A Summary on Modified Carrier based Real-Time Selective Harmonic Eliminationt Technique Sri Nikhil Gupta Gourisetti
Advisor: Hirak Patangia
College of Engineering and Information Technology University of Arkansas Little Rock, USA e-mail:
[email protected]
College of Engineering and Information Technology University of Arkansas Little Rock, USA e-mail:
[email protected] presented in [4]. The reference and carrier sinusoidal signals can be represented as linear vectors in a two dimensional coordinate system (Fig. 1). The direction of the vector depends upon the polarity of reference signal. The reference and carrier signals are moving at frequencies fo and fc=kfo.
Abstract—Selective Harmonic Elimination (SHE) is a wellknown power electronics technique that is commonly used to suppress the noise harmonics in applications such as inverter design and AC Drives. But the existing methods are complex to be readily applied in real-time applications such as motorcontrol and frequency tuning. In addition, these methods involve tedious problem solving for each condition set. The paper focuses on designing a comparative based harmonic elimination technique using a modified carrier signal and a reference. It can be used for any desired frequency and fundamental strength eliminating the need for solution of complex transcendental equations. Simulation and laboratory results are provided to support the proposed research.
I.
Fig.1 Rotating Vector Representation for Two Different Cases
INTRODUCTION
The switching angles for a simple sine-sine PWM has been shown to be:
Eliminating unwanted harmonics is an import challenge in several electrical systems such as variable frequency drives commonly used in power and automation industries. To maintain current close to the ideal set value, usually the drives are interfaced with narrow band filters. Such precise filters are expensive and requirements vary as per the application and sensitivity requirements. One way to minimize the system cost is to eliminate the low frequency harmonics by signal manipulation techniques so that the complex filters are eliminated. Comparison based selective harmonic elimination using a modified reference is a technique that can be used in such applications. Recently, an algorithm has been presented where a modified signal is used to improve the fundamental strength with no specific attention to harmonic elimination [1]. Although this approach improves the net THD but would still require complex filters to eliminate the lower order harmonics. This paper focuses on modifying the sinusoidal carrier signal in a way that unwanted harmonics are eliminated and fundamental is maintained at a desired strength. This method also has an advantage over the techniques that involve the use of digital signal processors [2]. II.
α1 =
k +1
where α1 and α2 are first two transition points of the PWM signal. For k=5, α1=π/4 & α2= π/3. Perturbation angles φ1 and φ2 are inserted to modify the equations of the Fourier coefficients of the PWM signal as shown in (1). The perturbation angles should be less than the original switching angles i.e., φ1
