Three-Level Inverter Power Estimation via Neutral Point Voltage
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Solution Overview
Problem
Existing methods for controlling and estimating the active and reactive components of output power or current in inverters require expensive current sensors, increasing system costs and complexity.
Innovation Solution
A method that estimates active and reactive components of output power in a three-level inverter using only DC link voltage measurements, specifically by determining third harmonic components of the neutral point voltage, allowing for the elimination of current transducers and improving the accuracy of torque and flux control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensors are used to measure output current for controlling inverter, then measurement accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent uses DC link voltage measurements as an intermediary to indirectly estimate output current and power components. Instead of directly measuring current with sensors, the method measures voltage at the DC link and neutral point, then calculates current components through mathematical relationships, eliminating the need for current transducers while maintaining control accuracy
Solution Approach 2:
The patent replaces physical current sensing hardware with a computational approach. By substituting mechanical/electrical current measurement devices with voltage measurement and mathematical estimation algorithms, the system achieves the same control function without expensive current sensors, reducing both cost and system complexity
2Device complexity
If current transducers are eliminated to reduce system cost, then device complexity is reduced, but measurement precision deteriorates
Solution Approach 1:
The method uses feedback from DC link voltage measurements and neutral point voltage potential to continuously estimate output power components. The system feeds back the relationship between DC link voltage variations and output power, using this feedback loop to maintain accurate power estimation without direct current measurement
Solution Approach 2:
The patent changes the measurement parameter from direct current measurement to DC link voltage measurement. By measuring voltage instead of current and using the mathematical relationship between these parameters, the system achieves accurate power estimation while using simpler, less expensive voltage measurement circuitry
Data Source
Figure 1
AI summary
The present disclosure describes a method and a device implementing the method for a three-level inverter comprising a DC link divided into two halves by a neutral point. The method comprises determining a voltage ripple at the neutral point, determining a magnitude of a third harmonic component of the voltage ripple in a rotating coordinate system that rotates synchronously with an output voltage of the inverter, and calculating a component of an output current or power in the rotating coordinate system on the basis of the magnitude of the third harmonic component.