UPS Repetitive Servomechanism Controller for Harmonic Rejection and Transient Response

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Solution Overview

Problem

Repetitive controllers for UPS systems face challenges in stabilizing fast, sub-cycle responses and maintaining steady-state performance, particularly when dealing with various types of loads, as they tend to sacrifice accuracy for stability and struggle with harmonic rejection.

Innovation Solution

A repetitive servomechanism controller is introduced, comprising an inner control loop with a discrete sliding mode current controller and an outer control loop that combines a repetitive controller, a harmonic servomechanism controller, and a feed-forward controller, which regulates inverter current and voltage respectively, using a PWM drive signal and a frequency compensator that focuses on fundamental frequency to enhance stability and response.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a simple repetitive controller is used for harmonic rejection, then harmonic rejection performance is improved, but fast sub-cycle response capability deteriorates

Engineering Contradiction:

Improveharmonic rejection performanceVSAvoidtransient response speed

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The controller is segmented into two independent parts: a repetitive controller for harmonic rejection and a proportional-resonant controller for fast transient response. Each controller operates independently on the same current reference signal, allowing both functions to coexist without interfering with each other's performance characteristics.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent merges the repetitive controller and proportional-resonant controller into a unified control system where their output signals are summed together. This combination allows the system to simultaneously achieve excellent harmonic rejection from the repetitive controller and fast transient response from the proportional-resonant controller.

Inventive Principle:

Principle #5Merging (Combining)

2Measurement precision

If repetitive control is implemented for periodic signals, then steady state voltage performance is improved, but system stability deteriorates

Engineering Contradiction:

Improvesteady state voltage performanceVSAvoidcontroller stability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The proportional-resonant controller acts as an intermediary that enhances the stability of the repetitive controller. By carefully designing the proportional-resonant controller parameters and combining it with the repetitive controller, the system achieves both high steady-state accuracy and improved stability across various load conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent optimizes the parameters of both controllers to achieve the desired performance. By adjusting the gain parameters and frequency characteristics of the repetitive and proportional-resonant controllers, the system achieves both high steady-state voltage performance and improved stability margins.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3078096B1Repetitive servomechanism controller for uninterruptible power supply system

Publication Date: 2018.01.10 VERTIV CORP

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AI summary

A repetitive servomechanism controller for a UPS system has an inner control loop and an outer control loop. The inner control loop regulates inverter current and the outer control loop regulates inverter voltage. The outer control loop includes a repetitive controller in combination with a harmonic servomechanism controller and a feed-forward controller.