Model based predictive control with a fixed switching frequency applied to a single-phase cascade H-bridge multilevel STATCOM

The research object of this paper is single-phase PWM rectifier, the purpose is to reduce the total harmonic distortion (THD) of the grid-side current. A model predictive current control (MPCC) with fixed switching frequency and dead-time compensation is proposed. First, a combination of an effective vector and two zero vectors is used to fix the switching frequency, and a current prediction equation based on the effective vector’s optimal action time is derived. The optimal action time is resolved from the cost function. Furthermore, in order to perfect the established prediction model and suppress the current waveform distortion as a consequence of the dead-time effect, the dead-time’s influence on the switching vector’s action time is analyzed, and the current prediction equation is revised. According to the experimental results, the conclusion is that, firstly, compared with finite-control-set model predictive control, proportional-integral-based instantaneous current control (PI-ICC) scheme and model predictive direct power control (MP-DPC), the proposed MPCC has the lowest current THD. In addition, the proposed MPCC has a shorter execution time than MP-DPC and has fewer adjusted parameters than PI-ICC. In addition, the dead-time compensation scheme successfully suppresses the zero-current clamping effects, and reduce the current THD.

Classic finite-set model predictive control techniques are distinguished by a variable switching frequency which causes noise, large voltage and current ripple. This paper presents an enhanced predictive current control technique with fixed switching frequency applied to the six-phase drives and a Kalman Filter estimator. Simulation results are provided to show the efficiency of the current control algorithm using the mean square error and total harmonic distortion as a figures of merit, thus concluding that the system can work properly with this enhanced technique.

Despite the intensive research work on the application of model predictive control (MPC) for multi-phase machines, there are many challenges still to be handled such as high circulating currents, variable switching frequency, and high computation burden. This paper proposes a simple, yet efficient predictive current control (PCC) for six-phase induction motor (IM) that reduces considerably circulating current, computation cost, and switching frequency. In the proposed method, a group of four candidate voltage vectors (VVs) is formed in each control sample. Unlike similar methods reported in literature, these candidate vectors are generated based on a simple lookup table and the previous optimal VV. The lookup table is designed such that it allows only one commutation in each control sample. The performance of the proposed method is assessed experimentally using a one kW asymmetrical six-phase induction motor (A6PIM). Different performance indices are investigated to compare the proposed method against two different PCC methods in literature at different operating conditions. The experimental results confirm that about 50% reduction in average switching frequency and 15% in current total harmonic distortion at different speed ranges are observed with the proposed method compared to the conventional one.

Variable switching frequency hybrid PWM technique for switching loss reduction in a three-phase two-level voltage source inverter

Harmonic analysis currently plays an important role for the power quality analysis because the non-linear loads, as source of the harmonic distortion, have significantly increased. The harmonic distortion influences power quality in power systems such as overheating of electrical equipment and aging of electrical equipment. Therefore, non-linear loads should be monitored in real time. This research proposes the design and implementation of the prototype current harmonic analysis that can be applied in real time based on S-transform Method. The equipment of this prototype can be explained as follows: CT-235, TZ2L9 and CT for KWH meters as current sensor, microcontroller AT mega 8535 as data acquisition, and Visual Basic software as displaying current waveform, current spectrum, rms current value, and total harmonic distortion (THD) for current. S-transform method is used to obtain the THD for current. The experimental result is validated by FLUKE 43B and the THD for current is accurately measured.

The single-stage electrolytic capacitor-less on-board charger (OBC) is attracting attention with the possibility of achieving high efficiency, high power density, and low component count. However, under universal input and wide battery voltage, the single-stage OBC has a difficulty in achieving ZVS turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> while maintaining unity power factor. In order to achieve ZVS under wide voltage range, the conventional single-stage OBC uses multiple control variables including switching frequency where the switching frequency usually varies widely, which complicates the converter design and optimization. In this regard, a totem-pole based single-stage electrolytic capacitor-less OBC was introduced in [36]. It uses one control variable and fixed switching frequency. However, this topology is not able to achieve full ZVS under wide voltage range and has high grid current total harmonic distortion (THD). This article proposes a simple modulation strategy that uses an adaptive duty-cycle and phase-shift modulation to achieve full ZVS under universal input and wide battery voltage. In addition, the fourth-harmonic injection method greatly reduces the grid current THD. The effectiveness of the proposed modulation was validated on a 3.84-kW prototype with 100–240 V ac input and 460–800 V battery voltage. The efficiency is also increased up to 2.3%p under low-voltage grid compared to the previous work.

Conventional finite-set model-based predictive control (FS-MBPC) methods inherently present a variable switching frequency which causes harmonic distortion as well as excessive voltage and current ripple. An indirect power control strategy with fixed frequency capability is presented in this paper for a DFIG driven by an indirect matrix converter. The system initial conditions are maintained for the proposed method, showing improvement in terms of power quality when compared to the conventional FS-MBPC even when a lower sampling frequency is imposed. This strategy is verified to be feasible by successful simulation results, furtherly proving the predictive control capabilities of fast dynamic response and intuitive inclusion of nonlinear constraints into the control algorithm.

This paper presents a decoupled power control method for a single-phase grid-tied inverter that uses model predictive control (MPC) to minimize the number of switch state changes required to control the output bridge while simultaneously constraining the output current harmonics. On one hand, minimizing the number of switch state changes in the output bridge of the inverter results in minimizing switching losses. On the other hand, lower switching frequencies typically result in larger harmonic currents. The proposed controller evaluates a cost function with an adjustable weight factor. Total harmonic distortion (THD) of grid side current is the constraint of the controller which seeks to minimize switch state changes to lower switching losses while meeting the THD constraint. Thus the MPC performs constrained multi-objective optimization. Because the controller is harmonic-constrained, the single-phase inverter has robust operation under pulsating dc-link voltage, which allows a smaller dc-link capacitor and higher bus ripple voltage. The weight factor can be chosen from an engineering tradeoff between the output current THD and the switching frequency. The simulation results are verified experimentally by implementing the controller using DS1007 platform by dSPACE.

Direct torque control (DTC) is known for its fast control in AC motor drives due to its simple control structure that directly controls the torque without the need for modulation blocks or frame transformations. However, when used in induction motor (IM) drives it has three main drawbacks: large torque ripples, variable switching frequency, and sector flux-droop at the low-speed region due to the employment of the torque hysteresis controller (THC). Torque ripple minimization can be achieved in DTC drives by replacing the originally proposed two-level inverter with a three-level neutral-point clamped (3L-NPC) inverter. Nevertheless, the switching frequency remains variable and low, which produces an elevated torque ripple and asymmetrical switching signals for the inverter. In addition, sector flux-droop resulting from driving the IM at the low-speed region produces a high current distortion that consequently eliminates the robustness of DTC. To alleviate these problems, an interleaving constant switching frequency torque controller-based DTC (CSFTC-DTC) was implemented. It improves the operation of the IM at the low-speed region by increasing the duty-cycle of the applied active voltage vector and reducing the duration of the applied zero vectors. Although the conventional CSFTC-DTC regulates the stator flux of the IM at the low-speed region and minimizes the total harmonic distortion (THD) of the stator current, it produces a high torque ripple-one of the main disadvantages of classical DTC. In this paper, an interleaving CSFTC-DTC is proposed to subdivide the duty cycle of the applied vectors of the 3L-NPC inverter to limit the influence of the large duty-cycle of the applied vectors on flux-regulation and torque ripples. The simulation and experimental results presented validate the effectiveness of the proposed method over the conventional method.

To reduce the conducted common-mode (CM) electromagnetic interference (EMI) and current total harmonic distortion (THD) in permanent magnet synchronous motor drive systems, this article proposes a finite control set–model predictive control (FCS–MPC) method for an H8 inverter considering the dead-time (DT) effect. In a real system, the DT causes unexpected peak common-mode voltages (CMVs) and distortion of the inverter output voltage, which deteriorates both the CM EMI and current THD. The conventional double active voltage vector (VV) based MPC methods with an H6 inverter may not be a good solution because of the numerous CMV variations and the limit of the VV transitions. In contrast, the proposed FCS–MPC method allows all VV transitions possible without the peak CMVs by instantly operating the series-connected switch of the H8 inverter based on the previous VV, predicted current sector, and next optimal VV. Furthermore, the nonlinearity of the inverter output voltage due to the DT is compensated in a discrete-time model used for the current prediction, considering the calculation delay of the digital controller. Consequently, the current THD as well as the CM EMI can be improved. The simulation and experimental results are presented to verify the effectiveness of the proposed method.

The focus of this paper is a theoretical calculation of current Total Harmonic Distortion (THD) for a current source single-phase multilevel PWM inverter with CL-filter. Analytical approach to current ripple mean square / current THD calculation was introduced in the 1980s for a 2-level voltage source inverter with inductance dominated RL-load. This paper presents a generalization of this approach for a single-phase multilevel current source PWM inverter with an arbitrary number of current levels accounting for the CL-filter effect. The output of this research is a closed-form analytical current THD solution. Though one of the assumptions is large switching-to-fundamental frequencies ratio, the formulas are practically accurate for the said ratio larger than 20-25. The formulas become quite compact and simple without a loss of accuracy when using a Bessel function approximation. They demonstrate a single-phase PWM current source inverter current THD dependence on CL-filter parameters and current modulation index.

Offline pulse width modulation (PWM) techniques are employed to reduce the line current distortion in induction motor (IM) drives where the switching frequency is highly constrained. An optimal PWM technique is proposed here for a neutral point clamped (NPC) inverter fed IM drive to minimize the motor current distortion, subject to constraints on number of switching instants per quarter cycle. Two types of pole voltage waveforms of the NPC inverter are considered, namely type-I and type-II. This paper reports optimal switching angles for both type-I and type-II waveforms to minimize the resulting total harmonic distortion (THD) in motor current. In general optimal type-II is found to result in lower THD than optimal type-I PWM. The optimal type-II PWM offers superior performance in terms of motor current distortion than synchronized sine-triangle PWM and selective harmonic elimination PWM, as shown by simulation and experimental results on an NPC inverter fed 3.7 kW induction motor drive.

For a single-phase Shunt Active Power Filter (SAPF) with a two-step prediction, this research presents a modified current control based on a Model Predictive Current Control (MPCC) technique. An H-bridge inverter, a DC link capacitor, and a filter inductor comprise the single-phase SAPF topology. The SAPF reference current is computed using the DC-link capacitor voltage regulation-based PI control technique. The weighting factor-based model predictive current controller is used to track the current commands. The essential dynamic index for evaluating waveform quality is the Total Harmonic Distortion (THD) of a source current and switching frequency of power switches. The conventional methods the THD and switching frequency are not considered as an objective function, so that a weighting factor-based MPCC technique is used to obtain a good compromise between the THD of the source current and switching frequency of power switches. Through MATLAB simulation and experimentation with the Cyclone-IV EP4CE30F484 FPGA board, the usefulness of the proposed control technique is proven. As compared with hysteresis, predictive PWM, and conventional MPCC control methods, the cost function-based MPCC algorithm provides a lower switching frequency (13.4 kHz) with an optimal source current THD value.

Electric propulsion ships have garnered significant attention for addressing the environmental impact associated with conventional shipping vessels. Their performance critically depends on the inverters that control propulsion motors. This study aims to enhance inverter control by addressing the limitations of conventional model predictive control (MPC), particularly its high current errors and total harmonic distortion (THD) owing to the limited switching frequency. Herein, a discontinuous MPC is proposed that is capable of reducing the switching losses by implementing discontinuous switching during high current periods. This approach employs zero-voltage vectors that are selected based on the polarity of the offset voltage to prevent unnecessary switching losses. Experimental results indicate that the proposed approach reduces the current error by up to 45%, THD by up to 30%, and switching losses by 15–25%. Therefore, this study demonstrates the potential of the proposed control strategy to improve the efficiency and reliability of electric propulsion systems, thereby contributing to the advancement of inverter control technology and development of eco-friendly shipping vessels.

Inverters have many application areas including the variable frequency drives applications of the motor industry. Three-phase inverters based on the three-phase system that we are using are becoming more common. The implementation of the space vector PWM (SVPWM) modulation technique in three-phase inverters is more advantageous than other modulation techniques due to the lower harmonic content and higher DC bus utilization it provides. A delay time, also called the dead-time, is added to the rising edge of the PWM signals for triggering the gates of the switches to avoid shoot-through faults in the inverters. Although it has a protection advantage, it has some disadvantages such as output voltage drop, phase shift, zero current clamping and increase in total harmonic distortion (THD) of the output current. In this study, these effects of dead-time are compensated by employing the simple yet effective feedforward method using the SVPWM technique. Moreover, the relationship between the effects of the dead-time and switching frequency is investigated. The results exhibit that the THD of the current is optimized when the switching frequency is controlled rather than kept constant.