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When permanent magnet synchronous motors (PMSM) are used in pump and fan applications where no excessive performance is required, the V/f scalar control method can be applied to enhance the ease of use for end users. For the voltage reference generation in V/f control, existing methods requires motor parameters such as the stator resistance, inductance, and back EMF constant of the permanent magnet, which is identified before or during operation. However, this paper proposes a simple and convenient V/f control method that utilizes the motor parameters given on the name plate. In the proposed method, stable operations are ensured for the rated speed and load ranges without position sensors. For successful starting operation, a DC current control loop is included to calculate the initial offset voltage reference for the V/f pattern. The stability and effectiveness of the proposed method are analyzed and verified by MATLAB/Simulink and 3.7 kW IPM motor drive experiments. [ABSTRACT FROM AUTHOR]

Generally, position controllers for servo motor drives utilize cascaded structures with speed and current controllers in inner loops. This structure provides easy gain setups and independent limits for control variables such as maximum torque or speed. However, it suffers from a large computation time and poor dynamic characteristics for the position control since the bandwidth must be low enough to guarantee those of the speed and current controllers. To cope with this, two non-cascaded position controllers where speed controller is removed are proposed. The first one is equivalent to the conventional controller in terms of the dynamic characteristics. However, the number of gains for the position control is reduced. The second one is aimed at improving the dynamic characteristics with more complicated structures. The proposed methods are effectively validated through MATLAB/Simulink simulations and 3.7 kW IPM motor drive experiments. [ABSTRACT FROM AUTHOR]

One of the recent trends in power electronics field is to achieve high efficiency and compact size by using wide bandgap power devices such as silicon carbide (SiC) or gallium nitride switches. This paper compares the efficiency, the motor terminal voltage quality (dv/dt), and the common mode current of the SiC-based variable frequency drives (VFDs) according to the inverter topologies with and without the output filters. For this purpose, both the 2-level (2L) and 3-level (3L) topologies with SiC devices are built and tested. Here, the well-known 2L half-bridge inverter is compared with the well-known 3L T-type neutral point clamped inverter. A dv/dt filter and a sine wave filter have been discussed to satisfy the National Electrical Manufacturers Association standards as well. The experiments have been carried out with a 380-V/60-Hz, 3.7-kW induction motor and the custom designed power stages. Additionally, the experiments with both a 3-m and a 50-m cable length between the VFD and the induction motor are performed and reported. [ABSTRACT FROM AUTHOR]

In this paper, it is described how the circulating current flows between inverters that have isolated dc link such as cascaded H-bridge (CHB) topology when they are operating in parallel. In this case, zero sequence circulating current, which normally flows through shared dc link, cannot flow between inverters in parallel. However, circulating current is provoked by asynchronous switching instant of devices, difference of dc-link voltages of parallel inverters, and unbalanced impedance. The circulating current should be suppressed by a sharing inductor that is inserted between inverters. Generally, all of the inverters should synthesize the same output voltage reference for load current control to minimize the size of this sharing reactor. However, this conventional method cannot guarantee diminishing circulating current in the transient state and even in the steady state. In this paper, in order to reduce sharing reactance, after deriving circulating current model from general case of n-parallel operation, circulating current control method is devised based on the model. This proposed algorithm is applied to active front end five-level-CHB inverter system for medium voltage drive. Simulation and experimental results are provided to verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]