1、 Core Technologies and Key Considerations
Before replacement, a comprehensive evaluation must be conducted to ensure that the new system can meet the performance requirements of the original equipment.

Performance matching and selection

Power and torque: The rated power and torque (especially starting torque and overload capacity) of an AC motor must be at least equal to or better than the original DC motor.
Need to analyze load types (constant torque, constant power, fan pump, etc.).

Speed range: DC motors are known for their wide speed regulation range.
The speed of the AC motor itself is relatively fixed, but with the help of a frequency converter, speed regulation can be achieved.
It is necessary to confirm whether the target AC motor can meet the highest and lowest speed requirements of the process under variable frequency drive.

Inertia matching: For dynamic applications that require rapid start stop, the rotational inertia of the motor rotor needs to be considered to ensure the system’s response speed.

Replacement of control system (core changes)

DC drive system: usually controlled by a DC speed regulator, with a relatively simple structure.

Communication drive system: A frequency converter must be equipped.
A frequency converter converts AC power with fixed voltage and frequency into AC power with adjustable voltage and frequency, thereby controlling the speed and torque of an AC motor.

Selection of frequency converter: The power of the frequency converter must match or be slightly greater than that of the AC motor.
At the same time, the performance level of the frequency converter should be selected according to the application requirements (such as vector control type, V/f control type).
For high-precision speed regulation and low-speed high torque applications, vector control frequency converters should be selected.

Mechanical installation and connection

Installation dimensions: The base size, shaft diameter, keyway, mounting flange, and foot hole positions of AC and DC motors may be different.
Careful verification and design of the adapter board or replacement of the mounting base are required.

Connection method: It is necessary to ensure that the coupling, pulley or gearbox can perfectly match the shaft of the new motor.
If necessary, new connectors need to be processed.

Electrical wiring and renovation

Power supply: DC motors use DC power supply, while AC motors use three-phase or single-phase AC power.
We need to lay the cables again.

Brake: If the original DC motor is equipped with a brake, it is necessary to confirm whether the new AC motor can also be equipped and ensure that its control circuit is compatible with the new frequency converter or control system.

Feedback device: For systems that require high-precision speed or position control, DC motors usually come with speed generators or encoders.
When replacing, it is necessary to install an encoder of the same type on the AC motor and connect the feedback signal to the frequency converter to form a closed-loop control.

2、 Specific replacement steps
A standardized replacement process is as follows:

Preliminary evaluation and recording:

Record all nameplate parameters of the original DC motor, including power, voltage, current, speed, excitation voltage, etc.

Record the mechanical installation dimensions and connection methods.

Analyze load characteristics and work cycles.

Evaluate the existing power and control system space.

New system selection and procurement:

Based on the evaluation results, choose a suitable AC motor (usually an AC asynchronous motor or a permanent magnet synchronous motor) and matching frequency converter.

Purchase necessary mechanical fittings, encoders, and cables.

Power outage and safety isolation:

Completely cut off the power supply of the equipment and perform lock and tag procedures to ensure safety.

Demolition of old system:

Remove all power and control wires from the DC motor.

Release the mechanical connection and lift off the old motor.

New system installation:

Install the mechanical adapter board and new AC motor to ensure reliable alignment and connection.

Install feedback devices such as encoders.

Electrical wiring:

Connect the three-phase power supply to the input terminal of the frequency converter.

Connect the output terminal of the frequency converter to the AC motor.

Connect control signals (start/stop, speed setting, etc.) from the original PLC or console to the frequency converter.

Connect the encoder feedback line.

Parameter setting and debugging (key steps):

Set the motor nameplate parameters (power, voltage, current, speed) in the frequency converter and perform motor parameter self-tuning.

Set the control mode (such as vector control), speed source, acceleration/deceleration time, overcurrent protection value, etc. according to the application settings.

Conduct no-load and load test runs, finely adjust PID and other parameters to ensure smooth operation, accurate speed, and sufficient torque.

Acceptance and Document Update:

Conduct continuous running tests to verify that the performance meets the requirements.

Update electrical drawings and equipment maintenance manuals.

3、 Advantages and Challenges
Main advantages:
High reliability, low maintenance: AC motors (especially squirrel cage asynchronous motors) have no brushes and commutators, eliminating the main fault points of DC motors and requiring almost no maintenance, resulting in a longer lifespan.

Higher efficiency: In most operating conditions, modern high-efficiency AC motors combined with frequency converters have higher efficiency and significant energy-saving effects than DC drive systems.

Better environmental adaptability: The brushless structure makes it more adaptable to harsh environments such as dust, moisture, and flammable and explosive materials.

Cost effectiveness: Although the initial investment may be high, the full lifecycle cost is usually lower due to extremely low maintenance costs and energy-saving effects.

Faster dynamic response (when using high-performance vector control): Permanent magnet synchronous motors combined with vector control frequency converters can achieve better dynamic performance than DC motors.

Challenges and precautions:
Initial investment cost: It is necessary to purchase both an AC motor and a frequency converter, and the initial investment may be higher than repairing a DC motor.

Technical complexity: Higher requirements are placed on technical personnel, who need to understand the principles and parameter settings of frequency converters.

Harmonic interference: Frequency converters can generate electromagnetic harmonics, which may interfere with the power grid and other equipment. If necessary, input reactors or filters need to be installed.

Space required: The frequency converter requires additional installation space and heat dissipation conditions.