Place the chicken wings, vegetables, salt, and black peppercorns in a 7-quart pressure cooker. Pour in enough water just to cover everything. Do not fill above the cooker's "maximum fill" line, or 2/3 full. Cover and lock the lid. Bring to pressure over high heat, about 20 minutes. Reduce the heat to low, so that you barely hear hissing from the pot. Cook for 40 minutes.
Release the pressure using the cooker's release device (read the manual), or cool the cooker by running cold water over the lid for 30 seconds. Open carefully.
Set a cheesecloth-lined colander in a large bowl or container and strain the broth. Discard the solids. Refrigerate the stock overnight, or until the fat solidifies. Remove the fat. Store in an airtight container in the refrigerator for up to 3 days, or freeze for up to 6 months.