One-cycle controlled three-phase PWM rectifiers with improved regulation under unbalanced and distorted input voltage conditions

In this paper, a modified one-cycle-control (OCC) scheme is proposed for regulating three-phase pulsewidth-modulated (PWM) rectifiers operating under unbalanced and distorted supply conditions. Mathematical analysis is first presented to show the dominant harmonic-voltage components appearing across the dc link of the PWM rectifier when it is controlled by an existing OCC scheme. Such dc-link harmonics when produced may aggravate harmonic currents flowing into the input terminals of the three-phase rectifier. To address these interrelated unbalance and harmonic concerns, the concept of reconstructing the appropriate reference signals in the OCC control core is introduced, before modifications are recommended for altering the key control equation. The improved OCC controller eventually developed is proven to exhibit minimal input-current distortion and a smoother dc-link voltage without using large capacitance. Other advantages exhibited by the traditional OCC scheme, such as no phase-locked loop, no frame transformation, and constant switching frequency, are also retained by the improved controller, whose theoretical findings are fully verified by experimental results obtained from a 1.2-kW three-phase PWM rectifier built in the laboratory.

In this paper, a dual-converter three-phase pulse width modulation (PWM) rectifier based on unbalanced one-cycle control (OCC) strategy is proposed. The proposed rectifier is used to eliminate the second harmonic waves of DC voltage and distortion of line currents under unbalanced input grid voltage conditions. The dual-converter PWM rectifier employs two converters, which are called positive-sequence converter and negative-sequence converter. The unbalanced OCC system compensates feedback currents of positive-sequence converter via grid negative-sequence voltages, as well as compensates feedback currents of negative-sequence converter via grid positive-sequence voltages. The AC currents of positive- and negative-sequence converter are controlled to be symmetrical. Thus, the workload of every switching device of converter is balanced. Only one conventional PI controller is adopted to achieve invariant power control. Then, the parameter tuning is simplified, and the extraction for positive- and negative-sequence currents is not needed anymore. The effectiveness and the viability of the control strategy are demonstrated through detailed experimental verification.

In three-phase PWM rectifiers, variations in the dc voltage reference or load can affect the stability and dynamics of the system. Traditional proportional-integral (PI) control has weak adaptability, as its parameters cannot be adjusted in real-time according to the operating state, potentially leading to poor system stability and slow dynamic response. To address these challenges and the complexity of existing PI self-tuning methods, this article proposes a PI self-tuning method based on stability-and-dynamics-constrained fuzzy backpropagation neural network (SDC-FBPNN) for three-phase pulsewidth modulation (PWM) rectifiers. The effect of the right-half-plane zero is considered, and a series compensation method is adopted to convert the non-minimum phase system into a minimum phase system. On this basis, the phase margin and crossover frequency are used as constraints for stability and dynamic performance, respectively. Consequently, PI parameters can be adjusted by the SDC-FBPNN in real-time according to the operation conditions. Under abrupt variations in voltage reference and load, the proposed method significantly reduces voltage fluctuations and shortens the settling time while ensuring system stability. Finally, a 2 kW prototype was built to validate the feasibility and effectiveness of the proposed PI self-tuning method.

A Pulse Width Modulation (PWM) rectifier with strong DC disturbance rejection is presented based on Model Predictive Control (MPC). The design of outer voltage square loop and inner current loop using model predictive control is presented, where voltage square loop indicates the square of output DC voltage calculated to be linear with active current. A discrete-time model of the rectifier is constructed to predict the future current for all voltage vectors. Then, one voltage vector minimizing the current errors is selected by solving the cost function. Two weighting matrices, which affect the performance of the rectifier greatly, are used in the cost function to weight prediction error and control actions. This paper indicates the function of the two different weighting coefficients and the way to choose proper weighting factors on a typical three phase PWM rectifier under different conditions. The static, dynamic, pre-charging performance and anti-disturbance ability are discussed upon the proposed rectifier model. The results are proved by simulation that the proposed method can achieve strong DC immunity and a fast dynamic performance with pre-charging strategy compared to the traditional method.

In this paper, the mathematical model and work principle of the three-phase voltage source pulse width modulation (PWM) rectifier (VSR) are analyzed. Then, the control strategies without feed-forward and with feed-forward are compared, which based on the power factor, the total harmonic distortion (THD) and DC voltage stability. Voltage-Oriented Control (VOC) and direct current control method were adopted to obtain current tracking control. Meanwhile, a simplified algorithm was presented for space vector PWM (SVPWM), which simplifies the arithmetic process. Contrastive analysis of two control strategy results show that without feed-forward control strategy exits the faults of low power factor, high THD and so on, although its model is simple. While feed-forward control strategy has been proved more effective.

In this paper, an adaptive voltage-oriented control (VOC) for three-phase grid-connected pulse-width modulation (PWM) rectifier is developed. As the control loop behavior is affected by the PWM rectifier operating conditions, the effects associated to the PWM rectifier losses and uncertainty in the inductance should be inserted in the model. Thus, equivalent resistance and inductance are estimated online by means of an adaptive linear neuron (ADALINE). The proposed ADALINE estimator is inserted in the current control loop to perform an adaptive VOC scheme. Hence, an online updating of the decoupling terms and the current controller gains is achieved. The ADALINE capability to estimate accurately the equivalent inductance and resistance as well as the adaptive VOC scheme performances are finally evaluated by experiments. Experimental results show improved performances and accurate estimation.

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.

This work proposes a very fast phase angle estimation algorithm for a single-phase system under a sudden phase angle jump condition. When a source voltage changes in a step manner, the normal phase angle detector, such as a phase locked loop (PLL) and a (low pass) filter, typically generates phase delay and results in a sluggish response, and causes some time-critical machine to malfunction. This work proposes a method of estimating the fundamental component, the phase angle and the frequency of a single-phase line voltage without a significant delay, even when the amplitude and the phase angle of the line voltage changes in a step manner, by using the weighted least-squares estimation (WLSE) method with the covariance resetting technique. An example application of a single-phase pulse width modulation (PWM) rectifier for a traction is presented in an appendix. This method can be applied to uninterruptable power supply (UPS), PWM rectifier, active filters, etc.

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.

This paper discusses reduction of capacitances of dc capacitors in the previously proposed smart charger (SC) with a sinusoidal charging-discharging lithium-ion battery for electric vehicles in single-phase three-wire distribution feeders. The dc-capacitor current of the three-leg pulse-width modulated (PWM) rectifier, which is included in the SC, is detected, and then added to the reference value of the battery-charging or — discharging current for a bidirectional dc-dc converter. Addition of the detected dc-capacitor current to the reference value for the dc-dc converter sinks the voltage ripples in the dc capacitors of both the PWM rectifier and bidirectional converter. This results in a substantial reduction in the capacitances of the dc capacitors. Simulation results demonstrate that balanced source currents with a unity power factor are achieved, reducing the capacitances of the dc capacitors in the previously proposed SC.

The voltage-regulated pulsewidth-modulated (PWM) rectifier is prone to instability. The system can be stabilized by proportional-plus-integral feedback control, but its transient response is slow. This paper describes results of a study of digital control to improve the system dynamic response by pole placement through state feedback. The control algorithm is implemented for real-time operation by using a custom designed system of three high-speed microprocessors. Results from an experimental study with a 1 kW hardware laboratory model of the PWM rectifier shows that the dynamic response can be significantly improved even when the DC link capacitor is substantially reduced.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In recent years, electronic power transformer (EPT), which is also called solid state transformer, has attracted great interest and has been used in place of the conventional power transformers. These transformers have many important functions as high unity power factor, low harmonic distortion, constant DC bus voltage, regulated output voltage and compensation capability. In this study, proposed EPT structure contains a three-phase pulse width modulation rectifier that converts 800 Vrms AC to 2000 V DC bus at input stage, a dual active bridge converter that provides 400 V DC bus with 5:1 high frequency transformer at isolation stage and a three-phase two level inverter that is used to obtain AC output at output stage. In order to enhance dynamic performance of EPT structure, neuro fuzzy controllers which have durable and nonlinear nature are used in input and isolation stages instead of PI controllers. The main aim of EPT structure with the proposed controller is to improve the stability of power system and to provide faster response against disturbances. Moreover, a number of simulation results are carried out to verify EPT structure designed in MATLAB/Simulink environment and to analyze compensation ability for voltage harmonics, voltage flicker and voltage sag/swell conditions.

This paper proposes a novel circuit topology for a three-phase power factor correction (PFC) rectifier using a harmonics current injection method. In consideration of lower cost, the harmonics injection method is more suitable than a conventional six-arm pulse width modulation (PWM) rectifier. The harmonics injection current is simply generated by only one switching leg. As a result, the proposed circuit has the advantage of only two switches. An optimal injection current is achieved in order to obtain an input current of sinusoidal waveforms. This paper discusses the basic operation and optimal design method for the proposed circuit. In addition, the validity of the proposed circuit is confirmed by simulation and experimental results. An input current of almost sinusoidal waveform was obtained and an input current total harmonic distortion (THD) of 8.5% was obtained at a load of approximately 1 kW.

Generally, AC-DC conversion system in the power system use the diode-bridge based rectifiers that cannot be reversible and causes high current distortion. Besides, they reduce the power factor and energy quality. recently, the application of three-phase pulse width modulation (PWM) rectifier has been risen quickly due to breakthrough advancement in the power devices. This converter offers sinusoidal input currents and minimized harmonic distortion and unity power factor. This work presents an improved sensorless control for performance enhancement purpose of the PWM-rectifier. The proposed control strategy uses the virtual flux principle with second-order generalized integrator (SOGI) in order to overcome the accompanying drawbacks of using pure integrator of low-pass filters for estimation. The integration of improved virtual flux estimator with direct power control saves the cost of using many voltage sensors which can increase the reliability and effectivity of the control system. Moreover, it improves control robustness and against highly distorted network. The different proposed approaches have been investigated through simulation using MATLAB/Simulink software.

EV chargers with output power levels in the range of tens of kW are typically employing a front-end three-phase boost-type PFC rectifier stage for sinusoidal input current and DC-link voltage control, and a series-connected isolated DC/DC converter controlling the actual output/charging current or voltage. This paper explores a new synergetic control of both converter stages, which utilizes the DC/DC converter also for varying the DC-link voltage with six times the mains frequency, such that the currents of two mains phases are shaped sinusoidally. Accordingly, two bridge legs of the rectifier stage can remain clamped in 60°-wide intervals of the mains cycle and the pulse width modulation (PWM) can be restricted to the phase carrying the lowest current, i.e., only one of the three bridge legs is operated with PWM, designated as 1/3-PWM. Furthermore, the DC-link voltage that is switched by the operating rectifier phase is kept to the minimum and the system features high efficiency and low EMI, but still maintains boost capability, i.e., the option of conventional PWM of all three rectifier bridge legs (thus denominated as 3/3-PWM), which is advantageous in case a wide input or output voltage range needs to be covered. The new control concept is derived starting from a conventional approach with constant DC-link voltage, and is verified by simulations for a three-level Vienna Rectifier front-end and two cascaded DC/DC modules supplied from the halves of the symmetrically partitioned DC-link voltage. First, the operating behavior of the system utilizing the proposed control is described analytically. Next, the performance improvement achievable with the proposed control scheme is comparatively evaluated for a 20kW system designed for operation in a wide mains voltage range (260-530V rms line-to-line) and an extremely wide DC output / battery voltage range (150-750V dc ), according to EV charging equipment supplier requirements of the State Grid Corp. of China. Finally, simulation results are presented which validate the operating principle of the proposed modulation and control scheme.