Introduction to frequency converter switch power supply for repairing frequency converters
The switch power supply circuit provides power for the overall control of the frequency converter, which is a prerequisite for the normal operation of the frequency converter. The switch mode power supply circuit used in frequency converters is a DC AC continuous inverter circuit, which is a voltage and power converter that converts DC voltage and power into pulse voltage, and then rectifies it into another DC voltage. The input and output voltage are isolated by a switch transformer, which plays a role in power transmission and voltage/current conversion. The switch transformer is a step-down transformer. The characteristics of switch mode power supply are as follows:
1) The oscillation and voltage regulation method of switching power supplies is to adjust the output voltage by changing the pulse width or period, which is called time proportional control. It is also divided into PWM (width modulation) and PFM (frequency modulation) control methods.
2) From the energy conversion characteristics of the circuit, it can be divided into two working modes: forward and flyback. When the switching tube saturates and conducts, the rectifier connected to the secondary winding is cut off due to reverse bias, and the primary winding of the switching transformer flows current and stores energy (electromagnetic conversion). When the switch is turned off, the secondary winding releases electrical energy (magneto electric conversion) through the load circuit. The forward excitation method is the opposite and has limited practical applications.
3) From the perspective of the primary circuit structure of switch transformers, there are two types of circuit forms: those composed of discrete components and those composed of integrated oscillation chips. Therefore, from the source of oscillation signals, they can be divided into self-excited (discrete parts) and separately excited (IC circuit) switching power supplies. Both circuit structures have applications.
4) Switching tubes can use bipolar devices or field-effect transistors.
5) Small power inverters use a single ended forward circuit, while large and medium power inverters often use a dual ended forward circuit. The switch mode power supply of general frequency converters often provides the following voltage outputs:+5V power supply for CPU and auxiliary circuits, control circuits, and operation display panels; ± 15V power supply for current, voltage, temperature and other fault detection circuits and control circuits; 24V power supply for control terminals and working relay coils. The power supply of four mutually isolated driving circuits with a voltage of about 22V is often processed into+15V, -7.5V positive and negative power supplies by the voltage stabilizing circuit to provide excitation current for the IGBT inverter output circuit.
The failure rate of the power circuit in any electronic device is always quite high because it needs to provide the power supply for the entire machine, which is the heaviest burden. The switch power supply circuit of the frequency converter is relatively simple in form and structure. However, simple circuits may also cause difficult faults. The maintenance of switch mode power supplies is not as intuitive as that of linear power supplies. Any small link in the circuit, such as oscillation, voltage stabilization, protection, and load abnormalities, can cause various fault phenomena in the circuit.
No response after power on, no display on the operation display panel, and the frequency converter seems to be not powered on. The control voltage and 10V frequency adjustment voltage of the measurement control terminal are both 0. If the resistance of the main wiring terminal of the frequency converter is normal, it can be roughly concluded that the problem is in the switch power supply circuit.
