Droop control is a well-known strategy for the parallel operation of inverters. However, the droop control strategy changes its form for inverters with different types of output impedance, and so ...far, it is impossible to operate inverters with inductive and capacitive output impedances in parallel. In this paper, it is shown that there exists a universal droop control principle for inverters with output impedance having a phase angle between -(π/2) rad and (π/2) rad. It takes the form of the droop control for inverters with resistive output impedance (R-inverters). Hence, the robust droop controller recently proposed in the literature for R-inverters actually provides one way to implement such a universal droop controller that can be applied to all practical inverters without the need of knowing the impedance angle. The small-signal stability of an inverter equipped with the universal droop controller is analyzed, and it is shown to be stable when the phase angle of the output impedance changes from -(π/2) rad to (π/2) rad. Both real-time simulation results and experimental results from a test rig consisting of an R-inverter, an L-inverter, and a C-inverter operated in parallel are presented to validate the proposed strategy.
Conventional droop control methods cannot achieve accurate proportional reactive power sharing, due to the mismatch of components, system disturbances, etc. In this paper, an uncertainty and ...disturbance estimator (UDE)-based robust droop controller is proposed to address these problems. As a result, the model nonlinearity and uncertainty (e.g., power angle and uncertain output impedance) and system disturbances (e.g., variations of output impedance, load change, and fluctuating dc-link voltage) can be estimated and compensated. Experimental results from a single-phase system with two inverters are provided to demonstrate the effectiveness of the proposed strategy. In order to further demonstrate the advantage and flexibility of the proposed UDE-based control strategy, simulation results from a three-phase system with two inverters are presented with comparison to a robust droop control strategy reported.
Simulating and Mitigating Crosstalk Winick, Adam; Wallman, Joel J.; Emerson, Joseph
Physical review letters,
06/2021, Letnik:
126, Številka:
23
Journal Article
Recenzirano
Odprti dostop
We describe an efficient and scalable framework for modeling crosstalk effects on quantum information processors. By applying optimal control techniques, we show how to tune-up arbitrary ...high-fidelity parallel operations on systems with substantial local and nonlocal crosstalk. As an example, we simulate a 2D square array of 100 superconducting transmon qubits. These results suggest that rather than striving to engineer away undesirable interactions during fabrication, we can largely mitigate such effects with software through careful characterization and control optimization.
Abstract
The power distribution of inverters in parallel operation is uneven due to the difference in line impedance. In this paper, the parallel operation of two inverters is taken as an example, ...the power distribution mechanism is derived and the relevant mathematical model is established, and the influencing factors of the parallel inverter power distribution are analyzed. Then, the virtual impedance is introduced based on the voltage and current double closed-loop of the photovoltaic inverter, and an improved strategy based on the virtual impedance is proposed. Finally, PLECS simulation proves the effectiveness of the proposed method.
Abstract
A virtual synchronous generator control strategy based on the power angle characteristics of synchronous generators is designed for the independent distributed generation system. The control ...strategy designed has good stability, and realizes the zero difference control of the virtual synchronous generator frequency. The virtual synchronous generators can coordinate the power output in real-time, and show good stability in single-machine operation and multiple parallel operations. Finally, the effectiveness of the designed control strategy is verified by Matlab/Simulink simulation.
We present a NAND-like spintronics memory (NAND-SPIN) device for high-density non-volatile memory applications. Fast erasing and programming of magnetic tunnel junction (MTJ) are implemented with two ...unidirectional currents generating spin orbit torque (SOT) and spin transfer torque (STT), respectively. The asymmetric switching drawback of STT mechanism can be definitively overcome as only anti-parallel to parallel operation happens for NAND-SPIN programming, which allows lower switching current, smaller access transistor, and reduced maximum write voltage across the MTJ. By sharing the SOT-induced erase operation in a nanowire, the area overhead due to the three-terminal structure can be also eliminated. Simulation results show that NAND-SPIN can achieve <inline-formula> <tex-math notation="LaTeX">\text {3}\sim \text {5}\times </tex-math></inline-formula> reduction in write energy compared to STT-MRAM, and <inline-formula> <tex-math notation="LaTeX">\text {2}\sim \text {4}\times </tex-math></inline-formula> less bit-cell area than SOT-MRAM at 28 nm node.
Based on the equivalent circuit model, the interactions of multi-parallel modular grid-tied inverters and their coupling effect with grid impedance are analyzed in this letter. The analysis shows ...that interactive instability could happen in the inverter system even when identical inverters have been used. However, if the control and circuit parameters are designed systematically, the system can be exempted from both common and interactive instability. The outcome of this research provides a practical general design paradigm for modular grid-tied inverters with inductor-capacitor-inductor ( LCL ) filters which can be used in the parallel operation with unknown number of modules. Experimental results are provided for verification.
In this paper, the inherent limitations of the conventional droop control scheme are revealed. It has been proven that parallel-operated inverters should have the same per-unit impedance in order for ...them to share the load accurately in proportion to their power ratings when the conventional droop control scheme is adopted. The droop controllers should also generate the same voltage set-point for the inverters. Both conditions are difficult to meet in practice, which results in errors in proportional load sharing. An improved droop controller is then proposed to achieve accurate proportional load sharing without meeting these two requirements and to reduce the load voltage drop due to the load effect and the droop effect. The load voltage can be maintained within the desired range around the rated value. The strategy is robust against numerical errors, disturbances, noises, feeder impedance, parameter drifts and component mismatches. The only sharing error, which is quantified in this paper, comes from the error in measuring the load voltage. When there are errors in the voltage measured, a fundamental tradeoff between the voltage drop and the sharing accuracy appears. It has also been explained that, in order to avoid errors in power sharing, the global settings of the rated voltage and frequency should be accurate. Experimental results are provided to verify the analysis and design.
AC and dc microgrids (MGs) are key elements for integrating renewable and distributed energy resources as well as distributed energy-storage systems. In the last several years, efforts toward the ...standardization of these MGs have been made. In this sense, this paper presents the hierarchical control derived from ISA-95 and electrical dispatching standards to endow smartness and flexibility to MGs. The hierarchical control proposed consists of three levels: 1) The primary control is based on the droop method, including an output-impedance virtual loop; 2) the secondary control allows the restoration of the deviations produced by the primary control; and 3) the tertiary control manages the power flow between the MG and the external electrical distribution system. Results from a hierarchical-controlled MG are provided to show the feasibility of the proposed approach.
This paper studies parallel operation of identical actuators cooperatively driving a common plant. The objective of the parallel operation is to regulate the output of the plant accurately while ...allowing the actuators to fairly share the input of the plant. To address the parallel operation problem, it is assumed that the plant and the actuators are modeled by general linear systems as opposed to the existing results. Further it is assumed that the controllers for the actuators share their local information with each other through communication. A feedback control law for each actuator is proposed by using the plant output error measurement and the exchanged local information. Assuming the existence of the spanning tree in the graph representing the communication topology among the controllers, it is shown that the output regulation and plant input sharing properties can be achieved by the proposed control law. The design of the proposed control law is demonstrated by a numerical example.
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