In order to enable the current cordless kitchen system to the 3.68 kW power level, measures needs to be taken to reduce the mains harmonics. The problem is that with the increase of the power level from 2.40 kW to 3.68 kW, the amplitude of the undesired harmonics in mains current will exceed the limit according the mains harmonics standard (IEC). Hence, this project aims to investigate means and measures to reduce the undesired mains harmonics.
In the cordless kitchen system, the mains harmonics are generated due to the existence of the communication time slot around the zero crossing of the mains voltage. The background of having a communication time slot in this system is introduced in detail in section 2. To remove the negative effect of communication time slot on the mains harmonics, a compensator is built which is connected in parallel with the DC input terminals of the existing transmitter stage. The compensator can fix the mains current, such that the amplitude of undesired harmonics are reduced.
The compensator consist of a Boost converter and a Buck converter. The duty cycles of the two converters depend on the compensation current needed. Therefore a current sensor, a zero crossing detector and a control circuit were developed and described in this report.
Finally, the simulation result and practical result are provided and evaluated. As a result of this work, the amplitudes of the mains harmonics are significantly reduced, such that the cordless kitchen system meets the standards for mains harmonics.