A Centralized Control Strategy for Grid-connected High-speed Switched Reluctance Motor Drive System with Power Factor Correction
Abstract : Conventionally, the converter of switched reluctance motor (SRM) is fed by the uncontrollable diode bridge rectifier (DBR), which leads to a low grid-side power factor (PF) and high current total harmonic distortion (THD). In this paper, an alternative solution for the grid-connected high-speed SRM drive system with improved PF is proposed. In the proposed drive system, the three-level active front end (AFE) is connected in cascade with the midpoint converter for SRM operation. A centralized strategy, which controls the AFE and SRM together, is proposed to govern the motor speed and grid-side PF by regulating the real power and reactive power of the system, respectively. Specifically, the real power, reactive power, and the voltage balancing of split capacitors are controlled by the model predictive directed power control (MP-DPC) algorithm, which significantly reduces the control complexity and guarantees the fast dynamic response. Consequently, satisfying speed regulation, high PF, low current THD, and bi-directional power-transfer capability are achieved. An idea-proofed testbench is constructed in laboratory, and the applicability of the proposed drive system is verified by a series of experimental results.
? In all the existing SRM drive systems with PFC, the front-end PFC converter and SRM are two independent control units.
? In those systems, the controller of the front-end PFC converter takes charge of the regulation of the grid-side PF and THD, and the controller of SRM takes charge of the regulation of the speed.
? The “bidirectional energy flow” has not been realized in the existing SRM drive systems with PFC. For the high-power systems, if the energy in deceleration process cannot flow back to the grid in the application scenarios that requests frequent speed adjustments (e.g., electric locomotive), the capacity of the DC-link capacitor must be large enough to absorb the feedback energy for the safety of the system, which increases system volume.
? Low power factor (PF) can result in many problems, such as enlarged power capacity, increased loss, and extra system cost. Some researches concentrate on the motor-side PF improvement of the SRM drive system.
? The grid-side PF should be corrected to improve the performance of the SRM drive system, but how to realize it with a simplified implement solution is still a problem.
? Although some methods have been researched, all of them regarded the SRM and the front end as two independent control units, which unavoidably increases the control complexity of the system.
• SRM converters need DC power for operation, so generally, it is fed by a DC power supply or by a diode bridge rectifier that takes AC source as input. Given the cost performance, the diode bridge rectifier is frequently adopted.
• Nevertheless, for the system with the diode rectifier, the performance decays due to the uncontrolled DC-link voltage and degraded power quality. Some topologies are proposed to improve the power quality of the SRM drive system.
• In, a bridgeless Zeta converter is proposed to reduce the conduction loss and to correct the grid-side PF.
• In, a single-phase boost-type switch-mode rectifier is proposed to drive the SRM.
? Proper converters should be chosen to guarantee the performance of SRM drive system.
? Besides the conventional SRM converters, the novel converters for SRM are proposed in some papers.
? Although excellent performance can be obtained, considerations should be paid to several redundant states to realize the capacitors balancing control.
? In , a Vienna-based converter is connected before the SRM converter for power factor correction (PFC).
? However, the voltage balance of DC-link capacitors, which is vital for high performance, is not taken into account.
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