A simple input current wave-shaping technique for three-phase diode and SCR converters

A centralized control scheme is proposed for modular multi rectifier system as a popular front-end rectifier solution for the industrial application where multiple motors are supplied by the Silicon Controlled Rectifier (SCR). Normally under conventional balanced grid voltage, the input current distortions can be improved by implementing the appropriate SCR firing angles in each unit. However, the three-phase grid voltage may be either amplitude or phase angle unbalanced, which deteriorate the performance of the conventional harmonic mitigation method. In order to remedy this issue, the three-phase total input currents 3rd harmonic components are extracted and included in the closed-loop control using PI controller, and a reset unit with the input of inductor current is adopted to reset the integrator. The proposed control strategy is able to obtain the appropriate SCR firing angle compensation, and then consequently achieve harmonics improvement in the input current under unbalanced grid voltage. Simulation results based on PLECS and experimental results have validated the effectiveness of the proposed improved control strategy under unbalanced grid voltage.

This paper proposes a current ripple cancelation method in DC side for an isolated AC-DC converter with a matrix converter. In this system, input currents are distorted by an error between a reference and actual input current caused by a ripple component at a dc current in the output side when the smoothing inductor in the output side is minimized. The proposed ripple cancellation method combines current slopes during positive with negative cycles of a high-frequency current. In addition, dead-time-induced voltage error is also reduced by the extension of a minimum pulse width of each switch in the matrix converter with the proposed method. It is demonstrated that the input current total harmonic distortion (THD) is improved by eliminating the ripple components regardless of the amplitude of the ripple component. From the experimental results with the 10-kW prototype, the input current THD is reduced from 8.2% to 5.3% at the 0.2 p.u..

A low cost indirect type AC voltage regulating system is proposed to overcome the grid pollution of silicon controlled regulating circuit and the high cost of chopping sine wave regulating circuits. The system consists of full bridge rectifier, filter and full bridge inverter. The bipolar SPWM control signal for inverter is generated by the STM32 micro controller. The circuits is developed and used in the dimming of 400 W high pressure sodium lamp inductive loads. Continuous dimming with slight distortion of the sine wave is obtained. The system is attractive in the replacement of silicon controlled dimming circuit, and promotes the energy saving project. Introduction China's urbanization continues to accelerate, owning to people’s greatly improved living standard and the development of the economy. As an important indicator of urban modernization, traffic lighting and landscape lighting is developing rapidly and consuming more and more energy. Energy shortage and environmental pollution problems is a common concern of all humanity, energy and environmental protection are increasingly being taken seriously. According to the external light intensity and flow of people, appropriate steps down lightening, can effectively save energy, thus reduce carbon emissions [1]. The AC regulating system is the core block for light dimming. The AC regulating circuit based on Silicon Controlled Rectifier (SCR) is used widely in dimming [2], with advantages of low cost and simple structure. However, the SCR based dimming circuit adjusts the output voltage by changing the conduction angle of SCR. Thus the output is not a standard sine wave, but contains a large number of high-order harmonics, which will disturb other equipment’s in the grid. With the development of electronic devices IGBT, dimming circuit based on chopping is proposed and used in the stage dimming, as well as hotels [3]. The output is pure sine wave and will not affect other equipment’s in the grid any more. However, the chopping based dimming circuit is relatively complex and the filter circuit depends on the load characteristics, which resulting in higher system costs and can only be applied in expensive entertainment places [4]. In this paper, a low cost AC regulating system with simple structure is proposed and realized. The output is continuously adjustable standard sine wave, and compatible for resistive, inductive and capacitive loads. System Design The system consists of full bridge rectifier, full-bridge inverter and filer circuit, as shown in Fig. 1. The input 220V/50HZ sine wave is rectified to DC voltage firstly, and then enters into the fullbridge inverter circuit and filter circuit, where the input DC voltage is inverted to AC voltage. The output voltage is adjusted by changing the control signal of full-bridge inverter. The output is insensitive with the load characteristics, owning to the inverter circuit. International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) © 2015. The authors Published by Atlantis Press 996 Fig. 1: Schematic of the indirect regulating system The full-bridge inverter is the core block of the system. The inverter consists of 4 seriesand parallel -connected IGBT devices, as shown in Fig. 2. The 4 IGBTs are driven by SPWM signal generated by the STM32 microcontroller. According to detected voltage and current of the input and output ports, the STM32 microcontroller dynamically changes the SPWM driving signal to satisfy the output voltage. These are two types of SPWM driving signal, unipolar SPWM and bipolar SPWM. For inductive load in our application, bipolar SPWM is chosen for driving the IGBTs, since it is far easier to get a good output waveform. In Fig. 2, the left half-bridge consists of IGBT T1 and T, and the right half-bridge consists of IGBT T3 and T4. For bipolar IGBT driving circuit, the high-side and low-side IGBTs (e.g. T1 and T2) have complementary driving signal, and the diagonal IGBTs (e.g. T1 and T4) have the same driving signal. The output is close the peak of the sine signal as the duty cycle of the SPWM is close to 0% or 100%, meanwhile the output is close to 0 as the duty cycle of the SPWM is close to 50%, which is shown in Fig. 3. To simplify the system complexity and lower the cost, two complementary driving signals with dead zone are generated by the STM32. Fig. 2: Topology of full-bridge inverter Fig. 3: Bipolar SPWM driving signal T1

Bridgeless Cuk PFC converter with full load range soft switching operation by using a simple auxiliary circuit

A harmonic current's compensation method suitable for an electrical distribution system is described. The compensation method involves the operation of a harmonic currents generator in parallel with the nonlinear loads and the distribution system. The controlled harmonic current's source is realized using a power transistor inverter. Computer-aided simulation and experimental results obtained in the case of a single phase compensator scheme confirm the validity of the proposed method.

This paper provides a brief comparison between two different modulation methods for direct matrix converter (DMC). The power semiconductors are modelled as ideal bidirectional switches and the DMC is controlled using Venturini method, optimized Venturini and space vector modulation respectively. These methods are compared and analysed in some aspects such as total harmonic distortion and harmonic spectrum analysis of output voltage and input current. A simple model of DMC is proposed to represent the power circuit, including the input filter and a three-phase Y-connected RL load. Simulated input and output parameters of DMC are presented using PSIM software for both modulation strategies.

This paper proposed an electronic ballast that uses an input current shaper to reduce the total harmonic distortion of the line input current, that only process a small part of the total power. Base on the minimum value of the conduction angle to satisfy the requirements of the IEC 61000-3-2 Class-C standard, the conduction loss of the ICS stage can be reduced. The input current shaper is achieved by using a bridge rectifier which acts as the Class-DE resonant rectifier. By using this topology the conduction angle of the diode can be increased to high enough for satisfy the IEC 61000-3-2 Class-C standard requirements. The proposed electronic ballast is designed for 36-W fluorescent lamp and operated at a line rms voltage of 220 V, a line frequency of 50 Hz with the switching frequency fixed at about 76 kHz. The experimental results show that the total harmonic distortion is 29.5%, the power factor is 0.96, a lamp-current crest factor is 1.42, and 95.2% efficiency at full power.

Harmonic analysis currently plays an important role for the power quality analysis because the non-linear loads, as source of the harmonic distortion, have significantly increased. The harmonic distortion influences power quality in power systems such as overheating of electrical equipment and aging of electrical equipment. Therefore, non-linear loads should be monitored in real time. This research proposes the design and implementation of the prototype current harmonic analysis that can be applied in real time based on S-transform Method. The equipment of this prototype can be explained as follows: CT-235, TZ2L9 and CT for KWH meters as current sensor, microcontroller AT mega 8535 as data acquisition, and Visual Basic software as displaying current waveform, current spectrum, rms current value, and total harmonic distortion (THD) for current. S-transform method is used to obtain the THD for current. The experimental result is validated by FLUKE 43B and the THD for current is accurately measured.

Wireless power transfer (WPT) systems are power electronic converters which can be installed under the road and charge the butteries of the electric vehicles. High total harmonic distortion (THD) of the input current is an important challenge in WPT system design. In this paper a new topology is proposed for WPT systems to reduce their input current THD. In the proposed topology, a quasi-Z-source inverter (QZSI) is used in series with a LLC resonant network. In addition to the DC voltage boosting, QZSI shapes the input current. The simulation results verify the performance of the proposed structure in THD reduction and power factor correction in comparison with the conventional Z-source resonant converter.

Concentric neutral cables are commonly used in medium-voltage power distribution systems. Presently, the cable ampacity calculation methods can take into account only the fundamental frequency current and the harmonic currents in the phase conductors. In reality, the cable neutral can carry fundamental frequency and harmonic currents (induced and unbalanced), leading to a further increase of cable temperature. In view of the increased harmonics and load imbalance in power distribution systems and the need to determine their impact on concentric neutral cables, this paper presents a method to estimate the ampacity of concentric neutral cables, especially for multigrounded neutral systems. The proposed cable derating factor can be used to determine the increase in cable loading caused by unbalanced load and harmonics. A chart is also presented as a simplified method for cable ampacity and cable loading estimation, for which only the total harmonic distortion and zero-sequence current ratio of the phase current are needed.

Wireless power transfer (WPT) systems are widely used in various applications due to their convenience and efficiency. However, the performance of WPT systems can be significantly affected by misalignment and load variations. This letter proposes a method to estimate mutual inductance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i>) and load resistance (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{R}_L})$</tex-math></inline-formula> in WPT systems using total harmonic distortion (THD) of input current. A numerical method to estimate these parameters has been developed by deriving an analytical relationship between THD, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i>, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{R}_L}$</tex-math></inline-formula>. Experimental validation demonstrates that the proposed method provides accurate estimates of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{R}_L}$</tex-math></inline-formula> under varying conditions by only using transmitter current, with maximum estimation errors of 5.1% for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> and 3.6% for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{R}_L}$</tex-math></inline-formula> when estimated separately by keeping the other parameter constant. The proposed method is extended to simultaneously estimate <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R_L</i> with a maximum estimation error of 4.9%. This method can be adopted for real-time monitoring and control strategies, such as frequency control, system identification, and diagnostic applications, in WPT systems.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> High-power converters for regenerative drives and distributed generation need a network-friendly operation, low harmonic conductive electromagnetic emission for low electromagnetic interference and high electromagnetic compatibility reaching high reliability and performance. Nevertheless, the converters must be controlled with low switching frequency in order to reduce the commutation losses. These two requirements can be satisfied if an optimal modulation strategy is used. The selective harmonic elimination (SHE) is one of the low-switching-frequency strategies most used today. However, this strategy only eliminates a reduced set of harmonic components from the input current. This paper presents a novel optimal modulation strategy whose objective is to reduce the total harmonic distortion of the input current. Six- and twelve-pulse three-level neutral-pointclamped pulsewidth modulation rectifiers are used in order to implement both modulation techniques. The results confirm the advantages of the proposed strategy, namely, less input current distortion and remarkable reduction of higher order harmonics compared with the SHE method, while keeping a low-switching behavior. </para>

Introduction. To improve the power quality of a supply system, the total harmonic distortion (THD) is the most important parameter in the quantification of harmonics caused by nonlinear loads. In practice, it must be less than 5 %. The novelty of the proposed work consists in the use of a cascaded five level active filter, when the converter consisting of six H-bridge pairs, each one includes four transistors. Purpose. To increase the efficiency of this filter, two techniques for quantification of harmonic currents are proposed, first the PQ-theory which is simple but can only be used in case of a balanced grid, and second the synchronous reference frame theory (SFR-theory), which is capable of creating harmonic current not only in an unbalanced grid, but also in an unbalanced and distorted beam. Methods. Using the control techniques, the harmonic current is extracted from load current and considered as a reference. The constructed current should follow this reference. Results. The estimation of the active and reactive powers is based on the measurement of the currents crossing the load and the network voltages, these powers are used to determine the shape of the harmonic (reference) current. Using the PI regulator, the output current of the five-level inverter follows the reference current perfectly. The inverters output current is injected into the grid to eliminate harmonic currents. Practical value. In practice, the harmonic distortion rate THD is the most widely used criterion for criticizing the waveform of the currents and judging the quality of the energy involved. For currents on the source side, the THD is considered acceptable if it is less than 5 %, in our proposal the THD is 0.85 % with the PQ-theory and 2.34 % with SFR-theory, so it is optimal.

This chapter focuses on commonly used high‐power semiconductor devices including silicon controlled rectifiers (SCRs), gate turn‐offs (GTOs), gate commutated thyristors (GCTs), and insulated gate bipolar transistors (IGBTs) for medium voltage (MV) drives. It discusses the static and dynamic voltage equalization techniques for series connected devices, and compares the performance of these devices. A new type of emerging power semiconductor devices is the silicon carbide (SiC), which is a compound semiconductor composed of silicon and carbon. The SiC power devices are able to operate at higher switching speed and higher temperature with lower switching and conduction losses in comparison to the silicon devices such as IGBTs. The static and dynamic voltage equalization techniques for the GCT devices can be equally applied to the IGBTs. In addition, an active overvoltage clamping scheme can be implemented to limit the collector‐emitter voltage during switching transients.

The focus of this paper is a theoretical calculation of current Total Harmonic Distortion (THD) for a current source single-phase multilevel PWM inverter with CL-filter. Analytical approach to current ripple mean square / current THD calculation was introduced in the 1980s for a 2-level voltage source inverter with inductance dominated RL-load. This paper presents a generalization of this approach for a single-phase multilevel current source PWM inverter with an arbitrary number of current levels accounting for the CL-filter effect. The output of this research is a closed-form analytical current THD solution. Though one of the assumptions is large switching-to-fundamental frequencies ratio, the formulas are practically accurate for the said ratio larger than 20-25. The formulas become quite compact and simple without a loss of accuracy when using a Bessel function approximation. They demonstrate a single-phase PWM current source inverter current THD dependence on CL-filter parameters and current modulation index.