Chapter 4 Power Inverter Design Topology
4.5 Simulation Results and Discussions
A rule of thumb in control theory is that the frequencies of such configuration have to at least a factor of 10 between them to decouple the effects. According to this rule, for 50Hz fundamental frequency, the resonant frequency has to be at least 500Hz, and a pulse frequency has to be at least 5,000Hz [38].
The simulation of the full bridge inverter is carried out with the coupling of
LC low pass filter. The filter inductor was chosen as 20mH and the capacitor is 100uF. PWM source is the comparison of the fundamental frequency of 50Hz to the different values of the carrier frequency. The carrier frequency of the inverter ranges from 1 kHz to 4 kHz. The load is a pure resistive load and constant throughout the simulation.
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Implementation of a Digital Signal Processing (DSP) Boost Inverter for Fuel Cell Energy Generation
Figure 4.11 is the output of the PWM inverter when the 50Hz fundamental frequency is compared to 1 kHz carrier signal.
Figure 4.11 PWM Inverter Output (50Hz compared to 1kHz carrier signal)
Figure 4.12 is the output of the PWM inverter when the 50Hz fundamental frequency is compared to 2 kHz carrier signal.
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Figure 4.13 is the output of the PWM inverter when the 50Hz fundamental frequency is compared to 3 kHz carrier signal.
Figure 4.13 PWM Inverter Output (50Hz compared to 3 kHz carrier signal)
Figure 4.14 is the output of the PWM inverter when the 50Hz fundamental frequency is compared to 4 kHz carrier signal.
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Implementation of a Digital Signal Processing (DSP) Boost Inverter for Fuel Cell Energy Generation
The results of the simulation show the different characteristics of a PWM inverter when a fundamental frequency of 50Hz is compared to the different values of the carrier signal. It was confirmed from the simulation that the higher the carrier or switching frequency used, the smoother the output current and voltage of the waveform of the PWM inverter.
Another simulation is done using variable duty cycle for the PWM inverter. The variable duty cycle is simulated using the highest carrier or switching frequency value of 4 kHz which is considered a smooth waveform from the sample. Everything stays the same, the fundamental frequency of 50Hz, the carrier signal of 4 kHz and the load. Only the duty cycle varies.
Figure 4.15 is the output of the PWM inverter with a 25% duty cycle.
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Figure 4.16 is the output of the PWM inverter with a 50% duty cycle.
Figure 4.16 50% PWM duty cycle
Figure 4.17 is the output of the PWM inverter with a 75% duty cycle.
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Implementation of a Digital Signal Processing (DSP) Boost Inverter for Fuel Cell Energy Generation
Figure 4.18 is the output of the PWM inverter with a 80% duty cycle.
Figure 4.18 80% PWM duty cycle
The results of the simulation shows the different characteristics of PWM inverter output when a variable duty cycle is applied. The load current and voltage increases as the duty cycle increases. Another point of observation in the simulation is the presence of ripple in the waveform. As the duty cycle rises, the presence of ripple also decreases. This denotes that duty cycle is significant in the circuit design of a PWM inverter.
4.6 Conclusion
The design of power inverter using a PWM technique is a very powerful tool as a controller in switching an electronic device. The basic PWM is generated by comparing a reference sinusoidal waveform with a triangular carrier waveform into a comparator. It was also proven in the simulation that by integrating a low pass filter, in the output of a PWM inverter, the output waveform improves. The purpose of a
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low pass filter is to eliminate the harmonics of the output voltage. It was also verified from the result that by comparing the 50 Hz reference frequency to an increasing carrier frequency signal makes the output waveform smoother.
Furthermore, the selection of duty cycle is also important for the design of a PWM inverter. The duty cycle commands the correct magnitude of the output of the inverter. As the duty cycle increases to the specified value, the output current and voltage of the inverter increases and become stable. Similarly, ripples also decreases to make the waveform looks smoother.
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CHAPTER 5
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Systems Configuration and Results
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Science is organized knowledge. Wisdom is organized life.
Immanuel Kant (1724 – 1804)
This Chapter presents the systems equipment, schematic and project prototype of the thesis. A comprehensive analysis of the overall systems configuration of the prototype are discussed and illustrated. The experiment and hardware operation is demonstrated using the CCS software. The actual results of the research are explained and concluded.
5.0 Introduction
The introduction of DSP has started in the early 1980’s when electronic technology is moving in a fast pace. Research came in a long way by digitizing signals for analysis in complex computer runs of programs. Early signal processors require an extra external circuit to produce fast analog to digital converters. The basic problem met in integrating an external circuit to a system is an intrusion of small