Starter-Alternator Pre-Magnetization for Current Peak Suppression
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Solution Overview
Problem
The frequency limitation of inverter switching in polyphase synchronous rotating electrical machines with a large number of poles per phase leads to difficulties in maintaining precise control, resulting in significant current peaks during transitions between passive and full-wave operational modes.
Innovation Solution
A method that includes a pre-magnetization step to create a peak electromotive force equal to the nominal voltage by determining a reference value of the rotor excitation current based on the electrical pulse, followed by charging 'bootstrap' capacitors to control the phase currents, allowing a smooth transition to full-wave control mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If inverter switching frequency is increased to maintain precise control at high rotation speeds, then control precision is improved, but switching frequency limitations are exceeded causing current peaks
Solution Approach 1:
The patent applies preliminary action by pre-magnetizing the stator core before transitioning to full-wave control mode. The excitation current is gradually increased from zero to a reference value based on the electrical pulse, creating a pre-established magnetic flux that prevents sudden current peaks during mode transition. This preparatory magnetization ensures smooth transition while maintaining control precision at high rotation speeds.
2Speed
If full-wave control mode is activated without pre-magnetization, then operational responsiveness is improved, but significant current peaks occur during transition
Solution Approach 1:
The patent implements preliminary action by executing a pre-magnetization routine before activating full-wave control. The excitation current is gradually built up to a reference value determined by the electrical pulse, establishing the necessary magnetic flux in advance. This eliminates sudden current peaks during transition while maintaining fast operational responsiveness.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the excitation current from zero to a reference value based on the electrical pulse frequency. The reference value is calculated as a function of the electrical pulse, allowing the system to adapt the magnetization level to the current operating conditions. This gradual parameter change prevents harmful current peaks while enabling fast mode transition.
3Measurement precision
If PWM control is used for precise control, then control precision is improved, but switching frequency limitations prevent effective implementation at high speeds
Solution Approach 1:
The patent applies preliminary action by pre-establishing the magnetic flux through gradual excitation current increase before switching to full-wave control mode. This pre-magnetization allows the system to transition from PWM to full-wave control without losing control precision, effectively bypassing the switching frequency limitation at high rotation speeds.
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 current peaks during transitions, minimizing the need for oversized semiconductor switching elements and lowering costs, as demonstrated by reducing stator current from 300 Aeff to 50 Aeff during a transition to full wave at 4750 rpm.
Implementation Method 1
A pre-magnetization step comprises a determination of a reference value of the rotor excitation current as a function of an electrical pulse of the machine so as to create a peak electromotive force between phases substantially equal to the nominal voltage
Implementation Method 2
phase currents being controlled by an inverter comprising, in a particular embodiment, arms formed, on the one hand, by first power switches controlled by control circuits supplied by switching tripping capacities called 'bootstrap' capacities
Data Source
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AI summary
The method according to the invention is of the type comprising a control step for a motor operation of the machine (12) in which phase currents are controlled in full wave mode in phase windings (u, v, w) of a stator (10) of the machine that is connected to an on-board electrical network (2, 15) powered by a battery (2) at a predetermined rated voltage (Ubat). According to the invention, the control step is preceded by a step of open-circuit premagnetization of the stator, in which a peak electromotive force between phases that is substantially equal to the rated voltage is produced by a rotor excitation current (Ir) of a rotor (8) of the machine.