"working principles" is a correct and usable phrase in written English.
You could use it for example in a sentence such as, "We must adhere to the strictest working principles in order to meet our goals."
In this paper research targets, working principles.
Chapter 14 introduces the working principles of rotating biological contactors.
Different types of engines and their working principles are described.
Different nanostructure evaluation techniques with their working principles are briefly explained.
These droplets are separated according to the working principles of ordinary axial cyclones.
Figure 1 provides the working principles of the intermittent control system.
Here, the inner working principles of these blocks will be elaborated.
The working principles for the low-frequency disturbance-generating device are summarized as follows.
Zissis et al. [31] discussed the TPAs working principles and its security concerns.
This paper introduced the working principles and current technology trends of DC breakers.
A prototype has been fabricated to verify the working principles, designs and simulations.
