A Hybrid PWM-Based DC-Link Voltage Balancing Algorithm for a Three-Level NPC DC/AC Traction Inverter Drive

Abstract

This paper presents a hybrid pulse-width modulation (H-PWM) technique, for a 3-level neutral point clamped (NPC) electric vehicle (EV) traction inverter drive. The proposed strategy depicts the advantages of both classic space-vector pulsewidth modulations (SV-PWM) as well as carrier-based PWM.The duty-cycles for the traction inverter switches are calculated using carrier-based PWM, to reduce the computational time and control complexity of the system. The redundancies of the switching states are then used to balance the 2 DC-link capacitor voltages, similar to the SV-PWM based strategy. The proposed scheme is capable of maintaining the difference between the 2 DC-link capacitor voltages for a wider range of machine speedtorque variations. Furthermore, a single carrier is used for PWM, instead of multiple carriers, which further reduces computational complexity. A detailed comparative study is carried out, to prove the performance difference between the low switching loss-based SV-PWM techniques, which is previously proposed by authors and the present proposed hybrid-PWM strategy. In addition, total harmonic distortion of voltage and current (%THD v,i ), duty-cycles of the switches, total inverter power loss as well as DC-link voltage balancing capabilities are also compared. The balancing ability of the proposed strategy by changing the neutral point potential control is also demonstrated. Detailed simulation and experimental studies are carried out to prove the performance of the proposed control strategy with a 6.0 kW, surface-mounted permanent magnet synchronous machine (SPMSM). Simulation and experimental test results prove the desired performance of the proposed scheme.

Analysis of disturbing effect of 3 kV DC supplied traction vehicles equipped with two-level and three-level VSI on railway signalling track circuits

“…23, presents a comparison between the I cat spectra for both solutions with limits recalculated for 4 and 8 drives operating in parallel in one EMU. It can be observed that changing the solution from 'SOL1' into 'SOL2' maintains the operating point (M1,f fal -unchanged), but the fulfils limits recalculated even for the 8 …”

“…The techniques of neutral point voltage balancing in multilevel inverters are described in literature for both PWM [8] and SHE [7] modulations. However, this article does not present balancing techniques due to the fact that their influence on generated harmonics is outside of the scope of this paper.…”

“…3b). This solution requires an additional modification of modulation to eliminate the neutral point voltage fluctuations [5,7,8]. …”

FPGA-Based Controller for a Permanent-Magnet Synchronous Motor Drive Based on a Four-Level Active-Clamped DC-AC Converter

“…It is noteworthy that [8,9] state that the modulation scheme used here cannot work properly with dynamic loads such as motors, because the converter would not be able to keep the capacitor-voltage fluctuations low, leading to a system instability. This modulation is implemented here together with the VBC to drive a PMSM, demonstrating the feasibility of the proposed controller for motor-drive applications.…”

PWM strategy with harmonics injection and modulated frequency triangular carrier. A review

“…With space vector based hybrid PWM techniques is possible to reduce the current ripple [2]. Other way could be using a hybrid method combining both the generated-carrier-based PWM and the space-vector-based hybrid PWM [3].…”