Xuning Zhang

Grid-Interface Bidirectional Converter for Residential DC Distribution Systems—Part 2: AC and DC Interface Design With Passive Components Minimization

With the emerging installations of multitype renewable energy sources and energy storage elements, the dc electronic distribution systems in residential houses/buildings (dc nanogrid) are becoming an alternative future system solution, achieving a zero net-energy consumption and optimized power management. One of the critical components in such a dc system is the grid-interface bidirectional ac–dc power converter, namely the energy control center. Besides, the basic power conversion function, the system interface solution in grid-interface converter is important to successfully interconnect the ac and dc systems as well as fulfill the power quality and EMI regulation codes on both dc and ac sides. This paper presents a complete discussion of several aspects of system interface design for the grid-interface converter under both single-phase and three-phase system conditions. A passive plus active filter solution is proposed to accomplish the common-mode-related noises minimization as well as a dramatic reduction of the converter system volume.

On discussion of AC and DC side EMI filters design for conducted noise suppression in DC-fed three phase motor drive system

This paper discusses EMI filter design methodology for DC-fed three-phase motor drive system. An analysis of noise source and propagation path impedances of motor drive systems is conducted, a new filter design model for both AC side and DC side filter is proposed based on the impedance mismatching between the EMI filter impedances and noise source/load impedances. Using this model, the in circuit attenuation of EMI filter can be accurately predicted. The interaction between AC and DC filters is also studied in this analysis. By applying some constraint, EMI filters can be designed. This new design procedure is suitable for both DC and AC side EMI filters. Simulation and experimental results give a firm support to the proposed method.

EMI filter design and optimization for both AC and DC side in a DC-fed motor drive system

This paper proposes an EMI filter design and optimization method for both AC and DC side in a DC-fed motor drive system. Based on the noise generation and propagation mechanism, the analysis of common mode (CM) and differential mode (DM) EMI noise equivalent circuits is provided. Based on those equivalent circuits, this paper investigates the system EMI noise between AC and DC side, which shows the interaction between DM and CM noises and the interaction between adding AC and DC side filters. With these considerations, an optimized EMI filter design procedure is proposed to design CM and DM filters for both AC and DC sides. To minimize the impact on the EMI noise of one side caused by adding filter on the other side, certain order must be followed to design AC and DC CM and DM filters. Moreover, the EMI filter weight optimization method is also discussed to get the minimum weight of EMI filter and improve system power density. Simulation and experimental results verify the interaction between AC and DC filters and show that EMI filters can be designed to suppress both AC and DC EMI noise to meet the standard with the proposed EMI filter design method.

Low-Frequency Common-Mode Voltage Control for Systems Interconnected With Power Converters

In this paper, an active common-mode (CM) duty cycle injection method is proposed to control the dc and low-frequency CM voltage in grounded systems interconnected by power converters. Specifically, a 380-V dc nanogrid and a single-phase ac distribution system interfaced with a transformerless ac-dc converter is considered. In such architecture, the ac and dc CM quantities are coupled through the ground; while the high-frequency noise is filtered by passive components, the dc and low-frequency CM voltage need be controlled to generate symmetric dc-bus voltages and effectively mitigate the ground leakage current. Using a two-stage bidirectional ac-dc converter as an example, the operating range of the proposed method is identified under different ac and dc voltages and alternative grounding schemes. Further, a CM equivalent circuit is derived and experimentally validated, and used to design the controller of the proposed control system. Experiments with resistive and constant power loads in rectification and regeneration modes are used to validate the performance and stability of the control method. As a result, the dc-bus voltages are rendered symmetric with respect to ground, and the leakage current is suppressed. Finally, the control method is generalized to three-phase ac-dc converters for larger power systems.

Filter design oriented EMI prediction model for DC-fed motor drive system using double fourier integral transformation method

This work proposes a frequency-domain EMI prediction model for common mode (CM) and differential mode (DM) noises for the purpose of designing EMI filters before the system construction. The parameters in the model can be extracted from system detail switching model or measured from the real system. The Double Fourier Integral Transformation (DFIT) method is used to calculate the noise sources in the model. When the system topology modulation method and modulation index is fixed, the system EMI noise can be predicted from the calculation of the equivalent model. Verifications are carried out through simulation and experiment system by comparing the calculated EMI spectrums and simulated and measured EMI spectrums. Based on the proposed model, this paper also proves that the resonances in EMI noise propagation path will have a significant impact on the EMI filter design for DC fed motor drive system with long cables.

Comparison of three-phase ac-ac matrix converter and voltage dc-link back-to-back converter topologies based on EMI filter

This paper presents a comparison of a direct matrix converter, a two-level dc-link back-to-back converter, a two-level interleaved dc-link back-to-back converter and a three-level dc-link back-to-back converter for a 30 kW permanent magnet synchronous motor drive based on passive component and electromagnetic interference (EMI) filter volume and weight. The results show the tradeoff between different converter topologies.

Common-mode EMI noise reduction for grid-interface converter in low-voltage DC distribution system

More attention to the electromagnetic interference (EMI) issues arises in grid-interface converter system where the radio frequency (RF) conducted emissions have to be considered on both dc and ac-side, such as in the application of photovoltaic (PV) system, dc distribution system, and charging system in electric vehicles (EVs). This paper presents a brief overview of the recent EMI research activities in such applications as well as the EMI filter design and measurement considerations. The common-mode (CM) conducted EMI noises pose more challenges of filter design in the grid-interface converter system due to the noise propagation paths are coupled between dc and ac side through the grounding capacitors. This paper presents a discussion on an ac EMI filter structure in the single-phase grid-interface converter for low-voltage dc distribution system, which helps reduce the coupling between dc and ac-side, and thus simplifies the CM EMI filter design process.

Impact of interleaving on common-mode EMI filter weight reduction of paralleled three-phase voltage-source converters

This paper presents a detailed analysis on the impact of the interleaving angle on EMI filter weight reduction in a paralleled three-phase VSI motor drive system. The EMI noise analysis equivalent circuits are given in frequency domain and EMI filter design methods for a motor drive system are discussed. Based on the analysis, design examples are given for DC and AC common-mode (CM) EMI filters showing that minimum corner frequency in this case cannot ensure minimum EMI filter weight. In effect, the EMI filter weight is also determined by the volt-seconds on the inductor. With this consideration, the impact of interleaving is analyzed based on the equivalent circuit developed. Specifically, it is shown that interleaving can either reduce the volt-second on the inductor or help reduce the inductance needed, which has a different impact on the filter weight when the design condition is different. EMI filters are designed for both AC and DC sides as examples, showing the impact that different interleaving angles can have on filter weight reduction. Verifications are carried out both in simulation and experimentally on a 2 kW converter system.

Impact of interleaving on EMI noise reduction of paralleled three phase voltage source converters

This paper presents a systematic design method to select the interleaving angle to reduce the EMI noise in a paralleled three-phase voltage-source converters motor drive system. The EMI noise analysis equivalent circuits for a motor drive system are given and double Fourier integral analysis is used to analyze the impact of interleaving on EMI noise sources. With the consideration of noise propagation path impedance, the design method of interleaving angle selection is analyzed in detail. When system switching frequency and system load and source impedance are determined, the optimal interleaving angle can be calculated based on the system impedance resonant frequency and system switching frequency. Verifications are carried out through both the simulation of a 100kW motor drive system and the experiment on a scale-downed 2kW system. The results show that by using calculated optimal interleaving angle based on the method proposed in this paper, the EMI noise can be reduced by 10~12dB in the impedance resonant frequency range which can reduce the EMI filter size significantly.

Impact of interleaving on input passive components of paralleled DC-DC converters for high power PV applications

This paper investigates and evaluates the impact of interleaving on input passive components for a paralleled DC/DC boost converter in a high power PV application. A detail ripple reduction analysis for the interleaving topology and inductor design method are provided for the high power application. To reduce the circulating current, a coupled inductor was added to the circuit to reduce the size of input inductor. The benefit of coupled inductor is analysed and the coupled inductor design method is also conducted. The result shows that due to the material limitation (Silicon Steel) if maintaining the current stress on IGBT, interleaving will increase the weight and loss, while the overall current ripple will be smaller, which make the input and dc link capacitor smaller. By adding coupled inductor and interleaving, it is possible to use low core loss material (Amorphous) for coupled inductor, which makes the total loss and weight reduced significantly. Moreover, asymmetric interleaving is also proposed to optimize the total cost of the Silicon Steel and Amorphous material. Detailed analysis is carried on the design and value selection of coupled and non-coupled inductor for different interleaving angle. The design result shows the trade-off of using different interleaving angle to get minimum system weight.