Design of the hottest small power single-phase int

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The design of low-power single-phase intelligent frequency converter

1 introduction

the frequency conversion and speed regulation of single-phase AC induction motor is widely used in many consumer products (fans, washing machines, etc.) and industrial products (blowers, pumps, etc.). People can use single-phase general-purpose frequency converter, but the general-purpose frequency converter is expensive, complex in structure, large in volume, and can only be installed outside the motor, which increases the inconvenience of use, Too many setting functions cause waste. Therefore, this paper designs a small intelligent frequency conversion control circuit for single-phase motor. It only needs an IC controller ML4421, an IPM power amplification drive module, some capacitor resistors, no software development, simple structure, small volume, and can also be placed in general induction motor, which can not only realize the electromechanical integration of frequency converter, but also increase the convenience of installation and use

2 control circuit

design the control circuit uses the special chip ML4421 for frequency conversion control of single-phase motor produced by micronear company. It is a PWM intelligent control chip with simple external connection and comprehensive functions. It is internally solidified with a control program. It has two waveform generators, PWM modulators and slip control with 90 ° mutual difference. It works in a real linear proportional, integral and differential (PID) feedback loop, provides a 10:1 speed control range, and provides a constant and programmable v/f ratio. Because there is no requirement of software programming, the development cost is saved. The wiring of ML4421 is shown in Figure 1. The description is as follows:

the wiring of figure 1ml4421

(1) pins 1 and 2 are connected to the motor current feedback input from the current transformer, ISA and ISB together constitute the differential input, detect the current, voltage and current phase difference of phase a, and then jointly determine the given phase angle with the front-end voltage feedback (it is effective when precision slip control is used); (2) Pin 3 is the setting of slip angle (only effective when precision slip control is used)

(3) fine tune the amplitude of sine wave during 4-pin precise slip control, and do not conduct precise slip control when this pin is grounded

(4) the amplitude and frequency of sine wave can be controlled by adjusting the input voltage of pin 6. If C0 is the starting capacitance of 0 ° sine wave generator, then the frequency of 0 ° sine modulated wave f= (r6/r5)/(2 × c0 × 0.356), similarly, the frequency of 90 ° sinusoidal modulation wave can be obtained

(5) select different resistance R8 on pin 8, and set the dead time t, t=r8/(5.2 × 104);

(6) 9 and 10 are connected to the sine wave generator starting capacitors C0 and C1. Pin 11 sets the reset time, pin 12 sets the PWM carrier frequency, and the carrier (triangular wave) frequency f=vref/(rref) × seven point two × cpwm);

(7) 13 pin forward and reverse selection. When the most typical data processing has the following points to drive the two-phase motor, controlling its high and low levels can realize forward/reverse rotation; (8) 14 foot braking time selection, 15 foot overcurrent protection input from the current converter, current limiting protection resistance r15=0.5v/imax; 16. 25 sine wave test points

(9) 18 ~ 23 pin drive 6-channel PWM waveform output, 18 ~ 20 low-end output, 21 ~ 23 high-end output; (10) Pins 26 ~ 28 are connected to voltage feedback input, which refers to the average value of PWM output voltage of two phases of the motor after voltage division. The above capacitance, resistance and other parameters can be selected according to the actual application to meet different control effects [1]

3 main circuit and drive circuit

the power drive and inverter circuit of the traditional frequency converter consists of two modules. Now these two parts can be completed by a small IPM power module. IPM consists of high-speed, low-power IGBT, preferred gate driver and protection circuit. Among them, IGBT is the combination of GTR and MOSFET, and the GTR is driven by MOSFET. Therefore, IPM has the advantages of GTR high current density, low saturation voltage, high withstand voltage, high input impedance of MOSFET, high switching frequency and low driving power. The protection functions include control power undervoltage locking protection, overheating protection, overcurrent protection and short circuit protection. When any of the protection functions acts. IPM will output fault signal fo. Therefore, IPM power module is powerful and can simplify the circuit design. In order to ensure that the main and auxiliary windings of single-phase motor have a strict difference of 90 ° during variable frequency speed regulation, the main circuit adopts three-phase full bridge inverter, and each winding is equivalent to an independent full bridge inverter. The split phase capacitor is eliminated, the disadvantage of frequency instability caused by the split phase capacitor is overcome, and the DC bus voltage utilization rate is high [2]. Therefore, Mitsubishi pm20csj060 (20a/600v) with 6 units is selected to drive 0.75KW single-phase AC induction motor [3]

ipm wiring is shown in Figure 2. The N and P pins are connected to the DC power supply. The DC power signal is obtained by printing the experimental results or saving the phase rectification circuit or DC bus. In order to prevent external signal interference, photoelectric isolation circuit is added between ML4421 and IPM. High speed optocoupler hcpl4504 is selected as PWM waveform input end, low speed optocoupler PC817 is selected as fault output end and braking input end, and isolation power supply m57140l is selected. M57140l can provide four groups of +15v isolation power supply. Up, VP, WP, UN, VN and wn are respectively connected to the six PWM waveforms (HA, HC, Hb, La, LC and LB) output by ML4421 through high-speed optical coupling. U and V are respectively connected to the two-phase windings of the motor, and the bypass capacitance is 0.01uF

figure 2ipm wiring

4 conclusion

this paper uses the inorganic architectural coating jg/t 26 ⑵ 00 for external walls. This product is the second product of the company since it was launched in 2015. 2ml4421, IPM power module, some capacitive resistors, designed a low-power single-phase frequency converter, without software development, low hardware cost, simple structure, high reliability, strong protection ability, shortened the system development time, and manufactured low-cost Small volume single-phase inverter provides an idea

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