Micropulse Control for PWM Converter Voltage Steepness
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Solution Overview
Problem
Existing PWM frequency converters generate steep voltage pulses that cause stress on motor windings due to rapid voltage changes, leading to insulation issues and the need for large and expensive filters to mitigate reflections, which increase cost, size, and weight.
Innovation Solution
The solution involves controlling the rising and falling edges of output voltage pulses by introducing micropulses instead of conventional on-off switching, allowing for a controlled speed of change and using a small filter to adjust the pulse width, with fast power switches and silicon carbide technology to minimize losses and filter size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional PWM switching with fast on-off controls is used, then switching losses are minimized, but voltage pulses have steep edges causing stress on motor windings and requiring large expensive filters
Solution Approach 1:
The patent divides a single switching action into multiple micropulses (typically 3-7 pulses) within each switching period. Each micropulse has a controlled width and spacing, transforming the single steep voltage edge into a series of smaller, controlled voltage steps. This segmentation reduces the dv/dt of each individual transition while maintaining the overall switching frequency and average voltage output.
Solution Approach 2:
The patent dynamically adjusts the width and spacing of micropulses based on operating conditions such as motor speed, torque requirements, and cable length. The control system varies micropulse parameters in real-time to optimize both switching efficiency and voltage edge steepness, adapting to different load conditions and motor characteristics.
2Object-affected harmful factors
If filters are added to reduce voltage reflections and protect motor windings, then motor insulation stress is reduced, but filter size, weight, and cost increase significantly
Solution Approach 1:
The patent introduces micropulses as an intermediary control mechanism between the power switches and the motor. Instead of directly filtering the output voltage with large passive components, the control system mediates the voltage transitions by generating controlled micropulse sequences, thereby reducing reflections at their source rather than attempting to suppress them downstream.
Solution Approach 2:
The patent changes the temporal parameters of voltage pulses by introducing multiple micropulses with specific width and spacing characteristics. This parameter modification transforms the voltage waveform from a single steep edge to a distributed sequence of smaller steps, fundamentally altering the reflection characteristics without requiring physical filter components.
3Object-affected harmful factors
If micropulses are introduced to control voltage edge steepness, then motor winding stress is reduced and filter size is minimized, but switching frequency and control complexity increase
Solution Approach 1:
The patent employs periodic micropulse sequences within each switching period, where the pattern of micropulses repeats systematically. This periodic structure allows the control system to use predetermined templates and lookup tables for different operating conditions, reducing the computational burden compared to completely arbitrary pulse generation while still achieving fine-grained control.
Solution Approach 2:
The control system generates micropulse patterns that automatically adapt to operating conditions by using feedback from motor current and voltage sensors. The system self-regulates the micropulse width and spacing based on real-time motor state, reducing the need for complex external control circuitry and manual tuning.
Data Source
Figure 1~2
Figure 3~4
Figure 5a~5b
AI summary
Method and arrangement for controlling the output voltage pulses of a PWM frequency converter, in which PWM frequency converter is a network bridge (10) for rectifying the alternating voltage of the supply network into the DC voltage (UDC) of the DC intermediate circuit, which is filtered with a filtering capacitor (CDC), a load bridge (11) comprised of phase switches implemented with power semiconductor components, which forms the AC output voltage (U, V, W) from the DC voltage of the intermediate circuit for controlling the load (M), in which for setting the average speed of change in the output voltage in connection with each change of state of the output voltage at least one power component controlled by a phase switch is controlled such that before the output voltage remains in its position subsequent to the change of state it is on at least once for a short period, typically of less than 1µs (a micropulse), in the position prevailing before the change of state.