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A high step-up switched-capacitor based converter is proposed in this paper. The proposed converter features high conversion ratio, low voltage stress and continuous input current, which makes it very suitable for renewable energy applications like photovoltaic systems. More importantly, the proposed switched-capacitor cells in series with converter can be generalized in two ways, resulting in dc-dc...
For a grid-connected Voltage-Source Converter (VSC), dynamics of the grid synchronization plays an important role in affecting the converter performances and stability. Due to its significance, this paper gives a comparative analysis about some basic grid synchronization schemes, through viewpoint of dynamic performances, which appeared as the impacts of voltage perturbation on the estimated angle...
Voltage-sensorless control has been investigated for Voltage Source Inverters (VSIs) for many years due to the reduced system cost and potentially improved system reliability. The VSI based Resistive Active Power Filters (R-APFs) are now widely used to prevent the harmonic resonance in power distribution network, for which the voltage sensors are needed in order to obtain the current reference. In...
This paper presents dynamic analysis of a Modular Multi-Parallel Rectifier (MMR) based on state-space modelling. The proposed topology is suitable for high power motor drive or multi-parallel AC-DC applications, which can reduce line current harmonics emissions significantly. However, a proper controller is required to share and control current through each rectifier. Mathematical analysis and simulations...
This paper addresses the harmonic current control for LCL-filtered Voltage-Source Converters (VSCs) connected to ultra-weak (high-impedance) grids. It is shown that the harmonic current controllers tend to be unstable as the Short-Circuit Ratio (SCR) of the system reduces. An active stabilizing control scheme is thus proposed by feeding back the filter capacitor voltage and the converter-side current...
Static Synchronous Compensators (STATCOMs) are being applied for offshore wind power plants to satisfy the grid codes under both normal operation and grid fault conditions. This paper investigates the performances of Modular Multilevel Cascade Converters (MMCC) for the STATCOM application, with special focus is on asymmetrical Low-Voltage-Ride-Through (LVRT) operation under grid faults. The design...
Single-phase grid-connected inverters with LCL filter are widely used to connect photovoltaic systems to the utility grid. Among the existing control schemes, predictive control methods are faster and more accurate but also more complicated to implement. Recently, the Model Predictive Control (MPC) algorithm for single-phase inverter has been presented, where the algorithm implementation is straightforward...
Due to the parasitic capacitances of the transformer and inductor in Dual Active Bridge (DAB) converters, resonance happens in the transformer currents. This high frequency resonant current flowing into the full bridges will worsen their soft-switching performance and thereby reduce its efficiency. In order to study the generation mechanism of this current resonance, the impedance of the transformer...
To help mitigate some of the challenges associated with the wide spread adoption of the stochastic wind power, wind turbine with full-scale power converter (Type D) is preferred. Since full power is processed by the power converter in a type D wind turbine, it is important to improve its efficiency and reduce the cost per kW to achieve lower cost of energy. The power produced by the wind turbine varies...
With the increasing penetration of wind power, reliable and cost-effective wind energy production are of more and more importance. As one of the promising configurations, the doubly-fed induction generator based partial-scale wind power converter is still dominating in the existing wind farms, and its reliability assessment is studied considering the annual wind profile. According to an electro-thermal...
In this paper, a separation test method for eliminating the effects of different current densities on the bond wires is proposed. The separation test method makes it possible to study the effect of different current density on the fatigue damage of bond wires without changing the temperature swing and average temperature during the test. By analyzing the output characteristics of the linear region...
High-stiffness servo system is easy to cause mechanical resonance in elastic coupling servo system. Although on-line adaptive notch filter is effective in most cases, it will lead to a severer resonance when resonance frequency deviated from the natural torsional frequency. To explain this phenomenon, an improved discrete system model is proposed. This paper quantitatively analyzes the influence of...
Nowadays capacity of the photovoltaic systems in the grid is remarkable and provides a major part of energy in the grid. Therefore, an abruption of these systems from the grid can create a damage to the grid. Unlike in the past that PV systems disconnected from the grid when a voltage drop occurred, nowadays these systems should have Low Voltage Ride-Through (LVRT) capability. The PV system should...
In this paper, magnetically-coupled impedance source (MCIS) three-phase four-switch inverters are introduced for renewable energy applications. This inverter utilizes two single-phase MCIS inverters to obtain a three-phase output, where less component-count is achieved in order to reduce the inverter volume. On the other hand, as a result of the reduced number of switches, the proposed inverter suffers...
In this paper, an eigenvalue-based harmonic stability analysis method for offshore wind farm is proposed. Considering the internal cable connection layout, a component connection method (CCM) is adopted to divide the system into individual blocks as current controller of converters, LCL filters, collection system cable impedance, transmission cable impedance and grid impedance. By using this method,...
In order to reduce the Common-Mode Voltage (CMV) in three-to-five phase indirect matrix converters, three improved Space Vector Pulse Width Modulation (SVPWM) methods are proposed and discussed. The improved modulation schemes are achieved by reorganizing zero vectors from the inversion stage to the rectification stage. The proposed methods can not only theoretically reduce the CMV peak value by up...
Multi-modular converters have proven to be one of the most suitable topology to be used in high and power applications. The modularity of these configurations offer several advantages, such as: high quality voltage, redundancy and high efficiency. In these converters, the series connection of modules increase the number of voltage levels, but also the floating voltage of modules with respect the neutral...
Grid voltage unbalance, which is considered as most common disturbance in distribution networks, may significantly affect the normal operation of the grid-connected power electronics devices including Adjustable Speed Drives (ASD), and may result in a remarkable performance degradation. In this paper, the main aim is to analyze the effects of the grid unbalanced voltage on the multi-unit three-phase...
For motor control applications, the speed loop performance is largely depended on the accuracy of speed feedback signal. M/T method, due to its high theoretical accuracy, is the most widely used in incremental encoder adopted speed measurement. However, the inherent encoder optical grating error and A/D conversion error make it hard to achieve theoretical speed measurement accuracy. In this paper,...
This paper presents a family of cost-effective magnetically-coupled impedance source inverters for renewable energy systems. The inverters are derived from magnetically-coupled impedance source networks, featuring low cost and no ground leakage current when used in PV system. The numbers of required semi-conductor switches is reduced. More important, the elimination of leakage currents makes it particularly...
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