SINAMICS S120 vs G120

Overview

In the realm of industrial automation, Siemens’ SINAMICS drive family stands as a benchmark for reliability, scalability, and performance. However, choosing the incorrect drive category can lead to either underperforming machinery or unnecessarily inflated project budgets. The two most prominent lines in this family are the SINAMICS G120 and the SINAMICS S120.

The SINAMICS G120 is designed as a modular, general-purpose variable frequency drive (VFD). It is engineered primarily for single-axis applications requiring variable speed control of induction (asynchronous) motors. It is the workhorse for standard machinery, focusing on pumps, fans, compressors, and basic material handling conveyors.

In contrast, the SINAMICS S120 is a high-performance vector and servo drive system designed for complex, high-dynamic, multi-axis motion control applications. Built on a modular platform that allows a single central Control Unit (CU) to govern multiple Motor Modules over a specialized digital bus, the S120 is tailored for coordinated, high-precision operations in packaging, printing, metal working, and continuous web handling systems.

---

Key Differences at a Glance

While both drives are modular and reside within the Siemens Totally Integrated Automation (TIA) portfolio, they target fundamentally different tiers of machine architecture.

---

Specifications Comparison

To select the appropriate drive, engineer-level specifications must be evaluated side-by-side. The table below outlines the core hardware and operational limits of both systems.

---

Performance & Capabilities

Dynamic Response and Torque Control

The SINAMICS G120 excels at speed control. With Vector Control with or withoutencoder feedback (using Control Units like the CU250S-2), the G120 achieves excellent speed accuracy and high torque at low speeds. However, its dynamic response time is limited, making it unsuitable for applications requiring instantaneous speed changes or microsecond-level synchronization.

The SINAMICS S120 represents the pinnacle of premium motion control. Supporting clock-cycle synchronous control (isochronous mode), the S120 achieves execution cycles down to 125 microseconds. This allows it to handle extremely dynamic servo operations where high acceleration rates, precise position control, and zero-speed torque holds are required.

Power Architecture and Regenerative Capability

The G120 uses a standardized, modular configuration consisting of a Control Unit (CU) and a Power Module (PM). The standard power module (PM240-2) relies on a passive diode-bridge rectifier and requires an external braking resistor to dissipate kinetic energy during deceleration. If regeneration is required, the PM250 power module must be specified, which uses an Active Infeed capable of returning kinetic energy to the supply grid.

The S120, when configured as a multi-axis system, splits power conversion into separate units:

• Line Modules (Infeed): Convert AC line voltage to DC bus voltage. Choose from Basic Line Modules (BLM - non-regenerative), Smart Line Modules (SLM - regenerative, block commutation), or Active Line Modules (ALM - regulated DC link, regenerative, low harmonics).
• Motor Modules (Inverters): Draw from the common DC bus to drive individual motors. This shared DC bus enables energy exchange between motoring and braking axes directly, drastically reducing overall energy consumption without needing grid regeneration.

---

Programming & Software

The programming and engineering workflow depends on the complexity of your control scheme and the software environment utilized.

+-------------------------------------------------------------+
|                     TIA Portal / Startdrive                 |
+-------------------------------------------------------------+
               |                               |
               v                               v
     [ SINAMICS G120 ]               [ SINAMICS S120 ]
  +-----------------------+     +---------------------------+
  | - Simple Parameters   |     | - Advanced Multi-axis     |
  | - Guided Wizards      |     | - DRIVE-CLiQ Topology Mgmt|
  | - Basic S7 Logic      |     | - Drive Control Chart(DCC)|
  +-----------------------+     +---------------------------+

Engineering Tools

Both drives are fully integrated into the Siemens Totally Integrated Automation (TIA) Portal via Startdrive, or can be configured using the legacy STARTER commissioning tool.

• Configuring G120: G120 configuration is highly wizard-driven. Programmers map basic digital and analog I/O, set acceleration/deceleration ramps, and configure motor parameters via standard motor nameplate entry.
• Configuring S120: S120 requires a more rigorous commissioning process. Because of its multi-axis architecture, you must configure individual drive objects (DOs), map the high-speed DRIVE-CLiQ network topology, and establish clock-synchronized communications with a motion controller (such as a SIMATIC S7-1500T).

Advanced Logic and Technology Functions

The G120 features basic logic blocks and PID controllers. With a CU250S-2, it can run basic positioning (EPOS), transforming the VFD into a basic single-axis positioning drive.

The S120 supports Drive Control Chart (DCC), allowing engineers to program complex closed-loop control and logic blocks directly inside the drive using graphical CFC blocks. S120 also integrates sophisticated technology tasks like synchronization, electronic gearing, and camming natively at the drive level.

---

Communication & Networking

Modern industrial automation depends heavily on deterministic, high-speed communication networks.

Standard Fieldbus Networks

The G120 supports standard fieldbus networks. Most industrial variants feature dedicated PROFINET (RT) ports, but options for PROFIBUS DP, EtherNet/IP, Modbus RTU, and CANopen are readily available via specific Control Unit part numbers.

Integrated High-Speed Fabrics (DRIVE-CLiQ)

The S120 is built around DRIVE-CLiQ, a specialized, high-speed, Ethernet-based communication interface designed by Siemens. DRIVE-CLiQ connects the central Control Unit (CU320-2) to motor modules, sensor modules (SMC/SME interface cards for converting legacy encoder feedback), and terminal modules.

DRIVE-CLiQ components feature electronic nameplates. When connected, the S120 automatically detects the precise serial numbers, motor windings, thermal models, and encoder configurations of connected Siemens motors, drastically reducing commissioning times and preventing wiring-related configuration errors.

---

Pricing & Lifecycle

Engineers and purchasing agents must balance upfront component costs with total cost of ownership (TCO).

Upfront Hardware Investment

The SINAMICS G120 has a lower entry cost. Since it is designed for standalone induction motor operations, an entire G120 drive assembly (Control Unit + Power Module + Operator Panel) is inexpensive and highly cost-effective for general industrial processes.

The S120 is an enterprise-class motion control platform. Due to the high-end processing power of the CU320-2 Control Unit, dedicated encoder modules, and specialized Line Modules, the initial capital expenditure is higher. However, in multi-axis setups, the shared DC-bus design can yield massive savings on cabling, cabinet footprint, line filters, and energy monitoring.

Lifecycle & Spare Parts Availability

Both the G120 and S120 are major active product lines with long-term support guarantees from Siemens.

• G120 systems utilize active power modules (like the PM240-2) and are regularly updated with new communication cards and firmware.
• S120 remains the primary system for high-end heavy industrial systems, packaging systems, and metal rolling mills. Because of its massive installation base worldwide, spare parts—such as booksize motor modules, line reactors, and control units—are highly accessible in distribution.

---

When to Choose Each

Select the SINAMICS G120 if you are engineering:

1. Standard Centrifugal Systems: Water/wastewater pumps, exhaust fans, and cooling tower blowers.
2. Basic Material Handling: Single, non-synchronized conveyor belts or transport rollers.
3. Simple Speed Regulation: Air compressors, non-precision mixers, or grinders.
4. Cost-Controlled Projects: Standalone machinery where complex synchronization and registration marks are not required.

Select the SINAMICS S120 if you are engineering:

1. Multi-Axis Synchronized Machinery: High-speed packaging machines, cartoning systems, and automated bottling lines.
2. Continuous Web Handling: Paper production machines, metal slitting lines, and textile manufacturing winders.
3. Servo Positioning & Robotics: High-precision CNC milling interfaces, pick-and-place gantries, and flying shears.
4. Energy-Scavenging Systems: Large crane hoists, test benches, or high-inertia applications where regenerative deceleration energy can be captured and transferred to other motoring axes on a shared DC bus.

---

Migration & Upgrade Path

If you are currently maintaining legacy Siemens installations, understanding the migration path to modern SINAMICS drives is critical to avoiding plant downtime.

• Migrating from Micromaster 440 to G120: Standard VFD applications using legacy Micromaster drives should be updated to G120. Siemens provides migration helpers in TIA Portal, allowing parameter conversion to modern PM240-2 power modules and CU240E-2 control units.
• Migrating from MASTERDRIVES to S120: High-performance legacy installations running Siemens MASTERDRIVES Vector Control (VC) or Motion Control (MC) must be retrofitted to SINAMICS S120. Because MASTERDRIVES lacked DRIVE-CLiQ, encoders must be routed through Sensor Modules (e.g., SMC30 or SME20), and central control structures must be migrated from legacy PROFIBUS to deterministic PROFINET with IRT.

---

Frequently Asked Questions (3-5 Q&A)

1. Can a SINAMICS G120 run a synchronous servo motor?

While the G120 is designed primarily for induction motors and synchronous reluctance motors, the high-end CU250S-2 control unit allows closed-loop control of permanent magnet synchronous motors (PMSM). However, it does not support high-speed servo synchronization or the advanced dynamic clock cycles of the S120.

2. Can I use the S120 as a single-axis drive?

Yes. Although most famously configured as a multi-axis system (using a common DC bus), the S120 is also available in a S120 AC/AC single-axis block format (similar physically to a G120 but featuring DRIVE-CLiQ, S120 firmware, and full servo capabilities).

3. What is the difference between a Smart Line Module (SLM) and an Active Line Module (ALM) in an S120 system?

A Smart Line Module (SLM) is a regenerative infeed that uses block commutation; it can return energy to the grid but cannot regulate the DC-link voltage. An Active Line Module (ALM) uses high-speed switching transistors (IGBTs) to provide a constant, step-up, fully regulated DC-link voltage regardless of line fluctuations, keeping supply line harmonics exceptionally low.

4. How do I choose between TIA Portal Startdrive and STARTER for programming these drives?

Both tools are fully capable. However, if your plant standardizes on modern SIMATIC S7-1500 PLCs and TIA Portal, configuring both G120 and S120 through Startdrive keeps all code, drives, and network configurations inside a single, integrated project file.

---

Related Articles

• An Overview of DRIVE-CLiQ Technology in Modern Siemens Systems
• Configuring the SINAMICS G120 with TIA Portal: Step-by-Step
• Active Line Modules vs. Smart Line Modules in SINAMICS S120 Systems