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In many applications, a current measurement that can measure ac currents with dc offset is required. This is not possible using conventional current transformers (CTs) due to the core saturation because of the dc offset. In this paper, a new sensor concept is presented, which consists of a wideband CT and a demagnetizing circuit. The sensor concept is capable of measuring ac currents with dc offset, which have periodic zero crossings, as given in power-factor-corrected (PFC) circuits. Using the demagnetization circuit, the core is actively reset during the zero crossing intervals. The operation principle and design equations are discussed in detail in this paper. For validating the presented concept, three sensors have been built using different core materials, and measurements of the transfer functions as well as operation in a PFC system are presented. A bandwidth from dc up to 20 MHz has been achieved. Index Terms--Current measurement, current transformer (CT), nanocrystalline material.

Conventional linear power amplifiers (LPAs) show a high output voltage quality but are characterized by high power losses and/or low power density. Therefore, there is a growing interest in increasing the efficiency of LPAs, e.g., for the realization of high power testing voltage sources. In this paper, a high-frequency isolated boost-type tracking power supply (TPS) system is proposed for the conditioning of the input voltage of an LPA. The output voltage of the TPS is varied according to the voltage to be formed by the LPA so that the voltage drop across the power amplifier output transistors is reduced to low values. This results in a significant increase of the total system efficiency. The operating principle of the proposed system is described. A design method for the output filter using the power supply rejection ratio of the LPA is proposed. This method ensures that the amplifier output voltage has minimal switching frequency components. Furthermore, a control system design method is presented that ensures good performance in the control of the constant inductor current of the switch-mode tracking stage. Finally, the theoretical considerations are verified by measurements on a 1-kW laboratory prototype. Index Terms--Linear power amplifier (LPA), supply voltage conditioning, testing power supply, tracking power supply (TPS).

A novel three-phase ac-ac sparse matrix converter having no energy storage elements and employing only 15 IGBTs, as opposed to 18 IGBTs of a functionally equivalent conventional ac-ac matrix converter, is proposed. It is shown that the realization effort could be further reduced to only nine IGBTs in an ultra sparse matrix converter (USMC) in the case where only unidirectional power flow is required and the fundamental phase displacement at the input and at the output is limited to [+ or -][pi]/6. The dependency of the voltage and current transfer ratios of the sparse matrix converters on the operating parameters is analyzed and a space vector modulation scheme is described in combination with a zero current commutation method. Finally, the sparse matrix concept is verified by simulation and experimentally using a 6.8-kW/400-V very sparse matrix converter, which is implemented with 12 IGBT switches, and USMC prototypes. Index Terms--Ac-ac converter, matrix converter, reduced switch count converter, sparse matrix.

This paper presents an improvement of the well-known conventional three-phase diode bridge rectifier with dc output capacitor. The proposed circuit increases the power factor (PF) at the ac input and reduces the ripple current stress on the smoothing capacitor. The basic concept is the arrangement of an active voltage source between the output of the diode bridge and the smoothing capacitor which is controlled in a way that it emulates an ideal smoothing inductor. With this the input currents of the diode bridge which usually show high peak amplitudes are converted into a 120[degrees] rectangular shape which ideally results in a total PF of 0.955. The active voltage source mentioned before is realized by a low-voltage switch-mode converter stage of small power rating as compared to the output power of the rectifier. Starting with a brief discussion of basic three-phase rectifier techniques and of the drawbacks of three-phase diode bridge rectifiers with capacitive smoothing, the concept of the proposed active smoothing is described and the stationary operation is analyzed. Furthermore, control concepts as well as design considerations and analyses of the dynamic systems behavior are given. Finally, measurements taken from a laboratory model are presented. Index Terms--Active rectifier, dc-link supply, three-phase power factor correction.

This paper presents a novel dc-ac converter for applications in the area of distributed energy generation systems, e.g., solar power systems, fuel-cell power systems in combination with supercapacitor or battery energy storage. The proposed converter is realized using an isolated multicell topology where the total ac output of the system is formed by series connection of several full-bridge converter stages. The dc links of the full bridges are supplied by individual dc-dc isolation stages which are arranged in parallel concerning the dc input of the total system. Therefore, all switching cells of the proposed converter can be equipped with modern low-voltage high-current power MOSFETs, which results in an improved efficiency as compared to conventional isolated dc-ac converters. Furthermore, the cells are operated in an interleaved pulsewidth-modulation mode which, in connection with the low voltage level of each cell, significantly reduces the filtering effort on the ac output of the overall system. The paper describes the operating principle, analyzes the fundamental relationships which are relevant for component selection, and presents a specific circuit design. Finally, measurements taken from a 2-kW laboratory model are presented. Index Terms--Interleaved pulsewidth modulation, multicell, renewable energy converter, solar inverter.

This paper presents a novel switch-mode power amplifier based on a multicell multilevel circuit topology. The total output voltage of the system is formed by series connection of several switching cells having a low dc-link voltage. Therefore, the cells can be realized using modern low-voltage high-current power MOSFET devices and the dc link can easily be buffered by rechargeable batteries or 'super' capacitors to achieve very high amplifier peak output power levels ('flying-battery' concept). The cells are operated in a phase-shifted interleaved pulsewidth-modulation mode, which, in connection with the low partial voltage of each cell, reduces the filtering effort at the output of the total amplifier to a large extent and, consequently, improves the dynamic system behavior. The paper describes the operating principle of the system, analyzes the fundamental relationships being relevant for the circuit design, and gives guidelines for the dimensioning of the control circuit. Furthermore, simulation results as well as results of measurements taken from a laboratory setup are presented. Index Terms--Class-D amplifier, interleaved pulsewidth modulation, multicell, switch-mode amplifier.

In this paper, the conduction losses of power MOSFET's are calculated analytically for application in three-phase voltage dc-link pulsewidth modulation (PWM) converter systems. Contrary to a conventional calculation, the dependency of the turn-on behavior on the drain current is considered in terms of a quadratic approximation. The derived relationships are represented graphically; they can be included directly into the dimensioning of the power transistors. Index Terms - Conduction losses, on-state resistance of power MOSFET's, voltage dc-link pulsewidth modulation converter.

This paper presents a combined power amplifier system consisting of a linear amplifier unit with a switched-mode (class D) current dumping stage arranged in parallel. With this topology, the fundamental drawback of conventional linear power amplifiers - the high loss - is avoided. Compared to a pure class D (switching) amplifier, the presented system needs no output filter to reduce the switching frequency harmonics. This filter (usually of multistage type) generally deteriorates the transient response of the system and impairs the feedback loop design. Furthermore, the low-frequency distortions of switching amplifiers caused by the interlock delay of their power transistors are avoided with the presented switched-mode assisted linear amplifier system. This can be considered as a master-slave system with a guiding linear amplifier and a supporting class D slave unit. The paper describes the operating principle of the system, analyzes the fundamental relationships for the circuit design, and presents simulation results. Finally, various further topologies of switched-mode assisted linear amplifiers are given. Index Terms - Class D converters, dc-ac power conversion, power amplifiers, switching amplifiers.

In this paper the low frequency harmonic distortion of the mains current of a three-phase single-switch discontinuous-mode boost-rectifier is calculated. The system analysis is based on application of space vector calculus and on substitution of discontinuous time shapes within a pulse period by quasicontinuous time shapes. The quasicontinuous time shapes are defined by averaging over the pulse period. The dependency of the shape of the input currents on the voltage transformation ratio is given for various control methods in analytical form. The results of the theoretical analysis are verified by digital simulation and by measurements on a laboratory model. A good consistency of the results has been found.

In this paper the peak, mean, and rms values of the component currents of a three-phase single-switch discontinuous inductor current mode boost rectifier are calculated analytically. The values are given in rated form in dependency on the output power and on the ratio of output voltage to the amplitude of the mains voltage. Furthermore, the influence of the voltage transfer ratio on the shape of the mains currents and on the power factor of the system is analyzed. The theoretical analysis is verified by digital simulation and a good consistency is achieved. Finally, the approach of the converter dimensioning based on the graphical representation of the calculation results is described and illustrated using a specific example. The correctness of the dimensioning is verified by measurements on a laboratory model.

In this paper, a new three-phase single-switch ac-dc flyback converter system is presented. The system operates in the discontinuous mode. The simple structure of its power and control circuit, low mains current distortion, and resistive fundamental behavior, as well as the high-frequency isolation of the controlled output voltage, have to be pointed out. Besides the analysis of the stationary operating behavior, the dependencies of the peak values, average values, and rms values of the device currents, and of the maximum blocking voltages across the power electronic devices on the circuit parameters, are given as analytic approximations. The theoretical analysis is verified by digital simulation.

This paper treats the possibility of transferring the modulation method developed for a pulse width modulated (PWM) converter with a dc voltage link (VLC) to a PWM converter with dc current link (CLC) based on the inverse current and voltage behavior of these two systems. The duality between VLC and CLC has been intuitively clear. This 'duality' is treated here in a scientific approach. Especially, transferring of modulation methods from VLC to CLC and vice versa are beneficial for practical applications. The nonplanar property of three-phase bridge circuits leads to a quasidual relation of the switching states of the two systems. The code conversion of the binary switching functions of a VLC into control signals of the power electronic devices of a CLC is given. The remaining degree of freedom of the correspondence is set by the requirement of minimum switching frequency of the converter.

In the course of the More Electric Aircraft program frequently active three-phase rectifiers in the power range of several kilowatts are required. It is shown that the three-phase \Delta-switch rectifier (comprising three \Delta-connected bidirectional switches) is well suited for this application. The system is analyzed using space vector calculus and a novel PWM current controller modulation concept is presented, where all three phases are controlled simultaneously; the analysis shows that the proposed concept yields optimal switching sequences. Analytical relationships for calculating the power components average and rms current ratings are derived to facilitate the rectifier design. A laboratory prototype with an output power of 5 kW is built and measurements taken from this prototype confirm the operation of the proposed current controller. Finally, initial EMI-measurements of the system are also presented. [ABSTRACT FROM AUTHOR]

Active three-phase rectifiers operated at switching frequencies of 500 kHz and above, in order to increase their power density, require high-speed current controllers. If these current controllers are implemented purely digitally, which is well established today for 20-200 kHz converter systems, then very high numerical data processing demands result. In this paper, two different types of field-programmable gate arrays (FPGAs) are evaluated for realizing high-speed converter current control. For the implementation of such controllers, not only the FPGA has to be considered but rather the entire signal chain. Two alternative A/D interfaces (including high-speed low-voltage differential signaling data transmission) that are able to handle data sampling rates up to 25 MSa/s are verified. Subsequently, a digital current controller is designed and it is shown how hardware multiplier blocks of modern FPGAs can be used advantageously. Furthermore, the FPGA implementation of high-resolution pulsewidth modulation providing symmetrical pulse patterns for high switching frequencies is described. Measurements taken from a 10 kW VIENNA rectifier laboratory prototype finally demonstrate the high performance of the proposed control concept and show that a low mains current total harmonic distortion of 1.4% can be achieved for such ultrahigh switching frequency converters. [ABSTRACT FROM AUTHOR]

Highlights an article which focuses on an analysis of the conduction losses of power metal oxide semiconductor field effect transistors (MOSFETs) using three-phase voltage direct current-link pulsewidth modulation (PWM) converter systems. What the on-state resistance power of MOSFET is influenced by; Calculation of on-state power losses for constant on resistance; Information on conduction losses for current-dependent on-state resistance.