Multilevel STATCOM Research Articles

Analysis of Cascaded Three-Level Inverter based Multilevel STATCOM in High Power Applications

Analysis of Cascaded Three-Level Inverter based Multilevel STATCOM in High Power Applications

Harmonics elimination PWM based direct control for 23-level multilevel distribution STATCOM using differential evolution algorithm

This work describes the application of a soft computing technique—known as the differential evolution (DE) to implement the harmonics elimination pulse-width modulation (HEPWM) for the direct control of distribution static synchronous compensator (D-STATCOM). The main contribution of the work is the application of DE to solve eleven HEPWM switching angles to synthesize a 23-level cascaded multilevel voltage source inverter (MVSI). The key feature of this algorithm is the wide modulation index (MI) range that can be produced (i.e. 5.40–8.15p.u) with very small step size (0.01), while maintaining the total harmonic distortion (THD) of the MVSI output voltage below 5%. Furthermore, the utilization of high levels MVSI allows for the output voltage of the D-STATCOM to be sufficiently high, thus avoiding the use of step-up transformer. The correctness of the computed HEPWM angles is validated using single phase 23-level cascaded MVSI experimental rig. Then, the proposed method is compared to the phase-shifted PWM (PS-PWM) using a ±6.5 MVAr/11kV D-STATCOM modelled in MATLAB-Simulink. For the same switching frequency, the HEPWM switching results in a superior harmonics spectra and lower switching losses. Furthermore, if the switching frequency is fixed to a particular value, the size of the series coupling inductor can be reduced to at least half. Dynamically, the steady state value of the reactive current (iCq) is reached in less than one mains cycle when a transition from the full inductive to full capacitive modes is imposed.

Power Quality Enhancement Based on Multilevel STATCOM for High Power Applications

Power Quality Enhancement Based on Multilevel STATCOM for High Power Applications

Closed loop fractional order pid controlled multilevel statcom for ten bus system

Closed loop fractional order pid controlled multilevel statcom for ten bus system

Multilevel Statcom Based on PID and Fuzzy Control

To investigate the performance of Multilevel STATCOM based on PID with fuzzy controller under fault conditions. Static Synchronous Compensator is used to inject voltages by regulating DC link voltages in the system which consists of two standard inverters associated in cascaded to obtain five level output. Generally DC link voltages are controlled by PI controller. When there is a fault occurrence in the system, then time response of PI controller will be slow and overshoot problems raised. To rectify this problem, PID with fuzzy controller is proposed. By using PID with fuzzy controller, DC link voltages are synchronized; a dq reference frame theory is used in this system for STATCOM to recompense the harmonics. The proposed controller gives less Total Harmonic Distortion, Response Time, Settling Time and Rise Time.

Simulation and Hardware Implementation of Multilevel STATCOM for Smart Grid

The increase in penetration of intermittent renewable energy source has created the need to investigate problems encountered with grid connection. Flexible AC Transmission Systems (FACTS) controllers have proved to be effective in improving system stability of interconnected power system. This paper investigates the improvement of system stability in smart grid using Multi Level STATic COMpensator (MLS) with penetration of Wind Turbines. The control algorithm for improving the dynamic response of the system is implemented using FPGA processor. The Hardware-In-Loop (HIL) testing facility of MATLAB combined with xilinx FPGA was used to represent a real time STATCOM control. The designed hardware for multilevel STATCOM was tested on an IEEE 13 Bus system using the HIL feature, for various operating conditions.

Fast Model Predictive Control for Multilevel Cascaded H-Bridge STATCOM with Polynomial Computation Time

To solve the issue of exponentially increasing computational burden of finite control set model predictive control (FCS-MPC) for multilevel converters, a fast MPC scheme for multilevel cascaded H-bridge STATCOM is presented. The proposed approach consists of three steps. First, with the partially stratified optimization approach, the multiobjective programming of MPC is divided into two suboptimization problems, i.e., current-control MPC and voltage-balancing MPC. Second, a dynamic programming algorithm is proposed for the optimization of current-control MPC. Third, a mixed algorithm, which combines dynamic programming and greedy algorithm (0-1 programing), is proposed to select the optimal switching combination from all the redundant switching combinations for the voltage balancing MPC achieving a global optimization. Through the analysis of the time complexity, with the proposed scheme, the total computation of FCS-MPC can be reduced to polynomial time from exponential time. The proposed approaches will not deteriorate the control performance. The control performance is validated by simulation results and the effectiveness is further demonstrated by implementing the algorithm on a low-cost DSP (TMS320F28335) in real time.

불평형부하를 가지는 다단 H-bridge STATCOM에서 상간 직류전압 불평형의 제어

불평형부하를 가지는 다단 H-bridge STATCOM에서 상간 직류전압 불평형의 제어

Cascaded Two-Level Inverter-Based Multilevel STATCOM for High-Power Applications

In this paper, a simple static var compensating scheme using a cascaded two-level inverter-based multilevel inverter is proposed. The topology consists of two standard two-level inverters connected in cascade through open-end windings of a three-phase transformer. The dc-link voltages of the inverters are regulated at different levels to obtain four-level operation. The simulation study is carried out in MATLAB/SIMULINK to predict the performance of the proposed scheme under balanced and unbalanced supply-voltage conditions. A laboratory prototype is developed to validate the simulation results. The control scheme is implemented using the TMS320F28335 digital signal processor. Further, stability behavior of the topology is investigated. The dynamic model is developed and transfer functions are derived. The system behavior is analyzed for various operating conditions.

Research on the Multilevel STATCOM based on the H-bridge Cascaded

This paper mainly studies the main circuit topology, the working principle, modulation technique and control strategy of the STATCOM based on H-bridge. The STATCOM direct power control algorithm based on the virtual flux is used to control the AC side reactive power compensation, and in accordance with the principle of conservation of power, the DC side voltage imbalance factors are analyzed, and a distributed DC voltage control algorithm is also introduced. The DC side control algorithm is divided into upper and lower control parts, of which the upper control section is aimed at the average of DC side capacitor voltage of the sub-module unit for the STATCOM device, the lower control part is mainly for each sub-module DC side capacitor voltage. Finally, the control strategy is verified in a three level chain STATCOM system with VME control box as its core controller, and the experimental results show that the algorithm is feasible.

Cascaded Multilevel Converter-Based Transmission STATCOM: System Design Methodology and Development of a 12 kV ±12 MVAr Power Stage

This paper deals with the design methodology for cascaded multilevel converter (CMC)-based transmission-type STATCOM (T-STATCOM) and the development of a ±12 MVAR, 12 kV line-to-line wye-connected, 11-level CMC. Sizing of the CMC module, the number of H-bridges (HBs) in each phase of the CMC, ac voltage rating of the CMC, the number of paralleled CMC modules in the T-STATCOM system, the optimum value of series filter reactors, and the determination of busbar in the power grid to which the T-STATCOM system is going to be connected are also discussed in this paper in view of the IEEE Std. 519-1992, current status of high voltage (HV) insulated gate bipolar transistor (IGBT) technology, and the required reactive power variation range for the T-STATCOM application. In the field prototype of the CMC module, the ac voltages are approximated to sinusoidal waves by the selective harmonic elimination method (SHEM). The equalization of dc-link capacitor voltages is achieved according to the modified selective swapping (MSS) algorithm. In this study, an L-shaped laminated bus has been designed and the HV IGBT driver circuit has been modified for the optimum switching performance of HV IGBT modules in each HB. The laboratory and field performances of the CMC module and of the resulting T-STATCOM system are found to be satisfactory and quite consistent with the design objectives.

Optimization of Switching Losses and Capacitor Voltage Ripple Using Model Predictive Control of a Cascaded H-Bridge Multilevel StatCom

This paper further develops a model predictive control (MPC) scheme which is able to exploit the large number of redundant switching states available in a multilevel H-bridge StatCom (H-StatCom). The new sections of the scheme provide optimized methods to tradeoff the harmonic performance with converter switching losses and capacitor voltage ripple. Varying the pulse placement within the modulation scheme and modifying the heuristic model of the voltage balancing characteristics allows the MPC scheme to achieve superior performance to that of the industry standard phase shifted carrier modulation technique. The effects of capacitor voltage ripple on the lifetime of the capacitors are also investigated. It is shown that the MPC scheme can reduce capacitor voltage ripple and increase capacitor lifetime. Simulation and experimental results are presented that confirm the correct operation of the control and modulation strategies.

Research on Novel Structure of Diode Clamed Multilevel StatCom

The inverter technology gaining interest in high voltage high power is likely the multilevel inverter. The main characteristic of a multilevel inverter is able to reduce each power device voltage stress. Static Synchronous Compensator (StatCom) is the major application of the inverter to compensate reactive power in power system. Compared with traditional StatComs, multilevel StatComs exhibit faster dynamic response, smaller volume, lower cost, and higher ratings. A novel structure of StatCom with delta-connected multilevel inverter is proposed. The SPWM technique, which offers simplicity and good response, is used in the multilevel StatCom switching control strategy.

Multilevel Inverter Based DSTATCOM with Energy Storage Device

With the growth of industry manufacturers and population, power quality becomes more and more important issue, and is attracting significant attention due to the increase in the number of sensitive loads. A distribution static compensator (DSTATCOM) is a voltage source inverter (VS1)-based power electronic device, which is usually used to compensate reactive power and sustain the system voltage in distribution power system. Compared with the traditional STATCOM, multilevel STATCOMs exhibit faster dynamic response, smaller volume, lower cost, and higher ratings. A multilevel inverter connected to an energy storage device can control both active and reactive power flow, providing more flexible and versatile power transmission operation. SPWM is actually a kind of multi-pulse trigger mode and used to trigger the switches in DSTATCOM.

Implementation of Cascade Multilevel Inverter-based STATCOM

This paper deals with the real time implementation of 11-level cascade multilevel inverter-based STATCOM using personal computer (PC) and ADD-ON cards for power system voltage control at the point of common coupling. Complete hardware and software development procedures have been explained in depth for direct as well as indirect control schemes. Experimental results are presented and it is shown that voltage control is achieved using cascade multilevel inverter based STATCOM, thus verifying the very basic purpose of STATCOM. Real time implementation using PC-based control technique has certain merits over digital signal processor based implementation, and some of these merits are high processing speed and low cost of implementation; therefore, PC-based implementation can be used in industry as well as for utility applications.

Frequency-Domain Analytical Model for a Cascaded Multilevel STATCOM

This paper develops a frequency-dependent analytical representation for a multilevel cascaded converter, with fundamental frequency switching. The gain and phase angle are studied with the firing angle as a parameter, where the converter is subjected to oscillatory excitation at a range of frequencies. This paper presents analytical formulae for a single cell and for a generic cascade multilevel converter where the number of cells is a parameter. Also, the formula for fundamental frequency studies is separately developed. The equivalent capacitance concept is introduced and its convergence to a constant value for high frequencies is demonstrated. The analytical formulae are tested against detailed digital simulation and good matching is reported. The formulae developed in this study will be of particular importance in studying interactions between a multilevel STATCOM and the host ac grid (similar to harmonic resonance) and in studying converter transient responses.

Observer for DC voltages in a cascaded H-bridge multilevel STATCOM

Using an instantaneous model of a cascade H-bridge multilevel-based STATCOM, an observer for estimating the DC capacitor voltages of the multilevel inverter is presented. This design can be used to eliminate the voltage sensors in each H-bridge of this device. Simulation results are presented in order to validate the performance of the proposed observer applied to a cascade H-bridge multilevel-based STATCOM.

Regulating and equalizing DC capacitance voltages in multilevel STATCOM

Because of the high MVA ratings, it would be expensive to provide independent, equal, regulated DC voltage sources to power the multilevel converters which are proposed for STATCOMs. DC voltage sources can be derived from the DC link capacitances which are charged by the rectified AC power. This paper addresses two control issues: (1) regulation of the DC capacitance voltages and (2) their equalization. Equalization is necessary (i) to ensure the even sharing of voltage stresses in the gate-turn-off thyristors (GTOs), and (ii) to prevent the degradation of total harmonic distortion (THD) factors, as all harmonic elimination strategies depend on equal voltages in their assumptions. The strategies considered are: (a) the fundamental frequency method, and (b) the sinusoidal pulse width modulation method. Digital simulations are used to confirm the feasibility of the control methods.