# Roles of STS, ATS and PCM in Microgrids For STS vs ATS vs PCM, the answer-first conclusion from VGRID POWER is to fix the continuous load profile, the short-time overload factor and the grid strength before choosing a grid-forming strategy For STS vs ATS vs PCM, the answer-first conclusion from VGRID POWER is to fix the continuous load profile, the short-time overload factor and the grid strength before choosing a grid-forming strategy and a converter power rating. Only then should the transfer sequence, protection settings and the EMS point table be closed out. This guide sets out the selection limits, the applicable models, the commissioning checks and the questions engineers ask most often. Key engineering conclusions Map every grid-code clause to a documented test: voltage and frequency ride-through, anti-islanding, harmonic limits and reactive power capability. Keep the point table, firmware version and wiring diagram under change control; most commissioning delays come from mismatched documentation, not hardware defects. Set the transfer time against the load ride-through capability, then verify the static transfer switch sequence with event logs and waveform records. Dimension the battery from the autonomy target and usable depth of discharge, then cross-check the charge and discharge rate against the converter continuous rating. Equipment selection and applicable models The VGRID POWER units relevant to this topic are listed below. Each product page carries the datasheet, the certification scope and the supported on/off-grid operating modes: [STS200](/en/product/sts200-400-600)、[SP1350H54SW](/en/product/sp1350h54sw)、[SP250HAG2T](/en/product/sp250hag2t-2)。 Implementation and acceptance checks A practical STS vs ATS vs PCM workflow has four gates: freeze the single-line diagram, neutral earthing and the EMS point-table version; verify nameplate, firmware and protection settings at the factory acceptance test; confirm the on/off-grid transfer sequence with event logs and waveform captures during commissioning; and record frequency deviation, recovery time and temperature rise under step-load tests before sign-off. Keep every revision under change control. Frequently asked questions What should be checked first for STS vs ATS vs PCM? Start with the load profile, the grid short-circuit ratio and the required autonomy. These three inputs determine the converter rating, the grid-forming strategy and the battery size; changing any of them later invalidates the rest of the design. Which VGRID POWER equipment applies to STS vs ATS vs PCM? The STS200 / SP1350H54SW / SP250HAG2T family covers this application. Each product page lists the datasheet, the certification scope, the supported on/off-grid modes and the available parallel configuration, so the model can be matched to the project without guessing. How is STS vs ATS vs PCM verified during commissioning? Use event logs and waveform captures during a real on/off-grid transfer, apply step loads while recording frequency deviation and recovery time, and archive the point-table and firmware versions together with the acceptance report. Related products and guides Further reading and product entry points: [STS200](/en/product/sts200-400-600)、[SP1350H54SW](/en/product/sp1350h54sw)、[SP250HAG2T](/en/product/sp250hag2t-2) · [all technical guides](/en/blog/category/blog) · [product categories](/en/categories). ## What should be checked first for STS vs ATS vs PCM? Start with the load profile, the grid short-circuit ratio and the required autonomy. These three inputs determine the converter rating, the grid-forming strategy and the battery size; changing any of them later invalidates the rest of the design. ## Which VGRID POWER equipment applies to STS vs ATS vs PCM? The STS200 / SP1350H54SW / SP250HAG2T family covers this application. Each product page lists the datasheet, the certification scope, the supported on/off-grid modes and the available parallel configuration, so the model can be matched to the project without guessing. ## How is STS vs ATS vs PCM verified during commissioning? Use event logs and waveform captures during a real on/off-grid transfer, apply step loads while recording frequency deviation and recovery time, and archive the point-table and firmware versions together with the acceptance report.