MATLAB Code Implementation of Three-Level Inverter

A three-level inverter is a widely used topology in medium and high-voltage power conversion applications, offering advantages over traditional two-level inverters such as reduced output voltage harmonics and lower switching losses. Implementing its simulation in MATLAB involves several key aspects:

Topology Modeling Building diode-clamped or flying capacitor three-level circuit structures using Simulink's power electronics component library. Select IGBT modules and clamping diodes, ensuring the DC side incorporates voltage-divider capacitors for neutral point potential balance. Key implementation includes proper connection of switching devices and anti-parallel diodes using Simulink's Simscape Electrical components.

PWM Control Strategy Typically employs carrier disposition methods (like PD-PWM) or space vector modulation (SVPWM). Implementation requires generating two phase-opposed triangular carriers using Repeating Sequence blocks, comparing them with modulation waves through Relational Operator blocks. Logical Operator blocks then convert comparison results into switching signals for upper and lower arms. The PWM generator can be implemented using MATLAB Function blocks for algorithmic flexibility.

Closed-Loop Design (Optional) For voltage regulation or speed control, incorporate PI regulators. The voltage outer loop samples output side voltage using Voltage Measurement blocks, while the current inner loop detects load current via Current Measurement blocks. Dynamic response is achieved by adjusting modulation index through PID Controller blocks with tuned parameters.

Waveform Observation and Analysis Use Scope modules to capture output voltage/current waveforms, combined with FFT analysis tools to evaluate THD (Total Harmonic Distortion). Focus on smooth level transitions and neutral point potential fluctuations. Implement THD calculation using powergui's FFT analysis or custom MATLAB scripts with fft() function.

Recommended simulation approach: First validate PWM signal logic correctness using Test Bench models, then connect to main circuit to observe no-load/loaded waveforms. Finally optimize performance by adjusting dead-time parameters and switching frequencies. Comparative analysis between two-level and three-level output harmonics using spectrum analyzers demonstrates performance advantages clearly.