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.

Review of Three-Phase PWM AC–AC Converter Topologies

Control in Power Electronics : selected problems

As an important renewable energy source, the scale of wind energy utilization is growing rapidly worldwide in recent decades. The increasing capacity of both onshore and offshore wind power generation calls for higher requirements for the power level and reliability of generators and converters. Compared to the traditional three-phase wind power generation, multiphase wind power generation systems have obvious advantages in low-voltage high-power operation, enhanced fault-tolerant ability and increased degrees of control freedom, which help them gaining increasing popularity in modern wind power generation. This paper presents an overview on the multiphase energy conversion of wind power generation and introduces the pertinent technology advances, including the design of multiphase wind turbine generators, multiphase converter topologies, modeling and control of multiphase generators. Besides, this paper offers prospects of novel solutions brought by the redundant control freedom in multiphase system to cope with some difficult technical problems, such as Common-Mode Voltage (CMV) suppression, Low Voltage Ride Through (LVRT), and vibration & noise reduction.

A review of multiphase energy conversion in wind power generation

The matrix converter is a single-stage ac-ac power conversion device without dc-link energy storage elements. Any disturbance in the input voltages will be immediately reflected to the output voltages. In this paper, a modified space vector modulation strategy for matrix converter has been presented under the abnormal input-voltage conditions, in terms of unbalance, nonsinusoid, and surge (sudden rising or sudden dropping). By using the instantaneous magnitude and phase of input-voltage vector to calculate the voltage modulation index and input-current phase angle, this modified modulation strategy can eliminate the influence of the abnormal input voltages on output side without an additional control circuit, and three-phase sinusoidal symmetrical voltages or currents can be obtained under normal and abnormal input-voltage conditions. The performance of the input currents is analyzed when the matrix converter uses different modulation strategies. Some numerical simulations are presented to confirm the analytical results. Tests are carried out on a 5.5-kW matrix converter prototype. Experimental results verify the validity of the proposed strategy.

A Research on Space Vector Modulation Strategy for Matrix Converter Under Abnormal Input-Voltage Conditions

The standalone brushless doubly fed induction generator (BDFIG) has demonstrated excellent energy-saving performance in ship shaft power generation applications. As a standalone system, it exhibits unbalanced terminal voltages and poor performance under unbalanced loads. However, the existing control scheme of grid-connected BDFIGs cannot be directly applied to stabilize the amplitude and frequency of terminal voltage when the rotor speed and electrical load vary. This paper presents a new sensorless control scheme for the standalone BDFIG under unbalanced load conditions in the ship shaft power generation system. A second-order generalized integrator-based quadrature signal generator is introduced to realize the rotor speed observer for the standalone BDFIG feeding unbalanced loads. The compensation method of negative-sequence power winding voltage is proposed to eliminate the negative-sequence component of the unbalanced power winding voltage. Comprehensive experiments are carried out on a prototype BDFIG with and without the compensation of negative-sequence power winding voltage. The good performance of the proposed sensorless control scheme is verified by the experimental test results.

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Sensorless Control of Standalone Brushless Doubly Fed Induction Generator Feeding Unbalanced Loads in a Ship Shaft Power Generation System

In this paper, the transient control algorithm of the reactive current by the line-side converter (LSC) control is proposed when the inductive load is suddenly connected or disconnected from the stator power winding (PW) of the brushless doubly-fed induction generator. In stand-alone operation, the quality of the voltage waveform at the point-of-common coupling (PCC) will be strongly affected due to the reactive power change of load. Moreover, when the amplitude of the PCC voltage is higher than the dc-link voltage, the LSC cannot work normally. To tackle this problem, many control strategies, such as predictive current control, direct voltage control, etc., are usually developed in the machine-side converter to supply the reactive power, but the LSC can also assist in stabilizing the PCC voltage fluctuation by supplying or absorbing reactive current. This paper analyzes the transient state of the load current and the PCC voltage when the load is suddenly connected to the stator PW, and proposes a compensation algorithm which has a good transient-state performance. Then, the controllability of the LSC during the PCC voltage swell is analyzed when the load is disconnected from the stator PW. A high-voltage ride-through control strategy is proposed by using the reactive current of the LSC. The correctness of the proposed method is demonstrated by simulations and experiments.

Transient Control of the Reactive Current for the Line-Side Converter of the Brushless Doubly-Fed Induction Generator in Stand-Alone Operation

Limited by low availability, high price, and poor switching performance of high-voltage power devices, connecting low-voltage devices in series to block much higher voltages is always an option. However, severe voltage unbalance during turn-off transient remains to be solved. Most of the existing methods designed for low-speed silicon (Si) insulated gate bipolar transistor (IGBT) cannot be directly transplanted to the series-connected silicon carbide (SiC) MOSFETs with high switching speed. To maximum the switching performance of SiC MOSFETs, an elegant implementation of adjusting driving signal time delay method is proposed. In addition, a simplified model during drain–source voltage rising transient is discussed to basically reveal features and problems of the series-connected SiC MOSFETs. The factors affecting the appropriate time delay are discussed as well, especially the influence of the load current. The simplified model and the implementation are both verified by experiments. Indeed, the proposed active voltage balancing control works well and has no penalty of sacrificing switching performance of SiC MOSFETs.

An Active Voltage Balancing Control Based on Adjusting Driving Signal Time Delay for Series-Connected SiC MOSFETs

An inductor-capacitor (LC) filter is normally required at the input of the matrix converter, to assist in the commutation of switching devices and to mitigate input current harmonics. However, its presence, in turn, often results in degradation of dynamic performance and instability of the system. This paper gives a simple procedure to select the input filter parameters for the matrix converter and four conventional methods to employ real resistors to damp filter oscillation. Then, an effective damping method is proposed by using a virtual resistor that can be connected in parallel with the filter capacitor. And it only changes the calculation of the modulation index of the space vector modulation strategy for matrix converter. This method is suitable for the microcontroller implementation without sacrificing the power efficiency. Simulation and experiment results are included to verify the proposed method.

Damping of input LC filter resonance based on virtual resistor for matrix converter

SiC power semiconductors are the most promised next-generation power devices due to their high switching speed and low switching losses, which can greatly improve the efficiency of converters. However, accompanying with those advanced characteristics, there exists severe electromagnetic interference problem. And the circuits become much more sensitive to the stray inductances and the stray capacitances. In general, the passive snubber circuit is a simple, robust, and economical way to optimize the switching trajectory of power devices. In this paper, comparisons among three passive snubber circuits used in SiC applications, which are RC snubber, RCD snubber, and clamped RCD snubber respectively, are presented. The characteristics of each snubber circuit are revealed, also with the differences among three passive snubbers being concluded through large amounts of experimental data. The work in this paper contributes to understanding the characteristics of different passive snubbers and choosing a proper passive snubber circuit in actual applications.

Comparative Study of Three Different Passive Snubber Circuits for SiC Power MOSFETs

The zero-vector configurations have great influence on the performance of the practical implemented space vector modulated AC-DC matrix converter (MC). In this paper, the optimized switching pattern that reduces the output inductor current ripple and the narrow pulses is presented. The optimal zero-vector duty cycles for different switching patterns are derived based on the output inductor current ripple analysis. Further considering the commutation, the relationship of the duty cycles and the narrow pulses are discussed, and then the segmental optimized switching pattern is proposed. The proposed method can improve the input/output quality and realize wide-range output regulation. The experimental results verified the conclusions and validate the proposed strategy.

Hua Lin

Papers

Transient Control of the Reactive Current for the Line-Side Converter of the Brushless Doubly-Fed Induction Generator in Stand-Alone Operation

An Active Voltage Balancing Control Based on Adjusting Driving Signal Time Delay for Series-Connected SiC MOSFETs

Damping of input LC filter resonance based on virtual resistor for matrix converter

Comparative Study of Three Different Passive Snubber Circuits for SiC Power MOSFETs

Optimal zero-vector configuration for space vector modulated AC-DC matrix converter