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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...
The boost inverter can be an alternative grid interfacing power converter for renewable energy sources since it can generate an AC voltage whose peak value could be greater than the DC voltage. When it connects to the grid, high quality output current is required, therefore, grid current is hoped to be controlled directly. A novel control strategy to control grid current with only one closed control...
The grid-voltage unbalance can result in a double-frequency component in the output power of a three-phase grid-connected converter, which significantly degrades the system performance. To address this issue, the power decoupling concept, which was previously developed for the single-phase system to handle the double-frequency power oscillation, is applied to the three-phase system in this paper....
Due to the low inductance of an LCL-filter, the grid current generated by an LCL-filtered Voltage Source Inverter (VSI) is sensitive to low-order grid-voltage harmonics. This issue is especially tough for the control system with Inverter Current Feedback (ICF), because the grid-current harmonics can freely flow into the filter capacitor without control. To cope with this issue, this paper develops...
The output currents of high power Voltage Source Inverters (VSIs) are distorted by the switching harmonics and the backgroud harmonics in the grid voltage. In this paper, a hybrid power conversion system composed of a high power VSI with low switching frequency and an auxiliary series LC filtered VSI is proposed. The auxiliary VSI compensates both the switching harmonics of the high power VSI and...
In this paper a novel droop approach for power management in low voltage dc MicroGrids (MGs) based on a master-slave concept is presented. A virtual frequency is injected by a master unit, which is proportional to its output power. Other slave units determine their output power according to the corresponding frequency based droop characteristics. Unlike the dc voltage-droop methods, the proposed virtual...
Due to the simplicity and flexibility of the structure of the Second-Order Generalized Integrator based Quadrature Signal Generator (SOGI-QSG), it has been widely used over the past decade for many applications such as frequency estimation, grid synchronization, and harmonic extraction. However, the SOGI-QSG will produce errors when its input signal contains a dc component or harmonic components with...
Second-Order Generalized Integrator based Quadrature Signal Generator (SOGI-QSG) has been widely used in single-or three-phase power converter systems due to its simplicity and flexibility. However, its dynamic response is not only decided by its damping gain but also influenced by the input-signal parameters, especially when a fast response is required for usages such as grid synchronization. As...
Passive trap filters are widely used in high power Voltage Source Inverters (VSI) for the switching harmonic attenuation. The usage of the passive trap filters requires clustered and fixed switching harmonic spectrum, which is not the case for low pulse-ratio or Variable Switching Frequency (VSF) Pulse Width Modulation (PWM). Switching harmonic compensating using auxiliary power converters has been...
In this paper the effect of secondary controller on voltage regulation in dc Micro-Grids (MGs) is studied. Basically, centralized or decentralized secondary controller has been employed to regulate the voltage drop raised by the primary controller. However, in the case of high capacity MGs and long feeders with much voltage drop on the line resistances, the conventional methods may not guarantee the...
This paper proposes a unified impedance model for analyzing the effect of Phase-Locked Loop (PLL) on the stability of grid-connected voltage-source converters. In the approach, the dq-frame impedance model is transformed into the stationary αβ-frame by means of complex transfer functions and complex space vectors, which not only predicts the stability impact of the PLL, but reveals also its frequency...
Evaluation of modulation techniques for neutral-point-clamped inverters has been an extensively investigated theme. The conclusion at present is centered space vector modulation with phase-disposed carrier arrangement gives the best harmonic performance. This conclusion is however drawn at the inverter output terminals or with only a simple L-filter considered. It may therefore not be relevant for...
Active power decoupling now is commonly used in single phase converter for the purpose of replacing bulky electrolytic capacitors, which is usually install in dc side of inverter to mitigate the second harmonic ripple in the single-phase converter. One possible way is to using half-bridge and split dc capacitor to realize power decoupling, but the conventional power decoupling control scheme for this...
In this paper, a novel communication strategy called Power Talk is introduced to realize the power line communication among the Voltage Source Converters (VSC) of DC MicroGrids (MGs). Each VSC transmits information by changing the control parameters, and receives information by observing the local output power. By using common coding schemes, which transform the DC MGs in some familiar communication...
This paper introduces a new single-switch nonisolated dc-dc converter with very high voltage transfer ratio and reduced semiconductor voltage stress. The converter utilizes an integrated autotransformer and a coupled inductor on the same core to achieve a high step-up voltage gain without extreme duty cycle. Further, an integrated passive regenerative circuit recycles the leakage energy of the coupled...
This paper analyzes first the stability of single-loop digital voltage control scheme for the LC-filtered voltage source inverters. It turns out that the phase lag, caused by the time delay of digital control system and by the use of integral controller, can stabilize the voltage loop without damping of LC-filter resonance. The stability regions are then identified with alternative voltage controller...
The Second-Order Generalized Integrator (SOGI) was used as a building block for the SOGI-Quadrature-Signal Generator (SOGI-QSG) which has been widely used for grid synchronization, frequency estimation, and harmonic extraction over the past decade. This paper further investigates its integration and differentiation characteristics, with four new integrators and differentiators proposed. Theoretical...
Traditional droop-controlled systems assume that the generators are able to provide sufficient power as required. This is however not always true, especially in renewable systems, where the energy sources (e.g., photovoltaic source) may not be able to provide enough power (or even loss of power generation) due to the intermittency. In that case, unbalance in active power generation may occur among...
It is very important to estimate flux accurately in implementing high-performance control of AC motors. Theoretical analysis has been made to illustrate the performance of the pure-integration-based and the Low-Pass Filter (LPF) based flux estimators. A novel flux estimator based on Second-Order General Integrator (SOGI) with Frequency Locked-Loop (FLL) is investigated in this paper for induction...
Adjustable Speed Drives (ASDs) based on double-stage conversion systems may inject interharmonics distortion into the grid, other than the well-known characteristic harmonic components. The problems created by interharmonics make it necessary to find their precise sources, and, to adopt an appropriate strategy for minimizing their effects. This paper investigates the ASD s input current interharmonic...
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