tailieunhanh - Essentials of control techniques and Keyword Stats_9

Tham khảo tài liệu 'essentials of control techniques and keyword stats_9', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | More about Time and State Equations 229 But now the concept of rank gets more interesting. What is the rank of 1 0 0 2 0 1 0 3 0 0 1 4 The first three columns are clearly independent but the fourth cannot add to the rank. The rank is three. So what has this to do with controllability Suppose that our system is of third order. Then by manipulating the inputs we must be able to make the state vary through all three dimensions of its variables. x Ax Bu If the system has a single input then the B matrix has a single column. When we first start to apply an input we will set the state changing in the direction of that single column vector of B. If there are two inputs then B has two columns. If they are independent the state can be sent in the direction of any combination of those vectors. We can stack the columns of B side by side and examine their rank. But what happens next When the state has been sent off in such a direction the A matrix will come into play to move the state on further. The velocity can now be in a direction of any of the columns of AB. But there is more. The A matrix can send each of these new displacements in the direction A2B then A3B and so on forever. So to test for controllability we look at the rank of the composite matrix B I AB I A2B I A3B I It can be shown that in the third order case only the first three terms need be considered. The Cayley Hamilton theory shows that if the second power of A has not succeeded in turning the state to cover any missing directions then no higher powers can do any better. In general the rank must be equal to the order of the system and we must consider terms up to A -1B. It is time for an example. Q Is the following system controllable 0 1 0 x .-1 -2. x .1. u 230 Essentials of Control Techniques and Theory Now r 0 1 r0 r1 AB _-1 -2 _ L1J .-2 so 0 1 B I AB 1 -2 which has rank 2. The system is controllable. Q Is this system also controllable r0 1 -1 x x _-1 -2_ . 1 _ Q Is this third system .

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