Current Zero-crossing Distortion Research Articles

A Novel Modulation Method to Decouple Output Power and Suppress Current Zero-Crossing Distortion for Vienna Rectifiers in Bipolar Output Mode

A Novel Modulation Method to Decouple Output Power and Suppress Current Zero-Crossing Distortion for Vienna Rectifiers in Bipolar Output Mode

A Novel Modulation Method to Suppress the Current Zero-Crossing Distortion for Vienna Rectifier With Different Control Methods Under Unbalanced Grid

Vienna rectifier is a boost type rectifier with unidirectional energy flow, which is widely used in many applications. Under unbalanced grid, there will be even harmonics in dc-link voltage and odd harmonics in input current if traditional control methods are used. Therefore, two control methods for Vienna rectifier under unbalanced grid are introduced, which are balanced positive-sequence current control (BPSC) and instantaneous active power control (IAPC). The current zero-crossing distortion (CZCD) is an inherent issue for Vienna rectifier due to its special circuit topology. The displacement angle between the input current and the voltage is revealed, which is the essence of CZCD. The issue of CZCD is more complex under unbalanced grid than that under balanced grid, and CZCD cannot be addressed well under existing suppression method. A novel method that can minimize CZCD under unbalanced grid is also proposed. The proposed method works well under both balanced and unbalanced grid. Finally, an experimental platform is built, and the feasibility and superiority of the proposed method is verified by comprehensive experiments.

Decoupled Unipolar Hysteresis Current Control for Single-Phase Grid-Tied Inverter Without Current Zero-Crossing Distortion

Decoupled Unipolar Hysteresis Current Control for Single-Phase Grid-Tied Inverter Without Current Zero-Crossing Distortion

A Novel Suppression Method for Input Current Zero-Crossing Distortion of the Vienna Rectifier Based on Negative Sequence Current Regulation Under the Unbalanced Grid

A Novel Suppression Method for Input Current Zero-Crossing Distortion of the Vienna Rectifier Based on Negative Sequence Current Regulation Under the Unbalanced Grid

An Improved Modulation Strategy Without Current Zero-Crossing Distortion and Control Method for Vienna Rectifier

An Improved Modulation Strategy Without Current Zero-Crossing Distortion and Control Method for Vienna Rectifier

A Novel Modulation Method Based on Model Prediction Control With Significantly Reduced Switching Loss and Current Zero-Crossing Distortion for Vienna Rectifier

Finite control set model predictive control (FCS-MPC) is widely used in rectifiers due to its fast response. When there are multiple control objectives, the optimal switching sequence is selected by minimizing the cost function with weighting factors. However, the reduction of current ripple caused by output error and switching loss is in conflict to a certain extent for FCS-MPC. In addition, when multiple objectives are controlled, the selection of weighting factor is a serious challenge. Therefore, a modulation method based on continuous control set model predictive control is proposed in this article. Two phases are clamped and one phase is modulated, which not only can significantly reduce the switching loss without increasing the computational burden, but also can control the neutral point voltage without using weighting factors. In addition, when the proposed method is adopted, current zero-crossing distortion can be suppressed over the full range of modulation index. The effectiveness of the proposed method is verified by simulation and experimental results.

An Improved Sliding Mode Direct Power Control Strategy Based on Reactive Power Compensation for Vienna Rectifier

Vienna rectifiers are widely used in electric vehicle charging systems, wind power generation systems and other fields due to their excellent high-voltage resistance, small size and high efficiency. Aiming at the problems of the Vienna rectifier’s long response time, low anti-disturbance ability, and current zero-crossing distortion, a new sliding mode direct power control strategy based on disturbance compensation is proposed. Firstly, a model considering the uncertainty is established, and the neural network is used to estimate and compensate the uncertain disturbance. Secondly, aiming at the slow approach speed and slow system convergence of traditional control methods, a new approaching law sliding mode direct power control strategy is designed. Aiming at the current zero-crossing distortion, the reason is analyzed and a compensation method is proposed. Finally, simulations and experiments show that the proposed method has no voltage overshoot and converges faster, effectively improving the problem of different phases of voltage and current. The rectifier operates at unit power, has better steady-state performance and stronger anti-load disturbance ability. The current total harmonic distortion is controlled below 2%, and the current quality is effectively improved.

Novel Three-Layer Discontinuous PWM Method for Mitigating Resonant Current and Zero-Crossing Distortion in Vienna Rectifier With an LCL Filter

Vienna rectifier is widely employed in the electric vehicle charging system and wind turbine system due to its higher efficiency and lower total harmonic distortion. However, the Vienna rectifier with the LCL filter has the challenge of resonant current mitigation, current zero-crossing distortion elimination, neutral point (NP) voltage balance and switching loss reduction. Moreover, these problems are mutually coupled. To overcome these issues, the causes of resonant current with the conventional discontinuous pulsewidth modulation (PWM) (DPWM) method is analyzed, which reveals that the abrupt change of reference voltage has a wide range harmonics band and easily induces the resonant current at resonant frequency. Then, based on the analysis, a novel three-layer DPWM method with three offset voltages injection is proposed. In the first layer, the NP voltage balance is realized by injecting the first offset voltage. In the second layer, the second offset voltage, which makes the discontinuous reference voltages smooth is presented to reduce the losses and suppress the resonant current. In the third layer, the third offset voltage is elaborated to eliminate current zero-crossing distortion caused by different power factor and the LCL filter. Based on the proposed method, resonant current mitigation, current zero-crossing distortion elimination, NP voltage balance are realized simultaneously with reduced switching losses. The effectiveness and performance of the proposed method are verified by simulation and experiment.

Full Digital Control and Multi-Loop Tuning of a Three-Level T-Type Rectifier for Electric Vehicle Ultra-Fast Battery Chargers

The rapid development of electric vehicle ultra-fast battery chargers is increasingly demanding higher efficiency and power density. In particular, a proper control of the grid-connected active front–end can ensure minimum passive component size (i.e., limiting design oversizing) and reduce the overall converter losses. Moreover, fast control dynamics and strong disturbance rejection capability are often required by the subsequent DC/DC stage, which may act as a fast-varying and/or unbalanced load. Therefore, this paper proposes the design, tuning and implementation of a complete digital multi-loop control strategy for a three-level unidirectional T-type rectifier, intended for EV ultra-fast battery charging. First, an overview of the operational basics of three-level rectifiers is presented and the state-space model of the considered system is derived. A detailed analysis of the mid-point current generation process is also provided, as this aspect is widely overlooked in the literature. In particular, the converter operation under unbalanced split DC-link loads is analyzed and the converter mid-point current limits are analytically identified. Four controllers (i.e., dq-currents, DC-link voltage and DC-link mid-point voltage balancing loops) are designed and their tuning is described step-by-step, taking into account the delays and the discretization introduced by the digital control implementation. Finally, the proposed multi-loop controller design procedure is validated on a 30 kW, 20 kHz T-type rectifier prototype. The control strategy is implemented on a single general purpose microcontroller unit and the performances of all control loops are successfully verified experimentally, simultaneously achieving low input current zero-crossing distortion, high step response and disturbance rejection dynamics, and stable steady-state operation under unbalanced split DC-link loading.

A Modular Multilevel Dual Buck Inverter With Adjustable Discontinuous Modulation

Conventional single-cell dual buck inverters present high reliability, however they cannot be directly used in high voltage applications, because of the limited voltage rating of commercial switching devices. Therefore, a novel modular multilevel dual buck inverter (MMDBI), capable of processing voltage and power at higher levels, requiring a single dc input voltage, is proposed in this paper. Non-interleaved phase-shifted discontinuous modulation (NIPSDM) and interleaved phase-shifted discontinuous modulation (IPSDM) schemes are applied to the proposed inverter to reduce the current stress in the switching devices. Despite beneficial to the converter efficiency, the use of these discontinuous modulation approaches results in current zero-crossing distortion, which needs to be appropriately managed. In this work, theoretical values for the common-mode and differential-mode current ripples under NIPSDM and IPSDM modulation strategies are derived, and each switching operating mode is fully analyzed. From that, an adjustable current threshold value, which depends on the theoretical current ripple magnitude, is incorporated into the modulation strategy, producing a minimum switching overlap period between the two buck cells that eliminates the current zero-crossing distortion and produces a high-quality output current. Extensive simulation and experimental investigations are presented to demonstrate the feasibility and effectiveness of proposed topology and adjustable discontinuous modulation strategy.

Power Loss Model for GaN-Based MHz Critical Conduction Mode Power Factor Correction Circuits

Wide bandgap (WBG) devices allow power factor correction (PFC) circuits to operate at megahertz (MHz), which improves power density. In low-power applications, critical conduction mode (CrM) boost PFC circuits are widely used due to its simple structure and minimized turn-on loss. Compared with the kilohertz (kHz) operation, MHz PFC in CrM yields larger inductor valley current during the zero voltage or valley switching turn-on, and significant grid current zero-crossing distortion, both of which are not considered in conventional PFC behavioral models. As a result, the conventional PFC design tool shows substantial inaccuracy in the estimation of switching frequency, inductor current envelopes, and power loss. This article analyzes these issues and proposes an improved power loss model to aid the design of MHz CrM PFC. Experimental results are presented to validate the accuracy.

Hybrid Control Scheme for Three-Phase Multilevel Unidirectional Rectifier Under Unbalanced Input Voltages

In this paper, a hybrid control scheme for three-phase Y-connected multilevel bridgeless rectifier (TMBR) under unbalanced input voltages is presented, based on the mathematical model of the TMBR topology, with the emphasis on the discussion for power fluctuation suppression, dc-link capacitor voltages balancing and input current zero-crossing distortion elimination. With the hybrid control scheme, the power fluctuation can be suppressed and three-phase input currents can flow with a purely sinusoidal waveform, besides, three-phase dc-link capacitor voltages can be controlled to be equal to each other under unbalanced input voltages. Moreover, the proposed hybrid control scheme is applicable to all other three-phase three wire multilevel unidirectional rectifiers under unbalanced input voltages. The validity of the proposed control scheme is demonstrated by the mathematical deduction. The simulations and experimental results verify that, with the proposed control scheme, TMBR can stably operate not only under balanced input voltages but also under unbalanced input voltages.

Analysis to Input Current Zero Crossing Distortion of Bridgeless Rectifier Operating under Different Power Factors

The principles and operating characteristics of bridgeless rectifiers under different power factors are discussed with emphasis on analyzing the input current distortion. Firstly, two driving modes are analyzed and compared. Based on the results of comparison it is concluded that the complementary drive mode is a better choice in terms of reducing the current distortion when bridgeless rectifier operates on non-unity power factor. Then, the mechanism causing input current zero-crossing distortion is analyzed. The input current during the distortion is expressed by the piecewise function when a bridgeless rectifier operates under complementary drive mode. Based on the piecewise function, the harmonic analysis is performed. Besides, the relationships between the input current Total Harmonic Distortion (THD) and the filtering inductance, the input current amplitude and the power factor angle are also investigated, which is useful when designing bridgeless rectifiers and selecting the corresponding parameters. Finally, the accuracy of the theoretical analysis is verified through the simulation and experiment.

A DSOGI-FLL-Based Dead-Time Elimination PWM for Three-Phase Power Converters

The dead-time elimination pulsewidth modulation (PWM) enables the drive pulses of the upper and the lower switching devices to alternate according to the current polarity, thus abandoning the dead time and essentially avoiding the dead-time effect in power converters. However, the current zero crossing will be distorted by the current jump generated by the drive-pulse alternation, and the current zero-crossing distortion will be further intensified if errors exist in the detected current polarity. Thanks to the noise-attenuation and frequency-adaptability characteristics of the double second-order generalized integrator frequency-locked loop (DSOGI-FLL), it can obtain accurate current polarities even in harmonic and unbalanced conditions. A DSOGI-FLL-based dead-time elimination PWM is, therefore, proposed in this paper, and several improvements are made to minimize the current zero-crossing distortion. An underlap period is added when alternating the upper and lower drive pulses to smooth the current jump at zero crossing, and a delay compensation term is inserted in the DSOGI-FLL to compensate both the current measurement delay and the control delay. The effectiveness of the proposed DSOGI-FLL-based dead-time elimination PWM has been validated by experiments, respectively, in the unbalanced-current, power-change, and frequency-variation conditions with an RL load, as well as in a grid-connected converter.

Combined Reactive Power Injection Modulation and Grid Current Distortion Improvement Approach for H6 Transformer-Less Photovoltaic Inverter

In this paper, a combined reactive power modulation and grid current distortion improvement approach is proposed for an H6 transformer-less full-bridge single-phase photovoltaic (PV) grid-connected inverter. H6 transformer-less inverters with traditional modulation and control strategies may not satisfy the requirement of reactive power compensation or may result in more severe zero-crossing current distortion. Therefore, contrary to the traditional modulation, a novel reactive power injection space vector pulse width modulation (SVPWM) is proposed, which consists of two operation stages—inverter modulation and reactive power modulation. The implementation of SVPWM for reactive power modulation using a digital signal processor is also investigated. Furthermore, to suppress the current zero-crossing distortion in the reactive power injection mode, a global sliding mode function based on the proportion-integration-resonance current controller is designed, and the control law of the global sliding mode is derived. Using the segment modulation and grid current distortion improvement approach, the function of reactive current injection is implemented in commercial PV inverters, and the total harmonic distortion of the grid current is decreased significantly by more than 5% in the low-power segment, under the operating conditions of a lagging or leading power factor of 0.95. The effectiveness and feasibility of the proposed approach are verified through simulation and experiment using a 5-kVA prototype.

PFC Converter with Improved Input Current Zero-crossing Distortion

In this study, a voltage superposition concept is used without phase adjustment of the input current command and without enlarging the turn-on period of the switch in the vicinity of the zero input voltage, but only with a few components added to the PFC converter, so as to improve the zero-crossing distortion of the input current, thereby further reducing the total harmonic distortion. Eventually, the mathematical deductions and experimental results are provided to verify the effectiveness of the proposed circuit.

Topologies and Control Strategies of Cascaded Bridgeless Multilevel Rectifiers

This paper presents a new unidirectional cascaded bridgeless multilevel rectifier (CBR) well suited for serving as the rectifier stage of a transformerless cascaded multilevel converter. Compared to a traditional cascaded H-bridge rectifier, the proposed CBR utilizes fewer fully controlled switching devices by replacing the fully controlled H-bridge modules with bridgeless PFC modules, thus simplifying the control circuits, increasing the system reliability, and cutting down the implementation expenses. However, when a single-phase CBR is operating under a unity power factor, the input current will be severely distorted because of the unidirectional power flow property of the bridgeless PFC modules. Therefore, aiming at achieving a satisfactory current quality and power factor simultaneously, an improved control strategy and a revised topology for the single-phase CBR are provided as two effective solutions. Specifically, for the single-phase CBR under the improved control, the limitation of the maximum value of the boost inductance considering an acceptable power factor is derived. Besides, the method of determining the configuration of the modified single-phase CBR is given based on the steady-state analysis. In addition, for the three-phase CBR, the reason that the traditional control strategy is capable of realizing unity power factor rectification while mitigating input current zero-crossing distortion is analyzed. Finally, simulations in the MATLAB/Simulink environment and experimental results from scaled-down laboratory prototypes are provided to verify the proposed theories.

Improved Elimination Scheme of Current Zero-Crossing Distortion in Unipolar Hysteresis Current Controlled Grid-Connected Inverter

In this paper, the generation reason and the improved elimination scheme of the current zero-crossing distortion (ZCD) of single-phase grid-connected inverter controlled by unipolar hysteresis current control containing band are investigated in detail. A current ZCD elimination scheme by exchanging the control signal of low-frequency leg of inverter ahead of the zero-crossing points of grid voltage is proposed. The effect of the variation of the amplitude and frequency of tied grid and the filter inductor on the optimal leading exchanging phase angle (LEPA) is analyzed. A single-phase hybrid filter-based enhanced phase-locked loop is proposed to estimate accurately the information of the grid, even under nonideal input conditions. Then, an online filter inductor estimation scheme is proposed to obtain the accurate actual inductor value. The former estimated parameters are used to calculate the exact optimal LEPA online to improve the performance of the current ZCD elimination scheme. Comprehensive experimental results are represented to verify the accuracy and feasibility of the theoretical analysis and the proposed improvement.

Analysis and Solution of Current Zero-Crossing Distortion With Unipolar Hysteresis Current Control in Grid-Connected Inverter

In this paper, a kind of zero-crossing distortion (ZCD) generated in the grid-connected current of a single-phase grid-connected inverter with unipolar hysteresis current control is investigated. By establishing the mathematical model of the grid-connected inverter around the zero-crossing points (ZCPs), the reason for causing the current ZCD is presented. It is ascribed to the slope of the actual current less than that of the reference one around the ZCPs. The expressions of the critical phase angle (the starting point of the current ZCD) and the amplitude of the current distortion corresponding to the parameters of the inverter and connected utility grid are obtained, and the solution for the ZCD based on on-line leading phase angle compensation is proposed. Simulation and experimental results verify the accuracy and feasibility of the theoretical analysis and the proposed solution.

Cascade Dual Buck Inverter With Phase-Shift Control

This paper presents a new type of cascade inverter based on dual buck topology and phase-shift control scheme. The proposed cascade dual buck inverter with phase-shift control inherits all the merits of dual buck type inverters and overcomes some of their drawbacks. Compared to traditional cascade inverters, it has much enhanced system reliability thanks to no shoot-through problems and lower switching loss with the help of using power MOSFETs. With phase-shift control, it theoretically eliminates the inherent current zero-crossing distortion of the single-unit dual buck type inverter. In addition, phase-shift control and cascade topology can greatly reduce the ripple current or cut down the size of passive components by increasing the equivalent switching frequency. A cascade dual buck inverter has been designed and tested to demonstrate the feasibility and advantages of the system by comparing single-unit dual buck inverter, 2-unit and 3-unit cascade dual buck inverters at the same 1 kW, 120 V ac output conditions.