Drive Circuit Harmonic Cancellation via Stator Winding Interconnection
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Solution Overview
Problem
The use of pulse width modulation (PWM) power converters in drive circuits for electrical machines results in high magnitude PWM frequency current harmonics, leading to increased machine losses, heating, mechanical vibrations, and noise, particularly when using conventional two-layer stator windings.
Innovation Solution
Interconnecting stator coils of two-layer stator windings such that the vector sum of voltages across them is equal and in phase, eliminating the need for additional inductors and simplifying the drive circuit, while maintaining the conventional two-layer winding construction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If PWM power converters are used to drive electrical machines with conventional two-layer stator windings, then the drive circuit achieves modern power conversion efficiency and control capability, but high magnitude PWM frequency current harmonics are generated causing increased machine losses, heating, mechanical vibrations and noise
Solution Approach 1:
The patent segments the stator winding into multiple independent coil groups (first stator coil group, second stator coil group, third stator coil group, fourth stator coil group) with different connection configurations. Each coil group is connected to different phases of the PWM power converter, allowing independent control of their connection patterns to achieve harmonic cancellation while maintaining overall power conversion efficiency.
Solution Approach 2:
The patent employs asymmetric connection configurations among the stator coil groups. Specifically, the first and second coil groups are connected in one direction while the third and fourth coil groups are connected in the opposite direction. This asymmetric arrangement creates opposing voltage vectors that cancel PWM frequency harmonics while preserving the fundamental power conversion function.
2Object-generated harmful factors
If inductors are added between PWM power converters and stator windings to reduce PWM frequency current harmonics, then machine losses and heating are reduced, but the cost and space requirements increase significantly
Solution Approach 1:
The patent extracts the harmonic filtering function from external inductors and relocates it into the stator winding structure itself. By configuring the coil groups with opposite connection directions, the winding structure inherently provides the harmonic cancellation function that would otherwise require separate inductor components, thereby eliminating the need for additional inductors and reducing device complexity.
Solution Approach 2:
The patent makes the stator winding structure multi-functional by having it simultaneously perform both the power conversion function and the harmonic filtering function. The same stator coil groups that convert electrical power also provide the asymmetric connections needed for PWM harmonic cancellation, eliminating the need for separate harmonic filtering components.
3Object-generated harmful factors
If four-layer windings are used to place stator coils of both windings in the same stator slots, then PWM frequency current harmonics are reduced, but the manufacturing complexity and cost increase significantly
Solution Approach 1:
Instead of adding layers in the vertical dimension (which would require four-layer windings), the patent resolves the harmonic issue by utilizing the spatial arrangement and connection topology in the electrical connection dimension. The coils remain in conventional two-layer slots but are connected through multiple groups with opposite polarities, achieving harmonic cancellation without increasing winding layer complexity.
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 significantly reduces PWM frequency current harmonics, eliminating the need for costly and space-consuming inductors, thereby reducing machine losses and maintaining the low-cost, traditional two-layer stator winding construction.
Implementation Method 1
the first and second stator windings being in physical proximity to each other such that they are in mutual coupling
Data Source
Figure 1~2
Figure 3a~4
Figure 5~6
AI summary
The present invention provides a drive circuit for an electrical machine having a stator. The drive circuit includes an ac network (4) and first and second network rectifier/inverters (10 and 12), which can be active or passive, that are connected to the ac network in parallel. A first PWM rectifier/inverter (200) is connected to the first network rectifier/inverter 10 through a first dc link (204). A second PWM rectifier/inverter (202) is connected to the second network rectifier/inverter (12) through a second dc link (206). A first two-layer stator winding (208) having a plurality of individual stator coils is connected to the first PWM rectifier/inverter (200) and a second two-layer stator winding (210) having a plurality of individual stator coils is connected to the second PWM rectifier/inverter (202). The stator coils of the first stator winding (208) and the stator coils of the second stator winding (210) are interconnected such that, in use, the vector sum of voltages across the stator coils in the first stator winding is substantially equal to the vector sum of voltages across the stator coils in the second stator winding. This has the advantageous effect of reducing the PWM frequency current harmonics flowing in the first and second stator windings (208 and 210).