Manish Pande

DC-Link Current Minimization for High-Power Current-Source Motor Drives

In this paper, a loss reduction and DC link current minimization strategy for a high power current source inverter (CSI) fed drive is proposed. The proposed strategy consists of an inverter maximum modulation index control scheme and a flux optimization algorithm. Specifically, in the inverter modulation index control, the CSI modulation index is kept at the maximum value while the current source rectifier (CSR) is used to regulate a reduced variable DC link current and therefore to control the motor current magnitude. This control scheme can effectively reduce the dc link current and at the same time improve the line side and motor side harmonics. On the other hand, for the optimized flux control, the relationship between the rotor flux and the dc link current is first thoroughly investigated. Based on this analysis, the DC link current from the maximum inverter modulation index control can be further minimized by optimizing the rotor flux according to system variables such as the motor speed, the applied torque and the motor side capacitor size. With the proposed dc current minimization strategy, the drive current rating, semiconductor device losses and the drivepsilas DC link losses can be reduced. Both simulation and experimental results on a 4.16 kV 600 hp CSI fed drive system are obtained to verify the effectiveness of the proposed strategy.

An Input Power Factor Control Strategy for High-Power Current-Source Induction Motor Drive With Active Front-End

This paper proposes an input power factor control strategy for a current-source drive with active front-end. The proposed strategy is realized without modification of the drives pulsewidth modulation and speed control schemes through the collaborative use of two methods: a modulation index regulation method and a flux adjustment method. Specifically, the modulation index regulation method functions to directly control the dc-link current and voltage, and it can effectively correct a leading input power factor as long as the space vector modulation is used for the inverter. On the other hand, the flux adjustment method can improve the power factor when the power factor is lagging or when the selective harmonic elimination modulation is used for the inverter at high motor speeds. When implemented together, the two methods will complement each others functionalities and improve the overall compensation performance. Experimental results are obtained from a 600-hp and an 1100-hp drive system.

An Active Damping Method Using Inductor-Current Feedback Control for High-Power PWM Current-Source Rectifier

Due to the inductor-capacitor filter, a pulse width modulation current-source rectifier (CSR) may experience LC resonance. A smaller ratio between the switching frequency and the resonant frequency of the CSR presents a challenge in designing active resonance damping methods in high-power applications. In this paper, different feedback states of filter inductor current and capacitor voltage are investigated to damp out the LC resonances. Besides proportional capacitor-voltage feedback (CVF), the derivative inductor-current feedback (ICF) provides an alternative approach for active damping and is comprehensively analyzed. Compared with the virtual-resistance (VR)-based active damping strategy, controller design is simpler in this method. Furthermore, the active damping method is able to damp the resonance under short-circuited dc-link conditions. The ICF-based active damping strategy works well for CSRs with low switching frequencies. Simulation and experimental results verify the feasibility and validity of the method.

Power-Factor Compensation for PWM CSR–CSI-Fed High-Power Drive System Using Flux Adjustment

This paper presents a novel power-factor (PF) control strategy for a high-power pulsewidth-modulated current-source rectifier-current-source inverter-fed motor drive system. The PF regulation is realized by adjusting the motor flux in the drives field-oriented control scheme. The relationship between the motor flux and the drives input reactive power is first investigated. Based on this analysis, a flux-adjustment PF regulation scheme is proposed. The proposed PF regulation method, together with a properly designed input line capacitor, can ensure a unity PF throughout the whole speed range (including flux-weakening range). Furthermore, unlike all the other PF compensation techniques, the proposed flux-adjustment approach does not require online modulation index control of the rectifier and the inverter, and therefore, offline selective harmonic elimination modulation can be implemented on both the rectifier and the inverter to minimize the line-side and motor-side waveform distortions. Medium-voltage simulation results and experimental results from a low-voltage 30-hp induction motor drive are provided to verify the effectiveness of the PF correction strategy.

Medium-Voltage Current-Source Converter Drives for Marine Propulsion System Using a Dual-Winding Synchronous Machine

Medium-voltage (MV) drives are increasingly used in high-power marine applications for running thrusters and main propulsion motors. In this paper, an MV drive solution employing active front-end current-source converters is proposed for a synchronous-motor-based propulsion system. The proposed solution includes two independent drives, each to control one of the two sets of three-phase windings of the synchronous motor. A dedicated communication link between the drives allows continuous load sharing and robust system operation in a master-follower drive configuration. Field-oriented control with the use of an absolute encoder is implemented for providing high starting torque and smooth speed control over a wide speed range including a 30% overspeed region. The major advantages of the proposed solution include simple structure, increased system power rating, redundant operation, low-harmonic input/output waveforms, improved reliability, elimination of a bulky input isolation transformer, and parallel drive control without the need of a complex coordinated inverter gating system. In addition, the system offers input power factor compensation and dynamic braking to allow operation on a generator-based supply system. Field test results obtained on a 14-MW ship propulsion system are provided to demonstrate the system performance.

System Design of Adjustable Speed Drives, Part 2: System Simulation and ac Line Interactions

Part 1 of System Design of Adjustable Speed Drives [1] investigated the second-order effects that occur as interactions between adjustable speed drives (ASDs) and system-connected equipment, specifically with regard to commonmode (CM) voltage and ground noise current injected in the system and differential-mode (DM) voltage spikes on the load due to ASD semiconductor switching [1]. This article (Part 2) continues the investigation by proposing high-frequency ASDs, cable, and motor models used in system simulation to identify and mitigate the complex DM or CM injected. Theoretical component models were bridged with field experience to simulate and resolve a practical low-voltage (LV) field example of parallel high horsepower inverters having instantaneous overcurrent (IOC) trip issues due to circulating CM currents between inverters and ground. Component models are also used in a system electromagnetic interference (EMI) simulation example of a power structure, which induced line-to-ground noise current in an industrial plant ground grid.

DC link current minimization for high power current source motor drives

In this paper, a loss reduction and DC-link current minimization strategy for a high-power current-source inverter (CSI) fed drive is proposed. The proposed strategy consists of an inverter maximum modulation index control scheme and a flux optimization algorithm. Specifically, in the inverter modulation index control, the CSI modulation index is kept at the maximum value while the current-source rectifier (CSR) is used to regulate a reduced variable DC-link current, and therefore, to control the motor current magnitude. This control scheme can effectively reduce the DC-link current, and at the same time, improve the line-side and motor-side waveforms. On the other hand, for the optimized flux control, the relationship between the rotor flux and the DC-link current is first investigated thoroughly. Based on this analysis, the DC-link current from the maximum inverter modulation index control can be minimized further by optimizing the rotor flux according to system variables such as the motor speed, the applied torque, and the motor-side capacitor size. With the proposed dc current minimization strategy, the losses in the semiconductor devices and the DC-link can be reduced, and the drive current rating could be lowered. Both simulation and experimental results on a 4.16-kV 600-hp CSI-fed drive system are obtained to verify the effectiveness of the proposed strategy.

System Design of Adjustable Speed Drives, Part 1: Equipment and Load Interactions

The solid-state power converter markets are rapidly increasing due to the push for improved energy efficiency and reduced impact on the environment, using alternative and distributed energy generation. Power converters have a high growth opportunity, irrespective of low-voltage (LV) or medium-voltage (MV) technology. To meet these market expectations, designers and application specialists are forced to address both well-known and new technical hurdles.

Zero-Speed Operation of High-Power PWM Current-Source-Inverter-Fed Induction Motor Drive

Most research work in current-source inverter (CSI) fed motor drives has focused on general control strategies, pulsewidth modulation schemes, topologies, and efficiency evaluation. This paper, however, is dedicated to investigating zero-speed operation characteristics of CSI-fed induction motor drives (IMDs). Zero-speed operation can greatly increase the competitive value of the drive and expand its range of applications to include cranes, hoists, and draglines. The motor drive is controlled with rotor flux orientation, where stator currents and motor speed are employed for the rotor flux estimation. Unlike voltage-source-inverter-based drives, filter capacitors are required at the output of the CSI for current commutation and harmonics filtering. The influence of these capacitors on the system dynamic performance is comprehensively evaluated. Moreover, a classic load torque observer with feedforward control is employed to improve the speed dynamic response. Simulated and experimental results show that the CSI-fed IMD works well at zero speed with promising speed dynamic performance.

Inductor current feedback control based active damping for high power PWM current source rectifier

Due to the inductor-capacitor filter, a pulse width modulation (PWM) current-source rectifier (CSR) may experience LC resonance. A smaller ratio between the switching frequency and the resonant frequency of the CSR presents a challenge in designing active resonance damping methods in high-power applications. In this paper, different feedback states of filter inductor current and capacitor voltage are investigated to damp out the LC resonances. Besides proportional capacitor-voltage feedback (CVF), the derivative inductor-current feedback (ICF) provides an alternative approach for active damping and is comprehensively analyzed. Compared with the virtual-resistance (VR) based active damping strategy, controller design is simpler in this method. The ICF based active damping strategy works well for current-source rectifiers with low switching frequencies. Simulation and experimental results verify the feasibility and validity of the method.