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In large power electronic systems like a wind farm, the mutual interactions between the control systems of the power converters can lead to various stability and power quality problems. In order to predict the system dynamic behavior, this paper presents an approach to model a wind farm as a Multi-Input Multi-Output (MIMO) dynamic system, where the current control loops with Phase-Locked Loops (PLLs)...
This paper examines the accuracy of the zero-order hold (ZOH) model of the digital pulsewidth modulator (DPWM). The influence of the computational delay on the precision of this equivalent DPWM model is discussed in detail. A compensation method is proposed to compensate the deviation of this DPWM model for accurately calculating the stability region with different computational delay and duty-cycle...
Brushless doubly-fed induction generator (BDFIG) is a new type of ac induction machine and can be used for both grid-connected and stand-alone power generation. The conventional control methods for the BDFIG almost all rely on the encoder, which brings many limitations in terms of cost, complexity, reliability, and so on. This paper presents a new rotor speed observer (RSO) for the encoderless operation...
Z-source inverters (ZSIs), compared to the conventional two-stage architecture, embrace some interesting features, like the reduced size and complexity of the entire conversion system. Many research activities have been established to improve the performance of the so-called ZSI since it has been proposed in 2003, and several modifications have been introduced since then. These modifications include...
A major drawback of the NPC inverter is an unequal power loss distribution among the power devices which leads to unequal temperature stress among them. Therefore, certain power devices experience higher temperature stress, which is the main cause of power device module failure and thus both the power rating and lifetime of the NPC inverter are limited by the most stressed devices. In this paper,...
Reliability of dc-link capacitors in modern design of power electronic converters is an important aspect that needs to be considered. The requirement of applying condition monitoring for health status estimation in many reliability-critical applications have been a focused demand. The existing capacitor condition monitoring methodologies are suffering from shortcomings such as, low estimation accuracy,...
Harmonic and interharmonic distortions are considered as the main power quality issues especially in the distribution networks. The double-stage Adjustable Speed Drives (ASDs) in which the front-end diode rectifier is connected to a rear-end inverter through an intermediate DC-link filter may inject significant amount of harmonics and interharmonics into the grid and consequently degrade the grid...
Aalborg Inverter is a kind of high efficient Buck-Boost inverter. Since it may work in “Buck-Boost” mode, the control bandwidth should be high enough to ensure a good performance under any grid condition. However, during the “Boost” operation, the control bandwidth depends much on the grid impedance if the crossover frequency is traditionally chosen lower than the characteristic frequency of system...
A short-circuit fault protection strategy based on the direction of bus-side capacitor discharge current for a high-surety power supply, known as Super Uninterruptable Power Supply (Super UPS), is studied in this paper. It consists of multiple energy sources and storage components. All energy sources and storage components are connected to a common DC bus through converters in the system. If a short-circuit...
DC-link capacitor is one of the reliability-critical components in motor drive applications, which contributes to a considerable cost, size and failure. Its reliability performance depends on both inherent physical strength and external loading. The grid unbalances could alter the electro-thermal stresses of key components in a motor drive. Therefore, this paper investigates the impact of grid voltage...
Power cycling in semiconductor modules contributes to repetitive thermal-mechanical stresses, which in return accumulate as fatigue on the devices, and challenge the lifetime. Typically, lifetime models are expressed in number-of-cycles, within which the device can operate without failures under predefined conditions. In these lifetime models, thermal stresses (e.g., junction temperature variations)...
Due to the continuous demands for highly reliable and cost-effective power conversion, the quantified reliability performances of the power electronics converter are becoming emerging needs. The existing reliability modelling approaches for the power electronics converter mainly focuses on the predictions of lifetime, accumulated damage, constant failure rate or Mean-Time-To-Failure (MTTF), while...
In order to enable a more wide-scale utilization of PV systems, the cost of PV energy has to be comparable with other energy sources. Oversizing the PV array is one common approach to reduce the cost of PV energy, since it increases the PV energy yield during low solar irradiance conditions. However, oversizing the PV array will increase the loading of PV inverters, which may have undesired influence...
Problems with power quality in the grid have gained a lot of attention recently due to rapid increase in the amount of grid-connected power converters. The converter should produce sinusoidal currents also during abnormal conditions, such as unbalanced grid voltages. Several methods, like the delayed signal cancellation-based method (DSC), have been proposed to alleviate the detrimental effect of...
A highly accelerated power cycling test platform using current source converter for SiC-MOSFET power modules is proposed. The control principles of delta and average junction temperatures are introduced. By using isolated thermal fibers, the junction temperature (Tj) variations can be monitored during the test process without removal of silicone gel. The power module is tested in the conditions of...
Recently, an LCL-filter-based dual “Buck-Boost” AC/DC converter for DC Nano-grid with three terminal outputs was proposed. Since it is a high order filter based single-phase converter, a RC damper is adopted to keep the system stable. This converter has two work modes: “Boost” and “Buck”. During the “Buck” mode, the control-to-grid current transfer function of this dual “Buck-Boost” AC/DC converter...
Today's three-phase Adjustable Speed Drive (ASD) systems still employ Diode Rectifiers (DRs) and Silicon-Controlled Rectifiers (SCRs) as the front-end converters due to structural and control simplicity, small volume, low cost, and high reliability. However, the uncontrollable DRs and phase-controllable SCRs bring side-effects by injecting high harmonics to the grid, which will degrade the system...
The LCL-type grid connected inverter has been widely used as the intelligent power interface between the distributed generation unit and the power grid. To reduce the cost and volume of the filter, it is desirable to design the LCL filter with higher resonance frequency provided that the quality of injected grid current is not compromised. Actually, it is the typical case for the T-type or NPC three-level...
Junction temperature is of great importance to safe operating area of IGBT modules. Various information of the IGBT operating state is reflected on electrical characteristics during turn-on transient. A unified extraction method for internal junction temperature via dynamic thermo-sensitive electrical parameters (DTSEP) during turn-on transient is proposed. Two DTSEP, turn-on delay time (tdon) and...
For a converter using the digital processor for control system, the digital time delay is a main reason to reduce the system bandwidth, leading to a relatively slow dynamic or even unstable operation. To alleviate the negative impacts of digital delays, numerous time delay compensation methods have been developed, of which the model-free schemes are independent to model accuracy whereas the model-based...
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