SINAMICS S120 PolID for PMSM with Resolver on SMC10: Technical Reference

This reference documents pole position identification (PolID) for a permanent-magnet synchronous motor (PMSM) equipped with a two-pole resolver and connected to a SINAMICS S120 drive via an SMC10 Sensor Module. The document covers why certain motor/encoder combinations allow PolID to be skipped, the parameter set that controls the procedure, and the commissioning steps required when a PolID run is mandatory.

1. Pole Position Fundamentals for PMSM

Field-oriented control of a PMSM requires knowledge of the rotor magnetic axis (electrical angle = 0°) at every instant. The commutation angle the Control Unit supplies to the power section is constructed from the encoder raw angle plus the commutation angle offset (p0431) plus the pole pair number scaling.

For asynchronous motors the rotor field can be built freely from stator current, so the absolute angle at start-up is irrelevant. For a PMSM the rotor field is fixed, so any error between the angle fed back by the encoder and the true rotor magnet axis causes torque ripple, increased current, and uncontrolled motion in the worst case.

The error between encoder electrical angle and rotor flux axis at start-up is defined as the commutation angle offset Δϑ. The drive stores this value in p0431[0] (commutation angle offset) and the measured value remains valid as long as the mechanical coupling between encoder and rotor does not change.

2. Resolver and SMC10 — Hardware Block

2.1 Resolver mechanical model

A resolver is a rotary transformer with:

• One primary (rotor) winding excited at ~8 kHz (carrier) by the SMC10.
• Two secondary windings (stator, sin and cos, 90° mechanical apart).

The number of pole pairs on the resolver is the number of sin/cos full cycles per mechanical revolution. A "two-pole resolver" (resolver pole pair number = 1) gives one sin/cos cycle per revolution, the same resolution as an incremental encoder with one line pair. A "four-pole resolver" gives two cycles per revolution.

The SMC10 (catalog 6SL3055-0AA00-5AA3) demodulates the resolver carrier, performs a tracking-loop conversion, and presents an EnDat/SSI-compatible digital position to the Control Unit at the Drive-CLiQ port X500.

2.2 SMC10 parameters of interest

For a Siemens 1FT6/1FK7/1FT7 servo motor the resolver is factory-aligned to the rotor (p0431 = 0). For a third-party PMSM with a separately supplied resolver the offset must be determined once.

3. The Integer Pole-Pair Ratio Rule

The integer ratio rule is the key concept that decides whether PolID is required. The rule states:

The ratio of motor pole pairs (p0310 or p0314) to encoder pole pairs (p0408 or p0425) must be an integer number.

When the rule is satisfied, the commutation angle repeats identically at every electrical period, and a single offset measurement (or the factory pre-set) defines the rotor angle at every startup. PolID is not required.

The mathematical form is:

Integer = p_pole_motor / p_pole_encoder

If the result is a non-integer (e.g. 10 motor pole pairs and 3 encoder pole pairs → 10/3 = 3.33), the commutation angle drift per mechanical revolution is non-zero, and the drive must run PolID at every start-up to track the rotor.

3.1 Worked example: 10-pair PMSM with 1-pair resolver

This is exactly the case in the source scenario: 10 motor pole pairs and 1 resolver pole pair. The integer ratio is satisfied, so the drive can derive a stable commutation angle at every power-on from the resolver raw angle plus the stored offset p0431. A PolID run is only needed the first time if the resolver is not pre-aligned by the motor manufacturer.

3.2 Worked example: 5-pair PMSM with 2-pair resolver (fail)

5 / 2 = 2.5 — not an integer. The drive must execute a PolID routine on every start-up (or at least when the encoder has rotated through an unresolved ambiguity).

4. PolID Methods in SINAMICS S120

The SINAMICS S120 offers several PolID techniques selected by p1980[0] (technique) and the activation source p1981[0] (bit 0: technique, bit 1: motion-based, bit 2: saturation). The most common methods are summarised in the table below.

5. PolID Parameter Configuration on S120

5.1 Required parameters

5.2 p1981 (PolID activation) bit pattern

6. Commissioning Procedure (third-party PMSM with resolver)

1. Wire the resolver to SMC10: sin+ to X520-1/2, cos+ to X520-3/4, rotor (REF) to X520-5/6. Use shielded twisted pair, shield clamped at cabinet entry, not at motor side.
2. Set p0300 = 2 (PMSM), enter p0310..p0341 from the motor data sheet. Pay attention to p0314 (pole pairs) — verify by measuring line-to-line back-EMF over one mechanical revolution with the motor uncoupled and rotated by hand: count the zero-crossings of the back-EMF; that number equals 2 × pole pairs.
3. Set p0400[0] = 1001 and p0404[0] = 0x1 for the SMC10 resolver. Set p0408[0] = 1 and p0425[0] = 1 for a 1-pole-pair resolver. Drive-CLiQ port X500 on the SMC10 must be wired to the CU320-2 or the relevant Motor Module X200.
4. Configure the integer ratio in p1980 by selecting the technique you wish to use as a one-time commissioning PolID. Method 1 (saturation 1st harmonic) is the default for a salient PMSM. Set p1981 to execute PolID once at the next RUN command.
5. Verify safety: confirm the mechanical brake is engaged, the drive is in "commissioning" mode (p0009 = 1 or p0010 = 1 if the Safety Integrated commissioning is active), and that no axis in the machine can move. The PolID routine (methods 1, 2, 4, 5) can apply a brief current pulse that can move a non-braked, low-inertia rotor by a few electrical degrees.
6. Give the drive a RUN command (ON/OFF1 = 1) without enabling the setpoint. PolID executes automatically. The result is displayed in r1984 and r1985 and is written to p0431 if p1990 is set to 1.
7. After PolID, save the parameters (RAM-to-ROM, p0977 = 1). Then reconfigure p1980 to 10 and p1981 to disable further automatic PolID. The drive now uses p0431 directly.
8. Run a motor identification routine p1910 (or p1960 for rotating) with the motor uncoupled if possible, to refine the motor equivalent circuit and current controller gains.

7. Verification

7.1 Static checks

• Read r0027 (actual speed). Should be 0 rpm in standstill, no oscillation.
• Read r0080[0] (torque setpoint). Should be near 0 with no current injection.
• Read r0090 (motor angle) and r0091 (resolver angle). The difference between electrical and mechanical rotor angle must equal 0° + n × (360° / p0314).
• Read p0431[0]. The value should be in the range −180° to +180° and remain constant across power cycles if the encoder is not moved.

7.2 Dynamic check

Apply a small setpoint (e.g. 5% of rated speed) and check that:

• r0060 (actual speed) follows r0062 (speed setpoint) within the current controller cycle (typically 125 µs for S120).
• No fault F31111, F7900, F7901 is raised within the first 5 seconds of motion.
• Reversing the setpoint does not produce a sudden jump in r0027 > 5% of rated speed.

7.3 Repeatability check

Power-cycle the drive three times. After each power-on:

1. Issue ON.
2. Measure p0431[0] used by the drive (visible via r1984).
3. Confirm all three readings are identical within 0.5° electrical.

8. Signal Flow

9. Troubleshooting Matrix

10. Safety and Commissioning Notes

• PolID applies a DC current pulse (typical 20–60% of rated motor current for 100–500 ms). The rotor may move a small angle if it is not braked.
• For vertical axes, ensure the mechanical brake is fully closed and the load is mechanically supported during PolID.
• Safety Integrated functions (STO, SS1, SBC) must be commissioned before motion is enabled. PolID with safety functions active is permitted if the relevant safety parameters (p9601, p9602) are configured.
• Do not run PolID if the encoder is not yet electrically closed (e.g. no Drive-CLiQ link, no resolver excitation). The drive will report F3xxx (encoder fault).
• Always save parameters with p0977 = 1 (RAM-to-ROM) after a successful PolID. The data resides in non-volatile memory on the CFast card of the CU.

11. Parameter Set Summary for the Integer-Ratio PMSM

For a 10-pole-pair PMSM with a 1-pole-pair resolver on SMC10 where the resolver is factory-aligned to the rotor, the minimum parameter set is:

p0300 = 2           // PMSM
p0314 = 10          // motor pole pairs
p0400[0] = 1001     // resolver on SMC10
p0404[0] = 0x1      // resolver config
p0408[0] = 1        // 1 ppr equivalent
p0425[0] = 1        // 1 resolver pole pair
p0430[0] = 0x1      // SMC10 config
p0431[0] = 0.0      // factory offset (kept as 0 if resolver was pre-aligned)
p1980[0] = 10       // use stored offset, no PolID
p1981[0] = 0        // PolID deactivated

For a third-party PMSM with the same integer ratio but an unaligned resolver, run PolID once with p1980 = 1, p1981 = 16 (PolID at first power-on, then deactivated), save, and switch to p1980 = 10 for production operation.

12. Related Drive Function Parameters

13. References to Official Documentation

For complete parameter descriptions and commissioning flows, consult:

• SINAMICS S120 Commissioning Manual with Startdrive, 09/2021, section 5.7.3.9 "Pole position synchronisation"
• SINAMICS S120 Function Manual for Drive Functions, section 5.16.4 "Commutation angle offset"
• SINAMICS S120 List Manual (parameter list p1980, p1981, p1982, p1983, p0431, p0430)
• SMC10 Sensor Module Cabinet-Mounted Equipment Manual

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