Modulation Strategies For Matrix Converters Research Articles

The Conceptual Research over Low-Switching Modulation Strategy for Matrix Converters with the Coupled Reactors

In this paper, different Pulse Width Modulation (PWM) strategies for operating with a low-switching frequency, a topology that combines Conventional Matrix Converters (CMCs), and Coupled Reactors (CRs) are presented and discussed. The principles of the proposed strategies are first discussed by a conceptual analysis and later validated by simulation. The paper shows how the combination of CMCs and CRs could be of special interest for sharing the current among these converters’ modules, being possible to scale this solution to be a modular system. Therefore, the use of coupled reactors allows one to implement phase shifters that give the solution the ability to generate a stair-case load voltage with the desired power quality even the matrix converters are operated with a low-switching frequency close to the grid frequency. The papers also address how the volume and weight of the coupled reactors decrease with the growth of the fundamental output frequency, making this solution especially appropriate for high power applications that are supplied at high AC frequencies (for example, in airport terminals, where a supply of 400 Hz is required).

An Overmodulation Strategy for Matrix Converter Under Unbalanced Input Voltages

In this article, an improved space vector pulsewidth modulation strategy for matrix converter is proposed under unbalanced input voltages. First, to obtain the higher output voltage, two novel space vector pulsewidth modulation strategies based on the linear superimposition principle are presented by modifying the magnitude of the reference output voltage and the reference input current vectors. Second, in order to evaluate the performance of the proposed strategy, the harmonic characteristics of the input currents and output voltages are quantitatively analyzed by employing the double Fourier integral transform method. The novelty of this article lies not only in the modification of a conventional space vector pulsewidth modulation strategy for a higher output voltage under unbalanced input voltages, but also in a quantitative analysis that accurately evaluates the overmodulation performance with input unbalance using the double Fourier integral transform approach. Finally, the performance of the proposed strategy and the correctness of the harmonic analysis method are verified by the comprehensive simulation and experimental results for matrix converters.

Investigation of The impact of Unbalanced and Non-sinusoidal Supply Voltages on Converters.

In this paper two input current modulation strategies for matrix converters are experimentally analyzed under two different supply conditions: sinusoidal unbalanced voltages and non-sinusoidal balanced voltages. Both strategies use the Space Vector Modulation (SVM) technique in order to control the matrix converter accordingly to the input and output constraints. Strategy A modulates the input currents keeping the corresponding space vector in phase with the input voltage vector. Strategy B operates in order to keep the input current vector in phase with the positive sequence fundamental component of the input voltage vector. A comparison between the two strategies is made in terms of the reduction of the input current disturbances due to the unbalanced and non sinusoidal voltage on the grid. It is found that a dynamic current modulation strategy, independent of the voltage disturbances such as Strategy B, is more effective for the reduction of the RMS value of input current disturbances. The validity of the theoretical investigation i.e. the effectiveness of the current modulation strategy conforms to experimental tests result carried out on a matrix converter prototype.

Development of generalised relationship between active and rotating vectors in matrix converters

In the past, rotating vectors were not commonly used in most modulation strategies for matrix converters (MCs) because their angular positions always change over time, making it difficult to create a repetitive switching pattern. To make them easier to use, the relationship between active vectors and rotating vectors was analysed regarding the output voltage and input current, which are the main objectives of the MC-modulation strategy. Based on a theoretical analysis, an active vector is equivalently replaced with a set of rotating vectors. The proposed idea to apply the rotating vectors was evaluated with the conventional space vector modulation method and showed good input/output waveforms and zero common-mode voltage.

Research on Matrix Converter Based on Space Vector Modulation

In this study, we study the control strategy for matrix converter. Through absorbing ideas about virtual rectification put forward by P.D.Ziogas, the common control idea of AC-DC-AC convertor is introduced into control of matrix converter; SPWM modulation strategy and space vector modulation strategy for matrix converter are studied respectively. In terms of SPWM modulation strategy, it has some advantages: for example, main circuit structure is simple; control program is simple; control switch function does not need complex mathematical derivation and calculation. In terms of space vector modulation strategy, it has advantages as follows: the physical conception is clear; input power factor can be adjusted; output voltage and current sine degree are high. In this chapter, an in-depth analysis will be conducted for this control method.

Modulation strategies based on mathematical construction method for matrix converter under unbalanced input voltages

Owing to the direct coupling between the input and output of matrix converter, the abnormal power supply could disturb the output voltage easily. In this study, three modulation strategies for matrix converter based on mathematical construction are proposed under unbalanced input voltage conditions. The strategies are developed based on the construction of the rectifier and inverter modulation vectors in three different ways. By regulating appropriately the modulation index of inverter vector, the output voltages of matrix converter can maintain sinusoidal and balanced. The different rectifier vectors result in different input currents. Moreover, the analytical solutions for input currents with the three methods are presented, and the approximated solutions are derived to estimate their low-order spectrums. Comprehensive comparisons among the three methods are made in the aspects of the complexity of realisation, voltage-transfer capability and input current quality. Simulation and experimental results verify the correctness and effectiveness of the proposed methods.

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

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.

DFIG Wind Power System with a DDPWM Controlled Matrix Converter

This paper proposes a new doubly-fed induction generator (DFIG) system using a matrix converter controlled by direct duty ratio pulse-width modulation (DDPWM) scheme. DDPWM is a recently proposed carrier based modulation strategy for matrix converters which employs a triangular carrier and voltage references in a voltage source inverter. By using DDPWM, the matrix converter can directly and effectively generate rotor voltages following the voltage references within the closed control loop. The operation of the proposed DFIG system was verified through computer simulation and experimental works with a hardware simulator of a wind power turbine, which was built using a motor-generator set with vector drive. The simulation and experimental results confirm that a matrix converter with a DDPWM modulation scheme can be effectively applied for a DFIG wind power system.

New Time-Discrete Modulation Scheme for Matrix Converters

While the known modulation strategies for matrix converters are based on pulsewidth modulation (PWM)-or vector modulation-this paper presents a novel time-discrete modulation method based on real-time prediction calculation to select the switching states. The decision about which switching state is to be set for the following sampling period is made by the use of a predictive quality function. Using this approach, unity displacement factor is seen at the supply side with minimum line current distortion while the load currents follow their reference values with good accuracy. The quality function is derived from a mathematical model of the matrix converter and the controlled system. Measurements taken on a model plant, consisting of a matrix converter and a standard induction machine with a rated output power of 11 kW, show that the matrix converter, equipped with the control method presented here, offers advantages over systems with conventional frequency converters, especially in terms of the input current distortion.

Comparison of two current modulation strategies for matrix converters under unbalanced input voltage conditions

In this paper, the input current performance of matrix converters is analyzed, especially with reference to the operating conditions determined by unbalanced supply voltages. The space-vector modulation (SVM) technique is utilized to calculate the duty cycles of the active voltage vectors that must be applied, in each switching cycle period, in order to satisfy the input and output requirements. A detailed theoretical analysis of the input current harmonic content under unbalanced input voltage conditions is presented for two different current modulation strategies. On the basis of numerical simulations as well as measurements on a laboratory prototype setup, the strategies' performance are compared and the validity of the theoretical investigation confirmed. It is concluded that, when the input voltages are unbalanced to a significant extent, a dynamic input current modulation strategy has to be preferred, since a lower harmonic line current distortion will appear.