401 - Single-Phase Inverter¶

PWM inverter fundamentals for DC-AC conversion.

Overview¶

Single-phase inverters convert DC to AC using PWM switching strategies, essential for: - UPS systems - Solar inverters (residential) - Motor drives (single-phase) - AC power supplies

Topologies¶

Half-Bridge Inverter¶

       +Vdc/2
         │
         ├───┤S1├───┬─── AC out
         │          │
        Cdc        Load
         │          │
         ├───┤S2├───┘
         │
       -Vdc/2

Output: ±Vdc/2

Full-Bridge (H-Bridge) Inverter¶

      +Vdc ───┬────────┬───
              │        │
             S1       S3
              │        │
              ├─ Load ─┤
              │        │
             S2       S4
              │        │
      GND ───┴────────┴───

Output: ±Vdc

PWM Strategies¶

Bipolar PWM¶

Compare sine reference to triangle carrier
S1-S4 switch together, S2-S3 switch together
Output levels: +Vdc, -Vdc

Unipolar PWM¶

Two reference signals (positive and negative)
Each leg switched independently
Output levels: +Vdc, 0, -Vdc
Lower harmonic content, reduced filter size

Key Equations¶

Modulation Index: $$m_a = \frac{V_{ref,peak}}{V_{carrier,peak}}$$

Fundamental Output Voltage (linear region): $$V_{out,1} = m_a \cdot V_{dc}$$ (full-bridge)

THD Calculation: $$THD = \frac{\sqrt{V_2^2 + V_3^2 + ... + V_n^2}}{V_1}$$

Design Parameters¶

Parameter	Typical Value
DC Bus	400V (from PFC)
Switching Freq	10-50 kHz
Output Filter L	1-5 mH
Output Filter C	2-10 µF
Modulation Index	0.8-0.95

Simulation Exercises¶

Compare bipolar vs unipolar PWM
Observe dead-time effects
Analyze output spectrum (FFT)
Design LC output filter