A three-phase series-parallel resonant converter-analysis, design, simulation, and experimental results

The paper deals with a single-phase AC-to-DC convertor using a three-phase modified series–parallel resonant convertor. A systematic procedure is presented for the design of three-phase resonant-convertor components. Based on the analysis and design curves, a resonant convertor is designed for 2.5 kW rating. The minimum switching frequency of the convertor is 290 kHz at full-load condition. The simulation and experimental results are presented for variable-load conditions. The variable frequency and duty-ratio control scheme are implemented using a digital signal processor for output-voltage regulation. The use of a three-phase high-frequency invertor reduces the filtering requirements, peak component stresses on the resonant components and peak invertor output current. The proposed convertor maintains excellent input-line power factor without any active control of AC-input line current. Apart from this, it requires narrow variation in switching frequency for its output-voltage regulation.

A modified series resonant convertor (SRC) which overcomes the problems of a standard SRC is presented. A state-space approach is used for the analysis. The analysis shows that the converter enters into three different modes. Converter gain and other component stresses are plotted with variation in the load current. Detailed experimental results obtained from a 500 W, MOSFET converter are presented to verify the theory. A narrow variation in switching frequency is required to regulate the output voltage for a wide variation in the load current. The converter can operate with a load open circuit as well as a load short circuit. It is shown that by placing the parallel inductor on the secondary-side, the parasitics of the high-frequency transformer can be used profitably. >

The hysteresis current controllers (HCC) for grid-connected inverter (GCI) system is a well-known controller for its robustness, fast reference tracking, better dynamics, and easier implementation compared to other controllers. This article proposes a modified double-band HCC (MDBHCC) for single-phase GCI system with LCL -filter. The proposed algorithm implements an unipolar symmetrical pulse width modulation (PWM) strategy for reducing inverter switching losses through a sequential logic, with an adaptive clock. It improves the variation in switching frequency and limits the maximum switching frequency of HCC while enhancing the total harmonic distortion (THD) of the injected current into the grid. In order to alleviate power quality problems, two such MDBHCC schemes, i.e., MDBHCC1 and MDBHCC2, are implemented. Where MDBHCC2 operates at the higher switching frequency with lesser % THD and MDBHCC1 operates at lower switching frequency. Simulation and experimental results are presented with a significant decrease in switching frequency and an improvement in grid current harmonics at both steady-state and dynamic conditions.

Electric motors are actively used in various industries. Acoustic noise is crucial in electric motors, and specific standards are depending on their application areas. Despite better performance, including acoustic noise, than brushed motors, brushless motors still generate acoustic noise due to their mechanical, electrical, and electronic components. This study investigated the impact of varying the switching frequency through the driver on the acoustic noise of an external rotor brushless DC motor. Tests were conducted on a surface-mounted magnet brushless motor with different switching frequencies, and detailed information about the sections of the control board governing the brushless motor was provided. The study includes measurements of motor speed, current, switching frequency, phase signal, and acoustic noise measured at two different locations in decibels. It was observed that the acoustic noise increased at specific switching frequencies. Furthermore, the variation in switching frequency also affected the heating due to losses in the switching elements. Increasing the switching frequency in the 12-28 kHz range reduced motor speed and the measured acoustic noise, while temperature increases were observed in various frequency ranges.

A full bridge high-frequency link series parallel resonant converter (SPRC) operating in discontinuous current mode is analyzed using the state-space approach. The equations are solved using the PROMATLAB software. Design curves for the converter gain and other component stresses are presented in normalized form. The converter has been optimized for peak component stresses, and the corresponding design curves obtained from PROMATLAB and SPICE3 simulation are presented. Using the optimal design curves, a 250-kHz experimental converter operating on a wide input voltage (1:2) has been built to verify the theoretical and SPICE3 simulation results.

Compared with the widely used constant switching frequency pulse-width-modulation (PWM) method, variable switching frequency PWM can benefit more because of the extra freedom. Based on the analytical expression of current ripple of three-phase converters, variable switching frequency control methods are proposed to satisfy different ripple requirements. Switching cycle $T_{s}$ is updated in DSP in every interruption period based on the ripple requirement. Two methods are discussed in this paper. The first method is designed to arrange the current ripple peak value within a certain value and can reduce the equivalent switching frequency and electromagnetic interference (EMI) noise; the second method is designed to keep ripple current RMS value constant and reduce the EMI noise. Simulation and experimental results show that variable switching frequency control could improve the performance of EMI and efficiency without impairing the power quality.

Finite control set model predictive control (FCS-MPC) has been widely studied and applied to the power converters and motor drives. It provides the power electronics system with fast dynamic response, nonlinear system formulation, and flexible objectives and constraints integration. However, its variable switching frequency feature also induces severe concerns on the power loss, the thermal profile, and the filter design. Stemming from these concerns, this article investigates the variable switching frequency characteristics of FCS-MPC on the grid-connected inverters. An intuitive relationship between the switching frequency and the magnitude of the converter output voltage is proposed through the geometry analysis, where the switching frequency is maximized when the converter output voltage is around one-third of the DC bus voltage and decreasing when the output voltage moves away from this value. The impacts of this variable switching frequency property on the power loss and current harmonics are also analyzed. Simulation and experimental results both verify the proposed property. With this intrinsic property, FCS-MPC can autonomously achieve a less-varying temperature profile of power modules and an improved reliability compared with the conventional control strategy.

For the power management of a wireless power transfer system for implantable mechanical heart pumps, an additional boost DC-DC converter stage is needed in order to control the power delivered to the implant. Particularly, battery powered and implantable medical devices pose special demands on the efficiency and/or power density of the employed converters. Accordingly, soft-switching and/or high switching frequencies must be targeted. Modulation schemes that allow for Zero-Voltage-Switching (ZVS) such as Triangular Current Mode (TCM) offer a highly efficient operation, but suffer from a large operating frequency variation, which is mainly limited by the digital control. Therefore the Clamp-Switch TCM (CL-TCM) converter can be employed which allows also for the control of the switching frequency variation. In this paper, the CL-TCM and the TCM converter are compared regarding the power conversion efficiency and the power density of the converter. Since the CL-TCM converter is not well known in the literature, the converter is analysed in detail and a modulation scheme is explained that allows for ZVS for all switches in the entire range of operation. In addition, the requirements for ZVS and a control scheme (i.e. timing calculations) are provided for the converter in order to limit the maximum switching frequency. The modulation and control scheme are verified with a hardware prototype. Finally, the performance of the CL-TCM converter is measured and compared to the performance of the converter operated in TCM mode. The measurements show that the CL-TCM converter offers similar performance compared to the TCM operation at lower inductor power density, but has the advantage of a significantly reduced switching frequency variation. In applications, where a very high power density is needed, the TCM converter outperforms the CL-TCM converter in terms of efficiency.

In this paper, a modified full bridge dual inductive coupling (LCL) resonant converter for electric vehicles (EVs) battery charging applications is proposed. The main objective of the proposed topology is to operate the converter in constant voltage (CV) and constant current (CC) mode during battery charging. The presented topology's uniqueness comprises the following: i) isolated charging and power factor correction (PFC), ii) to achieve zero-voltage switching (ZVS) and zero-current switching (ZCS) for inverter switches, iii) reduction of number of rectifier diodes to reduce the conduction and switching losses, and iv) reducing the magnetizing current. The output voltage dependence of resonant converter is reduced using a PFC converter against the variations of the alternating current (AC) grid input voltage. The variations of the wide range output voltage and load is compensated by a small variation in switching frequency. The proposed topology's detailed operation is simulated using the MATLAB/Simulink tool.

A variable inductor concept based on a magnetic structure consisting of a composite of magnetic materials is introduced to meet designed inductance function of current. A design of the inductor, termed hetero-magnetic swinging inductor (HMSI), was fabricated using a toroid core with a gap that was filled by a custom-developed low-permeability magnetic powder + polymer material. Having the gap filled with the magnetic material allowed for greater flexibility in L-I design with added benefit of low fringe field. We applied this swinging inductor to a Critical Conduction Mode (CRM) Boost power factor correction (PFC) converter to reduce its switching frequency variation range. First, the required L-I curve of the HMSI needed for narrow range of switching frequency was calculated. Then, the HMSI core structure consisting of two magnetic materials was designed. Circuit simulations showed that for a 110-Vrms input, the converter with the HMSI had a switching frequency variation factor, defined as $\Delta\text{f}/\text{fmin}$ , six times less than that of the converter using a linear inductor. A prototype of the HMSI was fabricated and tested. The effectiveness of using the HMSI to narrow the range of switching frequency variation was verified in a 150 W CRM PFC converter.

The conventional direct torque control (DTC) method features fast dynamic response, but it also has notable drawbacks such as high torque and flux ripples, variable switching frequency and acoustic noise. The proposed DTC scheme based on model predictive control (MPC) is studied in the paper for permanent magnet synchronous machine drive. The paper aims to reduce the torque and flux ripple. Firstly one- and two-step delay MPC methods are employed with or without the torque/flux and switching frequency compensation. Furthermore linear extrapolations N-step delay MPC method is taken into account. Compared to simulation results, the two-step delay DTC scheme is better than the one-step scheme in the steady response and dynamic performance, at the same time the torque and frequency compensations can reduce switching frequency from high value to a low constant one. Simulation results are presented to validate the effectiveness of the proposed schemes in this paper.

Single-phase grid-tied microinverters are required to operate over a wide power range in photovoltaic applications. It is desirable to improve the efficiency over the entire power range without extra cost. This article proposes a variable switching frequency (VSF) multimode control scheme to optimize the device losses at each operating point for a single-phase T-type hybrid-bridge inverter. The proposed optimal control scheme is devised based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V–I</i> plane analysis and can therefore be applied in both unity power factor (PF) and nonunity PF operations. With reasonable simplifications and curve fitting, neither a multidimensional lookup table nor excessive computational burden is required for the controller. A 1-kW prototype is built to verify the proposed optimal VSF scheme and compare it with the conventional constant switching frequency (CSF) scheme. The experimental results show that the proposed optimal VSF scheme can achieve higher efficiency than the CSF scheme over a wide power range. The weighted average efficiency of the proposed scheme is improved by a maximum of 1.3% in unity PF operation and 0.63% in nonunity PF operation.

Reactive current compensation is a method to improve the load power factor by locally supplying the reactive current requirement of the load using shunt compensators. Current controller of shunt compensators is usually designed using conventional PI controllers, in spite of the improved dynamic performance offered by hysteresis controllers. Conventional hysteresis current controller brings up different issues like variable switching frequency, non-optimal switching etc. Because of these issues, hysteresis current controllers are generally not preferred by the researchers even though it is easy to implement. This paper proposes a constant switching frequency hysteresis current controller for shunt compensators. Simulation results are presented to validate the effectiveness of proposed controller.

Three phase induction machines are widely used in the industry due to their low cost and ease of maintenance, however, their lagging power factor is an inherent disadvantage which is compensated by use of various methods. Variable frequency drives for induction motors offer a mechanism for both power factor correction and efficient control but requires an internal energy buffering for reactive power at line frequency. Our paper introduces a way of synchronizing the operation of multiple induction motors in an organization through networked VFDs driven either through a common DC bus or directly from the AC mains to improve the power factor without the need of energy buffering or use of external capacitor banks. The processed power supplied to the machines through VFDs is phase shifted in voltage to create a time delay in requirement of reactive power allowing the operation of selected induction machines in leading power factor mode. This paper presents the analysis, simulations and experimental validation through results in the lab by implementing two custom 3-phase induction motor drives and their synchronous operation from a common DC bus. The obtained results validate that this approach can be applied to larger networks of induction motors in a larger industrial setup.

In this paper, a new control scheme for buck converters was proposed. The buck converter utilizes the dual control loop to improve transient response and has the constant switching frequency. The control scheme is mainly as follows: (a) The switch-ON time is regulated by the constant frequency mechanism. (b) The switch-OFF time is regulated by the output voltage. The spec/features of the proposed converter are listed as: (1) The buck converter has an output of 1.0–2.5 V for the input of 3.0–3.6 V. The load current ranges from 100 mA to 500 mA. (2) The actual current sensor is not required. (3) The simulation results show that the recovery time is less than 1.6 μs during load changes. (4) The variation in switching frequency is smaller than 1.05% over the output range of 1.0–2.5 V. (5) This circuit can be fabricated in future by UMC 0.18 μm 1P6M CMOS processes. This paper depicts the control scheme, theoretical analysis, and implementation.