Power-Saving Contactor Circuit with Active PFC and Square Wave Control
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Solution Overview
Problem
Existing contactor power-saving technologies fail to improve the power factor while reducing active power consumption, making it difficult to achieve the primary level of energy efficiency, especially for low-power applications where active Power Factor Correction (PFC) technologies are not commonly used.
Innovation Solution
A power-saving circuit for AC contactors that includes a rectification and filtering circuit, a PFC circuit, an auxiliary power supply circuit, and a square wave generation circuit, which controls the duty cycles of switch tubes to manage current effectively during pull-in, transition, and holding stages, ensuring the PFC circuit operates in discontinuous mode to enhance power factor and reduce active power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If existing power-saving technologies (AC to DC, high-current pulling in, low-current holding) are used, then active power consumption is reduced by more than 90%, but power factor deteriorates to 0.3 or lower
Solution Approach 1:
An auxiliary circuit comprising a switching element, diode, and capacitor is introduced as an intermediary component. This auxiliary circuit works in conjunction with the existing coil structure to provide reactive power compensation, thereby improving power factor without requiring a complete redesign of the power-saving mechanism
Solution Approach 2:
The invention changes the operating parameters by controlling the switching element to operate at specific duty cycles during different stages (pull-in and holding). During pull-in stage, the switching element operates at a first duty cycle to provide high current, while during holding stage, it operates at a second duty cycle to maintain magnetic field with reduced current, thus maintaining both power savings and power factor
2Use of energy by moving object
If pulse form is used to power the electromagnetic coil with constant small current, then active power consumption is reduced, but power factor deteriorates to extremely low values (smaller than 0.3)
Solution Approach 1:
The invention employs periodic switching action where the switching element is turned on and off at specific intervals. During the on-period, the auxiliary circuit provides reactive power support; during the off-period, the stored energy in the capacitor maintains the magnetic field. This periodic action synchronizes with the AC cycle to improve power factor while maintaining reduced current operation
Solution Approach 2:
The auxiliary circuit with switching element, diode, and capacitor acts as an intermediary that bridges the gap between the pulse-powered coil and the AC supply, providing reactive power compensation that raises power factor from below 0.3 to above 0.9
3Use of energy by moving object
If electromagnetic coil is excited when input AC voltage is just over zero, then active power consumption is reduced, but power factor deteriorates to smaller than 0.1
Solution Approach 1:
The invention implements a feedback mechanism where the switching element is controlled based on the voltage waveform detection. The control circuit monitors the AC voltage and triggers the switching element at the optimal moment (when voltage is just over zero), and adjusts the duty cycle based on the operating stage, providing feedback control that maintains both low power consumption and high power factor
Solution Approach 2:
The invention dynamically changes the duty cycle parameter of the switching element based on the operating stage. During pull-in stage, a first duty cycle provides high current for magnet activation; during holding stage, a second duty cycle provides reduced current while the auxiliary circuit compensates reactive power, thus maintaining power factor above 0.9 throughout
4Object-generated harmful factors
If Power Factor Correction (PFC) circuits are used to achieve primary energy efficiency, then power factor is improved, but device complexity increases due to active PFC technology requirements
Solution Approach 1:
The invention extracts only the essential PFC function from complex active PFC circuits. Instead of implementing a full active PFC system with multiple switches and control circuits, it extracts the core reactive power compensation function and implements it with a simple auxiliary circuit containing one switching element, one diode, and one capacitor
Solution Approach 2:
The auxiliary circuit components (switching element, diode, capacitor) are simple, inexpensive components that can be easily replaced. The circuit design avoids expensive active PFC ICs and complex control electronics, using instead basic passive components and a single switching element that can be implemented with standard discrete components
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
The power factor is significantly improved from less than 0.3 to 0.9 or more, allowing the contactor to meet the primary level of energy efficiency as per national standards, with active power consumption reduced to below 1 VA.
Implementation Method 1
a rectification and filtering circuit (11), a PFC circuit (12)
Implementation Method 2
rectification and filtering circuit (11), filtering an input narrow-pulse current into a smooth current
Implementation Method 3
The PFC circuit receives rectified and filtered electric energy, enables an effective value of the input current to change along with an input voltage
Implementation Method 4
An attractive force is generated between the static iron core and the armature when the contactor coil is energized
Implementation Method 5
a counterforce spring. An attractive force is generated between the static iron core and the armature when the contactor coil is energized. When the attractive force is greater than the spring reactive force
Data Source
AI summary
A power-saving circuit for a contactor includes a coil drive circuit, and further includes a rectification and filtering circuit, a PFC circuit, an auxiliary power supply circuit, and a square wave generation circuit. The square wave generation circuit outputs a first square wave signal to the PFC circuit via a first output end according to a set timing sequence, and outputs a second square wave signal and a third square wave signal to the coil drive circuit via a second output end, so as to respectively control duty cycles of a first switch tube in the PFC circuit and a second switch tube in the coil drive circuit. The auxiliary power supply circuit supplies electric energy to the square wave generation circuit during a holding stage of the contactor. The rectification and filtering circuit is used for rectifying an input AC into a pulsating DC, and filtering an input narrow-pulse current into a smooth current to be outputted to the PFC circuit after eliminating higher harmonic components other than a fundamental frequency component of 50 Hz. The PFC circuit receives rectified and filtered electric energy, enables an effective value of the input current to change along with an input voltage, and outputs the input current to the coil drive circuit and the auxiliary power supply circuit. The coil drive circuit is used for controlling the current of a contactor coil. Wherein during a pull-in stage of the contactor, the PFC circuit does not work and the power-saving circuit provides a large current to the contactor coil to pull in; during a transition stage, the PFC circuit starts to work and the power-saving circuit controls the current of the contactor coil to decrease gradually; and during a holding stage of the contactor, the PFC circuit keeps working and the power-saving circuit controls the current of the contactor coil to be kept as a small current required for holding.