⚡ MATLAB Simulation of Five-Level Hybrid Multilevel Inverter

MATLAB/Simulink simulation of a Five-Level Hybrid Multilevel Inverter, and we will compare two modulation techniques:✅ Pulse Width Modulation (PWM) and ✅ Nearest Level Modulation (NLM).

This blog explains the topology, operating modes, switching states, modulation logic, and output waveform variation by changing the modulation index.

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🧩 1) Five-Level Hybrid Multilevel Inverter Topology

This five-level inverter is built using:

• 🔷 One H-Bridge inverter

• 🔁 One bidirectional switch (auxiliary switch)

• 🔋 Two DC voltage sources (V1 and V2)

• 🧰 Load (R or RL load)

The key advantage is: with only one H-bridge + one bidirectional switch + two sources, we can generate five output voltage levels.

🔋 2) DC Source Assumption

For easy understanding, we assume:

• V1 = Vdc/2

• V2 = Vdc/2

So by combining these two sources, we can achieve:✅ +Vdc, ✅ +Vdc/2, ✅ 0, ✅ −Vdc/2, ✅ −Vdc

⚙️ 3) Mode of Operation (Five Voltage Levels)

The output levels are produced by selecting specific switch combinations.

✅ Level 1: +Vdc

• Turn ON: S1 and S2

• Output across load: V1 + V2 = Vdc

✅ Level 2: +Vdc/2

• Turn ON: SA (or S5) and S2

• Output across load: V2 = Vdc/2

✅ Level 3: 0 V (Zero Level)

Two possible switching combinations:

• Turn ON: S2 and S4 ✅ or

• Turn ON: S1 and S3 ✅➡️ Load is shorted and output becomes zero.

✅ Level 4: −Vdc/2

• Turn ON: S3 and SA (or S5)

• Output becomes negative half level

✅ Level 5: −Vdc

• Turn ON: S3 and S4

• Output across load: −(V1 + V2) = −Vdc

👉 This is the basic working principle of the five-level inverter.

🧪 4) MATLAB/Simulink Implementation Overview 🖥️

In Simulink, the model includes:

• 🔋 Two DC sources

• 🔁 Bidirectional switch section

• 🔷 H-bridge stage

• 🧲 Load block

• 🎛️ Modulation selection block (PWM / NLM)

• 📈 Scopes for inverter voltage and current

🟦 5) Nearest Level Modulation (NLM) – Working 🔍

Nearest Level Modulation is a simple level comparison technique.

✅ Concept

• Compare a sinusoidal reference with fixed threshold levels:

  • +0.75, +0.25, −0.25, −0.75

Based on where the sine wave lies, the inverter output is selected as:

• Above +0.75 → +Vdc

• Between +0.25 and +0.75 → +Vdc/2

• Between −0.25 and +0.25 → 0

• Between −0.75 and −0.25 → −Vdc/2

• Below −0.75 → −Vdc

📌 So NLM produces a stepped waveform, and switching is done only when sine crosses the thresholds.

✅ Advantage: Less switching, simple logic ⚡⚠️ Limitation: Step waveform, harmonic quality depends on levels

🟥 6) PWM Modulation – Working 🔄

PWM uses a carrier-based technique.

✅ Concept

• Compare sinusoidal modulating signal with triangular carrier

• The pulse width varies based on modulation index (m)

This generates a high-frequency switching pulse to control the inverter switches.

✅ Advantage: Better waveform shaping, smoother output ✅⚠️ Limitation: Higher switching frequency → more switching loss 🔥

🎚️ 7) Modulation Index Variation (m) and Output Changes 📉📈

In the model, modulation index is initially set to:

• ✅ m = 0.9

What happens when m changes?

• When m is high (0.9 or 1.0)

  • Output voltage is higher

  • Load current increases

  • Inverter utilizes full five levels ⚡

• When m reduces (0.7, 0.5, 0.2)

  • Output levels reduce تدريجياً

  • Voltage magnitude reduces

  • Current reduces

  • At very low m (below 0.25), inverter may not generate output in NLM mode 🚫

📌 Example observation from simulation:

• m = 0.5 → output may reduce from 5-level to 3-level

• m = 0.2 → below threshold, switches remain OFF (no output)

• m = 0.3 → output starts again since it crosses 0.25 threshold

🔁 8) PWM vs NLM – Key Comparison ✅

Feature	PWM 🟥	NLM 🟦
Switching Frequency	High 🔥	Low ✅
Output Smoothness	Better ✅	Step waveform
Harmonic Performance	Better THD ✅	Depends on thresholds
Control Complexity	Medium	Very simple ✅
Switching Loss	Higher	Lower ✅

✅ Conclusion 🎯

This MATLAB/Simulink model demonstrates:✅ Five-level hybrid inverter operation using two DC sources + bidirectional switch + H-bridge✅ Implementation of PWM and Nearest Level Modulation✅ Effect of modulation index on inverter voltage levels and current✅ Clear differences in waveform nature between PWM and NLM