Current Source Rectifier Research Articles

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.

Complex State-Space Modeling and Nonlinear Control of Active Front-End Converters

This paper presents the modeling and control of active front-end (AFE) converters using complex state-space representation, a technique developed and thus far mostly employed for the analysis of ac machines. Particularly, three-phase PWM voltage-source and current-source rectifiers are thoroughly studied using the graphical capabilities of this approach, namely, complex signal flow graphs. These are used to directly and intuitively derive high-performance nonlinear control laws based on input-output feedback linearization. Specifically, a cascaded and a paralleled control scheme are investigated for the voltage-source rectifier, whereas a cascaded scheme is considered for the current-source rectifier. Under these strategies both converters exhibit linear and decoupled d-q axes dynamics, while also attaining a reactive power compensation capacity. Moreover, linearization of their respective dc-link voltage and current loops utterly enforces and ensures their operating stability. All this is achieved without the elaborate mathematical complexity of input-output linearization, effectively shunned out by the proposed complex state-space approach. Finally, experimental results from 5-kVA digital-signal-processor-based laboratory prototypes verify the analysis and downright performance evinced by these AFE converters.

A unity-power-factor three-phase PWM SCR rectifier for high-power applications in the metal industry

A new thyristor current-source rectifier that achieves unity power factor, low-current total harmonic distortion (THD), and DC-bus current and voltage control is presented. The rectifier is suitable for high-power applications such as induction heating and DC arc furnaces. It combines a traditional six-pulse thyristor bridge and a DC chopper that together solve power quality problems such as poor power factor and flicker generation. This topology achieves low input current THD and DC power control without additional power-factor-correction equipment, harmonic trap filters, use of multiple pulse rectifiers or high-K-factor transformers.

Selective harmonic elimination and current/voltage control in current/voltage-source topologies: a unified approach

This paper presents a unified approach for generating pulsewidth-modulated patterns for three-phase current-source rectifiers and inverters (CSR/Is) that provides unconstrained selective harmonic elimination and fundamental current control. The approach uses the chopping angles or gating patterns developed for voltage-source rectifiers and inverters in combination with a logic circuit to generate the gating patterns for CSR/Is. The circuit also includes naturally and symmetrically distributed shorting pulses. Thus, the approach avoids the hassle of positioning the shorting pulses and defining and solving a set of nonlinear equations dedicated to CSR/Is. Moreover, the approach can eliminate an even or odd arbitrary number of harmonics (e.g., fundamental current control and elimination of the 5th, 7th, and 11th harmonics). This is an improvement over existing techniques and a new approach to pattern generation. Simulated and experimental results for both static and dynamic operating conditions are presented in order to validate the effectiveness of the approach.

Three-Phase Soft-Switched Current-Source Rectifier Operated in Pulse Width Modulation

Three-phase soft-switched current-source rectifier with two resonant switches, connected to a thyristor bridge in series and in parallel in order to provide zero-voltage switching or zero-current switching, is studied. The arrangement tested, using four insulated-gate bipolar transistors and six thyristors, is implemented to investigate the soft-switching operations under the sinusoidal pulsewidth modulation. The experimental results confirm that AC current can be controlled with a reversible power flow and with a near sinusoidal waveshaping.

Dynamic and steady state analysis of a three phase buck rectifier

Current source rectifiers among other alternatives, offer several advantages over line commutated rectifiers. Advantages include displacement power factor control and reduced line current harmonic distortion. This paper analyzes the current source rectifier (CSR) in transient and steady state, the models are developed in a synchronous reference frame. The load behavior is characterized for two load conditions, resistive load or, in general, increasing current for increasing voltage, and constant output power, decreasing output current for increasing voltage. Constant power operation can occur for a converter system supplying a pulse width modulation (PWM) inverter with high dynamics. Several static converter characteristics such as power factor, real and reactive power are analyzed for both types of load. Transient characteristics are analyzed for both types of load by exact small-signal model with full set of equations.

State variable decoupling and power flow control in PWM current-source rectifiers

Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line-commutated rectifiers as a source of variable DC power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2 kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations.

DSP-based space-vector PWM pattern generators for three-phase current source rectifiers and inverters

Current source converters (rectifiers and inverters) are usually modulated using off-line pattern generators, due to the complex requirements of the switch gating signals. However, on-line patterns (carrier- and space-vector-based) offer a number of control advantages, such as tracking-error minimization, zero steady-state error, and potential implementation of enhanced control strategies. With the capability of microprocessors and digital signal processors (DSPs), digital space-vector modulation offers an interesting alternative to standard carrier-based modulation techniques. This paper addresses practical issues such as switching-frequency minimization, uncharacteristic-harmonic reduction, and delay compensation. Improved space-vector algorithms are derived that (a) reduce switching frequency, (b) improve reference tracking, and (c) reduce harmonic distortion. Experimental results on a 2-kVA current source rectifier are used to validate the proposed algorithms and control techniques.

Current-source converter on-line pattern generator switching frequency minimization

On-line pulsewidth modulation (PWM) pattern generators for current-source rectifiers and inverters offer a number of control advantages over off-line optimized patterns. However, when implemented using the principles which apply to voltage-source inverter PWM pattern generators, the switching frequency is equal to: (1) the carrier frequency in standard carrier-based implementations and (2) a function of the cycle frequency, sequence of space vectors, and selection of the zero space vector in space vector implementations. This paper shows that this frequency can be reduced to one-half of the respective frequencies. Two pattern generators are investigated: (1) an analog on-line carrier-based technique, namely, the modified dead-band technique and (2) a digital on-line space vector-based technique, where advantage is taken of the extra zero state available in current-source converters. It is shown that the switching frequency reduction is achieved with no penalty in the line current harmonic distortion. Moreover, a significant reduction of AC line current distortion is obtained with the modified dead-band technique for modulation indexes greater than 0.4. The principles of operation of the proposed schemes are explained, Experimental results on a 5 kVA current-source rectifier and a 5 kVA current-source inverter confirm the feasibility and features of the proposed pattern generators.

Optimal Control of Sinusoidal Input Current Three Phase PWM Rectifiers.

A new design method based on the linear-quadratic control theory is developed for the control of PWM rectifiers with sinusoidal input current. The PWM rectifiers are promising because they can supply DC power while keeping a sinusoidal AC current with unity in the fundamental power factor. There are two types, a voltage-source rectifier and a current-source rectifier. The former is required to simultaneously control both the fundamental power factor and DC voltage, while the latter does so for both the fundamental power factor and DC current. State feedback control is essentially suited for multi-input and multi-output systems such as those. Here a discrete-time optimal regulator is applied to their control because it provides a microprocessor-based robust feedback system without steady-state errors in response to step reference and/or disturbance change. The regulator is implemented using a digital-signal-processor. Experimental results demonstrate the validity.

Harmonic and interharmonic distortion modeling in multiconverter systems

The problem of modeling multi-power converter systems in presence of harmonic and interharmonic distortion is considered. Specifically, current source rectifiers are considered as distortion sources, some supplying DC motors and the remaining supplying inverters feeding AC machines. The classical analogue, frequency domain and time domain models proposed in the literature to study harmonic distortion in a multi-power converter system are considered and, for each model, suitable extensions to include the interharmonic distortion are presented and critically analysed. The results of several experiments are reported to show the usefulness and to compare the accuracy of the different extensions considered. >

Input Filter Design for PWM Current-Source Rectifiers

Pulse-width modulated (PWM) rectifiers are increasingly used because they allow the elimination of low-order harmonics, and therefore a reduction in input filter components. Filtering requirements for PWM current-source rectifiers are usually satisfied through the use of low-pass LC input filters. This paper offers a systematic and user-friendly approach to choosing the filter components. Design of LC filters involves the positioning of the resonant frequency to meet the harmonic attenuation requirements (THD), and introducing damping at the resonant frequency to avoid amplification of residual harmonics. The problem is further complicated by considerations related to cost, power factor, voltage attenuation, system efficiency, and filter parameter variation. The systematic approach proposed in this paper focuses on PWM rectifiers, but can easily be extended to other classes of converters. Practical design considerations are detailed and design equations derived. Simulated results are presented to validate the design approach

Single-phase step-up/down current-source rectifier with suppressed resonance

The paper presents a novel single-phase, single-way, current-source rectifier. This is based on the cascade combination of a diode bridge rectifier and a current-source Cuk power convertor. The supply current can be sinusoidally waveshaped with suppressed resonance by an appropriate switching strategy, whereas a parallel inductance-capacitance circuit of a conventional form excites the resonant frequency. Furthermore, step-up and step-down characteristics of the output current and near-unity power factor operation can be obtained. To predict steady-state and transient characteristics of the rectifier with a digital PI controller, rigorous and approximate state-space analyses are introduced. The experimental and predicted results confirm the usefulness of the rectifier presented.

Real-time multi-DSP control of three-phase current-source unity power factor PWM rectifier

The design of a real-time multi-DSP controller for a high-quality, six-valve, three-phase, current-source, unity power factor, PWM rectifier is discussed. With the decoupler preprocessor and the dynamic trilogic PWM trigger scheme, each of the three input currents can be controlled independently. Based on the a-b-c frame system control and the fast parallel computer control, the pole placement control method is implemented successfully to achieve fast response in the AC currents. The low frequency resonance in the AC filter LC networks has been damped effectively. The experimental results are obtained from a 1 kVA bipolar transistor current-source PWM rectifier with a real-time controller using three TMS320C25 DSPs. >

Unity PF current-source rectifier based on dynamic trilogic PWM

One remaining step in perfecting the stand-alone, unity power factor, regulated current-source pulse-width-modulated (PWM) rectifier is to reduce cost, by bringing the twelve-valve converter (consisting of three single-phase full bridges that operate with two-level or bilogic PWM) to the six-valve bridge. However, the six-valve topology requires a three-level or trilogic PWM strategy that can handle feedback signals. A general method of translating three-phase biologic PWM signals into three-phase trilogic PWM signals is presented. The method of translation retains the characteristics of the bilogic PWM, including the frequency bandwidth. Experiments show that the trilogic PWM signals produced by the method can handle not only stabilizing feedback signals but also signals for active filtering. >

Three-Phase Step-Up/Down Current-Source Rectifier with Sinusoidal Supply Currents.

This paper presents three-phase current-source rectifier, which is based on the cascade combination of buck-boost and buck DC-DC converters and has the step-up and step-down characteristics of output current, whereas the conventional current-source rectifiers have no step-up characteristics. The introduction of pulsewidth modulation makes it possible to obtain the widely controllable output current and to sinusoidally waveshape the supply currents with a near unity power factor. Three insulated-gate bipolar transistors (IGBTs) provide the necessary control over the currents for unidirectional power flow. To countract the oscillatory transient operations with single-loop output current feedback, the tested system includes the minor loop for the current in flyback inductor. The controllability of the output current is examined for the variation in its reference. The experimental results and state-space simulations for steady-state and transient conditions confirm the relevance of the presented configuration as an useful rectifier with near unity power factor sinusoidal supply currents and satisfactory output current regulation.

Operating limits of the current-regulated delta-modulated current-source PWM rectifier

A stand alone, three-phase, delta-modulated, current-source PWM rectifier has been built and has been shown to be capable of operating with near sinusoidal current waveforms, unity power factor. and good DC current regulation. A mathematical model that has been justified against experimental measurements and results from digital simulations is presented. The current waveform distortion limit and the asymptotic stability limit are established. It is shown that the rectifier can operate safely within these limits in the entire range of its power ratings. >