Predictive Load Angle and Stator Flux Control of SynRM Drives for the Full Speed Range
Nowadays, several types of electric motors are utilized in industrial applications, namely induction motors (IMs), permanent magnet synchronous motors (PMSMs) and synchronous reluctance motors (SynRMs). Owing to the high cost of PMSMs and due to the rotor losses of IMs, SynRMs can be considered an i...
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| Formato: | doctoralThesis |
| Idioma: | eng |
| Publicado em: |
2020
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| Texto completo: | http://hdl.handle.net/10400.19/6150 http://hdl.handle.net/10316/87350 |
| País: | Portugal |
| Oai: | oai:repositorio.ipv.pt:10400.19/6150 |
| Resumo: | Nowadays, several types of electric motors are utilized in industrial applications, namely induction motors (IMs), permanent magnet synchronous motors (PMSMs) and synchronous reluctance motors (SynRMs). Owing to the high cost of PMSMs and due to the rotor losses of IMs, SynRMs can be considered an ideal choice for some applications. These motors have a simple structure, are robust, and have a low cost due to the absence of permanent magnets or windings in the rotor. To exploit the advantages of SynRM drives, an adequate control strategy is essential. In recent times, due to the development of fast and cheap microprocessors and FPGAs, the category of control strategies known as finite control set model predictive control (FCS-MPC) has attracted significant attention in both academia and industry. FCS-MPC has as main advantages, an intuitive and simple implementation, very fast dynamic response and the ability to tackle several constraints in a straightforward manner. Due to these advantages, it can be considered an ideal alternative to field-oriented control (FOC) and direct torque control (DTC) in high performance motor drives. In spite of its advantages, FCS-MPC has been barely proposed for the control of SynRM drives, especially if we consider that some applications require the drive system to operate in the full speed range. This thesis proposes three different FCS-MPC control strategies for high-performance SynRM drives. The first two control strategies combine the concepts of active flux and torque control in order to operate the SynRM in the constant torque region. The first control strategy, baptized as predictive active flux and torque control (PAFTC), regulates the active flux and the electromagnetic torque of the SynRM in an independent manner. It follows the standard implementation steps of FCS-MPC, namely by predicting the values of the state variables for all possible switching states of the inverter, and by using a cost function with a weighting factor which needs to be tuned. A second control approach, known as simplified PAFTC (S-PAFTC), is a simplified version of the PAFTC in the sense that the predictions of the state variables are replaced by the calculation of an equivalent reference voltage, performed only once in a sampling period. This procedure leads to a smaller computational time, when the control strategy is implemented in a digital control platform, and to the use of a cost function without any weighting factor, overcoming one of the challenging tasks in classical FCS-MPC strategies which is the choice of the optimal value(s) for the weighting factor(s). The simulation and experimental results obtained with these control strategies demonstrate the very good steady-state and dynamic response of the SynRM drive in the constant torque region. With the aim to safely operate the SynRM drive in the full speed range, while ensuring at the same time the exploitation of all its potentialities and limits, including its operation with optimal efficiency, a third control strategy, known as predictive load angle and stator flux control (PLASFC), is proposed for SynRM drives. The PLASFC, implemented in a stator flux reference frame, regulates the stator flux and the load angle of the SynRM in an independent manner. While the stator flux regulation is straightforward, the torque is regulated indirectly by controlling the load angle, bringing benefits in terms of a smooth transition between the different motor operating regions. Similarly to the S-PAFTC strategy, an equivalent reference voltage is calculated instead of predicting the values of the motor state variables for all possible switching states of the inverter, and the cost function does not include any weighting factor. In the PLASFC strategy, the SynRM is easily operated in the full speed range: constant torque region (including zero speed), constant power region and constant load angle region, the last two being part of what is usually known as field-weakening (FW) region. With this control strategy, the voltage, current and load angle limits are easily exploited by simple mathematical relations and saturation blocks. In addition, a loss minimization algorithm is developed and incorporated in this control strategy thus allowing to operate the SynRM with minimum copper losses for a given load torque. Furthermore, to improve the performance of the control system, some parameters namely the motor apparent inductances, are estimated online. Several simulation and experimental results presented demonstrate the excellent steady-state and dynamic performance of the SynRM drive when operating with the PLASFC strategy, thus clearly demonstrating the benefits of using FCS-MPC strategies in the field of electric drives in general and SynRM drives in particular. |
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