Distribution Of Switching Losses Research Articles

Modified Modulation Strategy of 1: 1: 2 Asymmetric Nine-Level Inverter and Its Power Balance Method

The three unit nine-level inverter can output more voltage levels with fewer h-bridge units, while having better output waveform quality. However, in the conventional hybrid frequency modulation strategy, only one low-voltage unit adopts pulse width modulation (PWM), which causes the problem of switching loss and uneven heat distribution between the two low-voltage units. At the same time, the output power of the conventional modulation strategy is unbalanced. Aiming to resolve the above problems, a modified hybrid modulation strategy and a power balance control method under the strategy is proposed in this paper. The modulation strategy achieves output power balance between the three units and an even distribution of switching losses between the two low voltage units while maintaining the same output power quality. Simulation and experimental results verify the feasibility of the modulation strategy.

Discontinuous Hybrid-PWM-Based DC-Link Voltage Balancing Algorithm for a Three-Level Neutral-Point-Clamped (NPC) Traction Inverter Drive

This paper presents a hybrid pulse width modulation-based discontinuous modulation (D-HPWM) strategy with dc-link voltage balancing for a three-level neutral-point-clamped (NPC) traction inverter drive. The results are then compared with continuous-hybrid-PWM (C-HPWM) to check the performance improvement. The HPWM strategy uses both the advantages of carrier- and space-vector-based PWM strategies. The duty cycles are generated using the carrier-based strategy to reduce the computational time and complexity of the system and redundant vector states are used to keep the two dc-link capacitor voltages balanced. As discontinuous PWM (DPWM) reduces the switching losses considerably compared to the continuous PWM, the DPWM strategy is developed in this paper for the HPWM-based strategy. Detailed comparison studies are then carried out in MATLAB/Simulink and PLECS to show the conduction and switching loss distribution with change in modulation index for different power switches. A 54.0-kW surface permanent magnet synchronous machine (PMSM) is used for this simulation studies. Moreover, the total inverter loss and losses in each insulated gate bipolar transistor (IGBT) are also compared. Detailed experimental performance analysis is also carried out with a scaled down prototype of a 6.0-kW surface PMSM, NPC inverter, and real-time emulator DSpace, to show the capacitor voltage deviation with both control strategies.

Optimal Low-Switching Frequency Pulsewidth Modulation of Medium Voltage Seven-Level Cascade-5/3H Inverter

Low-switching frequency modulation of multilevel inverters for medium-voltage high-power industrial ac drives is essential to reduce switching losses and, thus, improve the overall energy efficiency of the system. However, minimizing the switching frequency increases the total harmonic distortion (THD) of machine currents. Synchronous optimal pulsewidth modulation (SOP) is an emerging technique for controlling multilevel inverters at low-switching frequency without compromising on the THD of machine currents. The goal of our experiment was to implement SOP technique for controlling seven-level cascade inverter for an induction motor drive at an average device switching frequency limited to rated fundamental frequency. First, optimal seven-level waveforms were obtained by ofline optimization assuming steady-state operating conditions. Then, the switching angles for each semiconductor device were obtained that ensure equal distribution of switching losses as well as minimal unbalance in dc-link capacitor voltages. The proposed SOP technique is validated by experimental results obtained from the seven-level cascade inverter feeding a 1.5-kW induction motor.