In the test system, the capacitor voltage and arm current waveforms within 1 s are extracted. The voltage and current waveforms in one cycle are randomly selected to calculate the capacitance. As shown in Fig. 7, when the sampling points are 22, 82, 116, and 357, the SM is inserted into the system, and the capacitor voltage rises.
Charge Transfer is not a term specific to capacitive sensing. It refers to the transfer of charge from one location to another through a series of switches. This same technique is used in MEMS for physical measurements. Charge Transfer for capacitive sensing uses a switched capacitor network to accumulate charge onto an integrating capacitor.
The sensor capacitor serves as a switched capacitor resistor equivalent to the analog input, which is attached to a large external capacitor often through internal circuitry. As the charge in the external capacitor increases, so does the voltage across it. This voltage is also one input of a comparator.
Sun et al. established a capacitance estimation model based on the relationship between the capacitor voltage and current, and used an estimation method based on model reference adaptation to estimate the capacitance.
At the heart of this development are the sensing methods themselves, the process by which capacitance is measured and converted into digital values that can be processed, manipulated and interpreted. Charge Transfer, Successive Approximation, Sigma-Delta, and Mutual Capacitance Measurement are the most commonly used sensing methods.
The largest error was less than 0.6% under different power levels. The proposed method depends on the high sampling accuracy and bandwidth of the inductance arm current and capacitance voltage sensors, which significantly decrease with increases in the high-power level. This leads to large deviations in the monitoring results.