Motor Drive DC Link Voltage Sensing With Adaptive ADC References
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Solution Overview
Problem
Conventional motor drive systems lack the ability to precisely measure DC link voltage, leading to reduced measurement resolution and inadequate fault detection, particularly for overvoltage and undervoltage conditions, which can cause undefined behavior and operational failures.
Innovation Solution
A motor drive system incorporating a voltage divider circuit, multiplexer, and fault detection circuit with comparators to scale DC link voltage and perform Built-In-Test (BIT) functions, enabling precise fault detection and dynamic adjustment of reference voltages for improved resolution and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional voltage measurement methods are used in motor drive systems, then the system structure remains simple, but the DC link voltage measurement resolution is insufficient and fault detection capability is inadequate
Solution Approach 1:
The voltage measurement function is segmented into multiple independent modules: voltage divider circuit for voltage scaling, multiplexer for signal routing, ADC for conversion, and fault detection circuit for monitoring. Each module performs a specific function, improving measurement resolution while keeping individual modules simple and manageable.
Solution Approach 2:
A multiplexer is introduced as an intermediary component between the voltage divider circuit and the ADC. The multiplexer dynamically switches between different voltage reference inputs (VREF1, VREF2, VREF3) based on the DC link voltage level, enabling adaptive measurement resolution without requiring complex direct measurement circuitry.
2Adaptability or versatility
If a single fixed reference voltage is used for ADC conversion, then the system is simple to operate, but the measurement resolution cannot be adapted to different voltage ranges
Solution Approach 1:
The system dynamically selects different reference voltages (VREF1, VREF2, VREF3) based on the actual DC link voltage level. The multiplexer switches between references automatically, allowing the measurement resolution to adapt to different operating conditions without manual intervention or complex configuration.
Solution Approach 2:
The reference voltage parameter is changed dynamically based on the DC link voltage range. By switching between multiple fixed reference voltage values, the system achieves variable measurement resolution - using higher reference voltages for low DC link voltages and lower reference voltages for high DC link voltages, optimizing ADC utilization across the full operating range.
3Reliability
If conventional fault detection methods are used, then the system remains simple, but overvoltage and undervoltage conditions cannot be reliably detected, leading to undefined behavior
Solution Approach 1:
The fault detection circuit continuously monitors the DC link voltage against predefined threshold values (VUV for undervoltage, VOV for overvoltage) before faults occur. By maintaining continuous monitoring and comparing against predetermined thresholds, the system can detect and respond to abnormal conditions promptly, preventing undefined behavior and operational failures.
Solution Approach 2:
The same ADC and multiplexer infrastructure used for normal voltage measurement is also utilized for fault detection. The fault detection circuit shares the voltage measurement path, adding monitoring functionality without requiring completely separate dedicated hardware, thus improving reliability while controlling complexity.
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
Enhances DC link voltage measurement resolution and effectively detects overvoltage and undervoltage conditions, ensuring proper drive operating modes and protecting the system by dynamically adjusting reference voltages and initiating protective measures.
Implementation Method 1
a DC scaling circuit (120) configured to measure a DC link voltage (VDC) present on a DC link (10)
Implementation Method 2
a fault detection circuit (130) configured to receive the output DC link voltage, an under-voltage (U/V) reference voltage (VREF U/V ), and an over-voltage (O/V) reference voltage (VREF O/V ), and to provide a Built-In-Test (BIT) function
Data Source
Figure 1
Figure 2
AI summary
A motor drive system includes a MUX circuit (102), a DC voltage scaling circuit (120), a fault detection circuit (130), an ADC (14), and an FPGA (150). The MUX circuit selectively establishes a MUX input signal path and a MUX output signal path. The DC voltage scaling circuit measures a DC link voltage. The fault detection circuit receives the output DC link voltage and outputs one of a normal operation signal or a fault signal in response to comparing the DC link voltage to one or both of a U/V reference voltage and an O/V reference voltage. The ADC converts one or more input analog voltages into respective corresponding output digital voltages. The FPGA is in signal communication with the ADC output (ADCOUT) and the MUX circuit, and is configured to control the motor drive system based on a comparison between one or more of the output digital voltages.