfiguration characteristic of the RBBC; that is, the unified model is valid for a Buck, Boost, and Buck-Boost converter or a reconfigurable combination. The simulations and experimental data shown in the previous sections allow validating the analytic results for modeling, controller design, and stability.

While other control techniques, as sliding mode, are beneficial for implementations, where the high overshoot, no-adjustment, and settling time are not a critic issue, the proposed control strategy allows performing a fine tuning, even for the nonexpert. That is, sliding mode and other control techniques have large benefits; however, they are very sensitive to large changes in the parameters. In contrast, the presented control strategy stabilizes the voltage output even when abrupt changes on the parameters occur, as long as they vary within the design bounds. Even more, since voltage feedback is used the implementation cost is very low.

In this work, a new reconfigurable converter (RBBC) is presented. The reconfigurable converter has three operating modes/configurations, Buck, Boost, and Buck-Boost that are possible with only two MOSFETs which implies that the implementation cost is very low. In this reconfigurable converter, the output voltage can vary within a wide range from negative to high positive values (Boost) and the reconfiguration can be done on the fly. In view of the above, the presented reconfigurable converter can be used in a wide range of applications, for example, in electric propulsion/traction applications where forward and reverse direction are required.

A dynamical model for the reconfigurable converter is obtained in a unified sense for the Buck, Boost, and Buck-Boost configurations. That is, the dynamical model structure is the same and the control input

Moreover, in this work the methodology for the design of a robust controller for the reconfigurable converter is presented. The closed-loop stability is demonstrated by using a polytopic model and a common Lyapunov function and provides several advantages as simplicity, low implementation cost by voltage feedback, and adjustable gains. Comparative results are provided in order to illustrate the dynamical behavior against changes in parameters as capacitance, inductance, load resistance, and input voltage, with respect to a sliding mode controller.

Output capacitor values, nominal, minimum, and maximum

Maximum (design) current and voltage ripple

Power source voltage values, nominal, minimum, and maximum

PWM switching frequency

Inductance current value

Peak (design) load current demand

Controller gains

Inductance values, nominal, minimum, and maximum

Output resistor values, nominal, minimum, and maximum

Idealized resistance values of the MOSFET

Duty cycle in Mode 1 (Buck)

Duty cycle in Mode 2 (Boost)

Duty cycle in Mode 3 (Buck-Boost)

Control input of the RBBC

Idealized averaged supply voltage

Nominal (design) output voltage in Mode 1, 2, and 3

Output resistor voltage.

The authors declare no conflicts of interest for this paper.