Space Phasor Based Hysteresis Controller Research Articles

Fractal Approach Based Simplified and Generalized Sector Detection in Current Error Space Phasor Based Hysteresis Controller Applied to Multilevel Front-End Converters

The current error space phasor (CESP) based hysteresis controller employed for front-end converter requires two (inner and outer) hysteresis bands for vector selection and sector detection, respectively. As a result of this, the CESP moves out of the fixed (hexagonal) inner boundary many times in one fundamental cycle (and touches outer hysteresis band) to detect appropriate sector. This distorts the supply current waveform and increases the implementation complexity. To provide effective solution to the said issue, in this article, a fractal approach with a triangularization technique is proposed and analyzed to eliminate the outer hysteresis band and lookup table for sector change detection. The novelty proposed in this article is the integration of the fractal approach to CESP-based hysteresis controller, which reduces the complexity of the implementation of CESP-based hysteresis controller for any general multilevel front-end converter. The detailed analysis of the proposed technique for sector detections is presented considering the voltage space phasor structure of three-level and five-level converters. A generalized flowchart for any multilevel converter employing CESP-based hysteresis controller with proposed sector detection technique is developed and presented. Laboratory prototype is developed for a three-level flying capacitor front-end converter with an effective capacitor voltage balancing scheme. The experimental results are presented to validate the effectiveness of the proposed current controller in terms of unity power factor and low harmonic distortion in the line current under various practical conditions.

Current Controller for Multi-level Front-end Converter and Its Digital Implementation Considerations on Three-level Flying Capacitor Topology

This paper presents behaviour analysis and digital implementation of current error space phasor based hysteresis controller applied to three-phase three-level flying capacitor converter as front-end topology. The controller is self-adaptive in nature, and takes the converter from three-level to two-level mode of operation and vice versa, following various trajectories of sector change with the change in reference dc-link voltage demanded by the load. It keeps current error space phasor within the prescribed hexagonal boundary. During the contingencies, the proposed controller takes the converter in over modulation mode to meet the load demand, and once the need is satisfied, controller brings back the converter in normal operating range. Simulation results are presented to validate behaviour of controller to meet the said contingencies. Unity power factor is assured by proposed controller with low current harmonic distortion satisfying limits prescribed in IEEE 519-2014. Proposed controller is implemented using TMS320LF2407 16-bit fixed-point digital signal processor. Detailed analysis of numerical format to avoid overflow of sensed variables in processor, and per-unit model implementation in software are discussed and hardware results are presented at various stages of signal conditioning to validate the experimental setup. Control logic for the generation of reference currents is implemented in TMS320LF2407A using assembly language and experimental results are also presented for the same.

Power quality-improved front-end converter employing space phasor-based current control technique

This paper presents analysis of two-level front-end converter employing current error space phasor-based hysteresis controller. In general, for such current controllers with inner and outer bands, the current error space phasor moves out of inner boundary six times in fundamental cycle for sector change detection. This deteriorates shape of line current waveform. In the proposed work, sector change detection logic is developed and implemented, which uses information of instantaneous values of three line voltages. It does not demand outer hysteresis band and lookup table to detect sector changeovers. This results in improvement in waveshape of line current. Proposed controller is also tested with different dynamic conditions like load variation, overmodulation, reverse power flow and line side variations, and the results of unity power factor and low total harmonic distortion in supply side current are presented. Conventional hysteresis controller is implemented using TMS320LF2407A DSP processor, and the results are discussed for unity power factor.

A Rotor Flux Estimation During Zero and Active Vector Periods Using Current Error Space Vector From a Hysteresis Controller for a Sensorless Vector Control of IM Drive

This paper proposes a sensorless vector control scheme for general-purpose induction motor drives using the current error space phasor-based hysteresis controller. In this paper, a new technique for sensorless operation is developed to estimate rotor voltage and hence rotor flux position using the stator current error during zero-voltage space vectors. It gives a comparable performance with the vector control drive using sensors especially at a very low speed of operation (less than 1 Hz). Since no voltage sensing is made, the dead-time effect and loss of accuracy in voltage sensing at low speed are avoided here, with the inherent advantages of the current error space phasor-based hysteresis controller. However, appropriate device on-state drops are compensated to achieve a steady-state operation up to less than 1 Hz. Moreover, using a parabolic boundary for current error, the switching frequency of the inverter can be maintained constant for the entire operating speed range. Simple σLs estimation is proposed, and the parameter sensitivity of the control scheme to changes in stator resistance, Rs is also investigated in this paper. Extensive experimental results are shown at speeds less than 1 Hz to verify the proposed concept. The same control scheme is further extended from less than 1 Hz to rated 50 Hz six-step operation of the inverter. Here, the magnetic saturation is ignored in the control scheme.

Novel Current Error Space Phasor Based Hysteresis Controller Using Parabolic Bands for Control of Switching Frequency Variations

A current error space phasor based simple hysteresis controller is proposed in this paper to control the switching frequency variation in two-level pulsewidth-modulation (PWM) inverter-fed induction motor (IM) drives. A parabolic boundary for the current error space phasor is suggested for the first time to obtain the switching frequency spectrum for output voltage with hysteresis controller similar to the constant switching frequency voltage-controlled space vector PWM-based IM drive. A novel concept of online variation of this parabolic boundary, which depends on the operating speed of motor, is presented. A generalized technique that determines the set of unique parabolic boundaries for a two-level inverter feeding any given induction motor is described. The sector change logic is self-adaptive and is capable of taking the drive up to the six-step mode if needed. Steady-state and transient performance of proposed controller is experimentally verified on a 3.7-kW IM drive in the entire speed range. Close resemblance of the simulation and experimental results is shown