Simulation is an effective method for studying the feasibility and performance of systems, including converter and control algorithms. Using code to realize digital control in simulation tools can be more flexible and similar to using C2000™ control. This application note introduces how to implement a single-phase, off-grid inverter with all digital control in a simulation tool and provides a verification method for off-grid control in the PMP23338 TI reference design. Voltage and current loops with a PI compensator are used in the control algorithm. A true RMS calculation block is configured in the voltage loop as the input sample signal. Totem-pole modulation is used to increase the efficiency of the GaN-based inverter or in power factor correction (PFC) circuits like PMP23338. A detailed implementation and code for each block are included in this application note, and the simulation results verify the correctness of the code and simulation model.
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Inverters are widely used in various applications. For example, solar inverters, uninterruptible power supplies (UPS), and onboard chargers (OBC) utilize an inverter to convert DC power to AC. In these systems, the inverter performance has a significant impact on the performance of the entire system. So, many topologies and control algorithms are proposed and investigated to improve the performance of the inverter. One effective way to preliminarily verify the feasibility and performance of the converter is simulation. Besides, digital control is widely used to control the power stage in realistic situations and code is more flexible than a control block in simulation software. Hence, the purpose of this application note is to introduce the implementation of a single-phase off-grid inverter with digital control, and another purpose is to verify the performance of totem-pole modulation with multiple loop control. In conventional control methods, the input signal of the voltage loop comes directly from the sampling AC voltage in output. But in this application note, the RMS value of the output voltage is used as the reference value in the voltage loop. The benefit of this method is discussed in this note.
The PMP23338 is TI's 3.6kW, single-phase totem-pole bridgeless power factor correction (PFC) circuits reference design with e-meter function. The totem-pole bridgeless structure allows this reference design to support the inverter function. Two active half bridges form this topology: one half bridge works at a low frequency and the other one works at a high frequency.
The high-frequency half bridge in the PMP23338 consists of two LMG3522R030 devices. LMG3522R030 is TI's 650V GaN FET with an integrated driver and protection. Compared with Si FETs, the GaN FETs switching loss is much lower due to the lower COSS. In addition, the unique structure of the GaN FETS brings zero reverse recovery charge, which further improves the performance of GaN FETs at high frequencies.