A High-Accuracy Decoupling Balance Control Method for an Auto-Balancing Bridge Based on a Variable-Domain Fuzzy-PID Controller

The auto-balancing bridge method is an impedance measurement method with higher accuracy than other traditional methods. The balance control algorithm within the auto-balancing bridge is a crucial component. Its performance in maintaining symmetry between the current flowing through the test element and the current flowing through a known reference resistor determines the impedance measurement accuracy. However, using the imaginary impedance of a practical reference resistor in the bridge diminishes the convergence accuracy of the auto-balancing bridge. In this paper, a feedforward decoupling module is first constructed to compensate for the imaginary part of the reference resistor and decouple the auto-balancing bridge into two independent balance control channels, namely, the real and imaginary channels. Then, two balance controllers based on the variable-domain fuzzy-PID algorithm are used for these two separated balance control channels in order to improve the convergence accuracy and adaptability of bridge balancing. Finally, the particle swarm optimization method is used to automatically tune the controller’s parameters to enhance the development efficiency of the auto-balancing bridge. Experimental results show that this bridge balance control algorithm can quickly stabilize the unbalanced current of the bridge. For the practical auto-balancing bridge circuit, its relative impedance measurement error remains below 0.05%. This method effectively improves measurement accuracy and provides crucial technical support for the application of auto-balancing bridges in the high-precision measurement field.