532 Digital Control Technology

In a typical DG power system, three aspects or layers of control must be considered. The first and most demanding is the "micro" level of control required to manage the switching of the high power transistors in the power electronic converters. This task requires very high-speed real time control, with sampling rates on the order of microseconds.

The second aspect is the "macro" level of control that is required to manage the system at large, i.e., control the power flow among the energy source, energy storage element, and load. The requirements of this particular task are dependent on the specific generation technology, but sampling rates on the order of milliseconds are typically required. State-of-the-art DG power systems use digital controls to perform these functions. The advantages of digital electronics over analog electronics are well understood, including accuracy, flexibility, and repeatability. In addition, the DG industry is taking advantage of the example set by the computer industry: digital data processing results in higher reliability with increasingly lower cost. However, real time digital control systems are extremely complex, and a significant amount of time and resources go into developing the control software for an advanced DG power system.

Figure 5.12 illustrates the basic principle of a digital control system. After removal of unwanted spectral content, an analog-to-digital converter (ADC) is used to sample the physical analog signal of interest. A high-speed digital signal processor (DSP) is used to perform advanced control algorithms using these signals and produce the desired control action. This processing must be accomplished in real time, meaning that the time it takes from the instant the data is sampled to the instant the output is produced must be small compared to the dynamics of the process being controlled. For example, in the control of a DC-to-AC converter, the voltage and current produced by the converter are sampled, and the DSP subsequently computes the required on and off times of the various high power transistors in order to control the energy conversion process. In the case of controlling an MT engine, the exhaust gas temperature may be sampled, and the DSP computes the required fuel flow in order to control the engine.

FIGURE 5.12

Digital signal processing and control.

The third and final aspect of control in a DG system is that of communications to external equipment and the outside world. Advanced DG systems provide a variety of digital communications interfaces so that the system can be remotely monitored and controlled. This capability is required in order to aggregate significant numbers of DG systems into larger power generation systems.

A crucial and often overlooked aspect of DG power system design is that the micro level control over the power electronics, the macro level control over the energy source, and the communications function must all be considered together. This aspect makes the system design very difficult and requires close interaction and cooperation between the designers of the power electronics and the designers of the energy source. When this is done well, a very high performance and highly integrated product results.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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