Inverter Parallel Unit Current Balancing via Zero Crossing Blocking
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Solution Overview
Problem
Existing inverters with parallel AC power units face issues of circulating currents and imbalances due to differences in impedance and switching behavior, leading to thermal losses, overloading, and idle power intake, which require complex control systems and additional components to mitigate.
Innovation Solution
Synchronous control of semiconductor switches in parallel AC power units during individual zero crossings of the output alternating current, allowing inductivities to discharge via freewheeling diodes, thereby balancing sub-output currents and reducing circulating currents without the need for additional control or components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If parallel AC power units are operated with common direct voltage input, then the output alternating current can be supplied, but circulating currents occur due to impedance differences and switching behavior variations causing current distribution imbalances
Solution Approach 1:
The semiconductor switches are blocked during individual zero crossings of the output alternating current periodically, allowing the inductivities to discharge via freewheeling diodes. This periodic blocking action resets the current distribution balances without requiring continuous complex control
Solution Approach 2:
The system uses its own zero crossing moments to automatically discharge the inductivities through freewheeling diodes, eliminating the need for external balancing components or additional control systems. The inverter self-corrects its current distribution imbalances using inherent operational characteristics
2Object-generated harmful factors
If additional control systems are implemented to balance current distribution, then circulating currents can be reduced, but device complexity increases
Solution Approach 1:
The inverter uses its own operational characteristics (zero crossings) to automatically balance current distribution without external intervention. The system self-corrects imbalances using existing components and operational moments, eliminating the need for additional balancing control systems
Solution Approach 2:
The harmful circulating currents are eliminated by removing the need for complex balancing control systems entirely. The solution extracts the essential function (current balancing) and achieves it through simple periodic blocking rather than complex continuous control
3Object-generated harmful factors
If semiconductor switches are blocked during zero crossings, then sub-output currents are balanced and circulating currents reduced, but thermal losses occur during blocking period
Solution Approach 1:
The blocking period, which could be seen as causing thermal losses, is converted into a beneficial discharge phase where inductivities release stored energy through freewheeling diodes. The energy that would otherwise contribute to circulating currents is safely dissipated, and the brief blocking duration minimizes thermal impact while achieving current balance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively balances current distribution among parallel AC power units, reducing circulating currents and thermal losses, allowing for a simpler and cost-efficient system operation without additional control complexity or components, while maintaining a high-quality alternating voltage output.
Implementation Method 1
the inductivities are discharged via the freewheeling diodes of the semiconductor switches
Data Source
AI summary
The invention relates to a method for operating an inverter (1) and to an inverter (1) for converting a direct voltage (UDC) into an alternating voltage (UAC) with a specified grid frequency (fAC) for supplying loads (12) and/or feeding into a supply grid (13), comprising a direct voltage input (2) and multiple AC power units (6) which are connected in parallel and comprise semiconductor switches (7) in a bridge circuit and freewheeling diodes (8) arranged parallel thereto. The outputs of the AC power units (6) are connected to an alternating voltage output (10) via a respective inductivity (9). A common controller (11) is provided for synchronously controlling the semiconductor switches (7) of the AC power units (6) connected in parallel with a switching frequency (fS) in order to prevent imbalances between the parallel AC power units (6), said controller (11) being designed to block the semiconductor switches (7) of the AC power units (6) during individual zero crossings of the output alternating current (IAC) over a specified duration (tF) such that the inductivities (9) can be discharged via the freewheeling diodes (8) of the semiconductor switches (7) and the sub-output currents (IAi) of the parallel AC power units (6) can thus be balanced.