K. Rigbers

A Novel Phase-Interleaving Algorithm for Multiterminal Systems

This paper introduces a novel phase-interleaving algorithm for asymmetric multiterminal power converters. Using a variable phase interleaving (VI), the first harmonic of the dc-link current and voltage can be thoroughly eliminated even under the situation where the input voltage and current of each converter differ. This means that the cost and size of the dc-link capacitor can be significantly reduced compared to when the standard (symmetric) interleaving algorithm is used. The VI-algorithm does not require any additional hardware and has only slight influence on the control loop of the converters when compared to the standard solution, which simplifies the integration of this algorithm. As a concrete application, the VI-algorithm is integrated into a photovoltaic inverter with three independent input converters. This paper also provides a method for determining the required dc-link capacitance through a worst-case analysis. Furthermore, a performance comparison between edge-aligned fixed interleaving, center-aligned fixed interleaving and VI and is given.

Behavior and Loss Modeling of a Three-Phase Resonant Pole Inverter Operating with 120° Double FlatTop Modulation

This paper describes the loss modeling and optimization of a grid-connected resonant pole inverter operating with 120deg double flattop modulation (Rigbers et al., 2005). The proposed architecture achieves soft-switching with highly reduced current stresses compared to the conventional resonant pole inverter (Divan and Skibinski, 1987) and (Divan et al., 1988) without additional components. This concept is based on the fact that a symmetrical three-phase system delivers or draws always constant power to/from the grid with 120deg phase shifted sinusoidal phase voltages of same amplitude and coherent sinusoidal phase currents. Simple analytic behavior and loss models for all active and passive components are derived and verified using a 5 kW prototype

High-efficient Soft-Switching Converter for Three-Phase Grid Connections of Renewable Energy Systems

Despite their high efficiency, soft-switching three-phase inverters ca have disadvantages like higher conduction losses (resonant pole inverter), voltage stress and sub-harmonics (resonant DC-link inverter) or the need for additional components (auxiliary resonant commutated pole inverter). In contrast to single-phase grid connection, the three-phase grid connection provides a continuous power flow without the need for large energy storage devices. If the inverter is fed by a constant power source, it is possible to overcome these disadvantages by using the novel double 120deg flattop modulation, which results in an inverter with low conduction losses, small dc-link capacitance and soft-switching operation without the need for additional components. The developed inverter prototype in the kW-range operates with a total dc-link capacitance of only 10 muF. All these characteristics make it promising for grid-connection of renewable energy systems

A Dynamic Boost Converter Input Stage for a Double 120° Flattop Modulation Based Three-Phase Inverter

This paper presents a dynamic boost converter as input stage for a high efficient double 120deg flattop modulation based three-phase inverter. The boost converter can be regulated with hysteresis control or predictive PWM. The objective of the input stage is to provide a dynamic and accurate current into a pulsating DC-link. The algorithms are verified with simulations and experiments using a prototype. Both results show that the designed input stage can provide the required dynamics and accuracy for the three-phase inverter operating with double 120deg flattop modulation.

Experimental analysis of a flyback converter with excellent efficiency

Power conversion modules in consumer products are optimised for cost and not for efficiency. On the other side, efficiency has a value when using renewable energies such as photovoltaic. A bidirectional active-clamped flyback converter has been investigated to identify its maximum possible conversion efficiency for the principal use as maximum power point converter. A power train efficiency has been measured from a 200 W prototype that is above 91 % between 10 % and 100 % of the rated power and reaches a peak value of 96 %.

A novel phase interleaving algorithm for multi-terminal systems

This paper introduces a novel phase interleaving algorithm for asymmetric multi-terminal systems. Through variable phase interleaving (Vl-algorithm) the fundamental frequency component in the DC-link current and voltage are thoroughly eliminated even if the input voltage and current of each phase differs from each other. Therefore the cost of the DC- link capacitor can be significantly reduced compared to the standard interleaving algorithm. As a concrete application, the Vl-algorithm is integrated into a photovoltaic inverter with three-phase input stage. The paper also provides a method for determining the required DC-link capacitance through a worst case analysis. The experimental results show that the Vl- algorithm does not require any additional hardware and has only slight influence on the control loop of the converters simplifying the integration of this algorithm.

Modular thermal design approach for semiconductor modules in power electronic converters

This paper presents a new modular approach for the thermal design of semiconductor power modules that serves to determine the number and size of the power semiconductor chips, the used packaging technology and the heat sink design at an early stage of the design process. As in various applications like for example photovoltaic inverters the thermal design is mainly dependent upon the worst case stationary operation conditions, the model refers to the static thermal behavior of the system only. It consists of three parts: first, a 2D simulation based calculation of the thermal resistance between the semiconductor chips and the heat sink, second, an analytic model for designing forced air cooled heat sinks and last, a routine for suitable combination of modules and heat sinks.

Estimation of the lifetime consumption of power semiconductors due to power cycling in a photovoltaic inverter

This paper deals with the estimation of the lifetime consumption of power semiconductor modules due to power cycling with regard to a 125 kW photovoltaic inverter. The described calculation model takes into account a demanding photovoltaic mission profile, the operating point dependent behavior of the photovoltaic inverter, the amount of parallel semiconductor chips and the cooling system design. Different packaging technologies including state-of-the-art and new technologies with improved power cycling capability are considered based on power cycling diagrams published by semiconductor module manufacturers and the possible influence of the usage of silicon carbide instead of silicon chips is discussed. As a result, the calculated lifetime consumption as a function of the maximum junction temperature of the inverter design is presented.

High efficient galvanically isolated resonant multi-input DC-DC converter topology

In this paper, a multi-input converter topology is proposed, which combines a series resonant converter (SRC) with a boost converter in a way that switching losses of the boost part can be significantly reduced, by using the resonant current of the SRC. This allows an efficient energy conversion from different power sources over a wide input voltage and power range. The gain of each terminal can be adjusted independently between 50 % and 100 % of the clamping voltage. An input voltage and input power dependent efficiency of up to 96.9 % has been measured with a demonstrator of several kW.

Unipolar Bidirectional Current Source (UBiCS) Converter

In general, current source inverters (CSI) consist of a controlled current dc-link, which is connected to an inverter. Since the dc-link current as well as the output current have to be controlled, CSIs require a large amount of controllable semiconductors. In this paper a new topology, the Unipolar bidirectional current source (UBiCS) converter, is introduced. Although the input quantity of the UBiCS converter is a constant dc voltage, the converter behaves like a current source. The current in the inductor and the output current can be controlled only with three active switches. Similar to CSIs, no forbidden switching states exist. Unlike CSIs the output voltage of the UBiCS converter is unipolar but it allows two quadrant operation. In this paper, the basic operating principles of the UBiCS converter are explained and its advantages are derived. The validity of the concept is proven by means of experimental results. Furthermore, possible applications for the UBiCS converter are discussed.