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Low-pass ac filters are frequently adopted in microgrid power electronic interfaces that convert distributed generators' dc power to ac power because most of today's distribution grids have ac voltages. Compared to a simple L filter, higher-order filters, such as LC or LCL filters, are preferred due to their more effective reduction of switching-frequency harmonics and smaller sizes. As the converter...
In this paper, design and implementation of a sinusoidal flux controller has been proposed for a core loss tester for eliminating the higher order harmonics from the flux passing through the core. The core loss test is performed with a toroidal transformer that consists of a main and sense windings wound on a toroidal core. The flux through the core is calculated with the numerical integration of...
This paper presents an active islanding detection method which has zero non-detection zone. This method is the advanced version of the conventional slip mode frequency shift islanding detection method (SMS IDM). In this method the parameters of SMS IDM change based on the local load impedance value. The parameters value are calibrated periodically by measuring the impedance of the local load. The...
This paper presents the stability analysis of a hybrid AC/DC power distribution system, for embedded applications, particularly for more electric aircraft. In the studied system, a balanced AC source supplies the hybrid system, and a DC distribution system feeds multi-converter controlled loads. The load converters are tightly controlled, behaving as constant power loads with low damped LC input filters...
Active Power Filters (APFs) are widely applied devices in the power quality field for control flexibility and effective attenuation of the harmonic, reactive and negative components of the grid current and voltage. As the interface connecting an APF with the grid, an LCL-filter is preferred over an L-filter for its smaller size and lower price. However, the LCL-filter is a third-order system and hence...
This paper proposes a general and an improved methodology for the design of the passive elements of Active Regenerative Rectifiers (ARR). The proposed strategy for the L-filter is based on the current area error in the time domain and on the high order current harmonics in the frequency domain. This strategy is independent of the type of control technique and it can be implemented for different modulation...
There has been a growing demand of using multi-function inverters for grid-connected systems applied to nonconventional energy sources, such as solar, wind and so on. In addition to power quality conditioning, the inverter can also be used for bidirectional active power exchange with a three-phase four-wire grid. Therefore, the inverter acts as a multi-function compensator. The functions of the proposed...
Ac transmission line emulator is the bridge to interconnect ac systems to fulfill the grid emulation function, where all the emulator elements such as generators, loads and lines are implemented by universal three-phase voltage source converters. In this paper, three design issues are addressed. First, the impact of ac voltage switching noise on the performance of a transmission line emulator in terms...
Repetitive control strategies have been commonly applied in pulse-width modulated (PWM) inverters for many industrial applications. The phase delay in the overall control system, e.g. the delay caused by the digital duty cycle calculation, PWM generation and the repetitive controller, has to be compensated by elaborately designed phase lead filters in order to prevent control performance deterioration...
In stand-alone brushless doubly fed generator (BDFG) based shaft power generation system, the output voltage of BDFG is strong influenced by the filter of load side converter (LSC) because of the coupling caused by the stator power winding leakage inductance. In order to eliminate the harmonic of the voltage, the LC-L filter based on the leakage inductance is put forward in this paper. The relationship...
In single-phase AC onboard chargers for electrified vehicles, second-order harmonic current and corresponding ripple voltage exist on the DC bus. The low-frequency harmonic current is normally filtered using a bulk capacitor or an additional active filter (AF) circuit. This presents an obstacle for improving the power density as well as reducing the cost. In this paper, a dual active bridge (DAB)-based...
Due to relatively low cost and flexible performance, Dynamic Capacitor (D-CAP) is often designed to implement dynamic reactive power compensation, whose output current might distort under the effects of background harmonic voltage from the grid or non-ideal PWM mode caused by non-linear switch characteristics. This paper presents a reactive power compensation control strategy with waveform quality...
This paper presents an adaptive dc-link voltage controller for the purpose of decreasing the operating dc-link voltage in a back-to-back converter system. An outer loop to control the maximum modulation (Mmax) index is added to the conventional dc-link voltage controller, and hence the system can online adapt its dc-link voltage reference based on the system operating state. Furthermore, the relationship...
This paper presents the analysis and control of a current imbalance compensator designed to eliminate upstream negative- and zero- sequence current components caused by single-phase loads in three-phase four-wire systems. The proposed compensator significantly reduces the fundamental-frequency current component in the neutral conductor and can potentially be used to eliminate harmonic currents. The...
Objective functions and constraints for electric losses and component volume are derived to gain an optimal design of a line filter for grid rectifiers with power factor correction (PFC). The gained characteristics described by these models are valid for coupled inductors with toroidal cores and conventional capacitors. A modified noise predicting technique for a Totem-Pole rectifier is then used...
This paper presents the performance evaluation under grid voltage sags of a two parallel-interleaved grid-connected converters employing low switching frequency. A current controller based on the synchronous reference frame including voltage feed-forward is used. The dominant frequency components from the direct- and quadrature-axis voltage Vd and Vq are eliminated by using an adaptive moving average...
An application of an input current harmonic filtering technology, namely power semiconductor filter (PSF), for conventional flyback AC/DC converter will be presented. By connecting a series-pass device (SPD) in series with the input of the flyback converter, the input current of the entire system has the waveform profiled to be in phase with the supply voltage and its magnitude adjusted to perform...
CRM Boost PFC converter features zero-current turn-on for the switch and no reverse recovery in diode. However, its switching frequency varies over a wide range, which leads to the efficiency deterioration and the EMI filter design complexity. In this paper, a minimum switching frequency variation range control (MFVC) strategy is proposed by injecting the optimal 3rd harmonic into the input current...
This paper proposes a novel ac-to-dc adaptor circuit with ultra-high power density and efficiency, which is based on a two-stage topology, consists of a bridgeless boost converter followed by a LLC converter. The bridgeless boost converter is in charge of regulating output voltage and minimizing bulk capacitor, while the LLC converter is operated as a dc transformer (DCX) and plays a role of providing...
For grid-connected LCL-filtered inverters, recent applications often observe a weak grid at the point of common coupling (PCC) with non-negligible grid impedance. In this case, the previous control methods would perform poor or even cause the inverter protection. Especially when the feedforward of PCC voltage is designed to suppress grid current harmonics, phase and gain margins will be largely reduced...
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