Accurate Extraction of Noise Source Impedance of an SMPS Under Operating Conditions

An accurate measurement method to extract the common mode (CM) and the differential mode (DM) noise source impedances of a switched mode power supply (SMPS) under its operating condition is developed and validated. With a proper pre-measurement calibration process, the proposed method allows extraction of both the CM and the DM noise source impedances with very good accuracy. These noise source impedances come in handy to design an electromagnetic interference (EMI) filter for a SMPS systematically with minimum hassl

Performance of common-mode chokes

A low-cost method for experimental investigation of common-mode chokes for reducing high-frequency motor ground-currents of inverter-based drive systems of several hundred kW is presented. It provides a powerful tool during the design stage of such chokes to verify their predicted performance. The method draws from the mainly capacitive behavior of machines at very high frequencies. Results of experimental tests for drives with peak ground-current amplitudes of more than 60 Amperes, carried out on a 4 kW test-bed, are presented. They confirm the feasibility of such tests as well as the capability of small, inexpensive, single-turn chokes to effectively reduce the ground-current

Common-Mode Noise Cancellation in Switching-Mode Power Supplies Using an Equipotential Transformer Modeling Technique

Electromagnetic interference (EMI) is a significant challenge in the design of high-efficiency switching-mode power supplies due to the presence of common-mode (CM) noise. In many power-supply designs, a variety of noise suppression schemes must be implemented in order to meet EMI requirements. Most of these schemes create power loss that lead to efficiency and thermal issues. In this paper, a transformer construction technique is proposed that effectively reduces the CM noise current injecting across the isolated primary and secondary windings. This technique is based on the zero equipotential line theory. A transformer design with the proposed CM noise cancellation technique can achieve high conversion efficiency as well as substantial CM noise rejection.published_or_final_versio

Modeling strategy for EMI filter and flyback transformer

“The switch-mode power supply is key to miniaturizing power adapters. However, the switching nature of the circuit introduces issues in conducted emissions. In a flyback converter, the transformer serves as the path for common mode current flowing from the primary side to the secondary side. Different winding technologies have been invented and implemented to reduce the capacitance between the primary side and the secondary side. But the repeatability of the winding is still poor due to the fluctuations of the winding machine. Thus, the resulting conducted emission has a fluctuation that can lead to failure in the compliance tests. EMI filter is another module implemented to reduce the conducted emissions. Due to the miniaturization, the components inside a filter are closely placed, therefore, strong mutual parasitics. These parasitics degrade the performance of the EMI filter. Overall, it would be beneficial if the performance of the EMI filter and the fluctuation of the transformer can both be analyzed through pre-design simulation. In this dissertation, a model strategy for EMI filters is developed and validated through comparison with measurement. The strategy covers different types of film capacitors, common mode chokes, and circuit topologies. This dissertation also provides an approach to asserting the parasitic capacitance of transformers through 2D analysis. Contradictory to the existing models that relate the parasitic capacitance and conducted emissions, the best-performance capacitance is found not zero. A simplified circuit model is developed to associate the conducted emissions with the parasitic capacitance of the transformer. This circuit model leads to an analytical formulation for evaluating the best-performance parasitic capacitance of the transformer, and its prediction matches with the observed relationship in the measurement. In conclusion, the research in this dissertation clarified the procedure for utilizing computer-aided simulation to guide the design of EMI filters and flyback converters in compact designs”--Abstract, page iv

COMMON MODE VOLTAGE ELIMINATION IN THREE-PHASE FOUR-LEG INVERTERS UTILIZING PULSE DENSITY MODULATION

Common mode (CM) electromagnetic interference (EMI) is a phenomenon that negatively affects power electronics to include voltage source inverters. Typically, CM EMI reduction is achieved through passive measures such as CM chokes and passive filters. This thesis research explores removing the need for these passive devices in three-phase, four-leg grid-following inverters by eliminating CM EMI using pulse density modulation (PDM) in conjunction with model predictive control (MPC) and delta modulation. A physics-based model of the equipment under test (EUT), utilizing state-space modeling, was analyzed using computer simulations and a laboratory prototype, utilizing SiC switching devices, was designed to validate the model. The physics-based model of the proposed control system was converted to Verilog, a hardware description language (HDL) utilizing MATLAB HDL coder in order to control the laboratory prototype via a field-programmable gate array (FPGA). Simulated and experimental results demonstrate that both the unbalanced load requirements in MIL-STD-1399 and the conducted emission limits in MIL-STD-461G are met with the proposed controller, while the grid-following converter supplies a desired current to the load.Office of Naval Research, Arlington VA 22203-1995Outstanding ThesisLieutenant, United States NavyApproved for public release. Distribution is unlimited

Mitigation Emission Strategy Based on Resonances from a Power Inverter System in Electric Vehicles

Large dv/dt and di/dt outputs of power devices in the DC-fed motor power inverter can generate conducted and/or radiated emissions through parasitics that interfere with low voltage electric systems in electric vehicles (EVs) and nearby vehicles. The electromagnetic interference (EMI) filters, ferrite chokes, and shielding added in the product process based on the black box approach can reduce the emission levels in a specific frequency range. However, these countermeasures may also introduce an unexpected increase in EMI noises in other frequency ranges due to added capacitances and inductances in filters resonating with elements of the power inverter, and even increase the weight and dimension of the power inverter system in EVs with limited space. In order to predict the interaction between the mitigation techniques and power inverter geometry, an accurate model of the system is needed. A power inverter system was modeled based on series of two-port network measurements to study the impact of EMI generated by power devices on radiated emission of AC cables. Parallel resonances within the circuit can cause peaks in the S21 (transmission coefficient between the phase-node-to-chassis voltage and the center-conductor-to-shield voltage of the AC cable connecting to the motor) and Z11 (input impedance at Port 1 between the Insulated gate bipolar transistor (IGBT) phase node and chassis) at those resonance frequencies and result in enlarged noise voltage peaks at Port 1. The magnitude of S21 between two ports was reduced to decrease the amount of energy coupled from the noise source between the phase node and chassis to the end of the AC cable by lowering the corresponding quality factor. The equivalent circuits were built by analyzing current-following paths at three critical resonance frequencies. Interference voltage peaks can be suppressed by mitigating the resonances. The capacitances and inductances generating the parallel resonances and responsible elements were determined by the calculation through the equivalent circuits. A combination of mitigation strategies including adding common-mode (CM) ferrite chokes through the Y-caps and the AC bus bar was designed to mitigate the resonances at 6 MHz, 11 MHz, and 26 MHz related to the CM conducted emission by IGBT switching and the radiated emission of the AC cable. The values of Z11 decreased respectively by 15 dB at 6 MHz, 0.4 dB at 11 MHz, and 11.5 dB at 26 MHz and the values of S21 decreased respectively by 8.6 dB at 6 MHz, 7 dB at 11 MHz, and 6.3 dB at 26 MHz. An equivalent model of the power inverter system for real-time simulation in time domain was built to validate the mitigation strategy in simulation software PSPICE

Common-Mode Current Prediction and Analysis in Motor Drive Systems for the New Frequency Range of 2–150 kHz

Due to the significant advances in fast switching semiconductor devices, harmonic emissions caused by the adjustable speed drives (ASDs) have been changed in terms of frequency range and magnitude. The frequency range of 2-150 kHz has been distinguished as a new interfering frequency range, disturbing the distribution networks. This article proposes a behavioral model of an ac motor to predict the common-mode (CM) current in ASDs. An approach is presented to calculate the parameters of the model, through which the dominant impact of each element at a specific frequency is considered. Moreover, along with the proposed motor model, a system modeling strategy is presented for filter design considerations at an emerging frequency range of 2-150 kHz. To verify the effectiveness of the proposed model, real-time experiments are conducted. The results prove that the introduced model can accurately predict the resonances of the CM loop created by the motor. Consequently, the proposed model is suitable for electromagnetic interference (EMI) filter design covering the 2-150-kHz standard. </p

High Density EMI Filter Design in High Power Three-Phase Motor Drive Systems

High density EMI filter is important in the application of more-electric-aircraft (MEA). In this work, the author is focusing on several major aspects of EMI filter design that would influence the power density. In Chapter 1, the feature of EMI study and conventional design methods are reviewed. The interaction between the common-mode (CM) and differential-mode (DM) noise is one key factor introducing unnecessary weight to EMI filter design. In Chapter 2, the author explains the origin of the mixed-mode (MM) noise on the output side of three-phase motor drives. Experimental results have verified the existence of the MM noise in three-phase motor drives and its impact on power density. In Chapter 3, the noise mode transformation (NMT) in three-phase motor drives due to system impedance unbalance is discussed. Simulation and experimental results show that the NMT will cause EMI filter overdesign if not considered during the design stage. In Chapter 4 the author discusses the possibility of adding a CM inductor at the motor front and chassis end to reduce CM EMI filter weight. Experimental results show that the motor-end filter is effective in attenuating low frequency noise and has the benefit of being light weight comparing with the traditional three-phase CM choke. Cooling of the filter is of great importance in high power systems. In Chapter 5, a practical liquid-cooling design procedure for EMI filters in high power motor drives has been discussed. Potting and thermal modeling are analyzed. Thermal test results verify the effectiveness of the procedure. In Chapter 6, the author models the impedance impact of potting material and cooling cases on both CM and DM inductors. Experimental results match well with the developed models. In Chapter 7, a comprehensive design procedure for high density EMI filter in high power motor drives has been proposed, based on the knowledge of previous chapters. As the verification of the procedure, a high density EMI filter is designed and tested in a 100 kW three-phase motor drive system for MEA application. Conclusion and future work are summarized in Chapter 8