Generac Power Systems 941-2, 940-2 Why Variable Speed Control?, Section GENERATOR FUNDAMENTALS

Section 1.1

GENERATOR FUNDAMENTALS

3.When the generator circuit breaker is turned to the “ON” position, AC voltage is delivered to the Full Bridge Rectifier. The AC volt- age is rectified to DC and thus becomes DC Link voltage.

4.AC voltage from the stator PS1/PS2 is delivered to the inverter. This is used as the power supply for the inverter circuit board.

5.AC voltage from the stator TIM1/TIM2 is delivered to the system controller. This is used for engine speed sensing.

6.The system controller sends signals to the inverter for inverter operation.

7.The system controller senses load voltage and signals stepper motor operation to achieve required engine speed for correct voltage output.

WHY VARIABLE SPEED CONTROL?

Most electrical loads will operate satisfactorily only within a relatively small voltage band. In order to pro- vide useful voltage at larger load currents, it is neces- sary to increase engine speed.

In conventional AC generators, some form of voltage regulation is needed to provide correct voltage in the full range of load current. This is often accomplished by regulating excitation current to the Rotor (field) which then regulates the strength of the Rotor's mag- netic field. The voltage induced into the Stator wind- ings is proportional to the strength of the Rotor's mag- netic field.

The Impact Plus computer controlled generator uses a Rotor having a fixed and permanent magnetic field. The strength of this magnetic field is fixed and cannot be regulated.

The output voltage on Impact Plus computer con- trolled generators tends to droop with increasing elec- trical loads. The SYSTEM CONTROLLER maintains a constant AC output voltage by increasing engine and Rotor speed as the load current increases, to off- set this inherent voltage droop.

Page 1.1-5