DC Current Harmonics Research Articles

DC Current Harmonics Reduction in Multi-Inverter Topology

This letter presents a Space Vector Pulse Width Modulation (SVPWM) strategy for reducing the DC-link current harmonics in a multi– Voltage Source Inverter (VSI) topology with common DC-link bus. The DC current harmonic reduction is achieved by phase-shifting the PWM pattern of individual VSIs, with the inverters sharing the system total power. Simulation and experimental results are shown to validate the proposal.

Improved Speed Sensorless Vector Control Algorithm of Induction Motor Based on Long Cable

In many applications, especially electrical submersible pump required remote operation of inverter via a long motor cable. The conventional control algorithm of induction motor (IM) didn’t operate effectively, which ignored the influence of the cable length, and didn’t consider the effect of long cable distribution parameters. A speed sensor technique was also difficult to achieve. In this paper, an improved speed sensorless vector control algorithm (ISSVCA) for IM based on long cable was proposed. Based on the analysis of long cable motor drive system of the inverter, the two-port π network model of the long cable was established. The functional relationship between the voltage/current parameters of the two ports of the long cable and the cable distribution parameters was deduced. The function expression was transformed to the α − β stationary reference frame, the accurate motor terminal voltage/current was calculated, so that the flux model was constructed to realize the observation of the flux, accurate velocity identification, and closed-loop control of the torque, flux and current. Simulation and experimental results showed that the proposed ISSVCA based on long cable increased the starting electromagnetic torque, decreased speed dip and speed recovery time caused by sudden loads, reduced the DC current harmonics, and had good dynamic and static characteristics.

Hybrid Energy Storage System Microgrids Integration for Power Quality Improvement Using Four-Leg Three-Level NPC Inverter and Second-Order Sliding Mode Control

Rising demand for distributed generation based on renewable energy sources (RES) has led to several issues in the operation of utility grids. The microgrid is a promising solution to solve these problems. A dedicated energy storage system could contribute to a better integration of RES into the microgrid by smoothing the renewable resource's intermittency, improving the quality of the injected power and enabling additional services like voltage and frequency regulation. However, due to energy/power technological limitations, it is often necessary to use hybrid energy storage systems (HESS). In this paper, a second-order sliding mode controller is proposed for the power flow control of a HESS, using a four-leg three-level neutral-point-clamped (4-Leg 3L-NPC) inverter as the only interface between the RES/HESS and the microgrid. A 3-D space vector modulation and a sequence-decomposition-based ac-side control allow the inverter to work in unbalanced load conditions while maintaining a balanced ac voltage at the point of common coupling. DC current harmonics caused by unbalanced load and the NPC floating middle point voltage, together with the power division limits, are carefully addressed in this paper. The effectiveness of the proposed technique for the HESS power flow control is compared to a classical PI control scheme and is proven through simulations and experimentally using a 4-Leg 3L-NPC prototype on a test bench.

Impedance-Based Stability Analysis of MVDC Systems Using Generator-Thyristor Units and DTC Motor Drives

This paper develops a generalized ac impedance model for synchronous generators and then a dc impedance model for generator-thyristor systems. The impedance model of a medium voltage dc (MVdc) system is built for impedance-based stability and harmonics analysis. DC current harmonics from a high-power neutral point clamped (NPC) direct torque control (DTC) motor drive is examined. It is found that dc network resonance is a major cause of dc current harmonics amplification and propagation in MVdc systems. As a result, adding a dc side input filter can attenuate current harmonics from NPC DTC drives. Three criteria to design the dc-side filter are deduced from the impedance analysis. The effectiveness of the design criteria is tested and verified by time-domain simulations.

Parasitics-Assisted Soft-Switching and Secondary Modulated Snubberless Clamping Current-Fed Bidirectional Voltage Doubler for Fuel Cell Vehicles

A current-fed full-bridge bidirectional voltage doubler with secondary-assisted device voltage clamping and zero-current commutation (ZCC) is proposed for fuel cell vehicles (FCVs). The proposed topology is suitable for interfacing energy storage and/or fuel cell stack with a dc bus in FCVs. A voltage doubler on the secondary side is selected to enhance the gain by 2 $\times$ , reduce transformer size, and efficiently reduce the low-frequency dc current harmonics. Parasitics-based zero-voltage switching (ZVS), secondary-based zero-current switching of low-voltage-side devices, and ZVS of secondary devices are achieved. The proposed secondary modulation technique naturally clamps the voltage across the primary-side devices with ZCC, thus eliminating the necessity for traditional active-clamp or passive snubbers. Switching losses are reduced, owing to the soft-switching of all semiconductor devices. Steady-state analysis and design are studied and explained. The experimental results of a 1-kW proof-of-concept hardware prototype are shown to demonstrate the performance and confirm the proposed claims.

Measurement and Characterization of Harmonics on the Taipei MRT DC System

The harmonics of the propulsion power supply system on the Taipei Mass Rapid Transit System (TMRTS) are characterized. This study applies a new measurement method based on the railway magnetic field measurement technique, to record the dc current harmonics of the TMRT system under various operating conditions. Analysis of the data obtained through these field measurements reveals the presence of both typical and atypical harmonics while the trains are running. The monitored information from the TMRTS during dynamic operation helps engineers (planners) to identify how many orders and levels of harmonics may be present.

Steady-state model of direct connected generator–HVdc converter units in the harmonic domain

A new twelve-pulse unit connection model is formulated and solved in the harmonic domain. The model takes into account the effects of generator saliency and saturation, interaction of the converter with the DC system, and variation in the firing and end of commutation angles caused by AC voltage and DC current harmonics. The reactive power control by generator excitation in the absence of converter transformer on-load tap-changers is also modelled. The solution of a test system is validated by means of time domain simulations.

A Newton solution for the harmonic phasor analysis of AC/DC converters

The steady state equations that describe the power converter and DC system in the harmonic domain are solved by means of Newton's method, in a manner suitable for embedding in an iterative harmonic analysis of the complete power system. The solution includes the interaction of the power converter with the DC system, and the effect of variation in the firing and end of commutation angles caused by AC voltage and DC current harmonics. The convergence of Newton's method is investigated, and methods for accelerating the solution are implemented. Finally, the solution obtained is validated by means of time domain simulation.