Output Current Control Research Articles

Communication/Model-Free Constant Current Control for Wireless Power Transfer Under Disturbances of Coupling Effect

In this article, we propose a communication-free, continuously regulated, and no additional circuit control scheme to ensure the constant current (CC) output under the inevitable variation of coupling effect between the transmitter and the pickup of wireless power transfer (WPT) systems. By comparing with previous studies on the impact of varying loads, the corresponding key technical challenge is to deal with the untestability of the mutual inductance. Especially for single-side and communication-free control schemes, the impact of coupling effect significantly increases the difficulty for the CC control of WPT systems. Thus, a communication/model-free (C/M-free) CC control is proposed and implemented by using the pretrained neural network, which aims to ensure the expected output current with respect to varying relative position between the transmitting and the pickup coils. Particularly, the pretraining scheme is adopted to reduce the implementation difficulties and the impact of the measurement inaccuracy. In addition, the analysis of robustness and generalization is also carried out to reveal the impact of parameter drifting and load disturbance on the performance of the proposed C/M-free CC control. In this article, the exemplified WPT prototype can realize the constant output current control with the accuracy of 97.6%.

Simplified predictive current controller for three-to-five-phase direct matrix converter

PurposePredictive current control (PCC) of three-to-five-phase direct matrix converters (DMCs) is computationally expensive. For this reason, this study aims to consider a reduced number of switching states of DMC in PCC algorithm to predict the control objectives, such as output current control and input reactive power control.Design/methodology/approachThe switching sequences which yield the voltage vectors of variable amplitude at a constant frequency in space are considered for the prediction and optimization step of PCC algorithm. For the selected voltage vectors, the phase angles of the output vectors are independent on the phase angles of the input vectors. In a three-to-five-phase DMC, there are 243 valid switching states. Among the switching states, only 91 states are considered using the aforementioned concept of variable amplitude output at a constant frequency. This reduced number of switching states simplifies the computational complexity of MPC based current control of three-to-five-phase DMC.FindingsThe computational complexity of the proposed PCC based DMC is lower than the all 243 vectors based PCC. The current total harmonic distortion, transient current response and input reactive power control for the simplified 91 vector based PCC are similar to the all 243 vectors based PCC.Originality/valueA reduced number of switching sequence is considered for the prediction and optimization step of PCC algorithm. Hence, PCC algorithm can be sampled at a high frequency in real-time applications. Then, the performance of the PCC will be improved.

Dynamic-Balancing Robust Current Control for Wireless Drone-in-Flight Charging

This article proposes an enhanced timely and robust constant current (CC) control for wireless in-flight charging systems. The challenge for practical wireless in-flight charging systems is to maintain a CC output for hovering drones under circumstances of the continuous variation of coupling effect, various charging power requirements, and the parameter shifting, which is nearly unexplored in previous studies on wireless power transfer technologies. In order to address the issue, this article adopts the online-trained radial basis function neural network (RBFNN) to ensure the expected CC output for battery charging, which aims to handle negative impacts of the continuously varied coupling effect, the disturbance of parameters, and the change of charging current. In this article, both simulated and experimental results are given to verify the effectiveness of the proposed control scheme, wherein the accuracy of the controlled output current is within 5% and the average response time is less than 100 ms. It shows that the proposed dynamic-balancing robust current control is an ideal technical solution for wireless in-flight charging of drones by means of remarkable characteristics of the adopted RBFNN-based controller, namely, the increased rapidity and the enhanced robustness.

Modulated Model Predictive Control for Multilevel Cascaded H-Bridge Converter-Based Static Synchronous Compensator

The model predictive control (MPC) methods have been widely applied due to the fast dynamic performance and multiple control targets. However, they show certain limits when applied to the multilevel converters, such as unfixed switching frequency, large computation burden, and complex weighting factors selection. This article proposes a novel modulated MPC (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PC) method for cascaded H-bridge (CHB) converter-based static synchronous compensator (STATCOM). Instead of multitarget integration and weighting factor design, the proposed method disintegrates the voltage balancing control process from the cost function. The evaluated control sets for output current control is decided by the search step and the search range in each period. By proper design and selection of the adaptive search step for the output voltage references under <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α–β</i> coordinate, the search range can be reduced, which greatly reduces the number of evaluated control sets in each control period. Therefore, the dynamic of output characteristics and the low computation burden of the MPC method are guaranteed simultaneously. In addition, with the simple and independent integration of the capacitor voltage balancing control, the proposed method can be easily applied in the CHB converter-based STATCOM application. Furthermore, this article provides a delay compensation for the prediction process, and it provides a fixed switching frequency for each H-bridge cell. Simulation and experimental results verify the effectiveness of the proposed M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> PC method.

커플드 인덕터기반의 계통 연계형 Ćuk CCM 인버터의 동적 모델링과 제어기 설계

This paper presents a dynamic modeling and controller design for a grid-connected Ćuk continuous conduction mode (CCM) inverter with a coupled inductor. The primary- and secondary-side inductors of the conventional Ćuk converter are integrated into one coupled inductor in the presented Ćuk CCM inverter, and it reduces the number of passive components. To make the Ćuk CCM inverter with a coupled inductor connected with the grid utility, an output current controller should be designed appropriately. However, the output current control of the presented Ćuk inverter is difficult due to the existence of the right-half plane (RHP) zeros in its transfer function. To solve the problem, a dynamic model of the Ćuk CCM inverter with a coupled inductor is developed and a repetitive controller (RC) coupled with feedback and feedforward controllers is applied to this inverter. A practical design guideline is also presented to select control parameters. Experimental results using a 200-W prototype demonstrate the acceptable performance of the proposed controller.

A Flexible Pulse Generator Based on a Field Programmable Gate Array Architecture for Functional Electrical Stimulation.

Non-invasive Functional Electrical Stimulation (FES) is a technique applied for motor rehabilitation of patients with central nervous system injury. This technique requires programmable multichannel systems to configure the stimulation parameters (amplitude, frequency, and pulse width). Most FES systems are based on microcontrollers with fixed architecture; this limits the control of the parameters and the scaling to multiple channels. Although field programmable gate arrays (FPGA) have been used in FES systems as alternative to microcontrollers, most of them focus on signal acquisition, processing, or communication functions, or are for invasive stimulation. A few FES systems report using FPGAs for parameter configuration and pulse generation in non-invasive FES. However, generally they limit the value of the frequency or amplitude parameters to enable multichannel operation. This restricts free selection of parameters and implementation of modulation patterns, previously reported to delay FES-induced muscle fatigue. To overcome those limitations, this paper presents a proof-of-concept (technology readiness level three-TRL 3) regarding the technical feasibility and potential use of an FPGA-based pulse generator for non-invasive FES applications (PG-nFES). The main aims were: (1) the development of a flexible pulse generator for FES applications and (2) to perform a proof-of-concept of the system, comprising: electrical characterization of the stimulation parameters, and verification of its potential for upper limb FES applications. Biphasic stimulation pulses with high linearity (r2 > 0.9998) and repeatability (>0.81) were achieved by combining the PG-nFES with a current-controlled output stage. Average percentage error in the characterizations was under 3% for amplitude (1–48 mA) and pulse width (20–400 μs), and 0% for frequency (10–150 Hz). A six-channel version of the PG-nFES was implemented to demonstrate the scalability feature. The independence of parameters was tested with three patterns of co-modulation of two parameters. Moreover, two complete FES channels were implemented and the claimed features of the PG-nFES were verified by performing upper limb functional movements involving the hand and the arm. Finally, the system enabled implementation of a stimulation pattern with co-modulation of frequency and pulse width, applied successfully for efficient elbow during repetitions of a functional movement.

Simplified cascade multiphase DC-DC buck power converter for low voltage large current applications: part II --- output current controller

&lt;span lang="EN-US"&gt;This paper proposes a control method for new simplified cascade multiphase direct current-direct current (DC-DC) buck power converters used for low-voltage large-current applications such as cathodic protection. To control the proposed converter, a proportional-integral (PI) controller is used to regulate the output current of the converter. The control scheme analysis is carried out by linearizing the small-signal model of the proposed converter to form the output current transfer functions. This transfer function will be analyzed by using phase and gain margin approach to obtain the control parameters (Kp, Ki, and Ti). Simulation and experiment results are included to show the validity of the proposed concept.&lt;/span&gt;

MSVM ‐based hybrid energy‐fed quasi‐Z‐source cascaded H‐bridge inverter for grid‐connected system

Hybrid energy sources are much needed to meet the power demand for various real-time applications, and the desired output level is attained with the help of various advanced power converter topologies. Here, the hybrid energy source-fed quasi-Z-source cascaded H-bridge inverter (QZS-CHI) is implemented for a grid-connected system. The conventional multilevel inverter topologies are suitable for voltage buck operation, but this proposed system includes quasi-Z-source inverter network, which leads voltage buck-boost operation without any additional dc-dc converter. Modified space vector modulation (MSVM) technique is developed to control the QZS-CHI system, which leads to reduced total harmonic distortion(THD), reduced common-mode voltage (CMV), controlled output current, and improved output voltage. The proposed system QZS-CHI is energized using a hybrid energy source with a photovoltaic (PV) system and wind energy conversion system (WECS). With the help of shoot through mode in QZS, the output voltage is boosted without an additional converter and CMV is minimized by the proper utilization of medium and small switching state vectors. To assess the proposed technique, a laboratory prototype model is built and analyzed under different cases. From the obtained results, it is observed that the proposed method reduces THD to 2.15% for output voltage and 2.99% for output current, and common-mode voltage is reduced to Vdc/6 times of applied dc voltage.

Microsecond Enhanced Indirect Model Predictive Control for Dynamic Power Management in MMC Units

The multi-modular converter (MMC) technology is becoming the preferred option for the increased deployment of variable renewable energy sources (RES) into electrical power systems. MMC is known for its reliability and modularity. The fast adjustment of the MMC’s active/reactive powers, within a few milliseconds, constitutes a major research challenge. The solution to this challenge will allow accelerated integration of RES, without creating undesirable stability issues in the future power system. This paper presents a variant of model predictive control (MPC) for the grid-connected MMC. MPC is defined using a Laguerre function to reduce the computational burden. This is achieved by reducing the number of parameters of the MMC cost function. The feasibility and effectiveness of the proposed MPC is verified in the real-time digital simulations. Additionally, in this paper, a comparison between an accurate mathematical and real-time simulation (RSCAD) model of an MMC is given. The comparison is done on the level of small-signal disturbance and a Mean Absolute Error (MAE). In the MMC, active and reactive power controls, AC voltage control, output current control, and circulating current controls are implemented, both using PI and MPC controllers. The MPC’s performance is tested by the small and large disturbance in active and reactive powers, both in an offline and online simulation. In addition, a sensitivity study is performed for different variables of MPC in the offline simulation. Results obtained in the simulations show good correspondence between mathematical and real-time analytical models during the transient and steady-state conditions with low MAE. The results also indicate the superiority of the proposed MPC with the stable and fast active/reactive power support in real-time simulation.

Sensorless rotor position estimation of PMSM for low and high rotor speed

In this paper, a sensorless permanent magnet synchronous motor (PMSM) drive was presented based on calculating the back EMF using the reference stator voltages, which are the output of the d-axis current controller, which includes information about the rotor position. Sensorless control estimates the position information necessary for vector control of the motor without using position sensor or encoder. This can provide effects such as increased system reliability and cost and volume reduction. The back EMFs are calculated in a new coordinate based on the estimated speed to minimize the rotor speed estimation error. The estimated rotor position and rotor speed may fail to track the real rotor position and real rotor speed in extremely low speed since the position error can be amplified from the current controller output voltage, and this may cause the instability problems of tracking controller. So, a compensator has been added to the detector to overcome this disadvantage. In order to verify the validity of the proposed sensorless control technique, an experiment was performed on the PMSM, and the results showed fast-dynamic response, low ripples in motor’s currents, and good performance in tracking speed and power references.

SiC-MOSFET shunt active power filter based on half-cycle SDFT and repetitive control

The switching frequency of traditional active power filter (APF) is usually between 10 kHz and 20 kHz. To better suppress switching subharmonics, the output filters of APFs usually use LCL-filters. However, LCL-filters not only have complex parameter design but also introduce resonance points, which complicate the design of the circuit and control algorithm of APFs. In this paper, SiC-MOSFET is used as the power device of APF, the switching frequency of APF is increased to 50 kHz. In this case, using L-filter instead of LCL-filter can also suppress the switch subharmonics to a smaller level, which simplifies the circuit design and control algorithm design at the same time. In addition, when the sampling frequency and switching frequency are higher, the sampling points and switching times in a power frequency cycle increase exponentially, so the accuracy of harmonic extraction and output current control will be higher. Then, the common harmonic extraction algorithms of APFs, sliding window discrete Fourier transform (SDFT) and current control algorithm, repetitive control (RC), are analyzed in the frequency domain. A modified half-cycle SDFT and half-cycle RC are proposed, which reduces the inherent delay of the algorithms by half, and reduces the dynamic response time of APFs from two to one power frequency cycle, thus improving the dynamic response performance of APFs.

Research on Automatic Control System of MR Damper Based on Neural Network Algorithm

The use of MR dampers can achieve the absorption of harmful vibrations such as seismic waves that affect the structure of the building itself. The current control of the MR damper generally uses a pulse width modulation system to control the current input to the MR damper, thereby controlling the MR damper. But this is a semi-automatic control method, and the error is relatively large. This article introduces an MR damper control system that introduces a neural network algorithm. The system uses a half-bridge drive circuit for output current control in the circuit part and uses the Shen BP network algorithm for numerical prediction and fitting. The experimental research and tests conducted in the project show that the use of this fuzzy algorithm can make the MR damper achieve good damping effects under different conditions, and can well improve the original semi-automatic control method.

An ARMAX-DFIG model based adaptive controller for a wind energy conversion system

This paper presents design of an adaptive model predictive current controller for a Doubly-Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS). An Autoregressive Moving Average with Exogenous input (ARMAX) model is developed to represent the dynamics of DFIG. The parameter vector of DFIG is estimated by employing the recursive least square algorithm. A predictive current controller based on model predictive concept is designed for output current control of the Rotor Side Converter (RSC) to achieve the desired control performance. Extensive simulation studies are pursued by implementing the proposed controller in MATLAB/SIMULINK environment. The performance of the proposed Adaptive Predictive Current Controller (APCC) is evaluated under various operating conditions such as sub-synchronous speed, synchronous speed, and super-synchronous speed. The performances of the proposed controller are compared with that of the conventional MPC. It is found that the proposed controller exhibits superior performance in terms of improved reference tracking of rotor currents.

Modular Circulating Current and Second Harmonic Current Suppression Strategy by Virtual Impedance for DC Solid-State Transformer

This article proposes a circulating current and second harmonic current (SHC) suppression method by introducing virtual impedance into the circulating current and output current feedback control loops of the dc solid-state transformer (DCSST). The virtual impedance is employed to adjust impedance in the circulating current feedback control loop to decrease the circulating current when the transmission efficiency of each dual active bridge is different. And a SHC suppression method, which introduces the virtual impedance containing a bandpass filter, is adopted to reduce the SHC and improve the dynamic performance of the DCSST. Moreover, a relatively independent modular control method, which is conducive to the modular expansion of the DCSST, is proposed. Compared with traditional DCSST control methods, the proposed method can simultaneously realize the output current sharing and effectively reduce the SHC with modular control. Finally, a DCSST prototype is built and the results of the experiment verify the validity and effectiveness of the proposed control strategy and solutions.

Backstepping Control of High-Frequency Link Matrix Rectifier for Battery Chargers

High-frequency link matrix rectifier (HFLMR) is getting much interest in electric vehicle charger applications due to its high efficiency and compact volume. However, the inputs and outputs of HFLMR are highly coupled resulting in reduced system dynamic performance and robustness. This article proposes a dual closed-loop backstepping control (DCL-BSC) strategy to solve these problems, which consists of a dc output current outer-loop controller and a grid current inner-loop controller. First, the nonlinear mathematical model of HFLMR is established, and the six-segment space vector pulse width modulation scheme is used as the modulation method. Then, the DCL-BSC scheme is designed in detail based on the Lyapunov stability theory. And a compensation method based on the phase-shift angle is developed to realize the unity power factor. Compared with the conventional dual closed-loop PI control method, the proposed method has a better steady-state and dynamic performance, and robustness against system disturbances. Simulation and experimental results are used to verify the effectiveness of the proposed control scheme.

Dynamic Characteristic Improvement of Phase-Shift Full-Bridge Center-Tapped Converters Using a Model Predictive Control

This article proposes a dynamic characteristic improvement of phase-shift full-bridge center-tapped (PSFB-CT) converter using a model predictive control (MPC) method. The PSFB-CT converter is widely used for low-voltage dc–dc converters in electric vehicles. In general, its output voltage is a control object which is usually controlled using a proportional–integral control-based output voltage controller and current controller. However, it has a disadvantage such as undesirable dynamic characteristic of the PSFB-CT converter and the necessity of gain tuning. Especially, if the gain of the PI control is increased to improve the dynamic characteristic of the PSFB-CT converter, an overshoot of the output voltage can occur. In this article, the advanced voltage control using the MPC method is proposed to improve the dynamic characteristic of the PSFB-CT converter without overshoot of the output voltage. As a result, the proposed method has advantages with not only fast dynamic characteristic but also robustness from a sudden change of load impedance. The effectiveness of the proposed MPC method was proved by the simulation and experimental results.

Estimation of the capacitor voltages in flying capacitor multi‐level converters

Flying capacitor multi-level converters use charged capacitors as a critical element. For proper operation, the capacitor voltages must be known and regulated. Direct measurement is straightforward, but when the number of required measurements is high, this is a complicated approach. This paper introduces an estimation method for n capacitor voltages. The scheme is based on a system of ( n + 1 ) equations, which is defined in a way that it incorporates information of the actual capacitor voltages and open-loop estimates of the capacitor voltages. The solution of the system gives the best estimates of the capacitor voltages in the sense of least square errors. The method requires only output voltage and output current sensors and its computational burden is low, saving cost and design efforts, and simplifying the hardware system. The performance of the proposed scheme is evaluated experimentally in a 9-level flying capacitor chopper, where the estimates are used by the voltage balancing strategy and by the output current controller.

A Double-Integral Sliding Mode-Based Hybrid Control for a Single-Input-Multiple-Output Buck Converter

A hybrid single-input-multiple-output (SIMO) buck converter is recently proposed for high-voltage-step-down and transformerless dc-dc applications. By far, no closed-loop control scheme has been designed for the SIMO buck converter in achieving output current and output voltage control. This article bridges the research gap by proposing a double-integral sliding mode-based hybrid control (DISMHC) to accurately regulate the output current and output voltage of the SIMO buck converter. The DISMHC comprises a double-integral sliding mode control for the first module of the converter and multiple linear control for the remaining modules. Both simulation and experimental results validate that the DISMHC can be implemented in inexpensive digital controllers to regulate the SIMO buck converter with negligible steady-state errors and superior dynamic performance than a proportional-integral-based hybrid control. This, thereby, protects the loads and constituting components of the SIMO buck converter from undesirable overshoots/undershoots and settling time.

A Novel Sliding-Discrete-Control-Set Modulated Model Predictive Control for Modular Multilevel Converter

Model predictive control (MPC) method has been recognized as one of the most promising technologies for the modular multilevel converter (MMC) due to the fast dynamic response and its simple realization. However, conventional finite control set (FCS) MPC methods for MMC are facing some challenges, such as high computation burden, poor steady-state performance, dependence on weighting factors, and variable switching frequency. In order to solve these problems, a novel sliding-discrete-control-set (SDCS) modulated MPC (MMPC) is proposed for MMC in this paper. Based on the adaptive search step in the output current control, only three control sets are evaluated in each period. In addition, the independent circulating current controller is applied in the proposed MMPC method. With the circulating current controller, the circulating currents are well regulated, and the arm capacitor voltage balancing is realized by circulating current injection. As a result, there is no weighting factor involved in the proposed MMPC method. Compared with the conventional MPC methods, the proposed method obtains a fixed switching frequency in each submodule (SM) and a low comparable computation burden. Simulation and experimental results verify the effectiveness of the proposed method.

Improving Inverter Output Current Controller Under Unbalanced Conditions by Using Virtual Impedance

Improving Inverter Output Current Controller Under Unbalanced Conditions by Using Virtual Impedance