Two-Half-Bridge Frequency Converter With Neutral-Point Output
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Solution Overview
Problem
Current frequency converters for induction machines and transformers with variable frequency and amplitude supply require expensive and energy-loss-prone controllable semiconductor switches, leading to increased costs and inefficiencies.
Innovation Solution
A frequency converter topology with only two half-bridges in the machine power converter and a corresponding number of half-bridges in the mains power converter, integrated into a single power electronic component, reducing the number of semiconductor switches and heat losses while enabling efficient power factor control and reactive power compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional frequency converter with three half-bridges in the machine converter is used, then the machine can be supplied with three-phase voltage, but the number of semiconductor switches increases leading to higher costs and energy losses
Solution Approach 1:
The patent extracts the neutral point connection from the conventional three-half-bridge machine converter topology. By connecting the neutral point of the machine converter directly to the neutral point of the supply network, the patent eliminates the need for one half-bridge (and its two semiconductor switches) while still providing three-phase voltage to the machine. This reduces the number of semiconductor switches from six to four, lowering costs and energy losses.
Solution Approach 2:
The patent makes the line converter half-bridges serve dual functions: they not only perform power factor correction and reactive power compensation but also directly provide two phases of the three-phase supply to the machine converter. This multi-functionality allows the system to operate effectively with fewer switches in the machine converter, as the line converter half-bridges compensate for the reduced switching capacity.
2Power
If more semiconductor switches are used in the frequency converter, then better power control is achieved, but heat losses and operational costs increase
Solution Approach 1:
By removing one half-bridge from the machine converter and directly connecting the neutral points, the patent reduces the number of semiconductor switches from six to four. This extraction eliminates the switching operations and associated heat losses in the removed switches while maintaining sufficient power control capability through the remaining switches and the supportive role of the line converter half-bridges.
Solution Approach 2:
The line converter half-bridges perform additional functions to compensate for the reduced machine converter capacity. They provide reactive power compensation and assist in power factor correction, effectively serving the system's power control needs with fewer switches in the machine converter, thereby reducing overall heat losses.
3Device complexity
If a simplified converter topology with fewer half-bridges is used, then costs and heat losses are reduced, but the ability to provide three-phase supply may be compromised
Solution Approach 1:
The patent extracts the neutral point connection functionality from the machine converter and establishes a direct connection to the supply network neutral point. This allows the machine converter to operate with only two half-bridges (four switches) while still providing three-phase voltage to the machine, as the third phase is derived from the neutral point connection.
Solution Approach 2:
The line converter half-bridges are designed to perform multiple functions: power factor correction, reactive power compensation, and direct provision of two phases to the machine. This multi-functionality compensates for the reduced machine converter topology, ensuring full three-phase supply capability is maintained despite the simplified machine converter structure.
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 configuration reduces circuit complexity and costs, minimizes heat losses, and allows for efficient operation with reduced semiconductor switches, enabling effective power conversion and reactive power compensation, thus optimizing energy efficiency and operational costs.
Implementation Method 1
In a DC link 5 connected to the grid converter 4, with capacitors C dc acting as energy storage, the generated DC voltage is stabilized. This compensates for fluctuations in the power fed into the DC link 5 from the grid converter 4 via the supply network 1, or for fluctuations in the power drawn from the DC link 5 by a load.
Data Source
Figure 1
Figure 2
Figure 2a
AI summary
The invention relates to a frequency converter (2) for supplying a rotating field machine (3) or a transformer, comprising a line converter (4) with first semiconductor switches (T1, T2) for converting an alternating voltage into a direct voltage, a machine converter (6) with controllable second semiconductor switches (T3... T6) for converting the direct voltage into a supply voltage, and a DC link (5) carrying the direct voltage with an upper and a lower DC link branch (9a, 9b) connected to each other at a common center point (16). The machine converter (6) consists of only two half-bridges (10, 12) containing the second semiconductor switches (T3... T6) to provide a first phase at a first output terminal (14a) and a second phase at a second output terminal (14b). The center point (16) is provided at a third output terminal (14c).The grid converter (4) consists of a number of half-bridges (7) containing the first semiconductor switches (T1, T2). The aforementioned semiconductor switches (T1 ... T6) are integrated into a single power electronic component (15).