Reactive Power Control in Three-Phase Grid-Connected Current Source Boost Inverter Mahdi Saghaleini, Student Member, IEEE, Department of Electrical and Computer Engineering Florida Int’l University, Maimi, FL Behrooz Mirafzal, Senior Member, IEEE Department of Electrical and Computer Engineering Kansas State University, Manhattan, KS Abstract— Reactive power control and consequently voltage regulation in a micro-grid is one of the main control requirements, particularly when the micro-grid operates in an islanding mode. In this paper, the capability of a single-stage boost inverter in providing reactive power is investigated. The presented boost inverter utilizes the current-source topology and applies a modified space vector pulse-width-modulation (SVPWM) switching technique, here called phasor pulse-width- modulation (PPWM). It is demonstrated that the injected active and reactive power can be controlled through two modulation indices introduced in the PPWM switching algorithm. The capability of reactive power generation using a three-phase current source boost inverter (CSBI) was experimentally verified and the results are presented in this paper. Keywords: Reactive power control, grid-connected inverter, boost inverter, current source topology, micro-grids. I. INTRODUCTION The drive towards sustainable/renewable resources is shifting energy production to regional nodes, making the distributed generation of electricity an increasingly significant feature of the energy grid. These sustainable energy sources are often connected to the energy grid by means of grid-connected inverters – power electronic devices that transform dc to ac. There are several inverter topologies that are used in motor- drives and sustainable energy conversion systems, such as voltage source inverters (VSIs), current source inverters (CSIs), multi-level inverters, and matrix converters. In the past several decades, CSIs have been replaced with VSIs in many industrial applications. However, the CSI topology has the capability to be used as a grid-connected single-stage boost inverter [1]. The most attractive merit of this topology lies in the capability of boosting and inverting in a single stage, as well as the capability of transferring electrical energy from a low dc voltage source (e.g. PV or Fuel Cell) to a larger ac voltage (e.g. ac grid). It should be emphasized that the VSI topology cannot be utilized as a single-stage boost inverter. The presented CSBI can also control the injected reactive power through a switching pattern, here called phasor pulse- width-modulation (PPWM) technique. This characteristic makes CSBI one of the best choices for sustainable energy conversion systems in micro-grids. It should be emphasized that CSBI can provide reactive power for the ac grid, only if the inverter input power has a non-zero value. There have been many investigations reported on the control of reactive power in literature. For instance, static var compensator (SVC) can provide reactive power through a bank of individually switched capacitors in conjunction with a thyristor-controlled reactor [2], or static synchronous compensator (STATCOM) that is based on the topology of voltage source converters, which can act as either a source or sink of reactive power for the ac grid. In STATCOM, the amount of injected reactive power is proportional to the voltage difference between the voltage amplitudes of the grid,  ௚ , and the inverter,  ௜௡௩ , while the angle between them is zero, i.e. ߜൌ ݒס ௜௡௩ െ ݒס ௚ ൌ 0. This can be clarified using the classical equations that describe the active and reactive power flow from inverter to the grid through the link transformer and filter reactance, X, i.e. ൌ0 and ൌ ௚ ሺ ௜௡௩ െ  ௚ ሻ/, at the grid side and for ߜൌ0. The amount of reactive power provided by the STATCOM is more than the SVC at the low voltage limits. This is because at a low voltage limit, the reactive power drops off as the square of the voltage for the SVC, whereas it drops off linearly with the STATCOM. This makes the reactive power controllability of the STATCOM superior to that of the SVC, particularly during times of system distress. The CSBI behavior is different from the STATCOM and SVC. For instance, CSBI cannot provide any reactive power at ൌ0. In CSBI, the generated reactive power is adjusted by controlling the inverter output current through the modulation indices,  and ߙ ଴ , of the PPWM technique [1]. However, from the point of view of the inverter output circuit,  ௜௡௩ sinሺߜሻ is regulated based on the maximum deliverable active power of the inverter source, e.g. PV arrays, and the grid active power demand, whichever is smaller, while  ௜௡௩ cosሺߜሻ is controlled based on the grid reactive power demand. In addition to the inverter reactive power contribution, the CSBI output circuit (filter) might also provide some reactive power. Some proposed approaches for controlling reactive power using semiconductor circuits is presented in the next section. II. REACTIVE POWER CONTROL BY SEMICONDUCTOR CIRCUITS In 1979, Gyugyi presented how the reactive power can be generated and controlled by thyristor circuits, so-called all solid-state realization of static var source [3]. He demonstrated that passive storage elements theoretically are not needed to generate reactive power. In 1984, Akagi et al. defined the concept of instantaneous reactive power on the same basis as the conventional instantaneous power in three-phase circuits, and according to this theory no energy storage components (capacitors and inductors) are practically required for the reactive power control [4]. In recent years, the control of reactive power using sustainable energy sources (e.g. PV arrays and Fuel Cells) becomes a challenging issue for micro-grids. There are several 978-1-4577-1216-6/12/$26.00 ©2012 IEEE 904