Segmented Linear Motor Inverters With Mid-Point Voltage Balancing
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Solution Overview
Problem
Long stator linear electric motors face inefficiencies due to high impedance, requiring high voltage power converters, leading to increased manufacturing costs and low efficiency, especially when the mobile motor element is shorter than the stator, resulting in suboptimal power delivery and voltage balancing issues under high reactive loads.
Innovation Solution
The motor is segmented with pairs of multi-level inverters connected via a mid-point bridge, allowing adjacent stator segments to be driven by different inverters, reducing voltage oscillations and improving efficiency by interleaving odd and even numbered segments with switches, and using additional inverters as external balancers to compensate for voltage imbalances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a long stator is used to increase the performance of the drive system, then the power and thrust are improved, but the impedance increases leading to higher manufacturing costs and lower efficiency
Solution Approach 1:
The long stator is divided into multiple segments, each driven by its own inverter. This segmentation allows each segment to operate independently with optimized current control, reducing the overall impedance impact while maintaining high power output. The modular approach also reduces manufacturing complexity and cost compared to a single long stator driven by one high-voltage converter.
2Power
If a long stator is used to increase the performance of the drive system, then the power and thrust are improved, but the efficiency decreases due to high reactive power requirements
Solution Approach 1:
Dividing the long stator into segments allows each segment to be controlled by a dedicated inverter, optimizing the current waveform and reducing reactive power requirements. This improves overall system efficiency by minimizing energy losses in each segment while maintaining high power output.
Solution Approach 2:
The invention changes the electrical parameters by using multi-level inverters that can generate stepped voltage waveforms. This parameter change reduces harmonic content and reactive power requirements, improving efficiency while maintaining high power output in long stator applications.
3Ease of manufacture
If the number of inverters is reduced to lower system cost, then the manufacturing cost decreases, but the power delivery continuity is compromised during vehicle movement between segments
Solution Approach 1:
The stator is segmented into multiple sections, each with its own inverter. This allows the vehicle to be continuously powered as it moves from one segment to another, with overlapping active segments ensuring no gap in power delivery. The segmentation enables cost-effective design with fewer inverters than a fully redundant system while maintaining reliability.
Solution Approach 2:
The invention ensures continuous power delivery by maintaining overlapping active segments during vehicle transition. As the vehicle moves from one segment to another, both segments remain active briefly, ensuring uninterrupted thrust and power delivery while using a minimal number of inverters.
4Loss of energy
If multi-level inverters are used to improve efficiency and reduce harmonics, then the system efficiency increases, but the voltage balancing becomes more challenging under high reactive loads
Solution Approach 1:
Dividing the system into segmented inverters allows independent voltage balancing control for each segment. This reduces the overall complexity by localizing the balancing problem to smaller, manageable units rather than attempting to balance a single large inverter under high reactive loads.
Solution Approach 2:
The invention introduces a neutral point clamp structure as an intermediary element in the multi-level inverter circuit. This neutral point serves as a reference for voltage balancing, simplifying the control complexity while maintaining the efficiency benefits of multi-level operation under high reactive loads.
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 enhances power delivery efficiency, reduces manufacturing costs, and improves reliability by minimizing voltage variations and power losses, making the system more cost-effective and efficient for long stator applications like train and tram drives.
Implementation Method 1
each drive unit comprising a DC input circuit section and a multi-level inverter connected to the DC voltage source via the DC input circuit section, the multi-level inverter comprising a multiphase output connected to a drive circuit connection end (12) of coils of the corresponding stator segment
Implementation Method 2
The DC input circuit section of each drive unit comprises at least two link capacitors connected in series between a positive and a negative voltage supply line (V+, V-) and having a mid-point therebetween
Implementation Method 3
The mid-point of the first multi-level inverter is connected via a bridge connection to the mid-point of the second multi-level inverter such that the mid-points of the first and second multilevel inverters are at a common electric potential
Implementation Method 4
a linear electrical motor comprising a stator (3) comprising a plurality of stator segments (3a, 3b) and a drive system comprising at least one pair of drive units (4a, 4b), a first drive unit (4a) of said pair connected to a first stator segment (3a) and a second drive unit (4b) of said pair connected to a second stator segment (3b) adjacent the first stator segment (3a)
Data Source
Figure 1
Figure 2
Figure 3~3B
AI summary
Linear electric motor (1) comprising a stator (3) comprising a plurality of stator segments (3a, 3b, ...3n) and a drive system comprising at least one pair of drive units (4), a first drive unit (4a) of said pair connected to a first stator segment (3a) and a second drive unit (4b) of said pair connected to a second stator segment (3b) adjacent the first stator segment, the drive units (4a, 4b) connected to a DC voltage source (6), each drive unit comprising a DC input circuit section (14) and a multi-level inverter (7) connected to the DC voltage source via the DC input section, the multi-level inverter comprising a multiphase output (10) connected to coils (5) of the corresponding stator segment. The DC circuit section of the drive units comprises at least two link capacitors (C1, C2) connected between a positive and a negative voltage supply line (V+, V-) and having a mid-point (8) therebetween. The mid-point of the first multi-level inverter (7a) is connected via a bridge connection (9) to a mid-point of the second multi-level inverter (7b) such that the mid-points of the first and second multi-level inverters are at a common electric potential. The drive circuit connection end (12) of the first multi-level inverter is arranged adjacent the drive circuit connection end of the second multi-level inverter (7b), or a star connection end of the coils (5) of a first stator segment (3a) is positioned adjacent a star connection end (11) of a second stator segment (3b).