Variable-frequency drive

About: Variable-frequency drive is a research topic. Over the lifetime, 837 publications have been published within this topic receiving 5691 citations. The topic is also known as: VFD.

High-low-voltage conversion star multi-phase variable-frequency drive system

Abstract: The present invention provides a high-low-voltage conversion star multi-phase variable-frequency drive system and relates to a high-voltage high-power motor and drive control thereof. The variable-frequency drive technical solution which is commonly used at present mainly has the disadvantages that a frequency converter is added to a common motor, the insulation life of the motor is short and the heat dissipating ability of the motor is poor. The system comprises a phase-shifting transformer, rectifying circuits, inverter circuits, a multi-phase motor, and a control circuit connected with the phase-shifting transformer, the rectifying circuits, the inverter circuits and the multi-phase motor, wherein primary windings of the phase-shifting transformer are connected with an alternating-current power source, and secondary windings of the phase-shifting transformer are connected with the rectifying circuits; and is characterized in that the number of the secondary windings is the same as the number of the rectifying circuits, one secondary winding is connected with one rectifying circuit, all rectifying circuits are in common-ground connection to form a common-ground direct-current power source, and output ends of the rectifying circuits are connected with the inverter circuits. By adopting the technical solution, high voltage and large currents are realized, simultaneously the structure is simple, the insulation requirement is lowered, the heat dissipating ability of the motor is improved and the power density is increased.

Novel High-Efficiency High Voltage Gain Topologies for AC–DC Conversion With Power Factor Correction for Elevator Systems

Abstract: Novel power factor corrected ac–dc rectifier topologies suitable for induction motor drive based elevator application are proposed. These converters make use of coupled inductor for power conversion and are capable of providing high voltage gain at low duty cycle and high efficiency. The current flowing through the coupled inductor is controlled through a feedback control loop to achieve unity power factor. The total harmonic distortion (THD) value of the current is observed to be approximately 4.8%, which is within the limits prescribed by various standards. With the use of coupled inductor, the voltage stress of the switches operating at high frequency is reduced, which reduces switching losses. The loss comparison with the conventional converters shows a reduction of at least 22% of losses. The proposed scheme also results in reduction of the variable frequency drive's dc-link capacitance value as an ultracapacitor bank is interfaced with the dc link through a bidirectional converter for improving efficiency and providing transient power requirements. This also helps in increasing the reliability and dynamic response of the system. The settling time for a step change in voltage reference is observed to be reduced by nearly 50%. Proposed topologies and schemes are validated through MATLAB/Simulink simulations and experiments.

Effect of different methods of pulse width modulation on power losses in an induction motor

Abstract: We consider the calculation of modulation power losses in a system "induction motor–inverter" for various pulse width modulation (PWM) methods of the supply voltage. Presented values of modulation power losses are the result of modeling a system "DC link - two-level three-phase voltage inverter - induction motor - load". In this study the power losses in a system "induction motor - inverter" are computed, as well as losses caused by higher harmonics of PWM supply voltage, followed by definition of active power consumed by the DC link for a specified value mechanical power on the induction motor shaft. Mechanical power was determined by the rotation speed and the torque on the motor shaft in various quasi-sinusoidal supply voltage PWM modes. These calculations reveal the best coefficient of performance (COP) in a system of a variable frequency drive (VFD) with independent voltage inverter controlled by induction motor PWM.

Technical and economic feasibility of using a variable-frequency drive in micro-irrigation systems

Abstract: Irrigation is essential for the development of crops in regions with scarcity or irregular rainfall distribution, enabling high productivity. However, the use of water resources and electrical energy leads to a concern with irrigation efficiency. Pressure demand varies during the operations of irrigation systems and the appropriate pressure can be regulated by variable-frequency drives for the power supply of the motor-pump set. This study aimed to analyze the technical and economic feasibility of using a variable-frequency drive to adjust the pressure in subunits of micro-irrigation systems. Laboratory tests were carried out to determine the electrical power consumed in each irrigated subunit for different slopes and the application or not of the variable-frequency drive. Thus, an economic analysis was carried out considering the electricity tariff for group B and rural consumer class, as well as different annual irrigation times. The results showed the potential for energy saving with the use of the variable-frequency drive. Thus, the economic analysis showed that the variable-frequency drive was a better alternative than the dissipative method.

Induction motor-controlling device

Abstract: PROBLEM TO BE SOLVED: To save power, and to miniaturize inverter power supply capacity. SOLUTION: In a control means 7, a frequency detection means 8 for detecting an operating frequency (f) of an inverter 2 while the variable frequency of an induction motor 3 is being driven, and a target value setting means 10 for setting the various target values are connected, and a clocking means 70 for clocking commercial power supply operation time (t) is incorporated. When the operation frequency (f) of the inverter 2 becomes lower than a frequency (f0) of the commercial power supply and reaches a setting frequency (f1) being preset by the target value setting means 10 or more, a switching means 5 for connecting the inverter 2 to the induction motor 3 is opened, and a switching means 4 for connecting the commercial power supply 1 is closed for changing to commercial power supply operation. When the commercial power supply operation time (t) being clocked by the clocking means 70 becomes setting time (t1), the switching means 5 for connecting the inverter 2 to the induction motor 3 is closed, and the switching means 4 for connecting the commercial power supply 1 is opened for changing to variable frequency drive by the inverter 2.