Multi-Phase Machine Block Commutation Angle Control
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Solution Overview
Problem
Block-commutated multi-phase machines experience high starting currents, particularly at low speeds, leading to thermal overload, oversized output stages, and unwanted voltage dips in the vehicle electrical system, with no effective method to reduce these currents through clocking due to the absence of sufficient intermediate circuit capacitance.
Innovation Solution
A method for current control in multi-phase machines with block commutation, involving a stepped adjustment of the block commutation angle using a control scheme that allows for the omission of intermediate circuit capacitors, particularly in five-phase systems, to limit starting currents and optimize output stage design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If block commutation is used to operate the multi-phase machine, then intermediate circuit capacitance is minimized, but starting current becomes excessively high
Solution Approach 1:
The block commutation angle is dynamically adjusted based on operating conditions. At low speeds, a smaller block commutation angle is used to limit starting current, while at higher speeds, the angle is increased to maximize power output. This dynamic adjustment resolves the contradiction by adapting the commutation strategy to the specific operating point.
Solution Approach 2:
The invention changes the block commutation angle parameter to control starting current. By reducing the block commutation angle during start-up, the current waveform is modified to reduce peak currents while maintaining acceptable power transfer. This parameter change allows operation without large intermediate circuit capacitance while limiting starting current.
2Device complexity
If high starting currents are allowed to simplify output stage design, then device complexity is reduced, but thermal load and voltage dips increase
Solution Approach 1:
The control system preliminarily adjusts the block commutation angle during the start-up phase to prevent excessive currents before they occur. By proactively limiting current during start-up, the output stages are protected from thermal overload and voltage dips without requiring oversizing, thus maintaining simple design while eliminating harmful effects.
3Power
If PWM commutation is used to limit starting current, then starting current is reduced, but intermediate circuit capacitance requirements increase
Solution Approach 1:
The system dynamically switches between block commutation and PWM commutation based on operating speed. At low speeds, block commutation with reduced angle limits current without requiring large capacitance. At higher speeds, PWM commutation is used for optimal performance. This dynamic switching resolves the contradiction by using the appropriate commutation method for each operating condition.
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 starting currents, enabling more favorable output stage dimensioning, increasing efficiency, and reducing thermal and voltage-related issues, while allowing for automatic current limitation at higher speeds and protecting against overvoltages.
Implementation Method 1
During run-up of a block-commutated, belt-driven starter generator or another electrical machine, there are high starting currents, which decrease as the speed increases due to the increasing mutual induction.
Data Source
Figure 1
Figure 2
Figure 3a~3d
AI summary
The method involves controlling switches (S1-S10) e.g. power MOSFETs, by a drive schema to control current of a multiphase machine, for stepped adjustment of a block commutation angle, where the phase number of the multiphase machine is larger than 3. The drive schema having a series connection of phase windings (1-5) e.g. stator windings, is used as a function of an operating point. Rotation speed of a rotor of the machine is determined, and the current control is performed depending upon the rotational speed that is less than a predetermined threshold.