The article proposes an algebraic synthesis for PWM methods, which is based on a graphical representation of the 2 levels VSI (Voltage Source Inverter). This theory can be the starting point for every PWM method representation. In order to understand the historical evolution of the PWM methods the authors propose two classification groups of the main PWM techniques. The main classification is based on the movement of the neutral point (zero-voltage V N0 evolution). The details of PWM methods presented here are also seen from the graphical representation perspective. The equivalence between the well-known SVM (Space Vector Modulation) practically DDT realized (Direct Digital Technique) and the three-phase PWM with a carrier based industrial realization is shown. The principles of the three-phase PWM and the 3 rd harmonic injection PWM (THIPWM4, THIPWM6) are compared the same as the DPWM (Discontinuous PWM) methods. These classifications and equivalences between different techniques show that the number of contemporary used PWM principles can be reduced. The general complex space representation and the classifications proposed here are simple to comprehension educational tools and they simply the way towards practical implementation.
The main problems that appear when using a long cable connection between a Variable Frequency Drive (VFD) and the AC motor are over-voltages and bearing currents. The last one concerns especially EMC, while the over-voltage transients can be fatal to the motor. This paper firstly investigates the "converter -cable -motor" system behaviour concerning overvoltages. Then it proposes an online identification of the cable parameters. This result could be used in order to reduce over-voltages. We introduce here an algorithm that decreases the amplitude of the adverse over-voltage effect. The algorithm is based on the modification of the applied PWM pattern.
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