Capacitor voltage ripple and capacitance evaluation in a direct three-phase to single-phase ac/ac MMC

This paper introduces the capacitor current and voltage ripple evaluation of a direct three-phase to single-phase ac/ac modular multilevel converter with full-bridge sub-modules. Based on a desired sub-module capacitor voltage ripple, the required capacitance is calculated, which is valuable to dimension sub-modules’ energy storage in many applications. Simulations and measurements using a scaled-down prototype validate the analysis

Switching Loss Reduction for an MMC-Fed AC/DC Converter

Medium-voltage connected ultra-fast chargers are getting more popular for charging electric vehicles with large battery capacities. Here, the solution based on a modular multilevel converter is more promising, since the isolation stage can be realized as a single medium-frequency transformer interconnecting the modular multilevel converter to a single-phase ac/dc converter. A new operating scheme is proposed for this converter, enabling zero-voltage switching and nearly zero-current switching across the entire load range. In contrast to the conventional phase-shift control method, the proposed scheme effectively reduces the reactive power through the ac/dc converter, leading to decreased turn-off switching losses in the ac/dc converter and a lower RMS current stress in the power path. A control scheme, integrating the operating principle, is developed for the modular multilevel converter. The method is verified through simulation and measurements on a scaled-down prototype. The results validate the theoretical analysis and practical feasibility of the proposed operating principle and the developed control scheme

Extended operating region of modular multilevel converters using full-bridge sub-modules

This paper presents an application of modular multilevel converters to remove line-frequency transformers from ultrafast charging stations, reducing cost and volume. The converter analysis with full-bridge sub-modules enables an operating region, that converts a medium-voltage grid into a lower voltage DC-bus, ideal for charging batteries rapidly

Candidates of motor drives for 48V automotive applications

Abstract-In automotive systems, reliability and cost are paramount for the success of electrical drive systems. Considering the interior permanent magnet motor, the cost of the rareearth permanent magnet is becoming a big concern. In this paper, the switched reluctance motor, variable flux reluctance motor and synchronous reluctance motor are analyzed and compared as candidates for the 48V automotive applications. A recommendation is given for the selection of the motor drives

Auto-Tuning Control of a Switched-Mode Power Converter for Tailored Pulse-Shape Biased Plasma Etching Applications

For reaching a high selectivity in plasma etching, it is required to precisely control the plasma ion energy. This can be realized by applying a tailored pulse-shaped voltage waveform to bias the reactor table. The bias waveform is divided into an etching phase and discharge phase, based on the status of the plasma reactor. During the etching phase, the waveform is a negative voltage slope while during the discharge phase, the waveform is a short positive voltage pulse. Recent research has shown that switched-mode power converters can be used to generate this kind of bias waveform. To obtain a narrow ion energy distribution, the voltage slope rate during the etching phase should be accurately tuned. Traditionally, the voltage slope rate is tuned manually by finding the optimal ion energy distribution from the measurements by a retarding field energy analyzer. However, measurements using a retarding field energy analyzer is interactive with the plasma thus affecting the etching process. On the other hand, the manual-tuning is inefficient since iterative retuning is required if the operating condition is changed. In this paper, an auto-tuning method is proposed, which enables the power converter to generate the optimal waveform automatically. The control method is fully based on the measurements of voltage and current waveforms on the converter side. Therefore, it is nonintrusive and does not interact with the plasma etching process

Closed-Form Spectral Computation of Intermodulation Distortion for Shunt-Based Current Measurements

This work presents a closed-form analytic approach to calculate the distortion introduced in resistive current measurements due to thermal properties of shunt resistors. As a shunt’s resistance varies with temperature, the sensed voltage becomes distorted. This non-linear effect depends on the thermal interface, dissipated power and material properties of the shunt resistor. It is presented, how to simplify the non-linear equation of the shunt temperature and calculate the resulting voltage spectrum, without the use of computationally extensive time-to-frequency-domain transforms. The results of the presented method match simulations including the non-linear behaviour, enabling a quick search through a solution space. The method is experimentally verified by use of a linear amplifier with an output distortion of −90 dB at low frequencies. In the experiment, a total harmonic distortion of up to −70 dB is observed in several shunt resistors covering a range of different thermal properties. Based on the presented method, shunt resistors can be chosen according to the minimum distortion required in a given application. Depending on the frequencies of interest, shunt resistors with a high temperature coefficient might still offer sufficient distortion performance

Spectral Steady-State Analysis of Inverters With Temperature-Dependent Losses Using Harmonic Balance

Accurate calculation of semiconductor losses and temperature is the foundation of any design methodology for a power electronic converter. Computation accuracy and speed play a vital role if a large set of parameters needs to be considered. Averaged loss models often neglect the temperature dependence of transistors, leading to fast, but inaccurate results. In contrast, iterative methods and simulation tools, which can include temperature dependence, take significantly longer to compute, but yield more precise results. This paper presents a best of both worlds approach, by using the harmonic balance method to obtain the steady-state solution for any inverter topology including temperature dependent conduction and switching losses. The proposed method solves for the discrete Fourier series of the device temperature, by expressing the temperature dependence and operating parameters in the frequency domain. The set of equations for each coefficient is solved by a single matrix inversion, resulting in very fast computation for steady-state temperature cycles. The steady-state operation of over one thousand possible inverter designs is calculated within less than one minute, matching iterative simulation in device temperature, conduction and switching losses, at a fraction of the computation time. In addition, the method shows good agreement with temperature measurements of a three-phase silicon-carbide inverter

Accurate Ion Energy Control in Plasma Processing by Switched-Mode Power Converter

Plasma processing, such as plasma deposition and etching, requires accurate control of the plasma ion energy. It can be realized by biasing the reactor table with a tailored voltage waveform. Switched-mode power converters can be used to generate the tailored waveforms. Since the plasma reactor is capacitive, it forms an LC circuit with the stray inductance in the loop, which could cause severe resonances to the output waveform. In order to accurately control the ion energy, a smooth tailored voltage waveform is required. In this research, a trajectory control method is introduced based on the equivalent electric circuit model of the plasma reactor. The control method is able to deliver a well-defined output waveform by controlling the switching sequence properly, rather than using passive and dissipative resistive damping

A three-level three-phase dual active bridge DC-DC converter with a star-delta connected transformer

This paper investigates a three-level three-phase Dual Active Bridge (DAB) dc-dc converter with a star-delta connected transformer. The soft-switching region is analyzed for two and three-level operation, using symmetrical voltage waveforms, showing an increased ZVS range for three-level operation. A large number of switching modes are identified and are modeled with piecewise-linear equations. To facilitate a practical implementation of a controller, a modulation strategy is proposed that results in a Zero Voltage Switching (ZVS) operation and relies on analytical equations, using a small amount of switching modes, while obtaining close-to-minimal rms currents. The ZVS range and the proposed control strategy are supported by measurements obtained from an experimental setup

A real-time control system architecture for industrial power amplifiers

Power amplifiers are a highly important component in a range of industrial applications, such as, servo-drives, magnetic resonance imaging, energy systems, and audio. The control system for power amplifiers should satisfy a range of requirements, e. g., offset free tracking, stability margins, and fast transient response. The intrinsic switching behaviour of modern power amplifiers and the sampled nature of digital control systems represent additional design challenges. This paper presents a complete development cycle for a cascaded digital control system for an industrial current amplifier. The inner control loop contains an optimal state-feedback controller and observer to ensure fast transient response. To guarantee reference-to-output frequency-domain specifications an outer control-loop is designed. Lastly, a rate-limiter is added to prevent clamping in the control input and overstress of the amplifier components. A special attention is given to synchronization in between sub-assemblies of the control system within the FPGA implementation. The paper concludes with the real-time measurements and comparison with the original control systems of the industrial amplifier