Affiliations and memberships

IEEE / Senior Member


Research interests


Postgraduate research supervision




My monograph entitled A New Framework for Discrete-Event Systems has been published in Foundations and Trends® in Systems and Control (https://www.nowpublishers.com/article/Details/SYS-028)

The monograph mainly contains two contributions: an open-loop control theory (OCT) framework for verifying and enforcing properties in discrete-event systems (DESs) and a new class of automata - labeled weighted automata over monoids (LWAMs).

Real-world problems are often formulated as diverse properties of different types of dynamical systems, so property verification and synthesis/enforcement are long-standing research interests in different areas. 

Ramadge and Wonham's closed-loop supervisory control theory (SCT) framework (1987) for enforcing properties in DESs led the development of DESs in the past 3 decades. Compared with the SCT, my OCT has better scalability and wider implementability. Therefore, the theoretical framework and applied areas of DESs will must be largely extended. The SCT cannot be implemented in polynomial time, because its implementation is EXPTIME-hard, while my OCT can be implemented in polynomial time for polynomially verifiable properties. Hence my framework has better scalability. Currently it is known that the SCT can only be fully implemented on finite automata, while my OCT can be fully implemented on decidable properties of partially-observed systems with finitely many events, e.g., labeled Petri nets and labeled timed automata. Hence my OCT can be implemented in much more systems.

The LWAMs provide a natural generalization of finite automata in the sense that each transition carries a weight from a monoid, and the weight of a run is the product of the weights of its transitions. Weights have diverse physical meanings such as time consumptions and position deviations, so the LWAMs have much more applications compared with finite automata. Furthermore, by developing original computing techniques, I proved that two basic tools -- concurrent composition and observer (a nontrivial extension of Rabin and Scott's powerset construction for nondeterministic finite automata, 1959) are computable for labeled weighted automata over the monoid of rational vectors with + operator, thus, plenty of results obtained in finite automata in the past 3 decades can be extended to this new class of automata. 

The OCT framework has just been finished, and the study in LWAMs has just started. 

K. Zhang and J. Raisch (2021) Diagnosability of labeled weighted automata over the monoid $(\mathbb{Q}_{\ge0},+,0)$. In the 60th IEEE Conference on Decision and Control, Austin, Texas, USA, December 13-15 2021.
L. Zhang and K. Zhang (2013) Controllability and observability of Boolean control networks with time-variant delays in states. IEEE Transactions on Neural Networks and Learning Systems, 24(9), 1478-1484, 2013.
K. Zhang (2022) How attacks affect detectability in discrete-event systems? 2022 American Control Conference, July 8-10, 2022, Atlanta, USA, accepted.
W. Dong, X. Yin, K. Zhang, S. Li (2022) On the verification of detectability for timed systems. 2022 American Control Conference, July 8-10, 2022, Atlanta, USA, accepted.
X. Han, K. Zhang, Z. Li. (2022) Verification of strong K-step opacity for discrete-event systems, accepted, the 61st IEEE Conference on Decision and Control, December 6–9, 2022, in Cancún, Mexico.
K. Zhang (2023) A survey on observability of Boolean control networks, accepted, Control Theory and Technology, 33 pages
Observability is a fundamental property of a partially-observed dynamical system, which means whether one can use an input sequence and the corresponding output sequence to determine the initial state. Observability provides bases for many related problems such as state estimation, identification, disturbance decoupling, controller synthesis, etc. Until now, fundamental improvement has been obtained in observability of Boolean control networks mainly based on two methods — Edward F. Moore’s partition and our observability graph (or their equivalent representations found later based on the semitensor product (STP) of matrices (where the STP was proposed by Daizhan Cheng)), including necessary and sufficient conditions for different types of observability, extensions to probabilistic Boolean networks (PBNs) and singular BCNs, even to nondeterministic finite-transition systems (NFTSs); and the development (with the help of the STP of matrices) in related topics such as computation of smallest invariant dual subspaces of BNs containing a set of Boolean functions, multiple-experiment observability verification/decomposition in BCNs, disturbance decoupling in BCNs, etc. This paper provides a thorough survey for these topics. The contents of the paper are guided by the above two methods. First, we show that Moore’s partition-based method closely relates the following problems: computation of smallest invariant dual subspaces of BNs, multiple-experiment observability verification/decomposition in BCNs, and disturbance decoupling in BCNs. However, this method does not apply to other types of observability or nondeterministic systems. Second, we show that based on our observability graph, four different types of observability have been verified in BCNs, verification results have also been extended to PBNs, singular BCNs, and NFTSs. In addition, Moore’s partition also shows similarities between BCNs and linear time-invariant (LTI) control systems, e.g., smallest invariant dual subspaces of BNs containing a set of Boolean functions in BCNs vs unobservable subspaces of LTI control systems, the forms of quotient systems based on observability decomposition in both types of systems. However, there are essential differences between the two types of systems, e.g., “all plausible definitions of observability in LTI control systems turn out to be equivalent” (by Walter M. Wonham 1985), but there exist nonequivalent definitions of observability in BCNs; the quotient system based on observability decomposition always exists in an LTI control system, while a quotient system based on multiple-experiment observability decomposition does not always exist in a BCN.