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This paper presents the capacitor size reduction of a MMC-based transformer-less STATCOM for medium voltage ac distribution system. The instantaneous power swinging flows into the single-phase configuration results in a high capacitance needed; however, by accepting the swinging voltage in the capacitor, the capacitance can be drastically reduced. This paper analyzes the dimensional size reduction...
This paper proposes a methodology for characterization of medium voltage (MV), medium frequency (MF) rectifier diode valve. The intended application is for 10MW dc/dc converters used in DC offshore wind turbines. Sensitivity to semiconductor component parameter variation, snubber component tolerance, influence of temperature and stray capacitance are analyzed. It is concluded that the largest impact...
A synchronous variable reluctance machine (VRM) can work with either a grid connection or a capacitor bank, each would need to provide the machine with positive reactive power to counter the machine inductive coils. Simulation shows that synchronous Variable capacitance could improve the VRM power transfer, when working both as a generator and as a motor. A 3∼synchronous VRM was modelled and simulated...
The rms value of capacitor ripple current is one of the important parameters for capacitor selection in Modular Multilevel Converter (MMC) based medium voltage adjustable speed drives. In this paper, an expression for the rms value of ripple current of each submodule capacitor in MMC is derived analytically. The analysis reveals that like capacitor ripple voltage, the ripple current also increases...
This paper presents a novel design calculation scheme for low voltage Modular Multilevel Converters. One of the most important design values is to estimate the lifetime of the electrolytic cell capacitor. Therefore, a novel calculation method for the arm capacitor root mean square current is presented. Additionally, a new algorithm to estimate the power losses without a detailed simulation of the...
This paper suggests a current-fed double inductor push-pull converter for the use as a preamplifier stage of a constant current charger for HV capacitors. With this converter it is possible to offer a wide input voltage range for the use in mobile applications with a 24 V or a 48 V battery. A novel snubber technique for current-fed converters is introduced, so that transistor conduction losses can...
Silicon carbide (SiC) trench MOSFET half-bridge and full-bridge power modules with hybrid integrated gate drivers on aluminium nitride (AlN) substrate were designed with electro-thermal co-simulation and soldered on an aluminium heatsink, achieving 0.3 K/W junction-to-heatsink thermal resistance. A 2 kW single-stage PV-inverter with active energy-buffer was built around the modules, achieving a weighted...
In this paper, a dc series offshore wind farm with an onshore modular multilevel converter (MMC) is presented with consideration of different cable models. Normally, the dc cable is represented either by a small capacitance or by pi-sections, which implies that the frequency-dependent effects of the HVDC cable are neglected. One should be careful when using these cable models for high frequency simulations,...
This paper presents a systematic methodology for design and tuning of the controller of LCL grid-connected converters. The proposed approach is derived from the impedance/admittance stability formulation, which eases the controller modelling of LCL grid-connected systems. After system modelling, a modified sensitivity function is defined to analyze the closed loop dynamics. For practical development,...
A photovoltaic generator (PVG) is usually connected to a DC micro-grid via a multi-stage-step-up power converter to improve system modularity, minimise shading effects and boost PVG voltage. Under varying operating conditions, the nonlinear characteristics of a PVG may affect performance of the entire PVG system. Further, if these issues are not properly taken into account at the design stage, significant...
At inverter-fed traction drives stray currents due to parasitic capacitances in frequency converters and machine cause high frequency voltage components spreading into all conductive components of the drive system. These hf voltages are harmful and origin from the inverter side through fast switching power semiconductors with high levels of output voltage steepness. Additionally overvoltage at the...
Oscillations in power electronic circuits with fast switching semiconductors are commonly known and the corresponding parasitic elements have been investigated in multiple literature. However, this paper investigates the triggering of these electromagnetic interference (EMI)-critical oscillations. An analytical description is derived using a boost converter circuit. Based on this description an optimization...
A technique to actively balance the voltages on series-connected capacitors designated to split DC sources whose loads comprise power converters is presented. It performs such balancing dynamically, enabling the voltage equalization even for small capacitors under wide power and voltages ranges. Proposal consists on lightly controlling the power of one input capacitor for each pair, measuring their...
This paper proposes a method to mitigate the problems related to series arcing in low voltage dc (LVdc) micro-grids by performing voltage drop detection using the power electronic device at the load-side. Specifically, the selectivity of the designed series arc detection algorithm is shown for two constant power loads connected in parallel at the point of common coupling with a stable voltage dc micro-grid...
In this paper, the detection of insulated-gate bipolar transistors (IGBT) short-circuit failures based on the gate charge characteristic is investigated. The main focus are impacts of the parasitic inductances and the operating point on the gate charge characteristic, as well as limitations for this protection concept by this effects. An analogous detection circuit is developed and relevant implementation...
With the aim to solve the unbalanced thermal behavior in the modular multilevel converter, introduced by mismatch in the submodule parameters, a thermal balancing control strategy is proposed here. The proposed solution ensures a balanced junction temperature for the power devices, while the balance between the capacitor voltages is maintained.
Predicting semiconductor and inductor losses together with designing the EMC filter for grid feeding inverters requires great effort, when high and variable pulse frequencies and triangular current mode are applied. In this paper an effective method is proposed to quickly evaluate the effect of circuit and control strategy on losses and inverter size. With this approach the system is modeled using...
In operation of series-connected IGBTs a voltage balancing is necessary, during short circuits it is even more important. Within this paper the behavior of series-connected IGBTs and diodes during the short-circuit type 2 and 3 is analyzed. The dv/dt during the short circuit is determined by one of two equivalent circuit capacitances. One is the plasma capacitance and the second one is the Miller...
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