Interior Permanent Magnet (IPM) machines are widely used in automotive applications for their wide-speed range operation and low maintenance cost. The proposed Constant Current based IPM motor drive control strategy can achieve seamless transition between non-field-weakening and field-weakening regions while keeping a large output EM torque. The detailed control block diagram is presented and a pump-back system is proposed to verify control effectiveness. PLECS simulations have been conducted to compare the performance of the proposed control strategy with the curve fitting based method proposed in the previous work. A 5 kW three-phase motor drive inverter prototype has been built based on current industrial requirements, and the prototype power density has reached 92 W/inch3. Meanwhile, Insulated Metal Substrate (IMS) board and single-layer layout technique are used for better heat dissipation. Pump-back system experiments have been performed and the results are presented.