Parallel DC Current Control for High Dynamic Response
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current source converters in motor drive applications face limitations in dynamic performance due to the dynamic limitations of the inner DC link current control loop, which restricts the ability to respond quickly to load changes and motor control setpoint changes, especially at higher switching frequencies and torque demands.
Innovation Solution
Implementing a parallel DC current control loop that operates independently of other motor control loops, using a fixed command signal or a gain factor greater than unity to enhance dynamic performance, allowing for improved adaptability and efficiency in current source inverters, and allowing user-adjustable gain values based on motor control loop error signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional multi-loop control architecture is used with inner DC link current control loop, then system stability is maintained, but dynamic response to load changes and setpoint step changes is limited
Solution Approach 1:
The patent segments the control architecture by separating the DC link current control from the motor control loops. The DC link current controller operates independently with its own PI controller, while motor control loops (speed, torque, flux) operate as outer loops. This segmentation allows the inner DC link current loop to respond dynamically without being constrained by the slower outer motor control loops, thereby improving overall system dynamic response while maintaining stability through the hierarchical structure.
2Speed
If CSR switching frequency is increased to improve dynamic performance, then response speed improves, but switching losses increase
Solution Approach 1:
The patent implements dynamic control of the DC link current by enabling the CSR to switch at higher frequencies when dynamic response is needed, while the independent DC link current controller manages the switching demands. The controller adapts the switching operation based on load conditions and dynamic requirements, allowing high-frequency switching only when necessary to improve dynamic performance, thereby reducing overall switching losses compared to continuous high-frequency operation.
3Speed
If DC link choke size is reduced to improve dynamic performance, then response time improves, but current ripple increases
Solution Approach 1:
The patent employs a PI (Proportional-Integral) controller in the DC link current control loop that provides feedback control. The controller continuously monitors the DC link current and adjusts the CSR switching duty cycle to maintain the desired current level. This feedback mechanism compensates for current ripple caused by smaller DC link chokes, allowing the system to achieve fast dynamic response with reduced choke size while maintaining current stability through active compensation.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Current source converters and control methods are presented for high dynamic performance by implementing a DC link current control loop parallel to one or more motor control loops, with a DC link current control command value for operating the current source rectifier being derived at least partially independent of the motor control command values, wherein certain implementations drive the current source rectifier to its maximum rated value, or the DC current command value can be set above an amount required by the current source inverter using a gain factor which can be fixed or can itself be adjusted based on one or more motor control error values for balancing as-needed dynamic performance and efficiency.