Discrete Inverter Current Control With ZOH and Time Delay
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Solution Overview
Problem
In high-speed and large-capacity AC motor systems, the limited sampling frequency of digital inverters due to arithmetic operation time and heat issues leads to degraded current control performance and stability, reducing modeling accuracy and command convergence.
Innovation Solution
The method involves determining voltage equations on stationary and synchronous coordinate systems, reflecting zero-order hold and time delay effects, and designing transfer functions for current control in a discrete time domain to improve system modeling and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sampling frequency of the digital inverter is increased to improve current control performance and stability, then the modeling accuracy and command convergence improve, but the arithmetic operation time and heat generation increase, limiting the practical sampling frequency
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing voltage equations and transfer functions in lookup tables before operation. During real-time control, the controller retrieves pre-computed values based on measured rotor position and speed, avoiding time-consuming real-time calculations. This allows the system to achieve high sampling frequencies without excessive arithmetic operation time, resolving the contradiction between control stability and computation time.
Solution Approach 2:
The patent changes parameters by deriving voltage equations and transfer functions that explicitly account for the actual sampling frequency of the digital inverter. By incorporating the sampling frequency as a parameter in the control model, the system optimizes control performance for the specific hardware constraints, achieving stable current control without requiring excessively high sampling frequencies that would increase arithmetic operation time and heat generation.
2Measurement precision
If the sampling frequency is increased to improve modeling accuracy, then command convergence performance improves, but heat generation from power devices increases
Solution Approach 1:
The patent pre-computes voltage equations and transfer functions offline and stores them in lookup tables, eliminating the need for high-speed real-time calculations. This approach achieves accurate modeling without requiring high sampling frequencies, thereby reducing power device switching losses and heat generation while maintaining precise current control.
Solution Approach 2:
The patent replaces the traditional high-frequency switching mechanism with a computational approach using pre-calculated transfer functions and lookup tables. This substitution allows accurate modeling and control without relying on high sampling frequencies, reducing the thermal stress on power devices while maintaining control precision.
3Device complexity
If conventional voltage equations without ZOH and time delay reflection are used, then the control algorithm is simpler, but modeling accuracy decreases and stable operating range is limited
Solution Approach 1:
The patent incorporates ZOH and time delay effects into pre-calculated voltage equations and transfer functions that are stored in lookup tables. During real-time operation, the controller simply retrieves these pre-computed values based on measured parameters, maintaining algorithm simplicity while achieving high modeling accuracy that expands the stable operating range.
Solution Approach 2:
The patent changes the control approach by using transfer functions that explicitly include ZOH and time delay parameters. By incorporating these parameters into the pre-computed control model, the system achieves accurate representation of the digital inverter's actual behavior without increasing real-time computational complexity, thereby expanding the stable operating range.
Data Source
AI summary
An apparatus and a method for inverter control are disclosed. A method according to an embodiment of the present disclosure comprises: discretizing, in a continuous time domain, a voltage equation for a motor in a stationary coordinate system in which a zero-order hold and time delay is reflected; and determining a voltage equation for the motor in a synchronous coordinate system in a discrete time domain by reflecting the position and speed of a rotor of the motor.