Project
| # | Title | Team Members | TA | Documents | Sponsor |
|---|---|---|---|---|---|
| 5 | Adaptive Power Factor Correction Device |
Luke Kang Ryan Irvin Saadullah Ehsan |
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| # Adaptive PF Correction Team Members: - Ryan Irvin (ryanri2) - Luke Kang (lukejk2) - Saad Ehsan (sehsa2) # Problem Many electrical loads such as motors, transformers, and power supplies are inductive in nature, which causes current to lag behind voltage. This results in a low power factor, increased current draw, and inefficient use of electrical power within AC systems. Poor power factor leads to higher real power losses, reduced system capacity, and inefficient power delivery. Most power factor correction methods usually use fixed capacitor banks, which are not adaptive to changing loads or done at a large scale and are not achievable for small commercial tenants. As a result, they are unable to maintain an optimal power factor when loads vary over time. There is a need for a low-cost, real-time system that can measure power factor and automatically apply corrective compensation based on load conditions our project aims to achieve this with the goal of laying the foundation for a model that can be scaled up to a 480V 3phase commercial electrical panel. # Solution Our proposal is for the design and implementation of an adaptive power factor correction system that measures voltage and current waveforms in real time, computes power factor using digital signal processing, and switches capacitor banks to improve the power factor. The system operates at low-voltage AC for safety while prototyping and demo purposes while maintaining scalability for other real-world AC power systems. The system has three main subsystems: 1. Sensing (of the voltage and currents) 2. Microcontroller Unit (Processing and computation) 3. Switching stage (Switched capacitor banks for Q compensation) A microcontroller continuously samples voltage and current waveforms using ADC channels, computes real power and power factor, and determines the required capacitance for the desired PF. Capacitors are switched in discrete steps using controlled switching synchronized to the AC waveform. # Solution Components ## Subsystem 1: Sensing This subsystem measures the AC voltage and current waveforms and converts them into safe analog signals for the microcontroller. For the voltage sensing, the input is scaled down by a voltage divider and is biased to shift it into the Microcontroller’s ADC voltage range. - Components: - Resistive voltage divider components - Biasing network (mid-supply reference ~1.65V) - Potentially a filter for any signal noise For current sensing, the input would be fed into a current transformer to convert into appropriate voltage and then biased the same as the voltage for the ADC. - Components: - Current Transformer (CT), SCT-013-005 (5A:1V) The output of both sensing circuits would be a centered AC waveform with a 1-2 V peak biased around the midpoint of the MCU’s voltage range. ## Subsystem 2: MCU This subsystem processes digitized voltage and current signals to compute power factor and determine required compensation. ADC: It would first convert the signals into digital by sampling both the voltage and current at 5-10 kHz. Then, it would unbias the signals to recreate the original zero-centered waveforms. PF Calculation: After that, it would compute the rms voltage and currents then multiply them to get the apparent power (S = Vrms × Irms). Then, it would compute the real power (P = avg(v(t)*i(t))) and divide it by S to obtain the current power factor (PF = P/S). Capacitance Calculation: Once the current power factor is obtained, it would find the current reactive power Q = sqrt(S^2 - P^2). Then we find our desired apparent power by dividing the real power by our desired PF target of 0.95. Using the target apparent power, it calculates the target reactive power which is used to find the required capacitance value. We would implement a lower bound for the PF (~0.92) to prevent oscillation and rapid capacitor switching. - Components: Microcontroller (like STM32) Software for real-time sampling and computation ## Subsystem 3: Capacitive Switching This subsystem dynamically connects or disconnects capacitors to correct reactive power. The switching subsystem will take GPIO outputs from the microcontroller and safely add or remove parallel capacitance to the load to improve the power factor. To safely perform power factor correction, two major considerations must be addressed: zero-cross detection and inrush current. The switching path will be: GPIO Output -> Gate Driver -> Power Triac -> Inrush Resistor -> Capacitor The gate driver isolates the microcontroller from the AC portion of the circuit and provides the gate-trigger current needed to turn on the power triac. The power triac acts as a solid-state AC switch, connecting the capacitor to the AC circuit when triggered. The inrush resistor limits the initial current when the capacitor is switched on. We potentially may after a safe delay, have the resistor be bypassed to provide a nearly purely capacitive load in parallel for optimal power factor correction (the bypass is dependent on later calculations if it is not needed we may not implement it). A bleeder resistor is connected in parallel with the capacitor to safely discharge it after the microcontroller determines that the capacitor is no longer needed and switches it off. Components: - Capacitor bank (discrete stages, 1, 2, 4, 8… magnitude to be determined by general load size) - Power TRIACs (STMicroelectronics BTA16-600SW) - Optocoupler-based gate drivers (MOC3023 random-phase optotriac driver) - Inrush-limiting resistor (approximately 10–100 Ω, final value determined through testing) - Inrush resistor bypass switch to short inrush resistor (second TRIAC + MOC3023 driver) - Bleeder resistors (high-value resistors across each capacitor for safe discharge, while having limited effect on PF Correction) Function: - Switch capacitor stages in/out based on controller command - Safely synchronize switching with the AC waveform using zero-cross detection on the sensing subsystem and limit capacitor inrush current during initial connection - Safely discharge disconnected capacitors using bleeder resistors - Use multiple capacitor combinations to provide different levels of reactive power compensation # Criterion For Success For our project to be deemed successful we need to properly integrate all 3 subsystems and be able to demo it. This we be measurable if the following are successful: Accurate Measurements: The system can accurately measure voltage and current AC waveforms The microcontroller can accurately calculate the PF and required capacitance The microcontroller outputs are used to switch capacitive loads and dynamically adjust them. PF correction is seen on output display for user verification. Safe switching operation: Matching 0 crossings and adding hysteresis for safety of in rush Real time operation/Demo: 15V AC can be applied to a variable inductive load(potentiometer and inductor in series), and that load can be changed in real time by changing the resistive value to demonstrate real time PF correction as loads change. # Alternatives Commercial reactive power compensation systems already exist, but they are generally designed for larger installations, often above 75 kVA. Our project targets a smaller scale application, such as individual tenant electrical panels where a large commercial compensation system would not be practical. The prototype is designed as a single-phase system, but the architecture is intended to be scalable. The same sensing, control, and capacitor-switching structure could be applied independently to each phase for split-phase residential systems or 3 phase commercial tenant panels. For the ECE 445 prototype, the system will operate at approximately 15 V AC. This voltage allows the design to demonstrate the same power factor correction concepts while remaining manageable for safe laboratory development using standard bench equipment. |
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