Three-level Active Power Filter Research Articles

Three-Level Active Power Filter Based on Model Predictive Control

The model predictive control (MPC) algorithm is used in the harmonic compensation of active power filter (APF), which has a fast dynamic response and does not require a PWM modulation model. However, this method has some shortcomings, such as the mass computing and difficult selections of weight factors. To solve these problems, this paper proposes a single objective function improved MPC algorithm based on sector judgment, which only takes the reference current and feedback current as the objective function, omits the weight coefficient setting process, and reduces the number of rolling optimization from 27 to 7, thus reducing the computing time and control complexity. The improved model predictive control is applied to APF. Finally, the simulations and experiments show that the improved MPC algorithm is accurate and efficient.

Power Quality Enhancement in Four-Wire Systems under different distributed Energy Resource Penetrations

Reactive and harmonic currents that are being injected into the power supply by nonlinear loads, cause an increasing deterioration of the power system voltages and currents, whereas active power filter (APF) has been widely used to overcome this problem and to improve the power quality delivered by the power supply. In this paper, a three-level four-legged active power filter based on a neutral-point-clamped (NPC) inverter is presented. To fulfil the requirement of the active power filtering function under balanced, unbalanced, and distorted (including 3rd and 5th harmonics) power supply voltages, a control method based on the instantaneous power theory has been used and discussed. On the other side, the inverter switching state control has been achieved based on PWM current controller. The performance of the proposed topology under the control approach has been finally discussed through the obtained simulation results.

A Novel FCS-MPC Method of Multi-Level APF Is Proposed to Improve the Power Quality in Renewable Energy Generation Connected to the Grid

When photovoltaic, wind, energy storage batteries, and other new forms of energy are connected to the grid, power electronic converters are needed, and there are a lot of nonlinear devices in the grid. The characteristics of sustainable energy generation determine the variability and intermittency, which will produce harmonic components. Active power filters (APF) are commonly used in industry for harmonic compensation, so it is of great significance to control APF quickly and effectively. The multi-objective, single-factor, multistep finite control set model predictive control (FCS-MPC) of an APF proposed in this paper is suitable for a multi-objective, multi-level converter control. This method is applied to the three-level APF structure, which changes the traditional three-level FCS-MPC control method. The traditional three-level FCS-MPC includes four control objectives, stable control of the DC-side voltage, power grid harmonic currents generated under non-linear loads, and balance of the capacitor voltage on the DC side when switching frequency. This method uses the redundant switching state of the three-level structure to achieve the voltage balance of the two capacitors on the DC side, which reduces the difficulty of target optimisation caused by the selection of weight factors. Based on the multi-step prediction, power feedback control is added on the DC side to increase the DC side’s reaction speed, eliminate the influence of uncertainty, and realise better dynamic performance. According to the simulation results, we can observe that the proposed method has good followability, can compensate for the harmonics of the power grid, reduces the harmonic content to less than 5%, and can balance the DC-side capacitor voltage.

Fixed frequency Finite Control Set Model Predictive Control For Three-level APF

Active power filter can compensate harmonic and reactive power, Three level neutral point clamp (ANPC) has the characteristics of low output harmonic and low device loss. The control of three-level active power filter needs to consider multiple objectives. Finite control set model predictive control (FCS-MPC) is a new method which can add constraints and multi-objective control. According to the limit of the switch state, it can track the reference current, which has the characteristics of fast dynamic response and good compensation effect. This method not only keeps the neutral point voltage balance, but also solves the problem of unstable switching frequency.

Research on Finite Control Set Model Predictive Control Strategy of Three-level APF

Active power filters (APF) can compensate for harmonics and reactive power. The traditional APF PI control has difficulty in parameter setting, and has the characteristics of control lag, and the control accuracy of current is low. The control of three-level APF needs to consider multiple objectives. Finite Control Set Model Predictive Control (FCS-MPC) is a newly proposed method that can increase constraints and multi-objective control. According to the limited switching state, it tracks the reference current and has dynamic Fast response and good compensation results. In this paper, the finite set model predictive control algorithm of three-level APF is studied, and the results show that the harmonic content of the power grid is low, which meets the relevant requirements.

Three-level Generalized Discontinuous Pulse-width Modulation Strategy Considering Neutral Point Potential Balance

Traditional discontinuous pulse width modulation (DPWM) cannot be efficiently used in some inverters like active power filters (APFs) whose currents are difficult to predict. Therefore, this paper proposes a new generalized discontinuous pulse width modulation (GDPWM) strategy considering neutral point potential balance for neutral-point clamped (NPC) three-level inverters. The core of the proposed strategy is the optimal efficiency modulation strategy. The optimal efficiency modulation strategy determines the clamp mode in real time based on the current flowing through the converter. This strategy minimizes switching losses by clamping the converter to the phase with the largest absolute value of current. At the same time, according to the neutral point potential shift, the neutral point balance strategy and the optimal efficiency modulation strategy are switched to achieve the balance between the switching loss and the neutral point potential. The proposed strategy can be efficiently applied in NPC three-level APFs to minimize the switching losses without the need of predicting the currents and to make neutral point potential balance. In this paper, the proposed modulation strategy is theoretically analyzed, and simulation and experimental verification are carried out.

Design and implementation of a three-level active power filter for harmonic and reactive power compensation

This paper presents a unified design and implementation of active power filters (APF) for medium-voltage high-power applications. A fast and accurate harmonic extraction technique based on the time transformation algorithm (TTA) is developed. A novel approach is used to derive the mathematical model describing the relation between the output current and the control signal of the NPC inverter for active power filter. Accordingly, the current controller and voltage controller are designed using the derived model. The neutral-point voltage is maintained near zero using a feed-forward controller. The designed three-level APF is feasible to implement, comparatively cheaper and reduces the filter size. From both the simulation and experimental results, it is found that the developed system provides excellent performance in regulating voltage and reducing harmonics significantly, from 26.3% to 4.0%.

Reducing neutral-point voltage fluctuation in NPC three-level active power filters

Shunt active power filters (SAPFs) have been widely used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads. This paper presents a new method for improving the performance of SAPFs using neutral-point-clamped (NPC) three-level inverters. NPC three-level inverters often suffer excessive voltage fluctuations at the neutral-point of DC-link capacitors, which may damage switching devices and cause additional high harmonic distortion of the output voltage. In order to solve the problem, two compensating schemes are proposed to restrict voltage fluctuation in the inverters. The first is voltage dependent, adopting a voltage compensation method, while the second is current dependent, using a current compensation method. The paper describes the respective circuit architectures and principles of operation. Corresponding models are mathematically formulated and evaluated under typical balanced and unbalanced working load conditions. The results show that both schemes are able to alleviate considerably voltage oscillations and hence harmonic distortions, and the current-compensated NPC inverter outperforms the voltage-compensated NPC inverter. Consequently, it is shown that the proposed approaches are effective and feasible for improving power quality of the grid when connected to nonlinear loads.

A simplified PWM strategy based on MPC for NPC three-level APF systems

As a control algorithm for high performance of active power filter (APF) systems, finite control set model predictive current control (FCS-MPC) has the disadvantages of unfixed switching frequency and large amount of calculations for three-level APF systems. Therefore, in order to overcome the drawback of FCS-MPC, a simplified Pulse Width Modulation (PWM) strategy based on MPC is proposed in this paper. First, the strategy, with no rolling of all the 27 vectors, adopts the idea of a cost function to obtain the optimal reference vector of each phase. Second, the duration time of each vector in this strategy can be directly calculated by judging the sector of the virtual reference vector. Third, the neutral-point balancing problem is solved by modifying the duration time. In the meantime, the strategy is studied in detail and verified experimentally in this paper. The experiment results indicate the validity and effectiveness of the proposed strategy.

Specific order harmonics compensation algorithm and digital implementation for multi‐level active power filter

A specific harmonic compensation control based on the nth specific order d–q transformation in the nth synchronous coordinates is proposed in this study. The distorted load currents are transformed into the nth– dq components in the separate nth harmonic frequency channels. These components corresponding to the specific nth harmonics are individually controlled in closed-loop by the decoupling regulators, which can track the amplitude and phase angle of the specific order harmonic with zero steady-state error. Meanwhile the current references would be transformed to voltage references. Therefore, the voltage references generated by these separate harmonic control channels could be accumulated together to form the final real-time modulation voltage references to drive the voltage-source inverter including two-level and multi-level structures. The control algorithm is analysed and its parameters are designed. The three-level active power filter simulation and a small-scale prototype are established. The simulation and experimental results indicate that the harmonics can be specific eliminated and controlled. The total harmonic distortion of source currents could be reduced from 20 to 0.5% with the specific filtering of 5th, 7th, …, 31st harmonics.

Improved Negative Sequence Current Detection and Control Strategy for H-Bridge Three-Level Active Power Filter

A three-phase three-wire shunt active power filter based on a H-bridge three-level converter as its main circuit is presented. The dc-link voltage stable conditions and the effects of the fundamental sequence components on the input active power of the inverter are described in details. Then a dc-link voltage control strategy based on the negative sequence current control method is proposed. The dc-link voltage controller is composed of two parts, the first one is to maintain the dc-link average voltage at its reference value, and the second is to achieve the balance of the dc-link voltage by controlling the output negative sequence current. To eliminate the ill effect of the negative sequence fundamental components in load current, a novel harmonic detection algorithm implemented in dual- dq axis is proposed. Finally, experiments are implemented to verify the proposed control strategy, which demonstrate the excellent performance of the new control algorithm.

Type-2 Fuzzy Logic Controlled Three-level Shunt Active Power Filter for Power Quality Improvement

This article proposes a three-level shunt active power filter for power quality improvement using a type-2 fuzzy logic controller (T2FLC). The reference compensating current is extracted using the P-Q theory. The majority of works previously reported are based on two-level inverters with a conventional Proportional integral (PI) controller, which requires rigorous mathematical modeling of the system. In this paper, a T2FLC controlled three-level active power filter is proposed to overcome the problem associated with PI controller. The T2FLC algorithm is applied for controlling the DC-side capacitor voltage as well as the harmonic currents of the three-level active power filter. The active power filter with a T2FLC is simulated in MATLAB Simulink environment (The Math Works, Natick, Massachusetts, USA). The simulated response shows that the proposed shunt active power filter controller has produced a sinusoidal supply current with low harmonic distortion and in phase with the source voltage. To verify the simulated response, a prototype model of inverter has been developed, and the control pulses for the active power filter are generated using a dSPACE1104 (dSPACE GmbH, Paderborn, Germany) controller. The experimental results demonstrate that the T2FLC greatly improves the transient performance of the three-level active power filter.

Supervisory Nearly Constant Frequency Hysteresis Current Control for Active Power Filter Applications in Stationary Reference Frame

This paper proposes a new constant frequency space-vector hysteresis-band current control (CF-SVHCC) in the stationary reference frame (SRF) for three-level active power filter applications when applied to isolated neutral point (INP) systems. CF-SVHCC is designed based on two recognized modulation methods: 1) space-vector modulation and 2) adaptive hysteresis current control. The proposed technique consists of a simple circular hysteresis strategy around the current-error vector in SRF with the purpose of employing the zero- and nonzero-voltage vectors of the three-level voltage source inverter. CF-SVHCC continuously estimates an adaptive outer hysteresis-band in the SRF using the inverter switching signals by a simple and fast artificial neural network method called the adaptive linear neuron algorithm. The main part of CF-SVHCC is a supervisory control unit that operates in the SRF to avoid interphase dependency and systematically uses the voltage vectors associated with the estimated outer hysteresis-band to prevent a high switching frequency and, in turn, maintain the switching frequency constant. CF-SVHCC retains most benefits of the conventional HCC and also introduces additional advantages, including a constant switching frequency and the interphases independency in three-phase INP systems.

Research on Predictive Current Control for Three-Level Four-Leg APF

Taking three-level four-leg active power filter (APF) as research object, this paper establishes the corresponding mathematical model. In addition, the paper establishes the Matlab model based on predictive current control strategy, and then the theoretical analysis and simulation research are conducted. The simulation and experimental results show that the APF with predictive current control strategy can compensate harmonic current and neutral current well and make the two capacitors voltage balance effectively.

A PI Control Algorithm with Zero Static Misadjustment for Tracking the Harmonic Current of Three-Level APFs

Tracking harmonic current quickly and precisely is one of the keys to designing active power filters (APF). In the past, the current state feedback decoupling PI control was an effective means for three-phase systems in the current control of constant voltage constant frequency inverters and high frequency PWM reversible rectifiers. This paper analyzes in detail the limitation of the conventional PI conditioner in the APF application field and presents a novel PI control method. Canceling the delay of one sampling period and the misadjustment for tracking the harmonic current is the key problem of this PI control. In this PI control, the predictive output current value is obtained by a state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by a repetitive predictor synchronously. The repetitive predictor can achieve better predictions of the harmonic current. By this means, the misadjustment of the conventional PI control for tracking the harmonic current is cancelled. The experiment results with a three-level NPC APF indicate that the steady-state accuracy and dynamic response of this method are satisfying when the proposed control scheme is implemented.

Design of LCL-Filter Based Three-level Active Power Filter

This paper proposes an improved design of LCL-Filters for Three-Level Shunt Active power filters (APF). Available design principles are presented to achieve high compensation bandwidth and low switching frequency current. Then, affecitons of different parameters are taken into consideration of constraints on LCL-Filter design with detail analysis of ripple current. A simple and practical design procedure of LCL-Filter for Three-Level APF is subsequently proposed. The first step is to choose the resonant frequency of LCL-Filter according to the highest order harmonic needed to be compensated. Then it is aim to optimize the parameters of the LCL-Filter based on the design principles and constraints. The simulation results verify the effectiveness of the proposed method. DOI : http://dx.doi.org/10.11591/telkomnika.v12i1.3441

Deadbeat Control with a Repetitive Predictor for Three-Level Active Power Filters

Three-level NPC inverters have been put into practical use for years especially in high voltage high power grids. This paper researches three-level active power filters (APFs). In this paper a mathematical model in the d-q coordinates is presented for 3-phase 3-wire NPC APFs. The deadbeat control scheme is obtained by using state equations. Canceling the delay of one sampling period and providing the predictive value of the harmonic current is a key problem of the deadbeat control. Based on this deadbeat control, the predictive output current value is obtained by the state observer. The delay of one sampling period is remedied in this digital control system by the state observer. The predictive harmonic command current value is obtained by the repetitive predictor synchronously. The repetitive predictor can achieve a better prediction of the harmonic current with the same sampling frequency, thus improving the overall performance of the system. The experiment results indicate that the steady-state accuracy and the dynamic response are both satisfying when the proposed control scheme is implemented.

A Simplified Control Scheme for Three-Phase Three-Level (NPC) Series Active Filter to Compensate All Voltage Perturbations

This paper presents a simplified control scheme for three-phase three-level series active power filter to compensate all load voltage perturbations such us harmonic unbalances, sags and swells. The standard configuration of three-phase series active power filter uses the two-level three-phase voltage source inverter with hysteresis controller. This configuration presents some drawbacks and is limited to low power systems. Today three-level (NPC) inverter is one of the most successfully employed topology in various industrial applications. In this paper a new scheme to increase the capability of series Active Power Filter (APF) voltage controller based on three-level inverter using simplified Pulse Width Modulation (PWM), is proposed. The control strategy adopted use instantaneous reactive power theory, easy to implement and gives good performance for all load voltage perturbations. The numerical simulation results carried with MATLAB-Simulink and SimPowerSystem Toolbox show the effectiveness of the proposed control scheme.

Systematic analytical-based generalised algorithm for multilevel space vector modulation with a fixed execution time

A generalised algorithm is proposed for multilevel space vector modulation (SVM), which is applicable to any number of levels. The algorithm is based on numerical analysis and gives a fixed execution time when implemented in a digital signal processor, irrespective of the number of levels. In addition, the algorithm procedures eliminate the difficulty in determining the reference vector location, the on-time calculations and switching state selection. A visualisation of the multilevel SVM analysis is detailed, without using any representative technique. The redundant paths can be readily utilised for capacitor balancing. The proposed algorithm caters for over modulation and minimum pulse, and is validated by Matlab/Simulink simulations and practical implementation. A 6 kW three-level active power filter is implemented practically using the proposed algorithm. It is shown that the algorithm is readily codable and time efficient.

Three-phase three-level active power filter with a clamped capacitor topology

An eight-switch voltage source inverter for harmonic elimination and reactive power compensation is presented. The adopted inverter is based on a three-phase two-leg clamped capacitor circuit topology to reduce the voltage stress on the power semiconductors. Four active switches and one clamped capacitor are used in each inverter leg to achieve three-level pulse-width modulation. The adopted inverter is operated as a controllable current source to supply the necessary active power to compensate for the inverter losses, to eliminate current harmonics and to compensate the reactive power. Therefore, the sinusoidal line currents are drawn from the AC source. Three control loops are used in the control scheme to obtain the constant DC-link voltage, to track the line current command and to balance the neutral-point voltage. The redundant operating states in the adopted inverter can be selected to compensate the clamped capacitor voltage. A mathematical model of the proposed inverter for an active power filter is derived and the control scheme provided. Simulations and experiments based on a laboratory scale-down prototype are presented to verify the effectiveness of the proposed control scheme.