Siemens 6SE6420-2UD21-5AA1 AC Variable Frequency Drive – MICROMASTER 420

Siemens 6SE6420-2UD21-5AA1 — Single-Phase Input AC Drive in the MICROMASTER 420 Platform

The Siemens 6SE6420-2UD21-5AA1 is a 1.5 kW (2 HP) AC variable frequency drive belonging to the MICROMASTER 420 (MM420) product family. It accepts a single-phase 200–240 V AC supply and delivers a regulated three-phase output to standard induction motors, making it a practical solution for retrofit installations where only single-phase infrastructure is available. The drive operates across an output frequency range of 0 to 650 Hz, enabling both sub-synchronous speed reduction and limited over-speed operation within motor nameplate limits.

Within a control loop, the 6SE6420-2UD21-5AA1 functions as the final power-conversion element between the supervisory controller and the motor shaft. It receives a speed reference — either as an analog 0–10 V / 4–20 mA signal, a fixed frequency setpoint stored in parameters P1001–P1015, or a USS serial command from an upstream S7 PLC — and translates that reference into a pulse-width-modulated (PWM) output voltage. The internal V/f characteristic (parameter P1300 = 0) maintains a constant volts-per-hertz ratio to prevent magnetic saturation of the motor core at reduced speeds. The optional Flux Current Control (FCC) mode (P1300 = 2) improves torque linearity at low speeds without requiring a shaft encoder, which is significant for pump and fan loads where encoder installation is impractical.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

The 6SE6420-2UD21-5AA1 is built around a three-stage power conversion architecture: an uncontrolled diode rectifier bridge, a DC link capacitor bank, and a three-phase IGBT inverter stage. The single-phase rectifier produces a DC bus voltage of approximately 310–340 V DC under nominal input conditions. The DC link capacitance is sized to limit bus ripple to within ±5% at rated load, which directly constrains the low-frequency torque ripple transmitted to the motor shaft — a critical parameter for precision pump control where pressure pulsation must be minimized.

The IGBT gate drive circuitry incorporates desaturation detection: if an IGBT collector-emitter voltage rises above the desaturation threshold during conduction (indicating overcurrent or short-circuit), the gate driver shuts off the affected switch within 2–3 µs and latches a fault (F0001 or F0002). This hardware-level protection operates independently of the firmware control loop, ensuring the power stage is protected even during a CPU exception or watchdog reset.

EMC performance is addressed at two levels. Internally, the DC bus incorporates a common-mode choke that attenuates high-frequency leakage currents flowing through motor cable capacitance to earth. Externally, the drive is compatible with Siemens Class A and Class B EMC filter modules (6SE6400-2FA00-6AD0 series), which add a line-side LC network to suppress conducted emissions below EN 55011 limits. For installations with screened motor cables exceeding 25 m, an output reactor (6SE6400-3CC00-4AB3) is recommended to limit dV/dt stress on motor winding insulation to below 500 V/µs.

The control board uses a 16-bit fixed-point DSP running the V/f and FCC algorithms at a 2 ms task cycle. The parameter memory is stored in non-volatile EEPROM, retaining all P-parameter values through power cycles without a battery. The BOP/AOP operator panel interface uses a proprietary serial protocol over the front-panel connector, allowing parameter upload/download and real-time monitoring of output frequency, current, voltage, and DC bus level simultaneously.

System Integration Benefits

• Direct USS integration with S7 PLCs: The RS-485 USS protocol is natively supported by Siemens S7-200 (USS library), S7-300/400 (FC3/FC4 function blocks), and S7-1200/1500 (USS_Drive_Control instruction). No third-party gateway is required, reducing BOM cost and eliminating an additional failure point in the communication chain.
• Deterministic speed reference response: The analog input (ADC1) has a 10-bit resolution with a 10 ms filter time constant (adjustable via P0753). For applications requiring tighter response, the USS serial setpoint update rate can be configured to 20 ms cycle time, providing a predictable and bounded latency for closed-loop PID control implemented in the upstream PLC.
• Parameterized fault transparency: The drive maintains a fault history buffer of the last 8 fault codes with timestamps (P0947–P0949). Each fault code maps to a specific hardware or software condition, enabling maintenance personnel to diagnose root causes without oscilloscope access. Fault codes are readable via USS, PROFIBUS, or the BOP panel.
• Motor thermal model: The integrated I²t motor thermal model (P0610–P0614) tracks estimated motor winding temperature based on output current history. When the model predicts thermal overload, the drive reduces output frequency before tripping, extending motor life and reducing unplanned downtime compared to a simple overcurrent relay.
• Kinetic buffering (KIB): During a brief input supply interruption, the drive can extract kinetic energy from the rotating motor to maintain the DC bus voltage above the undervoltage trip threshold (P1240). This allows the drive to ride through supply dips of up to 100–200 ms depending on load inertia, preventing nuisance trips in facilities with unstable grid quality.
• Flying restart: The flying restart function (P1200) allows the drive to synchronize to a coasting motor without first decelerating it to zero. This is essential for fan applications where the motor may be spinning due to airflow even after a power interruption, preventing the high inrush current that would occur if the drive applied full voltage to an out-of-phase motor.
• Scalable fieldbus expansion: The CB PROFIBUS module slots directly into the drive’s option port without additional wiring. Once installed, the drive appears as a standard PROFIBUS-DP slave with a 4-byte PPO (Parameter Process data Object) structure, compatible with Siemens STEP 7 GSD file integration and TIA Portal drive control blocks.
• Consistent parameter architecture across MM420 family: All MM420 variants share the same P-parameter numbering scheme. A parameter set backed up from one 6SE6420 unit can be restored to any other MM420 drive of the same or higher power rating, reducing commissioning time for multi-drive installations and simplifying spare-parts management.

Quality Assurance & Global Logistics

Every 6SE6420-2UD21-5AA1 unit supplied by siemensplc.com is sourced through verified channels and subjected to a pre-dispatch inspection protocol. Physical inspection covers label authenticity (holographic Siemens security label, date code, and country-of-manufacture marking), connector integrity, and absence of reflow or rework evidence on the PCB. Functional verification confirms that the unit powers up, displays the correct firmware version on the BOP, and passes a no-load output voltage symmetry check across all three output phases.

Serialized traceability records — including the unit serial number, inspection date, and inspector ID — are retained for a minimum of 24 months and are available to customers on request. Each shipment is accompanied by a packing list and, where required, a certificate of conformity referencing the applicable CE declaration of conformity document number.

Logistics operations are based in Xiamen, China, with direct access to Xiamen Gaoqi International Airport and Xiamen Port, two of China’s primary export hubs for industrial goods. Standard export packaging uses anti-static foam inserts and moisture-barrier bags to protect the drive’s PCB assemblies during ocean or air freight. Typical transit times are 3–5 business days to Southeast Asia, 5–7 days to the Middle East and Europe via air freight, and 7–10 days to North America. DHL, FedEx, and UPS express accounts are maintained for time-critical orders. All shipments include full commercial invoice and HS code documentation (HS 8504.40) to facilitate customs clearance.

The 12-month warranty covers manufacturing defects and component failures under normal operating conditions as defined in the Siemens MM420 operating instructions (A5E00127969). Warranty claims are processed with a target response time of 2 business days from receipt of the defective unit at our Xiamen facility.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
© 2026 siemensplc.com. All rights reserved.