Good Steady-state Performance Research Articles

Advanced model predictive current control for induction motor drive system fed by indirect matrix converter

To decrease both the number and tuning difficulty of weighting factors, an advanced model predictive current control is proposed for an induction motor drive system fed by an indirect matrix converter, where the input and output currents of the indirect matrix converter are designated as control objectives. The reference input currents are established on the basis of the instantaneous power theory and optimized using a low-pass filter. In addition, the reference output currents are determined using a reference flux vector based on the deadbeat theory. As a result, there is only one weighting factor for parameter tuning, and the predictive models are significantly simplified. In addition, both the phase and the quality of the input currents are considered and controlled, which can improve the grid power quality. Simulation and experimental results show that the sinusoidal grid/output currents, a unity power factor, and good steady-state and dynamic performances of the induction motor have been achieved. In addition, the execution time of the entire algorithm was noticeably shortened.

A New Step-Up Switched-Capacitor Voltage Balancing Converter for NPC Multilevel Inverter-Based Solar PV System

This paper proposed a grid connected solar Photovoltaic (PV) Systems with a new voltage balancing converter suitable for Neutral-Point-Clamped (NPC) Multilevel Inverter (MLI). The switched-capacitors used in the proposed converter is able to balance the DC link capacitor voltage effectively by using proper switching states. The proposed balancing converter can be extended to any higher levels and it can boost the DC input voltage to a higher voltage levels without using any magnetic components. This feature allows the converter to operate with the boosting capability of the input voltage to the desired output voltage while ensuring the self-balancing. In this paper the proposed converter is used for a grid connected solar PV system with NPC multilevel inverter, which is controlled using vector control scheme. The proposed grid connected solar PV system with associated controllers and maximum power point tracking (MPPT) is implemented in Matlab/SimPowerSystem and experimentally validated using dSPACE system and designed converters. The simulation and experimental results show that the proposed topology can effectively balance the DC link voltage, extract maximum power from PV module and inject power to the grid under varying solar irradiances with very good steady state and dynamic performances.

Wind-Speed Estimation and Sensorless Control for SPMSG-Based WECS Using LMI-Based SMC

To enhance system reliability and to reduce the cost and complexity, this paper presents an efficient wind-speed estimation method and a sensorless rotor-position/speed control method for a surface-mounted permanent-magnet synchronous generator (SPMSG)-based variable-speed direct-drive wind-energy conversion system (WECS). In this regard, sliding mode control (SMC) based on a linear matrix inequality (LMI) is proposed to estimate the rotor position of an SPMSG. This method depends on measured electrical quantities, such as stator voltages and estimated stator current error, to evaluate the back electromotive force components, which are used to estimate the rotor position. The rotor speed is assessed according to the rate of change of the estimated rotor position. The wind speed is estimated by estimating the backpropagation power flow according to the nonlinear dynamical power wind-speed characteristics of the wind turbine. In estimating the rotor position, the proposed LMI-based SMC design provides good steady-state and dynamic performances under all operating modes of the WECS. The proposed control schemes are validated by simulating a test system, i.e., a 250-kW SPMSG-based WECS, in MATLAB/Simulink. The results confirm the effectiveness and correctness of the designed control schemes in estimating and tracking the actual rotor position/speed and wind speed with trivial errors.

A Frequency-Adaptive Improved Moving-Average-Filter-Based Quasi-Type-1 PLL for Adverse Grid Conditions

The moving-average-filter-based quasi-type-1 phase-locked loop (MAF-QT1 PLL) can provide zero steady-state phase error in the presence of frequency drifts, achieving a high filtering capability. However, in the presence of an MAF and frequency drift, MAF-QT1 PLL cannot achieve a fast transient response and frequency-dependent characteristic under adverse grid conditions. To overcome this drawback of the MAF-QT1 PLL, this paper proposes a frequency-adaptive improved moving-average-filter-based quasi-type-1 PLL (FAIMAF-QT1 PLL). Aiming at the shortcoming of the slow dynamic response of the MAF-QT-1 PLL, a correction link is introduced, and an improved moving-average-filter-based quasi-type-1 PLL (IMAF-QT1 PLL) is obtained. To improve the anti-interference ability of the IMAF-QT1 PLL in response to grid frequency changes, a FAIMAF-QT1 PLL and a corresponding digital implementation scheme are proposed. The regulator parameter setting method is proposed based on the small-signal model of the FAIMAF-QT1 PLL. Simulation and experimental results show that the FAIMAF-QT1 PLL can accurately track the grid voltage phase in the presence of power grid frequency fluctuations, phase angle jumps, distorted harmonic injections and unbalanced voltage drops and has good steady-state and dynamic performance.

Controlling of an Under-Actuated Quadrotor UAV Equipped With a Manipulator

Unmanned aerial vehicles (UAV) equipped with a manipulator offer an additional flexibility and smart way to grasp the desired objects from inaccessible locations where the access of ground vehicles (GV) are not possible. In this research, we design an adaptive control based regulation, pole-placement and tracking (RST) control scheme for controlling the nonlinear behavior of an under-actuated quad rotor aerial vehicle. The overall performance of the system dealt by MIT rules. The aerial vehicle is equipped with a camera and a gripper that helps us to locate the wanted object from inaccessible location. The model of quad rotor UAV has six degrees of freedom (6-DOF) and the equipped gripper is about (2-DOF). For a successful flight operation UAV requires a reliable controller to stabilize the aerodynamic effects, disturbances that produced by the gripper. Due to aforementioned issue, design an adaptive RST controller, to control the dynamic behavior of the highly nonlinear complex system. Moreover, the effectiveness of the designed controller proven by applying computer-based simulation and it will verify experimentally. Lastly, it observes that the designed controller shows better robustness and good steady state performance to accomplish the given task.

A Hybrid Dual-Mode Control for Permanent-Magnet Synchronous Motor Drives

In order to obtain satisfactory transient and steady-state performances, a hybrid dual-mode control (HDMC) is proposed for surface-mounted permanent-magnet synchronous motor drives (PMSMs), which contains two control modes. The first one is the deadbeat predictive control (DBPC) mode, which is only implemented in the transient procedure. The second one is the field-oriented control (FOC) mode, which is mainly implemented in the steady-state operation. Besides, the FOC mode is also implemented in the transient procedure to eliminate the static current error. In the transient procedure, the FOC mode is activated after one-sampling-period implementation of the DBPC mode in the unsaturation state, and the desired voltage vector calculated in this sampling period is assigned as the initialized values of the proportional-integral current controllers in the FOC mode to avoid the switching chattering. When the voltage-source-inverter comes into the saturation state, the DBPC mode will be reactivated immediately. The proposed HDMC inherits the quick response ability of DBPC and the good steady-state performances of FOC. The effectiveness of the proposed HDMC is verified by the experimental results.

Research on Model Predictive Control of IPMSM Based on Adaline Neural Network Parameter Identification

This paper reports the optimal control problem on the interior permanent magnet synchronous motor (IPMSM) systems. The control performance of the traditional model predictive control (MPC) controller is ruined due to the parameter uncertainty and mismatching. In order to solve the problem that the MPC algorithm has a large dependence on system parameters, a method which integrates MPC control method and parameter identification for IPMSM is proposed. In this method, the d-q axis inductances and rotor permanent magnet flux of IPMSM motor are identified by the Adaline neural network algorithm, and then, the identification results are applied to the predictive controller and maximum torque per ampere (MTPA) module. The experimental results show that the optimized MPC control proposed in this paper has a good steady state and robust performance.

High Frequency Square-Wave Voltage Injection Scheme-Based Position Sensorless Control of IPMSM in the Low- and Zero- Speed Range

In this paper, a new sensorless control scheme with the injection of a high-frequency square-wave voltage of an interior permanent-magnet synchronous motor (IPMSM) at low- and zero-speed operation is proposed. Conventional schemes may face the problems of obvious current sampling noise and slow identification in the process of magnetic polarity detection at zero speed operation, and the effects of inverter voltage error on the rotor position estimation accuracy at low speed operation. Based on the principle analysis of d-axis magnetic circuit characteristics, a method for determining the direction of magnetic polarity of d-axis two-opposite DC voltage offset by uninterruptible square-wave injection is proposed, which is fast in convergence rate of magnetic polarity detection and more distinct. In addition, the strategy injects a two-opposite high-frequency square-wave voltage vectors other than the one voltage vector into the estimated synchronous reference frame (SRF), which can reduce the effects of inverter voltage error on the rotor position estimation accuracy. With this approach, low-pass filter (LPF) and band-pass filter (BPF), which are used to obtain the fundamental current component and high-frequency current response with rotor position information respectively in the conventional sensorless control, are removed to simplify the signal process for estimating the rotor position and further improve control bandwidth. Finally, the experimental results on an IPMSM drive platform indicate that the rotor position with good steady state and dynamic performance can be obtained accurately at low-and zero-speed operation with the sensorless control strategy.

Control Design of LCL Type Grid-Connected Inverter Based on State Feedback Linearization

Control strategy is the key technology of power electronic converter equipment. In order to solve the problem of controller design, a general design method is presented in this paper, which is more convenient to use computer machine learning and provides design rules for high-order power electronic system. With the higher order system Lie derivative, the nonlinear system is mapped to a controllable standard type, and then classical linear system control method is adopted to design the controller. The simulation and experimental results show that the two controllers have good steady-state control performance and dynamic response performance.

An Improved Model Predictive Direct Torque Control Strategy for Reducing Harmonic Currents and Torque Ripples of Five-Phase Permanent Magnet Synchronous Motors

Five-phase permanent magnet synchronous motors offer merits of high fault tolerant capability and high torque per rms ampere and, thus, are suitable for applications, such as aerospace and electric vehicles. However, the complex machine model causes difficulties in controller design. Besides, having 32 voltage vectors with various effects on currents and torque, the selection of the optimal switching state becomes a challenge to achieve a performance tradeoff. This paper proposes an improved model predictive direct torque control (MPDTC) strategy consisting of a quadratic evaluation method (QEM) and a harmonic voltage elimination method (HVEM). In QEM, the preliminary vector is first chosen from the vectors of the outer decagon according to a cost function for torque and flux regulation. This preliminary vector, composed of three sets of different amplitudes, is further synthesized according to the error between the actual torque/flux and the references. In this way, the optimal voltage vector can be obtained without significantly increasing the computational burden. In HVEM, by subtracting the harmonics voltage component from the vector determined previously in QEM, the final voltage vector is obtained for mitigating stator harmonic currents. The proposed control strategy is compared with the conventional MPDTC approach. The results confirm the effectiveness of the proposed methods with good steady-state performance while maintaining quick dynamic responses.

Grid current low‐order harmonics suppression of the three‐phase grid converter with an LCL filter under the distorted grid voltage

This article presents an extended backstepping control method to reduce the grid-side current harmonics caused by grid voltage distortion. A dynamic model considering the grid voltage as an external disturbance is derived in the stationary reference frame. The extended back-stepping design procedure based on pole displacement guarantees that the system is stable without damping. The proposed method has a general low-order harmonics suppression instead of selective harmonics elimination. Zero steady-state error can be obtained tracking the grid currents. Stability, as well as good transient and steady-state performance are verified through numerical simulation. A comparison with the state-of-the-art proportional resonant control with active damping is also conducted. The results show that a good low-order harmonics reduction in the grid current is achieved by the proposed control method.

An Alterable Structure Power Router with General AC and DC Port for Microgrid Applications

This paper proposes an alterable structure power router (PR) topology which shares the ability of general Alternating Current (AC) and Direct Current (DC) port. This alterable structure PR aims to better implement the interconnections among micro-grids, renewable energy, and traditional grids. The PR’s converter structure is alterable according to the system power. Based on the operation analysis of the PR, the mathematic model of the power router is established and the relationship between switch states and port voltage is analyzed. According to the PR mathematical model, the control method is designed to realize current control in both AC and DC mode. With the proposed power router topology, the PR’s port can be used in both AC and DC situations, which saves the cost of traditional PRs and increases economic efficiency. The simulation and experimental results prove the good steady-state and dynamic performance of the proposed power router topology.

Low-Power Hardware Implementation of Least-Mean-Square Adaptive Filters Using Approximate Arithmetic

Adaptive filters based on least-mean-square (LMS) algorithm are used in several applications in virtue of their good steady-state performance, numerical stability, and acceptable computational complexity. The hardware implementation of LMS filters requires a massive number of multipliers that significantly impact on the power consumption. Approximate computing, a design technique that trades off computation accuracy for better electrical performance, is a way to improve the energy efficiency of LMS filters. In this paper, we implement state-of-the-art approximate multipliers and evaluate their impact on the performance of the LMS algorithm. Moreover, a novel approximate multiplier, whose accuracy can be tuned at design time to better adapt to the application scenario, is proposed. Implementation results in 28-nm CMOS technology allow us to investigate the power versus quality trade-off of the considered LMS approximate filters in two different applications.

Robust Control for the IPT System With Parametric Uncertainty Using LMI Pole Constraints

In the inductive power transfer (IPT) system, coil misalignment, load variation, and external disturbance will unavoidably cause power fluctuation and worsen system performances. Currently, robust control has been successfully introduced in the IPT system for promoting its stability and performances. However, due to the diversity of poles distribution, all possible IPT subsystems always show different overshoot, settling time, and resistance capacity to uncertainty factors. So, robust control design for the IPT system via pole placement constraints in linear matrix inequality (LMI) region is studied in this paper. An IPT system model with structured parametric uncertainty relevant to mutual inductance and load is first established. Based on the derived closed-loop system with a two-degrees-of-freedom control structure, a method of variable replacement is then proposed to transform the robust D-stability problem with pole region constraints into the LMI form, which can be solved to obtain a robust controller. After analyzing the influence of the LMI region change on poles distribution and system performances, an optimized robust controller is finally chosen. Experimental results show that a robust controller can reach the prescribed dynamic performances even if mutual inductance or load may change into another value, and also a good steady-state performance by resisting parametric uncertainty and external disturbance.

Control strategy for inverters in microgrid based on repetitive and state feedback control

As for an ac microgrid, it’s important to supply the loads with a sinusoidal voltage. However, due to the majority of the loads being naturally nonlinear, when the microgrid is operating in the island mode, the output voltage of the inverters is always deformed. To improve the total harmonic distortion (THD) of the output voltage, a control strategy based on repetitive and state feedback control is proposed in this paper. Firstly, the state feedback control is used to implement the pole assignment of the controlled object, i.e., the LC filter. By this way, the resonance of the filter can be well suppressed. And the open-loop gain of the system is also increased in the low frequency band, which can improve the system dynamics. Combined with this, the repetitive control is adopted to ensure good steady-state control performance. Based on the sensitivity function and the regeneration spectrum theory, a parameter design method is proposed to simplify the design of a repetitive controller. Both simulations and experiments are provided to demonstrate the good control performance of the proposed strategy when supplying nonlinear loads in comparison to the PI controller. Moreover, the microgrid simulation results of two inverters have been presented to validate the effectiveness of the designed control strategy.

Modulated Model-Predictive Control With Optimized Overmodulation

Finite-set model-predictive control (FS-MPC) has many advantages, such as a fast dynamic response and an intuitive implementation. For these reasons, it has been thoroughly researched during the last decade. However, the waveform produced by FS-MPC has a switching component whose spread spectrum remains a major disadvantage of the strategy. This paper discusses a modulated model-predictive control that guarantees a spectrum switching frequency in the linear modulation range and extends its optimized response to the overmodulation region. Due to the equivalent high gain of the predictive control and to the limit on the voltage actuation of the power converter, it is expected that the actuation voltage will enter the overmodulation region during the large reference changes or in response to load impacts. An optimized overmodulation strategy that converges toward the FS-MPC ’s response for large tracking errors is proposed for this situation. This technique seamlessly combines PWM’s good steady-state switching performance with FS-MPC ’s high dynamic response during large transients. The constant switching frequency is achieved by incorporating modulation of the predicted current vectors in the model-predictive control of the currents in a similar fashion as the conventional space-vector pulsewidth modulation is used to synthesize an arbitrary voltage reference. Experimental results showing the proposed strategy’s good steady-state switching performance, its FS-MPC -like transient response, and the seamless transition between modes of operation are presented for a permanent magnet synchronous machine drive.

Three-Vector-Based Low-Complexity Model Predictive Direct Power Control Strategy for PWM Rectifier Without Voltage Sensors

A voltage sensorless control of low-complexity model predictive direct power control (LC-MPDPC) for pulsewidth modulation (PWM) rectifier is proposed. The conventional LC-MPDPC adopts one or two voltage vectors during one control period, which achieve good steady-state performance and quick dynamic response. In addition, based on the mathematical model of the real system, the conventional method only requires one prediction to find the optimal voltage vector, which reduces the control complexity and computational burden. However, the use of one or two vectors during one sampling interval presents abundant current harmonics and high power ripples, and the switching frequency is variable. In order to solve these problems while preserving all the advantages of the conventional LC-MPDPC, this paper presents a novel control scheme, with the aim of operating at a constant switching frequency and obtaining an excellent steady-state performance at a low switching frequency. The proposed method is based on an optimal application of three voltage vectors in a symmetrical way, which takes advantage of advanced PWM techniques. Furthermore, the virtual flux-based control scheme is introduced to achieve voltage sensorless control. The proposed strategy is compared with the conventional MPDPC methods and its effectiveness is confirmed by both simulation and experimental results from a three-phase PWM rectifier under 1000-W operation condition.

Finite Control Set Model Predictive Control for Parallel Connected Online UPS System under Unbalanced and Nonlinear Loads

In this paper, the finite control set model predictive control (FCS–MPC) technique-based controller is proposed for the inverter of the uninterrupted power supply (UPS) system. The proposed controller uses the mathematical model of the system to forecast the response of voltage for each possible switching state for every sampling instant. Following this, the cost function was used to determine the switching state, applied to the next sampling instant. First, the proposed control strategy was implemented for the single inverter of the UPS system. Finally, the droop control strategy was implemented for parallel inverters to guarantee actual power sharing among a multiple-parallel UPS system. To validate the performance of the proposed controller under steady-state conditions and dynamic-transient conditions, extensive simulations were conducted using MATLAB/Simulink. The proposed work shows a low computational burden, good steady state performance, fast transient response, and robust results against parameter disturbances as compared to linear control. The simulation results showed that total harmonic distortion (THD) for the linear load was 0.9% and THD for the nonlinear load was 1.42%.

A Hybrid Direct Torque Control Scheme for Dual Three-Phase PMSM Drives With Improved Operation Performance

The direct torque control (DTC) is widely used in motion control of electric drives, especially for the switching table based direct torque control (ST-DTC) and the space vector modulation (SVM) based DTC (SVM-DTC). The classical ST-DTC schemes can achieve fast dynamic response but may suffer from distinct torque and flux ripples in steady-state operation. On the other hand, the classical SVM-DTC schemes have lower ripples in torque and flux, but the methods slow down dynamic response of DTC. Different from them, a novel hybrid DTC scheme is proposed for dual three-phase permanent-magnet synchronous motor (PMSM) drives in this paper, which can achieve fast dynamic response of classical ST-DTC scheme and good steady-state performance of classical SVM-DTC scheme simultaneously. The key of the proposed scheme is to implement different torque control methods under dynamic operation mode and steady-state operation mode, respectively. A switching method has been designed to guarantee smooth transition between the two operation modes. Besides, the decoupling control of torque and stator flux is maintained with the proposed control scheme, and the stator flux is controlled stably all along. By experiments on a laboratory prototype, it has been verified that the proposed scheme can achieve both good steady-state and transient performance compared to other control methods for dual three-phase PMSM drives.

Extremum seeking control for efficient operation of an air-source heat pump water heater with internal heat exchanger cycle vapor injection

The vapor-injection (VI) technique is known effective for improving the performance of air-source heat pump (ASHP) in cold climates. Optimizing the intermediate pressure is critical for the efficiency of VI-ASHP under varying operating conditions, while model based control is cost prohibitive in practice. We propose an extremum seeking control (ESC) framework as a model-free optimal control strategy for internal heat exchanger (IHXC) based VI-ASHP, minimizing the total power consumption in real time. The ESC takes the total power as the only feedback, and the intermediate pressure setpoint as the manipulated input. A Modelica-based dynamic simulation model of an IHXC-VI ASHP water heater is developed. The water outlet temperature is regulated by the compressor capacity, while the injection-loop expansion valve regulates the intermediate pressure. Under fixed, staircase and realistic ambient temperature profiles, simulation results show that ESC can optimize the intermediate pressure for system efficiency with good steady-state and transient performance.