Paving the way : a future without inertia is closer than you think

Unless you have been hibernating in a remote cave for the past decade, you will have noticed the explosion of variable renewable generation. Wind power and solar photovoltaics (PVs) have been the subject of dozens of articles, just within the pages of IEEE Power & Energy Magazine. Charts illustrating relentless growth, such as the example from the United States shown in Figure 1 with futures tending toward 100% renewable energy, are common. This figure, provided by the National Renewable Energy Laboratory (NREL), reflects a low-cost, high-renewable projection scenario

Guest Editorial: Grid‐forming converters placement and utilisation to enhance transmission and distribution performances under high penetration of inverter‐based resources

Abstract Power systems around the world are rapidly transitioning to much higher shares of inverter‐based resources (IBRs) with few synchronous generators remaining online. IBRs and synchronous generators have fundamentally different dynamic performance characteristics resulting in a difference in the overall power system dynamic performance. IBRs are generally more flexible and controllable than synchronous generators; however, at the same time they exhibit significantly more complex control systems. Furthermore, new and emerging capabilities are being developed progressively and in particular the so‐called grid‐forming inverters (GFM). GFM offer several new capabilities not previously possible with conventional grid‐following inverters (GFL). However, they are not well understood currently when applied in a mega scale and moving forward when they will likely take over the role synchronous generators have been performing for several decades as the workhorse of system security support. Key questions currently in the technical community include the extent to which GFM shall be similar or different to each of the synchronous machines and conventional GFL, and how various control strategies can assist in maximising the grid support capabilities sought and minimise or ideally eliminate any adverse impacts. The objective of this special issue is to provide insights into some of these unknowns

Frequency Response Assessment: Parameter Identification of Simplified Governor Response Models Using Historic Event Data

With a growing share of inverter-interfaced generation in modern power systems, synchronous inertia is declining. This leads to faster frequency drop after large generation trip events. During low inertia conditions, frequency containment reserves might not be sufficient to arrest frequency before it reaches the threshold for underfrequency load shedding. It is therefore be-coming increasingly important for system operators to be able to assess frequency response in near real time. In contrast to detailed models, simplified models offer short simulation times and their parameters can be accurately identified and adapted to changing system conditions in near real time. In this paper, the parameters of governor response models are identified by minimizing the er-ror residuals between the simulation models' and the actual sys-tem's measured active power response. This is accomplished by using historic event data from two system operators: the Electric Reliability Council Of Texas (ERCOT) and the Swedish Svenska kraftnät (Svk). Then, the respective frequency response models are simulated to assess frequency response. The results show that, despite their simplicity, the models provide a very good fit com-pared to the actual response. The models of ERCOT and Svk are examined; however, a similar approach can be employed to repre-sent the frequency response of other power systems.QC 20200319</p

Asking for fast terminal voltage control in grid following plants could provide benefits of grid forming behavior

Abstract Conventional inverter based resource (IBR) plants generally have control loops with high bandwidth which enable them to maintain tight control of the active and reactive power injected by the IBR device into the grid. These control loops, if not tuned appropriately, can suffer from instability under reduced system stiffness. To bring about an increase in stability of a power network with large percentage of IBRs, recent research done around the world has resulted in the emergence of multiple different types of so‐called grid forming inverter control architectures. But, in order for inverter manufacturers to break the circular (or chicken‐and‐egg) problem, exact performance requirements must be known, which can only be specified either through standards and/or interconnection requirements. Through the use of both electromagnetic transient (EMT) time domain and linearized state space small signal analysis, this paper will provide a way to define interconnection requirements that are agnostic to the specific type of grid forming or grid following IBR control. Further, the benefit of defining grid forming interconnection requirements even when short circuit ratio is not low will be showcased

Frequency Response Assessment: Parameter Identification of Simplified Governor Response Models Using Historic Event Data

With a growing share of inverter-interfaced generation in modern power systems, synchronous inertia is declining. This leads to faster frequency drop after large generation trip events. During low inertia conditions, frequency containment reserves might not be sufficient to arrest frequency before it reaches the threshold for underfrequency load shedding. It is therefore be-coming increasingly important for system operators to be able to assess frequency response in near real time. In contrast to detailed models, simplified models offer short simulation times and their parameters can be accurately identified and adapted to changing system conditions in near real time. In this paper, the parameters of governor response models are identified by minimizing the er-ror residuals between the simulation models' and the actual sys-tem's measured active power response. This is accomplished by using historic event data from two system operators: the Electric Reliability Council Of Texas (ERCOT) and the Swedish Svenska kraftnät (Svk). Then, the respective frequency response models are simulated to assess frequency response. The results show that, despite their simplicity, the models provide a very good fit com-pared to the actual response. The models of ERCOT and Svk are examined; however, a similar approach can be employed to repre-sent the frequency response of other power systems.QC 20200319</p

Frequency Response Assessment: Parameter Identification of Simplified Governor Response Models Using Historic Event Data

With a growing share of inverter-interfaced generation in modern power systems, synchronous inertia is declining. This leads to faster frequency drop after large generation trip events. During low inertia conditions, frequency containment reserves might not be sufficient to arrest frequency before it reaches the threshold for underfrequency load shedding. It is therefore be-coming increasingly important for system operators to be able to assess frequency response in near real time. In contrast to detailed models, simplified models offer short simulation times and their parameters can be accurately identified and adapted to changing system conditions in near real time. In this paper, the parameters of governor response models are identified by minimizing the er-ror residuals between the simulation models' and the actual sys-tem's measured active power response. This is accomplished by using historic event data from two system operators: the Electric Reliability Council Of Texas (ERCOT) and the Swedish Svenska kraftnät (Svk). Then, the respective frequency response models are simulated to assess frequency response. The results show that, despite their simplicity, the models provide a very good fit com-pared to the actual response. The models of ERCOT and Svk are examined; however, a similar approach can be employed to repre-sent the frequency response of other power systems.QC 20200319</p

A hardware implementation of an online frequency dynamic parameter estimation

The current concerns with inertia and frequency response deterioration have increased the interest in data analytics tools to assess the dynamic state of power systems. These assessments have emerged because of the increasing control room data availability in SCADA and synchrophasor networks. Additionally dynamic metrics and parameters have been proposed to assist power system dynamic operation. This work present an experimental implementation of an online tool to identify inertia and the time constants describing a reduced-order model of system frequency dynamics. The implementation shows empirical results in the Chilean Power System

VALUTAZIONE DELLE PARTECIPAZIONI SECONDO IL METODO DEL PATRIMONIO NETTO

The degree to which changes in caregiver burden over a one-year period can be predicted by functioning of dementia patients and caregiver psychological stress was examined. The Direct Assessment of Functional Status (DAFS) was administered to 44 patients and the Caregiver Burden Inventory and the Brief Symptom Inventory were administered to their next-of-kin caregivers. All patients and caregivers were assessed at baseline and again in approximately one year with the same measures. Hierarchical regression revealed that baseline patient functioning predicted overall changes in caregiver burden, but that increases in psychological symptoms of caregivers such as depression, anxiety, and hostility were the best predictors for specific types of increased caregiver burden, such as social, developmental, or physical burden. These results suggest that interventions should target reduction of particular psychological symptoms in order to reduce caregiver burden over time