Harmonic Current Emission Research Articles

PROBABILISTIC HARMONIC ANALYSIS OF WIND GENERATORS BASED ON GENERALIZED GAMMA MIXTURE MODELS

Grid-connected wind generators pose the power quality problems such as harmonic propagation and summation, and these problems are hard to solve by deterministic harmonic analysis due to the random harmonic current emissions. In this paper, probabilistic harmonic analysis is utilized to approximate harmonic currents of wind generators. Generalized gamma mixture models based on Gaussian mixture models, phasor clustering and generalized gamma models, are proposed to approximate the probability density functions of harmonic propagation and summation. And the simulation network built on PSCAD/EMTDC is utilized to verify the proposed models and method.

Effects of Imperfect Sinusoidal Input Currents on the Performance of a Boost PFC Pre-Regulator

This paper investigates the effects of applying different input current waveshapes on the performance of a continuous-conduction-mode (CCM) power-factor-correction (PFC) boost pre-regulator. It is found that the output voltage ripple of the pre-regulator can be reduced if the input current is modified to include controlled amount of higher order harmonics. This finding allows us to balance the performance of output regulation and the harmonic current emission when coming to the design of the pre-regulator. An experimental PFC boost pre-regulator prototype is constructed to verify the analysis and show the benefit of the pre-regulator operating with input current containing higher order harmonics.

Harmonic emission limits and responsibilities at a point of connection

A customer expects to receive a voltage supply at his installation that meets the requirements of standards like (national) grid codes, EN50160 standard etc. under normal operating conditions. On the other hand, the devices connected to a customer's installation should meet power quality (PQ) requirements as given in the IEC standards (and other relevant product standards). In contrast, present standards give very limited information about the PQ requirements at a customer's point of connection (POC). Modern household customers use many power electronic-based devices for their daily usage. Those devices inject harmonic currents and all together distort the network's voltage. It is noticed from surveys that harmonic-related inconveniences are increasing in the power system. Some field measurements (on harmonics) in the Dutch low-voltage (LV) network will be discussed in this paper. Also, harmonic simulation is done on a typical LV network that supplies electricity to several households. Both the field measurements and simulation results are compared with the limit values of the standards. Further, harmonic current emission limits at different customers' installations are derived. This information would be helpful for the customers to know their rights and responsibilities in the network. Additionally, a proposal is made about new planning level values of harmonic voltages in the network. Finally, a methodology is developed to assess harmonics-related responsibilities of each of the involved parties in the power system, and it is shown where these can be applied.

Harmonic assessment of variable-speed wind turbines considering a converter control malfunction

This study is on variable-speed wind turbines with permanent magnet synchronous generator. Three different drive train mass models and three different topologies for the power-electronic converters are considered. The three different topologies considered are, respectively, a matrix, a two-level and a multilevel converter. A novel control strategy, based on fractional-order controllers, is proposed for the wind turbines. The influence of a converter control malfunction on the harmonic current emissions is studied. The performance of disturbance attenuation and system robustness is ascertained. Simulation results are presented, and conclusions are duly drawn.

A Study on the Harmonic Current Characteristic and Emission Value Assess Method Considering the Linear Load

In order to operate the power system satisfactory for both system operators and customers, it is important to limit the harmonic currents to the allowable levels which injected into the system from the distorting installations. In this regard, the principles for the allocation of emission limits on individual customer were introduced in the technical report of IEC61000-3-6. According to these general principles, the emission limits are dependent on the agreed power of the customer, the power of the harmonic-generating equipment, and the system characteristics. The considerations in this report are very comprehensive and the process introduced is practical enough to implement as it is. However, there is a fact not appropriately dealing in the report that could be a very tickle but has a huge impact on determining the emission limit. This is the effect of non-harmonic load currents. More precisely, these are from the equipments which do not emit any harmonic or may emit harmonics but this specific order under the consideration by themselves if the source power is sinusoidal. The load currents originated from these equipments have an effect of active filter against the specific order of harmonic therefore, these should be dealt as a significant factoron the process of determining the emission limits for individual customer.

국내 저압 전기기기의 고조파 유출 제한값 산정

배전계통의 고조파 방해(Harmonics Disturbance)현상은 배전계통에서 전압강하와 함께 순시 전력품질을 저해하여 중성선 및 NGR(Neutral Ground Reactor) 과열, OCGR 오동작 등의 문제를 발생시킴으로써 전력회사와 고객 모두에게 막대한 경제적인 손실을 주고 있어 동 분야에 대한 적극적인 대책이 필요하다.<BR> 이에 대한 해결 방안으로 유럽에서는 IEC 61000-3-2 규격을 통해 상당 16[A] 이하 저압 전기기기의 고조파를 제한하고 있다. 본 규격은 저압 전기기기를 4개의 등급으로 구분하여 관리하고 있으며， 분석결과 클래스 A등급 해당 전기기기의 고조파 유출제한 기준은 저압계통의 기준임피던스와 허용 최대전압을 바탕으로 산정되었으며， 타 등급(B， C， D등급)의 유출제한 기준들도 클래스 A의 유출제한 기준을 바탕으로 산정되었다. 따라서 본 논문에서는 IEC 61000-3-2 규격 분석결과를 바탕으로 국내 기준임피던스에 기초하여 국내 저압 전기기기의 고조파 유출 제한 값을 산정하였다.

Planning Approaches for the Strategic Placement of Passive Harmonic Filters in Radial Distribution Networks

This paper presents an approach to determine strategic buses for harmonic filter placement by correlating the sensitivity index based on the inherent structure theory network (ISTN) and harmonic current injection at buses of the distribution network/feeder. The strategic buses for the harmonic filter are characterized as either the bus with maximum total harmonic voltage distortion (THDV) in a distribution feeder, or the bus where the placement of the harmonic filter would result in maximum reduction in the overall average THDV in the distribution feeder. The advantage of using this approach is that it provides insight into the interaction of the network structure with harmonic current sources in the distribution network in regards to the performance of harmonic filters. The assessment of the performance of a strategically placed passive harmonic filter based on the proposed approach is evaluated for peak and offpeak load scenarios on a radial distribution network. The results indicate that passive harmonic filters that are placed based on harmonic current emission levels perform better than harmonic filters placed based on ISTN alone. The strategically placed passive harmonic filters are highly effective in controlling harmonic propagation in distribution networks

A unified and simple model for uncontrolled rectifiers

A simple model for uncontrolled rectifiers with capacitive filter working in discontinuous current mode is developed in this paper. The presented model allows the rectifier ac line current harmonics to be obtained in an easy way. Previously, both the width and the peak value of the ac current pulse are calculated by means of analytical equations. This model is obtained when the rectifier working point is defined by dc current consumption or dc power consumption. In the first case, the expressions of the width and peak value are analytical, whereas in the second case they are non-linear; thus, an iterative algorithm is proposed to solve them. The rectifier behaviour is also graphically characterised in both cases from the previous equations normalisation. Several examples of the proposed model application are presented. Lastly, it is exposed that the model allows harmonic current emission to be studied in an easy, friendly way, according to the present regulations for both rectifiers.

Development and testing of a multi-type air conditioner without using AC inverters

This paper reports the results from the development and performance testing of a cost effective, energy efficient, multi-type air conditioner that connected five indoor units (evaporators) to one outdoor unit (condenser) with a digital scroll compressor. Instead of using inverter technology, which has a potential risk of harmonic current emissions, this study used a digital scroll compressor, which provided the variable refrigerant volumes. The measured results for this innovative design showed: (1) The relationship between the degree of opening of the electronic expansion valves (s) and the compressor output ratio (%) could be represented by regression functions, which formed the basic parameters of the system control. (2) The developed system provided true zoning capability because it could run indoor units under part load conditions, therefore wasting little energy. The power consumption of the developed system was reduced from 100% to 25% when the full load was reduced to a partial load of 17%, saving more than 75% of the work required using a conventional un-loading method. (3) The developed system has a broader range of capacity output (from 17% to 100%) than that of an AC variable frequency control system (from 48% to 104%). The developed system cost 20% less than a comparable system with an AC inverter.

Development and testing of a multi-type air conditioner without using AC inverters

This paper reports the results from the development and performance testing of a cost effective, energy efficient, multi-type air conditioner that connected five indoor units (evaporators) to one outdoor unit (condenser) with a digital scroll compressor. Instead of using inverter technology, which has a potential risk of harmonic current emissions, this study used a digital scroll compressor, which provided the variable refrigerant volumes. The measured results for this innovative design showed: (1) The relationship between the degree of opening of the electronic expansion valves (s) and the compressor output ratio (%) could be represented by regression functions, which formed the basic parameters of the system control. (2) The developed system provided true zoning capability because it could run indoor units under part load conditions, therefore wasting little energy. The power consumption of the developed system was reduced from 100% to 25% when the full load was reduced to a partial load of 17%, saving more than 75% of the work required using a conventional un-loading method. (3) The developed system has a broader range of capacity output (from 17% to 100%) than that of an AC variable frequency control system (from 48% to 104%). The developed system cost 20% less than a comparable system with an AC inverter.