ILE – Institut für Leistungselektronik
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Es wird auf die Unterschiede von trafobehafteten und trafolosen Wechselrichtern und die daraus resultierenden, wesentlichen Merkmale eingegangen. Die kapazitiven Umladeströme, hervorgerufen durch die im Solargenerator befindlichen Kapazitäten machen eine bipolare Taktung bei der H-Brücke oder eine andere Topologie notwendig. Daraus resultieren auch unterschiedliche Belastungen in den passiven Bauelementen. Hier wird im Wesentlichen auf die Zwischenkreisströme eingegangen.
In recent years the undisturbed electrical power supply became very important, because of the increasing automation (Schmidt, et al., 1995). A protected electrical power supply is possible by using a static uninterruptible power supply (UPS), because its electrical energy is stored in a DC-link intermediate circuit, connected with a battery. An important cost factor and power loss producer is the usually inserted line frequency output transformer. The elimination of the transformer causes a changing of the circuit topology and a rising of the DC-link voltage. It is possible to omit the transformer by connecting the ground wire of the load to the centre point of the DC-link capacitor. The DC-link voltage has to be higher than the sum of the peak value of the sinusoidal output voltage and the voltage drop of the output filter inductance at maximum load (e.g. U/sub d/= 800 V) (Patt, M, 2002). A second cost factor is the DC-link capacitor. Its reactive power capacity becomes bigger compared to conventional UPS because the low-frequency load current flows through the centre point of the DC-link capacitors. This is an essential and an expenditure property (F. Renken et al., 2002). The centre of the paper is the analysis of the DC-link capacitor current in different topologies. In the first part of the analysis the current-loading of a two and a three level voltage source inverter will be described. In the second part of the paper a three phase two-level and a three phase three level-inverter will be compared.
One main aspect in the development of uninterruptible power supplies (UPSs) is the elimination or the reduction of ferromagnetic components. In this paper, the effects of reducing ferromagnetic components is illustrated by the example of two different single phase UPS topologies. In the first part of the article, the transformer in a continuous mode UPS is eliminated, and in the second part of the contribution, the couple line inductance in a bidirectional UPS is replaced by different kinds of AC/AC converters. Several advantages and disadvantages of these two different UPS-topologies are discussed.
In FPGA applications low core voltages of 1 volt or below at high currents are increasingly getting important. This topic provides a guide for designing a highly reliable DC/DC converter of 1V, 15A.PCB layout consideration, 4 layers arrangement and proper grounding technique are based on a focus on reliability. Due
to use of an enhanced operation controller there is possibility to minimize diode conduction losses related to
the MOSFETs to absolute minimum dead-time,resulting in high efficiency.
With automobiles getting more and more electrified, there is a large number of different applications where dc/dc-converters have to be placed. In new electric vehicle concepts it is necessary to connect two different voltage levels with galvanic isolation and assure power transfer with high efficiency. The presented paper describes a new approach to improve the advantages of the well known phase shift zero voltage switching (ZVS) converter to meet efficiency and volume requirements.
This paper describes a bidirectional solar-battery- grid inverter, its principle and features as well as control functions and recent semiconductors which are used. The device is designed for smart grid applications, where the operator decides about a power and its direction for each active device. The proposed inverter is able to supply power grid by power and phase shift which are defined by superior logic. Or it can take required amount of power from the grid and store it in battery. Stored energy is used later for covering deficiency of solar energy. Solar cells are efficiently driven by MPP tracker and power balancing function ensures maximal usage of all sources.
In order to incorporate renewable energies modern power converters with high efficiency and power density are essential. Resonant power converter topologies are implemented due to the reduction of switching losses, yielding higher switching frequencies which ultimately
reduce the size of the magnetic components. Resonant topologies are known for several decades and main goal remains to optimize them in terms of efficiency and dynamics. It is essential to implement dynamic and robust control schemes over a wide operating range. In order to guarantee robust control the transfer function of the plant has to be known. In this paper the plant of a Dual Active Bridge Converter (DAB) was measured using a Bode 100 from Omicron LAB. A nonlinear phenomenon in the output characteristic can be observed, when a transition from soft switching (ZVS) to hard switching occurs. In this region, the gain of the transfer function of the plant drops significantly, which leads to a high drop in bandwidth and thereby decreasing the dynamics of the converter. Furthermore a technique is described by which the nonlinear region can be cancelled.
Transformers are used when galvanically isolated energy transfer, i.e. according to the European standard EN61558, is necessary. Traditional
transformers are bulky and consist 80% of copper and iron. Since the 1960s the demand for refined copper has increased by 250% from 5 mil tons to 20 mil tons. Due to the increasing high demand of copper a continuous price increase in the next years is expected. To guarantee the availability of copper for the next decades and to counteract the expected price increase, it is essential to find resource friendly alternatives. Compared to a three stage power conversion system a one stage AC-AC converter based on a dual-active-bridge (DAB) converter does not incorporate electrolytic capacitors in the power path. The elimination of electrolytic capacitors makes it possible to reduce size and weight and reduce the amount of needed copper, without
sacrificing lifetime. The functionality of the one stage system is ensured with ohmic loads. The problem arises, when non ohmic loads are connected and the converter enters reactive power operation, which produces a highly nonlinear shape of the control parameter. Therefore an extremely dynamic control scheme is essential in order to keep track of the control parameter. Furthermore, due to the low capacitance on the output of the converter, the power stage is highly unstable. It is therefore essential to design and implement a control scheme with high dynamics and robustness. In this paper the drawbacks of an AC-AC DAB converter under reactive power operation are described. Furthermore a current mode control scheme is presented. Firstly the transfer functions of the control stages are measured and afterwards a current mode controller is implemented and optimized. Lastly the newly designed current mode controller is compared to a voltage mode control scheme and it is shown, that the bandwidth is increased. Therefore the proposed control scheme enhances the reactive power operation of a one stage AC-AC converter.
Battery driven vehicles with Voltage Source Inverters (VSIs) are widely used in power electronics for many years. Meanwhile the Pulse Width Modulation (PWM) Techniques to improve efficiency, output voltage quality, current harmonic spectrum and etc. is the topic
which gain massive attention through these years and many studies are accomplished in this regard. Nevertheless, DC-link capacitor as the main bulky and expensive element which is affected by generated current harmonics is the focus of this paper. Here we investigate this factor for single and double inverter with continuous and discontinuous PWM pattern and compare the capacitor values for each case.
In inductive power transfer systems a smooth variation of input power can be achieved by using a controlled rectifier. The power can be changed by varying the fundamental amplitude of the primary and secondary voltages along with the phase angle between them. The paper shows how the input power is controlled and under what circumstances Zero Voltage Switching (ZVS) is lost on primary and secondary side of the system.
This paper presents a 4 kVA single-phase isolated (230V/230V) ac/ac Dual Active Bridge (DAB) converter prototype suitable for Solid State Transformer (SST) applications. A solution for inductive load is introduced and a novel control scheme based on gain scheduling approach is employed to improve the DAB overall efficiency. Efficiency optimization is done based on global Zero-Voltage Switching (ZVS) analysis of the DAB converter operating range for dual phase-shift modulation. In this analysis, minimization of both the Reactive Power per Switching Cycle (RPSC) and the rms current of the high frequency inductance is taken into consideration to get the optimal modulation parameters. Simulation results are presented to validate the proposed control scheme.
Active phase shifting method incorporates change in phase and amplitude of fundamental primary inverter output and secondary rectifier input voltages of a resonant DC/DC converter. This paper
presents implementation of this method on four basic topologies of resonant tank configurations or
compensation circuits of a resonant converter. Smooth variation of input power along with Zero Voltage Switching (ZVS) regions both on primary and secondary side have been observed for different configurations. Equations for input power as a function of the phase angles, switching
frequency, input and output voltage amplitudes and the values of the reactive components have been derived. The results are verified with simulations of all the configurations and practical setup for one of the best configuration for IPT systems.