WEEEK 6
For this week, I still do the literature study by reading the past thesis at the library. There was a lot of type of online UPS system that I have read which depends on the type of the component that we used. So, for this week I read a thesis about design a 3-phase online UPS system with a full-wave rectifier and SPWM inverter. Three-phase UPSs are generally the preferred choice for high kVA applications, which are typically more sophisticated and have high compute densities. Large multi-story buildings, data centers and industrial facilities protecting high-power processes are typical three-phase UPS customers, as they need to distribute large amounts of power over relatively long distances. But it will require more cost because of the high application power.
Last week, we have met with our supervisor to discuss about our progress for the ENTRY 1. She asked us to create a problem statement and objective of this project. The problem statement must be a specific problem statement. Therefore, we can make a target for this project.
For my current possible problem are :
- How to design a new model for online UPS?
- Issues related especially on safety and battery.
- What is the main component that we need to use?
I need to do more literature study more related to this topic.
WEEK 7
for this week, after doing research on the three-phase online UPS system. then, the next thing that I want to learn is a single-phase on-line UPS system. Single-phase UPSs tend to be a sensible and economical option for simpler, smaller applications with low
kVA requirements, which are typically seen in the home, small businesses and in remote or satellite offices where computing power is less than 20,000 VA. then, for this week we try to do the simulation for each component that we need to use such as :
- Rectifier
- Battery
- Inverter
- PWM controller
so, we need to do the simulation for each component first. these 4 component is the 4 main component that we need to use in order to simulate the full configuration for online UPS system. The online UPS system is simulated by using MATLAB/Simulink software. Therefore, we need to design our online UPS system first. This is our current design system :
This design consists of a rectifier in which the function is to convert the main ac supply to dc. then, it will charge the battery and go to the inverter to convert to ac from dc.
WEEK 9
For this week, I am continuing my literature study on the PWM controller technique. There are several types of PWM, which is :
- Single PWM
- Multiple PWM
- Space Vector PWM
- Sinusoidal PWM
So. for our current design I am using the sinusoidal PWM controller. SPWM can be achieved by comparing between triangle carrier signals with a reference voltage or control voltage, which is a sine wave. The inverter then uses the frequency of the triangle wave as the switching frequency. SPWM is divided into two types which are bipolar and unipolar. Bipolar SPWM is widely used in a full-bridge inverter because it is simple to implement. However, Bipolar SPWM requires a large filter and filter size is known to influence the efficiency of the system. Meanwhile, Unipolar SPWM has many advantages since it requires a small filter and produces a better output waveform. So, I am using the Unipolar SPWM since it requires small filter and produces a better output waveform. In this process, the triangular carrier signal,vc is compared with two reference signals which are positive, vr and negative signals, -vr. The process of comparing these two signals results in the unipolar switching signal. The unipolar switching signal is used to trigger the power of electronic devices in the inverter. As the pulses are injected into the inverter, the AC waveform will be produced.
WEEK 8
For this week, we try to focus to do simulation and literature studies on the inverter and PWM controller. An inverter is known as a device to convert electrical energy of DC form into AC form. The main purpose of an inverter is to take DC power from a battery source and convert it to AC. A voltage source inverter is made up of GTOs, power transistors, MOSFETs or IGBTs. There are two types of single-phase inverter which are half-bridge inverter and full-bridge inverter. But for our design, we try to use the H-bridge inverter. The H-bridge inverter with a new robust control scheme is proposed for operation under the non-linear loading condition and provides the fast transient response during the change of modes which is mentioned during week 3 for ENTRY 1.
The PWM technique is widely used in the power electronics industry to produce a switching sequence for inverters and rectifiers. In PWM, pulses of constant amplitude but different duty cycles are generated by modulating the time periods. The figure below shows how a PWM signal is generated. This modulation is done by comparing carrier and reference signals. The sine wave signal represents the reference signal while the triangular wave is the carrier signal.
From the figure above, the modulation index and frequency ratio can be identified. Calculation of the modulation index and the frequency ratio, MR can be made using equations,
Modulation index, Mi = (Amplitude of the reference signal) /( Amplitude of the carrier signal)
Frequency ratio, Mr = (carrier frequency) / (reference frequency)