L. H. Diaz-Saldierna

Fuel-cell energy processing using a quadratic boost converter for high conversion ratios

A fuel-cell stack generates low and unregulated DC output voltage, which depends on the demanded current. Therefore, a DC-DC converter is required to step up and regulate the output voltage. This voltage can be used as an input for an inverter to generate an AC voltage. In this work, a quadratic boost converter with a single active switch is proposed to obtain high conversion ratios and regulated the output voltage. A controller of the switching regulator is designed using average current-mode control approach. Experimental results are shown for a 400 W laboratory prototype to verify the performance of the designed regulator. In this case, a power module with polymer electrolyte membrane (PEM) fuel cell is used as an input source. This module delivers an output voltage between 22 V and 42 V, depending on the demanded current. Load step changes are applied to exhibit the robustness of the switching regulator. Finally, system stability is verified with experimental frequency response analysis.

Control of high-step down voltage converters for voltage regulator modules

New technologies are requiring high step-down conversion voltages. A possible solution to this problem is to use several buck converters connected in cascade; however, a complex control circuitry is required. An alternative solution is to use an n-stage positive output cascade buck converter with a single active switch. This class of converters is suitable for VRM applications where low voltages and high currents are required. A controller design methodology for this class of converters is developed using average current-mode control. The proposed scheme employs the inductor current of the input stage and the capacitor voltage of the output stage; therefore, the full benefits of current-mode control are maintained. Experimental results are given for a 80 W switching regulator where the robustness of the proposed controller is tested under changes on the output load.

Multiloop Controller for N-Stage Cascade Boost Converter

In recent years, the development of new technologies is requiring wider conversion ratios. A possible solution to this problem is to use n-stages connected in cascade; however, the major drawbacks are: (a) the total losses are increased mainly by the active switches, and (b) a more complex control circuitry is required. An alternative solution is to use a cascade boost converter with a single active switch. In this paper, nonlinear and linear models are given for the above converter. A controller is developed using average current-mode control where the current of the first inductor is selected for feedback purposes. For the inner loop, a current gain and a high gain compensator are selected. For the output loop, a conventional PI-controller is designed.

Control Strategy of a Quadratic Boost Converter With Voltage Multiplier Cell for High-Voltage Gain

The need of dc–dc switching converters for power supplies with high-voltage gains has increased in the recent years due to new applications in areas as renewable energy systems, transportation, industrial, medical, and others. A quadratic boost converter is a useful topology to obtain a step-up output voltage; however, a major drawback is the presence of a higher voltage stress over the active and passive switches. In this paper, a quadratic boost converter is combined with a voltage multiplier cell and an output filter to offer a high-voltage gain converter with nonpulsating input and output currents. The expressions for the capacitor voltages and inductor currents are given, as well as the corresponding ripples that allow the proper design of the converter. The bilinear switched, nonlinear averaged and linear averaged models are derived such that the dynamical behavior of the converter is analyzed and used to design a control strategy. A step-by-step procedure is given to tune up a current-mode controller. Experimental results are shown from a prototype, which delivers an output voltage of 220 V and an output power of 300 W. Step load changes between 20% and full load are applied to exhibit the robustness of switching regulator.

Loop-shaping control of high-step converters for fuel-cell applications

Fuel-cell stacks are an attractive option for power generation; however, this technology presents some drawbacks as slow dynamic response and low unregulated DC output voltage, which depends nonlinearly on the output current. In this paper, a quadratic boost converter with a single active switch is proposed as an interface between a PEM fuel-cell stack and a load. The proposed topology is used to increase the output load voltage for a given stack-converter-load system, aiming to ensure high conversion ratios. In addition, a loop-shaping average current-mode scheme using a single control signal is proposed for load-side voltage regulation. A selection procedure for controller parameters ensuring system stability and output voltage regulation is established. Experimental results are shown in a 220 V @ 400 W prototype. Finally, system stability is verified via experimental frequency response and controller performance is tested by applying step changes in the load.