How to reduce 3rd harmonics with ST6200C motor control software
This application note presents a cost-saving solution for suppressing 3rd harmonic current in the power line of universal motors, which are widely used in home appliances like vacuum cleaners. The issue arises when TRIAC conduction is not in full wave mode, causing high amplitude 3rd harmonics that may not comply with IEC61000-3-2 standards, particularly for motors over 1200W.
The proposed solution is based on an asymmetrical phase control method (patented by KURZ) implemented via software on the ST6200C microcontroller. By modulating the phase angle delay times using a 'two long plus two short' half-wave pattern, the motor current waveform is adjusted to suppress specified harmonic components. Experimental results on a 1500W vacuum cleaner demonstrate that this method significantly improves harmonic performance compared to symmetrical phase control.
| Applicable Input Current | up to 16A |
|---|---|
| Nominal Frequency | 50Hz or 60Hz |
| Nominal Voltage (Single Phase) | up to 240V |
| Nominal Voltage (Three Phase) | up to 415V |
The IEC61000-3-2 standard sets maximum permissible values for harmonic components of the input current.
The solution is implemented using the ST6200C microcontroller.
It modulates the motor current by alternating between two long and two short half waves in the power cycles.
The efficiency was proven on a 1500W vacuum cleaner under various load conditions.