Pulse Width Modulation Rectifier Research Articles

Adaptive neural networks for AC voltage sensorless control of three-phase PWM rectifiers

In this paper, a new adaptive grid voltages estimator for AC voltage sensorless control of three-phase pulse-width modulation (PWM) rectifier is proposed. This method is based on a simple adaptive neural network (ANN) to estimate online the grid voltages. Its main advantages are the simplicity and low computational cost requirements. The proposed ANN estimator is inserted in voltage-oriented control (VOC) to perform an AC voltage sensorless control scheme. As the start-up is a common problem in case of sensorless control, a new start-up process is also proposed for estimating initial values of the grid voltages. Experimental tests are carried out to verify the feasibility and robustness of the proposed ANN estimator. Obtained results show good performances of the proposed AC voltage sensorless control scheme in normal and severe grid voltage conditions.

Power Decoupling Control for Capacitance Reduction in Cascaded-H-Bridge-Converter-Based Regenerative Motor Drive Systems

A cascaded H-bridge (CHB) converter-based medium or high-voltage motor drive system, that consists of three single-phase CHB chains, may suffer a severe second-harmonic ripple power issue. Oversizing dc capacitors and using active power decoupling control with additional active or passive components are the two possible ways to address this issue, but this is achieved at the expense of increased system cost and complexity. This paper proposes a power decoupling control to tackle this issue without using any extra components for regenerative CHB-based converters. By introducing a set of negative-sequence decoupling currents to the front-end pulsewidth-modulated rectifier of each submodule, the second-harmonic ripple power can be removed from the submodule dc capacitors, and all the ripple power in the transformer core legs can be counteracted without affecting the magnetic flux and the grid current. The decoupling current is derived from the input and output measurements of the CHB converter. It gives the minimal increase of the modulation index and has no impacts on the input and output power quality. The effectiveness of the proposed control is verified in simulations and a 72-kW experimental prototype.

Control of an active bus voltage limiter with modified space vector pulse width modulation strategies in regenerative applications

This paper proposes an active bus voltage limiter with a modified modulation strategy for bi-directional power flow applications. When the motor is braking, the regenerative energy raises the DC bus voltage. Additional shunt resistors are usually used to dissipate the regenerative energy, which is a waste. The active rectifiers, which are also mentioned as PWM (Pulse Width Modulation) rectifiers, can transfer the regenerative power to the power grid but the cost is high and not economic, especially when the regenerative power is comparatively low. This paper investigates the zero-sequence current produced by the active bus voltage limiter and then presents a modified space vector modulation strategy to effectively suppress the zero-sequence current and keep the unity power factor. The analysis about the control strategy of the topology is carried out. And the algorithms for regenerative applications are discussed. An industrial prototype is built to verify the configuration.

Direct Power Control of Pulsewidth Modulated Rectifiers Without DC Voltage Oscillations Under Unbalanced Grid Conditions

Direct power control with space vector modulation (DPC-SVM) features simple structure, fast dynamic performance, and little tuning work. However, the conventional DPC-SVM cannot achieve accurate power control under unbalanced grid conditions. A modified DPC-SVM is thus proposed for accurate power control under both ideal and unbalanced grid conditions. Though the power control accuracy is improved when compared with the conventional DPC-SVM, it still suffers highly distorted grid current and dc voltage oscillations with an unbalanced network. Therefore, a power compensation method is subsequently derived aiming at the following targets: eliminating dc voltage oscillations, achieving sinusoidal grid current, and obtaining unity power factor. To that end, average grid-side reactive power and oscillations in converter-side active power are controlled as zero by simply adding a compensation to original power reference. Additionally, the proposed method does not require extraction of a positive sequence or negative sequence component of grid voltage. Compared with the conventional DPC-SVM in an ideal grid, only additional compensation of power reference is required. As a result, control performance can be significantly improved without substantial increase in complexity. The superiority of the proposed method over the prior DPC-SVM is validated by both simulation and experimental results obtained on a two-level pulsewidth modulation voltage source rectifier.

A Novel Robust Model Predictive Controller for Aerospace Three-Phase PWM Rectifiers

This paper presents a novel Model Predictive Direct Power Control (MPDPC) approach for the pulse width modulation (PWM) rectifiers in the Aircraft Alternating Current Variable Frequency (ACVF) power system. The control performance of rectifiers may be largely affected by variations in the AC side impedance, especially for systems with limited power volume system. A novel idea for estimating the impedance variation based on the Bayesian estimation, using an algorithm embedded in MPDPC is presented in this paper. The input filter inductance and its equivalent series resistance (ESR) of PWM rectifiers are estimated in this algorithm by measuring the input current and input voltage in each cycle with the probability Bayesian estimation theory. This novel estimation method can overcome the shortcomings of traditional data based estimation methods such as least square estimation (LSE), which achieves poor estimation results with the small samples data set. In ACVF systems, the effect on the parameters estimation accuracy caused by the number of sampling points in one cycle is also analyzed in detail by simulation. The validity of this method is verified by the digital and Hard-in-loop simulation compared with other estimation methods such as the least square estimation method. The experimental testing results show that the proposed estimation algorithm can improve the robustness and the control performance of the MPDPC under the condition of the uncertainty of the AC side parameters of the three-phase PWM rectifiers in aircraft electrical power system.

Improved Modulation Mechanism of Parallel-Operated T-Type Three-Level PWM Rectifiers for Neutral-Point Potential Balancing and Circulating Current Suppression

In high-power applications, parallel-operated T-type three-level pulse width modulation (PWM) rectifiers (T3LPRs) are widely employed to improve the power capacity and system reliability. For parallel-operated T3LPRs, there are two important issues need to be properly addressed: 1) the neutral-point potential (NPP) balancing, and 2) the zero sequence circulating current (ZSCC) between the common ac and dc bus. In this paper, the fluctuation of NPP in a T3LPR and the generative mechanism of ZSCC in parallel-operated T3LPRs are first investigated. The zero sequence voltage (ZSV) difference between the parallel-operated T3LPRs is identified as the main excitation source of the ZSCC problem. Meanwhile, the disconnection of the neutral point and the control effect difference of NPP balancing in each T3LPR also affect the ZSCCs within the parallel-operated T3LPRs. To adjust the ZSV of T3LPRs, the dwell time of the positive small voltage vector in each switching period of the converter, which is usually adjusted to balance the NPP, is also required to be controlled to suppress ZSCC. Therefore, in this paper, to avoid the possible conflict, an improved modulation mechanism is designed to guarantee simultaneous ZSCC suppression and NPP balancing. The neutral points of each T3LPR are connected. Then, by adjusting the dwell time of the positive small voltage vector, the charging time of two dc capacitors is adjusted to balance the NPP, and the ZSV differences between different T3LPRs are adjusted to suppress ZSCCs. To avoid the control effect difference of independent NPP balancing in different T3LPRs, all T3LPRs share the same value marking the difference between two dc capacitor voltages. Thus, a communication with a greatly reduced baud rate requirement is needed for NPP balancing to transfer the difference between the two dc capacitor voltages. Moreover, no extra circuit is needed for ZSCC suppression. These approaches make the proposed improved space vector PWM strategy much more practical and easy to employ. The proposed method is verified with experiments on two 3-kW T3LPR prototypes.

Simple and effective open switch fault diagnosis of single-phase PWM rectifier

In order to obtain lower harmonics distortion and higher power factors, single-phase pulse-width modulation (PWM) rectifiers are adopted in AC railway drive systems. Therefore, its reliability is of most importance with regard to the safe operation of the train. In this paper, a fault diagnosis method for open switch fault in single-phase PWM rectifier is proposed based on the switching system theory. It requires no additional sensor, nor extra operation states need to be set. Four observers which correspond to four kinds of open switch faults are utilized to detect and locate the faults. Real-time simulations are carried out to validate the effectiveness of this method.

Virtual Flux Direct Power Control for PWM Rectifiers Based on an Adaptive Sliding Mode Observer

In the traditional virtual flux estimation for a three-phase pulsewidth modulation rectifier, the integration element causes problems for the initial value and dc bias, and the unstable grid voltage induces a nonconstant flux amplitude. To address these issues, an improved direct power control scheme based on an adaptive sliding mode observer is proposed in this work. The observer employs a sigmoid function as switch function to estimate the grid-side source voltage. Meanwhile, an adaptive compensator instead of pure integral element is also designed to dynamically adjust compensation. The stability of this observer is proved by the Lyapunov function; moreover, simulations and experimental results indicate that this new virtual flux observer substantially improves the observation accuracy based on voltage sensorless control. The application of this strategy successfully suppresses the fluctuation of the dynamic voltage response in the dc bus, eliminating high-frequency noise from the grid side, while simultaneously boosting the power quality.

Low-Frequency Oscillation Analysis of the Train-Grid System Based on an Improved Forbidden-Region Criterion

With the increasing number of electric locomotives and electric multiple units (EMU) operating in one power section simultaneously, low-frequency oscillation (LFO) may occur. LFO may cause serious railway accidents, which will dramatically influence the stable operation of the power system. In this paper, LFO is solved by establishing a simplified mathematical model of the generalized EMU and a dq-decoupled small-signal model of the single-phase pulsewidth modulation rectifier. Then, an improved forbidden-region criterion (IFRC) is proposed to analyze the stability of the train-grid system and a comparison of the classical criteria is listed to show the advantages of the IFRC. The proposed criterion has less conservatism and higher accuracy than the forbidden-region-based criterion, which has better performance than the classical criteria. Moreover, the analysis result is successfully reproduced by establishing the time-domain simulation model in MATLAB/Simulink and RT-LAB, which verifies the effectiveness and accuracy of the proposed criterion. Finally, the development of IFRC shows the influence of gird parameters, traction parameters, and control parameters of the train-grid system. Ten ways to suppress the LFO are provided according to the simulation results.

Variable Switching Frequency PWM Strategy of Two-Level Rectifier for DC-Link Voltage Ripple Control

The switching frequency is an important control parameter of pulse-width-modulation (PWM) rectifier to reduce switching losses and electromagnetic interference noise. This paper proposed a variable switching frequency PWM (VSFPWM) strategy for dc-link voltage ripple control in two-level rectifier. DC-link voltage ripple is determined by the dc-link current directly, and can be predicted synchronously with PWM signals. A real-time prediction model of dc-link voltage ripple is derived for a common voltage-oriented control PWM rectifier. Then, VSFPWM control is introduced, which changes the switching frequency cycle to cycle with a restriction of dc-link voltage ripple peak value. Furthermore, the dynamic behavior is also observed when the proposed VSFPWM control scheme is adopted. Detail simulation and experimental comparisons are carried out between VSFPWM and normal constant switching frequency PWM, which demonstrate the advantages of the proposed method.

Real and Reactive Power Control of SEIG Systems for Supplying Isolated DC Loads

A vector oriented control technique with a two-loop control scheme has been developed for operating a stand-alone three-phase SEIG for supplying DC loads through a three-phase Pulse Width Modulated (PWM) rectifier. The proposed controller maintains constant load voltage with reduced harmonics at the PWM rectifier input terminals. In addition, it controls the real and reactive power flow between the SEIG and converter system. The proposed control scheme has been implemented employing dSPACE 1103 real-time controller. The successful working of the proposed control strategy has been verified for different operating conditions, by modelling the system in MATLAB/Simulink toolbox and the results are presented. A prototype system consisting of an SEIG, PWM rectifier and associated control circuits, has been built in the laboratory environment and a close agreement between the simulated and experimental results has been confirmed.

An Approach to Suppress Low Frequency Oscillation in the Traction Network of High-Speed Railway Using Passivity-Based Control

The traction blockade in depots of multiple electric multiple units (EMUs) is generally considered to be caused by the voltage low frequency oscillation (LFO) of the high-speed railway traction network. As a possible solution, a strategy using single-phase EMUs rectifiers with passivity-based control (PBC) is proposed in this paper. First, the mathematical model of the four-quadrant pulse width modulation rectifier is constructed based on the port controlled Hamiltonian with dissipation. Next, with the insertion of damping, the new energy function can be minimized at the equilibrium point of the system, which enables the derivation of the rectifier control law based on the interconnection and damping assignments PBC. Comparison of simulation results with those of the traditional proportional integral (PI) scheme, autodisturbance rejection control and multivariable control verifies that the proposed PBC controller has better dynamic and static performance. Among all strategies considered, the resulting line current has the least total harmonic distortion, and the dc-link voltage of single-phase EMUs rectifier has the least oscillation and the shortest adjustment time, when using the PBC. Meanwhile, the simulations of multi-EMUs accessed a traction network show that the proposed method significantly suppresses the voltage LFO of the traction network. Finally, the LFO signal modal analysis is performed using the fast Fourier transform and the estimating signal parameters via the rotational invariance techniques. It indicates that PBC can suppress the symmetrical frequency components and effectively reduce the third, fifth, and other harmonic components compared with the PI control in EMUs.

Improvement in Harmonic Compensation of a Smart Charger with a Constant DC-Capacitor Voltage-Control-Based Strategy for Electric Vehicles in Single-Phase Three-Wire Distribution Feeders

This paper presents an improvement in harmonic compensation performance of a previously proposed smart charger (SC) with a constant dc-capacitor voltage-control (CDCVC) strategy for electric vehicles (EVs) in single-phase three-wire distribution feeders (SPTWDFs). A controller for 3rd harmonic currents in d-q coordinates is added to the previously proposed SC. This addition improves harmonic compensation performance of the source currents. We briefly introduce harmonic current compensation using the previously proposed CDCVC-based algorithm for the SC. Then, the basic principles of the proposed controller for the 3rd harmonic currents in d-q coordinates are discussed in detail. It is shown that synchronization of the current controllers for both the fundamental and 3rd harmonic components is required. The switching frequency of a three-leg pulse-width modulated rectifier with a bidirectional dc–dc converter, which performs the SC, is determined considering the synchronization of the current controllers. Simulation and experimental results demonstrate that balanced and sinusoidal source currents with a unity power factor are achieved during both battery charging and discharging operations in EVs, improving the harmonic compensation performance of the previously proposed SC. Experimental results also demonstrate that the total harmonic distortion values of source currents are improved by 8.4% and 3.6% with the proposed controller for 3rd harmonic currents, when the SC is discharging, for example.

A Maximum Current Control Method for Three-Phase PWM Rectifier for the ITER In-Vessel Vertical Stability Coil Power Supply

The required peak current and peak voltage of ITER in-vessel vertical stability (VS) coil power supply are up to 80 kA and 2.4 kV, so VS coil power supply needs a pulse width modulation (PWM) rectifier to achieve high power factor operation under the highly transient power demand of the value of 144 MW. A new maximum current control method for three-phase voltage source PWM rectifier based on its mathematical model in $d$ – $q$ frame and improved by dual-closed-loop control method has been presented. This control method meets the fast power charging demand and the dc-side voltage stabilization demand of power supply, and achieves a unity or high power factor operation; its controller is easier to be designed and implemented than dual-closed-loop control at charging mode. The advantages and feasibility of this control method have been verified by simulation and experiment.

Design and Implementation of Sensorless Voltage Control of Front-End Rectifier for Power Quality Improvement in Telecom System

In this paper, a three-phase three-switch three-level boost (Vienna) type pulse-width modulation rectifier is proposed as an active front-end power factor correction (PFC) rectifier for power quality improvement in telecom load. A sensorless voltage control technique is proposed and it does not rely on any input voltage information results in reliable and robust operation. A brief description on the principle of operation and the most advantageous modulation method of the proposed system are discussed. The feasible switching states are identified for the proposed active front-end converter resulting in reduced switching stress and dc ripples. A triangular carrier based control logic is applied and the input current reaches sinusoidal shape without the need of sensing the input voltage. The detailed analysis of front-end PFC converter is carried out by equivalent circuit analysis. Also, the complete loss and efficiency calculation of the converter is explicitly carried out with the help of hardware design guidelines. The performance of the proposed system and its capability of operating satisfactorily in the event of failure of one phase of the mains is verified through MATLAB Simulation, and the results obtained are presented. The experimental setup rated for 9 kW is developed in the laboratory to validate the simulation results. From the simulation and hardware results, it is observed and recorded that the power quality parameters are improved and are well within the IEEE and IEC standards.

Voltage Oriented Control(VOC) Of The PWM Rectifier Using Active Filtering Function

Pulse width modulation rectifier has gathered its demand during the recent years for modification needs of the ac-dc conversion systems need for industries, customer and power grid sectors. This bidirectional converter can act as ac to dc boost rectifier with near unity power factor at the grid side along with the regulated and ripple free output voltage at the dc side. This paper deals with the evaluation of control strategy called voltage oriented control with active filtering function, Total harmonic distortion (THD),dynamic performance and parameter sensitivity is studied theoretical concept is provided and results of computer simulations are given by using mat lab.

Real‐time gating signal generation and performance analysis for fully controlled five‐phase, ten‐pulse, line‐commutated rectifier

Fossil fuel prices and air pollution impel many countries to concentrate on renewable energy sources, of which wind energy is considered to be a pillar. Owing to the numerous advantages when compared with its three-phase counterpart, five-phase direct-drive permanent magnet (PM) generators are a key area of focus in power generation with renewable and wind energy systems. The generator output requires a converter, such as an AC–DC rectifier, to match load requirements. The objective of this work is to generate in real time the gating signals of a fully controlled five-phase, line-commutated rectifier, fed from a five-phase PM generator. A mixed-reality environment is used to implement the gating signal generation algorithm for the five-phase rectifier, where the required gating signals are successfully generated, even with some distorted prototype generator voltage waveforms. The performance of the rectifier is investigated practically and validated by using the MATLAB/SIMULINK platform. Moreover, a comparison with a five-phase pulse-width modulated current source rectifier in terms of losses, size, weight, and cost is presented.

Research on a new type of electromagnetic transmitter based on PWM technology

An electromagnetic transmitter transmits electromagnetic waves with variable frequencies to the ground to obtain underground structure information and the distribution of mineral resources. In order to improve the power factor and reduce the volume and weight of the transmitter, a novel transmitter topology with pulse width modulation (PWM) rectifier is designed. Similar with the flux-oriented control in the motor speed regulation system, this paper provides flux-oriented control for a permanent magnet synchronous generator PWM rectifier. The mathematical model of the generator rectifier is established under the rotating coordinate system. Then, a novel decoupling control strategy without the exact value of the generator stator inductance is proposed to regulate the active current and the reactive current, and an outer voltage linear control strategy with the control amount of the square of the voltage is proposed to regulate the output voltage. Simulation and experimental results demonstrate the effectiveness of the system.

Novel orthogonal signal generator for single phase PLL applications

Single-phase phase-locked loops (PLLs) are used in various types of power electronics applications, including voltage source inverters, pulse width modulation rectifiers and different types of grid-tied power converter utilities. The orthogonal signal generators (OSGs), used in single-phase PLLs, are generally based on various types of filters, and they need to operate robustly in relation to the grid voltage disturbances and frequency variations. In this study, a novel OSG is proposed based on a modified first-order all-pass filter, which enables the PLL phase detector to operate at different response speeds, tuned by means of a single parameter. The PLL is experimentally verified and compared with a number of conventional solutions. Tests include responses to phase angle disturbances, frequency steps, and PLL input voltage distortions. Results show that a novel OSG filter enables faster PLL responses when compared with several conventional OSG filters, all designed to have the same disturbance attenuation at double fundamental frequency.

On Reducing the Shaft Torque Ripple of Small-to-Medium-Scale Wind Energy Conversion Systems Using Multi-Pulse Autotransformer Rectifier

In a small-to-medium-scale wind energy conversion system (WECS), diode rectifiers rather than pulse-width modulated (PWM) rectifiers are widely adopted due to the features of high reliability and low cost. However, large current harmonics are induced in the generator phase current by commutations of diode rectifier, eventually causing large torque ripple on the drive-train of the WECS and making it more likely to be fatigue breakdown. In this paper, a 12-pulse autotransformer rectifier unit (ATRU) with reduced volume and weight is proposed for WECS application. By analyzing the characteristics of the input current and output voltage of the ATRU within the entire operation range of WECS, the method to properly design its parameters is proposed. A 1.2 kW direct-drive WECS demonstration platform using ATRU is built in the lab. A modified sensorless overall power control strategy is adopted to control the WECS. Experimental tests are carried out and the results not only validate the feasibility of implementing ATRU in WECS applications, but also prove its high torque ripple reduction ability.