Project
| # | Title | Team Members | TA | Documents | Sponsor |
|---|---|---|---|---|---|
| 72 | Single-Phase AC Power Analyzer |
Isaac Herink Jeffrey Pohlman Joseph Kim |
Eric Tang | design_document1.pdf other1.pdf |
|
| Team Members: - Isaac Herink (iherink2) - Jeffrey Pohlman (jpohl3) - Joseph Kim (joseph51) # Problem Basic voltage and current measurements do not provide insight into how power is actually being consumed by an AC load. Relevant quantities such as real power and power factor require time-synchronized measurements of voltage and current, which are typically only available from commercial power analyzers. These commercial analyzers are expensive and unnecessary for small-scale laboratory or educational purposes. # Solution Design and build a microcontroller-based, single-phase power quality analyzer that measures voltage and current supplied to a load using isolated sensing circuits. The microcontroller will sample both signals at the same time and compute RMS values, real power, and power factor in real time. Measurement data will be transmitted to a computer over USB for display and analysis. Example use cases include comparing real power and power factor across common loads (incandescent lamp vs. fan motor vs phone charger), measuring load startup behavior, and identifying inefficient or abnormal load behavior in educational lab experiments. It provides students with hands-on exposure to AC power measurements without needing expensive commercial equipment. The final system will provide a low-cost, embedded tool for monitoring and analyzing AC power behavior in laboratory and educational environments. # Solution Components ## Subsystem 1 - Power Path (Outlet -> Analyzer -> Load) This subsystem will provide a safe way to place the analyzer in line with the load without the analyzer acting as the load. The load current will flow through internal wiring (with optional fuse protection), and the analyzer measures current using a CT. This subsystem ensures the analyzer itself does not significantly affect load current/voltage. It also ensures a simple connecting interface between the outlet, analyzer, and load. Components: Inlet/Outlet Wiring Power Cord (McMaster Carr 71535K42), Receptacle (McMaster Carr 1333N53), Fuse (Littelfuse 0217005.MXP), Fuse holder (Littelfuse 01550900Z). ## Subsystem 2 - Voltage Sensing Provides an isolated low-voltage representation of the line voltage. The transformer secondary is routed to the PCB for conditioning. Components: AC Voltage transformer (120 VAC to 6-12 VAC) HQRP TR038 or equivalent. ## Subsystem 3 - Current Sensing Provides an isolated current measurement to the load. Components: Split-core CT 5A to 5mA (B0G1M449JN) - We may use a CT with a larger secondary current. Voltage and current sensing are isolated with a VT and CT to prevent direct electrical connection between mains and the MCU. ## Subsystem 4 - Analog Signal Conditioning Converts VT/CT signals into clean and bounded voltages that the MCU can sample accurately. This subsystem performs: - Voltage scaling: A resistor divider scales the VT secondary down to a target amplitude that is compatible with the ADC. - Current to voltage conversion: A burden resistor translates the CT secondary waveform into a proportional voltage waveform (for ADC input). - Input protection: Series resistors and clamp diodes to limit fault voltages and protect ADC ports. - Filtering: RC low-pass filters to reduce high-frequency noise and prevent aliasing. This subsystem ensures that the MCU receives waveforms that accurately represent line current/voltage. ## Subsystem 5 - Board Power The PCB will be powered from USB 5V (or an external 5V source). A 3.3V regulator supplies the MCU. Components: Voltage regulator (Diodes Inc AP2112K-3.3TRG1) ## Subsystem 6 - Bias Voltage Generation Both the voltage and current waveforms will be shifted (biased) to sit within the ADC input range, since the ADC cannot measure negative voltage. The PCB will supply a reference voltage of roughly 1.65V (Vmid = 1.65V) from the 3.3V rail using a resistor divider and decoupling capacitor. The conditioned waveforms are then centered around Vmid to remain between the 0-3.3V ADC range. ## Subsystem 7 - Embedded Processing (MCU) A microcontroller will sample voltage and current channels at a fixed sample rate. The firmware will remove DC offsets, apply any needed calibration factors, and compute: - RMS voltage/current - Real power from the average of v[t]i[t] - Apparent power, reactive power, and power factor Components: MCU (STMicroelectronics STM32F303CCT6 (LQFP-48)), SWD programming header (Samtec FTSH-105-01-F-DV-K). ## Subsystem 8 - Communication and Display This subsystem will present our computed values on a pc using USB serial (via a USB-UART bridge). A PC side program (Python or equivalent) will display Vrms, Irms, P, and PF over time. Components: USB-UART bridge (CP2102N), USB connector (GCT USB4085-GF-A). ## Enclosure We will design and 3D print an enclosure to contain our different subsystems. The enclosure will be self-contained and require only AC power and a USB connection. # Criterion For Success - Voltage and current waveforms are sampled at a fixed rate - The device measures voltage and current simultaneously - The device computes RMS voltage/current, real power, reactive power, and power factor - Measurements are displayed on a PC in real time - RMS voltage is measured within ±5% of a commercial analyzer for a resistive load -RMS current is measured within ±10% for at least one load in the 0–5 A range - Real and reactive power is computed within ±10% of a commercial analyzer for a resistive load - Power factor is reported within ±0.10 and correctly distinguishes resistive (PF ~ 1) and inductive loads (PF < 1) - The device is in a self-contained enclosure |
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