This is a highly specific and critical question, as power plant automation demands extreme reliability, safety, and specialized functionality. The choice amongYokogawa, Ovation (Emerson), and HollySysis not just about hardware; it's about selecting an ecosystem and a long-term partner for a mission-critical asset.

Here’s a detailed, professional comparison tailored for power plant automation.
Critical Comparison for Power Plant Applications

A. Technical & Functional Merit
Yokogawa (CENTUM VP / ProSafe-RS):
Strengths: Exceptional loop control stability and instrument health management. Their DNA for regulatory control is top-tier. Strong in heat balance and plant efficiency calculations. Integrated safety system (ProSafe-RS) is robust.
Best For: Plants where process optimization, fuel flexibility, and long-term operational precision are paramount (e.g., ultra-supercritical plants, biomass/waste-to-energy).

Emerson Ovation:
Strengths: Unmatched power-specific libraries: Embedded algorithms for turbine stress calculation, sootblowing optimization, SCR/SNCR control, and grid frequency response. Turbine Interface (Mark™ VIe integration) is seamless. Cybersecurity is designed per NERC CIP standards.
Best For: Greenfield fossil/combined-cycle plants and major retrofits in markets where it's the established standard. It is the "safest choice" for operators familiar with its ecosystem.

HollySys (HOLLiAS MACS / SMP):
Strengths: High redundancy and availability at a lower hardware cost. Strong localization (Chinese language, standards, interfaces). Increasingly competent in APC (Advanced Process Control) applications. Their Nuclear DCS (FirmSys) is certified and widely deployed in China.
Best For: Cost-sensitive projects (especially in Asia, Africa, Middle East), EPC contracts where budget is a primary driver, and markets where Chinese financing/influence is significant.

B. Commercial & Strategic Considerations
Cost Structure: HollySys typically offers the most competitive initial capital cost. Yokogawa and Ovation are premium-priced, with their cost justified in long-term reliability, efficiency gains, and support.

Total Cost of Ownership (TCO): Consider:
Ovation may have higher spare parts costs but vast global spare pools and third-party support.
Yokogawa's legendary durability can lower lifecycle costs.
HollySys requires careful evaluation of long-term support costs outside its home region.

Local Support & Ecosystem:
In North America, Europe, Middle East: Ovation has the deepest network of power-plant-specific engineers and service centers.
In Asia (especially SE Asia), Japan, India: Yokogawa has a formidable, long-standing pesence.
In China, Pakistan, Saudi Arabia, and Africa: HollySys has massive, rapidly growing local teams and partnerships.

C. Future-Readiness & Digitalization
Yokogawa:Heavily promotes its "Synaptic Business Automation" concept, with strong IIoT platforms (GA10, SensPlus) and AI/ML partnerships for predictive maintenance.

Emerson Ovation:Deeply integrated with Emerson's Plantweb™ Digital Ecosystem for asset performance management and operational certainty. Its Renewable Suite for solar and wind is strong.

HollySys:Aggressively developing its Industrial IoT platform (HiaCloud) and smart solutions. Their pace of digital feature development is rapid, though sometimes perceived as less mature than Western counterparts.

Decision-Making Matrix: Which is "Best"?
ChooseEmerson Ovationif:
You are building a large, baseload fossil-fuel or combined-cycle plant in North America, Europe, or the Middle East.
Grid compliance, turbine coordination, and operator familiarity are critical decision factors.
You prioritize a low-perceived-risk vendor with an unquestioned power-gen pedigree.

ChooseYokogawaif:
Your plant has complex, process-oriented challenges (e.g., multi-fuel firing, stringent emissions control, integration with desalination).
Long-term instrument and valve health, and overall plant efficiency (heat rate) are the top KPIs.
You value a vendor with a balanced excellence across power and broader process industries.

ChooseHollySysif:
Project capital cost is the primary constraint, but you still require a full-featured, high-availability DCS.
The project is in a region where Chinese technology partnerships, financing, or EPC firms are leading.
You are comfortable with a rapidly evolving, ambitious vendor and have assessed their local support capability as adequate for the plant's lifecycle.

Final Professional Advice
Benchmark the "Soft" Factors: For a power plant, the quality of 24/7 emergency support, training for your engineers, and cybersecurity update policies are as important as the hardware spec sheet.

Conduct a Feature "Bake-Off": Present a challenging, real-world scenario from your plant (e.g., managing a fast load ramp while controlling NOx emissions) and have each vendor demonstrate their solution in a simulation environment.