Summary
Highlights
The session begins by introducing the practical demonstration in MATLAB Simulink for chopper, rectifier, and inverter circuits, following previous theoretical discussions. The speaker hands over the session for demonstration.
The demonstration starts with a DC-to-DC buck converter. The speaker lists the necessary components such as a DC voltage source, diode, inductor, capacitor, switch (ideal switch), and resistor. The process of gathering these components from the Simulink library and assembling the circuit is shown. The buck converter is configured to convert 20V DC input to 10V DC output, achieved by controlling the ideal switch with a Pulse Width Modulation (PWM) generator.
Each component's role in the buck converter circuit is explained: the DC voltage source provides constant DC, the pulse generator controls the ideal switch's on/off time and duty cycle, the ideal switch acts as a power transistor, the diode is a freewheeling diode, the inductor smooths current flow, the capacitor removes ripple voltage, and the resistive load simulates a real-time load. The energy flow through the circuit during on and off states of the switch is described. The simulation is run, demonstrating the 20V input being bucked to 10V output using a 50% pulse width.
The applications of buck converters, particularly in EV circuits for stepping down high voltage to lower voltage for auxiliary components like headlights and indicators, are discussed. The formula for a DC buck converter, V_out = D * V_in, is explained, where D is the duty cycle (pulse width percentage). The simulation is re-run with different pulse widths (75% and 25%) to illustrate how the output voltage changes accordingly (e.g., 20V to 5V with 25% pulse width).
The next circuit is a DC-to-DC boost converter, which maximizes voltage. Similar to the buck converter, the components needed (DC voltage source, MOSFET switch, inductor, diode, capacitor, resistor, voltage measurement tools, pulse generator, and power GUI block) are gathered and assembled in Simulink. The purpose of each component, especially why a larger capacitor is used in boost converters, is clarified during the assembly.
The boost converter is simulated, demonstrating how a 25V input is boosted to 50V output with a 50% pulse width. The formula for a boost converter, V_out = V_in / (1 - D), is introduced and used to calculate output voltages for different duty cycles (e.g., 75% duty cycle results in 100V output from 25V input). The effect of changing the pulse width on the MOSFET’s on/off time is also visualized.
Applications of boost converters, particularly in EV charging circuits like fast chargers, are highlighted, where input voltage needs to be boosted for battery packs. Questions regarding not skipping capacitors in any circuit and the difference between buck and boost converters are addressed, emphasizing their use for power distribution in electrical vehicle systems.
The final circuit showcased is a three-phase rectifier, which converts AC to DC. The necessity of rectifiers in daily life (e.g., mobile chargers) is mentioned. Components required include a three-phase AC voltage source, thyristor switches, pulse generators, and measurement tools. The setup uses six thyristor switches in a bridge configuration. The AC voltage source is set to 230V with a 50Hz frequency, and phase shifts of 120 degrees for each phase are configured.
The session details the proper pairing of thyristor switches (e.g., T1 and T2, T3 and T4, T5 and T6) to avoid short circuits. Pulse generators are configured for each pair with a 50% pulse width and specific phase delays (e.g., 30 degrees for the first pair, 150 degrees for the second, 270 degrees for the third) to ensure correct sequential switching. Current and voltage measurement tools are integrated into the circuit to monitor input and output.
The three-phase rectifier simulation is run, showing the conversion of a three-phase AC input to a pulsating DC output. The waveform displays the 30-degree phase delay and 120-degree phase shifts. The output demonstrates the conversion of 230V AC to approximately 400V DC. The session concludes with a quick recap of all three converters (buck, boost, and rectifier), reiterating their formulas, working principles, and how pulse width modulation controls their output.