Active Power Decoupling Design of a Single-Phase AC–DC Converter

Three phase pulse width modulation (PWM) rectifiers have excellent performance when the grid voltages are balanced, and it is widely adopted in the industry. However, the asymmetrical loads or grid faults will lead to the unbalanced grid voltages. In addition, the negative sequence (NS) voltages and currents in the unbalanced grid result in the fluctuation of the dc bus voltage. In this article, the intrinsic mechanism between the voltage ripple amplitude and the NS currents is revealed. Furthermore, this article proposes a data-driven adaptive current control method. By shaping the NS currents, the corresponding amplitudes of the second-order harmonic voltage on the dc bus are observed. Based on the observation data, the reference currents that can minimize the dc bus voltage ripple are adaptively derived online. As a result, the dc bus voltage ripple can be suppressed effectively. In addition, the proposed method does not need the NS decomposition or the parameters such as the grid voltages and inductances. Therefore, it has a strong robustness against parameter mismatch. Finally, the accuracy of the theoretical analysis and the effectiveness of the proposed method are validated by experiments.

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.

This paper presents a closed-form analytical solution to the harmonic spectrum of output voltage of a single-phase H-bridge inverter, and gives the precise harmonic spectrum considering the effects of dead-time and DC bus voltage ripple in a digitally controlled system. Since H-bridge is the basic block in converters, this solution and spectrum can be extended and applied to a variety of pulse width modulation (PWM)-based topologies. The interaction between modulation waveform and triangular during modulation process is fully analyzed from a mathematical perspective, so that the combined effects of digital sampling, dead-time and DC bus voltage ripple on the output voltage are summarized in time and frequency domains. Furthermore, the presented harmonic spectra do not need to judge the current polarity in calculation, which means that the exact amplitude and phase of each output harmonic can be obtained accurately, providing the important theoretical basis for system parameter design and specific harmonic compensation or elimination. The presented analysis results are verified by simulations and experiments.

The aim of this paper is to obtain the AC voltage from DC source with the help of Space vector based Inverter. In a space-vector PWM (Pulse Width Modulation) inverter, which is widely used, the voltage utilization factor can be increased to 0.906, normalized to that of the six step operation. Three phase voltage-source pulse width modulation inverters have been widely used for dc/ac power conversion since they can produce a variable voltage and variable frequency power. However, they require a dead time to avoid the arm-short and snubber circuits to suppress the switching spike. Apart from these ancillary aspects, the PWM inverters have an essential problem that they cannot produce voltages as large as the six-step inverters can. That is, the dc bus voltage cannot be utilized to the maximum. To increase the voltage utilization of the sinusoidal PWM inverter, a method of the addition of the third harmonics to the reference voltage was proposed by which the fundamental component can be increased by 15.5%. In a space-vector PWM inverter, which is widely used, the voltage utilization factor can be increased to 0.906, normalized to that of the sixstep operation. On the other hand, different discontinuous PWM strategies were analyzed, where the modulation waveform of a phase has at least one segment of 60 which is clamped to the positive and/or negative dc bus for, at most, a total of 120 in a fundamental period during which no switching in either inverter arm occurs. Recently, it is shown that discontinuous PWM schemes and the space-vector PWM can be obtained by properly adding a zero-sequence voltage to the original modulation waveform.

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.

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.

The model predictive control (MPC) of voltage source pulse width modulation (PWM) rectififier is extremely dependent on system model in control process. System model mismatch will make the prediction results deviate from the actual value, seriously affect the system control results, even caused the system to be unstable. In addition, MPC is a control method based on state space model and predictive state of controlled system. In each control cycle, it performs an ergodic optimization to solve the online optimization, and thus determines optimal driving signal of the switching device. However, to obtain the optimal control variables online usually leads to a high amount of computation, which is one of the difficulties in the implementation of MPC on PWM rectifier. To solve these problems, neural network is used to approximate the unknown functions in system model. A finite set model predictive path integral control (FCS-MPPIC) based on neural network is proposed to effectively decrease computational complexity of control algorithm under premise of ensuring the distortion rate of the grid side current. At the same time, dynamic response speed of the system is improved. Finally, the availability of this method is verified through the simulation results.

A load current observer based feedforward control scheme for three-phase voltage source pulse width modulation (PWM) active rectifiers is presented. The observer is designed to identify the load current disturbance, which is then forwarded to an inner current controller. Details of the design of the inner current controller and outer dc voltage regulator are also presented. To cope with the delay time of the digital control loop, Smith-predictor is employed in the current control loop to stop overshoots and oscillations during transient current regulation. Simulation model has been set up using commercially available VisSim software and then implemented in a digitally controlled prototype of a three-phase PWM active rectifier. The simulation and experimental results show that without using an actual load current sensor, the proposed observer based feedforward control scheme provides almost the same performance as the traditional feedforward control based on actual load current measurement.

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.

New regulation imposes more limits on harmonics injected by Power converters that are achieved with Pulse width Modulation (PWM) Rectifiers. Therefore this paper presents the analysis and control of the three phase Voltage Source PWM rectifiers using Hysteresis Band Current Control technique. The proposed rectifier achieved unity power factor, DC voltage regulation, Line current harmonic mitigation and Bi-directional Power flow. The work is done in Matlab/Simulink environment.

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.

Voltage ripple of DC bus in 3L-NPC inverters is an important factor for determine the stability of the circuit. DC bus capacitor is also one of the most vulnerable components in the inverters. The mathematical model of voltage ripple of 3L-NPC inverters is established by analyzing the circuit. Then, the failure mechanism of capacitors and degradation performance of the circuit are analyzed. Whether the variation of voltage ripple is used as fault characteristic parameter to some extent, the rationality of the hypothesis is verified by simulation. Finally, 3L-NPC inverters control system is built RT-LAB hardware-in-the-loop(HIL) platform, and the HIL simulation is transplanted into the actual control system to further verify the rationality of the hypothesis.

This work presents a methodology to apply space vector modulation to unidirectional pulse width modulation (PWM) rectifiers and applied in three different groups of rectifiers. Converter switching stages are analyzed for each group of rectifiers to determine switch control signals for space vector modulation. A switching sequence is proposed to minimize the number of switch commutations and reduce the switching losses. Duty cycle functions are determined and the desired switching sequences are performed by a simple PWM, with no need to determine the present sector of the vector. For this purpose, it is necessary to impose the desired current sectors from input voltage references. Simulation results of proposed modulation techniques are also presented.

This paper presents a simple and reliable Pulse Width Modulation (PWM) and control technique for circulating current minimization of hard parallel connected Neutral Point Clamped (NPC) inverters. Interleaved operations are commonly used in parallel connected inverters for decreasing load current ripple. However, the interleaved operation increases the common mode circulating current between the hard-parallel connected inverters. To reduce the common mode circulating current, Phase Opposite Disposition (POD) PWM is used in this paper. Zero-sequence circulating currents increase, if there are any differences in DC bus voltages between parallel inverters. The zero-sequence circulating currents generate capacitor voltage unbalance in the DC bus of NPC inverters. The capacitor voltage unbalance can generate even order harmonic circulating currents. For reducing the zero-sequence circulating current, a simple DC current control method is proposed in this paper. The DC current controller decreases the circulating DC current and capacitor voltage unbalance of paralleled inverters. Finally, PLECS based simulation results of a 100kW parallel connected inverter system are presented in this paper to illustrate the effectiveness of the proposed approach.