Shift & night work – the positive impact, challenges and action to deal with it

Shift work means work that takes place on a schedule of employee outside the normal hours eight at morning until at five at evening. Well, it involves day and night shifts, which is whether in an early morning shifts, and rotating shifts. In Malaysia, shift work happens usually to the health care workers, precision production and repair workers, machines operator, and aviation workers and so on. Especially in manufacturing, employees tend to make sure machines run twenty-four hours per day rather than buying more machines to operate on a day shift

High-power converters for space applications

Phase 1 was a concept definition effort to extend space-type dc/dc converter technology to the megawatt level with a weight of less than 0.1 kg/kW (220 lb./MW). Two system designs were evaluated in Phase 1. Each design operates from a 5 kV stacked fuel cell source and provides a voltage step-up to 100 kV at 10 A for charging capacitors (100 pps at a duty cycle of 17 min on, 17 min off). Both designs use an MCT-based, full-bridge inverter, gaseous hydrogen cooling, and crowbar fault protection. The GE-CRD system uses an advanced high-voltage transformer/rectifier filter is series with a resonant tank circuit, driven by an inverter operating at 20 to 50 kHz. Output voltage is controlled through frequency and phase shift control. Fast transient response and stability is ensured via optimal control. Super-resonant operation employing MCTs provides the advantages of lossless snubbing, no turn-on switching loss, use of medium-speed diodes, and intrinsic current limiting under load-fault conditions. Estimated weight of the GE-CRD system is 88 kg (1.5 cu ft.). Efficiency of 94.4 percent and total system loss is 55.711 kW operating at 1 MW load power. The Maxwell system is based on a resonance transformer approach using a cascade of five LC resonant sections at 100 kHz. The 5 kV bus is converted to a square wave, stepped-up to a 100 kV sine wave by the LC sections, rectified, and filtered. Output voltage is controlled with a special series regulator circuit. Estimated weight of the Maxwell system is 83.8 kg (4.0 cu ft.). Efficiency is 87.2 percent and total system loss is 146.411 kW operating at 1 MW load power

Distributed control of a fault tolerant modular multilevel inverter for direct-drive wind turbine grid interfacing

Modular generator and converter topologies are being pursued for large offshore wind turbines to achieve fault tolerance and high reliability. A centralized controller presents a single critical point of failure which has prevented a truly modular and fault tolerant system from being obtained. This study analyses the inverter circuit control requirements during normal operation and grid fault ride-through, and proposes a distributed controller design to allow inverter modules to operate independently of each other. All the modules independently estimate the grid voltage magnitude and position, and the modules are synchronised together over a CAN bus. The CAN bus is also used to interleave the PWM switching of the modules and synchronise the ADC sampling. The controller structure and algorithms are tested by laboratory experiments with respect to normal operation, initial synchronization to the grid, module fault tolerance and grid fault ride-through

Self-Commissioning Algorithm for Inverter Non-Linearity Compensation in Sensorless Induction Motor Drives

In many sensorless field-oriented control schemes for induction motor (IM) drives, flux is estimated by means of measured motor currents and control reference voltages. In most cases, flux estimation is based on the integral of back-electromotive-force (EMF) voltages. Inverter nonlinear errors (dead-time and on-state voltage drops) introduce a distortion in the estimated voltage that reduces the accuracy of the flux estimation, particularly at low speed. In the literature, most of the compensation techniques of such errors require the offline identification of the inverter model and offline postprocessing. This paper presents a simple and accurate method for the identification of inverter parameters at the drive startup. The method is integrated into the control code of the IM drive, and it is based on the information contained in the feedback signal of the flux observer. The procedure applies, more in general, to all those sensorless ac drives where the flux is estimated using the back-EMF integration, not only for IM drives but also for permanent-magnet synchronous motor drives (surface-mounted permanent magnet and interior permanent magnet). A self-commissioning algorithm is presented and tested for the sensorless control of an IM drive, implemented on a fixed-point DSP. The feasibility and effectiveness of the method are demonstrated by experimental result

Hybrid photovoltaic-thermoelectric generator powered synchronous reluctance motor for pumping applications

The interest in photovoltaic (PV) pumping systems has increased, particularly in rural areas where there is no grid supply available. However, both the performance and the cost of the whole system are still an obstacle for a wide spread of this technology. In this article, a hybrid photovoltaic (PV)-thermoelectric generator (TEG) is investigated for pumping applications. The electric drivetrain comprises a synchronous reluctance motor and an inverter. A control strategy for the drivetrain is employed to execute two main tasks: 1) driving the motor properly to achieve a maximum torque per Ampere condition and 2) maximizing the output power of the PV system at different weather conditions. This means that the conventional DC-DC converter is not used in the proposed system. Moreover, batteries, which are characterized by short life expectancy and high replacement cost, are also not used. It is found that the motor output power and the pump flow rate are increased by about 9.5% and 12% respectively when the hybrid PV-TEG array is used compared to only using PV array. Accordingly, the performance, cost and complexity of the system are improved. Measurements on an experimental laboratory setup are constructed to validate the theoretical results of this work

Modeling Inverter Losses for Circuit Simulation

Transformer-like inverter models can represent a very good alternative to common switch-diode models for simulation, reducing convergence problems and/or calculation time. They may also provide easier insight into the converter operation and power loss effects, at least from the point of view of the applicants, aiding for design and teaching purposes. The paper shows how conduction and switching losses can be incorporated in the transformer-like inverter model in a simple and intuitive way, which requires very few parameters and allows for separate modeling of lossless behavior, conduction losses and the switching losses. Loss models are proposed in some versions differing for the accuracy and simulation easiness. In any case, the resulting inverter lossy model is very compact and can be implemented by just a pair of nonlinear controlled sources as basic building blocks, available in any circuit simulation program, as the free of charge and widely used PSpice student version

European White Book on Real-Time Power Hardware in the Loop Testing : DERlab Report No. R- 005.0

The European White Book on Real-Time-Powerhardware-in-the-Loop testing is intended to serve as a reference document on the future of testing of electrical power equipment, with specifi c focus on the emerging hardware-in-the-loop activities and application thereof within testing facilities and procedures. It will provide an outlook of how this powerful tool can be utilised to support the development, testing and validation of specifi cally DER equipment. It aims to report on international experience gained thus far and provides case studies on developments and specifi c technical issues, such as the hardware/software interface. This white book compliments the already existing series of DERlab European white books, covering topics such as grid-inverters and grid-connected storag

ASDTIC control and standardized interface circuits applied to buck, parallel and buck-boost dc to dc power converters

Versatile standardized pulse modulation nondissipatively regulated control signal processing circuits were applied to three most commonly used dc to dc power converter configurations: (1) the series switching buck-regulator, (2) the pulse modulated parallel inverter, and (3) the buck-boost converter. The unique control concept and the commonality of control functions for all switching regulators have resulted in improved static and dynamic performance and control circuit standardization. New power-circuit technology was also applied to enhance reliability and to achieve optimum weight and efficiency