Side-by-side comparison
| Parameter | SPWM | SVPWM |
|---|---|---|
| Full Name | Sinusoidal PWM (carrier-comparison method) | Space Vector PWM (rotating reference frame) |
| Reference Signal | Sinusoidal reference vs triangular carrier | Reference voltage vector V_ref in α-β plane |
| DC Bus Utilisation | Maximum V_out(ph-ph) = V_dc/√2 ≈ 0.707·V_dc (linear range) | Maximum V_out(ph-ph) = V_dc/√3 ≈ 0.577·V_dc × √3 = 1.0·V_dc (linear) — 15.5% more than SPWM |
| Modulation Index (max linear) | m_a = 1.0 | m = 1.155 (2/√3) |
| Switching Loss | Higher — each phase switches independently | Lower — zero vectors reduce total switch events |
| THD | Slightly higher at same f_sw | Slightly lower; harmonic energy shifted to higher frequencies |
| Implementation | Simple — three comparators, one triangle wave | Requires real-time vector calculation; DSP/FPGA (e.g. TMS320F28335) |
| Neutral Point Voltage | Significant neutral point oscillation in 3-level inverters | Controllable via zero-vector selection (e.g. 000 vs 111 preference) |
| Overmodulation | m_a > 1 gives 6-step; significant low-order harmonics appear | Smooth transition to 6-step; overmodulation region better managed |
| Common Usage | Low-cost single-phase and simple three-phase inverters | All modern industrial drives: ABB ACS880, Mitsubishi FR-A800 |
Key differences
SPWM compares three sinusoidal references (120° apart) with a common triangular carrier and fires each switch independently — implementation needs three analog comparators or three PWM timers with no inter-axis awareness. SVPWM treats the three-phase system as a single rotating vector V_ref in the α-β plane, selects two adjacent active vectors and one or two zero vectors, and distributes the dwell times to minimise ripple. The 15.5% DC bus utilisation gain of SVPWM comes from injecting a third-harmonic zero-sequence component (invisible in line-to-line voltage) that raises the peak of each phase reference beyond V_dc/2 without saturating the modulator. On a TMS320F28335 DSP, SVPWM runs as a 10 µs interrupt routine updating six compare registers per switching period.
When to use SPWM
Use SPWM when implementing a simple single-phase or low-cost three-phase inverter where DSP resources are minimal and the DC bus utilisation gap does not matter. Example: a DIY 500 W single-phase solar inverter implemented on a PIC16F877A uses SPWM at 10 kHz via a PWM comparator and a SG3525 IC.
When to use SVPWM
Use SVPWM for any industrial three-phase motor drive or grid-tied inverter where maximum voltage output from the available DC bus and lower switching losses are important. Example: the STM32F303 microcontroller in a 2.2 kW induction motor drive runs SVPWM at 8 kHz using a 60° clamp variant to reduce leg switching events by 33%.
Recommendation
For any three-phase inverter above 1 kW, choose SVPWM — the 15% DC bus gain reduces both the required DC capacitor voltage and motor current for the same output power. Use SPWM for single-phase applications or where DSP capability is absent. The implementation complexity of SVPWM is handled by every modern microcontroller with motor control PWM hardware, so it is no longer a valid reason to choose SPWM.
Exam tip: Examiners ask students to calculate the maximum output phase voltage for SPWM and SVPWM from a given DC bus voltage and explain why SVPWM gives a higher value — state SPWM gives V_dc/2, SVPWM gives V_dc/√3, and the ratio is 2/√3 = 1.155.
Interview tip: A placement interviewer at a motor drives company will ask you to explain the zero vector selection strategy in SVPWM and its effect on switching losses — explain that alternating between V0 (000) and V7 (111) symmetrically halves switching transitions compared to using only one zero vector, lowering switching losses by up to 30%.