Three-Phase Isolated Power Converter With Integrated Harmonic Injection
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Solution Overview
Problem
Existing three-phase galvanically isolated power supplies for applications like electric vehicle charging are bulky and expensive due to inefficiencies and the need for additional harmonic current injection circuits, leading to high total harmonic distortion and inefficient operation.
Innovation Solution
An electrical converter design with a first converter stage for three-phase AC to DC conversion, a second stage using stacked boost circuits for improved voltage control, and a third stage comprising galvanically isolated DC/DC converters that act as a current injection circuit, eliminating the need for additional harmonic injection circuits and optimizing component usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two series-in parallel-out coupled isolated DC/DC converters are used to handle high input voltage (700-800V) to low output voltage (250-450V) conversion, then voltage conversion capability is improved, but device complexity and volume increase
Solution Approach 1:
The power conversion process is divided into three distinct stages: first converter stage for three-phase AC to intermediate DC conversion, second converter stage with stacked boost circuits for voltage regulation, and third converter stage with galvanically isolated DC/DC converters for final voltage conversion. This segmentation allows each stage to be optimized independently, reducing overall system complexity while maintaining high voltage conversion capability.
Solution Approach 2:
The third converter stage with galvanically isolated DC/DC converters performs multiple functions simultaneously: it provides galvanic isolation, acts as a current injection circuit for harmonic compensation, and delivers the final voltage conversion. This multi-functionality eliminates the need for separate harmonic injection circuits and energy storage elements, reducing device complexity while improving power quality.
2Reliability
If traditional rectifier units with passive bridge rectifiers and boost circuits are used, then PFC operation is achieved, but total harmonic distortion increases and power factor decreases
Solution Approach 1:
The control unit monitors the AC input currents and adjusts the switching of active switches in the first and third converter stages to inject third-harmonic currents that cancel out distortion harmonics. This feedback mechanism dynamically compensates for harmonic distortion, reducing THD and improving power factor while maintaining reliable PFC operation.
Solution Approach 2:
The third converter stage with galvanically isolated DC/DC converters serves itself to perform harmonic compensation by acting as an active current injection circuit. The converter uses its own switching capability to generate compensating currents, eliminating the need for separate passive harmonic filtering components and achieving both voltage conversion and harmonic mitigation functions.
3Device complexity
If isolated DC/DC converters are used in Swiss-type rectifier configuration, then secondary isolated stage is eliminated, but input voltage goes to zero at AC phase crossings causing poor controllability
Solution Approach 1:
The first converter stage with active switches and the second converter stage with stacked boost circuits prepare the voltage conditions before the third converter stage operates. The stacked boost circuits maintain elevated voltage levels during AC phase crossings, ensuring that the isolated DC/DC converters always operate with sufficient input voltage headroom for reliable control, preventing the voltage from dropping to zero.
4Adaptability or versatility
If over-dimensioning of isolated DC/DC converters is performed to handle wide input voltage range, then adaptability is improved, but device volume and cost increase
Solution Approach 1:
Each converter stage is designed with specific local characteristics optimized for its operating conditions. The first converter stage handles three-phase AC input with active switching, the second stage with stacked boost circuits handles intermediate voltage regulation, and the third stage with isolated DC/DC converters handles final voltage conversion. This localized optimization allows each stage to be sized appropriately for its specific function rather than over-dimensioning the entire system for the widest possible voltage 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 solution results in more compact, economical power supplies with improved controllability and reduced total harmonic distortion, achieving sinusoidal mains currents with unity power factor without additional harmonic injection circuits and dispensing with electrical energy storage elements.
Implementation Method 1
a three-phase rectifier with power factor correction (PFC) unit
Implementation Method 2
The first converter stage comprises conversion circuitry configured for converting between the three phase voltages
Implementation Method 3
The second converter stage is configured for converting between a second signal at a fourth intermediate node and a fifth intermediate node and a third signal at a sixth intermediate node and a seventh intermediate node. The second converter stage comprises or consists of a boost circuit, comprised of a first boost circuit and a second boost circuit series stacked between the sixth and seventh intermediate node.
Implementation Method 4
The third converter stage comprises or consists of a galvanically isolated DC/DC converter stage comprising a first side and a second side galvanically isolated from each other
Data Source
Figure 1
Figure 2~5
Figure 6~7
AI summary
Electrical converter (100) for converting between an AC signal comprising three phase voltages and a galvanically isolated DC signal, comprising three phase terminals (A, B, C) and two DC terminals (P, N), a first converter stage (11) for converting between the three phase voltages provided at the three phase terminals and a first signal at a first intermediate node (T) and a second intermediate node (B), and comprising a phase selector (25) comprising first active switches (S s,a , S s,b , S s,c ) configured to selectively connect the three phase terminals (A, B, C) to a third intermediate node (I), a second converter stage (12) configured for converting between a second signal at a fourth intermediate node (r) and a fifth intermediate node (t) and a third signal at a sixth intermediate node (P') and a seventh intermediate node (N'), a link connecting the first intermediate node (T) to the fourth intermediate node, and the second intermediate node (B) to the fifth intermediate node, and a galvanically isolated DC/DC converter stage (141, 142, 140) comprising a first side connected to the sixth intermediate node (P'), a first common node (t) and the seventh intermediate node (N'), wherein the DC terminals (P, N) are connected a second side of the DC/DC converter stage galvanically isolated from the first side. The first common node (t) is operably connected to the third intermediate node (I). The DC/DC converter stage is configured to be operated such that a difference of a first current (i P ,) applied to the DC/DC converter (141) at the sixth intermediate node (P') and a second current (i N ,) applied to the DC/DC converter at the seventh intermediate node (N') is provided at the third intermediate node (I).