Power Converter Filter Current Estimation for Motor Control
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Solution Overview
Problem
Power conversion systems face challenges in accurately controlling voltages and currents provided to a load when an output filter is present, as feedback signals measured at the inverter output do not represent the actual load parameters, making it difficult to control motors or other loads without additional sensors or significant modifications to the inverter control system.
Innovation Solution
The implementation of a power converter system with an inverter and controller that determines filter currents or voltages based on inverter output feedback signals, allowing for the generation of inverter switching control signals to compensate for the filter dynamics, thereby facilitating improved control of loads like permanent magnet synchronous motors without requiring direct feedback sensors at the load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an output filter is added to reduce high frequency content from PWM output, then output waveform quality is improved, but control accuracy of load voltages and currents deteriorates
Solution Approach 1:
The patent introduces an intermediary computational model of the filter circuit that acts as a mediator between the inverter control and the actual filter dynamics. By calculating equivalent filter currents and voltages based on inverter output signals and filter parameters, the system bridges the information gap created by the filter, allowing accurate load control without direct sensing at the load terminals.
2Measurement precision
If feedback sensors are added at the load to directly measure load parameters, then control accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The system performs self-service by using its existing inverter output feedback signals to compute the filter currents and voltages that would otherwise require additional sensors to measure. The controller leverages available information (inverter output currents and voltages) combined with known filter parameters to derive the load-side electrical quantities, making the system self-sufficient without external measurement devices at the load.
Solution Approach 2:
The patent replaces the physical measurement system (sensors at the load) with a computational system. Instead of using hardware sensors to directly measure load voltages and currents, the system uses mathematical calculations based on inverter output signals and filter characteristics to determine the equivalent load parameters, substituting electronic computation for physical measurement.
3Device complexity
If inverter control is based on feedback signals at inverter output, then system simplicity is maintained, but load control accuracy deteriorates due to filter intervention
Solution Approach 1:
The patent applies preliminary action by pre-calculating the filter currents and voltages that result from the inverter output before these signals actually reach the load. By computing the equivalent load-side electrical quantities in advance based on inverter feedback and filter parameters, the controller can anticipate the filter's effect and adjust its control signals accordingly, maintaining accuracy without adding complex real-time measurement systems.
Data Source
AI summary
Power converters and methods are presented for driving an AC load connected through an intervening filter circuit, in which at least one filter current or voltage signal or value is determined according to feedback signals or values representing an output parameter at an AC output of the power converter, and AC electrical output power is generated at the AC output based at least partially on the at least one filter current or voltage signal or value.