70 Frequency Converters 2.7.4.2 Flux Vector (Closed Loop ) For the closed loop fl ux vector control method, an encoder or similar sensor is required on the motor shaft. The control software and the feedback resolution determine the accuracy of motor control. Control is performed in exactly the same way as with open loop methods. However, in this case the speed is calculated from the encoder signals rather than being estimated. Flux vector control is illustrated in Fig. 2.23 Structure closed loop fl ux vector control. Typical shaft output:
• Speed setting range 1:1000 to 10,000 • Speed accuracy (steady state) Dependent on the feedback signal (encoder) used • Acceleration torque 100 – 150% of rated torque • Speed control response time 5.00 – 50 ms • Torque control response time 0.50 – 5 ms Mains џ r.ref Speed controller џ r I s q.ref I s d.ref Encoder Motor Field weakening I mr.ref Flux controller kty I mr Flux model 2 3 Speed calc. Position Fig. 2.23 Structure closed loop fl ux vector control 2.7.5 Servo Drive Control The servo converter control method will not be explored in depth here. One common method is very similar to closed loop fl ux control, but to ensure high 3¾ I sta d, q a, b Is d.ref d, q a, b Is q.ref