Linear Control Approaches for DC-AC and AC-DC Power Converters
This chapter addresses linear techniques for controlling the average (low-frequency) behavior of power electronic converters that include not only DC but also AC power stages. Without being exhaustive, the chapter focuses on the most-used control methods
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Linear Control Approaches for DC-AC and AC-DC Power Converters
This chapter addresses linear techniques for controlling the average (low-frequency) behavior of power electronic converters that include not only DC but also AC power stages. Without being exhaustive, the chapter focuses on the most-used control methods applied to somewhat popular single-phase and three-phase PWM- or full-wave-operated power electronic converters (mostly voltage source inverters). This chapter deals with control structures designed using both the rotating frame – relying upon dq models developed in Chap. 5 – and the natural AC stationary frame for different grid-connected and stand-alone applications. A case study, a number of examples and a set of problems related to comprehensive applications are also included.
9.1
Introductory Issues
The main control goal of AC-based converters depends on the converter role, specifying how the power is to be conveyed to/from the AC grid. For example, if an AC isolated load needs to be supplied, the output voltage amplitude and frequency must be regulated. On the contrary, if the converter conveys power between DC and AC sources, the DC-side voltage regulation may be the main control goal (see, for example, Sect. 8.3.2 from Chap. 8). As in Chap. 8, all these major goals include specifications that suppose the suitable changing of the converter dynamic behavior in terms of steady-state error, bandwidth and damping. Generally speaking, converter models should be developed according to the stated control goal. As it has been explained in detail in Chap. 5, generalized averaged model (GAM) provides a mean of obtaining large-signal converter models that capture their most significant dynamic features. Further, these models (see, for example, Eq. (5.63) or (5.81)) may be linearized around a typical operating point in order to allow the application of linear control methods. Using phase-locked-loop (PLL)-based synchronization with the AC grid, the dq modeling derived from the GAM performs an amplitude demodulation that S. Bacha et al., Power Electronic Converters Modeling and Control: with Case Studies, 237 Advanced Textbooks in Control and Signal Processing, DOI 10.1007/978-1-4471-5478-5_9, © Springer-Verlag London 2014
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9 Linear Control Approaches for DC-AC and AC-DC Power Converters
transforms the original AC variables into DC variables. This makes possible the application of the methods used for DC-DC converters (already presented in Chap. 8) to converters that have AC stages. Also, this allows the separate control of active and reactive power components exchanged with the AC grid. As in the previous chapter, these methods – such as loop shaping or pole placement – may be applied within a suitable control paradigm. The specific structure of these converters including both DC and AC stages with clearly separable dynamics makes useful the two-loop cascaded control structure presented in Sect. 8.3 of Chap. 8. In this context, the main control goal refers to the slower DC variables and will affec
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