IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 28, NO. 4, APRIL 2013 1667 Grid-Interface Bidirectional Converter for Residential DC Distribution Systems—Part 2: AC and DC Interface Design With Passive Components Minimization Dong Dong, Student Member, IEEE, Fang Luo, Member, IEEE, Xuning Zhang, Student Member, IEEE, Dushan Boroyevich, Fellow, IEEE, and Paolo Mattavelli, Senior Member, IEEE Abstract—With the emerging installations of multitype renew- able 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. Index Terms—DC distribution, filter design, renewable energy. I. INTERFACE CONSIDERATION IN DC DISTRIBUTION SYSTEM P OWER quality and the corresponding environmental im- pact are gaining more attention in the chain of the electric power processing and delivery. Bad quality of the electric power wears out the system equipment quickly, increases the cost of maintenance, results in system failure or nuisance shutdown, and poses strong negative influence to environment [1], [2]. Power electronics not only reshapes the electric properties, such as voltage and current, but also needs to convert the electric power into a more clean and reliable form [3]. Lots of regulation standards specify the interconnection re- quirement [4]–[6] of distributed generation (DG) units in electric power system, especially in low-voltage distribution networks. Also, many standards define the interconnection requirement for electric loads [7]–[9], such as appliances, variable-speed motor drives, etc. Due to the dynamic decoupling achieved by the Manuscript received April 10, 2012; revised July 1, 2012; accepted August 6, 2012. Date of current version October 26, 2012. Recommended for publication by Associate Editor V. Staudt. The authors are with the Center for Power Electronics Systems, Vir- ginia Polytechnic Institute and State University, Blacksburg, VA 24061 USA (e-mail: dongd@vt.edu; fangluo@vt.edu; xuning45@vt.edu; dushan@vt.edu; mattavelli@ieee.org). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPEL.2012.2213614 grid-interface bidirectional converter in dc system, namely the energy control center (ECC) converter, the whole dc system will be either like a single distributed generation (DG) unit when the power is dispatched to the grid or like a load when power is de- livered to the dc system [10]. Thus, both standards for DGs and electric loads have to be applied to the design of ECC converter to interface to the ac low-voltage distribution system. Among various interface requirements, the power quality is one of the design aspects when ECC delivers the power to the grid. The IEEE1547 defined the injection current harmonics level and the total total harmonic distortion (THD) level. AC-side conducted electromagnetic interference (EMI) noise emission is also a con- sideration to reduce the pollution to ac grid and to minimize the interference to the adjacent devices when ECC behaves as an ac load. Recently, the similar EMI standards are also directly ap- plied to DG in the low-voltage distribution system, such as a PV inverter. In addition, many other utility-interface requirements exist, e.g., antiislanding protection, low-voltage ride through, and ancillary functions, which, however, are more related to control design and will not be discussed here. In terms of the dc side, currently there are several organi- zations, e.g., Electric Power Research Institute (EPRI), Inter- national Electrotechnical Commission (IEC), and Emerge Al- liance, developing different dc-system standards; however, there is no public and uniform standard for such residential dc sys- tems now. Currently, power quality and EMI can still be used as the design consideration similar to the ac-side. Mostly, ECC behaves as a voltage source on dc side; thus, the power qual- ity of output voltage is a design aspect. The dc-side conductive EMI noises should be minimized, though no specific standards, especially when relative long dc cables are deployed. There are several publications on the dc-side EMI study in residential PV systems [11]–[14]. Some other standards on dc system in dif- ferent applications, e.g., the dc distribution system in aircraft power system can be a reference. According to [15], the power quality of differential-mode (DM) and common-mode (CM) dc- bus voltage are required to be maintained within a small-voltage ripple. If in future there are more specific standards available, the dc-side interface requirement may change the design of filter and/or power-stage topology. In addition, system grounding schemes and type of utility systems are also the factors to design the converter system. According to the low-voltage distribution system practices, there 0885-8993/$31.00 © 2012 IEEE