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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....
In multi-bus islanded microgrids, the power quality requirements for different areas and buses can be different. This paper proposes a hierarchical control to realize optimal unbalance compensation for satisfying the power quality requirements in different areas. Primary and secondary controllers are applied to realize unbalance compensation for critical bus (CB) and at the same time, to make distributed...
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...
This paper proposes a hierarchical control strategy that achieves the power management and coordinated control of grid-connected DC microgrids. The proposed control architecture consists of two levels. In the primary control level, State-of-charge (SOC) based droop control is applied to the interfacing converters of storage elements (SE). The droop slope is adjusted according to individual SOC, aiming...
Transformer-less string PV inverter is getting more and more widely utilized due to its higher efficiency, smaller volume and weight. However, without the galvanic isolation, the leakage current limitation and operation safety became the key issues of transformer-less inverters. This paper simplifies the leakage current generation circuit model and presents a leakage current estimation method both...
In islanded microgrids, the existence of nonlinear electric loads may cause voltage distortion and affect the performance of power quality sensitive equipment. Thanks to the prevalent utilization of interfacing power electronic devices and information/communication technologies, distributed generators can be employed as compensators to enhance the power quality on consumer side. However, conventional...
In islanded microgrids (MG), distributed generators (DG) can be employed as distributed compensators for improving the power quality in consumer side. A multi-level hierarchical control is usually applied with each level dealing with different issues. In case of voltage unbalance compensation, droop control and virtual impedance can be applied in primary control to help the basic active and reactive...
In microgrids, the distributed generators (DG) can be used as distributed compensators so as to compensate the voltage unbalances in the critical bus. However, the power quality disturbance in generator sides and local buses may be affected and exceeds the limit. It can be more convenient to implement tertiary control so as to adjust the compensation efforts among DGs and ensure the acceptable power...
In this paper, a decentralized control for coordinate both active and reactive powers is proposed for islanded microgrids. Compared with the conventional droop control strategies, the proposed control realizes decentralized power distribution among renewable energy sources (RES) and energy storage systems (ESS) according to the local source conditions. Based on bus-signaling method, the ESS is able...
This paper proposes an autonomous active and reactive power distribution strategy that can be applied directly on current control mode (CCM) inverters, being compatible as well with conventional droop-controlled voltage control mode (VCM) converters. In a microgrid, since renewable energy sources (RES) units regulate different active power, the proposed reactive power distribution is adaptively controlled...
In order to achieve desirable power quality in the critical bus (CB) in microgrids, primary and secondary control can be used to realize unbalance compensation and at the same time, to make distributed generators (DGs) share the compensation efforts. Considering that the power quality requirements in different areas and for different consumers can be different, this paper implements a tertiary control...
This paper proposes a secondary voltage unbalance control approach that compensate voltage unbalances in three-phase four-wire islanded microgrid systems. It is implemented in the secondary control level of the microgrid hierarchical control structure. By sending information through low-bandwidth communication links to the primary control level, the required unbalanced factors at sensitive buses are...
This paper addresses control and analysis of droop and reverse droop control for distributed generations (DG). The droop control is well known applied to the voltage control mode (VCM) DG units, but has limitation when implemented on the current control mode (CCM) units. Therefore, this paper gives a more complete primary control for DG systems that integrates with both VCM and CCM units. The power...
In this paper, a distributed coordinated control scheme based on frequency-bus-signaling (FBS) method for a low-voltage AC three phase microgrid is proposed. The control scheme is composed by two levels. Firstly a primary local control which is different for the DGs and the ESS is proposed. The ESS adopts FBS control which is based on changing slightly the bus frequency in the microgrid when the state-of-charge...
In a flexible microgrid, the power regulation of each electronic-converter-based unit should be not only determined by the load demand, but also controlled according to the power and energy available in each unit. This paper proposes a coordinated control strategy in which each unit can operate in different operation modes taking into account the resource limitation. Firstly, a Primary-Frequency-Signaling...
With the individual capacity of wind power generation system increasing, the demand for high power grid-connected converters is growing, which is usually limited by the available semiconductor technology. One solution is multiple lower power units connected in parallel. LCL filters can provide much better ripple and harmonic attenuation. Therefore, they are more suitable for high power conversion...
Given the characteristics of MW-level direct-drive permanent magnet synchronous generator (PMSG), a simple sensorless low-pass-filter-compensation-integrator (LPFCI)-based rotor flux position estimation control method is proposed. Its implementation principle is introduced in detail. Furthermore, saturation feedback double integrator based on coordinate transform (SFDICT) and LPFCI are discussed in...
Ultra-high-frequency radio frequency identification (RFID UHF) vehicle license plate is a promising technology for traffic management because of its special advantages. In practical applications, the reading effect is closely related to the vehicle velocity. This paper analyzed the effective vehicle velocity for the steadily reading of the UHF RFID vehicle license plate. The smallest time for one...
With the individual capacity of wind power generation system increasing, the demand for high power grid-connected converters is growing, which is usually limited by the available semiconductor technology. One solution is multiple lower power units connected in parallel. In this paper, direct parallel and interleaved parallel are analyzed and compared. Then it focuses on two parallel interleaved converters...
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