Contents I. Introduction
Nonlinear loads are the main source of harmonic emissions and pollutions in power grids. Depending on the increase of nonlinear loads, some power quality problems related to harmonics have been increasing. Some of these problems are the increase in the losses of grid elements, failures and false tripping of some sensitive equipment, malfunction of protection relays, and undesired noises in communication systems. These problems cause economic losses directly or indirectly [1]. Maintaining the quality of grid voltage at a desired level is in the responsibility of grid utilities. However, this level is affected by the currents of nonlinear loads that is in the responsibility of consumer. In addition, distorted grid voltages can distort the currents drawn by customers. This is a “chicken and egg” discussion. Thus, it is an important and difficult task to determine the source and amount of distortions. Determination of the sources and amount of economic losses due to harmonic pollution and its allocation is an emerging issue of academic community [2]–[4]. The most important methods developed until now for this aim are active power direction method [5], reactive power direction method [6], conforming–nonconforming current method [7], current–voltage superposition method [8], harmonic current/voltage method [9], critical impedance method [10], and nonfundamental apparent power method [11]. These techniques can also be classified as multipoint and single-point methods. Multipoint methods require synchronous measurement of voltages and currents at different points of grids. As these methods give more accurate and reliable information about the harmonic pollution, they are difficult to implement and require an extremely complex and expensive measurement instrumentation. On the other hand, single-point methods have many advantages, e.g., easy implementation, low cost, and low risk of failure [12], [13]. In almost of these methods, harmonic emissions of individual loads at the point of common coupling (PCC) are obtained by the use of harmonic impedance which is difficult to compute and its value changes in the dynamic conditions of grids [14], [15]. Ultimate goal of all these works is to develop a fair, reasonable, and applicable method. These methods can be only put in practice by implementing them in a digital board. Thanks to high-speed microprocessor technology developed in recent years, the real-time measurement of harmonics and billing the resulted economic losses to consumer have become a matter of interest to grid utilities besides academic community [16].
