Electromagnetic interference in power converters is a crucial problem for circuit designers. Electromagnetically compliant converter design is required for the safety of an operation. A novel filter design approach considering ground leakage current, different winding styles for common mode choke, tolerance of filter capacitor is proposed in this study to solve the electromagnetic interference problem. In the study, electromagnetic compatibility issue is investigated for a 25 kW, 15 kHz switching frequency, three-phase/level T-type grid-connected solar inverter. The test setup is installed based on EN55011 standard, and the interferences emitted by the inverter to the grid through conduction are measured. Then, a filter design is made to prevent these interferences from being transmitted to the grid. After the filter is designed and engaged, the measurements are repeated. So, the noise attenuation of the EMI filter is verified experimentally. Experiences obtained from the hardware modification in the EMI filter, which is designed for an industrial solar inverter, have been discussed. It is observed that the result of conducted emission measurement is within the limits of the EN55011 Class B standard.

This paper proposes a bidirectional three-level T-type LLC resonant DC-DC converter operating with phase-shift control, which is simple and effective, variable frequency modulation to perform soft switching in a wide voltage ratio range and light loads, and pulse width modulation to reduce reactive circulating current. In this combined modulation method, three control parameters: switching frequency, the duty cycle of switches in the vertical arms, and phase shift between primary and secondary switches, are changed depending on the voltage conversion ratio and load. The circuit operates as LLC resonant in forward operation and series resonant in reverse operation. Thus, LLC and series resonant analyses of the proposed converter, operated in continuous current mode and buck mode, are presented. A simplified frequency domain analysis, including all harmonics, is used in the theoretical calculations. Thus, the control parameters are accurately calculated for forward and reverse operations. The current, voltage, and power formulas in the working principle of the converter are derived, and an analysis of the control parameters and zero voltage switching region is performed. Soft switching analysis is done by considering the junction capacitor of the MOSFET and the dead time. The theoretical performance of the proposed modulation method has been verified with a 2kW prototype. Soft-switching and loss analyses of the proposed converter have also been investigated under different load conditions and voltage conversion ratios. The proposed LLC resonant topology and modulation method improved significantly more efficiency than the phase-shifted modulated T-type converter under 30-100% load conditions.

Electromagnetic interference is the main problem in high switching power converters like DC-DC converters. One of the solution methods for electromagnetic interference reduction is to design a snubber circuit. The snubber circuit is a practical method to reduce fluctuations caused by parasitic components from the layout and non-ideal characteristics of switching devices. An effective snubber circuit design increases the converter's efficiency and reduces EMI noise. In this paper, electromagnetic interference is reduced using different snubber circuits in a three-level T-type isolated bidirectional DC-DC converter. The converter is simulated in PSIM to see the effectiveness of the noise reduction with the snubber circuits. CISPR 25 standard is used for the compliance assessment in the study.

Electricity is delivered to end users through generation, transmission, and distribution phases. The most important issues during energy journey is to provide selective, rapid, and safe protection to ensure energy continuity. In this context, when the operating conditions defined in the protection systems are exceeded, an effective protection system and coordination are required to provide that as few consumers as possible are affected by the energy outage and reliably isolate the fault. If the short circuit is not separate from the network quickly after a short circuit occurs, network equipment and electrical devices may be damaged because of overcurrent that occurs. In this study, the coordination of overcurrent protection relay at 34.5 kV voltage level of the distribution network in Sakarya Province, Serdivan District, Yazlık region is made and MATLAB/Simulink is used in the modeling of the system. All data of inspected distribution network is embedded to MATLAB/Simulink file and then optimum protection is provided on relay coordination settings by performing power flow analysis and short circuit calculations.