Inverter Switching Angles to Cut Reactive Power in Half-Bridges
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Solution Overview
Problem
In power converters operating as inverters, high reactive power levels and current rise rates occur due to the freewheeling path through antiparallel diodes, leading to additional losses and reduced efficiency, especially during partial-load operations.
Innovation Solution
The method involves dynamically adjusting the activation angular intervals of semiconductor switches based on pre-ignition and pre-quenching angles, which are determined by electrical power levels and current flow, to minimize reactive power and current rise rates, and adapting switch-on times to interlinked voltages in multiphase networks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If semiconductor switches are triggered in dependence upon the phase position of AC voltage phases to feed back electrical energy into the AC voltage network, then energy recovery operation is enabled, but a high level of reactive power arises which reduces partial-load efficiency
Solution Approach 1:
The patent applies preliminary action by determining pre-ignition angles and pre-quenching angles for each semiconductor switch before the actual switching operation. These angles are calculated in advance based on the electrical power level and current flow, allowing the control system to optimize the activation angular intervals proactively rather than reactively, thereby reducing reactive power generation before it occurs
Solution Approach 2:
The patent implements dynamics by making the activation angular intervals of semiconductor switches dynamically adjustable based on operating conditions. The control system continuously adapts the switch-on times and angular intervals according to the electrical power level, current flow, and interlinked voltages, transforming a static switching scheme into a dynamic one that optimizes performance across varying load conditions
2Ease of operation
If semiconductor switches are hard switched off to commutate current to freewheeling diodes, then current commutation is achieved, but high current rise rates occur which excite network filters and resonances
Solution Approach 1:
The patent applies preliminary action by determining pre-quenching angles for each semiconductor switch before the actual switch-off operation. This advance preparation allows the control system to smoothly transition current to freewheeling diodes by optimizing the timing and duration of switch-off intervals, preventing abrupt current commutation that would generate high rise rates and excite network resonances
3Power
If activation angular intervals are extended to increase power transfer, then electrical power level increases, but reactive power level and current rise rates increase
Solution Approach 1:
The patent implements dynamics by making the activation angular intervals dynamically adjustable based on operating conditions. The control system continuously adapts the switch-on times and angular intervals according to the electrical power level, current flow, and interlinked voltages, transforming a static switching scheme into a dynamic one that optimizes performance across varying load conditions
Solution Approach 2:
The patent applies parameter changes by systematically varying the activation angular intervals and switching angles as control parameters. By adjusting these angular parameters based on the electrical power level and operating conditions, the system optimizes the balance between active power transfer and reactive power generation, enabling efficient operation across different power levels
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 approach reduces reactive power levels and current rise rates, enhancing the efficiency of power converters by optimizing the operation of semiconductor switches and diodes, thereby minimizing losses and improving partial-load efficiency.
Implementation Method 1
the semiconductor switches are not triggered. A load-side power converter of the frequency converter then generates the AC voltage for the electric motor
Implementation Method 2
the power converter has at least one half-bridge which is connected to the AC voltage phase and has a high potential-side semiconductor switch and a low potential-side semiconductor switch
Data Source
AI summary
A method for operating a power converter as an inverter between a DC voltage and an AC voltage grid is disclosed. For each AC voltage phase of the AC voltage grid, the power converter has at least one half-bridge which is connected to the AC voltage phase and has two semiconductor switches. Each semiconductor switch is reversed-connected in parallel with a diode. An activation angle range is determined for each semiconductor switch within an angle period, the lower range limit of which activation angle range is formed by subtracting a pre-firing angle from the lower range limit of a switch angle range, and the upper range limit of which activation angle range is formed by subtracting a pre-extinction angle from the upper range limit of the switch angle range.