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AN1905 Datasheet(PDF) 72 Page - STMicroelectronics |
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AN1905 Datasheet(HTML) 72 Page - STMicroelectronics |
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72 / 77 page  72/77 ST7MC THREE-PHASE BLDC MOTOR CONTROL SOFTWARE LIBRARY ■ Tricks and traps – When tuning the PI parameters you should look for the worst case conditions, which may be when the load quickly and unpredictably varies, when the inertia is at a minimum, or when the mains voltage is maximum for an off-line application. –Frequency regulation output is a 10-bit variable. If the final application requires a different resolution (involving the PI routine to be rewritten), the output might be chosen as a power of 2 so that logical shift operations can be used as divisions (new duty = (max_duty x PI- output)>>10 for 10-bit returned value). This will result in compact code and will reduce the CPU time consumption while processing the PI output. To give sufficient accuracy to the control algorithm, the returned data should not be less than an 8-bit value, and shouldn’t be greater than 12 bits long (the same resolution as the MTC cell PWM timer). – A regulation tuned in no-load condition (at the highest) will most probably be unresponsive in the final application, and vice versa: a regulation tuned in the application may become unstable in no-load conditions. ■ Implementing the closed loop regulation Below is an example of the use of this regulation process. Note: Whatever the declared number of pair poles is, the ‘Set_Target_Electrical_Frequency’ rou- tine needs to be fed with an electrical frequency input. The ‘Pole_Pair_Num’ definition in ‘MTC_Settings_Sensorless.h’ or ‘MTC_Settings_Sensor.h’ file is just declared as a reference; it can be used for example in the final application in order to display the mechanical frequency instead of the electrical. ... if (ValBit(Flag_MTC,SAMP_EVT)) // Sampling time elapsed? -> update PWM { ClrBit(Flag_MTC,SAMP_EVT); Set_Target_Electrical_Frequency((u16)(your_frequency)); } ... |
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