An Islanding Detection Method for Multi-DG Systems Based on High-Frequency Impedance Estimation

Abstract

Abstract--Active islanding detection methods are generally employed for grid-connected inverter-based Distributed Generation (DG). However, there might be mutual influences and power quality issues caused by the disturbance signal when multiple inverters are involved. To address those problems, this paper analyzes the potential failure mechanism of the f-Q (frequency-reactive power) drifting active method in multiple-DG situations. Then, a novel high frequency transient injection based islanding detection method that is suitable for both single and multiple-DGs is proposed. Compared with the conventional injection methods, a high frequency impedance model for DG is provided for better theoretical analysis. By means of the intermittent Time Domain Low Voltage Condition (TDLVC) injection control, this method can achieve good accuracy and reduce disturbances to power system.  Index Terms--Islanding detection, active injection method, high frequency impedance estimation, multi-inverter-based DG.

Design Consideration and Performance Analysis of a Hybrid Islanding Detection Method Combining Voltage Unbalance/Total Harmonic Distortion and Bilateral Reactive Power Variation

“…Thus, the negative sequence voltage of PCC after islanding is (18) When the power mismatch is small, the deviation of positive sequence voltage Δv PS will be much smaller than v PS when islanding happens, so the positive sequence PCC voltage after islanding will be v' PS ≈ v PS , and ΔVU at the time when islanding happens can be presented as (19) To avoid the influence of grid impedance, further analysis is carried out. In specific, the short-circuit ratio (SCR) is defined as (20) t where, V t and P rated are the rated ac line to line voltage and the inverter power, respectively. Considering a DG operating at unity power factor, as the inverter power generation and the local load consumption are closely matched, the relationship between rated power and the load impedance is (21) t t…”

“…In comparison, active methods have a relatively small NDZ, but the power quality would be deteriorated as these methods introduce perturbations to the grid continuously. And when considering the inverters' count increases significantly in the grid, the active islanding detection methods are likely to fail when parallel connected inverters inject their own disturbance signals independently [18]- [20]. For instance, when some inverters inject perturbations to make the PCC frequency drift up while the others cause the frequency to drift down, they will counteract each other and affect the islanding detection performance.…”

“…Therefore, the perturbation introduced and counteraction between inverters are the two problems of great concern in inverter-based islanding detection technique. To deal with the counteraction problem, several new methods were proposed, such as the online grid impedance measurement [18], masterslave strategy [19] or external centralized disturbances injection [20], but they all need cooperation between inverters and increase the operation complexity. Besides, the perturbation problem was not considered in these methods.…”

Microgrid Islanding Detection Based on Mathematical Morphology

“…These methods usually inject a perturbation into the system and monitor the output power variations, active frequency drifts, and phase of the voltage at a point of common coupling (PCC) in islanding mode [27]. The dominant active techniques includes active frequency drift (AFD) [28], second harmonic drift [29], frequency jump [30], locking frequency band [31], active frequency drift with positive feedback [32], high frequency signal injection [33], and current injection [34,35]. Despite their effectiveness in islanding detection, active techniques need to continuously vary the DG output, which negatively affects power quality (PQ) and speed of detection while compromising the reliability of islanding detection at the PCC.…”

Optimal Performance Design Guideline of Hybrid Reference Frame Based Dual-Loop Control Strategy for Stand-Alone Single-Phase Inverters

“…D frequency with a fast dynamic response and zero steady-state errors [1][2][3][4]. For the single-phase inverters, the full-bridge pulse width modulation (PWM) inverter, whose major requirement of its control system is to control the voltage to achieve the steady state with zero steady-state error and a fast dynamic response, is widely used either in grid-connected or islanded mode voltage regulators in the distributed power systems [5].…”