Basic Principles of Rule Based Control Methods

Rule based control strategies can cope with the various operating modes of HEV. The rule based strategies are developed using engineering insight and intuition, analysis of the ICE efficiency charts shown in Figure 2 and the analysis of electrical component efficiency charts.

An example of developing rule based strategy can be explained using the ICE efficiency map shown in Figure 3 . The lines, which are drawn using engineering insight and intuition, divide the map into three regions: A , B , and C . The rules for operation of ICE in these three regions are:

1. In the region A only EM is used because in this region the fuel efficiency of the ICE is poor.
2. In region B only ICE is used since this the region of high fuel efficiency.
3. In region C both ICE and EM are used.

Deterministic Rule Based Strategies

Heuristics based on analysis of power flow in HEV drivetrain, ICE efficiency map and human experiences are utilized to design deterministic rules. These rules are generally implemented using lookup tables to split requested power between the ICE and EM. The most commonly used strategies are:

• Thermostat (on/off) control
• Power follower control
• Modified power follower
• State Machine based controller

In the following sections the controllers marked in bold are explained.