I am a bachelor student majoring on computer engineering and working on robotics. Last year as a part of my research, I worked together with a student and one teacher as a supervisor, so we published our article for conference together. But later we finished our research and all of us left the team. Now I am working on other research problem by myself and got some results and want to publish it. But this time I am alone, I have no supervisor on that research problem or any student partner. So I'd like to ask can I submit a paper for conference/journal by myself? P.S. My current research project has no relationship with old one.
You definitely submit a paper by yourself and if you write a high quality submission, it will be accepted.
When I was early in my research career I found it very helpful to have a collaborator such as a teacher/professor or a postdoc student with publishing experience to collaborate on papers. This often helps catching points or issues that you may overlook within your research as well as providing advice and guidance.
It is not uncommon for (PhD) students to publish independently of an advisor. So as eoinbrazil wrote already, if you have a submission of a high quality, you can give it a try. Many students do publish with their supervisors, however, for a couple of good reasons. Besides the obvious ones, here are some not-so-obvious ones:
Funding for conference travel: You mentioned conferences as publication venue yourself. Assuming that your paper gets accepted: do you have the funding to visit it?
The scopes of conferences/journals: there is often a disagreement between a call for papers and the types of papers that conferences or journals actually want. Having experience in this area helps a lot.
The community behind a conference/journal: different communities focus on different things: some want the sales pitch, some are find with just the results. Some care about experiments, for others, the theory is enough. Some have a set of standard benchmarks, some don't. These are just some examples. Again, having experience with a conference or journal helps a lot.
Selection of conferences/journals: Nowadays, with spamferences and spam-journals -- probably not a big deal for you, as your have published already and at the moment it is relatively easy to tell from a call for papers if a journal or conference is of reasonable quality. For the record, this may become harder, however.
Typically, you will be asked to state your institution at submission time. Does your university have rules about submissions? Some might have some reviewing process in place in order to avoid that papers are submitted that are so bad that even submitting them could harm the reputation of the university. If you publish with your advisor, she/he will make the "internal review".