What is the reason for using inverters instead of open circuit transformers in variable frequency drive applications?

In variable frequency drive (VFD) applications, using an inverter instead of an open-circuit transformer (also known as a linear transformer) is preferred for several reasons. Here are the main reasons:

1. Adjustable Output Frequency

Inverter: An inverter can generate AC power with a variable frequency, which is the core function of a VFD. By adjusting the output frequency, the speed and torque of the motor can be controlled precisely.

Open-Circuit Transformer: An open-circuit transformer can only provide a fixed frequency output, typically matching the grid frequency (50Hz or 60Hz), and cannot adjust the frequency.

2. Higher Efficiency

Inverter: Inverters operate using efficient switching devices (such as IGBTs) and can achieve high efficiency, often exceeding 95%.

Open-Circuit Transformer: Open-circuit transformers experience iron losses and copper losses, particularly at light or no load, resulting in lower efficiency.

3. Lower Inrush Current

Inverter: Inverters can control the inrush current during motor startup, avoiding large current spikes. This helps extend the life of the motor and reduces the impact on the power grid.

Open-Circuit Transformer: Open-circuit transformers cannot control the inrush current, leading to significant startup currents that can cause voltage drops in the grid and interfere with other equipment.

4. Fast Dynamic Response

Inverter: Inverters have fast dynamic response capabilities, allowing them to quickly adjust the output to adapt to load changes. This is crucial for applications requiring rapid response.

Open-Circuit Transformer: Open-circuit transformers have slower dynamic responses and cannot quickly adapt to load changes.

5. Rich Protection Functions

Inverter: Inverters typically come equipped with multiple protection functions, such as overload protection, short-circuit protection, and overheat protection, ensuring safe operation of the system.

Open-Circuit Transformer: Open-circuit transformers have limited protection functions and often require external protection devices.

6. Harmonic Suppression

Inverter: Modern inverters often include harmonic filters that effectively suppress harmonics, reducing grid pollution.

Open-Circuit Transformer: Open-circuit transformers cannot effectively suppress harmonics, potentially degrading grid quality.

7. Flexibility and Programmability

Inverter: Inverters offer high flexibility and programmability, allowing for complex functions to be implemented through parameter settings and programming, such as multi-speed control and PID regulation.

Open-Circuit Transformer: Open-circuit transformers have limited functionality and cannot achieve complex control and regulation.

8. Size and Weight

Inverter: Inverters are typically smaller in size and lighter in weight, making them easier to install and maintain.

Open-Circuit Transformer: Open-circuit transformers are larger in size and heavier, making installation and handling more difficult.

9. Cost-Effectiveness

Inverter: Although the initial investment may be higher, the high efficiency and energy savings of inverters can lead to significant cost savings over the long term, providing good cost-effectiveness.

Open-Circuit Transformer: Open-circuit transformers have a lower initial cost, but their lower efficiency and higher maintenance costs result in higher long-term operating costs.

Summary

In VFD applications, inverters offer numerous advantages over open-circuit transformers, including adjustable output frequency, high efficiency, low inrush current, fast dynamic response, rich protection functions, harmonic suppression, flexibility and programmability, smaller size and weight, and good cost-effectiveness. These advantages make inverters the preferred choice for VFD applications.