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Master of Science Thesis in Electric Power Engineering - page 74 / 114

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VOLTAGE ORIENTED CONTROL – IMPLEMENTATION

PWM

The PWM block have been replaced by the dSpace PWM block “DS1103SL_DSP_PWM3”. This is a sinusoidal symmetric PWM (Ftriangle = Fswitching = Fsampling). You can modify the carrier wave (triangle) and the deadtime duration. “PWM stop” allows to enable(PWM stop = 0) or disable(PWM stop = 1) the PWM block. This signal needs double type and not Boolean (but following “Simulink help” it should be Boolean). The Termination and Initialization values of the block should be set (see next section for explanation about Termination and Initialization).

The input range for “duty cycle abc” is [0;+1]. Finally, we have to send our three phase reference voltage to this block but a scaling block is needed. This block is included to the control block and shown in Figure 4.4.

Figure 4.4 : Scaling block

CONTROL SYSTEM AND PLL

You can find the detail of this block in APPENDIX G. Figure 0.43. You can see that the scaling block presented above is included to this block. The control is totally similar to the one presented in Chapter 3 except that :

  • All the sample & hold block have been removed but the system is still discrete.

  • The sample time "Ts" is replaced by " 1" (inherited).

The enable signal is maybe not useful. It could be removed. It depends how will be run the system. But if it’s used, the output port “Uabc_ref range [0;1]” should be set to the following characteristics :

  • Reset when disabled

  • Initial output = 0.

In this configuration, when the block is disabled, the output will be zero and the PWM block will see zero duty cycle and will open the switches.

TRIGGER SIGNAL, SYNCHRONIZATION

The sample & Hold have been removed. Now, we need to specify when acquire a sample. We know that we need to sample on the peak of the triangular wave of the PWM, ideally, on every peak that is the asymmetric PWM. We guess that more than one solution is possible to run the system. But for simplicity, as we said above, we decided to use the PWM block “DS1103SL_DSP_PWM3” using a symmetric PWM.

Furthermore, this block is link to an interruption “DS1103SLAVE_PWMINT”. The interruption is generated every POSITIVE PEAK of the triangular wave of block PWM3 as shown in Figure 4.5. Consequently we have : Finteruption = Fsampling = Ftriangle = Fswitching.

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