Virtual Synchronous Machine Control for Grid-Forming Inverters

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Solution Overview

Problem

The integration of wind power into the grid has increased, leading to instability due to the reduction of synchronous machines and the resulting fluctuations in grid voltage and frequency, which conventional asynchronous machines, such as doubly-fed wind turbine generators, struggle to manage effectively in grid-following modes, necessitating a more robust grid-forming control mechanism.

Innovation Solution

Implementing a method for inverter-based resources with asynchronous machines to emulate virtual synchronous machines, utilizing a vector-control approach to coordinate the operation of converters and additional devices like storage or reactive power compensation units, enabling closed-loop control of voltage and frequency at the point of interconnection with the grid.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If conventional grid-following control is used for asynchronous machines, then the control structure is simple and easy to implement, but the grid stability deteriorates due to inability to maintain voltage and frequency under high wind power penetration

Engineering Contradiction:

Improvecontrol implementation simplicityVSAvoidgrid stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The patent creates a virtual synchronous machine model that replicates the voltage and frequency characteristics of traditional synchronous machines. The controller emulates synchronous machine behavior by generating virtual terminal voltage based on measured terminal current and emulated impedance, thereby copying the stabilizing effects of synchronous machines without requiring actual synchronous machine hardware.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent transforms the control parameters from current-source characteristics to voltage-source characteristics. By changing the control objective from regulating current to regulating terminal voltage, the asynchronous machine with power electronic converters can provide grid-forming support similar to synchronous machines, thereby improving grid stability while maintaining operational simplicity.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If wind power penetration increases, then renewable energy utilization improves, but grid voltage and frequency stability deteriorate due to reduction in synchronous machines

Engineering Contradiction:

Improverenewable energy utilizationVSAvoidgrid voltage and frequency stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The virtual synchronous machine controller copies the grid-supporting characteristics of traditional synchronous machines by emulating their voltage regulation and frequency stabilization behaviors. This allows high penetration of inverter-based renewable energy sources while maintaining the stabilizing effects traditionally provided by synchronous machines.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces the mechanical inertia and electromagnetic coupling of physical synchronous machines with a control-based virtual model. The virtual synchronous machine uses power electronic converters and control algorithms to replicate the stabilizing functions of mechanical synchronous machines, enabling high renewable penetration without requiring physical synchronous machine infrastructure.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If asynchronous machines operate in grid-following mode, then device complexity is low, but the ability to provide grid-forming control under disturbances is insufficient

Engineering Contradiction:

Improvecontrol system complexityVSAvoidgrid-forming capability under disturbances

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent changes the operating mode parameters from grid-following to grid-forming by transforming the control objective. The controller now regulates terminal voltage magnitude and phase angle directly, enabling the asynchronous machine to provide voltage support and frequency stabilization under disturbances while maintaining relatively simple control structure.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The virtual synchronous machine controller provides multiple functions including voltage regulation, frequency stabilization, and disturbance ride-through capability within a single control framework. This multi-functional approach enables asynchronous machines to adapt to various grid conditions and provide grid-forming support without requiring separate control systems for each function.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS11456645B2System and method for operating an asynchronous inverter-based resource as a virtual synchronous machine with storage

Publication Date: 2022.09.27 GENERAL ELECTRIC RENOVABLES ESPANA SL

AI summary

A method for controlling an inverter-based resource having an asynchronous machine connected to a power grid to provide grid-forming control of the inverter-based resource includes coupling at least one additional device to terminals of a first converter of the inverter-based resource. Further, the method includes emulating, via a controller, at least one of the at least one additional device or the first converter as a first virtual synchronous machine. Moreover, the method includes coordinating, via the controller, operation of the first virtual synchronous machine and a second converter of the inverter-based resource using a vector-control approach to control at least one of voltage and frequency at a point of interconnection between the inverter-based resource and the power grid in a closed loop manner.