Cristian Blanco

Active Islanding Detection for Multiple Parallel-Connected Inverter-Based Distributed Generators Using High-Frequency Signal Injection

This paper proposes a method for islanding detection in microgrids with multiple parallel-connected inverters using high-frequency signal injection. In the proposed method, a master inverter injects the high-frequency signal which is used by the rest of inverters for islanding detection, with two distinguishing features: 1) The slave inverters work in a high-frequency current cancellation mode, what prevents interference and 2) in case of master failure or significant changes in the grid, the remaining inverters will dynamically reassign roles, the new master inverter being self-selected, based on a deterministic performance criteria and without the need of communications.

Sensorless Control of Doubly Fed Induction Generators Based on Stator High-Frequency Signal Injection

High-frequency-signal-injection-based methods have been widely investigated for sensorless position/speed control of induction machines (IMs), permanent magnet synchronous machines (PMSMs), and, more recently, doubly fed induction generators (DFIGs). When used with IMs and PMSMs, the high-frequency signal is injected in the stator windings, an asymmetric (salient) rotor being required for this case. Contrary to this, both stator and rotor terminals are accessible and sensored in DFIGs, being therefore possible to inject the high-frequency signal either in the stator or the rotor terminals. As a consequence of this, the method can be used even if the machine is nonsalient. In the implementation of the method with DFIGs, the high-frequency voltage signal is typically injected in the rotor, the high-frequency components (voltages of currents) induced in the stator being used for rotor position estimation. A drawback of this alternative is that the method is sensitive to the grid impedance in the stator side, which will be affected by the grid configuration, and is normally unknown. This paper proposes the sensorless control of a DFIG injecting the high-frequency voltage in the stator side and using a high-frequency current cancellation strategy in the rotor side. The main advantage of the proposed strategy is that the estimated position is independent of the grid characteristics.

Active islanding detection using high frequency signal injection

Islanding detection is of great importance for reliable operation of smart grids. Islanding-detection methods can be classified into three different groups, i.e., active, passive, and communication-based methods. Active methods inject a disturbing signal (typically a voltage) and analyze the system response (typically in the current). These techniques have a low nondetection zone (NDZ) but present the inconvenience inherent to injecting a disturbing signal. Passive methods monitor the grid condition from the grid variables. These techniques are easy to implement but present a large NDZ. Communication methods have the inconvenience of relying on communications, currently being of limited use. This paper proposes a new active islanding-detection method, based on the measurement of the grid high-frequency impedance by means of the injection of a high-frequency voltage. The advantages of the method are almost negligible adverse effects due to the injected high-frequency voltage and accurate and fast islanding detection, i.e., in the range of a few milliseconds. Furthermore, the estimated high-frequency impedance can be used for the adaptive control of the power converter.

Coordinated Operation of Parallel-Connected Inverters for Active Islanding Detection Using High-Frequency Signal Injection

The high frequency impedance measured at the terminals of inverters connected in a microgrid by means of the injection of a small magnitude, high frequency voltage, has been shown to be a reliable metric to detect islanding. While the implementation of this method is simple when only an inverter injects the high frequency signal, this case is of limited applicability. On the other hand, several concerns arise when multiple inverters work in parallel, primarily due to risk interference among inverters. Islanding detection using high frequency signal injection in microgrids with multiple parallel-connected inverters is studied in this paper. A strategy for the coordinated operation of the inverters, without the need of communications or pre-established roles is proposed. Simulation and experimental results will be provided to demonstrate the viability of the concept.

An Acoustic Resonance Band Detection Workbench for HID Lamps

This paper describes an automatic computer-controlled acoustic resonance detection workbench for high-intensity-discharge (HID) lamps. The detection method is based on optical measurements of the discharge arc path. With the aid of a dual lens projection system, relative light intensity measurements at different points of the arc are guided by fiber optic to a photodiode array. These measurements are statistically analyzed to identify when acoustic resonance occurs. Experimental results confirm this method to be a valuable tool to automatically obtain an acoustic-resonance-frequency map for HID lamps.

Grid synchronization of three-phase converters using cascaded complex vector filter PLL

Synchronization is a key issue in distributed power generation and storage (DPGS), fast and accurate estimation of the grid voltage phase angle being requested. Synchronization methods can be roughly divided among a) zero-crossing-methods, b) Phase-Locked-Loop (PLL) and c) Frequency-Locked-Loop (FLL) methods, with PLL implemented in a synchronous reference frame (SRF-PLL) likely being the most popular choice. A drawback of these methods is that, in general, they do not implement harmonic rejection strategies, their performance in polluted networks being therefore compromised; also their implementation and tuning is not straight forward, often being made by trial and error. This paper proposes a pre-filtering based synchronization method using cascaded complex-coefficient-filters (CCCF) and a complex PLL. The CCCF allows selection of the harmonic isolated/rejected, while the CPLL obtains the phase of the positive sequence component of the fundamental voltage needed for synchronization. The proposed method provides high rejection/adaptation capabilities against unbalances, frequency drift and harmonic distortion of the line voltages.

Synchronization in highly distorted three-phase grids using selective notch filters

Robust methods able to extract the magnitude and frequency of the positive sequence voltage in highly distorted grids is of paramount importance in distributed power generation (DPG) systems. Phase locked loop (PLL) synchronization methods are commonly used for this purpose. PLLs can be grouped into pre-filter stage methods and filter in the loop methods. Both provide similar performance and can be designed to reject one or more disturbing harmonic components. However, compared to pre-filter stage methods, filter in the loop methods are conceptually simpler and easier to tune. Conversely, filter in the loop methods can show an unstable behavior if they are not properly designed and do not include disturbance rejection strategies when the magnitude is distorted, their use not being therefore advisable e.g. when power calculation, droop control or magnitude synchronization are needed. This paper proposes a filter in the loop synchronization technique, able to isolate the magnitude and phase of the positive sequence voltage of the microgrid/grid even under high distorted conditions. The method combines an angle-tracking observer, to obtain the positive sequence phase angle, and a scalar product to obtain the positive sequence magnitude, enhancing the disturbance rejection capability for both phase and magnitude estimation.

Comparison between Different Discharge Lamp Models Based on Lamp Dynamic Conductance

Discharge lamp models based on dynamic lamp conductance are derived from physical equations that describe lamp behaviour. Lamp constructive data are not necessary to build the models, just lamp current and voltage data are necessary. In addition, these models have a relatively low complexity and not much calculation time is necessary to obtain them. They can be used to simulate low and high pressure lamps at low and high (20 kHz < f < 1 MHz) frequencies. Two of these models, derived from different physical equations, are tested and compared using fluorescent and HPS Na lamps.

Comparison of the Emission of a High-Pressure Sodium Lamp Working at 50 Hz and at High Frequency

A spectroscopic study of the behavior of a high-pressure sodium (Na) lamp is performed in this paper. The lamp works at 50 Hz and high frequencies. The study includes the analysis of the detected spectra from 400 to 700 nm, the determination of the lamp stabilization time, the Na vapor pressure, and the electronic excitation temperatures.

Islanding detection in grid-connected power converters using harmonics due to the non-ideal behavior of the inverter

This paper analyzes the use of the voltage distortions in PWM voltage-source-inverters (VSIs) caused by the non-ideal behavior of the inverter for islanding detection purposes. The non-ideal characteristic of the inverters, mainly due to the dead-time needed to have safe commutations, produces fundamental frequency dependent harmonics (-5th, 7th...) in the output voltage. Although these harmonics are in principle an unwanted effect, since they reduce the power quality, they can potentially be used for islanding detection purposes. The physical principles of the method would be the same as for high frequency signal injection methods that have already been proposed but without the need of injecting a high frequency signal.