12-06-2012, 02:08 PM
A NEW PROPOSAL FOR POWER QUALITY AND CUSTOM POWER IMPROVEMENT: OPEN UPQC
ABSTRACT
Power quality (PQ) is very important to certain customers. For this reason, many utilities could sell electrical energy at different prices to their customers, depending on the quality of the delivered electric power. Since most end users are connected to secondary. Currently, the quality of supplied power is important to several customers. Power quality (PQ) is a service and many customers are ready to pay for it. In the future, distribution system operators could decide, or could be obliged by authorities, to supply their customers with different PQ levels and at different prices. A new device that can fulfill this role is the OPEN unified power quality conditioner (UPQC), composed of a power-electronic series main unit installed in the medium-voltage/low-voltage (LV) substation, along with several power-electronic shunt units connected close to the end users.
The series and parallel units do not have a common dc link, so their control strategies are different than traditional UPQC control techniques. This device can achieve general improvement in PQ, reducing the most common disturbances for all customers that are supplied by the mains (PQ) by using only the series unit. Additional increments in PQ (i.e., mains power interruptions), can be provided to the customers who need it (custom power) by the shunt units. Therefore, this new solution combines an improvement in PQ for all end users, with a cost reduction for those that need high quality power. The proposed solution has been analyzed and described, and a model of a 400-kVA LV grid is considered a test network to evaluate the steady-state performance and functioning limits. The results obtained under steady-state conditions justify the configuration chosen and good device performance.
The OPEN UPQC apparatus is a good compensation system if wide installation of shunt units is needed. An increase in the percentage of the protected load enhances the voltage stabilization interval over which the OPEN UPQC can significantly improve the power quality, especially if the load power factor takes a high value. If the power factor of load is less than one, the power factor in section increases, to avoid nonnative power absorption from the mains. For low values of the parameter, the OPEN UPQC becomes expensive if there are few shunt units.
In this case, it is better to install other compensation device typologies (as UPS, UPQC, etc.) near the sensitive loads, and a non active compensator system near the nonsensitive loads if necessary. It is possible to conclude that installation of the series unit is a cost-effective way for distributors to improve the power quality level in the distribution networks in order to achieve the standards imposed by the authorities. Compensation improvement for the sensitive end users can be achieved by installing a shunt unit near them, instead of the more expensive UPS device. The OPEN UPQC working conditions are reported