Distributed Rectifier Loads in Electric Power Systems

Modern literature on power system harmonic problems, analysis, and solution is mostly of the case history type [1]. When the harmonic signal strength is low, the assumption of sinusoidal bus voltages is usually made, thereby simplifying analysis considerably. Since interest is often restricted to distribution circuits, simple radial circuit configuration is frequently assumed, and band (frequency) limitation of harmonics is also assumed. The proliferation of rectifier and other nonlinear loads, however, particularly in localized regions, suggests a renewed look at harmonic signals, especially at high harmonic content, near resonance, and cases of considerable bus voltage distortion. Xia and Heydt [2-3] have modified the Newton-Raphson power flow study algorithm to accommodate nonlinear loads without the assumption of superposition, radial circuitry, or sinusoidal bus voltage. Grady [7] has extended the Xia-Heydt algorithm to include nonlinear resistive loads (e.g. fluorescent lamps) and zero sequence signals. One of the primary reasons for the increased deployment of nonlinear loads is the successful development of high power semiconductor switching devices. Nonlinear loads are often characterized by either widespread distribution (such as the case in fluorescent lighting loads and electronic loads and such is the potential in the case of electric vehicle loads [4-6]). Also, the use of large industrial rectifiers directly on the subtransmission voltage system is not unusual in applications of large dc motors, electro-deposition installations, and induction furnaces. Static var devices are new electronic localized sources of harmonic signals.