Carrier-based discontinuous PWM modulation for current source converters

A new carrier-based discontinuous pulse-width modulation (PWM) scheme anchored on a novel space vector modulation methodology is proposed in this paper for four-leg converters. Using a space vector definition that includes the zero sequence voltage component and partitioning the feasible sixteen modes into three separate sets, the expressions for the modulation signals for the discontinuous carrier based PWM scheme are set forth. Significantly, the switching devices can be clamped either to the positive or negative rail for 120 degrees under all operating conditions of unbalanced three-phase voltages; ensuring the reduction of switching losses and the effective switching frequency of the inverters. The discontinuous PWM modulation methodology proposed which is shown by experimental results to synthesise desirable balanced or unbalanced three-phase voltage sets complements and further clarifies the results of the 3-dimensional space vector modulation scheme (3-D SVM) for four-leg converters reported in the literature.

Single-phase voltage source converter (VSC) is an important power electronic converter (PEC), including singlephase voltage source inverter (VSI), single-phase voltage source rectifier (VSR), single-phase active power filter (APF) and singlephase grid-connection inverter (GCI). Single-phase VSC as well as its modulation algorithms is widely used as the fundamental part of large scale PEC's, having a long list of applications. In the paper, as first, on the basis of the discontinuous pulse-width modulation (DPWM) of three-phase VSC, a new DPWM of single-phase VSR is presented in virtue of zero-sequence component injection, in order to reduce power loss and increased overall efficiency. And then by reconstructing the other two phase input voltages and currents, the transformation from stationary frame (abc) to rotating frame (dq frame) is designed. Finally, a PI regulator based controller for single-phase VSR is analyzed and simulated by means of MATLAB/SIMULINK by using the presented DPWM and dq transformation. The simulation results show the validation of the above DPWM algorithm and control theory.

Purpose Votage source converter (VSC) based or current source converter (CSC) based shunt active power filter (SAPF)? It is the main question in harmonic elimination project using SAPF.This paper presents some criteria based on which the designer can decide which type of filter is more suitable for implementation of the project according to the nature and characteristics of the project. Design/methodology/approach Owing to the importance of cost and power losses criteria, relevant equations will be formulated and comparative analysis will be carried out between conventional structures based on CSC or VSC. For validation of analyses, simulation results have been studied in the MATLAB–SIMULINK environment. Findings Simulation results have examined two important criteria of power losses and costs. Although the results show the superiority of VSSAPF to CSSAPF in both criteria, this comparison is performed in a general and conventional condition. Using third-order filters of inductive-capacitive-inductive (LCL) type in VSSAPF, using insulated-gate bipolar transistor (IGBT) with reverse-voltage blocking ability in CSSAPF, which eliminates the need to use series diodes, and the use of superconducting technology in the DC-side endpoint in CSSAPF, not only reduce the difference of cost and losses in two schemes but also may lead to the lower costs and losses in CSSAPF than VSSAPF. Originality/value This paper is the result of many years working on active power filter and can be useful for engineers who are engaged in industrial projects.

Toshiba has developed a new type of snubber loss free current source GTO converter (CSC). Applying this type of GTO converter, Toshiba studied the converter system for a 30 MW-SMES system. The current source converter and voltage source converter (VSC) with a DC chopper were compared from the viewpoint of cost, dimensions and loss. A SMES system using CSC and its control model are simulated by EMTDC. Many advantages in the current source converter were found if it was applied for an SMES system, because the DC power source, superconducting magnet, is inherently a current source.

Original optimal power flow (OPF) model of hybrid multi-terminal high voltage direct current (hybrid MTDC) system ignores the converter transformer of voltage source converter (VSC). The modulation of VSC may reach the upper limit losing regulation and VSC station works in the nonlinear modulation area. This paper presents a novel model of hybrid MTDC for OPF solutions using primal-dual interior-point method (PDIPM). This new OPF model is constituted of current source converter (CSC), VSC and its coupling transformer which is considered to be a tap-changing transformer. The new model represents well both AC system and DC system where the VSC is not assumed as idealized, controllable voltage sources but com pound transformer devices which take account of VSC internal switching losses, ohmic losses and reactive power design limits. Finally, the accuracy and effectiveness of the proposed OPF model are demonstrated on a modified IEEE-14 Bus system.

To facilitate the design of ac side filters, this work gives analytical expressions for the root mean square value of the total harmonic phase currents in voltage and current source converters depending on the modulation schemes and passive filter components. Novel equations were found for the calculation of total harmonic phase currents regarding the CSC with LC filter. The results are verified by appropriate measurements for selected PWM schemes and are valid for most common applications.

With the development of renewable energy (i.e. wind power and solar power) generation, its integration to the power grid has becoming a more and more important challenge. High voltage direct current (HVDC) transmission [1-2] is a suitable scheme for the integration. The key unit of HVDC is the converter. In general, there are two types of converters classified by the electronic devices. The one is named the current source converter (CSC) based on thyristors. The other one is named the voltage source converter (VSC) [3-4] based on insulated-gate bipolar transistors (IGBTs). The disadvantages of CSC are the probability of commutation failure, large harmonics, and inflexibility of power control. The advantages of CSC are high withstanding voltages and few losses. On the contrary, VSC has few harmonics and excellent output, but it has lower withstanding voltages and higher losses. And VSC cannot deal with direct current failure. To combine advantages of both topologies, an improved hybrid multilevel converter (HMC) is presented in this paper.

This paper compares the efficiencies of insulated gate bipolar transistor-based voltage and current source inverters. Test circuits that replicate the functionality of a single switching pole of each converter topology are used to measure the switching trajectories and loss characteristics of the semiconductor devices. These results are then used to simulate the losses for complete 3-phase voltage and current source inverters. Switching losses are shown to be dominant in the voltage source inverter whilst conduction loss is dominant in the current source inverter. It is shown that neither power converter operates more efficiently than the other over the complete operating range, with an equivalently rated voltage source inverter being preferable at lower power levels and the current source inverter being more efficient at higher power levels. (6 pages)

Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) technology is a very attractive power transmission technology. The VSC based HVDC transmission uses IGBT (Insulated Gate Bipolar Transistors) switches having turn-on and turn-off capability and having special characteristics compared to Current Source Converter (CSC) based conventional HVDC technology. Among various control methodologies used for VSC based HVDC, vector control, nonlinear control and independent P-Q controller based on analytic expressions have been developed and analyzed in this work for sending end control station 1. Similarly, in the receiving end station 2, DC and AC voltage controllers are realized with traditional PI controllers have been analyzed. The performance of the proposed controller has been investigated under different operating conditions including post fault recovery. The effectiveness of the proposed various controllers are demonstrated through digital simulation studies on VSC-HVDC transmission system, using PSCAD/EMTDC software package under short time Line-Ground fault in both AC systems in two terminal VSC - HVDC systems.

The shunt active filters are based on power converters driven to generate a current waveform injected in parallel to the system in order to compensate harmonics or to supply reactive power. Several topologies have been studied based either on voltage-source converters (VSC) or currentsource converters (CSC), from the standpoint of power topologies and from the point of view of control strategies. The topology-based on a CSC has advantages especially in variable load operations, but the losses appear as a disadvantage. This work presents a shunt active filter based on a multilevel current source topology where the total DC link current is divided into each power module. The proposed control scheme solves the problem of the DC link current equalization typical of the current source multilevel topologies while minimizes the DC link conducting losses.

A single phase Grid Connected Current Source Converter (GCCSC) for photovoltaic (PV) systems with sinusoidal grid current injection control is presented in this paper. The Voltage Source Converter (VSC) topologies are extensively used for connecting Renewable Energy Sources (RES) to the utility grid. The grid current injection control structure is quite tough or dependent on outerloop in case of VSC based PV compared with current source converter (CSC) based PV. The presented control structure and overall system achieves following functionalities (i) Always PV panel is operating at Maximum Power Point (MPP) mode by using Perturbation and Observation (P&O) algorithm (ii) Ripple current in the DC link is very less (iii) Unity Power Factor (UPF) (iv) Very less Total Harmonic Distortion (THD) of grid currents. To verify the effectiveness of control structure and overall system, simulation studies were done in MATLAB/SIMULINK environment.

Voltage source converters (VSC) and current source converters (CSC) transfer energy from a source to a load in a quantized fashion using semiconductor switches which are turned on and off at fast repetition rates. Space vector modulation (SVM) among other pulsewidth modulation techniques, offer several advantages such as minimizing the number of switchings or improving the utilization of the source voltage. This paper presents three alternatives for implementing SVM in a DSP-controller. The study is performed for a voltage source rectifier (VSR), but as well, it is adequate for a voltage source inverter (VSI). The three alternatives are compared from a theoretical and experimental point of view. The algorithms proposed provide a simple and effective solution for high-performance (VSR). Experimental results are given to verify the implemented algorithms.

The paper presents a new four-level voltage source converter (VSC). Compared to conventional four-level converters, this proposed converter has fewer components and can be used for a higher power density system in low and medium voltage applications. Its principles and advantages are studied in this paper. The effect of various redundant switching states on the voltages of flying capacitors is analyzed. The voltages of flying capacitors can be balanced by selecting proper redundant switching states. A carrier-based pulse width modulation (CBPWM) is used to control the proposed converter. The performance of the converter is investigated and simulated in MATLAB/Simulink as well as on a 5 kVA experimental prototype.

Three-phase voltage-source converters (VSCs) and current-source converters (CSCs) have multiple dualities. This paper specifically focuses on examining the conducted common-mode (CM) EMI of VSCs and CSCs when wide bandgap (WBG) devices are used. First, the CM EMI signature of the two converters with both rectifier and inverter stages are examined. The benefits of CSC over VSC in terms of lower CM EMI are identified. The impact of adding CM chokes at different locations and the use of an LCL filter for the VSC are examined. In addition, the CM EMI associated with having only the rectifier stage or the inverter stage for each of the two types of converters are examined. Finally, a promising CM EMI suppression scheme is examined for the CSC consisting of both the rectifier and the inverter stages that requires few EMI filtering components .

To implement the STATCOMs for transmission and distribution applications, high power converters are needed. A multilevel converter is a logical choice for such applications as it can meet the imposed line side current and voltage harmonic distortion standards without extending its device ratings. Several types of monolithic multilevel converters have been proposed based on different structures of a DC link voltage (or current) to generate staircase output voltage (or current) levels. The multilevel current source converters (CSC) are also a potential configuration for STATCOM. Multilevel CSCs using fully controllable switches have the advantages of low output harmonics and controllable active and reactive power. During the last decade, modular multilevel converters have shown a breakthrough and have made their way to commercial high power applications. Modularity, in general, refers to a technique to develop comparably large systems by combining smaller subsystems. For power converter topologies, this means, a cascaded connection of converter cells seems to be an interesting solution to reach high voltage and high quality waveforms with a minimum complexity. This chapter provides an overview on monolithic and modular multilevel converter topologies, targeting high-power applications and in particular STATCOM. Modular multilevel converters can be built either straightforward by applying the modular building block cells or by a combination of cells with monolithic multilevel topologies. The monolithic and modular CSCs can also be realized by employing the duality concept on each corresponding Voltage Source Converter (VSC). This chapter summarizes the most recent developments made for multilevel converter topologies, by covering new promising topologies and operational issues. In addition, emerging trends, challenges, and possible future directions of the multilevel converter technologies are outlined.