Differences Between Inverter Motors and Ordinary Motors
The core differences between inverter motors and ordinary motors (usually referring to fixed-frequency asynchronous motors) lie in their design objectives, structural characteristics, and operating methods. The former is optimized specifically for scenarios requiring “adjustable speed,” while the latter is only suitable for constant-speed operation with a “fixed-frequency power supply.” Below is a comparison across 7 key dimensions, supplemented by applicable scenarios and selection recommendations to help you fully understand the differences between the two:
I. Core Differences: Comparison Across 7 Dimensions
| Comparison Dimension | Ordinary Motors (Fixed-Frequency Asynchronous Motors) | Inverter Motors |
|---|---|---|
| Design Objective | Adapted to fixed-frequency power supplies (e.g., 50Hz in China, 60Hz in overseas markets) to achieve constant-speed operation, with a focus on “efficiency under rated working conditions.” | Adapted to variable-frequency power supplies (ranging from 0 to several hundred Hz) to enable wide-range speed adjustment, with an emphasis on “stability and reliability across the entire speed range.” |
| Motor Structure | 1. Rotor: An ordinary cast-aluminum rotor with low conductor bar resistance (prioritizing efficiency at rated speed);
2. Heat Dissipation: Relies solely on natural heat dissipation through the housing or a simple fan (fixed speed, resulting in constant heat dissipation capacity); 3. Insulation: Uses conventional insulating materials, which only withstand rated voltage fluctuations of the power grid. |
1. Rotor: A specially designed rotor (e.g., deep-slot rotor, copper conductor bars) with slightly higher conductor bar resistance (suppressing the “slip rate” at low speeds to reduce heat generation);
2. Heat Dissipation: Equipped with an independent forced cooling fan (powered by a separate power source, unaffected by motor speed, ensuring efficient heat dissipation even at low speeds); 3. Insulation: Adopts high-frequency and high-voltage resistant insulating materials (resisting “peak voltage” generated by variable-frequency power supplies to prevent insulation breakdown). |
| Speed Control | Speed is fixed (determined by power supply frequency: Speed ≈ 60 × Frequency / Number of Pole Pairs; for example, a 4-pole motor operating at 50Hz has a rated speed of approximately 1450 r/min), and active adjustment is not feasible (unless the number of pole pairs is modified, which involves complex operations). | Speed can be freely adjusted via a variable-frequency power supply (inverter) (ranging from 0 to 1.5 times the rated speed or even higher), featuring high adjustment accuracy (within ±0.5%) and fast response speed. |
| Operating Efficiency | Efficiency is highest only under rated speed/rated load; when deviating from rated working conditions (e.g., light load, low speed), efficiency drops significantly (for instance, efficiency may fall below 50% at low speeds). | Efficiency remains stable across the entire speed range (through optimized electromagnetic design and rotor structure, efficiency can still be maintained above 80% at low speeds/light loads), offering significant energy-saving advantages. |
| Starting and Braking | 1. Starting: Direct starting causes high inrush current (5-7 times the rated current), which easily impacts the power grid and mechanical loads; reduced-voltage starting (e.g., star-delta starting, autotransformer starting) is required, but starting torque is low;
2. Braking: Additional braking devices (e.g., electromagnetic brakes) must be installed, and the braking process is unstable. |
1. Starting: “Soft starting” is achieved via the inverter, allowing starting current to be controlled within 1.5 times the rated current, with adjustable starting torque (even higher than the rated torque) and no impact on the power grid;
2. Braking: Supports “dynamic braking” and “regenerative braking” (for some high-end models), ensuring stable braking and the ability to recover part of the energy (e.g., when elevators descend or fans decelerate). |
| Reliability and Lifespan | 1. When operating at low speeds, the speed of the cooling fan decreases synchronously, leading to easy overheating of the motor windings;
2. If an ordinary motor is forced to be driven by an inverter, the peak voltage of the variable-frequency power supply can easily break down the insulation layer, shortening its lifespan (usually 1-2 years). |
1. The forced cooling fan operates independently, ensuring sufficient heat dissipation across the entire speed range and keeping the winding temperature low;
2. High-frequency resistant insulating materials can resist peak voltage, resulting in a long lifespan (usually 5-8 years). |
| Cost | Purchase cost is low (approximately 50%-70% of that of an inverter motor with the same power), but additional filtering and heat dissipation devices are required when matching with an inverter, increasing the total cost. | Purchase cost is high (30%-50% more expensive than an ordinary motor with the same power), but no additional modifications are needed, and long-term energy-saving benefits can offset the initial cost. |
II. Applicable Scenarios: How to Choose?
1. Scenarios Where Ordinary Motors Are Preferred
- Fixed working conditions with no need for speed adjustment: Such as water pumps (fixed flow), fans (fixed air volume), and conveyor belts (fixed speed) driven by three-phase asynchronous motors;
- Short-term use scenarios with low reliability requirements: For example, small motors used in temporary construction projects;
- Scenarios with limited budgets and no energy-saving needs: Such as low-power (<1kW) household appliances.
2. Scenarios Where Inverter Motors Are Essential
- Working conditions requiring wide-range speed adjustment: For instance, central air-conditioning fans (adjusting speed based on room temperature), elevators (stable starting, stopping, and speed regulation), and CNC machine tool spindles (needing different cutting speeds);
- Continuous operation scenarios with high energy-saving demands: Such as factory air compressors and large water pumps (variable-frequency adjustment can save 30%-50% of energy);
- Scenarios requiring high stability in starting and braking: For example, medical centrifuges and precision conveying equipment (to avoid mechanical impact).
III. Common Misconception: “Ordinary Motor + Inverter = Inverter Motor?”
Many people believe that “connecting an ordinary motor to an inverter enables speed regulation,” but this is incorrect and risky:
- The heat dissipation of ordinary motors depends on their own speed; insufficient heat dissipation at low speeds will cause the windings to overheat and burn out;
- The high-frequency voltage output by the inverter generates “peak pulses,” which the insulation layer of ordinary motors cannot resist, easily leading to insulation breakdown and motor failure;
- Long-term use of ordinary motors in this way will shorten their lifespan from over 5 years to less than 1 year, and the maintenance cost will be much higher than directly purchasing an inverter motor.
Therefore, if speed regulation is required, it is essential to select an inverter motor specially designed for inverters, rather than modifying an ordinary motor.
In summary, the fundamental difference between inverter motors and ordinary motors lies in “whether they are optimized for speed regulation scenarios” — ordinary motors are “cost-effective choices for fixed working conditions,” while inverter motors are “reliable and energy-saving options for speed regulation scenarios.” The selection should be based on the actual speed requirements, energy-saving goals, and reliability needs of the working conditions.