Please, test if this commands will help for you:
sudo -i
echo on > /sys/bus/usb/devices/<your-webcam-usb-number>/power/control
Number of your device you can detect in this folder /sys/bus/usb/devices/. It should have folder "video4linux" in some subfolder. For example:
echo on > /sys/bus/usb/devices/1-4/power/control
Please, test if this commands will help for you: usb/devices/ <your-webcam- usb-number> /power/ control
sudo -i
echo on > /sys/bus/
Number of your device you can detect in this folder /sys/bus/ usb/devices/ . It should have folder "video4linux" in some subfolder. For example: usb/devices/ 1-4/power/ control
echo on > /sys/bus/