liminfoMotor & Drive Reference
Free reference guide: Motor & Drive Reference
About Motor & Drive Reference
The Motor & Drive Reference is a searchable technical guide designed for industrial automation engineers, maintenance technicians, and electrical designers working with motor control systems. It covers AC induction motor specifications (voltage, current, speed, efficiency ratings), synchronous speed formulas for 2/4/6/8-pole motors at 50 Hz and 60 Hz, and torque-speed curve characteristics including starting torque, breakdown torque, and rated torque calculations using T = 9550 * P / n.
The VFD (Variable Frequency Drive) section provides detailed inverter architecture (rectifier, DC link, inverter stage with IGBT PWM), V/f constant-flux control principles, essential parameter settings (motor nameplate data, accel/decel times, frequency limits), control mode comparisons (V/f open-loop, sensorless vector, closed-loop vector with encoder), Modbus communication register maps for PLC integration, motor protection settings (EOCR, thermistors), cable sizing guidelines, and EMC noise countermeasures including dV/dt and sine filters.
The servo and stepper motor sections cover AC servo specifications (rated/peak torque, encoder resolution up to 23-bit), servo drive tuning parameters (position/velocity loop gains, electronic gear ratios), inertia ratio guidelines (1:1 to 10:1), stepper motor types (2-phase vs 5-phase), microstepping modes, torque-speed curves, brake types, encoder interfaces (incremental vs absolute, BiSS/EnDat/SSI protocols), gearbox selection criteria, IE efficiency classes (IE1-IE5), and advanced motor types including linear motors, direct drives, and BLDC motors.
Key Features
- AC induction motor specs with synchronous speed formula (120*f/P) and slip calculations for 2/4/6/8-pole configurations
- Complete VFD parameter reference including motor nameplate settings, accel/decel times, and frequency limits
- V/f, sensorless vector, and closed-loop vector control mode comparison with application guidelines
- Modbus register map for VFD communication control (control word, frequency setpoint, status word, output monitoring)
- AC servo drive tuning parameters: position loop gain, velocity loop gain, torque filter, and electronic gear ratio settings
- Stepper motor reference covering 2-phase/5-phase types, full/half/micro stepping, and torque-speed characteristics
- Motor sizing calculation formula T = J*alpha + T_load with worked conveyor example from torque to kW selection
- Encoder types (incremental A/B/Z, absolute single/multi-turn), IE efficiency classes, and EMC noise countermeasures
Frequently Asked Questions
How do I calculate motor synchronous speed?
Use the formula: Synchronous Speed (rpm) = 120 * f / P, where f is frequency (Hz) and P is number of poles. For a 4-pole motor at 60 Hz: 120 * 60 / 4 = 1800 rpm. Actual speed is lower due to slip (typically 2-5%), so a 4-pole motor runs at approximately 1750 rpm.
What VFD parameters must I set for a new motor?
Essential parameters include motor rated voltage (P001), rated current (P002), rated frequency (P003), rated speed (P004), motor power (P005), acceleration time (P006), deceleration time (P007), maximum frequency (P008), and minimum frequency (P009). These must match your motor nameplate data exactly.
What is the difference between V/f control and vector control?
V/f control is simple open-loop control maintaining constant voltage-to-frequency ratio, suitable for pumps, fans, and conveyors. Sensorless vector control decomposes current into flux (Id) and torque (Iq) components for better low-speed torque, suitable for cranes and extruders. Closed-loop vector with encoder feedback enables torque control at zero speed, required for hoists and winders.
How do I control a VFD via Modbus from a PLC?
Typical Modbus registers include: Control Word (40001) with Run/Stop at Bit 0 and Forward/Reverse at Bit 1; Frequency Setpoint (40002) in units of 0.01 Hz (e.g., 3000 = 30.00 Hz); Status Word (40003) with Running at Bit 0 and Fault at Bit 3; and Output Frequency/Current monitoring registers.
What is a good inertia ratio for servo systems?
The inertia ratio (J_load / J_motor) should be 1:1 to 5:1 for general applications, below 3:1 for high-response requirements, and below 10:1 for low-response systems. High inertia ratios cause vibration and require lower gains. Use a gearbox to reduce effective load inertia: J_eff = J_load / (gear ratio)^2.
How do stepper motor stepping modes differ?
Full step gives 1.8 degrees per step (200 steps/rev for 2-phase). Half step halves this to 0.9 degrees. Microstepping further divides: 1/4 gives 0.45 degrees, 1/16 gives 0.1125 degrees. Finer microstepping provides smoother motion but reduces torque. Steppers lose torque at higher speeds and are prone to resonance.
How do I size a motor for my application?
Calculate required torque: T = J * alpha + T_load (where J is inertia in kg*m2, alpha is angular acceleration in rad/s2, and T_load is load torque). Then compute power: P = T * omega / eta (omega = 2*pi*n/60, eta = mechanical efficiency). For example, a conveyor needing 20 Nm at 1500 rpm: P = 20 * 157 / 0.9 = 3.5 kW, so select a 5.5 kW motor.
What is the difference between incremental and absolute encoders?
Incremental encoders output A/B/Z phase signals with resolutions of 1024-8192 pulses/rev, losing position on power loss. Absolute encoders provide actual position via digital communication (BiSS, EnDat, SSI, Hiperface) with single-turn (17-23 bit) or multi-turn capability. Servos typically use absolute encoders (20+ bit), while general applications use incremental encoders.