Inverter Phase Control for Stable Grid Connection of Static Inverters

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Solution Overview

Problem

In power systems with virtual synchronous generator control, static inverters face challenges due to inaccuracies in voltage and frequency measurements, leading to potential overload and shutdown when new inverters are introduced, as they may suck unnecessary power or exceed capacity, causing instability.

Innovation Solution

A power conversion device with an inverter, AC voltage measuring device, and AC frequency detection circuit that sets the frequency of the AC voltage target to the detected frequency and controls the phase to be at least leading when introducing a new inverter, preventing shutdown of existing inverters by managing power flow effectively.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a static inverter is introduced into the AC system with voltage control, then the inverter outputs power to the AC system, but measurement inaccuracies cause the inverter to suck unnecessary power or exceed capacity, leading to shutdown

Engineering Contradiction:

Improveinverter introduction capabilityVSAvoidinverter operation stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the inverter control circuit continuously monitors the actual AC voltage frequency and phase, compares it with the target values, and dynamically adjusts the output voltage frequency and phase to minimize the difference. This closed-loop control eliminates the power suction problem caused by measurement inaccuracies by constantly correcting deviations between actual and target parameters.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent applies preliminary action by setting the AC voltage target frequency and phase in advance based on the AC system's operating conditions before the inverter is introduced. The control circuit pre-configures the target values to match the system's actual frequency and phase characteristics, ensuring the inverter synchronizes properly from the start and avoids initial power suction or overload conditions.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If the inverter controls output voltage frequency and phase based on target values, then power is output to the AC system, but measurement inaccuracies cause phase differences leading to power flow instability

Engineering Contradiction:

Improvepower output capabilityVSAvoidpower flow stability

Core Design Contradiction:

ProductivityVSStability of the object's composition

Solution Approach 1:

The control circuit uses feedback to continuously monitor the phase difference between the inverter's output voltage and the AC system voltage. When a phase difference is detected, the control circuit automatically adjusts the output voltage phase to align with the system phase, ensuring stable power flow and preventing oscillations or instability caused by phase mismatches.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent dynamically changes the output voltage parameters (frequency and phase) based on real-time system conditions. The control circuit adjusts these parameters to match the AC system's actual state, ensuring the inverter operates in synchronization with the system and maintains stable power flow even as system conditions change.

Inventive Principle:

Principle #35Parameter changes

3Power

If voltage control is used to operate the inverter as a voltage source, then the inverter generates AC voltage, but inaccuracies in frequency and phase detection cause the inverter to operate inefficiently or cause system instability

Engineering Contradiction:

Improvevoltage generation capabilityVSAvoidfrequency and phase detection accuracy

Core Design Contradiction:

PowerVSMeasurement precision

Solution Approach 1:

The patent employs feedback to compensate for measurement precision limitations. The control circuit continuously monitors the actual frequency and phase of the AC system voltage, compares it with the target values, and uses this feedback information to adjust the output voltage parameters. This closed-loop approach eliminates the need for perfectly accurate open-loop measurements, allowing the inverter to operate efficiently despite measurement inaccuracies.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent replaces reliance on precise mechanical or electronic measurement systems with a control-based approach. Instead of depending on high-precision frequency and phase detectors, the system uses control algorithms that can tolerate measurement variations and actively correct for them through continuous adjustment of the output parameters.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS12166427B2Power conversion device including an inverter control circuit that controls a phase of an AC voltage target value

Publication Date: 2024.12.10 MITSUBISHI ELECTRIC CORP

AI summary

An inverter converts power outputted from a distributed power supply into AC power, and outputs to an AC system. An inverter control circuit generates an AC voltage target value at a time of controlling the inverter, and generates a command value for control of the inverter as a voltage source. When the inverter is introduced into the AC system, the inverter control circuit sets a frequency of the AC voltage target value to a frequency of an AC voltage detected by an AC frequency detection circuit, and controls a phase of the AC voltage target value to be at least a leading phase with respect to the AC voltage of the AC system when a target value of the AC power is in a running direction.