Characteristics of Voltage Regulation Principle for Generator Voltage Regulators

The rotor of the alternator is driven to rotate by the engine via belts. The speed ratio between the engine and the alternator ranges from 1.7 to 3, so the rotational speed of the alternator rotor varies across a wide range. This causes substantial fluctuations in the output voltage of the alternator, failing to meet the operating requirements of vehicle electrical equipment. To supply stable voltage for electric loads, an alternator must be equipped with a voltage regulator to keep its output voltage nearly constant under all engine operating conditions.

(1) Internal‑grounded regulator: An electronic regulator designed to pair with internal‑grounded alternators is defined as an internal‑grounded regulator.(2) External‑grounded regulator: An electronic regulator adapted for external‑grounded alternators is defined as an external‑grounded regulator.

For transistor regulators in service, it is optimal to adopt the model specified in the vehicle manufacturer’s manual. If an alternative model is used as a replacement, its rated voltage and other specified parameters shall match those of the original regulator; additionally, the substitute must share the same grounding type, and the wiring connections between the regulator and the alternator shall be correct. Improper matching may break the excitation circuit and disable normal alternator operation. Besides, the regulator must be controlled by the ignition switch.

Per the operating principle of alternators, the effective value of phase electromotive force generated by three‑phase windings is expressed as:\(E_\varphi=C_e\Phi n\)Where \(C_e\) = structural constant of the alternator, n = rotor rotational speed, \(\Phi\) = magnetic pole flux of the rotor. Namely, the induced electromotive force produced by the alternator is directly proportional to rotor speed and magnetic pole flux.

When the rotor speed rises, the induced electromotive force increases and the terminal output voltage \(U_b\) climbs. Once the speed exceeds the no‑load speed threshold, the output voltage approaches its upper limit. To stop the output voltage from rising along with increasing speed, the magnetic pole flux \(\Phi\) must be reduced. Since magnetic pole flux \(\Phi\) is proportional to excitation current \(I_f\), lowering flux can be achieved by decreasing the excitation current.