Proposed Pulse Width Modulation Method Research Articles

3레벨 4레그 PWM 컨버터의 커먼 모드 전압 저감

This paper presents a carrier-based pulse-width modulation(PWM) method for reducing the common-mode voltage of a three-level four-leg converter. The idea of the proposed PWM method is intuitive and easy to be implemented in digital signal processor-based converter control systems. On the basis of the analysis of space-vector PWM(SVPWM) and sinusoidal PWM(SPWM) switching patterns, the fourth leg pole voltage of the three-phase converter called "f leg pole voltage" is manipulated to reduce the common-mode voltage. To synthesize f leg pole voltage for the suppression of the common-mode voltage, positive and negative pole voltage references of f leg are calculated. An offset voltage is also deduced to prevent the distortion of a, b, and c phase voltages. The feasibility of the proposed PWM method is verified by simulation and experimental results. The common-mode voltage of the proposed PWM method in peak-to-peak value is 33% in comparison with that of the conventional SVPWM method. The transition number of the common-mode voltage is also reduced to 25%.

Novel carrier‐based hybrid pulse width modulation method for cascaded capacitor‐clamp multilevel inverter

This study presents a new carrier-based hybrid pulse width modulation (PWM) Method for the cascaded capacitor-clamp multilevel inverter (CCCMLI), which combines the benefits of a new alternative level-shifted carrier PWM and a phase-shifted carrier PWM. For modulating the CCCMLI, the phase disposition sub-harmonic PWM was first proposed, but does not show good performances in an even load sharing between inverter cells connected in series, flying-capacitor voltage balancing and output waveform quality. On the other hand, a proposed PWM method enables to achieve a balanced load sharing between cascaded cells even at low amplitude modulation indices as well as the excellent voltage balancing control of the flying-capacitors with a much smaller voltage ripple and the good harmonic characteristics in output waveforms. The proposed modulation is verified through both simulation and field-programmable gate array (FPGA) based experimental results.

Dual Three-Phase Indirect Matrix Converter With Carrier-Based PWM Method

This paper proposes an indirect matrix converter (IMC) topology with dual three-phase outputs and its effective carrier-based pulse width modulation (PWM) method. The proposed IMC topology can independently supply ac power for two three-phase loads from a single three-phase ac power source. This converter consists of a rectifier stage used in traditional three-phase IMC and a five-leg inverter. Besides a proposed IMC topology, the carrier-based PWM method suitable for this converter is also introduced. The proposed PWM method is easily implemented by using only one symmetrical triangular carrier signal to generate the PWM signals for a rectifier and five-leg inverter. Proposed IMC topology features the advantages of conventional three-phase IMC, such as sinusoidal input/output current waveforms, controllable input power factor, and simple commutation at the rectifier stage. Analysis, simulation, and experimental results are provided to demonstrate the advantages of the proposed IMC topology with dual three-phase outputs and to validate the effectiveness of the applied modulation strategy.

Digital Implementation of PWM Techniques for Two-phase Eight-switch Inverter fed Brushless DC Motor Drives

This paper reports an investigation of pulse width modulation (PWM) techniques for two-phase brushless DC (BLDC) motors fed by a two-phase eight-switch inverter in a fan application. The three-phase BLDC motor is widely applied in industry; however, a lower-cost two-phase BLDC motor and drive circuit has been greatly in demand in recent years. In this paper, we introduce a mathematical model of the two-phase BLDC motor with sinusoidal back electromotive forces (EMFs) based on traditional three-phase BLDC motors. To simplify the drive algorithm and speed up its application, we analyze the principle of block commutation for a two-phase BLDC motor drive in the 180-electrical-degree conduction mode, and we further propose five PWM schemes to improve the commutation performance of the two-phase BLDC drive. The effectiveness of the proposed PWM methods is verified through experiments.

Implementation of an LED tile controller for high-quality image display

The development of large-size light-emitting diode (LED) screen area is emerging as an important application to keep step with progress in image technology. Recent large LED screens are required to display high-quality images. However, rapid changes and high pulses of the LED current cause wide hot spots and EMI problems in highly dense LED arrays, making implementation in up-scale, energy-efficient, low-pitch LED screens aiming is difficult and expensive.This paper presents a novel LED control method and its architecture, based on pulse width modulation (PWM) dimming, to overcome the aforementioned problems. We proposed a system to stochastically choose the timing of PWM pulses, using affordable hardware cost, and to handle LED arrays for which size is unrestricted. The experimental results, obtained using a commercial LED tile, show that the proposed PWM method is very efficient in diminishing the magnitude as well as the average variation in the LED current. In addition, considering the scalability and feasibility of the hardware structure, the practical value of our proposed LED tile controller seems to be very promising and competitive.

Thermal Analysis of Interior Permanent-Magnet Synchronous Motor by Electromagnetic Field-Thermal Linked Analysis

This paper reports an investigation of pulse width modulation (PWM) techniques for twophase brushless DC (BLDC) motors fed by a two-phase eight-switch inverter in a fan application. The three-phase BLDC motor is widely applied in industry; however, a lower-cost two-phase BLDC motor and drive circuit has been greatly in demand in recent years. In this paper, we introduce a mathematical model of the two-phase BLDC motor with sinusoidal back electromotive forces (EMFs) based on traditional three-phase BLDC motors. To simplify the drive algorithm and speed up its application, we analyze the principle of block commutation for a two-phase BLDC motor drive in the 180-electricaldegree conduction mode, and we further propose five PWM schemes to improve the commutation performance of the two-phase BLDC drive. The effectiveness of the proposed PWM methods is verified through experiments.

Novel Single-State PWM Technique for Common-Mode Voltage Elimination in Multilevel Inverters

In this paper, a novel offset-based single-state pulse width modulation (PWM) method for achieving zero common-mode voltage (CMV) and reducing switching losses in multilevel inverters is presented. The specific active switching state of the zero common-mode (ZCM) voltage that approximates the reference voltage can be deduced from the switching state sequence of the reduced CMV phase disposition PWM (CMV PD PWM) method. From the reference leg voltages for the zero common-mode voltage, an N-to-2-level transformation defines a virtual two-level inverter and the corresponding nominal leg voltage references. The commutation process of the reduced CMV PD PWM method in a multilevel inverter and its outputs can be simply followed in a nominal switching time diagram for the virtual inverter. The characteristics of the reduced CMV PD PWM and the single-state PWM for zero common-mode voltage are analyzed in detail in this paper. The theoretical analysis of the proposed PWM method is verified by experimental results.

New Hybrid Pulsewidth Modulation Technique to Reduce Current Distortion and Extend Current Reconstruction Range for a Three-Phase Inverter Using Only DC-link Sensor

This paper proposes a new modulation technique that can reduce the current distortion and extend the current reconstruction range for a three-phase inverter using only dc-link sensor. The proposed pulsewidth modulation (PWM) technique is a hybrid method which consists of space vector modulation method and the PWM method without using null switching states. The former provides low current distortion; however, it is with narrower current reconstruction range. In contrast, the latter extends the current reconstruction range at the cost of higher current distortion. For the proposed method, in the measurable region of space vector modulation method, space vector modulation is used to reduce the current distortion. Moreover, as the modulation range is out of the measurable region, the PWM method without using null switching states is applied to extend the current reconstruction range. Furthermore, the current reconstruction limitation using only dc-link sensor is analyzed. The analysis shows that the reduction of PWM switching frequency and acquisition time can extend the current reconstruction range. Comparison of experimental results derived from a field-programmable gate array-based controlled inverter is included. It will be demonstrated that using the proposed hybrid PWM technique, the three-phase current signals of the inverter can be reconstructed even under very low modulation index range while providing low current harmonic distortion of inverter output.

Pulsewidth Modulation Method of Matrix Converter for Reducing Output Current Ripple

A matrix converter interfaces with three-phase ac voltage source, which creates three different virtual dc-link voltages. In this paper, a new pulsewidth modulation (PWM) method for the matrix converter is proposed to generally use these three virtual dc-link voltages. By using the two higher line-to-line voltages as the virtual dc-link voltages, the proposed method can create the identical switching sequences to those created by the conventional space vector PWM (SVPWM) method. Moreover, the proposed method is able to select the appropriate virtual dc-link voltage, according to the PWM purpose and/or load condition. In this paper, the virtual dc-link voltages adjacent to the output voltage reference are introduced to reduce output-current switching ripples. The feasibility of the proposed PWM method was verified by a computer simulation and experimental results. The output voltage and current waveforms produced by using the proposed method can be equal or better than those created using the conventional SVPWM method. Moreover, a new switching sequence that reduces output-current switching ripple can be easily adopted within the proposed PWM method. The harmonic characteristics of output current created using the proposed method are markedly improved over those using the conventional PWM method.

Parabolic PWM for Current Control of Voltage-Source Converters (VSCs)

A novel parabolic carrier pulsewidth modulation (PWM) method is proposed in this paper for direct current control in a voltage-source converter (VSC). This method employs a pair of parabolic PWM carriers (a positive one and a negative one) to determine the switching states of the two switches in a converter phase leg while limiting the current tracking error within a nonlinear hysteresis band. Similar to the hysteresis PWM method, the proposed parabolic PWM can regulate both dc current and ac current with excellent and accurate dynamic response. Furthermore, as a carrier-based PWM method, the proposed parabolic PWM can maintain a constant switching frequency by the automatic peak current error adjustment through the PWM process. In this paper, the basic operation principle of the proposed PWM method is discussed, and its implementation scheme is presented. Simulation and experimental results based on a single-phase VSC with bipolar PWM implementation are provided.

A Carrier-Based PWM Method With Optimal Switching Sequence for a Multilevel Four-Leg Voltage-Source Inverter

In a three-phase four-wire utility system, three-phase unbalanced loads and many single-phase nonlinear loads result in a neutral line current that is zero-sequence current. To deal with unbalanced and nonlinear loads in a high power system, this paper suggests a multilevel four-leg pulsewidth modulation (PWM) voltage-source inverter (VSI) as a topology for the high power applications where a function is required to control the zero-sequence component as well as dq components. This paper proposes a carrier-based PWM method for a multilevel four-leg PWM VSI along with introducing a novel offset voltage. The proposed offset voltage makes it possible for the switching sequence of all the legs to be optimized for minimizing the harmonic distortion of the output voltage irrespective of the number of inverter levels. The proposed PWM method based on digital signal processors is implemented and tested by using a prototype three-level four-leg VSI. The feasibility of the proposed PWM method is verified by the spectral analysis, simulation, and experimental results.

PWM Methods to Handle Time Delay in Digital Control of a UPS Inverter

With the popularity of micro-processors, digital controllers are widely used in uninterruptible power supply (UPS) inverters. These digital control systems of UPS inverters require a time interval for sampling and computation, which sometimes affects the performance of inverters. In this paper, the problem of time delay in digital control of a UPS inverter is discussed. Then two novel pulsewidth modulation (PWM) methods, the two-polarity PWM method and the asymmetric PWM method, are proposed to handle the time-delay problem. Both of these PWM methods can achieve a wide range of duty ratio between 0.05-0.95, which is independent of inverter model. Furthermore, they are easy to implement using a digital micro-controller. Experimental results are presented in the paper to verify feasibility of the proposed PWM methods.

パルス幅変調方式による空気圧シリンダの位置制御に関する一考察

This paper proposes a PWM (pulse-width-modulation) control of a pneumatic single-rod cylinder positioning system. In the system, the rod chamber pressure of the cylinder remains constant, and the head chamber pressure is controlled by two solenoid valves. The valves are under PWM mode control. In synthesizing the PWM servomechanism, the solenoid valves are characterized by a static characteristic equation incorporating the nonlinear elements caused by the switching time of the valve. The proposed PWM method can assign the steady-state duty ratios of the valves to the desired locations of their flow characteristics, which makes it possible for the system to avoid the dead-zone or the nonlinear region caused by the PWM solenoid valves. Also, a threshold near the desired position is set up so that the valves are closed at steady state. An experimental study of the proposed system is performed. These experiments verify the theoretical design work, and indicate that the proposed control system is feasible for pneumatic positioning.