The Article 29 Data Protection Working Group has published guidlines how and when it is mandatory to do a Data Protection Impact Assessment DPIA.
Data protection impact assessments
Importance of Data Protection Impact Assessment (DPIA) in Europe
How do we complete a data protection impact assessment (DPIA
What is a Privacy Impact Assessment, or PIA, under the GDPR, and
What is a Data Protection Impact Assessment (DPIA)?
PIA Vs DPIA GDPR Privacy Impact Assessment
Data Protection Impact Assessment under the GDPR
The DPIA: How to Identify Risks & Handle Risk Assessments
What Is a DPIA And Why Is It Important? - Tractivity
Data Protection Impact Assessment GDPR Icon. Risk Analysis. GDPR
Best Data Protection Impact Assessment (DPIA)
Guidelines to Data Protection Impact Assessment