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The Reference Generation block generates the reference control signal that drives the three-phase two-level grid-forming inverter. The output control signal of the reference generation block can be directly connected to a three-phase two-level inverter if it is modeled as an “average model (Uref-controlled)” inverter. On the contrary, if the inverter is modeled as a “switching devices”, an intermediate Pulse Width Modulation (PWM) block is required. The reference generation block shapes the direct and quadrature axis voltage references, set by the upstream control blocks according to the inverter’s voltage settings (input and output) and chosen modulation index. It also compensates for the voltage angle deviation created due to the mismatch of simulation sample time, set at the ‘Powergui’ block, and the sample time set at the reference generation block.

Mask and Parameters

The following information are required by the configuration mask of the Reference Generation block:

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Description

Reference Generation block conditions the d-q coordinate control signal, generated by the upstream control blocks, according to the nominal Input DC and output AC voltage of the Grid Forming (GFM) inverter and generates the final control signal in ABC coordinates. The block also helps to saturate the peak value of the control signal and correct the phase angle initiated due to the mismatch of simulation sample time, set at the ‘Powergui’ block, and the sample time set at the reference generation block. In addition, the block adjusts the phase angle of the final control signal to keep in synch with the cosine-based Park transformation adopted in the Signal Conditioning block. The work process of the Reference Generation block is given below:

1. Based on the measured DC voltage and nominal AC voltage of the inverter, the modulation index (MI) is calculated.

2. The reference d-q coordinate control signal, received at the input, is updated based on the MI. The calculation is as follows:

3. The amplitude and phase of the per phase voltage reference (x={a,b,c}) is calculated from the updated d-q coordinate reference control signal as follows:

4. The final control signal is generated as follows:

Where,  θ_x is π/2, as cosine-based Park transformation is adopted in the Signal Conditioning block and θ_correction is the correction angle, arising due to the sample time mismatch. 

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