Non-Isolated Bidirectional Converter Control for Leakage Current Mitigation
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Solution Overview
Problem
Existing power converters face challenges in achieving high efficiency, high power density, and low cost, while also dealing with issues such as leakage currents and common mode voltages that can damage motor components, particularly in bidirectional converters used in electric vehicles.
Innovation Solution
The implementation of non-isolated power converters with features like zero sequence voltage control, model predictive control (MPC), variable frequency critical soft switching (VFCSS), and modular converter blocks, along with LC filters and harmonic injection, to stabilize zero-sequence voltages and reduce switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a bulky line frequency transformer is installed to block leakage current, then leakage current is reduced, but cost, volume, and weight increase
Solution Approach 1:
The patent extracts and eliminates the bulky line frequency transformer from the system by implementing a non-isolated power converter topology. The transformerless architecture directly blocks the leakage current path through the power converter circuit design, removing the need for separate isolation transformers and significantly reducing system weight and volume.
Solution Approach 2:
The patent introduces an intermediary control mechanism - a control system with specific switching strategies - to manage the power conversion process without requiring a physical transformer. The control system mediates between the DC bus and AC grid, achieving leakage current reduction through intelligent switching rather than passive isolation components.
2Stability of the object's composition
If DC bus voltage is stepped up to twice the grid voltage amplitude to avoid saturation, then saturation is avoided, but switching losses increase and switch voltage tolerance challenges arise
Solution Approach 1:
The patent changes the voltage parameter relationship by operating the DC bus voltage at a level comparable to or only slightly higher than the grid voltage amplitude, rather than stepping it up to twice the amplitude. This parameter optimization reduces the voltage stress on switching devices and minimizes switching losses while maintaining stable operation through improved control strategies.
Solution Approach 2:
The patent implements dynamic control of the power converter operating points to adapt to varying grid conditions and load requirements. The control system dynamically adjusts switching frequencies and duty cycles to maintain optimal efficiency across different operating conditions, eliminating the need for excessive DC bus voltage margins.
3Weight of stationary object
If dual-purpose power converters are used for both charging and traction, then material costs and size are reduced, but design complexity increases
Solution Approach 1:
The patent implements a universal non-isolated bidirectional power converter that can operate in multiple modes - charging mode for battery charging and traction mode for motor drive. The same power converter hardware performs both functions by reversing power flow direction, eliminating the need for separate dedicated converters and reducing overall system size and material costs.
Solution Approach 2:
The patent segments the power converter into modular functional blocks with independent control loops for different operating modes. This modular architecture allows the single converter to be efficiently controlled for both charging and traction applications by activating appropriate control segments, managing design complexity through structured modularity.
4Loss of energy
If non-isolated power converters are implemented, then efficiency and power density are improved, but leakage current and common mode voltages increase
Solution Approach 1:
The patent converts the potential harm of leakage current in non-isolated converters into a beneficial control parameter. By implementing specific control strategies that manage common mode voltages and leakage current paths, the system maintains the efficiency advantages of non-isolated topology while actively controlling and minimizing harmful leakage effects through intelligent switching sequences.
Data Source
AI summary
Disclosed are implementations that include a power converter system and method including an N-phase power converter stage having to an alternating current (AC) side and a direct current (DC) side, with N≥1. The system and method further include an N-phase LC filter comprising one or more capacitors, wherein respective one or more neutral points of the one or more capacitors are electrically connected to a DC negative terminal of a DC source. A control system drives power switching elements of the N-phase power converter stage to convert received power and to output converted power. The control system drives the power switching elements using variable frequency soft switching at a frequency of at least 20 kHz. The power converter may have bidirectional operation to operate in a traction mode to drive a motor or a charging mode to charge a DC source.