Motor Emulator Switching Circuit for High-Frequency Current Control
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Solution Overview
Problem
Existing motor emulators face limitations in emulating medium-speed and high-speed motor operations due to current pulsation caused by digital control and DC terminal voltage shortages, restricting the emulated operation speed and accuracy, especially in high-frequency current emulation.
Innovation Solution
A motor emulator with a voltage following inverter and an output current control unit that includes a switching circuit and a second switching control unit, using SiC MOSFETs and independent DC voltage sources, to accurately control and estimate currents based on the output voltage and characteristics of the emulated target motor, reducing current pulsation and increasing switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the inductance of the motor emulator is increased to match the target motor (0.9 pu to 1.1 pu), then the high-frequency current emulation performance is improved, but the DC terminal voltage must be further increased through the boosting circuit, which is limited by the voltage rating of the devices
Solution Approach 1:
The patent changes the circuit topology from a conventional two-stage structure (voltage source inverter + current source inverter) to a direct voltage-source inverter structure with a special switching network. This topological parameter change eliminates the need for DC voltage boosting while maintaining the ability to emulate high-frequency currents, thereby resolving the contradiction between emulation precision and voltage requirements
Solution Approach 2:
The patent introduces a special switching network with auxiliary switches and capacitors as an intermediary element. This switching network acts as a mediator that enables the inverter to output currents with frequencies higher than its own switching frequency, achieving high-frequency current emulation without requiring increased DC terminal voltage
2Stress or pressure
If the inductance of the motor emulator is reduced (0.1 pu to 0.3 pu) to solve the voltage shortage problem, then the DC terminal voltage requirement is reduced, but large current ripple is generated due to digital signal processing delay
Solution Approach 1:
The switching network with auxiliary capacitors acts as an intermediary energy storage element that compensates for the current ripple caused by digital control delays. The capacitors provide instantaneous current compensation during the delay period, eliminating the harmful current pulsation even when the emulator inductance is reduced
Solution Approach 2:
The auxiliary capacitors in the switching network are pre-charged to provide instantaneous current compensation before the digital control delay expires. This beforehand cushioning prevents current ripple and pulsation, allowing the use of smaller emulator inductance without generating harmful current variations
3Productivity
If the switching frequency is increased to 100 kHz or above using SiC devices, then the current emulation band is extended to the switching frequency band (5 to 10 kHz), but the complexity of the circuit and control technique increases
Solution Approach 1:
The patent segments the current control into two independent parts: the fundamental wave current control and the switching frequency current control. The switching network handles the high-frequency switching currents while the main inverter handles the fundamental wave currents, allowing each part to be optimized independently and reducing overall system complexity
Solution Approach 2:
The voltage-source inverter structure with the switching network serves multiple functions simultaneously: it generates fundamental wave currents, generates switching frequency currents, and provides high-frequency current emulation. This multi-functionality reduces the need for separate circuit stages and simplifies the overall control technique
Data Source
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AI summary
Embodiments relate to a motor emulator for a motor driving inverter (or, an Inverter Under Test, IUT), and the motor emulator includes a voltage following inverter configured to cancel an output voltage of the IUT at least partially, and an output current control unit configured to control an output current of the IUT based on the output voltage of the IUT and an estimated current of an emulated target motor.