Parallel Inverter Self-Synchronization via Phase Feedback
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Solution Overview
Problem
Existing parallel inverter systems face challenges in maintaining synchronized operation and frequency accuracy without a dedicated synchronization line or common circuit, leading to reliability issues and cross current problems when phase changes occur.
Innovation Solution
A parallel inverter system design that includes inverter units with sinusoidal signal generating, PWM control, phase difference detecting, and feedback circuits, allowing for self-synchronization and load distribution without a dedicated synchronization line, using phase and frequency difference feedback to maintain output frequency and voltage synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a dedicated synchronization line or common circuit is used to maintain frequency accuracy in parallel inverter operation, then frequency accuracy is improved, but device complexity and reliability are worsened due to additional failure points
Solution Approach 1:
Each inverter unit independently detects the phase difference between its own output voltage and a reference voltage, then automatically adjusts its output frequency based on the detected phase difference. This self-regulating mechanism eliminates the need for dedicated synchronization lines or common circuits, allowing each unit to maintain frequency accuracy autonomously while improving overall system reliability.
2Object-generated harmful factors
If phase is changed to control cross current in parallel inverter operation, then cross current is reduced, but frequency accuracy deteriorates due to varying effective power
Solution Approach 1:
The system continuously detects the phase difference between output voltage and reference voltage, then feeds this information back to adjust the output frequency. This closed-loop feedback control allows the system to dynamically change phase to control cross current while simultaneously maintaining frequency accuracy by compensating for frequency deviations caused by varying effective power.
3Reliability
If switching operation is implemented to handle common circuit failures in parallel inverter system, then reliability is improved, but operation complexity increases
Solution Approach 1:
The system divides the parallel inverter operation into independent units, each with its own phase difference detection and frequency adjustment capabilities. This segmentation allows each inverter unit to operate autonomously and handle failures independently through natural decoupling, eliminating the need for complex switching operations while maintaining reliability.
Data Source
AI summary
A parallel inverter system needs neither a dedicated line for synchronizing common portions nor switching operations, and includes a plurality of inverter units operating in parallel. An inverter control circuit of each inverter unit includes a sinusoidal signal generating circuit, a PWM control signal generating circuit, a phase difference circuit, a frequency difference circuit, and a feedback circuit. The feedback circuit inputs to the sinusoidal signal generating circuit an addition result value which is obtained by adding to a commanded value for reference frequency a value obtained from multiplication of a phase difference by a predetermined gain and a value obtained from multiplication of a frequency difference by a predetermined gain. The phase difference among outputs from the inverter units occurring in the parallel operation of the inverter units is reduced by changing the output frequencies of the inverter units.