Fuel efficient crane system

Abstract

A system and method for efficiently regulating the fuel consumption of a variable speed combustion engine used to control loads such as a hoist motor in a mobile gantry crane based on load motor speed commands issued by a crane operator. The system and method can rely on a programmable logic controller to issue engine fuel commands to regulate engine speed based on interpolations derived from data representing the relationship between load motor voltage and engine speed and data representing the relationship between engine speed and engine power capacity. The method may also be used in modified form by combustion engines which need digital fixed speed commands.

1 . A method for providing a constant or nearly constant AC voltage to an auxiliary load on a crane having a variable speed combustion engine coupled to a generator producing a variable AC voltage onto a first AC bus which is converted into a variable DC voltage on a DC bus by a diode converter, wherein the variable DC voltage is further converted by an inverter into an AC voltage delivered on a second AC bus to the auxiliary load comprising:
 obtaining a signal proportional to the voltage on the DC bus wherein the signal is one selected from the group consisting of a DC bus voltage, an AC voltage, an AC frequency or a generator speed; and   calculating a normalized modulation index to present to the modulator inherent in the inverter.   
     
     
         2 . A method for providing a constant or nearly constant AC voltage to an auxiliary load on a crane having a variable speed combustion engine coupled to a generator producing a variable AC voltage onto a first AC bus which is converted into a variable DC voltage on a DC bus by a diode converter, wherein the variable DC voltage is further converted by an inverter into an AC voltage delivered on a second AC bus to the auxiliary load comprising:
 obtaining a feedback signal representative of the output of the AC voltage of the inverter;   calculating a modulation index to present to the modulator inherent in the inverter; and   regulating the output voltage of the inverter based on said AC voltage signal.   
     
     
         3 . A method for providing a constant or nearly constant AC voltage to an auxiliary load on a crane system having a variable speed combustion engine coupled to a generator producing a variable AC voltage onto a first AC bus which is converted into a constant DC voltage on a DC bus by a thyristor converter connected to an inverter further connected by means of a second AC bus to the auxiliary load, the crane system having further a DC bus voltage sensor connected to the DC bus, an AC voltage or frequency sensor connected to the first AC bus, an AC line voltage phase locked loop connected to the AC voltage or frequency sensor, a firing angle controller connected to the AC line voltage phase locked loop and a voltage controller connected to the firing angle controller and to the DC voltage bus sensor, comprising:
   detecting the DC bus voltage with a sensor connected to the DC bus;   feeding back the detected DC bus voltage to the voltage controller;   comparing the detected DC bus voltage against a reference DC bus voltage figure;   issuing a DC bus voltage command to the firing angle controller;   further detecting either the AC voltage or the frequency of the AC bus with the sensor connected to the first AC bus;   transmitting the detected AC voltage or frequency to the AC line voltage phase locked loop; and   issuing a firing angle command to the thyristor through the firing angle controller based on a combination of the output from the phase locked loop and the output of the voltage controller.     
     
     
         4 . The method of  claim 1 , further comprising regulating output AC voltage of the inverter, wherein the AC voltage, V ac     —     out , is determined by the equation:
     V   ac     —     out   =m *√(3/2)* V   dc /2,
   wherein V dc  is the voltage of the DC bus and “m” is the modulation index.   
     
     
         5 . The method of  claim 2 , wherein the obtaining of the feedback signal comprises selecting a desired AC voltage output from the inverter as a reference voltage and dividing the reference voltage by a feedback signal representing the DC bus voltage, or a signal proportional to the DC bus chosen from an AC voltage, an AC frequency, or a generator speed. 
     
     
         6 . The method of  claim 3 , wherein the DC bus voltage is fixed according to a minimum AC line-to-line voltage.