Discontinuous PWM Method Research Articles

DPWM 방식을 적용한 3상 계통 연계 인버터의 LCL-필터 설계

This paper proposes a design method of LCL-filter for a grid-connected three-phase inverter using a discontinuous PWM (DPWM) method. When using a DPWM method, many harmonic voltages are generated in the inverter output compared to a continuous PWM (CPWM) method. Therefore, an optimized grid-connected filter design is required for a DPWM method. The proposed design method provides generalized formula to design accurate LCL-filter without trial and error procedures. An inverter side inductance is designed by analyzing the current ripple injected to the grid. The Optimized parameters of LCL-filter can be designed by analyzing the total harmonic distortion (THD) and the ripple attenuation factor of the output current. The proposed LCL filter design method is demonstrated by simulation and experimental results.

Global synchronous discontinuous pulse width modulation method with fast calculation capability for distributed three-phase inverters

When multiple distributed converters are integrated, the high frequency harmonics will randomly accumulate at the point of common coupling (PCC). This paper proposes a new fast global synchronous discontinuous pulse width modulation (GSDPWM) method of three-phase inverters to effectively attenuate the high frequency current harmonics at PCC. Firstly, the basic principle and the realization method of GSDPWM for three-phase inverters are explained, which can be employed for different modulation types. Then a fast calculation method, which can equally derive the minimized total harmonic distortion (THD) of total current, is proposed to release the calculation burden. Finally, MATLAB simulations and experimental results are presented to verify the performance of GSDPWM.

A New DPWM Method to Suppress the Low Frequency Oscillation of the Neutral-Point Voltage for NPC Three-Level Inverters

In order to suppress the low frequency oscillation of the neutral-point voltage for three-level inverters, this paper proposes a new discontinuous pulse width modulation (DPWM) control method. The conventional sinusoidal pulse width modulation (SPWM) control has no effect on balancing the neutral-point voltage. Based on the basic control principle of DPWM, the relationship between the reference space voltage vector and the neutral-point current is analyzed. The proposed method suppresses the low frequency oscillation of the neutral-point voltage by keeping the switches of a certain phase no switching in one carrier cycle. So the operating time of the positive and negative small vectors is equal. Comparing with the conventional SPWM control method, the proposed DPWM control method suppresses the low frequency oscillation of the neutral-point voltage, decreases the output waveform harmonics, and increases both the output waveform quality and the system efficiency. An experiment has been realized by a neutral-point clamped (NPC) three-level inverter prototype based on STM32F407-CPLD. The experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed DPWM method.

Modified scalar discontinuous pulse‐width modulation method for two‐level three‐wire voltage source inverters under unbalanced and distorted conditions

The discontinuous pulse-width modulation (DPWM) method is well known and has a wide range of applications. This method uses phase values as reference signals. DPWM modulator improves the inverter efficiency and linearity range, while a poor inverter output is experienced at lower modulation indices. Under unbalanced and distorted conditions, online conversion of line-to-line values into phase values is not possible. However, the line-to-line voltages are measurable in any application. The proposed technique is the first scalar method that directly uses line-to-line voltages as reference signals. A modified DPWM method that shows better performance characteristics is introduced for three-phase three-wire two-level voltage source inverters. The proposed method achieves the maximum possible output voltage with an appreciable performance in terms of harmonic distortion and switching losses without injecting a zero-sequence signal. Therefore, the method is referred as implicit zero-sequence DPWM (IZDPWM). IZDPWM was verified under balanced, unbalanced and distorted conditions in both simulation and experimental testes. Simulation and experimental results demonstrate the validity and the performance of the proposed method.

Carrier-Based Discontinuous PWM Method for Vienna Rectifiers

Vienna rectifiers, which are nongenerative-boost types of rectifiers, are used in grid-connected applications with a unity power factor such as telecommunication systems and wind turbine systems. These rectifiers are advantageous in that they have low total harmonic distortion and efficiency. There are many switching methods, which are different from those of threelevel topologies, for Vienna rectifiers. In this paper, we propose a carrier-based discontinuous pulse width modulation (CB-DPWM) method. This method is simple compared to the discontinuous PWM (DPWM) method for Vienna rectifiers based on space vectors and guarantees normal rectifier operation for all modulation index (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) values. We perform experiments to verify the suitability and performance of the proposed CB-DPWM method.

An Effective Carrier-Based Modulation Strategy to Reduce the Switching Losses for Indirect Matrix Converters

In this paper, an effective carrier-based modulation (CBM) strategy to reduce the switching losses for indirect matrix converters (IMCs) is presented. The discontinuous pulse width modulation method is applied to decrease the switching numbers in one carrier cycle, and an optimum offset voltage is selected to avoid commutations of the high output phase currents. By decreasing the switching numbers along with avoiding commutation of the high currents, the proposed CBM strategy significantly reduces the switching losses in IMCs. In addition, the proposed CBM strategy is independent of load conditions, such as load power and power factor, and it has good performance in terms of the input/output waveforms. Simulation and experimental results are provided to verify the effectiveness of the proposed CBM strategy.

Phase-shifted Discontinuous Pulse-Width Modulation Methods for Multi-level Inverters Operated in Over-modulation Range

This article presents combinations of the generic phase-shifted pulse-width modulation method with conventional discontinuous pulse-width modulation methods operated in the over-modulation range. The treated discontinuous methods are the third harmonic injection, Depenbrock's DPWM1, and Ogasawara's DPWM2. The significant advantage of the present approach over the conventional phase disposition pulse-width modulation method is the equal power flow between the H-bridges and the improved distribution of the switching operations number between them. Furthermore, they provide improved linearity in the over-modulation range. The proposed pulse-width modulation methods are analyzed by extensive simulation results. Several aspects, such as the total harmonic distortion factor of the inverter output currents and voltages, harmonic content, frequency spectrum distribution, and switchings number, are studied.

Generalized Space Vector Pulse Width Modulation Technique for Cascaded Multilevel Inverters

In this study, a generalized space vector pulse width modulation (SVPWM) method is proposed for cascaded H-bridge multilevel inverters. An explicit modulation function expression of the generalized SVPWM method is established for a single-stage cascaded inverter. Various continuous SVPWM and discontinuous PWM methods are obtained easily by changing the zero vector distribution coefficient. The generalized SVPWM method for cascaded multilevel inverters is achieved via the carrier phase shift strategy. A simple digital realization method for the generalized SVPWM is also proposed. By using this method, complex trigonometric function calculations, coordinate transformations, space vector selections, and duration time calculations are avoided. Finally, the simulation model and experimental device of the eight cascaded multilevel inverters are built to test the proposed method. The harmonic characteristics of the different modulation method are also analyzed. Simulation and experimental results demonstrate the feasibility and effectiveness of the method.

Compatibility Issues Between the Filter and PWM Unit in Three-Phase AC Motor Drives Utilizing the Pure Sine Filter Configuration

Inserted between the inverter and the ac motor for the purpose of providing clean sinusoidal voltage at the motor terminals, the pure sine filter (PSF) involves common-mode and differential-mode suppression components. When using PSF in a motor drive and employing advanced pulsewidth modulation (PWM) techniques with discontinuous modulation waveforms, a large common-mode current may circulate through the inverter and the filter resulting in overcurrent stress in the inverter and significant acoustic noise in the filter inductors. This paper first discusses the PSF and advanced PWM techniques, then investigates the performance issues that may arise when combining advanced discontinuous PWM methods with PSF and provides a curement for the overcurrent stress problems by means of a rate of change limiter. The simulations and detailed experimental studies illustrate the inverter overcurrent stress problems and the feasibility of the proposed method to cure the problems. Via experimental performance evaluation of various PWM methods, the paper also suggests, along with PSF, the use of advanced continuous and discontinuous PWM methods with reduced common-mode voltage for the purpose of performance enhancement and filter size reduction.

An Optimized Discontinuous PWM Method to Minimize Switching Loss for Multilevel Inverters

This paper presents a novel approach to analyze carrier-based discontinuous pulse width modulation (DPWM) method for multilevel inverters. The separation of the offset into the main and additional components shows the use for analyzing PWM control characteristics of multilevel inverters. The results are then applied to propose a novel minimized loss DPWM method by varying the offset depending on peak values of three-phase load currents. As results of avoiding commutations at high currents, the switching loss can be reduced. The proposed method is theoretically analyzed and verified by experimental results.

Analysis and Simplification of Three-Dimensional Space Vector PWM for Three-Phase Four-Leg Inverters

The main objective of this paper is to simplify the implementation of continuous and discontinuous 3-D space vector pulsewidth modulations (SVPWMs). This paper analyzes the relationships, whether in or coordinates, between three-phase voltages and the following elements: the tetrahedron in which the reference vector resides, three adjacent active switching vectors (or three switching states), and their duration times. Based on the analysis, the calculation of the turn-on time of each switch in the actual implementation is simplified, and discontinuous PWM (DPWM) methods in three-leg inverters can be extended to four-leg inverters without the phase angle. In addition, two more DPWM methods that are peculiar to 3-D SVPWM are presented. This simplified algorithm does not use irrational operations or look-up tables, and it alleviates the computation burden of the processor. The simulation and experimental results are provided to validate the effectiveness of the proposed algorithm.

Direct torque control of induction motor based on advanced discontinuous PWM algorithm for reduced current ripple

In recent years several discontinuous pulse width modulation (DPWM) methods are reported to improve the performance of AC drives at high modulation indices. It is proved that the performance of the popular PWM methods is modulation index dependent and no single DPWM method provides satisfactory performance over the entire high modulation range. Two popular existing DPWM methods renowned with the names DPWMMIN, DPWMMAX clamp each phase for 120° duration in every cycle of its fundamental voltage. It is observed that only the zero state is different in these two sequences. In this paper, it is proposed that, utilizing these two DPWM sequences and by changing the zero state at any spatial angle γ, where γ is between 0° and 60°, an infinite number of DPWM sequences including the existing DPWM methods and advanced DPWM (ADPWM) methods can be generated which are categorized as “continual clamping” and “split clamping” sequences. Using these ADPWM techniques an optimal split clamping sequence-based DTC of induction motor is proposed. With the proposed DTC method it is shown that steady state line current distortion at higher line side voltages is reduced significantly compared with the CDTC as well as conventional SVPWM (CSVPWM)-based DTC.

A Scalar Resonant-Filter-Bank-Based Output-Voltage Control Method and a Scalar Minimum-Switching-Loss Discontinuous PWM Method for the Four-Leg-Inverter-Based Three-Phase Four-Wire Power Supply

An all-scalar-control and pulsewidth-modulation (PWM) approach for the four-leg-inverter (FLI)-based three-phase transformerless four-wire power supply (PS) is proposed. The output voltage of each phase is controlled independently, and its controller is formed by a stationary-frame resonant-filter bank accompanied with proportional-control and output-capacitor current-based active-damping loops. The simple and easy to implement scalar-control method exhibits superior overall steady-state and dynamic performance in the PS applications involving loads with high crest factor and/or significant load imbalance. Utilizing the inverter zero-state partitioning, a generalized form of scalar PWM for the FLI is developed. A novel minimum loss discontinuous PWM method, which provides minimum switching losses under all loading conditions (including load imbalance), is derived. This simple scalar method provides superior performance, and unlike the vector methods, it is easy to implement. The controller and modulator design and implementation details for the system are given. Linear and nonlinear loads for balanced and imbalanced load operating conditions are considered. The scalar-control and PWM methods are proven by means of theory, simulations, and thorough laboratory experiments of a 5-kVA PS.

A Discontinuous PWM Method for Balancing the Neutral Point Voltage in Three-Level Inverter-Fed Variable Frequency Drives

The paper describes a new discontinuous carrier-based pulsewidth modulation (PWM) method for use in variable frequency drives (VFD) driven by three-level inverters. The method introduces three different switching patterns for the full range of operating speeds. Depending on the actual operating speed, the proposed algorithm is developed to select the most suitable PWM switching pattern that improves the VFD performance. This results in low imbalance in the DC-link capacitor voltage, and low current distortions without increasing switching losses. Theory, simulation, and experimental results are presented.

Simple control strategy for balancing the DC-link voltage of neutral-point-clamped inverter at low modulation index

A simple control strategy is proposed based on the discontinuous PWM (DPWM) to balance the DC-link voltage of three-level neutral-point-clamped (NPC) inverter at low modulation index. It introduces new DPWM methods and one of them is applied to balancing the DC-link voltage. The current flowing into the neutral point of DC-link capacitors causes the fluctuation of neutral point potential in the NPC inverter. The proposed DPWM method changes the path and duration time of the neutral point current, which makes the overall variation of it zero during the sampling time of the reference voltage vector. Therefore, using the proposed strategy, the neutral point potential of DC-link capacitors can be balanced fairly well and its ripple is also reduced significantly. Moreover, compared with conventional methods that have to perform the complicated calculation, the proposed strategy has been very simple. The proposed DPWM method has been verified by experiment.

Graphical and Algebraic Synthesis for PWM Methods

The article proposes an algebraic synthesis for PWM methods, which is based on a graphical representation of the 2 levels VSI (Voltage Source Inverter). This theory can be the starting point for every PWM method representation.In order to understand the historical evolution of the PWM methods the authors propose two classification groups of the main PWM techniques. The main classification is based on the movement of the neutral point (zero-voltage VN0 evolution). The details of PWM methods presented here are also seen from the graphical representation perspective.The equivalence between the well-known SVM (Space Vector Modulation) practically DDT realized (Direct Digital Technique) and the three-phase PWM with a carrier based industrial realization is shown. The principles of the three-phase PWM and the 3rd harmonic injection PWM (THIPWM4, THIPWM6) are compared the same as the DPWM (Discontinuous PWM) methods. These classifications and equivalences between different techniques show that the number of contemporary used PWM principles can be reduced. The general complex space representation and the classifications proposed here are simple to comprehension educational tools and they simply the way towards practical implementation.