SLOA338 March   2025 TSD5402-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction TO RESOLVER and LVDT sensors
  5. 2Conventional Excitation Amplifier
  6. 3Excitation Amplifier Using Class-D Amplifiers
  7. 4Class-D Resolver Excitation Design Details
    1. 4.1 Components Selection for the Power Stage
    2. 4.2 Input Filter Components Selection
  8. 5Practical Experiments
    1. 5.1 Test Setup
    2. 5.2 Output Waveforms for Default Conditions
    3. 5.3 Amplifier Transfer Function
    4. 5.4 Using PWM for Generating the Reference Signal
    5. 5.5 Thermal Image and Comparison Against the Linear Design
    6. 5.6 Output Spectrum
    7. 5.7 Total Harmonic Distortion (THD)
    8. 5.8 Fail Events
  9. 6Summary
  10. 7References

5.2 Output Waveforms for Default Conditions

Figure 5-2 shows default output waveforms in normal operating conditions.

Output Waveforms Figure 5-2 Output Waveforms

M1 – differential voltage across the resolver primary winding

CH2 – current through the resolver

CH3 – EXC- signal (single-ended)

CH4 – EXC+ signal (single-ended)

Calculations Explained

Equation 1. V E X C + ( t ) = V P ∙ sin ⁡ ( ω t + 000 ° ) + V D C
Equation 2. V E X C - ( t ) = V P ∙ sin ⁡ ( ω t + 180 ° ) + V D C

Voltage seen by the resolver is...

Equation 3. V E X C ( t ) = V E X C + - V E X C - = 2 ∙ V P ∙ sin ⁡ ( ω t )
Equation 4. V E X C R M S = V P 2 = 9.9 2 = 7.000   V R M S

Average responding multimeter measures the input current to the excitation amplifier.

Equation 5. P I N = V I N ∙ I I N = 14.5 ∙ 0.0045   =   0.61 W

Oscilloscope measurements allow calculating the output power (apparent)

Equation 6. S E X C = V E X C ( R M S ) ∙ I E X C ( R M S ) = 7.01 ∙ 0 . 10592  

From the apparent power we can calculate real power dissipated on the resolver equivalent series resistance RRES=15.42 Ω.

Equation 7. P E X C = ( I E X C ( R M S ) ) 2 ∙ R R E S = 0 . 10592 2 ∙ 15.42   =   0.173 W
Power Vectors Plot Figure 5-3 Power Vectors Plot

Phase shift between output voltage and current acts as a calculation check.

Equation 8. cos ⁡ ϕ = r e a l   p o w e r a p p .   p o w e r = 0.173 0.742 = 0.233
Equation 9. ϕ   = arccos ⁡ 0.233 = 76.52 °

The readout value from the oscilloscope screen is ϕ=78.53°. This is a minimal error considering the test setup and oscilloscope readouts.

The power dissipation on the ampifier is the difference between peak input and output power.

Equation 10. P T P D = P I N - P E X C = 0.61 - 0.173 = 0.437 W