Generator Controller Isolates Voltage Ripple to Prevent DC Link Buildup
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Solution Overview
Problem
In synchronous generators, unbalanced short-circuit faults cause an increase in DC link voltage, leading to improper shutdowns, as the technology struggles to differentiate between this condition and other faults like diode faults, resulting in unnecessary generator shutdowns.
Innovation Solution
A controller system that monitors output voltage and current, isolates and shapes voltage ripples to generate a compensated signal, which counteracts armature reaction voltage ripples, preventing DC link voltage buildup by adjusting excitation to the exciter field winding without requiring hardware changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the generator shuts down in response to DC link voltage increase, then protection against diode faults is improved, but unnecessary shutdowns occur during unbalanced short-circuit conditions
Solution Approach 1:
The shutdown decision logic is segmented to respond only to specific characteristics of voltage increase. The controller distinguishes between sustained average voltage increases (indicating diode faults requiring shutdown) and transient voltage ripple (indicating unbalanced faults allowing continued operation). This selective response maintains protection while improving generator availability.
Solution Approach 2:
The excitation control system dynamically adjusts the DC current to the exciter field winding based on real-time analysis of the DC link voltage characteristics. During unbalanced short-circuit conditions, the system dynamically compensates for voltage ripple, allowing continued operation. During actual diode faults, the system dynamically responds by initiating shutdown, optimizing both protection and availability.
2Reliability
If the controller uses DC link voltage monitoring for fault detection, then safety is improved, but operational continuity is reduced due to false shutdowns
Solution Approach 1:
The fault detection system is segmented into multiple analysis paths: one path monitors average DC link voltage for safety-critical diode faults, while another path analyzes voltage ripple characteristics to identify non-critical unbalanced faults. This segmentation enables the system to maintain operational continuity during non-critical faults while ensuring safety response to critical faults.
Solution Approach 2:
The compensation loop serves as an intermediary that isolates the safety monitoring system from the disturbances caused by unbalanced faults. By compensating for voltage ripple before it affects the excitation system, the loop allows the monitoring system to focus on detecting actual safety-critical faults without being triggered by operational disturbances, thereby maintaining both safety and operational continuity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Prevents DC link voltage buildup during unbalanced short-circuit faults, allowing the generator to continue operating while isolating faults downstream, thereby avoiding untimely shutdowns and differentiating between fault types.
Implementation Method 1
a filter for isolating alternating current (AC) content from the average voltage value to obtain a voltage ripple signal
Implementation Method 2
unbalanced short circuit faults at the output of the generator are transmitted through armature reaction to the DC link voltage
Implementation Method 3
the DC link voltage is employed to provide a DC current of a desired magnitude to the exciter field winding. An AC voltage induced in the exciter rotor windings is converted to a DC voltage by a rotating rectifier circuit and provided as excitation to a main field winding
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A controller (36) employed in conjunction with a synchronous generator (10) monitors the output voltage (Va, Vb, Vc) of the generator. The controller employs the monitored output voltage as feedback that is used to control the excitation provided to an exciter field winding (20). In addition, the controller applies a control loop to the monitored output voltage that detects and modifies voltage ripple signals within the monitored output voltage to generate a compensated signal that is used to control the excitation to the exciter field winding. In particular, by detecting and modifying voltage ripple signals within the monitored output voltage, the controller is able to counteract armature reaction voltage ripples caused by unbalanced short-circuit faults, thereby preventing the build-up of voltage on the DC link.