This paper presents a method to extend the DC bus utilization on an induction motor (IM) by using a combination of Space-Vector Modulated Direct Torque Control (DTC-SVM) and conventional DTC. DTC-SVM along to stator flux orientation has several advantages over the more standardized indirect rotor field-oriented control (IRFOC). One of the most important advantages of DTC-SVM is its total independency on motor parameters, which are difficult to determine and dependent on external factors such as temperature. On the other hand, both DTC-SVM and IRFOC share a disadvantage, which is limited DC bus utilization during the linear region. However, the fact that torque and flux are directly controlled for DTC-SVM, allows a straightforward transition to the conventional DTC. Resulting in instantaneous transient response, motor parameters independency, and six-step operation capability. The scheme proposed in this paper exploits the advantages of both control methods. It allows to have low torque ripple and low current harmonic distortion (THD) during the linear region, as well as the fastest torque response up to the six-step operation region, always keeping the independency on rotor parameters. DTC-SVM is applied while the modulation index (MI) is within the linear modulation region limit. As soon as this limit is exceeded, the control algorithm will switch to conventional DTC. The paper describes a way to provide smooth transition between the two control schemes. Simulation and experimental results are presented to verify the feasibility of the proposed method.
This paper proposes a charge current controller based on a concept of partial-rated converter for capacitor discharge type pulse voltage generators. The required rated voltage of the partial converter can be 10% ∼ 20% of the system voltage rating of the pulse voltage generator. This paper presents an example of control method for this charge current controller and its pre-charge operation for capacitors. A laboratory-scale prototype was fabricated and experimental verification with the prototype was conducted. An estimation of the volume increase in capacitors is presented as a case study. The estimation indicates that the volume increase in capacitors by adding the proposed current controller is 3% for the case.
To decrease voltage stress of power devices and enhance LED average current accuracy, the dual-input LED driver with an adaptive off-time (AOT) control is presented in this paper. Thanks to the dual-input architecture, its low-voltage power switches can be on-chip to significantly reduce power loss with the same chip area. The AOT control with a current sensing signal automatically regulates the off-time duration based on the LED number and input voltages. Thus, precise average inductor current can be achieved with slight extra power. Experimental results demonstrate the theoretical analysis of the dual-input LED driver.
This paper proposes a mixed modulation combining unipolar and bipolar modulations with the off-time discrete control for the discontinuous current mode (DCM) grid-tied inverters to improve the efficiency. The proposed method has the advantages of the two conventional modulation. The off-time discrete control, which discretely adjusts the oscillation cycles during the zero-current period of the DCM, enables zero-voltage switching (ZVS). This paper presents a strategy to mix both modulations for achieving ZVS and the peak current reduction. The performance of the proposed method was validated by experiments with a 400 W class prototype.
This paper discusses a power loss, which occurs in a load-resonant inverter operating at megahertz for wireless power transfer (WPT) systems. A calorimetric method is applied to measure the power losses in the mega-hertz operation accurately. The loss is measured using a single chamber with temperature control of the internal chamber using a Peltier device. The loss can be measured within 10% error when the loss is less than 23 W with a prototype chamber in experiment. A drive circuit loss, conduction loss of GaN devices, and PCB pattern loss are measured using the measurement site. Moreover, the total loss of the inverter with 6.78-MHz operation is measured under the zero voltage switching (ZVS) condition. The losses on the inverter are separated by a combination of each measurement result. As a result, the loss, which is related to the mega-hertz operation under the ZVS condition, is 9.9 W when the output power is 417 W at 6.78-MHz operation.
