DC-Link Voltage Ramp-Up Using Nonlinear Thyristor Firing
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Solution Overview
Problem
Existing variable speed drives (VSDs) face challenges with high current draw, bulky and costly components, and high oscillating current spikes when using C-Less Links with small capacitors, which affect size, weight, and compliance with harmonic regulations.
Innovation Solution
Implementing a non-linear variation of firing angles for thyristors in the rectifier bridge, reducing the intensity of current peaks and oscillations by modifying the command law without adding passive or active components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If C-Less Links with small capacitors are used, then size and weight are reduced, but high oscillating current spikes occur
Solution Approach 1:
The control method applies preliminary action by gradually increasing the thyristor conduction angle from a small initial value before full power operation. This progressive ramp-up of the conduction angle (α) from 0° to 180° over multiple AC cycles prevents sudden current spikes when capacitors are connected, while still allowing the use of small capacitor values for reduced size and weight.
Solution Approach 2:
The invention applies dynamics by making the thyristor conduction angle variable rather than fixed. The control method dynamically adjusts the conduction angle during startup phases to limit inrush current, then transitions to normal operation with full conduction angle. This dynamic control enables small capacitors to be used without generating harmful current spikes.
2Device complexity
If conventional rectifier control is used, then simple control is maintained, but high current draw and oscillations occur
Solution Approach 1:
The control method implements periodic action by dividing the startup process into multiple AC cycles with different conduction angles. Instead of immediate full-power connection, the system applies periodic control where the conduction angle is adjusted in steps across several cycles, smoothing current draw and eliminating oscillations while maintaining relatively simple control logic.
3Productivity
If full power connection is applied immediately, then productivity is improved, but current peaks damage components
Solution Approach 1:
The method applies preliminary action by preparing the system for full-power operation through a controlled sequence of increasing conduction angles. This preliminary controlled ramp-up across multiple AC cycles prevents component damage from current peaks while still achieving full productivity once the startup sequence completes, balancing reliability during transition with productivity in steady state.
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
The solution results in a compact, lightweight, cost-effective VSD that meets harmonic regulations, offers good thermal management, and supports high-power motors by smoothing current ramp-up and reducing oscillations.
Implementation Method 1
The rectifier comprises at least one thyristor, and the control circuit is configured to determine a command law of the thyristor producing a non-linear variation of firing angles of the thyristor over time
Data Source
AI summary
A computer-implemented method for controlling a ramp-up of a voltage in a DC-link, a computer-readable storage medium, a variable speed drive, and a system including a variable speed drive configured to carry out the method.