Optimum harmonics injection to minimize bus capacitance of CRM boost PFC conveters meeting EN61000-3-2 Class D limits

Based on the energy-ripple perspective, this paper discusses the optimum 3 rd and 5 th order harmonic injection to minimize bus capacitance of CRM boost PFC converters. Within EN61000-3-2 Class D limits, 34% 3 rd and 19% 5 th order harmonics injection can theoretically achieve the maximum bus capacitance reduction of 36.1% for wide input application (100∼240Vac). However, the conventional on-time control ignores the deviation effect of CRM operation, which introduces the exceeding 3 rd and 5 th order injected harmonics than EN61000-3-2 Class D limits. In order to eliminate the deviation effect, a novel on-time compensation method is proposed to realize accurate harmonics injection. The experimental results from an 120W prototype show that the maximum bus capacitance reduction of 33% is achieved in practice meeting EN61000-3-2 Class D limits within 100∼240Vac input range.