Multiphase Converter Research Articles

Voltage regulation in an interleaved circular chain sliding mode controlled multiphase converter

In this article a multiphase synchronous buck converter controlled by a sliding mode control (SMC) in a circular chain control (CCC) configuration is presented. The proposed switching functions with the CCC architecture ensure a robust output voltage regulation when facing changes in the load or the input voltage, while providing current equalization among the phases. The novelty of the work is the simple control structure based on a first order SMC implemented by means of hysteresis-band comparators, requiring no external signals or additional hardware to lead the system to an interleaving operation, obtaining a harmonic cancellation that allows the size reduction not only of the output capacitor but also of the inductors. It is proved that, in the steady state, the switching function exhibits a periodic solution with a period equal to the switching period. Besides, the steady-state switching frequency expression as a function of the hysteresis bandwidth is derived. The work includes the analytical analysis of the proposed solution, a set of numerical simulations and, finally, an experimental validation. The numerical and experimental results confirm the predicted good performance of the proposed control.

Generalized Pulse Width Modulation Switch Model for Converters Based on the Multistate Switching Cell in Discontinuous Conduction Mode.

This work introduces a generalized version of the pulse width modulation (PWM) switch model applied in the small-signal modeling of converters based on the multistate switching cell (MSSC) operating in discontinuous conduction mode (DCM). It consists of extending the concept formerly introduced by Vorperian for the representation of multiphase converters in DCM, yielding a circuit-based approach that does not rely on matrix manipulations unlike state-space averaging (SSA). The derived dc and ac models are valid for any number of switching states and any operating region defined in terms of the duty cycle, thus allowing for determining the voltage gain and distinct transfer functions. A thorough discussion of results is presented to demonstrate the applicability of the derived models to represent distinct configurations of the MSSC.

Performance Evaluation of Per-Phase Model Predictive Control Schemes for Extending Lifespan of Voltage Source Converters

Unequal thermal stress among the phase legs of a multiphase converter leads to a reduction in the useful lifespan and reliability of that converter in general. Increasing the converter’s lifespan by relieving the stressed phase leg, which suffers excessive thermal stress due to aging, is crucial. This paper evaluates two control concepts, including two per-phase model predictive control methods for extending the lifespan of a voltage source inverter. These two per-phase techniques alter the switching pattern to reduce the losses of the most aged phase leg. Hence, the loss and the corresponding thermal stress of the leg that has aged the most are reduced. In such a way, the lifespan and reliability of the converter are prolonged. Two per-phase model predictive control techniques are executed in both simulation and experiment environments, where the corresponding results are provided to evaluate the behavior of these control strategies, considering several operational aspects both in steady state and transient operation. In addition to static load conditions, two per-phase techniques are verified for the correct operation under dynamic load (induction motor) conditions.

Review of the calculation of DC-link capacitor current

In the voltage source power electronic converter, DC-link capacitors usually work as buffering elements between the DC and AC sides. The high failure rate and large space occupied by the DC-link capacitors directly affect the reliability and power density of the converters. The analysis and calculation of the DC-link capacitor current is crucial to achieve the refined design of converters. In this work, the analysis and calculation methods of DC-link capacitor current are divided into three categories, according to the calculation principle, namely, simulation method, RMS analysis method, and spectral analysis method, and their calculation methods are summarized. First, the types of capacitors and their characteristics are briefly introduced. Second, the three-phase two-level converter is taken as an example to introduce the basic principles, calculation steps, application scope, advantages, and disadvantages of the latter two methods in detail, as well as the influence of non-ideal factors, such as the output ripple on the calculation results. This work also discusses the calculation of the multi-level converter’s DC-link capacitor current spectrum and the current characteristics of multi-phase converters, which are rarely reported. Third, the problem of resonance between the DC-link capacitors and the DC bus inductor is introduced. For the distributed arrangement of multiple DC-link capacitors on DC bus converters, this study proposes a method based on a constant current source equivalent circuit, which can accurately calculate the DC-link capacitor current spectrum that is affected by loop current and resonance. Finally, the current problems and future directions of the DC-link capacitor design are pointed out.

Multiphase Converter Voltage Optimization With Minimum Effort Principle

Multiphase Converter Voltage Optimization With Minimum Effort Principle

Common mode conductive noise cancellation for multiphase converter using auxiliary winding

AbstractA multiphase DC‐DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high‐power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC‐DC converter that hardly lowers the power density.

Four-Phase Interleaved Boost Converter for Maximum Power Extraction in PV System

The use of renewable energy is increasing, thus affecting the rapid use of DC-DC converter technology. The use of a conventional boost converter has a weakness, namely high current ripple. This input current ripple will enter the voltage source, so that the switching noise will spread to other circuits. This problem can be overcome by using a multiphase converter topology that can suppress current ripple. But the conventional multiphase topology has large power losses, because the value of the inductor used tends to be large. Ripple currents will also reduce the efficiency of solar power plants. This study aims to design a four-phase interleaved boost converter that is applied to PV (photovoltaic) with maximum power extraction. The topology method of this circuit is to assemble a conventional boost converter in parallel up to 4 levels, so that it can suppress the input current ripple. This topology modification series also uses the interleaved scaling method in order to reduce heat distribution on each switch. The test method in this study uses a standard boost converter circuit as a comparison, and observes its characteristics and performance through simulation. The converter system is also operated as Maximum Power Point Tracking (MPPT) using the PSO and P&O algorithm controls as a comparison. Based on the simulation results, the MPPT tracking speed has the same speed, which is 2 ms, but the speed to achieve ripple stability in the standard circuit and four-phase interleaved boost converter is 4.5 ms and 6.1 ms, respectively.

Common Mode Conductive Noise Cancellation for Multiphase Converter Using Auxiliary Winding

A multiphase DC-DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC-DC converter that hardly lowers the power density.

Sensorless Current-Sharing Scheme for Multiphase DC-DC Boost Converters

Accurate current sharing is beneficial to realize uniform heat distribution and electrical stresses in multiphase converters. Most of the present current-sharing schemes need many current sensors which increase the cost and decrease the system reliability. To solve this problem, a sensorless current-sharing scheme is proposed to balance the phase currents of multiphase dc–dc boost converters in continuous conduction mode. By converting the inner resistances of inductors and switches to series resistances on the input side, the actual converter model is simplified. Regarding one duty cycle as reference, the relationship between duty cycle and series resistance ratio (SSR) is derived for equal current distribution. After that, two methods are provided to obtain the SSRs. One is based on duty disturbance and the other is based on current measurement. Actually, the phase with largest series resistance is chosen as reference to improve the transient response. Despite phase number, only output and input voltages are measured to achieve output voltage regulation and current balance in the overall control scheme. The validity of proposed scheme is verified on a three-phase dc–dc boost converter.

Open-Circuit Fault-Tolerant Control for a Three-Phase Current-Fed Dual Active Bridge DC–DC Converter

Fault-tolerant methods have been recognized for improving the reliability of multiphase bidirectional dc–dc converters, including current-fed and voltage-fed dual active bridge converters. Fault-tolerant research for voltage-fed dual active bridge converters has caught much attention recently. In this article, a new fault-tolerant method for current-fed dual active bridge (CF-DAB) converters with blocking capacitors is proposed. The operation of the CF-DAB converter when an open-circuit fault occurs is comprehensively presented and analyzed. A frozen-phase fault-tolerant method with additional blocking capacitors on both sides of the transformer is proposed. The aim of the use of blocking capacitors is to block the dc current component of the high-frequency transformer, which could avoid the core saturation of the transformer. Also, the dc blocking capacitors help isolate the faulty phase when a frozen-phase fault-tolerant method is applied. The proposed method is shown to be a practical, simple, low loss, and effective solution for not only open-circuit fault isolation but also for shedding capability of the multiphase converter. The proposed concept could be applied for general multiphase current-fed converters. The experiment of a 6-kW prototype is implemented to confirm the proposed concept.

Loss analysis of perspective multiphase converter topology suitable for the automotive traction inverter

The paper deals with the power losses of semiconductor devices of alternative multiphase topology for traction inverters in the automotive industry. Multiphase traction inverters are getting increasingly more attention due to features that make them superior to conventional three-phase topology used nowadays in the automotive industry. Based on key features of multiphase traction inverter topologies, which are enhanced per-phase power management, fault-tolerance capabilities, and decreased size of DC-Link capacitors, are getting the attention of automotive constructors and their suppliers. Power loss calculation is one of the most important aspects of evaluating the estimated efficiency of the proposed topology of the traction inverter. Power Losses are calculated by using the software PLECS.

Analysis and Design of Zero-Voltage-Switching Multiphase AC/DC Converters

In this article, the generic analysis and design of zero-voltage-switching (ZVS) multiphase ac/dc converters are proposed. With the edge aligned pulsewidth modulation (PWM) (EA-PWM) scheme, all switches of ZVS multiphase ac/dc converters can realize ZVS operation. Besides, the switching frequency is fixed and the auxiliary switch only operates once in each switching period. Its operation stages in a switching cycle are analyzed and a generic ZVS condition is derived. Based on the proposed theory, a ZVS two-stage three-phase photovoltaic (PV) inverter is investigated, which is regarded as a five-phase converter. Its ZVS condition under different working conditions is discussed. Finally, a 10-kW prototype with 150 kHz switching frequency of the ZVS two-stage three-phase PV inverter is built and the experimental results are given to verify the analysis. In addition, the extension of the ZVS multiphase converter in different applications is introduced.

Parameter Extraction Technique for Evaluation of Inductive and Capacitive Elements of Three-Winding Coupled Inductor

Wide-bandgap devices have enabled miniaturization of magnetic components to enhance the power density of the converter. However, parasitic components become dominant at higher switching frequencies that actuate unwanted electromagnetic interference issues. Therefore, it is critical to model and evaluate them in compact magnetic structures. Since multiwinding coupled inductive structures are essential part of multiphase converters, this article introduces a measurement method to compute the parasitic elements of a three-winding coupled inductor. Results of the proposed method are verified by measuring the high-frequency emissions of the high-step-up converter with two inductor structures. Both inductors had similar inductances but different physical dimensions. With application of the proposed measurement methodology, parasitic capacitances of both inductors were computed. Results showed that one inductor structure has higher parasitic capacitance than the other. Since high-frequency emissions of the converter directly depend on the parasitic capacitance of the inductor structure, the emission profile of the converter showed that the converter indeed had lower noise peaks when the inductor with lower capacitance was employed. Hence, these results validate the capacitance trend as predicted by the proposed modeling technique. This method can be employed to any multiwinding coupled inductor to compute its parasitics to optimize the required electromagnetic interference filters.

Multiphase Interleaved IPT Based Current-Source Converter for High-Current Application

This article proposes a multiphase interleaved inductive power transfer (IPT) based dc–dc converter for high-current applications. There are three main contributions. First, the proposed converter is designed based on a loosely coupled IPT system with series compensation capacitors, which permits large leakage inductance and avoids magnetic saturation. Second, series capacitors are used to compensate the magnetic coupler, which achieves load-independent output current, namely a current-source converter. Third, a scalable multiphase converter is achieved with an input-parallel output-parallel structure for high current. Meantime, an interleaved control strategy is implemented to an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -phase system with an angle shift of 360°/(2× <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> ), reducing output current ripples. A 2-kW/100-A three-phase converter prototype is implemented with zero-voltage switching and harmonic loss suppression. Experimental results show a load-independent output current, which is linearly regulated by input dc voltage. With an input voltage of 480 V, the output current reaches 101.5 A with a small peak-peak ripple of 2.4 A. Output power reaches 2.07 kW with a 91.39% dc–dc efficiency. A steady-state test for a solid-state circuit breaker (SSCB) is conducted using the proposed high-current converter, showing its application in evaluating the steady-state efficiency and thermal performance of SSCB.

Output Current Ripple and Efficiency Optimal Control Method for Multi-Phase Interleaved LLC Resonant Converter

The interleaving technique is required for LLC resonant converters to achieve high power levels, handle higher input/output currents, and reduce output current ripple. However, the high system efficiency and the low output current ripple for the multi-phase LLC resonant converter cannot be achieved at the same time at low and medium power levels. Most methods try to keep the multi-phase LLC resonant converter in load-sharing mode regardless of the power level, which will result in low system efficiency at low and medium power levels. In this paper, an output current ripple and efficiency optimal control method with finite load distribution schemes is proposed for the multi-phase LLC resonant converter to balance the efficiency and output current ripple. The optimal control method improves the efficiency as much as possible while keeping output current ripple low. According to the calculation of output current ripple and efficiency, the optimal load distribution scheme is selected. The pulse-frequency modulation (PFM) and phase-shift modulation (PSM) hybrid control is applied to regulate the load of each phase. An analysis is provided, and a 540-W three-phase interleaved LLC resonant converter is built to verify the superiority.

Power losses analysis of multiphase DC-DC buck converter using OrCAD PSpice software

DC-DC buck converters have wide applications in portable electronic devices, battery chargers, and telecommunications. However, single-phase DC-DC buck converters have some drawbacks, especially in high current applications, where the increase in the size of the inductor will increase power losses, which significantly affects the overall efficiency of the converter. The multiphase configuration offers several advantages, such as reduction in output voltage ripple, input current ripple, conduction loss, and the physical size of the hardware. This paper presents an analysis of the power losses of the multiphase DC-DC buck converter with output power ranging between 50 watts to 250 watts. To verify the effectiveness of the multiphase converter, performance analysis was done using OrCAD PSpice software, where the number of phases was limited to five phases. This paper focused on power losses in the converter, namely conduction losses in diodes and MOSFETs, switching loss in MOSFETs, as well as losses in the inductor and capacitor. The relationship between the number of phases and factors of switching frequency, output, and the components’ internal resistance was also highlighted and discussed in detail.

Study of the Effects of Current Imbalance in a Multiphase Buck Converter for Electric Vehicles

The excessive use of fossil fuels has caused great concern due to modern environmental problems, particularly air pollution. The above situation demands that different areas of research aim at a sustainable movement to reduce CO2 emissions caused by non-renewable organic fuels. A solution to this problem is the use of Electric Vehicles (EV) for mass transportation of people. However, these systems require high-power DC/DC converters capable of handling high current levels and should feature high efficiencies to charge their batteries. For this application, a single-stage converter is not viable for these applications due to the high current stress in a switch, the low power density, and its low efficiency due to higher switching losses. One solution to this problem is Multiphase Converters, which offer high efficiency, high power density, and low current ripple on the battery side. However, these characteristics are affected by the current imbalance in the phases. This paper is focused on the study of the effects of the current imbalance in a Multiphase Buck Converter, used as an intermediate cover between a power supply and the battery of an EV. Analyzing the efficiency and thermal stress parameters in different scenarios of current balance and current imbalance in each phase.

A Novel Multiphase Interleaved DC-DC Boost Converter with Reduced Input Current Ripple for Renewable Energy Application

This paper presents a new multiphase boost converter with improved input current ripple characteristics. The low input current ripple is important due to its effect on the converter’s efficiency and upstream dc bus noise level. It will further affect other devices connected to the same bus. Furthermore, for battery-connected systems such as renewable energy systems, the low current ripple increases the battery life. The method in this research uses split inductance and capacitance configuration as an input filter. The input filter helps compensating for the rippled converter topology, it reduces conduction-switching noise without affecting transient response, and it minimizes the physical size. Therefore, in this new topology, the use of smaller sized components directly influences the converter's size. Interleaved is used for improved heat distribution on the physical circuit board while retaining the benefits of a multiphase converter. Additionally, the low current ripple implies using smaller sized components that directly affect the size of the converter. A three-phase example of the proposed boost converter will be described, along with the derivation of its state space equations. Compared with the standard three-phase boost, the proposed converter can reduce the input current ripple and the output current ripple by 21% and 43%, respectively.

Real-Time Simulation Modeling Method of Multiphase Converters Based on High-Order Approximation in Micro-grid

As more and more distributed energy resources accessing in a micro-grid, the electromagnetic transient simulation of the whole system becomes extremely complicated due to the increase of multiphase converters. The traditional real-time simulation models of multiphase converters are low in efficiency for their large number of electronic switches and power system nodes. To solve this problem, an efficient real-time simulation modeling method based on high-order approximation is proposed. Starting with the symmetry of structure, the twelve-phase converter and induction motor are equivalent to a three-phase converter and induction motor and thus reducing the order of the model. The switching function model of the three-phase converter is derived, and the mathematical expressions of switching functions are calculated by high-order approximation expansion of the Fourier series; then, the dc input current of the three-phase converter is formulated theoretically. Counteracting the harmonics by means of phase-shifting, the high-order approximation model of the twelve-phase converter is constructed. Finally, the real-time simulation platform and experimental platform of the twelve-phase frequency converter and induction motor are built; the simulation results verify the high efficiency and accuracy of the proposed real-time simulation model compared with traditional models of the multiphase frequency converter.

Fast‐converging robust PR‐P controller designed by using symmetrical pole placement method for current control of interleaved buck converter‐based PV emulator

AbstractIn this study, the interleaved buck converter‐based photovoltaic (PV) emulator current control is presented. A proportional‐resonant‐proportional (PR‐P) controller is designed to resolve the drawbacks of conventional PI controllers in terms of phase management, which means balancing currents evenly between active phases to avoid thermally stressing and provide optimal ripple cancelation in the presence of parameter uncertainties. The resonant path of the controller (PR) with a constant proportional unity gain is designed considering the changing dynamics of a notch filter by pole placement method (adding mutually complementary poles to the notch transfer function) at PWM switching frequency. The proportional gain path (P) of the controller is used to determine the compatibility of the controller with parameter uncertainty of the phases and designed by utilizing loop‐shaping method. The proposed controller shows superior performance in terms of 10 times faster‐converging transient response, zero steady‐state error with significant reduction in current ripple. Equal load sharing that constitutes the primary concern in multiphase converters is achieved with the proposed controller. Implementing of robust control theory involving comprehensive time and frequency domain analysis reveals 13% improvement in the robust stability margin and 12‐degree bigger phase toleration with the PR‐P controller. In addition to these, the proposed unconventional design process of the controller reduces the computational complexity and provides cost‐effectiveness and simple implementation. Moreover, implementing of auxiliary resistor‐capacitor (RC) circuits parallel with the inductors to sense the current in each phase removes the need for current measurement sensors that contribute to overall cost of the system.