Generator Inverter Torque Control for DC-Link Harmonic Suppression
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Solution Overview
Problem
Conventional methods for calculating torque reference in inverters driven by generators with harmonic frequency components in the mechanical frequency lead to reduced lifetime of batteries and capacitors due to phase shifts and power requirements, which are not effectively addressed by existing approaches.
Innovation Solution
A method and controller for inverters that determine a harmonic frequency component of the estimated mechanical frequency, calculate a torque reference value based on this component, and generate a switching signal to accurately control the inverter, using transfer functions and band-pass filters to compensate for harmonic frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional torque reference calculation method is used, then the control is simple, but harmonic frequency components in DC link voltage increase reducing inverter lifetime
Solution Approach 1:
The patent applies preliminary action by determining the harmonic frequency component of the mechanical frequency in advance and using it to calculate the torque reference value before the inverter operation. This proactive approach prevents harmonic frequency components from appearing in the DC link voltage, thereby extending inverter lifetime without adding complex real-time control mechanisms.
Solution Approach 2:
The patent skips the intermediate step of using estimated mechanical frequency directly in torque calculation. Instead, it rushes through to determine the harmonic frequency component first, then uses this component to calculate the torque reference value, thereby avoiding the phase shift problem and its harmful effects on inverter lifetime.
2Measurement precision
If low pass filtering is applied to estimated mechanical frequency, then noise is reduced, but phase shift between estimated and actual mechanical frequency occurs
Solution Approach 1:
The patent extracts the harmonic frequency component from the estimated mechanical frequency using low pass filtering. By taking out this specific component and using it directly for torque reference calculation, the method preserves the phase information while still benefiting from the noise reduction effect of filtering.
Solution Approach 2:
The patent uses the harmonic frequency component as an intermediary between the estimated mechanical frequency and the torque reference value. This intermediary allows the system to use the filtered frequency information without suffering from the phase shift that would occur if the entire estimated frequency were used directly.
3Reliability
If harmonic frequency component is maintained in torque, then power requirements increase, but this also requires additional power due to motor inductance
Solution Approach 1:
The patent converts the harmful effect of maintaining harmonic frequency component in torque (increased power requirements) into a benefit. By using the harmonic frequency component to calculate the torque reference value, the system eliminates the need for additional power compensation, as the harmonic component is already accounted for in the torque calculation.
Data Source
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AI summary
A method for operating an inverter (20) for driving a generator (22) is described. The inverter (20) comprises a DC-link (24) having a DC-link capacitor (26) and the inverter (20) being configured for converting a three-phase AC voltage (Uu, Uv, Uw) generated by the generator (22) into a DC-link voltage to be applied to the DC-link capacitor (26). The method comprises: receiving a power reference value (PREF) which is representative of a power to be provided by the generator (22); determining an estimated mechanical frequency (ΩEST) of the generator (22); determining a harmonic component (ΩH,EST) of the estimated mechanical frequency (ΩEST); determining a torque reference value (TREF) depending on the power reference value (PREF) and the determined harmonic component, wherein the torque reference (TREF) is representative of a torque to be generated by the generator (22); generating a switching signal (SWS) for the inverter (20) depending on the determined torque reference value (TREF); and operating the inverter (20) by supplying the switching signal (SWS) to the inverter (20).