Current Transformer Saturation Prevention via PWM Load Balancing
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Solution Overview
Problem
Current transformer (CT) saturation occurs due to unsymmetrical load conditions in module case circuit breaker (MCCB) applications, leading to inaccurate and nonlinear sensed current signals.
Innovation Solution
Implementing pulse width modulation (PWM) signaling in a closed loop of a shunt boost controller to reduce load imbalance, thereby preventing CT saturation by controlling the power switch circuit to redirect current and maintain symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the current transformer is used as a shunt-boost based power supply with unsymmetrical load, then the power supply function is achieved, but remanence occurs and causes CT saturation
Solution Approach 1:
The patent applies asymmetry principle by introducing PWM signaling to actively balance the unsymmetrical load conditions. The PWM controller adjusts the duty cycle of the power switch to compensate for the inherent asymmetry in the shunt-boost topology, ensuring symmetrical current flow through the CT during both positive and negative half-cycles, thereby preventing remanence accumulation and saturation.
Solution Approach 2:
The patent implements feedback control by using the CT output signal to control the power switch timing. The feedback network monitors the CT current and adjusts the power switch duty cycle accordingly, creating a closed-loop system that automatically compensates for load imbalances and prevents saturation while maintaining power supply function.
2Stability of the object's composition
If the power switch circuit turns on frequently to balance the load, then the load imbalance is reduced, but the complexity of the control system increases
Solution Approach 1:
The patent applies periodic action by using PWM signaling at a specific frequency to control the power switch. This periodic control mechanism creates symmetrical current flow patterns in the CT, balancing the load across AC cycles. The fixed frequency PWM approach provides systematic control without requiring complex real-time adjustments, thereby achieving load balance with manageable system complexity.
3Reliability
If PWM signaling is used to symmetrize the control signal, then the remanence is reduced, but the frequency of the control signal must be greater than the feedback signal
Solution Approach 1:
The patent applies preliminary action by introducing PWM signaling that operates at a higher frequency than the feedback signal. This higher frequency PWM control proactively shapes the current waveform symmetry before remanence can accumulate in the CT. By acting at a faster timescale, the system prevents saturation conditions from developing rather than correcting them after they occur.
Data Source
AI summary
The subject disclosure provides for utilizing pulse width modulation (PWM) signaling to influence a closed loop of a shunt boost controller and reduce an imbalance of a load. The imbalance reduction helps reduce remanence of a current transformer (CT) and thereby prevent saturation of the CT. A shunt boost controller provides the control signal to control flow of current to the load. A feedback network provides a feedback signal to the shunt boost controller based on a direct current (DC) voltage and causes a power switch circuit to turn on when a magnitude of the feedback signal exceeds a threshold magnitude. The PWM generator supplies a PWM signal to cause the control signal to be provided more symmetrical to the power switch circuit and causes the power switch circuit to turn on more frequently with the control signal to reduce the imbalance of the load.