J.A. Oliver

Multilevel Power Supply for High-Efficiency RF Amplifiers

In radio systems linear power amplifiers (class A, B or AB) are usually used as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has low peak-to-average power ratio. The Kahn envelope elimination and restoration (EER) technique is used to enhance efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a combination of multilevel converter and linear regulator. The proposed solution can reproduce any signal with maximal spectral component of 2 MHz and give instantaneous maximal power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, it has up to 15% higher efficiency than linear regulator that is used as a conventional solution. Additionally, the algorithm for selection of voltage levels for the multilevel converter is explained, as well.

Impedance-Based Stability and Transient-Performance Assessment Applying Maximum Peak Criteria

The impedance-based stability-assessment method has turned out to be a very effective tool and its usage is rapidly growing in different applications ranging from the conventional interconnected dc/dc systems to the grid-connected renewable energy systems. The results are sometime given as a certain forbidden region in the complex plane out of which the impedance ratio--known as minor-loop gain--shall stay for ensuring robust stability. This letter discusses the circle-like forbidden region occupying minimum area in the complex plane, defined by applying maximum peak criteria, which is well-known theory in control engineering. The investigation shows that the circle-like forbidden region will ensure robust stability only if the impedance-based minor-loop gain is determined at the very input or output of each subsystem within the interconnected system. Experimental evidence is provided based on a small-scale dc/dc distributed system.

Power supply for a radio transmitter with modulated supply voltage

RF power amplifiers can save energy if the supply voltage is modulated dynamically. The power supply requires a low output capacitance to obtain a fast voltage modulation at very high efficiency and small size. These requirements become a challenge if a very good regulation under aggressive load current variations is also required. In this paper, a detailed analysis of the filter design and control of the buck converter leads to a very high efficiency, small size design that meets dynamic regulation requirements, even aggressive load current variations, with low output capacitance. Interleaving of buck converters proves to be the enabling solution. A prototype has been built and the measurements agree with the theoretical results.

Buck+half bridge (d=50%) topology applied to very low voltage power converters

Buck+Half Bridge (d=50%) topology is a very suitable circuit for low output voltage, high output current applications with a wide input voltage range. Its small signal transfer function is very complex and should be considered to optimize the dynamic response, efficiency and size of the power converter. Small signal and large signal behavior of this topology are analyzed through their corresponding average models. Design guidelines, drawn from this analysis, are applied on two low-voltage (1.5 V) wide input voltage prototypes to validate the goodness of this topology.

Power Electronics Enabling Efficient Energy Usage: Energy Savings Potential and Technological Challenges

Power electronics is a key technology for the efficient conversion, control, and conditioning of electric energy from the source to the load. In this paper, the potential of power electronics for energy savings in four major application fields, buildings and lighting, power supplies, smart electricity grid, and industrial drives, is investigated. It is shown that by wider adoption of power electronics in these areas, the current European Union electricity consumption could be reduced by 25%. The technology challenges for exploiting this potential for all the four areas are identified in the paper.

Multilevel Power Supply for High Efficiency RF Amplifiers

In communication systems, linear power amplifiers (PAs) (class A, B, or AB) are usually used as a solution for the PA stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration technique is used to enhance the efficiency of RF transmitters by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a combination of multilevel converter and linear regulator. The proposed solution can reproduce any signal with maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, it has up to 49% higher efficiency than an ideal linear regulator that is used as a conventional solution. Additionally, the algorithm for the optimization of the voltage levels, for the multilevel converter, is explained as well.

A Wireless Charging System Applying Phase-Shift and Amplitude Control to Maximize Efficiency and Extractable Power

Wireless power transfer (WPT) is an emerging technology with an increasing number of potential applications to transfer power from a transmitter to a mobile receiver over a relatively large air gap. However, its widespread application is hampered due to the relatively low efficiency of current Wireless power transfer (WPT) systems. This study presents a concept to maximize the efficiency as well as to increase the amount of extractable power of a WPT system operating in nonresonant operation. The proposed method is based on actively modifying the equivalent secondary-side load impedance by controlling the phase-shift of the active rectifier and its output voltage level. The presented hardware prototype represents a complete wireless charging system, including a dc-dc converter which is used to charge a battery at the output of the system. Experimental results are shown for the proposed concept in comparison to a conventional synchronous rectification approach. The presented optimization method clearly outperforms state-of-the-art solutions in terms of efficiency and extractable power.

Nonlinear Control for DC–DC Converters Based on Hysteresis of the

The nonlinear and linear controls proposed by Alou and Soto provide very fast transient response (voltage step from 1 to 1.5 V in 2 μs). This nonlinear control is based on hysteretic control of Cout current. This system is very sensitive to effects, like aging, temperature, input and output voltage variation, etc., that modify the switching frequency. This paper proposes a frequency loop to avoid the frequency variation and to adjust the switching frequency to the nominal value by changing the hysteretic band. A 5-MHz buck converter is developed, and experimental results validate the loop design, obtaining the same fast transient response (from 1.5 to 2.5 V in 2 μs) while keeping switching frequency constant in steady state.

C_{\rm OUT}

Hybrid vehicles need a high voltage DC bus to supply power to the motor. Architectures of these vehicles usually include a DC-DC bi-directional converter between this voltage bus and the conventional battery. When the DC bus is held by a big capacitor, the selection and design of the aforementioned converter has an additional difficulty since the converter has to work with an output voltage ranging from 0 to 420 V in steady-state conditions. A bi-directional DC-DC converter for a hybrid vehicle is proposed in this paper. It can be used in the case that a big capacitor holds the voltage in the high side. The application forces three different operation modes being the converter able to operate in those conditions. Experimental results of a 1500 W prototype are included in the paper

Current With a Frequency Loop to Operate at Constant Frequency

Interleaved converters are an interesting alternative for many applications due to their advantage in terms of dynamic response, output ripple cancellation, EMI reduction, thermal management and optimized design. In this paper, the benefits of interleaving from the point of view of size and losses reduction of the passive components are quantified. An extensive study has been made considering actual components and technologies and their implication in the final design.