1、 Comparison of the working principles of two types of units
1. Working principle of energy feedback unit
The energy feedback unit is a braking device applied to variable frequency speed regulation systems, and its core function is to feedback the regenerated electrical energy generated by motor deceleration to the power grid through PWM modulation technology. When the motor is in a generating state (such as a potential energy load or a large inertia load deceleration), and the rotor speed exceeds the synchronous speed, the generated electrical energy will be stored in the DC bus filter capacitor of the frequency converter. The energy feedback unit automatically detects the DC bus voltage, inverts the DC power into AC power of the same frequency and phase as the grid, and connects it to the grid after multiple noise filters. The feedback efficiency can reach over 97%.
2. Working principle of braking unit
The braking unit (energy consuming braking unit) consumes regenerative electrical energy through an external braking resistor. When the DC bus voltage exceeds the set threshold, the braking unit conducts to allow current to flow through the braking resistor, converting electrical energy into thermal energy for dissipation. This design is simple and reliable, but it completely wastes energy and generates a large amount of heat, requiring additional heat dissipation measures.
3、 Feasibility and Challenges of Alternative Technologies
Feasibility Analysis
Economic feasibility: Actual cases have shown that in frequent braking scenarios (such as elevators and centrifuges), the investment payback period of energy feedback units usually does not exceed 2 years. For example, after being used by a certain VC production enterprise, a single device can save more than 9000kWh of electricity annually.
Technical feasibility: Modern energy feedback units have achieved fully automatic operation without parameter settings. Installation only requires connecting the DC bus to the grid side, making debugging simple.
Main technical difficulties
Grid compatibility: It is necessary to ensure that the feedback energy is synchronized with the grid and avoid current backflow
Harmonic suppression: THD<5% must be controlled to meet the IEC61000-3-2 standard
Dynamic response: Need to quickly track changes in bus voltage (ms level response)
System protection: need to improve overvoltage, overcurrent, and overtemperature protection mechanisms
4、 Typical application cases and benefits
Elevator industry: A residential area in Suzhou achieved a comprehensive energy-saving rate of 30.1% after installation, while reducing the temperature of the machine room by 3-5 ℃ and reducing air conditioning energy consumption by 15%.
Pharmaceutical centrifuge: After replacing the 22kW equipment braking unit with a feedback device, a company in Shenzhen shortened the deceleration time from 10 minutes to 3 minutes, saving 9000kWh of electricity annually and recovering investment within two years.
Industrial hoist: After the renovation of the inclined shaft hoisting system in a certain mine, the regenerative energy recovery rate reached 95%, and the system's heat generation was reduced by 70%.
5、 Alternative Decision Suggestions
Recommended alternative scenarios:
Frequent braking situations (such as elevators and cranes)
High energy consuming process equipment (such as centrifuges, rolling mills)
Environment sensitive to temperature in the computer room
Areas with high electricity costs
Retain the braking unit scenario:
Simple application with extremely low braking frequency
Projects with limited initial investment
Remote areas with poor power grid quality
Implementation path:
Conduct energy consumption audit first to determine energy-saving potential
Select equipment that meets the GB/T14549 standard
Apply for government energy-saving subsidies (subsidies up to 30% in some regions)
Prioritize the renovation of high energy consuming equipment in the top 20% of energy consumption