A Study on Multi-Object Oriented Digital Grid-Tied Inverter Design

Inverters are ac-to-dc power conversion devices that have been widely used to high power application such as motor drive, UPS, and active power filter along the low power 4C products such as cell phone and vehicular electronic. However, the control system of the inverter can vary greatly between various applications. Multi-object oriented inverters can increase not only the capacity utilization and power efficiency but also reduce the inverter initial and run-time cost. Conventional electric vehicle power system includes a PFC rectifier, a charger, a bidirectional buck-boost converter, and a three-phase inverter. The buck-boost converter is mainly used to promote the battery voltage for supplying the electric motor with lower current level for the purpose of power efficiency. The regenerative power earned from brake kinetic energy can be used to charge the battery and extend the endurance. Since the electric vehicle cannot be charged from grid utility during running, the PFC rectifier and the charger are therefore idle in this phase. To increase the inverter capacity utilization, this project tries to use the existing bidirectional buck-boost converter and a three-phase inverter in place of the PFC rectifier and the charger. The inverter operating mode can be switched from motor driving to PFC rectifier when the electric vehicle is stopped to drain the grid power to charge the battery. The charging current can then be determined by the existing buck-boost converter. Although only two power stages are employed, the power drained from the battery of the electric vehicle to grid (V2G) is also achievable. To facilitate the inverter with multi-objective orientation and establish the seld-contented technologies of industry, this three-year project is devoted to the development of key technologies for vehicular power system. The first year project is to develop a transformerless single-phase inverter with low leakage current analogous to the galvanic inverter, which is the key technology of inverter miniaturization. The result can be applied to the low-capacity charger and upgraded to three-phase system in the next two years. The studies arranged in this year are shown as follows: (1) single phase inverter modeling; (2) transformerless inverter circuit design; (3) noise immunity PLL; (4) robust and self-tuning current control; (5) digital filter design; (6) DSP-controlled inverter. To approach multiple objectives for the parallel inverters with limited capacity, the capacity distribution and current sharing are the core topics in the second year project and are detailed as follows: (1) multi-object oriented algorithm; (2) current sharing; (3) interleaved modulation; (4) active power filter design; (5) PLL for fundamental and harmonic voltage detection; (6) active and reactive power compensation; To accommodate the three-phase motor driver to grid utility and expand the inverter capacity, the transformerless parallel three-phase inverter are the key technology dedicated in the third year. For the studies arranged in this year are summarized as follows: (1) multi-object oriented algorithm; (2) three-phase inverter modeling; (3) interleaved modulation; (4) active power filter design; (5) active and reactive power compensation; (6) field orientation control. It is noted that the capacity of the parallel single-phase inverter and three-phase inverter in this project are designated at 10W and 25kW, respectively. The capacity of the inverter can be expanded and utilized in a very efficient manner due to the multi-object orientation approach.

Project ID:PB10308-2734
External Project ID:MOST103-2221-E182-031