DC Motor Servo Drive Switching Power Supply EMI Filter Design

DC servo drive dedicated power supply, has not only the traditional sense of switching power supply, it is directly involved in the control of DC motor, its unique computer interface timing control and power control for DC motor drive system in particular, relatively traditional Universal power supply has a clear technological advantage, the technical features of its multi-line motor-driven power system development. However, with the electronic design, computer and home appliances are a large number and wide popularity, growing power grid noise and create a public nuisance. In particular, transient noise, the increased speed, short duration, high amplitude voltage (several hundred volts to several thousand volts), random times, especially computer and servo drive systems will be easy to produce serious interference, often makes very hard to detect.

Electromagnetic interference filters (EMI Filter) have been used widely in recent years a new type of composite device. It can effectively restrain the power grid noise, servo systems and electronic equipment to improve anti-interference ability and reliability of the system can be widely used in electronic measuring instruments, computer room equipment, switching power supply, measurement and control systems. This article describes is a DC motor servo drive switching power supply EMI filter design.

Filter Design

According to DC switching power supply system, servo-driven features, the design of EMI filters using two-stage LC network design, two-stage LC network into the position of the switching power supply circuit shown in Figure 1.

DC Motor Servo Drive Switching Power Supply EMI Filter Design

DC Motor Servo Drive Switching Power Supply EMI Filter Design

Assume a low impedance DC power supply side voltage source for the US, DC / DC converter for high input impedance current source i (t). LC filter can then select the "Γ"-type structure, the most simple two "Γ"-type LC network shown in Figure 2. The frequency domain transfer function:

As the resonant LC network, it will have a huge current (voltage) peak, the network has three frequencies resonance peak is to be restricted, will have more EMI. Limit is three points, the peak frequency of this filter is to design the main guiding principle. These three frequencies are:

As the LC network resonance, will have greater power (pressure) peak, the network has three frequencies resonance peak is to be restricted, will have more EMI. Limit is three points, the peak frequency of this filter is to design the main guiding principle. These three frequencies are:

The resonant frequency of the first level filter:

DC Motor Servo Drive Switching Power Supply EMI Filter Design

The resonant frequency of the second stage filter:

DC Motor Servo Drive Switching Power Supply EMI Filter Design

The first three frequencies is the DC / DC converter switching frequency f.

Detailed discussion of the following filter design method, which select the LC network element parameters:

3 by the above formula, three frequencies correspond to the magnitude of the transfer function are:

DC Motor Servo Drive Switching Power Supply EMI Filter Design

Component parameter selection methods are discussed below:

In order to limit the resonant point of the arrow f1 peak demands insertion attenuation

zollogH1 = zologC1/C2 <0, ie C1

DC Motor Servo Drive Switching Power Supply EMI Filter Design

 

Component parameter selection steps are summarized as follows:

(1) from (7) ~ (9)-type defined ratio, so that only two parameters are independent;

(2) As the filters load side (switch current i (t) side) higher harmonic components, C2 should choose a large-capacity capacitor.

(3) (1), (2) preliminary result substituted into (9), then one can determine the other independent parameters.

(4) determined by the DC power supply capacitors rated voltage Us Uce ≥ 2Us.

For example: If the switching power supply switching frequency f = 50kHz, Us = 24V, selected by the principle of the above parameters, select the second set of parameters in Table 1.

DC Motor Servo Drive Switching Power Supply EMI Filter Design

Technical parameters of EMI filters and test methods

Main technical parameters

EMI filter of the main technical parameters: Rated voltage, rated current, leakage current, test voltage, insulation resistance, DC resistance, the use temperature range, working temperature Tr, insertion loss AdB, dimensions, weight, etc.. The most important parameter is the insertion loss (also known as insertion attenuation), it is to evaluate the merits of EMI filter performance key indicators.

Insertion Loss (AdB) is a function of frequency, expressed with dB. EMI filter designed to load into before and after the transfer of noise power were P1, P2, has the formula:

AdB = 101g (P1/P2) (10)

Assume that the load impedance has remained unchanged before and after the insertion, then P1 = V12 / Z, P2 = V22 / Z. Type of noise source V1 is directly added to the load voltage, V2 is inserted between the noise source and load after load on the electromagnetic interference filter noise voltage, and V1 <

AdB = 201g (V1/V2) (11)

Measurement of insertion loss

Insertion loss in decibels (dB) that the greater the dB values, indicating stronger ability to suppress noise interference. Measured insertion loss of the circuit shown in Figure 3. US is the noise signal generator, Zi is the signal source's internal impedance, ZL is the load impedance, and generally the 50Ω. Noise frequency range Optional 10kHZ ~ 30MHz. First of all, in different frequencies were measured before and after the load into the noise voltage drop V1, V2, and then substituted into (11) the formula to calculate the value of each frequency point of AdB, and finally draw the insertion loss curve.

DC Motor Servo Drive Switching Power Supply EMI Filter Design

Conclusion

Experimental results show that the design of LC two-stage filter has good filtering effect, simple, cheap, practical and so on.