Unipolar Pulse Width Modulation Research Articles

A Bipolar Voltage Modulation Spectrum Analysis

Features of power grid based on renewable energy sources are described. The necessity of isolated power converters in the power grid is shown. Low harmonics negative impact in modulated AC voltage based on unipolar pulse width modulation for transformer weight of isolated invertors is underlined. An approach of bipolar voltage generation with inverting every second modulation pulse that significantly decreases the low harmonics amplitude and allows to decrease the transformer weight in several times is described. A double Fourier series implementation for bipolar voltage analysis that allows expressing a signal spectrum characteristic in compact form for any multiplicity parameter value is proposed. Representation of modulated signal based on two variables of carrier and modulation functions is considered. Two different cases of modulated voltage generation depending on multiplicity parameter value are described. Bipolar voltage signal representation based on the sum of two unipolar signals with two times lower carrier function frequency is proposed. Bipolar and unipolar modulated signals spectrum components of double Fourier series are calculated. Spectrum characteristic of bipolar voltage modulation is analyzed. Transmission of the significant energy amount of bipolar voltage by harmonics with frequencies near two times lower value than carrier function frequency is proved. A case with multiplicity parameter which is multiplied to number four is noted as more desirable due to decreasing the first harmonic value. A proposition about subsequent improvements of bipolar voltage modulation is given

EMI and ground leakage current reduction in single‐phase grid‐connected power converter

Ground leakage current in a power converter is a major concern, which has stringent limitations due to safety concerns. Presence of high-frequency pulses, with high d v /d t due to switching actions in common-mode (CM) voltage, result in injection of current waveforms with large d i /d t spikes into the ground and causes high electromagnetic interference (EMI) noise level. In this study, a new method is proposed to make the CM voltage, of a single-phase grid-connected inverter, sinusoidal and free of high-frequency pulses. The proposed method consists of two parallel connected H-bridge power converters, which uses unipolar pulse width modulation (PWM) with carrier interleaving angle of 180°. The proposed method reduces the ground leakage current by more than an order of magnitude. A novel modification to the LCL filter is proposed which further reduces the leakage current by 48%. It is shown that these modifications make the overall system insensitive to circuit non-idealities. Experimental results based on ground leakage current measurements on a 7.5 kW parallel single-phase PWM rectifier are presented. These results validate the effectiveness of the proposed method.

Unipolar PWM predictive current‐mode control of a variable‐speed low inductance BLDC motor drive

This study presents the design and implementation steps of a digital predictive controller to regulate a low-inductance, three-phase, three-wire permanent magnet brushless DC motor currents. These types of motors are usually driven by multi-stage converters, switched at high frequencies, or use additional inductances to limit the current ripple. The motor's trapezoidal back electromotive force and rectangular currents waveforms make the design and the tuning process of linear controllers difficult. This task complexity increases when a wide speed range is considered. Digital predictive controllers are easily implemented in digital signal processors (DSPs), being successfully used to regulate currents of different types of power electronic converters. A unipolar pulse width modulation predictive controller is proposed here to regulate the rectangular currents of a brushless DC motor, without the need for any additional filter or converter. Experimental and simulation results using a 5 kW/48 V three-phase brushless DC (BLDC) motor are presented to demonstrate the feasibility of this proposal. It will be presented a methodology to compensate the conditioning and sampling circuits delays as well as the inverter's semiconductors voltage drop. The control algorithm was implemented in a TMS320F28335 DSP.

Comparative Analysis of Unipolar and Bipolar Control of Modular Battery for Thermal and State-of-Charge Balancing

Thermal and state-of-charge (SOC) imbalance is a well-known issue that causes nonuniform aging in batteries. The modular battery based on cascaded converters is a potential solution to this problem. This paper presents bipolar control (BPC) of a modular battery and compares it with previously proposed unipolar control (UPC) mode in terms of thermal/SOC balancing performance and energy efficiency. The BPC needs four-quadrant operation of a full-bridge (FB) converter using bipolar pulsewidth modulation (PWM) inside each module, whereas UPC only needs a half-bridge (HB) converter with unipolar PWM. The BPC, unlike UPC, enables charging of some cells while discharging others. An averaged state-space electrothermal battery model is derived for a convex formulation of the balancing control problem. The control problem is formulated on a constrained linear quadratic (LQ) form and solved in a model predictive control (MPC) framework using one-step-ahead prediction. The simulation results show that BPC, without even requiring load current variations, gives better balancing performance than UPC but at the cost of reduced efficiency. The UPC requires at least current direction reversal for acceptable balancing performance. In short, the UPC is a more cost- and energy-efficient solution for electric vehicle (EV) and plug-in hybrid EV applications, whereas the BPC can be beneficial in applications involving load cycles with high current pulses of long duration.

A Three-Level <italic>LC</italic>-Switching-Based Voltage Boost NPC Inverter

A single-stage high-voltage gain boost inverter is getting popularity in applications like solar photovoltaic, fuel cell, uninterruptible power system (UPS) systems, etc. Recently, single-stage voltage boost multilevel Z-source inverter (ZSI) and quasi-Z-source inverter (QZSI) have been proposed for dc–ac power conversion with improved power quality. Multilevel ZSI uses more number of high-power passive components in the intermediate network, which increase the system size and weight. Also, its input current is discontinuous in nature which is not desirable in some of the applications like fuel cell, UPS systems, hybrid electric vehicle, etc. In this paper, a continuous current input three-level LC -switching-based voltage boost neutral-point-clamped inverter is proposed, which uses comparatively less number of high-power passive components at the same time retains all the advantages of multilevel QZSI/ZSI. It is able to boost the input dc voltage and give required three-level ac output voltage in a single stage. Steady-state analysis of the proposed inverter is discussed to formulate the relationship between the input dc voltage and three-level ac output voltage. A unipolar pulse width modulation technique devised for the proposed inverter to eliminate first center band harmonics is also presented. The proposed converter has been verified by simulation in MATLAB Simulink as well as performing experiment with the help of a laboratory prototype.

반도체 변압기용 단상 계통 연계형 인버터의 소신호 모델링과 제어기 설계

In this paper, a small signal model for grid-connected inverter with unipolar pulse width modulation method is presented. Small-signal analysis allows to predict the stability and dynamics of the inverter. To regulate output voltage and to achieve power factor correction, inverter has two control loops. Loop gains are useful to identify the stability for multi-loop controlled system. Based on small-signal model, controllers are designed to improve audio susceptibility and output impedance characteristics. Proposed small-signal model and controllers are verified by PSIM simulation and experiments.

Comparative analysis of symmetric and asymmetric reduced switch MLI topologies using unipolar pulse width modulation strategies

Multilevel inverters (MLIs) are gaining familiarity in industries for high-voltage applications. This study is a comparison of symmetric and asymmetric reduced switch MLI topologies which require a lesser number of switches for generating the desired number of voltage levels. In both symmetric and asymmetric conditions, output voltage levels are generated using the same number of switches with different DC source magnitudes. Unipolar pulse width modulation strategy is adapted in these topologies to generate the switching pulses. Three different unipolar references (sine, trapezoidal, 60°) and three different carrier arrangements (phase disposition, alternative phase opposition and disposition and variable frequency) are taken and each reference is compared with three different carrier signals. The performance parameters such as total harmonic distortion (THD), crest factor and distortion factor are evaluated for different modulation indices and compared with both conditions. The proposed topology in symmetric and asymmetric conditions can generate 9-level and 31-level output voltages, respectively, which are simulated using MATLAB/Simulink and verified with the experimental setup. The calculation of %THD using analytical asymptotic formula is also carried out. The theoretical value of %THD is verified to match closely with the simulation and experimental results.

Dual Comparison One Cycle Control for Single Phase AC to DC Converters

Resistance emulation using one cycle control (OCC) has been used extensively in single-phase full-bridge boost rectifiers. This paper proposes a new control strategy called dual comparison OCC (DC-OCC), which eliminates the limitations of OCC. The advantages of the proposed control strategy is that it ensures the average current is equal to grid voltage scaled by emulated resistance, in each switching cycle. This eliminates issues such as dc offset due to the peak current comparison in OCC. It also ensures that there is no distortion in current when the converter is lightly loaded. It is analytically shown that the proposed DC-OCC does not have the light load instability concerns of conventional OCC. The proposed method is also shown to achieve unipolar pulse-width modulation without sensing the grid voltage resulting in lower effective switching frequency. The proposed control requires only one additional comparator and additional logical elements for implementation. Detailed simulation and experimental studies are carried to validate the proposed control and the high performance that can be obtained.

An Improved DTC for In-wheel BLDC motors in Micro All-electric Vehicles

The micro all-electric vehicle pertaining to this study is rear-driven, with motors in the left and right rear wheels. The motors are brushless dc (BLDC) using Hall effect sensors with a trapezoidal back-electromotive force. The control system is developed by using a digital signal processor. To thoroughly utilize the fast torque generation feature of BLDC motors, direct torque control (DTC) is preferable, but with conventional DTC, dead-time must be added. This paper proposes an improved DTC, where the switching device operating principle is equivalent to that of a unipolar pulse width modulation (PWM) technique named PWM-ON. Dead-time is not required, and switching losses are reduced. Further analysis showed that under the improved DTC the dc supply took up only the load current, confirming that there was no return of load energy to the dc supply, which protects the batteries. Experimental results are given to confirm validity.

Parallel Operation of Modular Single-Phase Transformerless Grid-Tied PV Inverters With Common DC Bus and AC Bus

In order to enhance the efficiency and reliability of dc-module-type photovoltaic (PV) generation systems, the single-phase transformerless full-bridge grid-tied inverters with a common dc bus and ac bus are utilized as the dc–ac stage. The high-frequency circulating current issue of parallel-operated single-phase grid-tied inverters with different topologies and modulation strategies are investigated. The conditions of high-frequency circulating currents elimination without additional hardware costs are revealed and presented. The analysis indicates that there are no high-frequency circulating currents between parallel-operated inverters with bipolar pulsewidth modulation (PWM). The parallel-operated inverters with unipolar double frequency PWM have high-frequency circulating currents, but the effects of the high-frequency circuiting currents on the fundamental components of split-filter inductor currents can be mitigated. The parallel-operated inverters with a unipolar PWM also have high-frequency circulating currents, but their effects on the fundamental components of split-filter inductor currents cannot be reduced. The single-phase transformerless full-bridge inverters with low-leakage currents, such as H5 and highly efficient and reliable inverter concept, meet the elimination conditions of the high-frequency circulating currents. Hence, these inverters are free of high-frequency circulating currents. A prototype of dc module-type grid-tied PV generation system is built up, and experimental tests with different topologies and PWM methods verify the analysis.

High Power Full-Bridge DC-DC Converter using a Center-Tapped Transformer and a Full-Wave Type Rectifier

This paper proposes a high power full-bridge DC-DC converter, using a center-tapped transformer and a full-wave type rectifier. The proposed converter realizes unipolar primary voltage switching, using the unipolar pulse-width modulation (PWM) technique. Also, the proposed converter reduces the freewheeling conduction loss, using the unipolar PWM technique and a resonant circuit, composed of a clamp capacitor and resonant inductor in the primary, and thus achieves high efficiency. However, because the proposed converter uses only a full-bridge circuit, center-tapped transformer, and full-wave type rectifier, the structure of the proposed converter is simple. In this paper, the operational principle of the proposed converter is described in detail, and a design example of a proposed converter prototype is shown. Finally, experimental results of the prototype are shown, to verify the feasibility of the proposed converter.

Combined Unipolar and Bipolar PWM for Current Distortion Improvement During Power Compensation

To eliminate leakage ground current while achieve high efficiency, many transformerless photovoltaic inverters with unipolar pulse width modulation (UP-PWM) have been proposed and verified with real power injection only. However, in 2011, German standard VDE-AR-N 4105 updated the requirement that the inverters should satisfy the power factor from 0.9 leading to 0.9 lagging at power level higher than 4.6 kVA. When compensating the reactive power under a leading power factor, the inverter with UP-PWM might not have sufficient voltage to magnetize the inductor, which results in current distortion at zero crossing. It is hard to comply with the requirement of 1% displacement-factor accuracy. The reactive power can be well compensated with a bipolar PWM (BP-PWM) scheme; however, this will result in high current ripple and high switching loss. In this study, for reducing the current distortion under leading power factors and increasing the inductor current in the negative power region, UP-PWM is changed to BP-PWM. While in the positive power region, the inverter operation is still kept with UP-PWM to yield higher efficiency and lower current ripple. The proposed combination of UP-PWM and BP-PWM can improve the current distortion and reduce THD, while still can sustain high efficiency even with the power factors other than unity. Experimental results measured from a 5 kVA PV inverter have verified the analysis and discussion of the proposed approach.

A Novel Reduced Switching Loss Bidirectional AC/DC Converter PWM Strategy With Feedforward Control for Grid-Tied Microgrid Systems

This paper presents a novel simplified pulse width modulation (PWM) strategy for the bidirectional ac/dc single-phase converter in a microgrid system. Then, the operation mechanism of the novel simplified PWM is clearly explained. The number of switchings of the proposed simplified PWM strategy is one-fourth that of the conventional unipolar PWM and bipolar PWM. Based on the novel simplified PWM strategy, a feasible feedforward control scheme is developed to achieve better rectifier mode and inverter mode performance compared with the conventional dual-loop control scheme. The proposed simplified PWM strategy with the proposed feedforward control scheme has lower total harmonic distortion than the bipolar PWM and higher efficiency than both unipolar and bipolar PWMs. Furthermore, the proposed simplified PWM operated in the inverter mode also has larger available fundamental output voltage VAB than both the unipolar and bipolar PWMs. A prototype system is constructed and the control scheme is implemented using FPGA Spartan-3E XC3S250E. Both simulation and experimental results verify the validity of the proposed PWM strategy and control scheme.

Design of New Multilevel Inverter Topology for Various Unipolar Triangular Carrier PWM Strategies

Multilevel inverters have been widely used for high power and high voltage applications as their performance is highly superior to that of conventional two level inverters due to reduced harmonic distortion, lower electromagnetic interference, and higher dc link voltages but it has some disadvantages such as increased number of components, complex pulse width modulation control method and voltagebalancing problem. In order to compensate the above described disadvantages a new topology with a reversing voltage component is proposed to improve the multilevel performance. This topology requires fewer components compared to existing inverters (particularly in higher levels) and requires fewer carrier signals and gate drives. Therefore, the overall cost and complexity are greatly reduced particularly for higher output voltage levels. Finally, a power circuit of the seven-level proposed topology is developed and simulated with different modulation strategies to show the performance of the inverter by simulation results using MATLAB-SIMULINK. By comparing the various Unipolar Pulse Width Modulation (UPWM) techniques, it is observed that UPDPWM provides less THD and UCOPWM techniques provide higher fundamental RMS output voltage. Compared to the conventional MLI’s like DCMLI, FCMLI and CMLI the proposed topology will reduce the number of switches, clamping diodes and clamping capacitors. The proposed topology will have the advantages if the number of levels is increased. The total harmonic distortion will be within IEEE standards. The main object of the proposed topology is to reduce the number of switches compared to conventional MLI’s and to achieve the THD within IEEE standards without any additional filter.

Comparison of performance between bipolar and unipolar double-frequency sinusoidal pulse width modulation in a digitally controlled H-bridge inverter system

By deriving the discrete-time models of a digitally controlled H-bridge inverter system modulated by bipolar sinusoidal pulse width modulation (BSPWM) and unipolar double-frequency sinusoidal pulse width modulation (UDFSPWM) respectively, the performances of the two modulation strategies are analyzed in detail. The circuit parameters, used in this paper, are fixed. When the systems, modulated by BSPWM and UDFSPWM, have the same switching frequency, the stability boundaries of the two systems are the same. However, when the equivalent switching frequencies of the two systems are the same, the BSPWM modulated system is more stable than the UDFSPWM modulated system. In addition, a convenient method of establishing the discrete-time model of piecewise smooth system is presented. Finally, the analytical results are confirmed by circuit simulations and experimental measurements.

DSPACE Based Implementation of Multicarrier PWM Strategies for Three Phase Five Level Cascaded Inverter

This paper presents the comparison of unipolar multicarrier Pulse Width Modulation (PWM) techniques for the Cascaded Multi Level Inverter (CMLI). Due to switch combination redundancies, there are certain degrees of freedom to generate the five level AC output voltage. This paper presents the use of Control Freedom Degree (CFD) combination. The effectiveness of the PWM strategies developed using CFD are demonstrated by simulation and experimentation. The simulation results indicate that the chosen five level inverter triggered by the developed UISCPSPWM and UISCVFPWM strategy with sine and stepped wave references and UISCAPODPWM strategy with THI PWM and 60 degree reference exhibis reduced harmonics. UISCCOPWM provides higher fundamental RMS output voltage for all four chosen references. PWM strategies developed are implemented in real time using dSPACE/Real Time Interface (RTI). The simulation and experimental outputs closely match with each other validating the strategies presented

Unipolar PWM Strategy for Transformerless PV Grid-Connected Converters

In domestic grid-connected PV applications, a single-phase converter is usually employed. In such low-power plants, it is possible to adopt converter topologies without galvanic isolation between the photovoltaic (PV) panels and the grid. The absence of a high- or line-frequency transformer permits us to reduce power losses, cost, and size of the converter. On the other side, in the presence of a galvanic connection, a large ground leakage current could arise due to parasitic PV panel capacitance. Leakage currents cause electric safety problems, electromagnetic interference increase and, consequently, a reduction of the converter power quality. This paper presents a converter topology able to minimize the ground leakage current also in the case of unipolar pulsewidth modulation without increasing inductive common mode filter size and preserving efficiency. Simulations and experimental results show the feasibility of the proposed solution.

A Voltage Controller in Photo-Voltaic System with Battery Storage for Stand-Alone Applications

This paper proposes the new voltage controller in photo-voltaic system for Stand-Alone Applications with battery energy storage. The output of the PV array is unregulated DC supply due to change in weather conditions. The maximum power is tracked with respect to temperature and irradiance levels by using DC-DC converter. The perturbation and observes algorithm is applied for maximum power point tracking (MPPT) purpose. This algorithm is selected due to its ability to withstand against any parameter variation and having high efficiency. The solar cell array powers the steady state energy and the battery compensates the dynamic energy in the system. The aim of the control strategy is to control the SEPIC converter and bi-direction DC-DC converter to operate in suitable modes according to the condition of solar cell and battery, so as to coordinate the two sources of solar cell and battery supplying power and ensure the system operates with high efficiency and behaviors with good dynamic performance. The output of DC-DC converter is converted to AC voltage by using inverter. The AC output voltage and frequency are regulated. A closed loop voltage control for inverter is done by using unipolar sine wave pulse width modulation (SPWM). The regulated AC voltage is fed to AC standalone loads or grid integration. The overall system is designed, developed and validated by using MATLAB-SIMULINK. The simulation results demonstrate the effective working of MPPT algorithm, control strategy and voltage controller with SPWM technique for inverter in AC standalone load applications. DOI: http://dx.doi.org/10.11591/ijpeds.v2i1.127

Torque Ripple Suppression of Brushless DC Motors with Non-Ideal Back EMF for EPS Applications

The torque ripple of brushless dc (BLDC) motors at low rotation speeds is prominent, while in the majority of working time of the automotive electric power steering (EPS) system, the steering rate is low and the assistant motor runs at low rotation speeds. Therefore, to develop a high-performance EPS system with a BLDC motor, the problem of torque ripple at low rotation speeds must be solved. Otherwise, the steering feel will not be smooth. This paper proposed an algorithm based on BLDC motors’ essential torque formula combined with the back-EMF (Electromotive Force) waveform coefficient to modify the target current to suppress the torque pulsation effectively. Meanwhile, the commutation process of this type motor is very short. Therefore, the torque coefficient can be regarded as constant during the commutation intervals. A direct pulse-width modulation (PWM) control method considering phase resistances is analyzed with a unipolar PWM scheme to reduce the commutation torque ripple further. Finally, simulations and experiments are conducted to verify the effectiveness of this method.

An Efficient Strategy to Generate High Resolution Three-Phase Pulse Width Modulation Signal Based on Field Programmable Gate Array

Pulse Width Modulation (PWM) is a common technique used in many different applications. This technique is the heart of the inverter system. This paper reported a modified strategy in asynchronous unipolar sinusoidal PWM (SPWM) switching scheme based on ACEX1K50TC144-3 Altera Field Programmable Gate Array (FPGA). The carrier frequency was designed for 20 kHz and the fundamental frequency was designed to adjust 1 to 100 Hz, with step increase in 1 Hz. A new SPWM signal generation strategy is proposed and compared to traditional SPWM generation technique. The design entry is conducted by Max+plus II version 10.2 through schematic and VHDL programming. The verification in level simulation and hardware realization has been done. As the result, the proposed modified SPWM signal generation strategy works properly and can reduces the usage of logic cell (LC) until 63.75%.