RMS Phase Current Measurement Circuit Using Summation Shunt
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Solution Overview
Problem
Existing methods for determining the effective value of phase current in three-phase inverters are cumbersome and costly, failing to provide a simple and efficient solution for accurate measurement.
Innovation Solution
A circuit arrangement using a bridge circuit with semiconductor switching elements and a sum shunt for peak value detection, employing operational amplifiers, diodes, resistors, and capacitors to convert clocked measurement signals into continuous signals representing maximum and minimum peak values, allowing for the determination of effective current values through peak value detection and filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional current measuring devices with multiple current sensors are used for RMS measurement, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts only the essential information needed for RMS calculation by using a single summation shunt to detect peak current values, rather than measuring all phase currents continuously. This extraction approach reduces the measuring device to its core function while maintaining sufficient measurement precision for RMS determination.
Solution Approach 2:
The summation shunt serves multiple functions: it detects peak current values, provides information for RMS calculation, and works for both sinusoidal and distorted current curves. This multi-functionality eliminates the need for separate measurement devices for different measurement scenarios.
2Measurement precision
If multiple current sensors are installed in each phase for accurate current measurement, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The invention merges the measurement function into a single summation shunt that captures peak current information from all phases. This consolidation reduces the number of sensors from three (or more) to one, significantly lowering manufacturing costs while preserving the ability to calculate RMS values accurately.
3Measurement precision
If continuous current measurement is performed using traditional methods, then measurement precision is improved, but use of energy increases
Solution Approach 1:
Instead of continuous measurement, the invention uses periodic peak detection followed by RMS calculation. The system measures peak values at critical moments and then computes RMS values through signal processing, reducing the continuous energy consumption of traditional analog measurement circuits while maintaining measurement precision.
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
This approach enables a cost-effective and efficient method for determining the effective value of phase current, capable of handling sinusoidal and distorted current curves, with a worst-case estimate for operating states, including direct current scenarios, without requiring additional phase voltage measurements.
Implementation Method 1
the capacitor charges up to a certain value corresponding to the phase current depending on the current maximum peak value of the phase current to be determined
Implementation Method 2
a circuit for this purpose has an operational amplifier, a diode and a first resistor and a capacitor in series with the diode
Implementation Method 3
a circuit for this purpose has an operational amplifier, a diode and a first resistor and a capacitor in series with the diode
Data Source
Figure 1~3
AI summary
The invention relates to a circuit arrangement for determining an effective value of a PWM-clocked three-phase inverter from measured peak values of the AC phase current, said three-phase inverter comprising: a bridge circuit, which has a plurality of switch pairs of two semiconductor switching elements each, which are connected to poles of a DC link; and a summing shunt for detecting the peak value of the presently greatest phase current, the circuit arrangement comprising at least one circuit topology (10) for detecting peak values of the AC phase current, which circuit topology is designed to determine the effective value of the current therefrom. For this purpose, the circuit (10) has an operational amplifier (11), a diode (D), and a first resistor (R1) and a capacitor (C) in series with the diode (D). The capacitor is charged, according to the present maximum peak value of the phase current to be determined, to a certain corresponding value.