Three Phase Single Stage Four Quadrant EV Charger using Model Predictive Control

Three phase single stage battery charger with four quadrant operation is presented here. Most of the battery chargers available today commercially are of two stage type. That means power conversion is not linked directly from AC to DC side rather there is an intermediate stage. Generally in dual stage system, the power conversion takes place in two steps, first AC to DC and then DC to DC conversion. A two stage operation requires a bigger DC link capacitor at the intermediate stage, which reduces the overall power density of the charger. In this work, the use of model predictive control (MPC) for a single stage battery charger with four quadrant operation is investigated. The matrix converter configuration is used for single stage charging operation. From the last decade, the use of predictive control for power converters has become very popular due to its ability to accommodate non linearity in the system as well as various constraints taken together. The instantaneous power control theory is applied to derive reference grid current based on desired real and imaginary power reference inputs applied to the converter. In the conventional two stage charging scheme, a voltage source converter is used on the grid side, which operates in boost mode and mandates the voltage of the intermediate DC link to be higher than the AC line voltage amplitude. This necessitates the use of bidirectional DC-DC converter with step up and step down operation. Further, a simple buck-boost converter may not perform well if the battery voltage is significantly low compared to DC link voltage and may require a high gain buck-boost converter in such conditions. The matrix converter allow bi-direction power flow with reactive power compensation on the grid side along with a high gain voltage bucking operation. Due to single stage operation and absence of a large DC link capacitor this configuration is more reliable and efficient compared to its counterparts.