Raúl González-Medina

Measurement of the Loop Gain Frequency Response of Digitally Controlled Power Converters

The study of the loop gain frequency response in a power converter is a powerful tool commonly used for the design of the controllers used in the control stage. As the control of medium- and high-power electronic converters is usually performed digitally, it is useful to find a method to measure the digital loop gains. The purpose of this paper is to present a method for properly measuring the loop gain frequency response of digitally controlled power converters by means of an analog frequency response analyzer (FRA). An analog sinusoidal reference signal generated by the FRA is injected through an analog-to-digital converter into the digital controller, and added to the discrete feedback signal. To obtain the frequency response of the open-loop gain, both feedback and disturbed feedback signals are sent back to the FRA by using the pulsewidth modulation peripherals of the controller.

Dynamic modeling of DC–DC converters with peak current control in double-stage photovoltaic grid-connected inverters

In photovoltaic (PV) double-stage grid-connected inverters a high-frequency DC–DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC–DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC–DC converter is regulated by the grid-connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small-signal model of the DC–DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230 W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC–DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full-bridge single-phase inverter. The time response of the whole system (DC–DC + inverter) is also shown to validate the concept. Copyright

Dynamic modeling of a dual active bridge DC to DC converter with average current control and load-current feed-forward

This work was supported by the Spanish Ministry of Economy and Competitiveness under grant ENE2012-37667-C02-01.

Synchronization of Power Inverters in Islanded Microgrids Using an FM-Modulated Signal

A microgrid can operate in island mode, isolated from the main grid during certain time intervals. When operated in island mode, the electronic converters of the microgrid must keep the voltage and frequency of the microgrid inside the desired range. The converters of a microgrid can be classified into three groups: 1) grid-feeding; 2) grid-supporting; and 3) grid-forming power converters. The grid-forming converters operate as a voltage source, and require an external synchronization signal provided by the microgrid central controller. Both the noise and the delay in the synchronization signals received by the grid-forming converters are critical issues, which deteriorate the quality of the microgrid voltage and may overload those converters. The synchronization signals must be robust and suitable for operating in noisy environments. In this paper, the synchronization signal is frequency-modulated to be transmitted, being robust against noise. The transmission is done through an industrial RS-485 line with a low delay. The demodulation is performed with a low computational load by the control processors of the grid-forming power converters.

Peer-to-peer decentralized control structure for real time monitoring and control of microgrids

In order to integrate a large number of distributed energy resources in distribution grids a robust decentralized information and communication control structure is required. This paper proposes an overlay peer-to-peer (P2P) architecture for controlling and monitoring microgrids in real time, which has a great capacity of adaptation to the demanding network requirements of these environments. The proposed concept has been implemented and experimentally tested on a microgrid. Real data analysis demonstrates that the system meets with the network performance parameters proposed for microgrids, such as latency and bandwidth, showing that peer-to-peer overlay networks are useful for energy grids in practice.

Comparison and combination of digital controls for single-phase boost PFC converters in avionic power systems

Achieving a low harmonic current distortion (THDi) along with a unit power factor (PF) in single-phase boost AC-DC converters with power factor correction (PFC) using classical controls requires a high current control bandwidth, which usually implies a high switching frequency, yielding high switching losses. This is a major problem in applications with a high value of the grid frequency, e.g., avionic power systems with a line frequency up to 800 Hz. Over the years, several control techniques have been proposed to improve the shape of the line current without increasing the switching frequency of the converter. This paper studies the viability of adding adaptive filters based on the second order generalized integrator (SOGI) structure in the current loop to maintain a switching frequency lower than 100 kHz with the same purpose. A notch filter based on SOGIs is also applied to the output voltage regulation loop in this study, in order to increase its regulation speed without degrading the reference current waveform, which would distort the line current. A comparison between the method based on SOGI filters and other control methods is shown. Finally, the combination of several methods is studied. Simulation results have been obtained by means of PSIM™ software.