Gopal Mondal

A Reduced-Switch-Count Five-Level Inverter With Common-Mode Voltage Elimination for an Open-End Winding Induction Motor Drive

The paper presents a five-level inverter scheme with reduced power circuit complexity for an induction motor drive. The scheme is realized by cascading conventional two-level and three-level neutral point clamped inverters in conjunction with an open-end winding three-phase induction motor drive. An inverter control scheme with common-mode voltage (CMV) elimination, along with a simple DC link voltage control, is developed by using only switching states with zero CMV for the entire modulation range. Theoretical considerations are experimentally verified for a variety of operating conditions.

A Dual Seven-Level Inverter Supply for an Open-End Winding Induction Motor Drive

This paper develops a seven-level inverter structure for open-end winding induction motor drives. The inverter supply is realized by cascading four two-level and two three-level neutral-point-clamped inverters. The inverter control is designed in such a way that the common-mode voltage (CMV) is eliminated. DC-link capacitor voltage balancing is also achieved by using only the switching-state redundancies. The proposed power circuit structure is modular and therefore suitable for fault-tolerant applications. By appropriately isolating some of the inverters, the drive can be operated during fault conditions in a five-level or a three-level inverter mode, with preserved CMV elimination and DC-link capacitor voltage balancing, within a reduced modulation range.

Twelve-Sided Polygonal Voltage Space Vector Based Multilevel Inverter for an Induction Motor Drive With Common-Mode Voltage Elimination

In this paper, a 12-sided polygonal voltage space vector generation with common-mode voltage elimination (CME) is proposed for an induction motor drive. An open-end winding configuration is used for the motor. The proposed multilevel structure is achieved by cascading only the conventional two-level inverters with asymmetrical dc link voltages. By appropriately selecting the voltage vectors with identical common-mode voltage from the opposite ends, a pulsewidth modulation (PWM) strategy with zero common-mode voltage variation can be achieved for the entire modulation range with a common dc link requirement for both the inverter systems. Along with the CME, the proposed 12-sided polygonal space vector based multilevel inverter structure has increased modulation range with the absence of 5th, 7th, 17th, 19th, etc., harmonics up to 12-step operation. The bandwidth problems associated with conventional hexagonal voltage space vector structure current controllers due to the presence of 5th and 7th harmonics in the overmodulation region are absent in the present 12-sided structure. So a simple PWM voltage control with linear voltage control up to 12-step operation is possible from the present 12-sided scheme with less current control complexity.

Experimental implementation of a multilevel converter for power system integration

This paper presents an overview of a modular, multi-cellular converter for flexible power management of future electricity networks. The proposed converter is capable of connecting asynchronous grids together as well as incorporating renewable energy systems into the grid and improving power quality. Target applications are expected to be at power levels of around 10MW and at a system voltage of 10–30kV. The prototype described in this paper is rated at 300kVA. The concept of the modular converter is presented along with an outline of its construction. Verification of the control methods for the converter structure is provided by initial experimental results from the prototype converter connected between two low voltage grid systems.

Construction and Testing of the 3.3 kV, 300 kVA UNIFLEX-PM Prototype

Summary This paper presents details of the experimental implementation of a prototype multi-cellular converter for application in future electricity supply networks. Such a converter is capable of independently controlling power flow between various parts of an electricity grid, interfacing renewable energy systems directly into the grid and connecting grids of different voltages and frequency. An outline of the challenges for converter construction are presented as well as experimental results for the converter operating at 300kVA whilst connected between two 3.3 kV grids.

A five-level inverter scheme with common-mode voltage elimination by cascading conventional two-level and three-level NPC inverters for an induction motor drive

Common-mode voltage generated by the PWM inverter causes shaft voltage, bearing current and ground leakage current in induction motor drive system, resulting in an early motor failure. This paper presents a common-mode elimination scheme for a five-level inverter with reduced power circuit complexity. The proposed scheme is realised by cascading conventional two-level and conventional NPC three-level inverters in conjunction with an open-end winding three-phase induction motor drive and the common-mode voltage (CMV) elimination is achieved by using only switching states that result in zero CMV, for the entire modulation range.

Control Challenges and Solutions for a Multi-cellular Converter for Use in Electricity Networks

Summary This paper presents the concept of a multi-cellular power converter structure targeted towards use in future electricity networks. Control of such a converter is challenging because of the distributed energy storage intrinsic to the concept. If the energy flow through the converter is not carefully controlled poor performance and even shutdown of the converter may result. This paper details the operation of such a converter and presents an example of a control scheme which can achieve the desired performance. Validations of the converter concept and the control principles are provided by experimental results at low voltage using a two port prototype.

Multilevel Inverter with 18-sided Polygonal Voltage Space Vector for an Open-end Winding Induction Motor Drive

A simple multilevel inverter scheme with 18-sided polygonal voltage space vector structure is proposed for an induction motor drive with an open-end winding configuration. The motor is fed from one end with a conventional two-level inverter and from the other end with a three level inverter, realised by cascading two conventional two-level inverters. The inverters are fed with asymmetrical DC link voltages. A simple linear PWM control scheme up to 18-step mode is proposed, based only on the motor reference phase amplitudes. The present scheme does not require complicated signal processing and control loop, as in the case of PWM scheme with conventional hexagonal voltage space vector structure, in over modulation regions. The proposed scheme gives and increased modulation range with the elimination of 5th 7th 11th and 13th order harmonics, when compared to any conventional schemes.

A Multilevel inverter with hexagonal and 12-sided polygonal space vector structure for induction motor drive

This paper proposes a multilevel inverter which produces hexagonal voltage space vector structure in lower modulation region and a 12-sided polygonal space vector structure in the over-modulation region. Normal conventional multilevel inverter produces 6nplusmn1 (n=odd) harmonics in the phase voltage during over-modulation and in the extreme square wave mode operation. However, this inverter produces a 12-sided polygonal space vector location leading to the elimination of 6nplusmn1 (n=odd) harmonics in over-modulation region extending to a final 12-step mode operation. The inverter consists of three conventional cascaded two level inverters with asymmetric dc bus voltages. The switching frequency of individual inverters is kept low throughout the modulation index. In the low speed region, hexagonal space phasor based PWM scheme and in the higher modulation region, 12-sided polygonal voltage space vector structure is used. Experimental results presented in this paper shows that the proposed converter is suitable for high power applications because of low harmonic distortion and low switching losses.

A DC-Link Capacitor Voltage Balancing with CMV Elimination Using Only the Switching State Redundancies for a Reduced Switch Count Multi-Level Inverter Fed IM Drive

Abstract Common mode voltage (CMV) variations in PWM inverter-fed drives generate unwanted shaft and bearing current resulting in early motor failure. Multilevel inverters reduce this problem to some extent, with higher number of levels. But the complexity of the power circuit increases with an increase in the number of inverter voltage levels. In this paper a five-level inverter structure is proposed for open-end winding induction motor (IM) drives, by cascading only two conventional two-level and three-level inverters, with the elimination of the common mode voltage over the entire modulation range. The DC link power supply requirement is also optimized by means of DC link capacitor voltage balancing, with PWM control, using only inverter switching state redundancies. The proposed power circuit gives a simple power bus structure.