The development of high-processing-capability microprocessors allows the implementation of new digital control methods for neutral-point-clamped (NPC) multilevel converter in power-electronic applications. This paper presents a new predictive digital control method for multilevel converters, called “fast predictive.” This method computes the optimal vector using the NPC three-phase multilevel dynamic model equations just once in each control cycle, while current predictive methods need 27 calculations. The closest vector to the optimal vector is found by minimizing the distance between each one of the 27 available vectors to the optimal vector. Space vector modulation could be also used. The obtained performance is similar to the predictive optimal control that uses the converter model to find all the 27 responses of the multilevel and then searches for the vector that minimizes control errors. Relative to predictive optimal control, the fast predictive improves digital processing speed by at least 150% in multilevel converters with 27 vectors. This speed improvement would allow multilevel converters with five or higher number of levels (125 instead of 27 vectors) to be controlled using the same sampling frequency of the three-level inverter. The fast-predictive controller is used in a multilevel rectifier with near-unity power factor to enforce the ac currents. Fast predictive control is also used in the rectifier dc voltage to reduce sensitivity of the dc voltage to dc load disturbances. The simulation and experimental results show that the fast-predictive controller is able to control the ac currents of a three-phase multilevel rectifier, achieving nearly 1.5% total harmonic distortion while balancing the capacitors' dc voltages. The use of predictive control to regulate the dc voltage shows an improvement of approximately 7% compared to a proportional-integral controller.

Most fuel cell electric vehicles (FCEV) require wide voltage-gain DC DC converters to increase and equalize the relatively low voltage of fuel cell stacks with DC link bus or energy storage devices (ESD), such as supercapacitors or batteries. This paper proposes two new non-isolated DC-DC converters suitable for such applications, which can be extended to other electric vehicles as well. The proposed converters combine the main characteristics of both quadratic Boost and Ćuk converters, offering high step up voltage and control simplicity using only one ground referenced active power switch. Additionally, the proposed topologies present reduced voltage stress across the active power switch when compared to other Boost converters. Considerations about the design of the proposed converters will also be presented. Experimental results obtained using a laboratory prototype validate the effectiveness and feasibility of the proposed topologies and its suitability for fuel cell electric vehicles.

This paper presents the optimal control of the AC currents, the DC voltage regulation, and the DC capacitor voltage balancing in a three-level three-phase neutral point clamped multilevel converter for use in power quality applications as an active power filter. The AC output currents and the DC capacitor voltages are sampled and predicted for the next sampling time using linearized models and considering all the 27 output voltage vectors. A suitable quadratic weighed cost function is used to choose the voltage vector that minimizes the AC current tracking errors, the DC voltage steady-state error, and the input DC capacitor voltage unbalancing. The obtained experimental results show that the output AC currents track their references showing small ripple, a total harmonic distortion (THD) of less than 1%, harmonic contents that are 46 dB below the fundamental, and almost no steady-state error (0.3%). The capacitor voltages are balanced within 0.05%, and the balancing is assured even when redundant vectors are not chosen. Near-perfect capacitor DC voltage balancing is obtained while reducing current harmonic distortion. Some experimental evidence of robustness concerning a parameter variation was also found, with the optimum controller withstanding parameter deviations from +100% to -50%. Compared to a robust sliding mode controller, the optimal controller can reduce the THD of the AC currents or reduce the switching frequency at the same THD, being a suitable controller for power quality in medium-voltage applications.

This paper presents an optimal predictive controller for a multilevel converter-based dynamic voltage restorer (DVR), which is able to improve the voltage quality of sensitive loads connected to the electrical power network. The optimal predictive controlled multilevel DVR can restore sags and short interruptions while reducing the total harmonic distortion (THD) of the ac line voltages to values lower than 1%. The DVR is based on a three-phase neutral point clamped converter to dynamically inject a compensation voltage vector in series with the line voltage, through series-connected transformer secondary windings. To assure high-quality voltages for sensitive loads, we devise optimal predictive control laws for the injected compensation ac voltages. A suitable quadratic weighed cost functional is used to choose the voltage vector, minimizing both the ac voltage errors through current injection and the dc side capacitor voltage unbalancing. The performance of the proposed predictive controller is compared to classical proportional integral (PI): synchronous frame and stationary frame (P+resonant) controllers. The line-side filter capacitor topology is compared to the regular converter-side filter capacitor. Obtained experimental results show that the ac voltages are almost sinusoidal in steady-state operation when facing balanced and unbalanced sags and short interruptions with unbalanced loads. Voltage THD is reduced to values lower than 1%; the DVR is behaving also as a series active power filter for the ac voltages.

A robust sliding-mode controller, suitable for the output voltage control of voltage-sourced unity-power-factor three-phase pulsewidth modulation (PWM) rectifiers, presenting no steady-state errors, is described. This "just-in-time" switching controller controls the output voltage and the line input currents, while providing bidirectional power flow, near-unity-power-factor operation, low harmonic content, fast dynamic response of the output voltage, and minimum switching frequency due to a new /spl alpha/-/spl beta/ space-vector current regulator. The voltage controller performance is compared with the behavior of the conventional proportional integral output voltage control, aided by PWM current-mode modulators, and with the nonrobust fast and slow manifold sliding-mode approach. The comparison shows that the proposed controller confers faster dynamics and does not present steady-state errors. Test results confirm that the performance of the controller is independent of system parameters and load and exceeds the performance of existing hysteretic current-mode control systems.

The analysis of a solid-state Marx modulator (S²M²) topology, which have been developed for repetitive high-voltage (in kilovolts) applications, needing positive or negative rectangular pulses, is presented. The proposed topology benefits from the intensive use of semiconductors, allowing kilohertz operation with different load conditions. In addition to resistive loads, capacitive loads can be discharged to ground after each pulse and inductive loads can be clamped and the energy recovered to the main capacitors. Furthermore, the presented topology and proposed switching sequence enables the use of typical half-bridge semiconductor structures currently integrated in modular packages, which is advantageous for circuit assembling and triggering the semiconductors. Discussion on the advantages and limitation will be given. Finally, experimental results of some modulator features will be presented.