米6体育平台手机版

SPRUJF4 October 2024

2.1.3 Motor Phase Voltage Sensing

The software for the TIEVM-MTR-HVINV allows for both the enhanced Sliding Mode Observer (eSMO) and the Flux, Angle, Speed, and Torque (FAST^™) sensorless observers. While the eSMO only requires the commonly used 3-phase motor current sensing, the FAST observer additionally requires requires 3-phase motor voltage sensing to improve low-speed performance and increase the precision of the motor speed estimation.

Note that the software parameter (USER_ADC_FULL_SCALE_VOLTAGE_V) depends on the circuit that senses the voltage feedback from the motor phases. Figure 2-4 shows how the motor voltage is filtered and scaled for the ADC input range using a voltage feedback circuit based on resistor dividers. The similar circuit is used to measure all three of both compressor and fan motors, and dc bus.

The maximum phase voltage feedback measurable by the microcontroller in this reference design can be calculated as given in Equation 1, considering the maximum voltage for the ADC input is 3.3 V.

Equation 1.

V_{F S} = V_{A D C_F S} \times G_{v} = 3.3 V \times 122.46 = 404.13 V

where

G_v is attenuation factor, G_v is calculated with Equation 2

Equation 2.

G_{V} = \frac{(R 62 + R 67 + R 70 + R 74)}{R 74} = \frac{(332 kΩ + 332 kΩ + 332 kΩ + 8.2 kΩ)}{8.2 kΩ} = 122.46

With that voltage feedback circuit, the following setting is done in user_mtr1.h:

//! \brief Defines the maximum voltage at the AD converter
#define USER_M1_ADC_FULL_SCALE_VOLTAGE_V         (404.1292683f)

The voltage filter pole is needed by the FAST estimator to allow an accurate detection of the voltage feedback. Make the filter low enough to filter out the PWM signals, and at the same time allow a high-speed voltage feedback signal to pass through the filter. As a general guideline, a cutoff frequency of a few hundred Hz is enough to filter out a PWM frequency of 5 to 20 kHz. Change the hardware filter only when ultra-high-speed motors are run, which generate phase-voltage frequencies in the order of a few kHz.

In this reference design the filter pole setting can be calculated with Equation 3:

Equation 3.

f_{f i l t e r_p o l e} = \frac{1}{(2 \times π \times R_{P a r a l l e l} \times C)} = 405.15 H z w h e r e, C = 47 n F R_{P a r a l l e l} = (\frac{(332 kΩ + 332 kΩ + 332 kΩ) \times 8.2 kΩ}{(332 kΩ + 332 kΩ + 332 kΩ) + 8.2 kΩ}) = 8.133 k Ω

The following code example shows how this is defined in user_mtr1.h:

//! \brief Defines the analog voltage filter pole location, Hz
#define USER_M1_VOLTAGE_FILTER_POLE_Hz           (416.3602877f)

TIEVM-MTR-HVINV Motor Voltage Sensing Circuit

Figure 2-4 Motor Voltage Sensing Circuit