Stability Analysis of Permanent Magnet Synchronous Machine with Inverter Output LC-Filter

Stabilitets Analyse af Permanent Magnet Synkron Maskine med Inverter Output LC-Filter

Vadstrup, Casper

4. term

Energy Engineering, Master

2013

2013-06-04

77

Hastighedsregulerede drivsystemer (ASD) med permanentmagnet-synkronmotorer (PMSM) bruges bredt, fordi de er energieffektive. Motorerne forsynes af pulsbredde-modulerede (PWM) invertere. Nye effektenheder baseret på materialer med stort båndgab kan tændes og slukkes meget hurtigt og muliggør høj koblingsfrekvens. Det giver dog høj dV/dt (meget hurtige spændingsændringer), som kan medføre ekstra tab, elektromagnetisk interferens (EMI) og lejestrømme. Derfor tilføjes filtre for at reducere dV/dt. Tidligere var sådanne filtre store, men højere koblingsfrekvens gør det muligt at bruge mindre filtre med højere resonansfrekvens. Da motoren dermed får mere jævn, filtreret spænding, kan filtrene potentielt øge systemets virkningsgrad. Et filter kan dog påvirke motorens regulering, så stabiliteten skal vurderes. I denne afhandling foreslås en LC-filterdesignprocedure, der reducerer dV/dt til et ønsket niveau. Induktansen og kapacitansen vælges ud fra to mål ved inverterens koblingsfrekvens: den ønskede forstærkning K (hvor meget af komponenten ved koblingsfrekvensen der slipper igennem) og strømamplituden IL af denne komponent. Designligningerne er afledt af filterets overføringsfunktion i frekvensdomænet. Simulationer af et ASD med LC-filter stemmer godt overens med ligningerne. For at styre PMSM'en blev et feltorienteret reguleringssystem (FOC) designet. Regulatorparametre blev valgt ud fra den ønskede båndbredde for strøm- og hastighedssløjferne. Da FOC kræver positionsinformation, blev en hastigheds- og positionsestimator udviklet. LC-filteret kan påvirke stabiliteten i det FOC-styrede drev, så der er gennemført en stabilitetsanalyse. Ved at simulere mange LC-filterkonfigurationer blev øvre og nedre grænser for strømregulatorens båndbredde identificeret. For at påvirke reguleringsstabiliteten mindst muligt bør K være 0,3 eller lavere med sensor og 0,2 eller lavere ved sensorløs FOC. Strømamplituder IL over 2 A gav stabilitet; IL kan være lavere, hvis K sænkes tilsvarende.

Adjustable speed drives (ASDs) that use permanent magnet synchronous machines (PMSMs) are widely used because they are efficient. These motors are powered by pulse-width-modulated (PWM) inverters. New power devices made from wide band gap materials can turn on and off very quickly and allow high switching frequencies. This also creates high dV/dt (very fast voltage changes), which can cause extra losses, electromagnetic interference (EMI), and bearing currents. Filters are therefore added to reduce dV/dt. In the past, such filters were large, but higher switching frequencies make it possible to use smaller filters with higher resonant frequencies. Because the motor then sees smoother, filtered voltages, these filters can potentially increase overall efficiency. However, adding a filter can affect how the motor is controlled, so it is important to check control stability. This thesis proposes an LC filter design procedure that reduces dV/dt to a chosen level. The inductance and capacitance are selected from two targets at the inverter’s switching frequency: the desired gain K (how much of the switching component is allowed through) and the current amplitude IL of that component. The design equations are derived from the filter’s transfer function in the frequency domain. Simulations of an ASD with the LC filter agree well with the equations. A field-oriented control (FOC) system was designed to control the PMSM. Controller parameters were set from the desired bandwidths of the current and speed control loops. Because FOC needs position information, a speed and position estimator was developed. The LC filter can influence the stability of the FOC-controlled drive, so a stability analysis was performed. By simulating many LC filter configurations, upper and lower limits for the current-control bandwidth were identified. To keep the impact on control stability small, K should be 0.3 or lower with a sensor and 0.2 or lower for sensorless FOC. Current amplitudes IL above 2 A ensured stability; IL can be lower if K is reduced accordingly.

[This abstract was generated with the help of AI]

PMSM ; Stabilitets anlyse ; dV/dt ; sensorless ; filter design ; LC-filter ; Wide band gap

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