Voice Recognition 1-Phase Motor Controller full report
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Voice Recognition 1-Phase Motor Controller
Because of advances in solid state power devices and microprocessors, variable speed AC Induction motors powered by switching power converters are becoming more and more popular. Switching power converters offer an easy way to regulate both the frequency and magnitude of the voltage and current applied to a motor. As a result much higher efficiency and performance can be achieved by these motor drives with less generated noises. The most common principle of this kind, is the constant V/Hz principle
which requires that the magnitude and frequency of the voltage applied to the stator of a motor maintain a constant ratio. By doing this, the magnitude of the magnetic field in the stator is kept at an approximately constant level throughout the operating range.
Thus, (maximum) constant torque producing capability is maintained. When transient response is critical, switching power converters also allow easy control of transient voltage and current applied to the motor to achieve faster dynamic response. The constant V/Hz principle is considered for this application.
The energy that a switching power converter delivers to a motor is controlled by Pulse Width Modulated (PWM) signals applied to the gates of the power transistors. PWM signals are pulse trains with fixed frequency and magnitude and variable pulse width. There is one pulse of fixed magnitude in every PWM period. However, the width of the pulses changes from period to period according to a modulating signal. When a PWM signal is applied to the gate of a power transistor, it causes the turn on and turn off intervals of the transistor to change from one PWM period to another PWM period according to the same modulating signal. The frequency of a PWM signal must be much higher than that of the modulating signal, the fundamental frequency, such that the energy delivered to the motor and its load depends mostly on the modulating signal.
Figure 1 shows two types of PWM signals, symmetric and asymmetric edge-aligned. The pulses of a symmetric PWM signal are always symmetric with respect to the center of each PWM period. The pulses of an asymmetric edge-aligned PWM signal always have the same side aligned with one end of each PWM period. Both types of PWM signals are used in this application.
Different PWM techniques, or ways of determining the modulating signal and the switch-on/switch-off instants from the modulating signal, exist. Popular examples are sinusoidal PWM, hysterises PWM and the relatively new space vector PWM. These techniques are commonly used with three phase Voltage Source power inverters for the control of three-phase AC induction motors. The space vector PWM technique is employed in this application.
Since we had to pass the ADC output through all of the filters faster than our sample time; the time it took do all the filter calculations was very important. We were able to run through 9 filters in under 4000 cycles, which is the amount of cycles available when sampling from the ADC at 4 KHz. The fingerprint comparison function did not have a speed requirement and so the cycle time for that was unimportant. The program was able to recognize five words, but sometimes it would become confused and match the incorrect word if the word that was spoken varied too much from the word stored in the dictionary. As a rough estimate the program recognized the correct word about 70% of the time a valid word was spoken. The program achieved success using Chirag
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