🚀 Inverter Slip Calculator & Simulator
- Set Motor Poles (P): Select the number of motor poles (2P, 4P, 6P, 8P) to establish the baseline for synchronous speed.
- Adjust Output Frequency (Hz): Adjust the operating frequency (5Hz to 120Hz) output by the inverter (VFD) to determine the magnetic field speed.
- Input Load Torque (Nm): Adjust the mechanical load torque acting on the motor shaft to observe the slip speed reduction.
- Real-Time 2D Dynamic Magnetic Field Monitoring: Observe the speed gap between the ultra-high-speed rotating magnetic field (Ns) created by the stator and the rotor (Nr) tracking with real slip factored in, as well as the real-time V/F mapping curve point.
📚 View Detailed Induction Motor V/F Inverter Control Formulas ▼
1. Basic Principles of VFD Control and Constant V/F Control
A Variable Frequency Drive (VFD), or inverter, is a core power control device that precisely and efficiently controls the rotational speed of a three-phase induction motor by dynamically varying the frequency (f) and voltage (V) of the supplied power.
- Constant V/F Control (Constant Volts-per-Hertz Control): If the voltage is kept constant while the frequency is lowered, the iron core becomes magnetically saturated, leading to overcurrent and motor damage. Therefore, the supply voltage is linearly reduced in proportion to the frequency to maintain a constant magnetic flux density inside the core.
- Low-Speed Torque Boost: In the ultra-low-speed range (below 10Hz), the voltage drop caused by the stator winding resistance becomes relatively significant, causing torque to drop sharply. To compensate for this, the inverter performs a torque boost by slightly increasing the voltage during low-frequency operation to maintain starting torque.
2. Derivation of Induction Motor Synchronous Speed (Ns), Rotor Speed (Nr), and Slip (s) Formulas
Inverter induction control design formulas follow these rotating machinery dynamics formulas:
① Synchronous Speed (Ns): This is the theoretical rotational speed of the rotating magnetic field formed when a three-phase current is applied to the stator windings.
N_s = (120 × f) / P [RPM]
② Slip (s) and Actual Rotor Speed (Nr): In an induction motor, current is induced in the rotor by the changing magnetic field, so the rotor always rotates slower than (lags behind) the speed of the magnetic field. This rate of speed deviation is called slip (s).
s = (N_s - N_r) / N_s | N_r = N_s × (1 - s) [RPM]
③ Mechanical Output Power (Power, P): The required output power is determined by multiplying the actual rotational speed Nr by the applied load torque T.
P_out = T × ω = T × (2 π × N_r / 60) / 1000 [kW]
3. Magnetic Field Starting Limits and Field Weakening Control
The inverter speed control range is divided into two regions based on the base frequency (50Hz/60Hz).
- Constant Torque Region: The region below the base frequency where the V/F ratio is kept constant, keeping the maximum available torque constant.
- Constant Power / Field Weakening Region: The high-frequency region above the base frequency. Since the voltage cannot be increased further due to grid/supply limits (clamped at constant voltage), only the frequency is increased to weaken the magnetic flux density. Consequently, while the output torque decreases inversely with frequency, the total mechanical output power (kW) remains constant.