Name / Giacomo Cocchiara / Session / 1
Company / University of Palermo / Block / 1
Address / Viale delle Scienze / Question n° / 3-1
90128-Palermo-Italy / Language used on the floor / English
Phone / +390916615207 / Accompanying visuals on file ? / Yes
e-mail /
SUPERCAPACITORS FOR CPD REALIZATION
In order to protect inverter static devices against over-currents a typical solution is the over-current limit operation, which implies a voltage reduction on the all installation fed by the inverter and, in some cases, can not assure the selectivity of the protection device situated on the load side or a direct on line start up of a large induction motor. (SLIDE 1)
A new possible solution of the above mentioned problem consists of installing a novel LC device, called Current Pumping Device (CPD) between the inverter and the customer’s load. CPD insertion produces an operation condition near to parallel resonance, increasing the current on the load side and reducing the problems related to protection selectivity and/or to motors start-up. At the same time, the current on inverter side decreases, relieving it from the overload condition and allowing to increase output voltage. (SLIDE 2)
Some simulations, carried out by means of the MATLAB, have shown that using aluminium electrolytic capacitors a considerable reduction of CPD costs and footprint can be obtained, despite their operation shifts from the ideal one more than polypropylene capacitors, due to their high dissipation factor. (SLIDE 3)
In the paper we also consider the possibility to use supercapacitors. In fact, supercapacitors can deliver extremely high currents for extended periods of time and have extremely small dimensions, so that capacitance of thousands Farads can be realized in very small devices. Besides, their cost will considerably reduce in the next years. (SLIDE 4)
On the other side, supercapacitors present high internal resistance (ESR) values and small rated voltage values. Besides, their capacitance is strongly dependent on frequency: it greatly decreases when frequency increases. Consequently, there are no benefits if we use them in CPD, since the current on the load side is equal to the current on the inverter side. (SLIDE 5)
In conclusion, actually supercapacitors do not seem suited for CPD realization: for this application a considerable reduction of their ESR is desirable. Moreover, actually it is difficult to develop high voltage supercapacitors (as suggested by constructors) and there is not a big market in AC applications: nowadays the efforts of the research are only oriented towards DC applications. (SLIDE 6)