The working principle of a braking resistor is actually a process of converting regenerated electrical energy into thermal energy

When the motor is decelerating, the rotational speed of the motor rotor is opposite to before deceleration. At this time, the motor is equivalent to a generator, that is, it is in a generating state and will continue to produce regenerative electricity. The generated three-phase AC electromotive force is rectified by the internal rectifying device of the frequency converter. In a frequency converter without an energy feedback system, the continuously generated regenerated electrical energy causes the DC bus voltage inside the frequency converter to continue to rise.

When the voltage on the DC bus rises to the pre-set starting voltage of the braking unit, the power switch of the braking unit is turned on, and the current flows through the braking resistor, causing it to discharge.

The conducting braking resistor begins to work, converting regenerative energy into thermal energy and releasing it. The regenerative energy on the circuit rapidly decreases, causing the motor speed to decrease and the voltage on the DC bus of the frequency converter to decrease.

When the DC bus voltage drops to the pre-set cut-off voltage of the braking unit, the power line of the braking unit is turned off. At this point, the braking resistor stops working and naturally dissipates heat, causing the temperature of the braking resistor to decrease.

When the voltage on the DC bus rises again to the pre-set starting voltage of the braking unit, the braking unit will repeat the above process, control the bus voltage within a range, ensure the normal operation of the system, and protect the control system and motor from damage.

• Resistance classification according to resistance value characteristics: fixed resistance, adjustable resistance, special resistance (sensitive resistance). What cannot be adjusted, we call a fixed or fixed resistance, and what can be adjusted, we call an adjustable resistance. A common adjustable resistor is a sliding rheostat, such as the radio volume adjustment device is a circular sliding rheostat, mainly used in voltage distribution, we call it potentiometer. According to the manufacturing material: carbon film resistor, metal film resistor, wire wound resistor, non-inductive resistor, film resistor, etc. Thin film resistance: A certain resistivity material is steamed on the surface of the insulating material by evaporation. Mainly as follows: carbon film resistor, metal film resistor, metal oxide film resistor, paint film resistor. Carbon film resistor: commonly used symbol RT as a sign; For the earliest and most commonly used resistor, the vacuum spraying technology is used to spray a layer of carbon film on the porcelain rod, and then the outer layer of carbon film is processed and cut into spiral patterns, and the resistance value is determined according to the number of spiral patterns, the more spiral patterns the larger the resistance value. Finally, the outer layer is coated with epoxy resin seal protection. Although the resistance error is higher than the metal film resistance, it is cheap because of the price. Carbon film resistors are still widely used in various products, and are the most basic components of electronic, electrical, equipment and information products.

• Color ring resistors are the most common type of resistance used in various electronic devices, and no matter how they are installed, maintainers can easily read their resistance values for easy detection and replacement. In practice, it is found that the order of some color ring resistors is not very clear, and it is often easy to read wrong, so in the identification, the following methods can be used to judge:
  
  Method 1: First find the color ring marking the error, so as to arrange the color ring order. The most commonly used color to indicate the resistance error is: gold, silver, brown, especially gold and silver rings, generally rarely used as the first ring of the resistance color ring, so as long as there are gold and silver rings on the resistance, you can basically identify this is the last ring of the color ring resistance.
  
  Method 2: The identification of whether the brown ring is an error marker. The brown ring is often used as both an error ring and a significant digit ring, and it often appears in the first and last ring at the same time, making it difficult to identify who is the first ring. In practice, it can be distinguished according to the spacing between the color rings: for example, for the resistance of a five-channel color ring, the interval between the fifth and fourth rings is wider than the interval between the first and second rings, according to which the order of the color rings can be determined.
   

• Method 3: In the case that the color ring order cannot be determined only by the color ring spacing, the production sequence value of the resistance can also be used to distinguish. For example, there is a resistor color ring reading sequence is: brown, black, black, yellow, brown, the value is: 100×104Ω=1MΩ error is 1%, belongs to the normal resistance series value, if the reverse sequence read: brown, yellow, black, black, brown, the value is 140× 100ω = 140ω, the error is 1%. Obviously, the resistance value read out according to the latter sort is not in the production series of resistors, so the latter color ring order is not correct. Resistance according to the material generally: carbon film resistance, metal film resistance, cement resistance, wire resistance and so on.
•  
• General household appliances use carbon film resistance more, because it is low cost. The metal film resistance has higher accuracy and is used on equipment with higher requirements. Cement resistor and wire resistor are able to withstand relatively high power, wire resistor precision is also relatively high, commonly used in demanding measuring instruments. Small power carbon film and metal film resistors generally use color rings to indicate the size of the resistance value, which is also a very important step in learning resistance. Resistance The unit of resistance is ohms. This is detailed below.