Showing papers by "Donghua Pan published in 2021"
TL;DR: In this paper, a step-by-step analytical method based on combining the linear and nonlinear models is proposed to analyze virtual synchronous generator's dynamic behaviors during a large disturbance, showing that the linear model is suitable for qualitative analysis to give an intuitive physical insight.
Abstract: The virtual synchronous generator (VSG) was proposed to emulate a synchronous machine's dynamics when integrating power electronic converter-based distributed energy resources to the power grid. However, the VSG's synchronization stability during grid faults is not fully explored. The underlying mechanism of loss of synchronization still needs to be further revealed due to VSG's nonlinear characteristics. In this article, a step-by-step analytical method based on combining the linear and nonlinear models is proposed to analyze VSG's dynamic behaviors during a large disturbance. The relationship between the linear and nonlinear models is first brought to light, showing that the linear model is suitable for qualitative analysis to give an intuitive physical insight. Simultaneously, the latter is adopted for quantitative analysis to assess stability after a grid fault. Moreover, to avoid the conflict of the synchronization stability and the inertia response, a transient damping method is added in the active power control loop, which can simultaneously improve the synchronization stability and frequency stability. Design guidelines are also proposed to identify the parameter of the transient damping with different inertia requirements. Finally, the experimental results verify the analytical method and the theoretical analysis.
64 citations
TL;DR: A hybrid active damping that combines the CCF and unit PCC voltage feedforward is studied, ensuring high robustness against both grid impedance variation and filter parameter fluctuation.
Abstract: Both the capacitor-current-feedback (CCF) active damping and the point of common coupling (PCC) voltage feedforward can provide damping for the LCL -type grid-connected inverter. They are usually individually adopted, and negative damping will occur in a certain frequency range due to the digital control delay, leading to a nonminimum phase behavior. In this article, a hybrid active damping that combines the CCF and unit PCC voltage feedforward is studied. With properly designing the CCF gain, the positive damping range could sweep the entire frequency range with the variation of grid impedance. As a reward, the maximum profit of damping cooperation can be harvested, ensuring high robustness against both grid impedance variation and filter parameter fluctuation. The simulation and experimental results are provided to verify the effectiveness of the hybrid active damping.
53 citations
TL;DR: An improved feedforward scheme which uses the grid voltage instead of the PCC voltage as the feedforward variable achieves superior harmonic rejection ability and strong stability under weak grid condition.
Abstract: The feedforward schemes of the voltage at point of common coupling (PCC) have been widely used in grid-connected inverters to reject the current harmonics caused by the grid voltage distortion. However, in weak grid, the PCC-voltage feedforward tends to destabilize the grid-connected inverters due to the effect of time delay. In this article, this stability issue is explicitly elaborated by the impedance-based stability criterion and then addressed with an improved feedforward scheme, which uses the grid voltage instead of the PCC voltage as the feedforward variable. Considering that it is hard to sense the real grid voltage directly, a method to extract the grid voltage from the sensed PCC voltage is put forward to implement the proposed feedforward scheme. By carefully arranging the sampling instants according to the duty cycle, a dual sampling mode is adopted to ensure an accurate extraction of the grid voltage. Finally, simulations and experiments are performed on a 6-kW single-phase grid-connected inverter, which confirm that the proposed grid-voltage feedforward achieves superior harmonic rejection ability and strong stability under weak grid condition.
40 citations
TL;DR: In this article, a temperature-dependent Cauer-type thermal model of the SiC MOSFET is proposed and extracted based on offline finite-element simulations, and the experimental measurement of transient thermal impedance was conducted under operating temperature variations (with virtual junction temperature ranging from 60.5 °C to 199.6 °C).
Abstract: This article characterizes the thermal behavior of a commercialized silicon carbide (SiC) power MOSFET module with special concerns on high-temperature operating conditions as well as particular focuses on SiC MOSFET dies. A temperature-dependent Cauer-type thermal model of the SiC MOSFET is proposed and extracted based on offline finite-element simulations. This Cauer model is able to reveal the temperature-dependent thermal property of each packaging layer, and it is suitable for the high-temperature thermal-profile prediction with sufficient computational efficiency. Due to the temperature-dependent thermal properties of the SiC die and ceramic material, the junction-heatsink thermal resistance can be increased by more than 10% under high-temperature conditions (up to 200 °C), which can considerably worsen thermal estimations of the SiC die and its packaging materials. Furthermore, the experimental measurement of transient thermal impedance was conducted under operating temperature variations (with virtual junction temperature ranging from 60.5 °C to 199.6 °C), and the effectiveness of the proposed temperature-dependent Cauer model was fully validated.
17 citations
TL;DR: In this article, a comprehensive investigation on three typical control schemes that utilize resonant pole cancelation is provided, and it is revealed that the resonant poles cancelation does not essentially eliminate the LCL resonance but merely hides it in the system, which can still be triggered and, thereby, turns into the culprit of the harmonic oscillation.
Abstract: Resonant pole cancelation is usually adopted in the current control or active damping to tackle the filter resonance in the LCL -type grid-connected inverter. However, its potential impact on the system stability has not been adequately assessed. This article provides a comprehensive investigation on three typical control schemes that utilize resonant pole cancelation. An important finding is drawn that the resonant pole cancelation violates the so-called internal stability, which can give rise to the undesired harmonic oscillation in grid current. From the physical insights, it is revealed that the resonant pole cancelation does not essentially eliminate the LCL resonance but merely “hide” it in the system, which can still be triggered and, thereby, turns into the culprit of the harmonic oscillation. The theoretical expectation is validated by the simulation and experimental results.
11 citations
TL;DR: A new STAR method (NSM) is proposed that uses an iterative method to compensate both the direction error and the distance error and results show that when comparing and analyzing the detection accuracy of the magnetic detection method, the results obtained by a latitude trajectory are one-sided, but a warp trajectory is both operable and accurate.
Abstract: The scalar triangulation and ranging (STAR) method is a magnetic detection method based on magnetic gradient tensor invariants, which has a wide application prospect Due to the asphericity parameter, there are distance error and direction error in the STAR method There have been studies to compensate the direction error, but the distance error has not been compensated This article proposes a new STAR method (NSM) that uses an iterative method to compensate both the direction error and the distance error Considering the convenience and feasibility of the operation, previous researchers analyzed the detection accuracy of the magnetic detection method by the detection error of the magnetic target on a latitude trajectory (latitude line in the spherical coordinate system of magnetic detection) But different latitude trajectories will lead to different analysis results In order to analyze the influence of motion trajectory on the detection error, the omnidirectional magnetic detection model (OMDM) is established The omnidirectional error expectation is used to more accurately measure the detection accuracy of the magnetic detection method Based on the OMDM, the warp trajectory (warp line in the spherical coordinate system of magnetic detection) that accurately measures the detection accuracy is found Simulation results show that NSM reduces the localization error of the STAR method, Lv-STAR method, and Wang-STAR method by 875%, 588%, and 125%, respectively Both simulation and experimental results show that when comparing and analyzing the detection accuracy of the magnetic detection method, the results obtained by a latitude trajectory are one-sided, but a warp trajectory is both operable and accurate
7 citations
TL;DR: In this article, the authors investigated the switching oscillations of three-level active neutral-point-clamped (3L-ANPC) inverters under three typical commutation modes (i.e., the full mode, outer mode, and inner mode).
Abstract: This article investigates the multifrequency switching oscillations of silicon carbide (SiC) MOSFETs in three-level active neutral-point-clamped (3L-ANPC) inverters under three typical commutation modes (i.e., the full mode, outer mode, and inner mode). Multiple switching-oscillation components with various frequencies are identified theoretically for both the full- and outer-mode commutations, due to their switching-loop diversities. Oppositely, the inner mode exhibits a single oscillation component as only one switching loop is involved. Three types of double-pulse tests (DPTs) are conducted on a 3L-ANPC inverter demonstrator with SiC MOSFETs, and the switching-oscillation components are extracted accordingly, which match well with the theoretical derivations. Moreover, other switching characteristics closely related, i.e., the oscillation peaks, current overshoots, capacitive charges, and switching energies, are studied and benchmarked according to the DPT results. It is concluded that the full- and outer-mode commutations share similarities in terms of switching oscillations, current overshoots, capacitive charges, and turn-on energies. The theoretical findings from this work provide a comprehensive knowledge of the multifrequency oscillation mechanisms associated with fast-switched 3L-ANPC inverters. Accordingly, the critical parasitic components are identified, and specific design considerations are proposed to achieve switching-performance improvements.
5 citations