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Current-controlled LCL-filtered inverters are usually paralleled together for interconnecting the renewable energy resources into the grid. When the inverter output impedance is not well designed, the harmonic circulating currents out of the control bandwidth may be easily aroused. To reveal this resonant phenomenon and to enhance the stability of the parallel system, this paper builds the parallel...
This paper describes a method to provide LV four-wire three-phase power converters with the capability of correcting unbalance as an ancillary service to the main role that they play in the distribution system (distributed generator, energy storage system, drive, etc). Typically, dedicated grid/load current sensors are needed to effectively comply with unbalance compensation tasks, increasing system...
The increasing use of grid-connected inverters to connect renewable energy sources to a power grid will have globally important effect on grid performance. A mismatch between the grid and inverter impedance may cause harmonic resonances, which can lead to instability of the grid and disruption of inverter operation. The grid dynamics vary over time, so the inverter should adapt to the varying conditions...
As the penetration of renewable energy sources (RES) increases, variation of system impedance seen from grid-connected converters becomes much larger than expected. In this situation, stable operation of converter becomes more challenging. One of the issues caused by system impedance is resonance harmonic problem. Typically active damping control is used and designed based on the known conditions...
In DC microgrids, constant power loads (CPLs) would lead to a destabilizing effect that may cause the main bus voltage oscillation. Hence, most researcher are exploring the stabilization methods for DC/DC buck converters feeding CPLs. In practical applications, buck converters are always cascaded with LC input filters to prevent the switching harmonics from returning into the source. With the addition...
The proportional power sharing has been identified as an important issue to guarantee reliability on the operation of low voltage AC-Microgrids. However, inaccurate reactive power sharing in scenarios with line impedance mismatches, and slow transient response remain important limitations of most of the conventional power sharing controllers. In this context, an improved method for power sharing control...
A battery-free power management circuit (PMC) for an impact-type piezoelectric energy harvester for micro wind is presented in this paper. As the energy generated by micro wind is intermittent, sleep mode is adopted for the PMC to save power. A new energy sensing circuit is designed to detect the energy level generated by the piezoelectric cantilever and then to control the operation modes, sleep...
Ultra sparse matrix converter(USMC) is a derived form of Indirect matrix converter(IMC) having less no of switches. Though it has unidirectional power flow capability it is very useful for specific applications such as wind energy systems, electrohydrostatic actuator, variable speed drives etc. However its main limitation is lower gain for which various control strategies and topological changes had...
Efficiency of induction machines can be determined using international efficiency test standards such as the IEEE standard 112, IEC 60034-2-1 and JEC 37. The methods presented in these standards involve tests such as the no-load test, lock rotor test and a dynamometer test. Performing the no-load test is simple with fewer requirements in terms of equipment. The dynamometer test and the locked rotor...
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...
A sub-harmonic mixer in hybrid technology is reported in this paper. Flip chip Schottky diode pairs are used as nonlinear elements. A novel solutions with split stubs is used for improving both W-band and LO signals' confinement near diode terminals. The design is validated with mixer structures of good dynamic range and similar conversion loss over 90–100 GHz band.
Applying RF circuit design techniques to dc-dc power conversion has pushed the switching frequency of power converters using discrete components beyond 100 MHz. This paper proposes a simple solution to implement synchronous rectification for resonant dc-dc power converters operating in the Very-High-Frequency (VHF) range, by using a symmetric bandpass matching network between the inverter and rectifier...
The stability analysis of multi-stage DC-DC converters system is a big challenge, since the interaction among the individual converters can lead to an instability of the whole system. This paper applied the stability analysis method based on Floquet theory for a three-stage DC-DC converters system. In this paper, the stability analysis method based on Floquet theory is reviewed at the beginning. Following,...
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...
With silicon carbide (SiC) MOSFETs becoming commercial available, high switching frequency is a prevailing trend to increase the power density and efficiency in power converters. Nevertheless, the device performance is critically determined by the values of parasitic inductances, where negative effects such as switching oscillations are usually presented. It is more likely troublesome for power modules...
This paper introduces a single-stage isolated 48V-to-1.8V point-of-load converter based on the impedance control network (ICN) resonant converter architecture. This point-of-load ICN converter achieves large step-down while maintaining high efficiency across a wide range of input voltage and output power. Large step-down is achieved through a combination of stacked inverters, a transformer and a resonant...
The grid inductance is a sensitive parameter to be considered in order not to degrade the control system performance and to guarantee the system stability. In this paper, the Grid Inductance estimation based on Generalized Integrators (GIGI) method is proposed. It carries out an online grid inductance detection, which disturbs the grid by injecting a time-limited and small-amplitude harmonic voltage...
Due to the high switching speed of SiC MOSFET, the parasitic parameters and the low damping in the circuit, the turn-off overvoltage and oscillation of the freewheeling diode and SiC MOSFET are very severe. Based on the terminal impedances during the turn-off transition of the freewheeling diode and SiC MOSFET, the mechanism of the turn-off overvoltage and oscillation are analyzed and the suppressing...
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...
Solid state transformers (SSTs) include dc subsystems to enable plug-and-play support of dc loads, generation sources, and energy storage. Dual active bridge (DAB) converters are a suitable topology for both the primary energy conversion and load interface applications in an SST. This study considers an SST that uses DAB converters for both applications, and describes a method of generating a full...
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