1. Field of the Invention
The present invention relates to a power generation controller of a vehicle power generator and, more specifically, to a power generation controller provided in a wound-field type synchronous generator for use with a vehicle with which a favorable voltage controllability is implemented when control is exercised over a to-be-generated voltage through ON/OFF switching of voltage application to a field winding.
2. Description of the Related Art
An exemplary conventional controller of a vehicle power generator is found in Japanese Patent No. 3329402 (referred to as Patent Document 1), which is shown in FIG. 9.
With such a controller, power generation control is exercised through pulse width modulation with ON/OFF switching that is taken place for voltage application to a field winding. For such power generation control, the ON/OFF switching is digitally timed by a microcomputer.
In FIG. 9, a generator 1 includes an armature winding 21, and a field winding 22. A microcomputer 30 includes a processor 301, ROM 302, RAM 303, a pulse width modulation (PWM) timer 304, an analog-digital (A/D) converter 305, a timer 306, and others.
In the generator 1, a rotor part is connected to a power source that is not shown and exemplified by internal combustion engine directly or indirectly via a belt or others. When the rotor part rotates, alternating current (AC) voltage induction responsively occurs to the armature winding 21, and the AC voltage is converted into direct current (DC) voltage by a rectifier 2.
The rectifier 2 is connected with an electrical load 5 through a battery 3 or a switch 4 for supply of a DC power.
Described next is the operation of a power generation controller 6. That is, first of all, the voltage of the battery 3, and current information equivalent to a field current indicating the voltage level and flowing into the field winding 22 via a shunt resistor 23 are forwarded to the A/D converter 305 via an interface 26. Such an input is subjected to digital value conversion for input to the processor 301. A rotation sensor 24 or a vehicle speed sensor 25 detects a rotation signal. Thus detected rotation signal is forwarded to the processor 301 via the timer 306, indicating the rotation speed of the generator 1.
In the processor 301, a deviation is calculated between the voltage of the battery 3 and a power generation target voltage Vref for first proportional integral (PI). Such an operation is hereinafter referred to as AVR operation. Another deviation is calculated between any detected field current value if and a first current limit value ifcMAX for second proportional integral (PI). Such an operation is hereinafter referred to as ACR operation.
With this being the case, the output result of the AVR operation will be a command value ALPHV for a current flow rate of the field winding, and the output result of the ACR operation will be a command value ALPHI therefor.
The AVR and ACR operations are not executed simultaneously but selectively in consideration of the value relationship among the detected field current value if, the first current limit value ifcMAX, and a second current limit value ifcMAX2, and the level relationship between the battery voltage and the power generation target voltage Vref. Those first and second current limit values are so set as to be ifcMAX>ifcMAX2. Such a setting allows switching between AVR and ACR operations with a difference hysteresis between the first and second current limit values ifcMAX and ifcMAX2.
To be specific, when the output current coming from the generator 1 is low in level with a low field current, the AVR operation is so executed that a to-be-generated voltage agrees with a target voltage, and the command value ALPHV drives a field switching element 7. On the other hand, when the field current exceeds any predetermined value ifcMAX2, control is so exercised that the maximum value of the field current becomes ifcMAX2 or lower. The ACR operation is then executed so as to prevent generator damage and belt slip, and the command value ALPHI drives the field switching element 7.
The issue here is that such a conventional technology poses a problem of varying power generation controllability depending on the operating point of a generator. In more detail, the to-be-generated power shows a change responsively when the field current changes, and the amount of change varies with the operating point. It means that, against the change of the operation amount of AVR for power generation control=current flow rate of a field winding, power to be generated by the generator varies differently with the operating point. Therefore, the change of battery voltage=input amount of AVR operation will not be uniform.
That is, even if a transient phenomenon of a sudden generator load change at a given operating point is defined by an operation constant of proportional integral with any appropriate response characteristics, it is still uncertain if any other operating points can derive desired response characteristics.