Question

Prepare a two-page project proposal dealing with electrical engineering technology. You should research the field of electrical engineering technology and come up with a project idea that is relevant and appropriate.

Answer 1

The main objective of static power converters is to produce an ac output waveform from a dc power supply or vice-versa. These are the types of waveforms required in adjustable speed drives (ASDs), uninterruptible power supplies (UPS), static var compensators, active filters, flexible ac transmission systems (FACTS), and voltage compensators, which are only a few applications.

The modulating techniques that trigger the switches on the converter are mostly the carrier-based technique (e.g., sinusoidal pulsewidth modulation, SPWM), the space-vector (SV) technique, and the selective-harmonic-elimination (SHE) technique. The basic principle is to construct the required ac output waveform from various voltage levels, which achieves medium-voltage waveforms at reduced dv/dt.

At present, the control strategies are implemented in digital systems, and therefore digital modulating techniques are also available. The SV-based modulating technique is a digital technique in which the objective is to generate PWM load line voltages that are on average equal to given load line voltages. This is done in each sampling period by properly selecting the switch states from the valid ones of the VSI and by proper calculation of the period of times they are used. The selection and calculation times are based upon the space-vector transformation. It is possible to design a converter and inverter using this space vector modulation technique. The objective of the SV technique is to approximate the line-modulating signal space Vc with the eight space vectors (V_i , i = 1; 2; . . . ; 8) available in VSIs. V1 & V8 are null vectors which give 0V output. Rest are known as active vectors.

If space vector technique is implemented the switching frequency is constant. This makes an easy environment for designing a filter at the output end. With a variable switching frequency it is not possible to construct any filter at the output side.

this technique also increases the dynamic performance of the drive system. The response time to any load change or voltage change is taken care in less time. Some of the improved space vector techniques are also the topic of research now. Scalar control it is not possible to control the torque component & the flux component. Space vector technique can be integrated with some of the modern control strategies like direct torque control, Flux oriented control, direct power control etc to achieve better result.