Rotary Transformer and DSP Synchronous Serial Port to Observe the Position of Motor Rotor
The magnetic pole position of the rotor is known. This article describes the method of magnetic pole position detection of the resolver rotor, which is achieved through the cooperation of resolver, resolver chip AD2S90 and DSP.
2: The basic principle of the A1 resolver The resolver is a device that relies on electromagnetic induction to detect the angular position. There are six external ports, two pairs of stator terminals, and a pair of rotor terminals. Both the stator and rotor terminals lead from the stator, as shown. Two pairs of stator-end windings are spatially placed orthogonal to the resolver schematic. When a sinusoidal excitation voltage of frequency w is connected to the rotor terminals Ri, R2, a sinusoidal voltage is also induced on the secondary side of the rotor. When the rotor rotates, it is induced on the two stator windings as shown respectively. Waveform. That is, 0 here is the shaft angle rotated by the rotor, sinwt is the sine wave induced on the rotor, and E0 is the amplitude of electromagnetic induction. After obtaining such a waveform, the position of the rotor can be solved based on their phase relationship.
2 The signal processing chip of the resolver is known from the principle of the resolver. To make the resolver work normally, a sinusoidal excitation must be applied at the rotor end. The sinusoidal excitation is provided by the AD2S99 programmable sinusoidal oscillator, which generates a standard sine wave from 2 kHz to 20 kHz. The frequency at which the sine wave is generated is controlled by pins SEL1, SEL2 and FBIAS. The logic diagram is as shown. , Select 12-bit solver AD2S90 can solve these two signals, get the corresponding angle value. The logic diagram of AD2S99 is shown as above, among them sin, sinLO, cos, cosLO is the stator output of the resolver.
Actually, inside the AD2S90 is a phase-locked loop. The two orthogonal sinusoidal signals from the stator are first processed in the high-precision sine and cosine signal solver, and an initial value Y in the up-down counter is calculated as follows. Phase-frequency mapping The unit and the high-speed dynamic voltage control oscillating unit quickly adjust the value of Y in the increase/decrease counter so that the value of sin(0−Y) tends to zero, so the value in the counter can represent the angular position of the rotor.
3Synchronous serial port of DSP and communication of AD2S90 The resolver output signal of AD2S90 is solved by AD2S90 to get a 12-bit value, which represents the position of the rotor, and finally transmitted to DSPTI's TMS320LF2407 in serial mode with universal synchronization. The serial port (SPI) can be easily communicated with the AD2S90 to give a schematic diagram of the connection between the AD2S90 and the DSP.
In the line output register, with the pulse edge of the clock SPICLK sent bit by bit, it takes 100 ns after the transmission of 12 bits before the chip selection can be cancelled to ensure the correct transmission of data. The maximum frequency of the transmission clock is 2MHz. Therefore, the shortest transmission time is (6(1)+(12X500)+100) ns=6.7. If the two signals are transmitted continuously, the chip select signal needs to be delayed by 250ns. The hardware circuit diagram is shown as follows. In order to avoid interference from the motor side, optical isolation can be added to the circuit. Optical isolation is used in the circuit to avoid interference from the resolver side to the DSP. In addition, in order to ensure that the resolver can get enough excitation, the sinusoidal signal of AD2S99 is amplified with an operational amplifier...
Table 1. Resolution 4.2.6 Offset adjustment The position offset of the integrator input side caused by drift and offset current is a maximum of 5.3'. If this error can be ignored, then R8 and R9 can be omitted. Otherwise, it can be adjusted by adjusting R9. Correcting position deviation: If there is no adjustment measure, when the change of 9 is less than one LSB 0 inch, in order to make AC error and DC error zero, the reversible counter will continuously add 1 and decrease 1 count. However, since the change of 9 is less than one LSB 0, it cannot be equal to 9 at all, causing the counter to count up or down continuously, that is, to “flickerâ€. In order to prevent the converter from "flickering", the chip internally derives a feedback signal from the VCO to the integrator. In this way, as long as the current of the input integrator is 100nA/bit, then the VCO counts only when the change of 9 is greater than one LSB, and the flicker phenomenon is effectively avoided.
If the high-frequency filter is omitted: Li Edc values ​​are shown in Table 1.
4.2.5 Voltage Controlled Oscillator (VCO) Speed ​​Signal Control Voltage Controlled Oscillator sends out count pulses to enable (adjustable resistance) 5 Summary This article describes the application of resolver and AD2S83 in permanent magnet brushless DC motor position detection. And elaborated the working principle of AD2S83 and the choice of peripheral circuit parameters. The position detection unit has stable working performance, can work under harsh working conditions for a long time, and can meet high precision requirements.
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