PWM Control Circuit Synchronization for Interference Reduction
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Solution Overview
Problem
Existing methods to reduce electromagnetic interference in switched control circuits, such as PWM-controlled loads, are costly and inefficient, as they require increasing capacitance or cable modifications, and synchronization of control signals is hindered by variations in electrical characteristics, thermal drift, and current levels.
Innovation Solution
A method for synchronizing slave control circuits with master control circuits by transmitting a synchronization signal to time-shift the slave control signal, reducing the interval between edges, and repeating the process until synchronization is achieved, which can also involve initial delaying of the master signal to create a synchronization margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the slew rate of current or voltage is decreased to reduce interference, then electromagnetic interference is reduced, but dissipated power increases and component size increases
Solution Approach 1:
The patent combines multiple control circuits and synchronizes their switching operations so that current edges occur simultaneously. This allows the circuits to share a common DC link capacitor, reducing the total capacitance required and thereby reducing dissipated power while maintaining electromagnetic compatibility through synchronized interference patterns
2Object-affected harmful factors
If capacitance at the input of voltage source is increased to decrease slew rate of current, then conducted interference is reduced, but cost increases
Solution Approach 1:
Multiple control circuits share a common DC link capacitor by synchronizing their switching operations. This reduces the total capacitance required compared to having separate capacitors for each circuit, thereby reducing cost while effectively reducing conducted interference through synchronized current edges
3Object-affected harmful factors
If cable bundle is modified by twisting wires or implementing shielding to decrease radiated interference, then radiated emission is reduced, but cost increases
Solution Approach 1:
The patent applies preliminary action by synchronizing the control signals before they reach the power switches. This ensures that voltage edges and associated radiated interference occur simultaneously at the source, eliminating the need for subsequent cable modifications such as twisting or shielding
4Reliability
If control signals are directly synchronized by synchronizing edges of control signals, then synchronization is achieved, but variations in electrical characteristics cause insufficient synchronization
Solution Approach 1:
The patent implements feedback by measuring the actual interval between slave edge and master edge, comparing it to a target value, and adjusting the slave control signal timing accordingly. This closed-loop approach compensates for variations in electrical characteristics, thermal drift, and current levels to achieve precise synchronization
Solution Approach 2:
The patent replaces direct mechanical/electrical edge synchronization with a measurement and adjustment system. Instead of relying on direct edge alignment, it measures the interval between edges and uses this measurement to calculate and apply the appropriate time shift, substituting a more reliable electronic measurement and control system
Data Source
AI summary
Disclosed is a method for synchronising at least one slave control circuit, controlled by a slave control signal having pulse width modulation, with a master control circuit, controlled by a master control signal having pulse width modulation, including the following steps: the master control circuit emitting a synchronisation signal indicating a master edge of an electrical quantity; the slave control circuit receiving the synchronisation signal; measuring a delay between a slave edge of the same electrical quantity and the master edge of the electrical quantity; time-shifting the slave control signal so as to reduce the delay; and repeating the measurement step until the delay is eliminated.