Parallel Inverter Voltage Synchronization via Delay Compensation

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Solution Overview

Problem

Existing parallel inverter devices experience voltage command value delays, leading to cross-current and potential damage to semiconductor switching elements due to differences in output voltages between inverters connected in parallel, which also result in increased capacity and cost of power converters and larger device sizes.

Innovation Solution

A parallel inverter device configuration where one inverter acts as a master, computing and transmitting a delayed voltage command value to slave inverters, ensuring synchronized voltage command values across all inverters, with delay devices adjusting for transmission time differences to prevent cross-current and reduce the need for additional reactors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If voltage command values are transmitted without delay adjustment to slave inverters, then transmission speed is fast, but voltage synchronization error occurs causing cross-current between parallel inverters

Engineering Contradiction:

Improvevoltage synchronization accuracyVSAvoidcontrol signal transmission delay

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The master inverter calculates and transmits the transmission time required for voltage command values to reach slave inverters in advance. Each inverter then applies this predetermined delay time to its voltage command value before output, ensuring that all inverters synchronize their voltage commands simultaneously without requiring real-time adjustment during operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A delay device acts as an intermediary between the voltage command value calculation and the power converter output. This delay device introduces a controlled time delay to the voltage command value, matching the transmission time to slave inverters, thereby synchronizing the voltage commands across all parallel inverters and preventing cross-current.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If cross-current suppression reactors are added to prevent cross-current, then reliability improves, but device complexity and size increase

Engineering Contradiction:

Improveprotection against cross-current damageVSAvoidnumber of additional components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of adding reactors to suppress cross-current, the invention converts the potential harmful effect of transmission delays into a useful control mechanism. By intentionally introducing a delay equal to the transmission time, the system proactively prevents cross-current generation at its source, eliminating the need for passive suppression reactors and their associated complexity and size.

Inventive Principle:

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

Solution Approach 2:

The invention extracts and eliminates the need for cross-current suppression reactors from the system. By addressing the root cause of cross-current (voltage synchronization error due to transmission delay) through delay adjustment, the harmful component (reactors) becomes unnecessary and is removed from the device configuration, reducing complexity and size.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If power converter capacity is increased to provide cross-current margin, then reliability improves, but cost and device size increase

Engineering Contradiction:

Improvecurrent capacity margin for cross-currentVSAvoidpower converter capacity

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The system performs preliminary delay adjustment on voltage command values to prevent cross-current generation before it occurs. By synchronizing voltage commands across all inverters in advance through delay compensation, the need for excess current capacity margin is eliminated, allowing power converters to be sized more efficiently without requiring additional capacity for cross-current suppression.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9236814B2Parallel inverter device and method for control thereof

Publication Date: 2016.01.12 FUJI ELECTRIC CO LTD

AI summary

Inverters connected in parallel each include a power converter that carries out a direct current to alternating current conversion and supplies voltage to a motor, and a control unit, where one of the inverters is a master inverter and the control unit computes a voltage command value for the power converter in the one inverter, while the other inverter is a slave inverter and the power converter in the slave inverter is driven by the voltage command value, a transmission means transmits the voltage command value, and the control unit of the master inverter includes a delay device that delays the voltage command value by a transmission time needed when transmitting a computed voltage command value to the slave inverter, and provides the voltage command value delayed by the delay device to the power converter of the master inverter.