BUCKET AS. 3228901 - Caterpillar

Illustration 2 g06029791
Switched Reluctance Inverter
(25) Capacitor
(26) Power transistor
(27) Diode
(28) To phase windings
(29) Bleed-down resistor
(30) Frame balance resistors
(31) DC bus connectors
(32) Bus shift resistorInverter (15) works together with generator (16) and generator ECM (14) as a system to provide a constant DC bus voltage. The inverter also contains the hardware for the insulation monitoring system.Inverter (15) provides precisely timed excitation voltages to generator (16). These excitation voltages enable the generator to produce electrical power. The inverter also converts pulsed direct current from the generator into direct current for the screed heat system and accessory power inverter (19).Power transistors (26) are controlled by generator ECM (14), and are used to excite the three phases of the generator in a precisely timed sequence. When a phase winding is in the excitation phase, control voltage is applied to the base of the transistor. In this case, the transistor is active and current can flow across the transistor. Under these conditions, the DC bus voltage is transmitted to corresponding phase windings (28).When a phase winding is in the generation phase, the corresponding power transistors are deactivated. Voltage returning from the phase windings is directed through diodes (27) to DC busses (31). Capacitor (25) stores the energy and helps to maintain the DC busses at a constant voltage.Bleed-down resistor (29) continuously dissipates a small amount of power when there is voltage on the DC bus. When the generator is disabled under normal conditions, residual voltage is dissipated by the generator. The bleed-down resistor prevents the DC busses from retaining hazardous voltages when the generator is not able to dissipate the residual voltage.Frame balance resistors (30) create a high-resistance path to ground (machine frame). These two resistors have the same resistance value. In a system with no other leakage to frame, there will be an equal voltage across each resistor. Unequal voltages across these resistors indicate a degradation of the electrical insulation system causing a ground fault.Bus shift resistor (32) allows another method for the system to monitor for ground faults. This high value resistance is periodically inserted and removed from the circuit. When this resistor is switched on, the resistor causes a predictable change in the voltages across the frame balance resistors. If the voltages respond to the resistance in an unexpected fashion, a ground fault is indicated.Note: For additional information regarding ground faults, refer to the appropriate screed documentation.Generator Power Control
Illustration 3 g06029796
Heater Power Modulation
(1) Generator ECM
(2) Machine ECM
(3) Engine ECM
(4) Accessory power inverter (optional)
(5) Screed power module
(6) HVIL cap
(7) Display unit
(8) Screed ECM
(9) Heater ECMThe generator does not supply power until a request signal is generated by the screed heat system or the optional accessory power system. Generator ECM (1) must receive an enable signal from machine ECM (2) in order for the generator to supply power.The generator cannot be enabled unless screed power module (5) is connected or HVIL cap (6) is installed. This high-voltage interlock loop (HVIL) must be satisfied to allow the generator to be enabled.When the key switch is in