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ADMC201 Scheda tecnica(PDF) 8 Page - Analog Devices |
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ADMC201 Scheda tecnica(HTML) 8 Page - Analog Devices |
8 / 15 page ADMC201 REV. B –8– VECTOR TRANSFORMATION BLOCK OVERVIEW The Vector Transformation Block performs both Park and Clarke coordinate transformations to control a three-phase motor (Permanent Magnet Synchronous Motor or Induction Motor) via independent control of the decoupled rotor torque and flux currents. The Park & Clarke transformations combine to convert three-phase stator current signals into two orthogonal rotor referenced current signals Id and Iq. Id represents the flux or magnetic field current and Iq represents the torque generat- ing current. The Id and Iq current signals are used by the processor’s motor torque control algorithm to calculate the re- quired direct Vd and quadrature Vq voltage components for the motor. The forward Park and Clarke transformations are used to convert the Vd and Vq voltage signals in the rotor reference frame to three-phase voltage signals (U, V, W) in the stator ref- erence frame. These are then scaled by the processor and written to the ADMC201’s PWM registers in order to drive the inverter. The figures below illustrate the Clarke and Park Transformations respectively. Iw Iu Iv Iy Ix 120 ° 120 ° 120 ° Three-Phase Equivalent Stator Currents Two-Phase Currents Figure 7. Reverse Clarke Transformation Iy Ix ρ Iq Id ROTOR REFERENCE FRAME AXIS 90 ° Rotating Stationary Reference Frame Reference Frame Figure 8. Reverse Park Transformation Vq Vd ρ Vy Vx 90 ° Stationary Rotating Reference Frame Reference Frame Figure 9. Forward Park Transformation Vy Vx W U V 120 ° 120 ° 120 ° Equivalent Three-Phase Stator Two-Phase Voltage Voltage Figure 10. Forward Clarke Transformation Operating/Using the Vector Transformation Block After powering up the ADMC201, RESET must be driven low for a minimum of two clock cycles to enable vector transformations. The vector transformation block can perform either a forward or reverse transformation. Reverse Transformation is defined by the following operations: (a) Clarke: 3-phase current signals to 2-phase current signals followed by (b) Park: 2-phase current signals cross multiplied by sin ρ, cos ρ which effectively measures the current components with respect to the rotor (stationary) where ρ is the electrical angle of the rotor field with respect to the stator windings. Forward transformation is defined by the following operations: (a) Park: 2-phase voltage signals cross multiplied by sin ρ, cos ρ fol- lowed by (b) Clarke: 2-phase to 3-phase voltage signal conversion. In order to provide maximum flexibility in the target system, the ADMC201 operates in an asynchronous manner. This means that the functional blocks (analog input, reverse transformation, forward transformation and PWM timers) operate indepen- dently of each other. The reverse and forward vector transformation operations cannot occur simultaneously. All vector transformation registers, except for RHO/RHOP, are twos complement. RHO/RHOP are unsigned ratios of 360 °. For example, 45 ° would be 45/360 × 212. Performing a Reverse Transformation A reverse transformation is initiated by writing to the reverse rotation angle register RHO and operates on the values in the PHIP1, PHIP2 and PHIP3 registers. When the reverse trans- formation is in 2/3 mode, PHIP1 is calculated from PHIP2 and PHIP3. This is used in systems where only two-phase currents are measured. The reverse transformation 2/3 mode is set by clearing Bit 10 in the SYSCTRL register and is the default mode after RESET. In order to perform a reverse transformation, first write to the PHIP2 and PHIP3 registers, and to the PHIP1 register if not in 2/3 mode. Then initiate the transformation by writing the re- verse rotation angle to the RHO register. The reverse rotation will be completed in 37 system clock cycles after the rotation is initiated. If Bit 6 of the system control reg- ister is set, then an interrupt will be generated on completion. When an interrupt occurs, the user must check Bit 1 of the SYSSTAT register to determine if the vector transformation block was the source of the interrupt. During the vector transformation, the vector transformation registers must not be written to or the vector rotation results will be invalid. |
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