Homero Miranda

A hybrid multilevel inverter for shunt active filter using space-vector control

In this paper, a current active power filter using a hybrid asymmetric multilevel inverter is presented and analyzed. The control proposed is based on a vector-control technique, generating an optimized switching pattern. The hybrid multilevel inverter increases the voltage levels number, reducing the harmonics associated to the commutation frequency. The hybrid multilevel inverter is structured by two cascaded-inverters, and the DC link voltage between the stages has the relation 1:3, generating 9 voltage levels. The signal reference is generated using a variant of the single-phase d-q Theory, allowing a fast transient response and stability. Simulated waveforms prove the viability of the control scheme and the multilevel active current filter proposed.

Compensation of voltage sags and swells using a single-phase AC-AC converter

In this paper, a topology to compensate voltage sags and swells simultaneously in critical loads is proposed. It consists in a single-phase AC-AC converter in a matrix arrangement, which keeps a continuous regulation in the output voltage. The proposed scheme has the capability to compensate up to 25% voltage sags and 50% voltage swells. The AC-AC converter does not require energy storage devices and it is connected between the AC mains and the load by using a series transformer. One of the advantages of this topology is that taps for the coupling transformer are no necessary to change the polarity of the compensation voltage. A four step switching technique is used to drive the AC-AC converter switches, executing snubberless operation. The reference signal is generated using single-phase d-q theory, obtaining a fast response time and high regulation. Simulation and experimental results of a 5 kW capacity, 127 V, 60 Hz equipment are presented.

Improving power flow in transformers using a BTB converter to balance low voltage feeders

This paper proposes a method to balance the power of transformers in low voltage distribution by using the Back-to-Back (BTB) converter. Through the exchange of active power and the compensation of reactive power between feeders, the overloading of transformers is avoided. In the proposed method, the load is considered as a variable that is constantly changing. The control structure is designed in the dq frame of reference and classical theory is employed. A test system composed by two 50kVA transformers supplying several loads is used to validate the efficacy of the method. For simulations a 30kVA BTB converter is used, and for experimental results a 10:1 BTB converter is implemented.

DC-bus voltage regulation scheme for asymmetric cascade H-bridge converter working as STATCOM and active filter

This paper presents how through a suitable DC link regulation strategy, the asymmetric cascade H-bridge converter can perform STATCOM and active filter functions simultaneously. Initially DC link regulation strategy for a STATCOM function is developed, and then an adaptation of the strategy is presented in order to show the device works as an active filter. A two cells binary prototype is used to evaluate the control scheme performance through simulation and experimental results.

Multilevel Cascade Inverter with Voltage and Current Output Regulated Using a Passivity - Based Controller

This paper presents a cascaded five-level inverter DC separated sources and output LC filter. The objective is to propose and develop a passivity-based controller (PBC) and empathize its advantages when is applied in multilevel inverters, especially in cascaded multi-cell power converters (inverter/rectifier). The focus of the developed PBC, is that the inductor current and/or the voltage capacitor tracks a desired reference, in order to use the multilevel inverter as a power line conditioner. Explanation of power stage, model and control design are developed in this paper. Simulation and experimental results are shown in order to validate the theoretical analysis and demonstrate the effectiveness of the PBC

Generalized DC voltage regulation strategy for η:1 relation cascade H-bridge converter-based STATCOM

This paper presents a generalized DC voltage regulation strategy, for both symmetric (η=1) and asymmetric (η=2,3) multilevel converters used in a static VAR compensator. The objective is to keep regulated the DC links and the reactive power compensation. The strategy is applied to a single phase converter with a combination of staircase and PWM technique. Simulation results on PSIM are presented showing a good performance of proposed control strategy.

On the Passivity-based Control for Multilevel Inverters

In this paper the problem of reducing the total harmonic distortion (THD) with fast transient response of buck-type multilevel power inverters is approached from a control point of view. The main contribution is the proposition of a control law that, considering a standard circuit topology driven by an also standard switching policy of the PWM type, solves the output voltage tracking control problem with remarkable THD low levels and very fast transient response. The proposed controller is designed exploiting the dissipation (passivity) properties of the (approximated) averaged model of the circuit while its evaluation is carried out in an experimental setting with the objective to examine its robustness properties with respect load uncertainty and dynamic transient response. The experiments were carried out considering both linear and nonlinear loads

Gain scheduling scheme assisting the control strategy for three-level NPC VSC-HVDC transmission system

In this paper a gain scheduling control scheme is presented for a three-level three-phase voltage source converter for high-voltage direct-current transmission system (VSC-HVDC), based on two neutral point clamped (NPC) converters in Back-to-Back configuration. The proposed model in dq0 is developed in detail and it has the advantage over other solutions of facilitating the mathematical analysis. Then a direct power control for the entire VSC-HVDC system, based on the dq0 model, is proposed where the control tasks are assign as follow: one NPC-VSC controls the active power flow, the other one regulates the dc voltage level, both converters have the capability to control the flow of active power. Additionally, a closed loop to minimize the voltage imbalance is defined and placed at each NPC-VSC in order to mitigate the imbalance at both system sides in a independently way. After that, a gain scheduling scheme is presented which has the ability to well assign new compensator tuning parameters considering system states as scheduling variables, solving an important neutral point clamped topology weakness. Finally, in order to test the control performance, a detailed computer simulation is implemented in PSCAD/EMTDC software.

A three-phase back-to-back converter for reactive power compensation, current harmonic filtering and active power compensation

This paper presents how a three-phase BTB converter is actively controlled to operate as a power compensator and a harmonic current filter, simultaneously. The main goal of the proposed control scheme is to analyze the current injected by the BTB converter at the PCC using three components. These components are used to compensate: the active power, the reactive power and the current harmonics. The current components of nonlinear loads are obtained and incorporated to the current controllers in order to achieve the filtering function. For the analysis, the active power compensation is a priority and it is accomplished. A 30 kVA BTB converter is used for simulations. Experimental tests were carried out with a 3 kVA prototype.

Real-time emulator of an induction motor: FPGA-based implementation

This paper presents an educational tool based on a novel approach to develop an FPGA-based real-time emulator of an induction motor using the dynamic model. The method exploits the parallelism and high speed characteristics of the FPGA. Different fixed-point representation of the external and internal signal is used. The emulator architecture is presented as well as peripheral units implemented along with the main unit. The real-time emulator is evaluated by experimentation under start-up and varaible load torque conditions. This emulator is the based to implement algorithms like speed and flux estimators, i. e. Extended Kalman Filter, Luenberguer-like observer, etc., and several control schemes like Direct Torque Control, Field-Oriented Control, etc. for induction motors.