Current Source Rectifier Research Articles

A Single-Phase Current-Source Bidirectional Converter for V2G Applications

In this paper, a single-phase current-source bidirectional converter topology for V2G applications is proposed. The proposed converter consists of a single-phase current-source rectifier (SCSR) and an auxiliary switching network (ASN). It offers bidirectional power flow between the battery and the grid in the buck or boost mode and expands the output voltage range, so that it can be compatible with different voltage levels. The topology structure and operating principles of the proposed converter are analyzed in detail. An indirect control algorithm is used to realize the charging and discharging of the battery. Finally, the semiconductor losses and system efficiency are analyzed. Simulation and experimental results demonstrate the validity and effectiveness of the proposed topology.

A power conversion system for PMSG-based WECS operating with fully-controlled current-source converters

We propose a new power conversion system for a permanent magnet synchronous generator (PMSG) based grid-connected wind energy conversion system (WECS) operating with fully-controlled back-to-back current-source converters. On the generator side, two independent current-source rectifiers (CSRs) with space-vector pulse width modulation (SVPWM) are employed to regulate and stabilize DC-link currents. Between DC-link and the electrical grid, a direct-type three-phase five-level current-source inverter (CSI) is inserted as a buffer to regulate real and reactive power fed to the grid and thus adjusts the grid side power-factor. We also present a current-based maximum power point tracking (MPPT) scheme, which helps the generator extract the maximum power through closed-loop regulation of the generator speed. By applying the multilevel modulation and control strategies to the grid-side five-level CSI, a multilevel output current waveform with less distortion is produced, and the bulk requirement of the output capacitor filter to eliminate the harmonic current is reduced. All the proposed concepts are verified by simulation models built in a PSIM environment.

Selective Harmonic Compensation (SHC) PWM for Grid-Interfacing High-Power Converters

Compensating the grid background harmonics in a grid-interfacing converter system, such as a drive system's active-front-end rectifier or a grid-connected inverter in a distributed generation system, is an effective method of reducing line side current harmonics. However, this harmonic compensation is particularly challenging in medium-voltage high-power applications (>1 MVA). This is mainly due to the low-switching frequency operation of high-power converters (300-800 Hz) to maintain low power loss. Therefore, the traditional tasks of active power filters with relatively high-switching frequency cannot be easily realized here. This paper proposes a new pulse width modulation technique, named selective harmonic compensation (SHC), which actively compensates the power system background harmonics, but still operates at very low-switching frequencies. Details of the proposed SHC are presented. An SHC application example on a high-power current-source rectifier is provided in this paper. The simulations and experiments show that the proposed SHC scheme can effectively compensate the system background harmonics and improve the line current harmonic performance.

Power-Dense Shipboard-Compatible Low-Horsepower Variable-Frequency Drives

A variable-frequency drive (VFD) having a 440-V front-end current source rectifier (CSR) interface to a voltage source inverter (VSI) feeding a Permanent-Magnet Axial-flux Air Core motor combination is a solution for low-horsepower pump and fan control that is both power dense and compatible with a shipboard environment. This paper describes the control and power platforms for the CSR/VSI and provides experimental results for a 250-V 3.3-kW system. Power density and efficiency comparisons are made between equivalent CSR/VSI- and voltage-source-conversion-based VFDs to demonstrate that the CSR/VSI-based VFD is more power dense.

Common Mode Voltage Cancellation in a Buck-Type Active Front-End Rectifier Topology

AC/AC power conversion is widely used to feed AC loads with a variable voltage and/or a variable frequency from a constant voltage constant frequency power grid or to connect critical loads to an unreliable power supply while delivering a very balanced and accurate sinusoidal voltage system of constant amplitude and frequency. The load specifications will clearly impose the requirements for the inverter stage of the power converter, while wider ranges of choices are available for the rectifier. This paper investigates the utilization of a buck-type current source rectifier as the active front-end stage of an AC/AC converter for applications that require an adjustable DC-link voltage as well as elimination of the low-frequency common mode voltage. The proposed solution is to utilize a combination of two or more zero current vectors in the Space Vector Modulation (SVM) technique for Current Sources Rectifiers (CSR).

Input filter pre-charge scheme for high-power PWM-current source rectifiers connected to a weak utility supply

High-power PWM current source rectifiers are normally connected to the ac grid by means of a lightly damped LC input filter. Pre-charge schemes employing pre-insertion resistors are typically used to mitigate the over-voltage across the filter capacitors during the connection to the grid. However, noticeable distortion of the grid voltage may still occur during the insertion of the input filter to the grid. This is particularly true at low ratios of the supply fault level to the converter-rated power and cannot be avoided when conventional pre-charge schemes are used. This study proposes a pre-charge scheme that yields a smooth and controllable connection of the input filter to the grid along with total absence of both over-voltage across the input filter capacitors and voltage distortion on the grid. This is novel and it is of particular interest whenever PWM-CSRs are connected to relatively weak grids. Pre-charge is carried out by the main PWM-CSR converter, which is in turn supplied on its dc-side by a small low-power low-voltage pre-charge converter. This completely eliminates the need for any pre-charge components on the ac-side [which can be bulky and expensive at medium voltage (MV) levels]. Experimental results obtained from a 150 kW PWM-CSR are included in the study.

Review of Three-Phase PWM AC–AC Converter Topologies

This paper presents first an overview of the well-known voltage and current dc-link converter topologies used to implement a three-phase PWM ac-ac converter system. Starting from the voltage source inverter and the current source rectifier, the basics of space vector modulation are summarized. Based on that, the topology of the indirect matrix converter (IMC) and its modulation are gradually developed from a voltage dc-link back-to-back converter by omitting the dc-link capacitor. In the next step, the topology of the conventional (direct) matrix converter (CMC) is introduced, and the relationship between the IMC and the CMCs is discussed in a figurative manner by investigating the switching states. Subsequently, three-phase ac-ac buck-type chopper circuits are considered as a special case of matrix converters (MCs), and a summary of extended MC topologies is provided, including three-level and hybrid MCs. Therewith, a common knowledge basis of the individual converter topologies is established.

An Active Damping Method Using Inductor-Current Feedback Control for High-Power PWM Current-Source Rectifier

Due to the inductor-capacitor filter, a pulse width modulation current-source rectifier (CSR) may experience LC resonance. A smaller ratio between the switching frequency and the resonant frequency of the CSR presents a challenge in designing active resonance damping methods in high-power applications. In this paper, different feedback states of filter inductor current and capacitor voltage are investigated to damp out the LC resonances. Besides proportional capacitor-voltage feedback (CVF), the derivative inductor-current feedback (ICF) provides an alternative approach for active damping and is comprehensively analyzed. Compared with the virtual-resistance (VR)-based active damping strategy, controller design is simpler in this method. Furthermore, the active damping method is able to damp the resonance under short-circuited dc-link conditions. The ICF-based active damping strategy works well for CSRs with low switching frequencies. Simulation and experimental results verify the feasibility and validity of the method.

Acoustic Noise Reduction and Power Factor Correction in Switched Reluctance Motor Drives

In this paper, a four-phase 8/6-pole 4-kW SR motor drive model is presented. Based on experimental data, the model allows an accurate simulation of a drive in dynamic operation. Simulations are performed and a laboratory type set-up is built based on a TI TMS320F2812 platform to experimentally verify the theoretical results obtained for a SR motor. To reduce acoustic noise and to correct the power factor of this drive, a two-stage power converter is proposed that uses a current source rectifier (CSR) as the input stage for the asymmetrical converter of the studied SRM. Employing the space-vector modulation (SVM) method in matrix converters, the CSR switching allows the dc link's capacitors to be eliminated and the power factor of the SRM drive to be improved. As the electrical motive force (emf) is directly proportional to the rotor speed, the input voltage to the machine can be programmed to be a function of the speed with the modulation index of the CSR, leading to a reduction in the acoustic noise of the SRM drive. Simulation of the whole SRM drive system is performed using MATLAB-Simulink. The results fully comply with the required conditions such as power factor correction with an improvement in the THD.

Medium-voltage pulse width modulated current source rectifiers using different semiconductors: loss and size comparison

In this study, a comparison of losses and physical size is presented for three semiconductor devices suitable for medium-voltage high-power applications. The comparison is made for medium-voltage pulse width modulated (PWM) current source rectifiers (CSRs) using a selective harmonic elimination technique. The devices are high-voltage insulated gate bipolar transistors and two types of hard-driven thyristors, namely the symmetrical gate commutated thyristor and the asymmetrical gate commutated thyristor. The study is based on practical devices using data sheets from semiconductor device vendors, taking into account accurate discrimination between turn-off and recovery states. The constant-voltage switching energy data sheet curves for voltage source converters are adapted to suit varying voltage applications like the PWM-CSR, with emphasis on how voltage is shared between series devices during each commutation instant.

Control and Resonance Damping of Voltage-Source and Current-Source Converters With $LC$ Filters

In this paper, the closed-loop control of both voltage-source converter (VSC) and current-source converter (CSC) systems with <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filters is investigated, with a focus being put on the damping of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance. First, both single-loop and multiloop control schemes for a voltage-source inverter (VSI) with output <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter are analyzed, where the design and tuning procedure can also be applied to a current-source inverter (CSI) with output <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CL</i> filter. It is shown that both VSI and CSI systems are subject to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance, even with multiloop control, while the CSI system is also subject to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonant frequency variations. On the other hand, the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonant frequencies in both current-source rectifier (CSR) and voltage-source rectifier (VSR) systems with input <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter circuits are relatively fixed due to the small variation range of source impedance. To further dampen the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance in these converter systems, active damping techniques such as virtual harmonic damper and control-signal-shaping methods are investigated, and their implementation into the converter systems is discussed in detail. Experimental results from both a VSC system and a CSC system are obtained.

A Predictive Control Scheme for Current-Source Rectifiers

Current-source rectifiers (CSRs) constitute a commonly used topology in high-power applications, featuring several advantages such as regeneration capability and high-quality currents. This paper presents a simple predictive control scheme for a CSR. The main achievements of the control scheme presented here are the simplicity in controlling the dc-link current and the generation of currents with unity displacement power factor. Experimental results are presented to validate the proposed control principle.

A Novel Self-Powered Supply for GCT Gate Drivers

The commercial power supply for the gate driver of integrated gate-commutated thyristors (GCTs) is an expensive proposition since the supply's output must withstand the high voltage of the GCT switch against all other relevant potentials in the converter. This voltage varies from a few thousand volts to several ten thousands of volts over the GCT application range. In this paper, a novel self-powered supply is proposed for the GCT gate driver, where the supply obtains energy from the snubber circuit of the GCT switch and then provides a regulated dc voltage for the gate driver. Since the snubber circuit is at the same potential as the GCT, the insulation level of the supply is reduced from thousands of volts to a couple of hundred volts, leading to a significant reduction in cost and size. The supply configuration is introduced and its operating principle is discussed. The design guidelines are discussed and experimental results from a 4160 V GCT current source rectifier are also provided.

DC-Link Current Minimization for High-Power Current-Source Motor Drives

In this paper, a loss reduction and DC-link current minimization strategy for a high-power current-source inverter (CSI) fed drive is proposed. The proposed strategy consists of an inverter maximum modulation index control scheme and a flux optimization algorithm. Specifically, in the inverter modulation index control, the CSI modulation index is kept at the maximum value while the current-source rectifier (CSR) is used to regulate a reduced variable DC-link current, and therefore, to control the motor current magnitude. This control scheme can effectively reduce the DC-link current, and at the same time, improve the line-side and motor-side waveforms. On the other hand, for the optimized flux control, the relationship between the rotor flux and the DC-link current is first investigated thoroughly. Based on this analysis, the DC-link current from the maximum inverter modulation index control can be minimized further by optimizing the rotor flux according to system variables such as the motor speed, the applied torque, and the motor-side capacitor size. With the proposed dc current minimization strategy, the losses in the semiconductor devices and the DC-link can be reduced, and the drive current rating could be lowered. Both simulation and experimental results on a 4.16-kV 600-hp CSI-fed drive system are obtained to verify the effectiveness of the proposed strategy.

Investigation of performance of UPFC without DC link capacitor

This paper presents an analysis of the dynamic operation of unified power flow controller without DC link capacitor. In this scheme of UPFC the shunt converter present in the static synchronous compensator is operated as a current source rectifier, which maintains a fixed DC voltage and DC current on the DC link without capacitor. The capacitor in the DC link is replaced by an AC filter on the line side with a very small value to reduce higher order harmonics. The voltage source inverter present in the series compensator is operated with space vector modulation technique. The proposed scheme is fully validated through digital simulation. The simulated results show that the DC link voltage is maintained constant without DC link capacitor; STATCOM provides good voltage regulation and static synchronous series compensator influences power flow over the transmission line. Transient responses of single machine infinite bus power system have also been presented.

Damping of PWM Current-Source Rectifier Using a Hybrid Combination Approach

An inductor-capacitor (LC) filter is normally required at the input of a pulse-width modulation (PWM) current source rectifier (CSR), to assist in the commutation of switching devices and to mitigate line current harmonics. To dampen the LC resonance introduced by the input filter, an effective damping method is proposed in this paper by using a hybrid combination of a virtual harmonic resistive damper and a three-step control signal compensator. The virtual harmonic resistor, which is immune to system parameter variations, can dampen the LC resonance caused by an external disturbance or control command changes without affecting the fundamental power flow. But the high-pass filter used for fundamental component elimination leads to poor dynamics. Therefore, a proposed three-step compensator is inserted into the DC current closed-loop control path which can effectively eliminate the resonance within the control loop by shaping the modulation signal. Compared to the two-step Posicast controller, the proposed three-step compensator has significant implementation advantages in medium voltage CSRs, where a low switching frequency is needed. By using a hybrid combination approach, dynamics of the virtual harmonic resistor can be improved with the transient overshoot mitigated by the three-step compensator. At the same time, the parameter sensitivity of the three-step compensator can be reduced, as any residual resonant oscillations can be dampened by the virtual resistor. Simulation and experimental results are provided to verify the effectiveness of the proposed approach.

Current-source-rectifier topologies for sinusoidal supply current: theoretical studies and analyses

For current-source-rectifier (CSR)-based systems, sinusoidal supply current and unity displacement power factor in the utility are achieved through either a pulsewidth-modulation CSR or a phase-controlled rectifier in conjunction with an active filter. This paper investigates theoretical studies and analyses for the two topologies from the standpoint of converter kilovoltampere rating and switch rating.

New Cascaded Control System for Current-Source Rectifiers

A control method for current-source rectifiers (CSRs), which realizes substantially sinusoidal line currents, unity displacement power factor, and a dc-link current control with excellent dynamic properties is presented. CSRs are usually operated by pulsewidth-modulation (PWM) or space-vector-modulation techniques. However, due to the mains LC filter resonant circuits when using these modulation methods the system stability has to be investigated, resulting in restrictions on the minimum PWM frequency and the minimum size of the LC filter. Furthermore most known dc-link current control loops use dc-link inductors of considerable size. This limits the dynamic performance and, therefore, reduces the attainable efficiency of CSRs. To overcome these problems, a new cascaded dc-link current control system for CSRs is presented. Its inner capacitor voltage controller is based on a time-discrete modulation method, which realizes a fundamentally stable control of the mains LC filter resonant circuits, avoiding the mentioned restrictions. The system controlled by the superimposed dc-link current controller is linearized by a new approach, allowing excellent dynamic performance and, therefore, a comparatively small dc-link inductor to be used. The paper includes guidelines on how to design the mains filter components and the dc-link inductor. The feasibility of the presented cascaded controller is confirmed by measurements taken on a 60-kVA model current-source converter and different loads.

Active Damping Control of a High-Power PWM Current-Source Rectifier for Line-Current THD Reduction

The use of active damping to reduce the total harmonic distortion (THD) of the line current for medium-voltage (2.3-7.2 kV) high-power pulsewidth-modulation (PWM) current-source rectifiers is investigated. The rectifier requires an LC filter connected at its input terminals, which constitutes an LC resonant mode. The lightly damped LC filter is prone to series and parallel resonances when tuned to a system harmonic either from the utility or from the PWM rectifier. These issues are traditionally addressed at the design stage by properly choosing the filter resonant frequency. This approach may result in a limited performance since the LC resonant frequency is a function of the power system impedance, which usually varies with power system operating conditions. In this paper, an active damping control method is proposed for the reduction in line current THD of high-power current-source rectifiers operating at a switching frequency of only 540 Hz. Two types of LC resonances are investigated: the parallel resonance excited by harmonic currents drawn by the rectifier and the series resonance caused by harmonic pollution in the source voltage. It is demonstrated through simulation and experiments that the proposed active damping control can effectively reduce the line-current THD caused by both parallel and series resonances.

Large Current Rectifiers: State of the Art and Future Trends

This paper presents the different technologies used in the generation of large controlled currents, in the kiloamperes range. After a brief review of processes requiring large currents, the paper discusses the working principles of thyristor phase-controlled rectifiers commonly used in these applications. Chopper-rectifiers using high-current insulated gate bipolar transistors are introduced as an alternative being considered in recent projects. The pulsewidth-modulated current-source rectifier, currently used in medium-voltage motor drives, is also analyzed as a future alternative for rectification in industrial processes. In addition, this paper presents the most important requirements and specifications to be considered in the applications of these high-power units. A system comparison is developed between thyristor and chopper-rectifiers in terms of quality of control, harmonics, power factor, losses, and efficiency.