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Low Frequency Lead Lag Compensator

IP.com Disclosure Number: IPCOM000048869D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Fennema, AA: AUTHOR

Abstract

A compensator circuit for a control system provides a low frequency phase lead and a higher frequency phase lag. An active circuit is added to the general circuit as a capacitance multiplier to allow the use of mid-ranged capacitors with operational amplifiers.

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Low Frequency Lead Lag Compensator

A compensator circuit for a control system provides a low frequency phase lead and a higher frequency phase lag. An active circuit is added to the general circuit as a capacitance multiplier to allow the use of mid-ranged capacitors with operational amplifiers.

The typical lead-lag compensator uses a single operational amplifier with a resistor in parallel with a capacitor in both the input and feedback branches. Component values, however, become impractical at low lead frequencies. As shown in the figure, the input frequency can be directed to a DC amplifier 1 and an AC amplifier 2. The outputs of the DC amplifier 1 and the AC amplifier 2 are directed to a summation circuit 3. Since the lead frequency occurs where the total gain is twice the DC gain, the output of the DC amplifier can be summed with the output of the AC amplifier, with the gains of the amplifiers selected to produce the required lead frequency.

The DC amplifier 1 includes an operational amplifier 4 having a gain determined by the value of the resistances R1 and R2. The DC amplifier 1 has a flat gain over the frequencies involved. The AC amplifier 2 acts as a capacitive amplifier. The AC amplifier 2 also includes an operational amplifier 5. Capacitance C1 is chosen to have a value of the maximum capacitance that the preceding circuit can drive. The lead frequency then determines the size of the resistor R3. The capacitance C2 is chosen to determine the lag frequ...