Discontinuous Modulation Strategy Research Articles

Thermally compensated discontinuous modulation strategy influence on DC-link capacitor current of CHB converters

Thermally compensated discontinuous modulation strategy influence on DC-link capacitor current of CHB converters

Predictive Discontinuous Modulation Strategy With Embedded Inter-Phase Cluster Voltage Control for Cascaded H-Bridge StatComs

Predictive Discontinuous Modulation Strategy With Embedded Inter-Phase Cluster Voltage Control for Cascaded H-Bridge StatComs

Discretized Discontinuous Modulation Strategy for Cascaded H-Bridge StatCom

This paper proposes a discontinuous modulation (DM) scheme for cascaded H-bridge (CHB) static compensators (StatComs) with star configuration. The proposed DM scheme guarantees zero steady-state active power in each converter phase-arm, even in the presence of severe grid imbalance conditions, thus remaining decoupled from the inter-phase capacitor voltage balancing controller. Moreover, the proposed DM scheme exploits the possibility of clamping to the zero-voltage level, thus providing a more flexible discontinuous operation than conventional DM methods. This involves lower zero-sequence-voltage injection requirements and lower switching losses. The proposed modulation scheme is experimentally corroborated and its performance under different grid voltage conditions is compared with traditional modulation schemes.

New Discontinuous Space Vector Modulation Strategies for Impedance-Source Inverter With Superior Thermal and Harmonic Performance

Impedance-source inverters provide a promising single-stage power conversion with boost-buck capabilities and inverter legs short-circuit immunity. To achieve superior thermal and output harmonic performance, two novel discontinuous modulation strategies for the three-phase quasi-Z source inverter, called the maximum-boost discontinuous space vector modulation (SVM) and the simple-boost discontinuous SVM respectively, are proposed in this article. By properly arranging the shoot-through states and clamping a certain switch to the positive or negative dc-link rail during one-third of the fundamental period, reduced thermal stresses and superior total harmonic distortion performance can be achieved. The proposed modulation strategies are analyzed and compared to the conventional ones in terms of current stresses, power losses, thermal stresses, and output harmonics. Finally, simulations and experimental tests are carried out to validate the performance of the proposed modulation strategies and verify the presented analysis.

Dual-Buck Three-Switch Leg Converters With Reduced Number of Passive Components

Like conventional two-switch leg converters, the three-switch leg converters also have short-circuit risks and a dangerous shoot-through current is generated if switches of the same leg are turned <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> simultaneously. In this article, a new dual-buck structure is proposed for three-switch leg converters. The proposed structure is reliable because of no shoot-through concerns and high quality of output waveforms can be obtained due to the reduction in pulsewidth modulation deadtime. Unlike the conventional dual-buck three-switch leg that uses many passive components such as four current limiting inductors and three external diodes, the new dual-buck three-switch leg uses only one current limiting inductor with two external diodes. To verify the performance, the proposed three-switch legs are used in single-phase dual-output inverter and detailed theoretical analysis, simulation, and experiments are performed. Both continuous and discontinuous modulation schemes are applied and it has been figured out that discontinuous modulation scheme can improve the dc-link voltage utilization in the common-frequency mode of operation.

Novel discontinuous PWM for dc-link voltage balancing of multilevel quasi-nested topologies

ABSTRACT The use of multilevel power converters for its application in high demanding industrial processes and grid connected renewable energy conversion systems has nowadays become the most suitable solution. The main advantages of these converter configurations are: reduction in the blocking voltage stress, lower harmonic ratings, smaller filters for output and input stages. The proposed quasi-nested topology merges the advantages of the classical multilevel topologies, such as the NPC and ANPC configurations, addressing less active switching devices, lower blocking voltage stress. A novel discontinuous modulation technique, with controlled discontinuous gain, is implemented in order to deal with the dc-link voltage unbalance. Simulation and experimental validation results in a scaled-down power 1,5 kW three-phase converter prototype under different operational conditions using different modulation index are presented. The proposed four-level converter topology allows generating an additional output voltage level with the same semiconductor count as conventional three-level inverters such as NPC and ANPC with superior waveform quality, with a THDv reduction of 34.54% in comparison to the clamped inverters. Experimental tests carried out in a 1.5 kW setup verify the feasibility of the proposed topology and the developed discontinuous modulation scheme, to achieve dc-link voltage compensation.

Modulation Strategies for Thermal Stress Control of CHB Inverters

Cascaded H-bridge inverters have attractive features in terms of availability as well as superior performances of power quality and power conversion efficiency in comparison to nonmodular topologies. However, as the operation time goes by, basic cells of a modular architecture have uneven remaining useful lifetime because of slightly different electrical and thermal parameters causing uneven lifetime degradation of individual cells. From this viewpoint, the lifetime of cells needs to be individually managed, and this shall bring further improved reliability of the entire system and reduced maintenance costs. This article proposes discontinuous modulation strategies, which have ability to reduce the thermal stresses of more aged cells, consequently enabling the individual lifetime management of cells. The proposed modulation strategies are analyzed in terms of capability of loss control and are implemented in a feedback controller to validate the feasibility. In addition, the proposed methods are validated on an experimental test bench.

Comparative analysis of switching losses and current ripple of continuous and discontinuous SVPWM strategies for unbalanced two‐phase four‐leg VSI Fed unsymmetrical two‐phase induction motor

This paper presents a comparative analysis of the continuous space vector pulse width modulation and the discontinuous space vector pulse width modulation in terms of the switching losses and current ripple reduction for the unbalanced two-phase four-leg voltage source inverter fed unsymmetrical two-phase induction motor. The main function of both space vector pulse width modulation strategies is to produce unbalanced two-output voltages with constant phase shift of 90° for main and auxiliary windings. The discontinuous space vector pulse width modulation principle is modified from a traditional two-phase four-leg voltage source inverter by placement of the space vectors to alternatively eliminate zero space vector in each switching sequence. As a consequence, the proposed unmodulation region or clamping zone of the discontinuous modulation strategy has 180° all the time. The experimental results illustrate the modulation waveforms of both methods, output voltage spectrum, normalized switching losses, output current ripple and inverter efficiency at high modulation index. The evaluation of the normalized average switching losses and the current ripple of the discontinuous space vector pulse width modulation method can be reduced more than that of the continuous space vector pulse width modulation method.

A novel impedance source inverter topology with active front-end for AC drives

A unique impedance Source Inverter with an Active Front-End is proposed in this paper, that can be used for controlling AC Drives. There are a number of modulation schemes that may be used with the three-phase impedance source inverters, ultimate reduction in the switching losses makes the discontinuous modulation schemes seem most appropriate. The discontinuous modulation schemes are differentiated into two classes based on the technique used for achieving shoot-through (ST) state: single-phase-leg ST-based and three-phase-leg ST-based (3P) discontinuous modulation schemes. In this paper, we discuss the improvements in Single Phase Maximum Boost Discontinuous Space Vector modulation (1P/MB/DSVM) scheme under similar operating conditions, by simplifying gate signal generation and improving the conversion efficiency. A simulated analysis and comparison of the conventional and the enhanced 1P/MB/DSVM schemes is also discussed using PLECS. Lastly, verification of the simulation outcomes and reported analysis is carried out by making use of a three-phase quasi-Z-source inverter (qZSI) prototype which demonstrates improvement in conversion efficiency, utilizing the refined 1P/MB/DSVM scheme.

Simple discontinuous PWM strategies to reduce the switching losses of an indirect matrix converter

This work proposes the new discontinuous pulse width modulation (DPWM) schemes for an indirect matrix converter (IMC) to reduce the switching losses. The use of discontinuous modulation signals reduces the switching losses of the IMC by reducing the switching counts per cycle of the output converter. The key feature of the proposed schemes is the easy implementation as compared to existing DPWM schemes of the IMC. The major drawback of the existing DPWM schemes is the absence of zero current commutation (ZCC). In the absence of ZCC, the switchings of the input converter are accomplished through four-step commutation which adds the difficulties to the implementation. The proposed scheme overcomes above limitation by using the triangular carrier instead of the sawtooth carrier for the modulation of input converter. Consequently, the ZCC is enabled on the input converter which allows the use of two-step commutation. The two-step commutation simplifies the implementation to a great extent. The presented scheme provides the required input/output performance similar to continuous PWM (CPWM) schemes. The proposed work is verified by the simulation and experimental results. The reduction in the switching losses of the IMC by the new scheme is verified based on the comparison with the CPWM scheme.

A Fast Processing Discontinuous Control Strategy for Vienna Rectifier

In this paper, Vienna rectifier has been inspected as one of the prominent topologies among three-level switched-mode rectifiers. A fast processing discontinuous modulation strategy has been proposed with the aim of improving the rectifier’s performance. The proposed method not only takes advantage of special properties available in three-phase three-level rectifiers, but also reduces the control design complexity and the switching loss. Moreover, neutral point voltage balancing is inherently realized. To achieve these goals, the rectifier is decoupled into two 2-level boost converters in every defined region, leading to simple modulation algorithm and fast processing control strategy. The validity of the proposed technique has been verified via simulation and experimental results conducted on a laboratory prototype.

Thermal optimized discontinuous modulation strategy for three phase impedance source inverter

A novel space vector modulation (SVM) strategy called maximum-boost discontinuous SVM (MBDSV) is proposed in this paper to reduce the thermal stress of three phase impedance source inverters (ISI). By exploiting the switch clamping mechanism and arranging the shoot-through (ST) states properly, the proposed strategy obtains the flowing merits: further optimize the thermal performance, improve the reliability, reduce the current stress and maximize the dc-link utilization of ISI. The proposed MBDSV was compared to the existing modulation strategies and the feasibility of the MBDSV had been benchmarked by simulation and experiments.

A Modular Multilevel Dual Buck Inverter With Adjustable Discontinuous Modulation

Conventional single-cell dual buck inverters present high reliability, however they cannot be directly used in high voltage applications, because of the limited voltage rating of commercial switching devices. Therefore, a novel modular multilevel dual buck inverter (MMDBI), capable of processing voltage and power at higher levels, requiring a single dc input voltage, is proposed in this paper. Non-interleaved phase-shifted discontinuous modulation (NIPSDM) and interleaved phase-shifted discontinuous modulation (IPSDM) schemes are applied to the proposed inverter to reduce the current stress in the switching devices. Despite beneficial to the converter efficiency, the use of these discontinuous modulation approaches results in current zero-crossing distortion, which needs to be appropriately managed. In this work, theoretical values for the common-mode and differential-mode current ripples under NIPSDM and IPSDM modulation strategies are derived, and each switching operating mode is fully analyzed. From that, an adjustable current threshold value, which depends on the theoretical current ripple magnitude, is incorporated into the modulation strategy, producing a minimum switching overlap period between the two buck cells that eliminates the current zero-crossing distortion and produces a high-quality output current. Extensive simulation and experimental investigations are presented to demonstrate the feasibility and effectiveness of proposed topology and adjustable discontinuous modulation strategy.

A Novel Discontinuous Modulation Strategy With Reduced Common-Mode Voltage and Removed DC Offset on Neutral-Point Voltage for Neutral-Point-Clamped Three-Level Converter

In this paper, a novel discontinuous pulsewidth modulation (DPWM) modulation strategy for a neutral-point-clamped (NPC) three-level converter (TLC) is proposed to reduce the switching loss, reduce common-mode voltage (CMV), and remove dc offset from the neutral-point (NP) voltage simultaneously, which is named as RCMV_DPWM. Based on the space vector diagram with reduced CMV, all clamping modes under RCMV_DPWM are revealed. Then, the NP voltage is controlled by selecting proper clamping mode. The realization of RCMV_DPWM is also discussed. Moreover, the performances of RCMV_DPWM are analyzed and compared with other PWM strategies in term of the NP voltage ripple, switching loss, and waveform quality. Finally, the feasibility and superiority of RCMV_DPWM are verified by experiments.

A Flexible Discontinuous Modulation Scheme With Hybrid Capacitor Voltage Balancing Strategy for Three-Level NPC Traction Inverter

Multilevel inverters are now-a-days being applied in electric vehicles (EV). Considering the dynamic operating conditions of an EV propelled by an induction motor, this paper proposes a flexible discontinuous modulation strategy for three-level neutral-point-clamped (NPC) inverter that can shift modulation pattern seamlessly from sinusoidal pulsewidth modulation (SPWM) to discontinuous PWM (DPWM). The modulation scheme is generalized at each degree of discontinuity to ensure minimum switching losses for variable load power factors. Additionally, a hybrid voltage balancing strategy, which comprises two sets of compensating offset signals with complementary features, has been introduced to mitigate voltage deviation problem at neutral point of the inverter. The unique feature of the proposed hybrid balancing approach is that it generates uniform compensating neutral current regardless of the level of discontinuity. This results in identical and predictable voltage balancing dynamics for the entire modulation transition covering SPWM and DPWM. It has been shown that the proposed hybrid balancing strategy does not lose its unbalance compensation strength even during transition from one modulation pattern to another. The effectiveness of the proposed scheme for wide variations in operating conditions is studied through extensive simulation, and validated in experimentation using a prototype NPC inverter with induction motor loads.

A Generalized Discontinuous PWM Scheme for Three-Level NPC Traction Inverter With Minimum Switching Loss for Electric Vehicles

A discontinuous pulsewidth modulation (DPWM) strategy for three-level neutral-point-clamped (NPC) traction inverter drive for electric vehicles (EVs) with minimum switching loss for the full power factor (PF) range is developed and presented in this paper. Considering the dynamic loading conditions in an EV propelled by an induction motor (IM), the discontinuous modulation strategy is generalized to obtain minimum switching loss for a wide variations in load PF and modulation depth. The dynamic operating conditions in EV may render frequent unbalances in dc-link capacitor voltages in NPC inverter. It is demonstrated that the addition of an appropriate offset signal with the reference discontinuous signals generates compensating neutral current in the right direction, which can be used to mitigate existing unbalance in two dc-link capacitor voltages. Minimum switching loss at variable PF is attained by positioning the nonswitching clamped regions of the reference auxiliary signals according to the load PF. The effectiveness of the proposed scheme for a wide range of torque/speed variations is studied through simulation by developing a MATLAB/SIMULINK model of an IM traction inverter drive with field-oriented control strategy for closed loop control. Finally, the modulation scheme is validated through experimentation in a small-scale prototype NPC inverter with motor loads.

Thermally Compensated Discontinuous Modulation Strategy for Cascaded H-Bridge Converters

A widely adopted multilevel converter topology is the cascaded H-bridge (CHB), as it can provide voltage and power scalability. However, since the CHB converter can be composed by cells with different remaining lifetime, it could be useful to delay a fault of higher aged cells in order to prolong the entire converter's lifetime. In this paper, a thermally compensated discontinuous pulse width modulation (DPWM) strategy is proposed in order to reduce the thermal stress for power semiconductors in power modules of higher aged cells. Considering the thermal cycles as the most influencing cause of wear out of power modules, the proposed method compensates the thermal cycles under a varying power profile by manipulating the clamping angle of the DPWM. Moreover, the proposed method obtains a comparable total harmonic distortion performance to the phase-shifted carrier modulation.

Discontinuous Space Vector PWM Strategy of Neutral-Point-Clamped Three-Level Inverters for Output Current Ripple Reduction

In order to meet the high performance and efficiency requirements, a new space vector-based discontinuous modulation strategy for neutral-point clamped three-level inverter is presented in this paper. Different from the conventional discontinuous PWM (DPWM) strategies, a new clamping state is applied to synthesize the reference voltage under the condition of low modulation index. The rms value of output current ripple for different clamping states are calculated, and then the distribution of the new clamping state and the other two clamping states adopted in conventional DPWMs is optimized based on the calculation results. The switching sequences are redesigned according to the new distribution of the three clamping states. The output voltage and current, switching loss, neutral-point voltage ripple and the common mode voltage of the proposed DPWM strategy and DPWM0–DPWM3 are compared by simulation and experimental results. The results show that by the use of the proposed strategy, the values of total demand distortion of output current ( I TDD) and weighted total harmonic distortion of output voltage $({\boldsymbol{V}_{{\mathbf{WTHD}}}})$ are the lowest. Furthermore, the product of switching loss and $I_{\rm TDD}$ of the proposed strategy maintains the lowest within a large range of modulation index-load angle plane. It can be concluded that the utilization of the new clamping state and optimal distribution of different clamping states could enhance the output performance of the inverter. Moreover, the high-efficiency requirement can also be realized at the same time.

Modulation Scheme for Three-Phase Differential-Mode Ćuk Inverter

Three-phase differential-mode inverters are single-stage inverters, which have the potential to reduce the number of devices and cost with higher power density. Among such inverter topologies, differential-mode three-phase Cuk inverter (DTCI) has some advantage over other topologies, including modularity, lower number of switches, bidirectional power flow capability, and galvanic isolation. DTCI is a promising configuration for renewable-/alternative-energy applications with isolated and nonisolated structures. The continuous modulation scheme (CMS), which was introduced originally for the DTCI, activates all of three modules of the inverter. CMS increases the circulating power in modules and hence increases inverter power loss. This paper describes a discontinuous modulation scheme (DMS) for the DTCI which deactivates one module at a time resulting in a discontinuous operation of the inverter modules. The experimental open- and closed-loop results of DMS- and CMS-based DTCI are provided and compared. DMS reduces the circulating power, device voltage ratings, and mitigates the DTCI losses. The DTCI exhibits a nonlinear voltage gain with both DMS and CMS. It has been demonstrated that by feed-forwarding the input voltage and incorporating a static linearization method, the harmonic distortion of the output voltage is considerably reduced.

Hybrid Modulation Scheme for a High-Frequency AC-Link Inverter

This paper describes a hybrid modulation scheme for a high-frequency ac-link (HFACL) multistage inverter comprising a front-end dc/ac converter, followed by isolation transformers, an ac/pulsating-dc converter, and a pulsating-dc/ac converter. The hybrid modulation scheme enables 1) removal of the dc-link filter evident in conventional fixed dc-link (FDCL) inverters placed after the ac/pulsating-dc converter stage and before an end stage voltage source inverter and 2) significant reduction in switching loss of the inverter by reducing the high-frequency switching requirement of the pulsating-dc/ac converter by two-third yielding higher efficiency, improved voltage utilization, and reduced current stress. Unlike the FDCL approach, in the HFACL approach, hybrid modulation enables the retention of the sine-wave-modulated switching information at the output of the ac/pulsating-dc converter rather than filtering it to yield a fixed dc thereby reducing the high-frequency switching requirement for the pulsating-dc/ac converter. Overall, the following is outlined: 1) hybrid modulation scheme and its uniqueness, 2) operation of the HFACL inverter using the hybrid modulation scheme, 3) comparison of the efficiency and losses, current stress, and harmonic distortion between the hybrid-modulation-based HFACL inverter and the FDCL inverter, and 4) scaled experimental validation. It is noted that the term hybrid modulation has no similarity with the modulation scheme for a hybrid converter (which are conjugation of two types of converters based on a slow and fast device) reported in the literature. The term hybrid modulation scheme is simply chosen because at any given time only one leg of the inverter output stage (i.e., pulsating-dc/ac converter) switch under high frequency, while the other two legs do not switch. The outlined hybrid modulation scheme is unlike all reported discontinuous modulation schemes where the input is a dc and not a pulsating modulated dc, and at most only one leg stays on or off permanently in a 60° or 120° cycle.