Chopper Assembly Phase Shift Control for Ripple Current Reduction
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Solution Overview
Problem
In variable-frequency drive systems, simultaneous activation of multiple braking choppers leads to high current pulses and excessive ripple current, causing thermal stress and component failure, as existing methods for controlling chopper units are either inaccurate or prone to failure if a master unit fails.
Innovation Solution
A chopper assembly with at least two units and a controlling unit that generates a control signal for phase shifting the activation of chopper units, either initially offsetting or adjusting the phase shift after a predefined time, to prevent simultaneous activation and reduce ripple current amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple braking choppers are activated simultaneously to limit DC bus voltage, then the DC bus voltage can be controlled within safe thresholds, but high current pulses occur causing excessive ripple current and thermal stress on components
Solution Approach 1:
The patent applies periodic action by sequentially activating chopper units in a cyclic manner rather than simultaneously. The controlling unit generates activation signals with different phase shifts for each chopper unit, creating a periodic switching pattern that distributes current pulses over time. This reduces the peak ripple current amplitude while maintaining effective DC bus voltage limiting through the combined action of all chopper units.
Solution Approach 2:
The patent segments the chopper activation process by dividing the simultaneous activation into separate, time-staggered activations. Each chopper unit is controlled independently with its own phase-shifted activation signal, breaking the unified activation event into multiple discrete segments. This segmentation reduces the instantaneous current demand and ripple current amplitude on the DC link.
2Ease of operation
If chopper units are controlled individually to distribute load, then measurement inaccuracies cause uneven load sharing, but if controlled simultaneously they create high current pulses
Solution Approach 1:
The patent implements feedback control where the controlling unit monitors the actual current distribution among chopper units and adjusts the phase shifts and duty cycles accordingly. This feedback mechanism compensates for measurement inaccuracies and ensures balanced load sharing while maintaining the phase-shifted sequential activation pattern that reduces ripple current amplitude.
Solution Approach 2:
The patent applies dynamics by making the chopper activation parameters (phase shifts, duty cycles) adjustable and adaptive rather than fixed. The controlling unit dynamically modifies these parameters based on real-time system conditions and measured current distribution, enabling optimal load sharing that prevents both uneven distribution and excessive current pulses.
3Reliability
If a master chopper unit and additional chopper units are operated simultaneously, then all chopper units may fail to function if the master unit fails, but operating them sequentially reduces redundancy
Solution Approach 1:
The patent segments the chopper control architecture so that each chopper unit operates with its own phase-shifted activation signal from the controlling unit. This segmentation eliminates the single-point-of-failure master unit architecture while maintaining redundancy, as each unit can independently contribute to DC bus voltage limiting. The sequential activation pattern inherently reduces current pulse impact on the DC link.
Data Source
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AI summary
A chopper assembly is disclosed. The chopper assembly includes a at least two chopper units, and a controlling unit configured to generate a control signal for controlling an activation of the corresponding chopper unit in cycle. The activations of the at least two chopper units are controlled by the controlling unit to be either initially offset by a phase shift or adjusted to have a phase shift after a predefined time duration, the phase shift indicating a time difference between rising edges or between falling edges of respective pulses of different signals. The chopper assembly according to the present disclosure effectively mitigates the negative impact to various components within the circuit. Moreover, by controlling the duty cycles of the control signals, loads of each of the resistors will be equal.