ZERO SPEED LEV = 3.0 %

67.6 ZERO SPEED LEV = 3.0 %

67.7 ZERO SPEED TIME = 1000 ms To minimize the "roll-back" (load dip) of a hoist conical motor when stopping, the flux

is reduced during stop to a level set in parameter 67.12 RED FLUX LEVEL. Default value 75 % is sufficient for most conical motors, but for larger motors (30-40 kW) there can be a need to lower this value further to minimize the "roll-back". Note that during stopping when reducing the flux the motor current will increase proportional. Due to this there can be a need to check converter sizing to have enough current margin. Normally one size bigger converter is selected.

This flux reduction is only active if conical motor function is activated with parameter

67.11 (=CONICAL). To minimize the "roll-back" (load dip) of a hoist conical motor at start, the flux level at

start can be increased to a level set in parameter 67.13 START FLUX LEVEL (100 - 140 %) during a time set with parameter 67.14 START FLUX TIME.

With parameter 67.7 ZERO SPEED TIME it's possible to delay the closing of conical motor brake at stop. For example to get faster response to a new start order within this time.

NOTE: When making ID Run with a conical motor, the REDUCED type of ID Run must be selected in parameter 99.10 . The STANDARD type of ID Run cannot be used as it is making measurements with low flux levels, making conical motor stop.

Conical motors used on hoist applications must have an encoder speed feedback.

Power optimization (68)

The power optimization function module can only be used in drives with an active (pulling) load, that is, in general only on hoist drives. Speed reference in hoisting direction must be positive value (Dir A).

When increasing the motor speed above motor nominal speed (base speed), field weakening is used. Field weakening, however reduces the maximum available torque of the motor. To ensure that the motor always is able to produce sufficient torque for controlling the load in the field weakening range, a maximum allowed speed is calculated. This function is called power optimization. This means that for a heavy load the maximum allowed speed is less than that of a light load.

When different acceleration rates for heavy and light load is required, a second ramp (“broken ramp”) my be defined.

Speed reference, Fieldbus mode

The speed reference from the PLC (DS1.2) when accelerating the hoist drive must

be limited to Base speed level (set in parameter 68.2, e.g. 50%). If maximum speed is requested by the driver, the signal HIGH SPEED, from the fieldbus Command word (DS1.1) bit 2, goes high. The power optimization then calculates the maximum speed reference in the field weakening area (above base speed) which is used as input to the ramp unit.

When the driver reduces the reference from maximum, the HIGH SPEED signal should be set to 0. The speed will now be below base speed unless PLC reference has been rescaled to be proportional to maximum reference (SPEED REF3 in DS4.1) reached during acceleration.

Speed reference, Stand alone mode

Speed reference is received through I/O (e.g. AI1 if JOYSTICK control mode is selected) or from PLC (DS1.2) if FB JOYSTICK control mode is selected (parameter

64.10 CONTROL TYPE used for Stand alone control mode selection). Speed reference is given as 0 - 100 % (% of parameter 69.1 SPEED SCALING RPM). The minimum of this requested reference and the reference calculated by power optimization is then used as input to the ramp unit. Note that parameter 64.3 HIGH SPEED LEVEL 1 should be set equal to the Base speed level (set in parameter 68.2) to get the HIGH SPEED signal correctly (this signal is created internally in Stand alone mode).

Common

To be active the parameter POWOP SELECT(68.1) must be set " True ". Parameters TQLIM UP (68.6) and TQLIM DWN (68.7) are maximum load torque

(power limits) in positive/negative running directions. When the speed, during acceleration towards base speed, has reached 90% of base

speed the module makes a calculation (using speed and torque measurements during 250 ms before reaching 90% of base speed) of the maximum allowed speed by the formula:

BASE SPEED × TQLIM

maximum speed =

TORQ HOLD

TORQ HOLD is the torque needed to hold the load (this level is equal to the motor torque value you can see when reaching steady state = constant speed), and is calculated by the module during acceleration. If the module receives the order HIGH SPEED = "1", commonly given when the master switch is in its outermost position, output SPEED REF POWOP is set to the calculated maximum speed reference. The quality of the calculation depends on the measurements done before reaching 90% of base speed. The speed must have a linear acceleration and without excessive ripple.

The power optimization output speed reference SPEED REF POWOP is set to zero if the input signal HIGH SPEED is set to "0". The calculated maximum reference is reset to zero when the actual speed SPEED ACT has decreased to a speed corresponding to the parameter POWOP RESET LEV (parameter 68.8).

The calculated reference value (before the "HIGH SPEED switch") can be seen in signal 2.25 POWOP SPEEDREF.

The TORQUE HOLD value mentioned above is continuously calculated by the power optimization module. It's available as signal LOAD TORQUE % (2.31), in % of the motor nominal torque. This signal is filtered with a filter time constant set in parameter 68.10 LOAD TORQ FILT TC.

This LOAD TORQUE signal is used to detect a "Slack rope" situation, that is load torque dropping below the level set in par. 68.11 SLACK ROPE TQ LEV. SLACK ROPE is indicated in signal 4.05 FB AUX STATUSWORD (DS12.1) bit 10. A detected slack rope will make a Fast stop1 of the drive. This Fast stop can be disabled via signal DISABLE SLACKROPE in fieldbus Dataset 5 Word 1: FB AUX COMMAND WORD (signal 3.07) Bit 7. Also setting of parameter 68.11 = -400% (default) will disable the Fast stop.

NOTE: When dimensioning the hoist motor it must be ensured that the available motor breakdown torque (Tmax) in the frequency converter duty, is sufficient for the total torque required during acceleration (hoisting) and deceleration (lowering) in the field weakening area. The breakdown torque decreases proportionally to 1/n2 in the field weakening area!

Power optimising will during acceleration, using total torque measured (load + accel), calculate the maximum speed possible in field weakening without exceeding the motors stated breakdown torque TMAX (parameter 68.9).

This value is used to limit the SPEED REF POWOP reference.

Broken acceleration ramp

A special case in power optimization is when two acceleration times are required for hoisting up; one with full load and one with light load.

The normal acceleration time (p 69.2) is set for full load and the acceleration then stops at base speed. With a light load it is possible to accelerate up to maximum speed. If the total acceleration time in this case is required to be shorter than what’s set in 69.2, then the acceleration above base speed can be increased by using the parameters 68.14 and 68.15.

The ordinary acceleration parameter, 69.2 ACC TIME FORW, is multiplied with the value of the parameter 68.14, RAMP RATE POWOP. When the value of 68.14 is less than 100%, a shorter ramp time is applied above the speed set in parameter 68.15, RAMP CHANGE SPEED. This results in a “broken ramp” according to the figure below.

The S-ramp function (parameter 69.5) applies also to the broken acceleration ramp.

(“S-ramp” function)

Max speed

Base speed

Required acc. time with t (s)

Required acc. time

with light load

heavy load (p 69.2)