Virtual Neutral Bridge Inverter for Low-Voltage Brushless Motors
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Solution Overview
Problem
Aircraft brushless DC synchronous motors face reduced performance due to low supply voltage, which limits current flow through multi-filar windings, especially in wye connected motors with buried neutral points, making it difficult to detect open circuits and maintain balanced current flow.
Innovation Solution
A virtual neutral bridge inverter circuit is introduced, allowing individual control of phase neutral ends and implementing a dual-space vector modulation scheme to apply full DC link voltage across each phase, enhancing current flow and torque output without increasing input voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If multi-filar windings are used in wye connected motors with buried neutral, then the motor can operate at low supply voltage, but open circuits in strands become difficult to detect and current flow becomes unbalanced
Solution Approach 1:
The patent extracts the neutral point from its traditional buried position within the motor windings and relocates it to an external position within the inverter circuit. This allows the neutral point to be accessible for measurement and control, enabling detection of open circuits in multi-filar windings while maintaining low voltage operation capability.
Solution Approach 2:
The patent introduces a virtual neutral bridge inverter circuit as an intermediary between the motor windings and the power source. This intermediary provides a controlled path for current flow through the neutral point, enabling both low voltage operation and reliable fault detection through its measurement capabilities.
2Device complexity
If traditional bridge inverter circuit is used, then the motor structure is simple, but full DC link voltage cannot be applied across each phase simultaneously, limiting current and torque output
Solution Approach 1:
The patent segments the traditional bridge inverter circuit into two independent sets of switches: one set for controlling the three-phase output and another set for controlling the neutral point connections. This segmentation allows independent control of phase voltages and neutral point potentials, enabling full DC link voltage application across each phase simultaneously while maintaining a manageable circuit structure.
Solution Approach 2:
The patent adds a new control dimension by introducing independent neutral point switching capability alongside the traditional phase control. This additional degree of freedom in the control space enables the system to apply full DC link voltage across each phase simultaneously, doubling the potential current and torque output compared to traditional single-dimension phase control.
3Productivity
If supply voltage is increased to overcome winding resistance and drive more current, then motor performance improves, but the aircraft electrical system voltage is limited and cannot be increased
Solution Approach 1:
The patent changes the voltage application parameters by using the virtual neutral bridge to apply full DC link voltage across each phase simultaneously during specific time intervals, rather than the traditional method where phases share the voltage. This parameter change enables higher current flow and improved motor performance within the existing voltage constraints of the aircraft electrical system.
Solution Approach 2:
The patent employs periodic switching action through the dual-space vector modulation scheme, where the virtual neutral bridge switches between different voltage application states in controlled time intervals. This periodic action allows the motor to receive full DC link voltage pulses that drive higher current through the windings, overcoming resistance limitations without requiring a continuous increase in supply voltage.
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 doubles the electrical current and torque output, improves phase resistance imbalance detection, and ensures balanced current flow, reducing losses and enhancing operating efficiency even at low supply voltages.
Implementation Method 1
a direct current (DC) synchronous motor operable to drive electro-mechanical actuators... a virtual neutral bridge inverter circuit... configured to control the on/off switching times of the first, second, and third input lead switch pairs and the first, second, and third neutral switch pairs
Data Source
AI summary
A motor drive system includes a three-phase motor and a virtual neutral bridge inverter circuit. The three-phase motor includes a first phase lead, a second phase lead, and a third phase lead. Each of the first phase neutral end, the second phase neutral end, and the third phase neutral end of the phase leads are separated from one another. The virtual neutral bridge inverter circuit includes a first neutral switch pair connected at a first neutral connection node, a second neutral switch pair connected at a second neutral connection node, and a third neutral switch pair connected at a third neutral connection node. The first phase neutral end is connected to the first neutral connection node, the second phase neutral end is connected to the second neutral connection node, and the third phase neutral end is connected to the third neutral connection node.