Electrical Machines Professor

Three Phase Inverter

In this experiment, a three-phase inverter was used to test it as a PWM pulse, a three-phase sine-wave generator, and as a control of a brushless DC motor. The inverter is a great controller for a DC brushless motor cause it provides a wide control action in terms of the duty cycle of a signal, which allows controlling the motor at a desired speed and torque. Also, computer simulations were made to test the inverter as a DC varying power supply, and as an AC power supply. Finally, a flow chart was established, which describes the process of controlling the motor using an inverter.

The uses of inverter in electrical applications are almost infinite. The control of a varying signal, even if it is DC or AC, provides a good tool to control many different loads for a specific application, and also, allows providing controlled voltage supply for sensitive instruments and machines.

The aim of this experiment is to understand the design, construction, simulation, and testing of an inverter in many different applications.

The aim of this experiment is to check if the inverter is operating correctly by generating three pairs of fixed duty cycle pulse width modulation (PWM) pulses. For this, it's necessary to implement two MOSFETs. After building the circuit, and building the software on the PIC, the measurements were taken on terminal points (outputs from the PIC to the MOSFET driver chip) in three pairs, which are: J1-J2, J3-J4, and J5-J6.
The gate-on voltage for terminals J1-J2 is shown in figure 2.1(a) and 2.1(b), respectively. The value for this parameter in both signals are represented in equation 1 and 2. On the figures, we can also determine the time on and time off for each signal, shown in equations 3 and 4, respectively. The frequency comes as the inverse of the period, as shown in equation 5. Duty Cycle is established on equation 6 and 7 for both points. And the dead time is the time delay between HI off and LO on, shown in equation 8.

Table 1. PWM signals on every terminal.