A Simple Virtual-Vector-Based PWM Formulation for Multilevel Three-Phase Neutral-Point-Clamped DC–AC Converters including the Overmodulation Region

Neutral-point-clamped (NPC) power conversion topologies are among the most popular multilevel topologies in current industrial products and in industrial and academic research. The proper operation of multilevel three-phase NPC DC–AC converters requires the use of specific pulse-width modulation (PWM) strategies that maintain the DC-link capacitor voltage balance and concurrently optimize various performance factors such as efficiency and harmonic distortion. Although several such PWM strategies have been proposed in the literature, their formulation is often complex and/or covers only particular cases and operating conditions. This manuscript presents a simple formulation of the original virtual-vector-based PWM, which enables capacitor voltage balance in every switching cycle. The formulation is presented, for the general case, in terms of basic phase voltage modulating signals, with no reference to space vectors, involving any number of levels and for any operating conditions, including the overmodulation region. The equivalence of the presented formulation to the original PWM strategy is demonstrated through simulation under different scenarios and operating conditions. Thus, this manuscript offers in a one-stop source a simple, effective, and comprehensive PWM formulation to operate multilevel three-phase NPC DC–AC converters with any number of levels in any operating condition.Peer ReviewedPostprint (updated version

AVERAGE-VALUE MODELING OF HYSTERESIS CURRENT CONTROL IN POWER ELECTRONICS

Hysteresis current control has been widely used in power electronics with the advantages of fast dynamic response under parameter, line and load variation and ensured stability. However, a main disadvantage of hysteresis current control is the uncertain and varying switching frequency which makes it difficult to form an average-value model. The changing switching frequency and unspecified switching duty cycle make conventional average-value models based on PWM control difficult to apply directly to converters that are controlled by hysteresis current control. In this work, a new method for average-value modeling of hysteresis current control in boost converters, three-phase inverters, and brushless dc motor drives is proposed. It incorporates a slew-rate limitation on the inductor current that occurs naturally in the circuit during large system transients. This new method is compared with existing methods in terms of simulation run time and rms error. The performance is evaluated based on a variety of scenarios, and the simulation results are compared with the results of detailed models. The simulation results show that the proposed model represents the detailed model well and is faster and more accurate than existing methods. The slew-rate limitation model of hysteresis current control accurately captures the salient detail of converter performance while maintaining the computational efficiency of average-value models. Validations in hardware are also presented

POWER QUALITY CONTROL AND COMMON-MODE NOISE MITIGATION FOR INVERTERS IN ELECTRIC VEHICLES

Inverters are widely utilized in electric vehicle (EV) applications as a major voltage/current source for onboard battery chargers (OBC) and motor drive systems. The inverter performance is critical to the efficiency of EV system energy conversion and electronics system electro-magnetic interference (EMI) design. However, for AC systems, the bandwidth requirement is usually low compared with DC systems, and the control impact on the inverter differential-mode (DM) and common-mode (CM) performance are not well investigated. With the wide-band gap (WBG) device era, the switching capability of power electronics devices drastically improved. The DM/CM impact that was brought by the WBG device-based inverter becomes more serious and has not been completely understood. This thesis provides an in-depth analysis of on-board inverter control strategies and the corresponding DM/CM impact on the EV system. The OBC inverter control under vehicle-to-load (V2L) mode will be documented first. A virtual resistance damping method minimizes the nonlinear load harmonics, and a neutral balancing method regulates the unbalanced load impact through the fourth leg. In the motor drive system, a generalized CM voltage analytical model and a current ripple prediction model are built for understanding the system CM and DM stress with respect to different modulation methods, covering both 2-level and 3-level topologies. A novel CM EMI damping modulation scheme is proposed for 6-phase inverter applications. The performance comparison between the proposed methods and the conventional solution is carried out. Each topic is supported by the corresponding hardware platform and experimental validation

Comparison of Three Space Vector PWM Methods for a Three-Level Inverter with a Permanent Magnet Machine Load

Much work exists on multilevel space vector pulse width modulation (PWM) to drive induction machines, in which the rotor currents are induced by stator rotating field effects. However, there are few investigations that analyze these modulation methods applied to permanent magnet (PM) and wound-field synchronous machines, in which the rotor induces a back emf in the stator. In this thesis, three different three-level space vector PWM switching sequences are applied to a three-level neutral-point-clamped (NP) inverter driving an internal permanent magnet (IPM) machine load. The inherent qualities of each of the switching sequences when under the influence of a forcing function (the back emf) created by the permanent magnets of the machine are investigated. In particular, output voltage quality, output current quality, and dc bus neutral point balance are analyzed and compared. Two machine operating conditions are considered: rated speed, rated load and half speed, rated load. By considering these two different operating speeds, the three switching sequences may be analyzed under both two-level operation and three-level operation of the inverter. A circuit model based on the machine state space model in the abc current frame of reference is used to model the IPM machine load. First, a short introduction to two-level inverters and a theoretical development of two-level space vector PWM are presented to introduce these basic principles. Then, an overview of the three main multilevel inverter topologies including their associated advantages and disadvantages is presented. A theoretical development of three-level space vector PWM is built upon the concepts introduced in the two-level case, and the three switching sequences under investigation are explained. The system model, including the IPM machine load, the three-level NPC inverter, and the space vector PWM algorithms, is implemented using MATLAB Simulink. All simulation results are analyzed based on output voltage and current distortion and neutral point imbalance, and a comparison between the three switching sequences is presented

Assessment and exploitation of the minimum current harmonic distortion under overmodulation in five-phase induction motor drives

This paper compares the most prominent overmodulation (OVM) techniques for five-phase induction motor drives with respect to the minimum current distortion (MCD) achievable. To attain a benchmark of the latter, two MCD OVM approaches are devised. Contrarily to previous strategies aimed at voltage distortion reduction/minimization, these MCD methods are focused on minimizing the harmonic stator copper loss (HSCL), thus minimizing the current total harmonic distortion (THD). One of these MCD strategies minimizes the HSCL while injecting only x–y harmonics. The other MCD method exploits α–β harmonic injection to further decrease the HSCL and to cover the whole OVM region. Moreover, the dual-mode OVM, which is one of the three-phase methods with the lowest distortion, is extended here for five-phase drives. The findings provide insight into how close the OVM methods are to the benchmark imposed by the MCD strategies. Notably, these MCD techniques yield a significant reduction of current THD, HSCL and peak current, especially for machines with negligible thirdorder space harmonic. The average switching losses are also decreased. Indications for real-time implementation of the MCD solutions are also givenAgencia Estatal de Investigación | Ref. PID2019-105612RB-I00Xunta de Galicia | Ref. ED431F 2020/07Xunta de Galicia | Ref. GPC-ED431B 2020/03Agencia Estatal de Investigación | Ref. RYC2018-024407-

Modulated model predictive control with optimized overmodulation

Finite Set Model Predictive Control (FS-MPC) has many advantages, such as a fast dynamic response and an intuitive implementation. For these reasons, it has been thoroughly researched during the last decade. However, the wave form produced by FS-MPC has a switching component whose spread spectrum remains a major disadvantage of the strategy. This paper discusses a modulated model predictive control that guarantees a spectrum switching frequency in the linear modulation range and extends its optimized response to the overmodulation region. Due to the equivalent high gain of the predictive control, and to the limit on the voltage actuation of the power converter, it is expected that the actuation voltage will enter the overmodulation region during large reference changes or in response to load impacts. An optimized overmodulation strategy that converges towards FS-MPC’s response for large tracking errors is proposed for this situation. This technique seamlessly combines PWM’s good steadystate switching performance with FS-MPC’s high dynamic response during large transients. The constant switching frequency is achieved by incorporating modulation of the predicted current vectors in the model predictive control of the currents in a similar fashion as conventional Space-Vector Pulse Width Modulation (SV-PWM) is used to synthesize an arbitrary voltage reference. Experimental results showing the proposed strategy’s good steady-state switching performance, its FS-MPC-like transient response and the seamless transition between modes of operation are presented for a permanent magnet synchronous machine drive

THREE-STAGE SYNCHRONOUS OVERMODULATION CONTROL OF FIVE-PHASE INVERTERS

Novel three-stage algorithm of synchronous PWM control of five-phase inverter in the zone of overmodulation has been proposed and investigated. It provides smooth transition from linear modulation range to the ten-step operation mode of five-phase system at the maximum fundamental frequency, with full DC-bus voltage utilization. Simulations give the behavior of five-phase system during synchronous PWM control in the zone of overmodulation

Multidimensional two-level multiphase space vector PWM algorithm and its comparison with multifrequency space vector PWM method

A multilevel multiphase space vector pulsewidth modulation (SVPWM) algorithm has been introduced recently, in which the reference is separated into an integer part and a fractional part. The fractional part is, in essence, a two-level multiphase space vector algorithm. This paper shows that, with appropriate adaptations, the fractional part of the general space vector multilevel multiphase PWM can be applied as a stand-alone PWM method in conjunction with two-level voltage-source converters with any number of phases. Simulation results of the five- and six-phase cases are shown, and the new algorithm is compared with another recent multifrequency SVPWM algorithm, which follows the standard approach of selecting the switching vectors and calculating their application times using planes. The experimental verification is provided using a five-phase two-motor series-connected induction motor drive, supplied from a custom-designed five-phase voltage-source inverter.Ministerio de Ciencia e Innovación | Ref. DPI2009-0700