Parallel Inverter Control for Circulating Current Mitigation
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Solution Overview
Problem
High power inverter systems face issues with high total harmonic distortion (THD), high input current ripple, and reduced mean time between failures (MTBF) due to circulating currents and inability to operate independently, which degrades system reliability and increases maintenance costs.
Innovation Solution
A high power control system that manages a single energy source with multiple inverters connected in parallel, using PWM and regulation control signals to prevent circulating currents and optimize inverter operation, allowing for independent control and reduced THD and ripple current under varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple inverters are operated in parallel to improve system reliability and reduce maintenance costs, then MTBF is improved and maintenance becomes easier, but circulating currents are generated among inverters and independent control is lost
Solution Approach 1:
The controller applies PWM control signals to inverters in a predetermined sequence before enabling their output switches. When adding an inverter, the PWM signal is applied first to establish proper synchronization, then the output switch is enabled. When stopping an inverter, the output switch is disabled first, then the PWM signal is removed. This preliminary sequencing prevents circulating currents by ensuring proper phase alignment and control state transitions before power flow begins or changes.
2Reliability
If multiple inverters are operated in parallel to improve system reliability, then MTBF is improved, but the inverters cannot be independently controlled and circular activation is prevented
Solution Approach 1:
The system implements dynamic control where each inverter can be independently activated or deactivated by the controller based on system conditions. The controller dynamically adjusts PWM control signals to each inverter individually, allowing flexible operational configurations. This dynamic control enables circular activation patterns where inverters can be sequentially brought online or taken offline, providing operational independence while maintaining parallel operation benefits for improved MTBF.
3Productivity
If parallel inverters are operated simultaneously to improve system capacity, then power supply continuity is improved, but THD requirements are not met under low-load conditions and input current ripple increases
Solution Approach 1:
The controller selectively activates only the necessary number of inverters based on current load conditions rather than operating all inverters simultaneously. Under low-load conditions, fewer inverters are activated to maintain THD performance, while under high-load conditions, more inverters are activated to meet power demands. This partial action approach ensures that system capacity is optimized without compromising THD requirements, as each active inverter operates within its optimal performance range.
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
The system effectively removes circulating currents, reduces THD and ripple current, and enhances MTBF by allowing for efficient operation of multiple inverters under different load conditions, improving system reliability and reducing maintenance costs.
Implementation Method 1
a controller configured to output a PWM control signal under control of the energy source management unit; a plurality of inverters configured to convert a direct current into an alternating current under control of the PWM control signal
Data Source
AI summary
A high power control system includes: a single energy source; an energy source management unit configured to manage the energy source; a controller configured to output a PWM control signal under control of the energy source management unit; a plurality of inverters configured to convert a direct current into an alternating current under control of the PWM control signal of the controller; a plurality of filters coupled to output terminals of the inverters; and a plurality of switches configured to regulate connections between the filters and a load under control of a regulation control signal of the controller.