Virtual Inertia Emulation to Improve Dynamic Frequency Stability of Low Inertia Microgrids

Due to low inertia and the intermittent nature of photovoltaic systems, dynamic frequency stability issues arise in microgrids with large photovoltaic systems. This limits the maximum amount of photovoltaic systems that can be penetrated in the microgrid. In order to increase the penetration of photovoltaic systems, the dynamic frequency controller, that is faster than the primary frequency controller (governor control) needs to be added in the microgrid system. For dynamic frequency control, inertial response can be provided from the energy storage system (such as battery, ultra-capacitor, photovoltaic system, etc.), which is termed as virtual inertia. A virtual inertia can be defined as the combination of an energy storage system, a power electronics converter and a proper control algorithm that improves the dynamic frequency stability of the microgrid. A virtual inertia supplies or absorbs the active power to and from the energy storage system to improve the dynamic frequency stability. This thesis presents the design and implementation of a hardware prototype of 1 kW virtual inertia in a microgrid with a real diesel generator and a load. For a step change in load, the virtual inertia improved the frequency response of the system from 57.39 Hz to 58.03 Hz. This improvement in frequency response proves the concept of existing proportional derivative based virtual inertia experimentally. With the addition of virtual inertia, the frequency of the system returns to the nominal frequency slower. Once the primary controller (governor control) of the system takes the action to regulate the frequency, virtual inertia no longer needs to add inertia to the system. So the dynamics of the VI needs to be improved so that the frequency returns to nominal frequency faster. This thesis also proposes an online learning controller based virtual inertia using adaptive dynamic programming that learns online and improves the dynamics of the controller of existing VI. The output of this controller supplements the output of the existing proportional derivative controller of virtual inertia. The supplementary controller is trained to increase the dynamics of the outer controller and to bring the system frequency to nominal frequency faster. Due to faster dynamics, the net energy delivered by the VI can be reduced significantly and improve the total possible discharge cycles from the battery. For performance evaluation, the proposed controller was implemented in a microgrid with a photovoltaic system, a diesel generator and a variable load. With the proposed controller, the frequency of the system returned to nominal frequency faster. The net energy delivered by the proposed controller in a photovoltaic diesel generator microgrid was 46.14% of the net energy delivered by the existing virtual inertia. Due to the decrement in the total energy delivered, the total number of possible battery discharge cycles with ADP based VI was 2.17 times of the total number of possible battery discharge cycles from VI

Outcome of everted end-to-end urethroplasty in traumatic bulbar and membranous urethra.

Introduction: Numerous options are available for the surgical management of urethral strictures. Everted End-to-end anastomosis is the utmost effective management for bulbar and membranous urethral strictures with a documented high success rate with low postoperative morbidity. Methodology: This study was conducted at department of Urology, Lahore General hospital, Lahore from May 2012 till May 2014. Total 30 patients were included in the study. Procedure was done by a single surgical team and Uroflowmetry and subjective evaluation was done on 2nd week, 1st month and 4th month and 12th month post operatively. Results: Mean age of patients was 24.43±12.39 years. Mean stricture length preoperatively was 1.83±0.63 cm. On follow up 50% of patients were in each grade whose subjective grading were 1 and 2 at 2 week post operatively. After 1-month post operatively 76.67% patients had Grade-1 and 6.67% patients had Grade-2. After 1 month follow up 63.34% patients presented with grade-1, 20% with Grade-2 and 6.67% presented with Grade-3. Only 80% of the patients at 4th month and 1-year post operatively presented with grade-1 subjective improvement. 10% of the patients had stricture recurrence at 1-month follow up and another 10% had recurrence at 4 months of follow up. Conclusion: Everted End-to-end urethroplasty is treatment of choice for short traumatic bulbar and membranous urethral strictures with a high success rate. Key Words: Urethral Strictures, Everted End-to-end Urethroplasty, Bulbar Urethra, Membranous Urethr

Accuracy of point of care ultrasound in the diagnosis of long bone fractures in the emergency department.

Introduction: Long bone fractures account for a significant portion of injuries in the emergency department (ED). This study aimed to determine the accuracy of point of care ultrasound (POCUS) compared to x-ray in the diagnosis of long bone fractures in the ED. Method: This cross-sectional study assessed 147 patients presenting to the ED of Patan Academy of Health Sciences (PAHS), with suspected long bone fractures, from Oct 2021   through Jun 2022. In all patients, POCUS examination was done by emergency fellows and then standard plain x-ray was performed. Data were analyzed by SPSS 28.0 to determine sensitivity and specificity. Result: A total of 147 patients were included in the study. Compared with x-ray, sensitivity, specificity, PPV and NPV of POCUS in determining fractures was found to be 86%, 98.96%, 97.72% and 93.2%, respectively. Based on bone injured, the highest sensitivity and specificity were obtained with forearm fractures, which was equal to 97.22% and 100%, respectively. Based on age categorization, the highest sensitivity (100%) and specificity (100%) were obtained in pediatric age group i.e. up to 16 years. Conclusion: This study demonstrated that POCUS has high sensitivity and specificity in the diagnosis of long bone fractures, compared to x-ray

Intra-articular autologous conditioned plasma reduces pain in early osteoarthritis and improves stiffness in advanced osteoarthritis knee: a prospective observation

Background: In this study, we aimed to investigate the effects of single-dose intra-articular autologous conditioned plasma injection as the treatment for early and advanced osteoarthritis knee. Methods: A single centre-based prospective observational analysis was conducted among patients who opt for conservative management by intra-articular autologous conditioned plasma Injection between July 2022 to June 2023. Total 46 patients were included and analysed in study on 1, 3, and 6 months’ follow-up after ACP injection. The WOMAC score and its sub scores were analysed and compared pre-procedure and on subsequent follow ups. Results: A total of 46 patients were analysed in the study, with male predominance of 56.5% with mean BMI of 27.37±5.35. On KL grading, 34.8% patients had KL grade II Osteoarthritis, 52.2% had grade III and 13.0% had grade IV. On comparison of WOMAC score and its sub-scales, all the values were found to be statically significant while comparing before injection (p value <0.0001) and one month follow up and before injection and six months’ follow-up (p value <0.0001). Conclusions: Six months following intra-articular autologous conditioned plasma injection, there was a noteworthy decrease in pain in early stages of osteoarthritis and improvement in knee stiffness in advanced stages of osteoarthritis as compared to the pre-treatment state

Effect of different nitrogen levels on yield and yield attributes of different rice varieties in DDSR condition at Kanchanpur, Nepal

An experiment on the effect of different nitrogen levels on yield and yield attributes of different rice varieties was conducted in Kanchanpur, Nepal, from March 2021 to July 2021. The experiment was laid in randomized complete block design with two factors: nitrogen levels and rice varieties, each factor having three levels (Nitrogen: 60kg/ha, 120kg/ha, and 180kg/ha and rice varieties: Hardinath 1, Hardianth 3 and Chaite 5) resulting in nine treatment combinations. Rice seeds were sown directly in experimental plots under the dry condition on March 24, 2021. The plant spacing was 20x20cm^2. Growth parameters, grain yield, and yield attributing traits of rice were recorded. The statistical results revealed significant differences between the treatments regarding agronomical parameters, yield attributing characters, and grain yield. The results indicated that the 180 kg/ha level of N application contributes to the higher plant height (74.502 cm), the number of tillers (1101.667), effective tillers (577.222), filled grain per panicle (116.490), panicle length (25.241 cm), grain yield (4.7 ton/ha) and straw yield (10.564 ton/ha). Among the varieties, Hardinath 3 produced significantly higher plant height (79.68 cm), panicle length (25.68cm), sterility percentage, and 1000 grain weight (24.60g) as compared to Hardinath 1 and Chapter 5, respectively. However, yield and yield attributing characters like grain yield, straw yield, effective tillers, and filled grains per panicle were significantly higher in Chaite 5. Therefore, a nitrogen level of 180 kg/ha and variety Chaite5 may be used for better productivity in Kanchanpur, Nepal

Adolescents with disabilities and caregivers experience of COVID-19 in rural Nepal

Introduction: Intersecting vulnerabilities of disability, low socio-economic status, marginalization, and age indicate that adolescents with disabilities in low-and middle-income countries were uniquely affected by the COVID-19 pandemic. Yet, there has been limited research about their experience. We conducted participatory research with adolescents with disabilities in rural, hilly Nepal to explore their experience of the pandemic and inform understanding about how they can be supported in future pandemics and humanitarian emergencies. Methods: We used qualitative methods, purposively sampling adolescents with different severe impairments from two rural, hilly areas of Nepal. We collected data through semi-structured interviews with five girls and seven boys between the age of 11 and 17 years old. Interviews used inclusive, participatory, and arts-based methods to engage adolescents, support discussions and enable them to choose what they would like to discuss. We also conducted semi-structured interviews with 11 caregivers. Results: We found that adolescents with disabilities and their families experienced social exclusion and social isolation because of COVID-19 mitigation measures, and some experienced social stigma due to misconceptions about transmission of COVID-19 and perceived increased vulnerability of adolescents with disabilities to COVID-19. Adolescents who remained connected with their peers throughout lockdown had a more positive experience of the pandemic than those who were isolated from friends. They became disconnected because they moved away from those they could communicate with, or they had moved to live with relatives who lived in a remote, rural area. We found that caregivers were particularly fearful and anxious about accessing health care if the adolescent they cared for became ill. Caregivers also worried about protecting adolescents from COVID-19 if they themselves got ill, and about the likelihood that the adolescent would be neglected if the caregiver died. Conclusion: Contextually specific research with adolescents with disabilities to explore their experience of the pandemic is necessary to capture how intersecting vulnerabilities can adversely affect particular groups, such as those with disabilities. The participation of adolescents with disabilities and their caregivers in the development of stigma mitigation initiatives and strategies to meet their needs in future emergencies is necessary to enable an informed and inclusive response

Virtual Inertia: Current Trends and Future Directions

The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems