Smart House with Smart Electricity The need for a DC Bus Yuval Beck Faculty of Engineering Holon Institute of Technology- HIT Holon, Israel e-mail: beck@hit.ac.il Gadi Golan President Holon Institute of Technology-HIT Holon, Israel e-mail: golan@hit.ac.il Edna Pasher Edna Pasher PhD & Associates Tel-Aviv, Israel e-mail: edna@pasher.co.il Abstract— The following work describes an ongoing idea that becomes more logical in the future of domestic and military electricity. This paper introduces the necessity for using a DC bus system in private homes as well as introducing an innovative bi-directional inverter for making the energy flow to and from the grid. The bi-directional inverter also enables smart control of the energy flow with harmonics cancelation, and the ability to be adjusted to the future demand of smart grids and multiple tariffs. The research also includes social aspects as an integrated subject in the control schemes of the electrical devices. Keywords- Smart house, Inverter, Smart grid, control circuits. I. INTRODUCTION THERE is a lot of interest in recent years in Smart Grid application. Dealing with these smart grid new concepts brings us back to basics and raises the question whether the current way of providing and consuming electricity is the correct or the best available way [1]. As for today, most of the electrical appliances that can be found in a typical house work on Direct Current (DC). A computer is assembled of DC circuits, TV is based on DC circuits, lighting and heating can also work on DC. The only appliances which require Alternating Current (AC) are the air-conditioners and the rotating machine based appliances, such as a washing machine and dryer. Although these appliances consume heavy loads, they consume only 30-60% of the total load. On the other hand, transporting energy for long distances is known to be more efficient in AC. Another factor that needs to be added to the new equation of the future energy world is the addition of renewable energy as a power source. Photovoltaic energy is DC and wind power which is AC based power sources. There is work done on DC distribution systems based on Photovoltaic generation and the electrical control strategy [3] , as well as on DC distributed systems for residential applications with the use of Bi directional Inverter [4]. The above mentioned situations lead to the question whether AC power in our home is the right way of providing our loads with the power [4],[5]. Moreover, the assimilation of communication and control capabilities in the future Smart grid enables us to control the efficiency of the power flow according to various criteria. These criteria can be influenced by the status of the total grid. As an example, let us consider a grid with over 30% renewable energy, and for stability issues the grid has to control the power flow from all renewable sources, namely, the photovoltaic inverters will not necessarily work in Maximum Power Point (MPP). This paper reviews the idea of combining a local DC bus grid in a few applications for increasing the total efficiency of energy transformations in the overall grid. A Bi- Directional Inverter (BDI) for enabling the dual DC/AC and AC/DC power flow with reduction of harmonics and control is presented. The converting systems are treated as Time Variable Transformers with advanced control that combines also non-electrical parameters. The paper also deals with micro-grids and synchronization issues by using the DC bus and the social aspects of controlling this electricity in the Smart Grid environment. II. DOMESTIC DC BUS In recent years private installations of PV generators and wind generators are becoming common in many countries. There are differences in the supporting laws in each country but in general these renewable generators are a financial business in which the investor wants to restore the investment on the system and make a profit on the electricity he sells to the grid. For achieving this goal, the current installed inverters are equipped with Maximum Power Point Trackers (MPPT) for maximizing the power extracted to the grid. When renewable energy will reach a dominant percentage of the grid current, other issues of stability of the grid will rise. In this case not all renewable generation will be allowed to penetrate the grid at all times. Furthermore, future storage that will be available, even in domestic facilities, will require a more complex control on the power flow. The fact that most of the appliances in our homes are operating on DC raises the question whether it is logical to have a PV generator on the roof, then invert the DC to AC, then convert the AC back to DC to power all of our electronic circuits. This two conversion process is obviously not efficient since each energy conversion reduces the total efficiency of the process. It is probably more logical to have a separate DC bus at our home, parallel to the AC grid (that will power all the AC appliances such as air conditioners etc.) as seen in Fig.1. In this case the future computer, TV and all other DC appliances will not need to have an AC/DC rectifier in their 21 Copyright (c) IARIA, 2012. ISBN: 978-1-61208-225-7 SMART 2012 : The First International Conference on Smart Systems, Devices and Technologies