Hybrid Control for Electrical Converter DC Link Stability
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Solution Overview
Problem
Existing control methods for electrical converters struggle to maintain a constant energy level in the DC link during large disturbances on the source and load sides, particularly when capacitive elements are undersized, leading to insufficient control and increased ripples in stored energy.
Innovation Solution
A hybrid control method that calculates reference control variables based on estimated and outer loop control variables, using a physical model to switch between different control parameters and regions, optimizing the control strategy to address dynamic changes and constraints, such as finite power storage capability, to ensure stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If separate control of inverter and active rectifier with power feedforward link is used, then device complexity is reduced, but energy storage stability deteriorates under large disturbances
Solution Approach 1:
The patent merges the separate control loops of the active rectifier and inverter into a unified model predictive control framework. By formulating a coordinated control strategy that simultaneously optimizes both converters based on a common cost function and system model, the patent achieves improved DC link energy stability under large disturbances while maintaining manageable device complexity through integrated control architecture.
2Stability of the object's composition
If model predictive control with online optimization is used, then energy storage stability is improved, but device complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the solution to the Riccati equation, which is the core computational element of the model predictive control algorithm. By preparing this mathematical solution in advance rather than computing it in real-time during operation, the patent reduces the online computational burden and control algorithm complexity while maintaining the stability benefits of model predictive control.
3Quantity of substance
If undersized capacitive elements are used in DC link, then device size is reduced, but energy storage stability deteriorates
Solution Approach 1:
The patent changes the control parameters and strategy to compensate for the reduced capacitive element size. By implementing a coordinated model predictive control approach that actively adjusts the operating parameters of both the active rectifier and inverter, the system maintains DC link energy stability even with smaller energy storage capacitors, thereby reducing overall device size without sacrificing stability.
Data Source
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AI summary
An electrical converter (12) comprises at least one of an active rectifier (20) and an inverter (22) interconnecting an electrical source (16) with an electrical load (18). A method for controlling an electrical converter (12) comprises: receiving at least one estimated control variable (38), which is estimated from measurement values measured in the electrical converter (12); receiving at least one outer loop control variable (36) provided by an outer control loop, the at least one outer loop control variable providing a desired steady-state operation point of the electrical converter (12); determining a control region (56a, 56b) based on a control error, which is a difference between the at least one estimated control variable (38) and the at least one outer loop control variable (36), wherein the control region is defined by one or more intervals of one or more control variables; selecting control parameters based on the control region (56a, 56b), wherein, when the control error is in an inner control region (56a), first control parameters are selected, and, when the control error is outside the inner control region but inside an outer control region (56b), second control parameters are selected; switching, based on the control error, between two and more control methods, which differ in control parameters, by predicting at least one reference control value (40) based on a solution (50) of a physical model (44) of the electrical converter (12), which comprises the selected control parameters, the physical model (44) being based on differential equations modelling the at least one estimated control variable (38) and the solution (50) being based on a constraint minimizing a difference between the at least one estimated control variable (38) and the at least one outer loop control variable (36); and determining switching states (42) of the electrical converter (12) based on the reference control value (40).