In digital implementation of vector control, the microprocessor must be equipped with analog-to-digital
converter in order to measure the phase currents and the DC-link voltage. If the speed of the machine is
measured with a tachometer, this signal also needs to be measured with the AD-conversion. If an incremental
encoder is used to measure the position of the rotor, the speed can be calculated from the position.
Considering the aliasing from the current ripple, the microprocessor should be able to trigger the sampling
of currents on the peak of the carrier wave as mentioned in Sec. 2.2, which also means that the sampling
could take place once or twice during one PWM switching period. Due to this fact, all the calculation steps
of the vector control algorithm must be finished in one or a half of PWM switching period.
The basic procedure of a vector control algorithm is that the measured three-phase currents are converted
into a complex space vector by Clarke Transformation. The space vector is then transformed from
the αβ-system to the dq-system by a Park Transformation where usually the flux angle is used as the transformation
angle. In this way a flux orientated system is obtained. For the DC-currents obtained after the
transformations, usually a standard PI-regulator together with some feed-forward terms are used. The output
of the current regulator is the stator voltage space vector, expressed in the dq-system. The stator voltage
space vector is transformed back to three-phase by Inverse Park and Inverse Clarke Transformations and the
obtained phase voltages are used as reference for the PWM in Fig. 2.4. In Fig. 2.8 the PWM is shown as the
block Duty Cycle Output. The vector control algorithm consists of a wide variety of mathematical calculations,
such as trigonometric functions sin(θ1), cos(θ1), multiplication, division, addition and subtraction.
To meet all the practical system demands(performing AD-conversion, all the calculations and updating the
PWM within one or a half of PWM switching period) the processor used for vector control system needs to
have a high execution speed [36].
Fig.
In digital implementation of vector control, the microprocessor must be equipped with analog-to-digitalconverter in order to measure the phase currents and the DC-link voltage. If the speed of the machine ismeasured with a tachometer, this signal also needs to be measured with the AD-conversion. If an incrementalencoder is used to measure the position of the rotor, the speed can be calculated from the position.Considering the aliasing from the current ripple, the microprocessor should be able to trigger the samplingof currents on the peak of the carrier wave as mentioned in Sec. 2.2, which also means that the samplingcould take place once or twice during one PWM switching period. Due to this fact, all the calculation stepsof the vector control algorithm must be finished in one or a half of PWM switching period.The basic procedure of a vector control algorithm is that the measured three-phase currents are convertedinto a complex space vector by Clarke Transformation. The space vector is then transformed fromthe αβ-system to the dq-system by a Park Transformation where usually the flux angle is used as the transformationangle. In this way a flux orientated system is obtained. For the DC-currents obtained after thetransformations, usually a standard PI-regulator together with some feed-forward terms are used. The outputof the current regulator is the stator voltage space vector, expressed in the dq-system. The stator voltagespace vector is transformed back to three-phase by Inverse Park and Inverse Clarke Transformations and theobtained phase voltages are used as reference for the PWM in Fig. 2.4. In Fig. 2.8 the PWM is shown as theblock Duty Cycle Output. The vector control algorithm consists of a wide variety of mathematical calculations,such as trigonometric functions sin(θ1), cos(θ1), multiplication, division, addition and subtraction.To meet all the practical system demands(performing AD-conversion, all the calculations and updating thePWM within one or a half of PWM switching period) the processor used for vector control system needs tohave a high execution speed [36].Fig.
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