Energy Storage | The Four Major Sects of PCS: Centralized, String, Distributed, and High-Voltage Cascade Systems in a Debate

In the world of energy storage, the PCS (Power Conversion System) is the key core. While all systems convert DC power from batteries into AC power usable by the grid, different approaches employ completely different methods.

Currently, the industry mainstream has formed four major schools: centralized, string, distributed, and high-voltage cascaded. Each school has its own standing, clear advantages, and disadvantages. With the explosive growth of industrial and commercial energy storage, distribution network energy storage, and grid-side energy storage, various technological routes are undergoing a new round of reshuffling. This article attempts to explain from an industry perspective why each school exists, which scenarios it is applicable to, and which typical manufacturers are behind it.

Centralized energy storage: Each device has a large capacity, with cells packaged into large battery clusters. All clusters are connected to a large PCS (Power Generation System), and then stepped up by a transformer before being fed into the grid. From megawatt-level grid-side energy storage to wind and solar infrastructure-based energy storage, this is the most mature, cheapest, and most standardized approach.

▌Technical Characteristics: Large and stable, simple and robust. Pack → Battery cluster (series) → Multiple clusters (DC parallel) → One large PCS. The control chain is simple, facilitating centralized scheduling; the larger the scale, the lower the cost.

▌Representative Companies (Partial List): Sungrow Power Supply (global leader in centralized systems, extremely high overseas market share); Kehua Data (significant advantages in centralized systems, also exploring other routes); Haibo Sicheng (numerous centralized projects, rapid overseas expansion); NARI Group, XJ Electric (traditional forces in the grid side); CELONG Electronics, Easun Group, CATL (some centralized system solutions); etc.

▌Advantages at a Glance:
1. Lowest cost, simple structure, fewer devices, optimal system integration cost.
2. Large-scale dispatch friendly: suitable for grid-level peak shaving and valley filling.
3. Mature project management: clear delivery logic, stable operation and maintenance methods.

▌Typical Weaknesses
1. Severe “weakest link” effect: Lifespan is determined by the weakest cell.
2. DC parallel connection introduces circulating current risk: Inconsistent battery health can easily lead to inter-cluster circulating current.
3. High safety pressure: Poor consistency increases the risk of overcharging and overheating.

▌Route Positioning
Large-scale grid-scale energy storage will remain the mainstay for a long time, but it will be surrounded by “enhanced” routes.

As energy storage applications expand to industrial and commercial sectors, distributed systems, and substations, centralized systems with their large-scale deployments are clearly too cumbersome. The string storage approach addresses this by giving each battery cluster its own “brain” (independent control unit), enabling “one cluster, one management.”

▌Technological Characteristics: Flexible, precise, and modular. Multiple independent energy storage clusters are connected in series or parallel, each with independent control, measurement, and protection capabilities, resulting in high overall efficiency in distributed scenarios.

▌Representative Companies (Partial List): Huawei (the most representative global company in string energy storage), BYD (widely used in industrial and commercial solutions), Sungrow Power (also deploying string energy storage in industrial and commercial applications), Goodwe, Ginlong Technologies, Shenghong Energy, Sungrow Power Supply (a core player in residential and industrial/commercial energy storage), Chint Power, KSTAR, Deye Energy, etc. TAICO (a leading domestic provider of mature industrial and commercial energy storage solutions).

▌Advantages at a Glance
1. Superior Battery Consistency: Each cluster operates independently, without hindering each other’s performance.
2. High Reliability: Single-cluster failures can be isolated, without affecting overall power supply.
3. Easier Maintenance: Faulty clusters can be precisely located; modules are hot-swappable.
4. Enhanced Safety: No DC circulating current between clusters.

▌Typical Shortcomings
1. Slightly higher system cost: Increased number of controllers and sensors.
2. Increased integration complexity: More complex debugging and inter-cabinet coordination.

▌Road Positioning
The main technology roadmap for commercial and industrial energy storage, distribution area energy storage, and zero-carbon industrial parks, offering the most sustainable future scale.

Distributed systems are a relatively new approach that has emerged in recent years. Building upon centralized systems, a DC/DC “isolated diode” is added before each battery cluster. It falls between centralized and string systems: it has fewer independent PCS than string systems and avoids the risks associated with DC parallel connections in centralized systems.

▌Technological Characteristics: Safer, More Stable, More Complex. Battery Cluster → DC/DC → DC Bus → PCS → AC, with the DC/DC converter responsible for buck-boost, isolation, and current control.

▌Representative Companies (Partial List):
Sungrow Power Supply (extensively used in high-end projects, multiple technology routes coexist); NARI Group Corporation, XJ Electric Corporation (distributed architecture deployed in large-scale energy storage projects); Kehua Data, Shenghong Energy, Sungrow Power Supply (also has distributed product lines); CATL, BYD (distributed DC/DC architecture used in large sites); Penghui Energy, Pylontech (DC/DC + PCS in system solutions); TAICO, etc.

▌Advantages at a Glance:
1. Completely avoids circulating current problems: parallel connection after each cluster voltage is consistent.
2. Precise control of charging and discharging: extends battery life and enhances safety.
3. Suitable for medium to large-scale energy storage: technically more stable than string systems and safer than centralized systems.

▌Typical Disadvantages:
1. Multi-stage conversion leads to efficiency reduction: DC/DC + PCS, two energy conversions.
2. High system debugging requirements: difficult coordination of multi-stage equipment.
3. Overall cost is higher than centralized systems.

▌Route Positioning:
Large-scale energy storage with enhanced security; future penetration rate will continue to rise.

High-voltage cascading is the most revolutionary aspect of the PCS technology roadmap: it allows multiple energy storage units (with H-bridges) to be directly connected in series, forming a 6kV/10kV/35kV high-voltage output without the need for a step-up transformer. This is a multi-level topology for energy storage, similar to a high-voltage direct-drive frequency converter.

▌Technical Characteristics: High voltage, high power, and extremely high engineering requirements. Each energy storage unit contains a small battery stack and an H-bridge. After series connection, it directly outputs high-voltage AC, with built-in redundancy, low harmonics, and no transformer required.

▌Representative Companies (Partial List): Zhiguang Energy Storage (one of the most active companies promoting high-voltage cascaded PCS in recent years); Invt, Sungrow Power, XJ Electric, and NARI Group (all possess high-voltage multilevel technology reserves); Sungrow Power Supply (some sites use high-voltage multilevel topology); Hitachi, Eaton, and Siemens (strong overseas multilevel topology reserves), etc.

▌Advantages at a Glance:
1. No step-up transformer required: saves 3-5% on losses and floor space.
2. No parallel cluster circulating current: structurally avoids this risk.
3. Suitable for ultra-large-scale sites: more economical in the 5MW-200MW range.

▌Typical Disadvantages:
1. Extremely high project threshold: engineering commissioning, EMC, and electromagnetic environment are all more complex.
2. High scale threshold: No economic viability below 5MW.
3. Operational validation still accumulating: The industry lacks large-scale, long-term commercial case studies.
4. High operation and maintenance complexity: DC and high-voltage AC operate in the same area, with extremely stringent safety requirements.

▌Route Positioning: A cutting-edge route for grid-scale ultra-large-scale energy storage, potentially becoming one of the options for “national team projects” in the future.

Energy storage is shifting from pursuing installed capacity to developing high-quality energy storage, and the future trend is very clear: centralized storage will remain the mainstay on the grid side, but upgrades in security are imperative; string storage will dominate industrial and commercial energy storage for a long time; distributed storage will continue to penetrate large-scale energy storage projects; high-voltage cascading is a “dark horse” route in the next three to five years, but it needs project verification to support its breakthrough.

As the scale of energy storage continues to expand and application scenarios become more diverse, various technical approaches will not reach a “final unification.” The optimal approach is not a single route, but rather the optimal architecture for a given scenario.