Discontinuous PWM Method Research Articles

A RANDOMIZED CARRIER-BASED DISCONTINUOUS PULSE WIDTH MODULATION STRATEGY FOR NEUTRAL POINT CLAMPED THREE-LEVEL INVERTER

This article introduces a novel approach called randomized carrier-based discontinuous pulse width modulation (RCDPWM) to address the challenge of mitigating both low-order and high-order harmonics concentrated at the switching frequency and its integer multiples in the output voltage and current of a three-level inverter. The proposed strategy reduces switching losses and a wide dispersion of voltage and current harmonics with significantly smaller amplitudes by integrating features from discontinuous and randomized PWM methods. This characteristic proves beneficial for enhancing efficiency and electromagnetic compatibility. The RCDPWM strategy involves three schemes: two simple schemes (one random parameter), randomized pulse position modulation (RPP-DPWM) and randomized carrier frequency modulation (RCF-DPWM), and a dual scheme combining the two previous ones (RPPRCF-DPWM). Power spectral density (PSD) is used to assess the effectiveness of the proposed strategy in quantitatively analyzing the harmonic dispersion degree. The results demonstrate that the proposed RCDPWM strategy significantly expands harmonic clusters around the switching frequency, reducing its intensity. The spectrum analysis revealed that the RPPRCF-DPWM scheme is the most effective in spreading the output voltage and current spectrum compared to simple schemes (RPP-DPWM and RCF-DPWM).

A Modified Discontinuous PWM Method for Three-Level Inverters With the Improved LCL Filter

A Modified Discontinuous PWM Method for Three-Level Inverters With the Improved <i>LCL</i> Filter

A Novel Discontinuous PWM Method With Hybrid Three-Step Commutation to Reduce Common-Mode Voltage for Direct Matrix Converter

A Novel Discontinuous PWM Method With Hybrid Three-Step Commutation to Reduce Common-Mode Voltage for Direct Matrix Converter

Development of Various Types of Independent Phase Based Pulsewidth Modulation Techniques for Three-Phase Voltage Source Inverters

Discontinuous pulse-width-modulation (DPWM) methods have been extensively used in the industrial area to reduce overall losses, which decreases the corresponding thermal stress on the power switches of converters. However, local thermal overload can arise due to different aging conditions of semiconductor devices or failure in the cooling system. This leads to reduced reliability of the converter system due to the low expected lifespan of the most aged switches or phase legs. In this paper, the modified DPWM strategies for independent control of per-phase switching loss are introduced to deal with this matter. The proposed per-phase DPWM techniques are generated by modifying the conventional three-phase DPWM methods for reducing the switching loss in a specific leg, whereas the output performance is not degraded. This paper reports on output performance, including output current total harmonic distortion (THD) and power loss of switching devices, analysis for the various modified DPWM strategies for independent control of per-phase switching loss, which is applicable in 2-level 3-phase voltage source inverters (2L3P VSIs). The results are compared to the corresponding continuous PWM technique to verify and analyze the effectiveness and accuracy of the modified DPWM strategies for independent control of per-phase switching loss.

Discontinuous PWM Technique With Reduced Low-Order Harmonic Distortion for High-Power Applications

The modulation techniques used in high power applications have to generate high quality waveforms with reduced switching losses. As an attractive alternative, Discontinuous PWM (DPWM) techniques present lower device switching frequencies than conventional continuous PWM methods lowering the converter switching loss. Considering the same cooling system, this allows to increase the carrier frequency of DPWM methods displacing the main switching harmonics to higher frequencies. As a main drawback, when low carrier to fundamental ratios are used, DPWM methods present some undesired low-order harmonics that are required to be filtered. This paper presents a low-order harmonic minimization method for synchronous DPWM methods by modifying the conventional modulating reference to limit low order harmonics amplitude, while keeping the same effective switching frequency and thus limited switching losses.

Dual randomized discontinuous pulse width modulation for three-phase inverter

ABSTRACT The discontinuous PWM technique, with its advantage over the continuous PWM technique in reducing switching losses in power converters, is gaining popularity. However, its deterministic nature results in discrete harmonics with significant amplitudes, which leads to electromagnetic interference (EMI) emissions. The randomised PWM technique is gaining more interest because of its effectiveness in spreading the harmonic spectrum and thus reducing EMI problems in power converters. This paper presents a carrier-based dual randomised discontinuous PWM (DRDPWM) method for a three-phase voltage inverter. The DRDPWM method combines the random carrier frequency (RCF-DPWM) and random pulse position (RPP-DPWM) schemes. In addition to reducing switching losses, DRDPWM can achieve a broad spread of the voltage spectrum with significantly smaller amplitudes. Furthermore, it produces less inverter output current distortion when compared to traditional DPWM and simple random (RCF-DPWM and RPP-DPWM) schemes. Simulations and experimental results confirm the effectiveness of the suggested method for spreading the voltage spectrum compared to simple random schemes. Additionally, an evaluation of the performance of all randomised discontinuous schemes is conducted based on a number of assessment metrics, including the switching loss factor (SLF), the power spectral density (PSD), the harmonic spread factor (HSF), and the quality factor (QF).

A Carrier-Based Discontinuous PWM for an 80 Kw PV Inverter With the Reduction of the DC-Link Voltage Ripple and Common Mode Current

Discontinuous pulse width modulation (DPWM) method is broadly used in three-phase inverter to achieve high efficiency through the reduction of the switching loss. The high-power rating photovoltaic (PV) inverter with DPWM has its intrinsic issues such as large DC-link voltage ripple and high-frequency resonant current due to the large stray capacitance proportional to the power rating. To extend the application of DPWM from 10 kW to 80 kW PV inverter, a new DPWM method (DPWMn) which divides the clamping period into <i>n</i> intervals is proposed to achieve the three objectives simultaneously: 1) reduction of the DC-link voltage ripple; 2) suppression of the high-frequency current oscillation; 3) improve the efficiency compared to the continuous space vector PWM (SVPWM). The proposed DPWMn is validated by an 80 kW three-phase T-type PV inverter. Compared to the SVPWM, the DPWMn has reduced 30&#x0025; switching loss while maintaining the similar power quality and the common mode current. Compared to the existing DPWM methods, DPWMn reduces the voltage ripple by 52&#x0025; and has the minimum energy ripples. Furthermore, the carrier-based DPWMn only utilizes the measured voltage and can be easily implemented.

Theoretical Study of Rampwise DPWM Technique to Reduce Motor Acoustic Noise

Motor acoustic noise generated near living environments such as elevators and electric vehicles may cause discomfort. In order to reduce the acoustic noise, the switching frequency is set to the high side of the audible frequency range. In this case, however, the switching loss is increased. The conventional discontinuous PWM (DPWM) method is widely used since it can reduce the switching loss drastically. However, it produces larger acoustic noise than the conventional sinusoidal PWM method. The authors have previously proposed Rampwise DPWM techniqueh which can reduce both acoustic noise and switching loss. In this paper, the line-line voltage with the proposed Rampwise DPWM technique is expanded into a real-valued Fourier series, and the frequency characteristics are analyzed. It is theoretically confirmed that the rampwise part in the Rampwise DPWM technique can achieve reduction of motor acoustic noise. Furthermore, the reduction effect of motor acoustic noise with the Rampwise DPWM technique is theoretically and experimentally verified.

태양광 시스템에서 불연속 전압 변조 방법 적용에 따른 단상 5-레벨 T-type NPC 인버터의 전력 반도체 소자의 전력손실 및 열 부하 분석

The pulse width modulation method has a significant effect on the power losses and thermal loadings of power devices of a single-phase five-level T-type NPC photovoltaic (PV) inverter. In this paper, the comparative analysis of the power losses and thermal loadings of a single-phase five-level T-type NPC inverter is performed under the different pulse width modulation methods. When the unipolar pulse width modulation method is applied, the power losses and thermal loadings of the power devices are evaluated, and the reliable critical power devices with the highest thermal loadings are identified. Subsequently, the power losses and thermal loadings of the power devices are analyzed by applying the discontinuous pulse width modulation methods such as one-pole clamping pulse width modulation method and equally distributed discontinuous pulse width modulation method. Their effects on the reliability of the inverter are evaluated. Additionally, the operation of a T-type NPC inverter with three PWM methods is verified through the experiment.

불연속 전압 변조 방법 적용 범위에 따른 태양광 NPC 인버터의 DC-link 커패시터 신뢰성 분석

The voltage modulation method has a significant effect on the performance of 3-level neutral-point clamped (NPC) inverters such as efficiency and output quality. Discontinuous pulse width modulation (DPWM) has been proposed to improve efficiency by reducing the switching loss of power devices. In previous research, the output quality, power loss, and reliability of the power device were considered when the DPWM method was applied. However, the influence of the DPWM on the reliability of DC-link capacitors, one of the reliability-critical components, has not been investigated. In this paper, the effect of DPWM on the reliability of DC-link capacitors is studied in the NPC inverter. Considering the mission profile of the photovoltaic (PV) system, the accumulated damage of DC-link capacitors is analyzed at the component level first under different applied angles of DPWM. The reliability of DC-link capacitors is then evaluated at the system level by considering all capacitors of the NPC inverter. In addition, the current of the DC-link capacitor is analyzed through the experiment to validate the negative effect of the DPWM on the reliability of the DC-link capacitor.

Reliability-Oriented Optimal DPWM Strategy for Single-Phase Five-Level T-Type Inverter in PV Systems

Many efforts have been devoted to improving the reliability of PV inverters with a focus on reliability-critical components such as power devices and capacitors. Discontinuous pulsewidth modulation (DPWM) methods are representative of improving the reliability of power devices by decreasing their thermal loadings. However, although the DPWM method affects the ripple current of the DC-link capacitor, prior-art research is only focusing on the power devices. There is a lack of study on the effect of applying the DPWM method on the reliability of the DC-link capacitor. It may have a negative effect on the reliability of the DC-link capacitor and thus affects the reliability of overall PV inverters. In this article, the influence of the DPWM method with different clamping periods on the reliability of power devices and DC-link capacitors of the single-phase five-level T-type inverter is investigated, where a 7-kW PV system and annual mission profile of PV system are considered as a case study. Then, a reliability-oriented optimal DPWM strategy is presented for the target lifetime of the T-type inverter by considering system-level reliability, including the lifetimes of both power devices and DC-link capacitors.

Advanced DPWM Method for Switching Loss Reduction in Isolated DC Type Dual Inverter With Open-End Winding IPMSM

This paper proposes an advanced discontinuous pulse-width modulation (DPWM) scheme for a dual inverter to reduce switching loss. A dual inverter is used to drive an open-end winding interior permanent magnet synchronous motor (OEW-IPMSM). It is composed of double two-level inverters with large switching loss owing to the use of 12 switching devices. When a current phase changes, the switching loss cannot be minimized by using a conventional DPWM scheme. As the conventional DPWM scheme uses reference voltage for switching, the switching loss cannot be minimized due to the difference between the phases of the stator current and phases of reference voltages. However, the proposed DPWM scheme with additional calculations of the current phase can minimize switching loss. When the current phase changes, the proposed DPWM is switched to ±30° of the maximum point of the current. Furthermore, the effectiveness of the proposed switching loss reduction ability is verified through simulations and experimental results.

An Improved DPWM Method for Single-Phase Five-Level ANPC Converters With Switching Loss Reduction and Capacitor Voltage Balance

Neutral-point (NP) voltage and flying capacitor (FC) voltage balance, and power loss reduction are important guarantees for the stable and high-efficiency operation of single-phase five-level active neutral-point clamped (5L-ANPC) converters. However, little reports about capacitor voltage balancing with the power loss reduction have been proposed for single-phase 5L-ANPC converters. In order to obtain the above merits, an improved discontinuous pulsewidth modulation (DPWM) method with capacitor voltage balance and power loss reduction is proposed. First, an optimized common-mode voltage is injected into the modulation waves to decrease the switching loss in each switching period. In particular, the calculation of the injected common-mode voltage is based on the analysis of the deviation of the NP voltage. Hence, a fast-dynamic response of the real-time NP voltage controlling is acquired in the meantime. Besides, in order to balance the FC voltage, the weight factors of NP voltage deviation and FC voltage deviation are compared to generate the selecting signals of redundant switching states. As a result, the capacitor voltage balance and power loss reduction are realized simultaneously. Finally, the simulation and experimental results validate the correctness and feasibility of the proposed DPWM method.

A Carrier-Based Discontinuous PWM Scheme With Optimal PWM Sequences for a Five-Level Flying Capacitor Rectifier

Five-level flying capacitor (5L-FC) rectifier is advantageous in unidirectional power applications due to its less power devices, higher power density, better reliability, etc. To further improve the efficiency, discontinuous PWM (DPWM) methods are preferred. This article investigates a carrier-based implementation of DPWM for the 5L-FC rectifier to reduce the switching losses. Since there is always a pair of redundant switching modes that have opposite effects on the neutral point (NP) in each region of the space-vector diagram, the NP voltage regulation can be easily realized by selecting suitable clamping modes in each control period, even with unbalanced dc loads. The generated PWM sequences based on the phase disposition PWM are also optimally redistributed to realize minimal switching loss with FC voltage balancing in two consecutive carrier periods. In addition, the permissible range of unbalanced dc loads is theoretically deduced. Finally, simulations and experiments are conducted to verify the performance of the proposed carrier-based DPWM scheme.

3-레그형 2상 인버터에서의 전류 복원 영역 확장

For measuring phase currents of two-phase motors driven by the three-leg inverters, the leg shunt resistors inserted between the lower switch of each inverter leg and the negative DC rail can be used instead of the expensive Hall-effect sensors. The two-leg shunt method using shunt resistors located on the two-phase legs has a limited current measurement range. In addition to this method, the three-leg shunt method can reconstruct the immeasurable phase currents by using an additional shunt resistor on a neutral leg. Therefore, the current measurement range can be wider than that in the two-leg shunt method. However, this method cannot properly reconstruct the currents in the specific areas where the voltage modulation index of the inverter is high, thereby decreasing the DC voltage utilization rate, and increasing the torque ripple of the motors. To improve this problem, this paper analyzed the current reconstruction areas of a three-leg type two-phase inverter applied CPWM(Continuous Pulse Width Modulation) method, and proposed a simple technique to expand the areas. The proposed technique can expand the current reconstruction areas by securing the turn-on time of the inverter lower switches utilizing the DPWM(Discontinuous PWM) method, which results in the improvement of DC voltage utilization rate.

Research and Development of Adjustable Discontinuous Pulse Width Modulation Method for Three-Phase Voltage Source Inverter

Continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM) strategies are used to control voltage source inverter operation. CPWM strategies allow for the reduction of total harmonic distortion values, while DPWM strategies provide a more effective reduction in inverter switching losses. The paper is devoted to the problem of improving the three-phase voltage source inverter efficiency by a controlled transition from CPWM to DPWM. The article proposes an adjustable discontinuous pulse width modulation (ADPWM) method, which means a transition from space vector PWM (refers to CPWM strategies) to DPWM in all inverter phases when the switches’ temperatures exceed the allowable value in at least one of the inverter phases. The method flowchart is presented and an algorithm for modifying the envelope curve within one sector is given. In order to test the ADPWM method a Simulink-model of a three-phase voltage source inverter and its control system were developed. A study of the proposed ADPWM method’s efficiency in comparison with CPWM, PCDPWM and NCDPWM methods was carried out using a Simulink-model. It was established that the proposed ADPWM method provides dynamic losses reduction in the inverter switches by 2.86 times compared to CPWM and by 1.89 times compared to PCDPWM and NCDPWM methods. Power supply systems for medium and high-power AC motors provide a promising area for application of the proposed ADPWM method.

DPWM 기법을 적용한 비엔나 정류기의 L 필터 설계

This paper proposes the L-filter design method of Vienna rectifier with the DPWM(Discontinuous Pulse Width Modulation) method for satisfying the desired input current THD(Total Harmonic Distortion) specification. The input voltage waveform of Vienna rectifier with DPWM method is analyzed in this paper. The input current ripple is decided by the voltage applied to both end-points of the L-filter, which is voltage difference between the gird voltage and the input voltage of Vienna rectifier. In addition, the RMS(Root Mean Square) value of the input current ripple is derived by using on the waveform of input current ripple. In this paper, the RMS value of the input current ripple is used to design the L-filter satisfying the current THD specification of Vienna rectifier with DPWM method. The effectiveness of the proposed L-filter design method for Vienna rectifier with the DPWM method is verified through simulations and experiments.

A Carrier-Based Discontinuous PWM Method for a Five-Level Flying Capacitor Rectifier With Unbalanced DC-Link Voltages

Unbalanced dc-link voltages occur when five-level flying capacitor (5L-FC) rectifier has dual dc loads of different rated voltages. Compared with traditional continuous pulsewidth modulation (CPWM) strategies, discontinuous PWM (DPWM) methods have more advantages in high-frequency and high-power applications for less commutation and higher efficiency. Therefore, this article proposes a carrier-based DPWM method for 5L-FC rectifiers with unbalanced dc-link voltages. The proposed method is first analyzed in the revised space vector diagram considering unbalanced dc voltages to divide subsectors and find available clamping modes, then it is implemented by applying carrier-based PWM with injecting clamping compensation component, which greatly reduces the implementation complexity. There is a pair of redundant clamping modes with opposite effects on the neutral-point (NP) in each subsector. Thus, the NP voltage can be actively controlled by selecting suitable clamping mode in each subsector. In addition, the allowable ranges of unbalanced voltage degree and unbalanced power degree are investigated in detail. Simulations and experiments verified the effectiveness and performance of the proposed method.

A Semidiscontinuous PWM Method for Suppression of the Resonant Current in a 48 Kw Grid-Tied PV Inverter

In conventional discontinuous pulsewidth modulation (DPWM) methods, the drastic change of the modulation index during the clamping transient results in grid current oscillation, which deteriorates the power quality. This article presents a semi-DPWM method for a three-level T-type grid-connected PV inverter. The semi DPWM is achieved by injecting a continuous sinusoidal signal during the clamping transient, which reduces the grid current oscillation and reduces the total harmonic distortion of the current. First, a detailed analysis of the grid current oscillation is presented, then a semi-DPWM method is proposed to suppress the oscillation current. The experiment is carried out on a 48-kW grid-tied PV inverter to validate the effectiveness of the method. Compared with the space vector PWM, results show that more than 42.5% switching loss has been reduced with the semi DPWM and the efficiency is increased from 97.03 to 97.22% at the rated load. Besides, the semi DPWM method significantly suppresses the current oscillation and maintains good power quality under various operation conditions.

Carrier Selection Strategy of Generalized Discontinuous PWM Method for Current Reduction in DC-Link Capacitors of VSI

This article proposes a new carrier selection strategy of generalized discontinuous pulsewidth modulation (GDPWM) method for the two-level three-phase voltage source inverter to reduce the dc-link capacitor current under all operating conditions while keeping the minimum switching losses. First, the root-mean-square value of dc-link capacitor current is effectively reduced by selectively using both single and double carrier signals and modifying the switching patterns of existing GDPWM method. Although the proposed carrier selection strategy depends on the power factor (PF), the PF calculation is avoided because the multicarrier signals are properly chosen based on the information of three-phase modulation signals and measured three-phase currents. Also, the switching losses can be kept to a minimum as the modulation signals of conventional GDPWM method, which are optimal in terms of the switching losses, remain the same and the proposed carrier selection strategy has little effect on the total number of switching events. The operating principle of proposed GDPWM method is theoretically analyzed. Then, its practical effectiveness is verified by experimental tests on a motor drive system.