F28069m ADC sampling frequency is different from the actual frequency

I used EPWM to trigger ADC sampling, with a PWM frequency of 10KHz. I used ADC to sample a 10Hz sine wave, but the actual sampled signal frequency was 20Hz, which did not match the actual signal. At the same time, the interval time between the two points of the sampled signal was 0.00055s, and the frequency did not reach 10KHz. What is the reason for this