Generac Power Systems NP-40G - Manual (Page 8)

Section 1.1- GENERATOR FUNDAMENTALS
WHAT IS A "CCG"?:
The initials “CCG” stand for “computer con­
trolled generator“. Such units are different from
conventional generators in that the performance of
the engine and AC generator are more accurately
matched over a wide range of power needs. The
CCG’s provide greater efficiency of both the engine
and the generator while maintaining electrical out­
put within an acceptable voltage and frequency
band.
CCG units have the ability to operate the engine
over a wide range of speeds, while conventional
generators will deliver correct AC frequency and
voltage only at a fixed rpm. The unit’s electrical
output is fed through an AC-AC converter which
reconstructs electrical waveforms to the correct
output frequency.
Unlike conventional AC generators, the CCG can
match engine speed to load requirements. This
provides several advantages, as follows:
П Smaller engines can be used to produce more
power than on a conventional generator, since
it can be allowed to run at a higher speed.
□ When the load is reduced, the engine can run
at slower than the usual speeds. This improves
fuel economy and reduces engine noise.
□ The CCG unit can be operated closer to its peak
power point at all times, because output volt­
age and current are functions of engine speed.
This allows fora much more compact generator
design.
CCG SYSTEM OVERVIEW:
introduction to CCG’s
in the diagram. Operation of the system may be
described briefly as follows:
Figure 10 is a block diagram of the CCG system.
The major elements of the system are represented
1. The engine is directly coupled to a permanent
magnet type Rotor, so the Rotor runs at the same
speed as the engine.
2. As the Rotor turns. Its magnetic field cuts across
the Stator windings to induce a voltage into the
Stator.
a. The Stator is a 2-phase type with center tap.
b. Stator AC output frequency Is between 336 and
540 Hertz. This corresponds to engine speeds of
2520 to 4050 rpm.
c. The load requires a nominal AC frequency of
60 Hertz. Thus, the generated frequency Is six to
nine times the desired range.
3. A Frequency Converter changes the high fre­
quency output to a useful frequency, I.e., one that
is compatible with load requirements of about 60
Hertz.
4. A Voltage Detector circuit senses load voltage
and signals a System Control circuit.
5. The System Control circuit establishes the RE­
QUIRED ENGINE SPEED for correct voltage and
delivers an output to an Engine Controller.
6.
The Engine Controller adjusts the engine’s
Throttle to change engine speed and establish the
correct AC output voltage.
7. The following facts should be apparent:
□ LOAD FREQUENCY IS CONTROLLED BY THE
“FREQUENCY CONVERTER“ DEVICE.
□ VOLTAGE IS CONTROLLED BY A “SYSTEM
CONTROL“ CIRCUIT WHICH CHANGES EN­
GINE SPEED TO MAINTAIN A CONSTANT
VOLTAGE AT VARYING ELECTRICAL LOADS.
Page 1.1-4