Power Converter Droop Control with Phasor Current Limiting
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Solution Overview
Problem
Droop control methods for power converters lack direct control over real and reactive currents, making it difficult to impose current limits and transition seamlessly between grid-connected and islanded states, potentially leading to converter damage or shutdown.
Innovation Solution
Implementing a virtual voltage-virtual impedance control technique that indirectly controls phasor currents by modifying the virtual source amplitude and phase, with instantaneous current limits to constrain operation within safe limits during transients, allowing seamless transitions between states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If phase shift virtual impedance droop control is used, then dynamic response and harmonic compensation are improved, but direct control of real and reactive currents is lost making it difficult to impose current limits
Solution Approach 1:
The patent merges phase shift virtual impedance droop control with instantaneous current limiting control into a unified control system. The controller simultaneously executes both control strategies, combining the dynamic response benefits of phase shift droop control with the current limiting capabilities of instantaneous control, thereby resolving the contradiction between improved dynamic response and lost current control capability
Solution Approach 2:
The control system is designed to perform multiple functions: it provides phase shift virtual impedance droop control for dynamic response and harmonic compensation, while also implementing instantaneous current limiting for safety. This multi-functional controller maintains both the dynamic performance and the current control capabilities that were previously mutually exclusive
2Loss of energy
If phase shift virtual impedance droop control is used, then harmonic compensation is improved, but converter safety is compromised due to inability to constrain operation within safe limits
Solution Approach 1:
The controller implements preliminary anti-action by proactively applying instantaneous current limits before the converter can be damaged. The control system continuously monitors and constrains the instantaneous currents within safe operating limits, preventing harmful effects before they occur while maintaining the harmonic compensation benefits of phase shift droop control
3Ease of operation
If direct phasor control is implemented, then current limits can be imposed, but seamless transitions between islanded and grid-connected states cannot be achieved
Solution Approach 1:
The control system employs dynamic switching capability that allows it to adapt between different operating modes. The controller can dynamically transition between phase shift virtual impedance droop control (optimized for islanded operation with harmonic compensation) and instantaneous current limiting control (optimized for grid-connected operation with current constraints), enabling seamless state transitions while maintaining the appropriate control characteristics for each mode
4Speed
If virtual impedance control is used, then dynamic response is improved, but operation with virtual impedance while grid connected becomes impossible
Solution Approach 1:
The control system dynamically adapts its impedance characteristics based on the operating state. When grid-connected, it maintains virtual impedance for dynamic response while incorporating instantaneous current limiting to ensure safe operation. When islanded, it fully utilizes phase shift virtual impedance droop control for optimal dynamic performance and harmonic compensation, thereby achieving versatile operation across both grid-connected and islanded states
Data Source
AI summary
A method and apparatus for power converter current control. In one embodiment, the method comprises controlling an instantaneous current generated by a power converter such that that power converter appears, from the perspective of an AC line coupled to the power converter, as a virtual AC voltage source in series with a virtual impedance.