CHB Converter Harmonic Control via AC Injection
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Solution Overview
Problem
Conventional cascaded H-bridge (CHB) converters in battery energy storage systems suffer from inferior harmonic performance, leading to increased losses and reduced battery lifespan due to uncontrolled DC side current harmonics, which are exacerbated by the need for large decoupling capacitors and high AC current harmonics to eliminate even-order harmonics.
Innovation Solution
The solution involves injecting odd-order current harmonics at the AC side of the CHB converter to balance and reduce DC side current harmonics through a constrained optimization problem, optimizing switching transitions and meeting IEEE standard 519 requirements, thereby reducing DC link voltage ripples without using DC current sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If big decoupling DC capacitors are used at the DC sides of CHB converters to control even-order current harmonics, then the harmonic performance is improved, but the device complexity and size increase
Solution Approach 1:
The patent changes the control parameters by injecting odd-order current harmonics (3rd, 5th, 7th) at the AC side to actively control and balance the even-order harmonics at the DC side. This parameter-based control approach replaces the need for large passive decoupling capacitors, thereby improving harmonic performance without increasing device complexity
Solution Approach 2:
The patent introduces odd-order current harmonics as an intermediary mechanism. By injecting these specific harmonics at the AC side, the system indirectly controls the even-order harmonics at the DC side through the converter's inherent coupling, eliminating the need for direct intervention via large decoupling capacitors
2Manufacturing precision
If huge AC current harmonics are injected at the AC side to eliminate low-order current harmonics on the DC side, then the DC side current harmonics are controlled, but the conduction power loss and switching power loss increase significantly
Solution Approach 1:
The patent applies partial action by selectively injecting only the necessary odd-order harmonics (3rd, 5th, 7th) in specific proportions rather than using huge AC current harmonics. The cost function in the control algorithm determines the optimal injection levels, achieving sufficient harmonic control while minimizing excessive current injection that would cause power losses
Solution Approach 2:
The patent converts the typically harmful AC current harmonics into a beneficial control mechanism. By deliberately injecting controlled amounts of odd-order harmonics, the system achieves precise control over DC side current harmonics while avoiding the energy losses associated with traditional methods that required much larger harmonic currents
3Productivity
If conventional multilevel converters are used for power grid connections, then the basic power conversion function is achieved, but the harmonic performance is inferior and battery lifespan is reduced
Solution Approach 1:
The patent implements a feedback-based control algorithm that continuously monitors the current harmonics at both AC and DC sides. The cost function evaluates the harmonic spectrum and adjusts the odd-order harmonic injection levels in real-time, creating a closed-loop control system that optimizes battery performance and extends lifespan while maintaining reliable power conversion
Solution Approach 2:
The patent introduces dynamic control by making the harmonic injection levels adjustable and adaptive. The control algorithm dynamically determines the optimal amount of odd-order harmonics to inject based on real-time operating conditions, allowing the system to adapt to varying load conditions and optimize both power conversion efficiency and battery lifespan
Data Source
AI summary
Systems and methods are configured to control DC side current harmonics of a cascaded H-bridge (CHB) converter that includes a plurality of cells. In various embodiments, an odd-order current harmonic is injected at the AC side of the CHB converter based on an optimization of a constrained optimization problem to achieve at least one of balancing the DC side current harmonics of the plurality of cells, reducing the DC side current harmonics of the plurality of cells, and meeting the requirements of the IEEE 519 standard. The optimization problem may include a cost function based on switching transitions of the CHB converter and at least one constraint based on, for example, an AC side current harmonic, a maximum demand load current of the CHB converter base on the IEEE 519 standard, and a zero-order current harmonic and an hth-order current harmonic for each cell of the CHB converter.