Nonlinear Droop Control for Stable DC Microgrid Power Sharing

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Conventional droop control in DC microgrids faces issues with power sharing accuracy and stability, especially when interfacing with constant power loads, leading to system destabilization due to negative incremental impedance.

Innovation Solution

Dynamic nonlinear droop control (DNDC) introduces a first-order nonlinear system with a positive fixed stable point, mimicking nonlinear dynamics to improve power sharing and stability, providing virtual inertia and a load-dependent droop coefficient for robust voltage regulation and power sharing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional droop control is used in DC microgrids, then power sharing between multiple sources is enabled, but power sharing accuracy deteriorates and voltage regulation becomes poor

Engineering Contradiction:

Improvepower sharing accuracyVSAvoidcontrol system complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent transforms the static droop control into a dynamic nonlinear control system. The control law incorporates time-varying voltage references that adapt based on power output and system state, allowing the droop characteristic to change dynamically rather than remaining fixed. This dynamic approach improves power sharing accuracy by adjusting the droop slope according to operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The invention changes the droop control parameters from constant values to time-varying parameters. The voltage reference is modified to include nonlinear terms that depend on power output and time, effectively changing the droop characteristic parameters dynamically. This parameter transformation enables accurate power sharing while maintaining system stability.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If conventional droop control is used, then decentralized power balance is achieved, but system stability deteriorates especially with constant power loads

Engineering Contradiction:

Improvesystem stabilityVSAvoidcompatibility with constant power loads

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent converts the harmful negative incremental impedance effect of constant power loads into a beneficial control mechanism. By incorporating the power output information into the dynamic voltage reference, the control system uses the same factor that causes instability (CPL operation) as part of the stabilization mechanism, effectively compensating for the destabilizing effect.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The invention introduces feedback mechanisms where the voltage reference is continuously adjusted based on measured power output and system state. This feedback loop allows the system to respond to changing load conditions, including constant power loads, by adapting the droop characteristic in real-time to maintain stability.

Inventive Principle:

Principle #23Feedback

3Device complexity

If simple conventional droop control is used, then device complexity is low, but voltage regulation deteriorates and power sharing accuracy becomes poor

Engineering Contradiction:

Improvecontrol system simplicityVSAvoidvoltage regulation accuracy

Core Design Contradiction:

Device complexityVSManufacturing precision

Solution Approach 1:

The control system is segmented into distinct functional blocks: power measurement unit, dynamic voltage reference generation unit, and converter control unit. This segmentation allows each block to perform a specific function, making the complex control strategy implementable through modular components while maintaining overall system simplicity in terms of control architecture.

Inventive Principle:

Principle #1Segmentation

4Reliability

If advanced control methods like MPC or backstepping control are used, then power sharing accuracy and stability improve, but device complexity increases

Engineering Contradiction:

Improvesystem stabilityVSAvoidcontrol algorithm complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs a control approach that is computationally simpler and easier to implement than MPC or backstepping control, while achieving comparable or superior performance. The dynamic nonlinear droop control uses straightforward calculations based on power measurement and time-varying references, avoiding the complex optimization and iterative computations required by advanced methods, thus reducing implementation complexity.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentUS20240171070A1Dynamic Nonlinear Droop Control

Publication Date: 2024.05.23 NORTH CAROLINA STATE UNIV

AI summary

Various examples are provided related to dynamic nonlinear droop control (DNDC). In one embodiment, a method for DNDC for direct current (DC) power conversion includes receiving an indication of an output of a DC power converter, generating a control signal based upon the indication, and adjusting operation of the DC power converter in response to the generated control signal. The indication can be a scaled measurement of output current or output power of the DC power converter. The control signal is based at least in part upon the indication, the power converter voltage and DNDC parameters.