Brushless Exciter Field Winding Segmentation for Load Balance
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Solution Overview
Problem
In AC brushless excitation systems, the transition between AC and DC excitation in multi-phase field windings causes load unbalance and output variations with changing generator speed, making it difficult to maintain constant field current and load balance.
Innovation Solution
A power generation system incorporating an electric power converter, a Scott transformer, a thyristor excitation device, and an excitation scheme changeover device that allows for variable voltage and frequency inputs to d-axis and q-axis windings, enabling AC excitation during startup and DC excitation during nominal operation, while maintaining balanced load and constant output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If connections to field windings of AC exciter are modified between AC excitation and DC excitation, then excitation mode can be switched, but load unbalance is caused on field windings
Solution Approach 1:
The field winding system is segmented into d-axis and q-axis windings that can be independently controlled. During AC excitation, both windings are energized; during DC excitation, only the d-axis winding is energized while q-axis is disconnected. This segmentation allows mode switching without causing load unbalance on the entire field winding system.
Solution Approach 2:
The connection configuration of field windings is made dynamic rather than fixed. The system automatically adjusts the connection state of d-axis and q-axis windings based on the operating mode (AC or DC excitation), enabling adaptable excitation while maintaining load balance through real-time reconfiguration.
2Ease of operation
If field current of generator is maintained constant during AC excitation, then excitation control is simplified, but output characteristics of brushless excitation apparatus change with generator speed
Solution Approach 1:
The system incorporates feedback control that monitors generator speed and automatically adjusts the excitation current magnitude and frequency. This feedback mechanism maintains constant output characteristics of the brushless excitation apparatus despite speed variations, while keeping the control system relatively simple through automatic adjustment.
Solution Approach 2:
The excitation system dynamically changes parameters (current magnitude and frequency) based on generator speed. During AC excitation, the system adjusts these parameters to maintain constant output characteristics, resolving the contradiction between simple control and stable output.
3Reliability
If DC voltage is applied to field windings of AC exciter during nominal operation, then stable excitation is achieved, but excitation capacity is excessive for low speed operation
Solution Approach 1:
The excitation system transitions from static DC excitation to dynamic AC excitation capability. During low-speed operation, AC excitation is used with reduced capacity; during nominal operation, DC excitation provides stable high-capacity performance. This dynamic adaptation matches excitation capacity to actual operational needs.
Solution Approach 2:
The field winding system is designed to perform multiple functions: it can operate under AC excitation for low-speed conditions and under DC excitation for nominal-speed conditions. This multi-functionality allows a single system to meet varying excitation requirements without excessive capacity.
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
This solution stabilizes the generator field current and load balance across windings, ensuring consistent output even as generator speed changes, and reduces excitation capacity requirements, particularly at low speeds, leading to a more compact and cost-effective system.
Implementation Method 1
a Scott transformer 15 having three-phase windings on a primary side, and a first single-phase winding and a second single-phase winding on a secondary side, with the three-phase windings connected to output ends of the electric power converter, for outputting electric power of alternating currents having a phase difference to each other
Implementation Method 2
a rotary rectifier connected to the rotating-type multi-phase windings, for rectifying multi-phase outputs from the AC exciter
Data Source
AI summary
A power generation system is provided in which, when a static frequency converter (SFC) is connected to synchronous generator's armature windings, an AC exciter performs AC excitation by allowing a d-axis winding and a q-axis winding of the AC exciter to configure d-q orthogonal axes; and, at the time of steady-state operation of the synchronous generator, an alternating current(s) supplied from an electric power source is rectified by a thyristor excitation device, and also the AC exciter thereby performs DC excitation by connecting the d-axis winding and the q-axis winding in series with each other.