Improvement of resonant harmonic filter effectiveness in the presence of distribution voltage distortion

Resonant harmonic filters (RHFs), are the most common devices installed in distribution systems for reducing distortion caused by harmonic generating loads. When such filters are applied in systems with a distorted distribution voltage their effectiveness may decline drastically. This dissertation explores the causes of degradation of RHFs effectiveness and suggests methods of their improvement both by optimization algorithms and by modification of the filter structure. An optimization based design method is developed for the conventional RHF. It takes into consideration the interaction of the filter with the distribution system and provides a filter which gives the maximum effectiveness with respect to harmonic suppression. The results for the optimized filters, applied in some typical cases, are given, and the limits of effectiveness for a common application are explored. For cases where the conventional RHF cannot be applied due to low effectiveness, a resonant harmonic suppressor, referred to as a RHF with line inductor, is investigated. It is formed by the addition of a line inductor to a conventional RHF, and it has a higher effectiveness in the presence distribution voltage distortion. A similar method of optimization based design is developed and evaluated for the RHF with line inductor as for the conventional RHF. Also, the limits of its effectiveness are explored. One major disadvantage of the RHF with line inductor is the load voltage reduction due to the additional impedance between the distribution system and load. For loads with variable reactive power, the voltage drop across the line inductor may reach an unacceptable level. Also, the fluctuation of the load voltage could increase. In order to reduce these effects, an adaptive capability with respect to load reactive power compensation is added to the filter. Such a filter, referred to as a semi-adaptive RHF, is obtained when a RHF is combined with a thyristor switched inductor (TSI). The addition of the TSI also increases flexibility in the design of the filter with respect to the line inductor’s value. Design aspects of the semi-adaptive RHF are explored and simulation results are presented

The effect of the design method on efficiency of resonant harmonic filters

Distribution voltage harmonics and load current harmonics other than harmonics to which a resonant harmonic filter (RHF) is tuned, deteriorate the filter efficiency in reducing harmonic distortion. The paper presents results of a study on dependence of this deterioration on the method of the filter design. The study was confined to four-branch RHFs of the 5th, 7th, llth, and 13th order harmonics, installed on buses that predominantly supply six-pulse ac/dc converters or rectifiers. The filters under investigation were designed according to two different approaches: a traditional approach and an approach based on an optimization procedure. In the traditional approach, the reactive power allocated to particular branches of the filter and their tuning frequencies are selected at the designer\u27s discretion, according to recommended practices. In the optimization based approach, the reactive power allocated to particular branches and tuning frequencies are resultants of an optimization procedure that minimizes the bus voltage and the supply current THD in the system with the filter under design. © 2005 IEEE

Effects of damping on the performance of resonant harmonic filters

The effectiveness of resonant harmonic filters (RHFs) in harmonic suppression is the resultant of two different types of resonance that affect the filters\u27 effectiveness in an opposite manner. They are the resonance of the filter branches and the resonance of the entire filter with the distribution system inductance. Damping these resonances by reduction of the filter Q-factor affects the filter performance in a complex way. There are suggestions in the literature on RHFs that such a damping would improve the filter effectiveness. Unfortunately, no quantitative information to support such a suggestion is available. This paper presents the results from a study of the effect of the Q-factor on the filter effectiveness and on the loss of active power in the filter

An optimization based method for selection of resonant harmonic filter branch parameters

Resonant harmonic filters (RHFs) are effective devices for reducing supply current harmonics when only those load generated harmonics for which they are tuned are present. Other current harmonics as well as supply voltage harmonics may reduce the effectiveness of RHFs in harmonic suppression. To counter such reductions in effectiveness, an optimization based method for selection of filter branch parameters is developed for the conventional RHF. It takes into consideration the interaction of the filter with the distribution system and provides filter parameters that give the maximum effectiveness with respect to harmonic suppression. To accomplish this, a cost function is developed, its behavior examined, and appropriate constraint functions are developed. The results for optimized filters, applied in a test case, are given. © 2006 IEEE

Does surgery followed by physiotherapy improve short and long term outcome for patients with atraumatic shoulder instability compared with physiotherapy alone? - Protocol for a randomized controlled clinical trial

Background: Shoulder instability is a common problem affecting young adults. Stabilization surgery followed by physiotherapy rehabilitation has been shown to reduce the chance of further episodes of shoulder dislocation and to improve quality of life in patients who sustain a shoulder dislocation as a result of a high collision trauma, but it is unclear if surgical intervention is beneficial for patients with atraumatic shoulder instability who have structural damage at the shoulder. The aim of this randomized controlled clinical trial is to determine if the addition of surgical intervention to physiotherapy rehabilitation improves outcomes for patients with atraumatic shoulder instability who have sustained soft tissue damage at their joint. Methods/Design: 140 participants will be recruited. Patients with feelings of insecurity (apprehension) at their shoulder joint, which is not the result of a collision injury, with physical signs of shoulder joint instability will be invited to participate. Consenting participants will undergo arthroscopic investigation of the shoulder joint. Patients with capsulolabral damage will be randomly allocated using a concealed allocation procedure to either stabilization surgery immediately following the arthroscopic examination or no additional surgical procedure. All participants will then receive the same postoperative physiotherapy protocol for up to 6 months. Outcomes (pain, functional impairment and number of shoulder dislocations sustained) will be evaluated prior to surgery and, together with participant-reported improvement, again at 6, 12 and 24 months after randomization. The primary endpoint will be pain and functional impairment at 2 years. Participants, clinical staff (but not surgeons) and assessors will be blind to whether stabilization surgery was performed. Data analysis will be conducted on an intention-to-treat basis with the focus on estimation of the effect. Discussion: This trial will have a direct and immediate impact on clinical decision making by establishing if patients presenting with soft tissue shoulder damage associated with atraumatic shoulder instability should be referred for stabilization surgery before commencing physiotherapy rehabilitation in order to ensure optimal outcome. This in turn will ensure effective, efficient use of scarce health resources to manage this common often disabling musculoskeletal condition. Trial registration: Study was registered with National Institutes of Health Clinical Trials Protocol Registration System in December 2012. ClinicalTrials.gov Identifier: NCT01751490