Microgrid Converter Control for Motor-Start Voltage and PF Stability

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Isolated microgrids face challenges in maintaining unity power factor at synchronous generator terminals and managing high current demand and voltage fluctuations during the direct starting of induction motors, which can lead to overloading and equipment failure.

Innovation Solution

A control process utilizing Power-Based Control (PBC) and a modified Volt-VAr function to coordinate distributed converters like frequency inverters, injecting or absorbing reactive power to regulate voltage and power factor, especially during transient events.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If direct starting of induction motors is used, then simplicity and cost-effectiveness are improved, but high current demand and voltage fluctuations occur

Engineering Contradiction:

Improvesimplicity of motor startingVSAvoidhigh current demand and voltage fluctuations

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The control system detects scheduled transitional events (such as planned motor starting) in advance and pre-configures the distributed converters to operate in autonomous Volt-VAr mode during the transient period. This preliminary action allows the system to prepare reactive power support before the high current demand occurs, mitigating voltage fluctuations without requiring complex soft-start equipment.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Distributed converters (frequency inverters, VFDs) act as intermediary devices between the induction motor and the main grid. During direct starting transients, these converters autonomously inject or absorb reactive power to stabilize voltage, mediating the harmful effects of high inrush current while allowing the motor to start directly without complex starting equipment.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If distributed converters operate in centralized Power-Based Control mode, then steady-state power factor regulation is improved, but response time during transients increases

Engineering Contradiction:

Improvepower factor regulationVSAvoidresponse time during transients

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The control system dynamically switches between centralized Power-Based Control mode for steady-state operation and autonomous Volt-VAr mode for transient events. During normal operation, centralized PBC optimizes power factor regulation. When a scheduled transient is detected, the system automatically transitions distributed converters to autonomous mode for faster response, then returns to centralized mode after the event.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The control mode parameter of distributed converters is changed based on system conditions. In steady-state, converters operate with centralized PBC parameters for optimal power factor. During transients, the parameter switches to autonomous Volt-VAr control with modified voltage thresholds, enabling faster local response without waiting for centralized commands.

Inventive Principle:

Principle #35Parameter changes

3Power

If generators operate with power close to unity, then active power supply availability is improved, but voltage regulation capability during transients deteriorates

Engineering Contradiction:

Improveactive power supply availabilityVSAvoidvoltage regulation capability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

Distributed converters are designed to perform multiple functions: their primary function is motor drive control, but they also serve as reactive power compensation devices during transients. By utilizing the idle capacity of these multi-functional converters for voltage regulation during scheduled events, the system maintains unity power factor operation for maximum active power while ensuring voltage stability capability when needed.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

During scheduled transient events, distributed converters autonomously detect voltage deviations and self-regulate reactive power injection/absorption without external commands. This self-service capability allows generators to maintain unity power factor operation while the converters independently provide voltage regulation support during transients.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS12525798B2Process for controlling isolated microgrids based on power-based control and modified Volt-VAr function methods

Publication Date: 2026.01.13 PETROLEO BRASILEIRO SA PETROBRAS

AI summary

A control process for microgrids for voltage regulation on the main bus and power factor (PF) regulation at generator terminals is presented, especially in events scheduled in the microgrid that result in electrical transients, such as direct starting of induction motors (IM). The technology takes advantage of idle capacity of distributed converters (for example: frequency inverters, “variable frequency drive” or VFD) of microgrids making them, in coordinated manner, injecting and/or absorbing reactive power, in addition to exploit the reduced latency of autonomous VFD control during the transient. The Power-Based Control (PBC) technique is used and a modified Volt-VAr function is created applied during the transitional regime.