The widespread use of electronic equipment, such as information technology equipment, power electronics such as adjustable speed drives ASDprogrammable logic controllers PLCenergy-efficient lighting, led to a complete change of electric loads nature. Power quality problems and new solutions photo by:
Internally, the filters cause the harmonic current to resonate at its frequency. This prevents the harmonic current from flowing back to the power source and causing problems with the voltage waveform.
A disadvantage of the passive filter is that it cannot be perfectly tuned to handle the harmonic current at a significant frequency.
When a capacitor is placed in shunt, the voltage at the Point of Common Coupling PCC forces a fixed leading current to flow. This compensates for the lagging current drawn by the load.
Obviously, the disadvantage is that the leading current drawn is fixed by the PCC voltage and when the load is varying, there will always be improper compensation. Capacitor banks were used with manual switches as shown in Figure 1. Capacitors will be switched in and out of the system manually, according to the load.
However, the compensation was still not exact. Actually, it acts as a variable voltage source behind a reactance as shown in Figure 1. The advantages of synchronous condensers over fixed and switched capacitors are: They can be controlled to follow the reactive current demand of the system 2.
They can provide both lagging and leading reactive currents Figure 1. They cannot respond quickly to varying load conditions. The response is sluggish owing to the inertia of the mechanical parts involved. They cannot be used to compensate for harmonic currents absorbed by the load.
The major disadvantage is that the compensating system itself will inject harmonics into the system due to switching action. Conventional passive filters have been used to eliminate current harmonics.
These filters work well if the harmonics of interest are well known and relatively invariant over time. However, the passive filter must be tuned to the frequencies of the harmonics to be removed and when the harmonics change the filter effectiveness is reduced.
If multiple harmonics are to be removed, the passive filter will require multiple stages, increasing size and cost. Passive filters can also produce harmonics due to resonance between the filter and source impedance.
For overcoming the drawbacks of passive filters and reducing power quality problems, a number of attempts have been made on the design, analysis and optimal control development of Active Power Filter APF. The APF is a power electronic device that can dynamically suppress harmonics and compensate reactive power regardless of the changes of their frequencies and amplitudes.
Active filters act as a harmonic attenuation device.
The capacity and performance of the active power filter is determined by the choice of components and the execution of the power circuit. With the advent of harmonic loads, the capacitor based compensation techniques had a set back as the capacitors got heated up due to large harmonic current flows and sometimes there was failure due to resonance phenomenon too.
The synchronous condensers and SVCs also could not compensate for the harmonic currents and hence there was a need for developing newer methods of power quality compensation.
Active power filters were the result of research in this direction and they aid in dynamic compensation of reactive and harmonic currents demanded by the load. As shown in Figure 1. They can be controlled to continuously track and compensate for the reactive current demanded by the load.
In open loop mode, the harmonic currents are measured on the load side of the active filter, which are used to calculate the required compensating current to be injected into the network.
In closed loop control, the resulting current in the network is measured and the active filter injects a compensating current in order to minimize it. The open loop control system is easier to implement but is less efficient and require higher accuracy current sensors.
The closed loop control is more precise. The reference current generator and the control circuit are the two most important parts of an active power filter. The IGBT bridge uses a dc voltage source in the form of a capacitor and the generated voltage is coupled to the network via reactors.Power Quality, Power Quality problems, Power Quality costs, Power Quality solutions.
Introduction Power Quality (PQ) related issues are of most concern nowadays. The widespread use of electronic equipment, such as information technology equipment, power.
However, the quality of power supplied is affected by various internal and external factors of the power system.
The presence of harmonics, voltage and frequency variations deteriorate the performance of the system. In this project the frequently occurring power quality problem- voltage variation is discussed. The arguments that led to the development of the thesis are: the continuous and rapid increase of the number of nonlinear receivers connected to the office buildings electrical installations, the increasing concerns regarding the energy efficiency and the sensitivity of modern equipment to .
4 | Power Quality Issues, Impacts, and Mitigation for Industrial Customers IEEE , “IEEE Recommended Practices and Requirements for Harmonic Control in Electric Power Systems,” is the standard for harmonics in North America.
power quality problems and types of sag/swell. If a DSTATCOM is a successful device, the control is able to handle most sags/swells and the performance must be maximized according to the equipment inserted. Otherwise, the DSTATCOM may not be able to avoid tripping and even cause additional.
The paper starts with a short introduction to power quality issues (see section 2).
In section 3, the solutions reviewed from various sources for power quality are given. A detailed literature review on codes and standards re-lated to power quality are illustrated in sections 4.
Finally, section 5 presents the summary and conclusions. 2.