FWIW I think it makes little sense to use an author-year output in a document that has numeric citations otherwise. If for some reason you want to discuss the author or year of a work you cite do that explicitly in the text as in
In 1998 Sigfridsson and Ryde found that ...
or if you insist on using biblatex
commands
In \citeyear{1998} \citeauthor{1998} found that ...
In those cases I would probably still add a proper reference to the work in numeric format with \cite{sigfridsson}
so that it can be found more easily in the bibliography.
Mixing citation styles is often ill advised and can lead to confusion or at least irritation due to the inconsistency.
This is a copy of authoryear.cbx
's \textcite
renamed to \aytcite
so that we don't overwrite the old name.
\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[backend=biber, style=ieee, labeldateparts, sorting=nyvt, maxbibnames=99, maxcitenames=2, mincitenames=1]{biblatex}
\addbibresource{biblatex-examples.bib}
\providebool{cbx:parens}
\newbibmacro*{citeyear}{%
\iffieldundef{shorthand}
{\iffieldundef{labelyear}
{\usebibmacro{cite:label}}
{\usebibmacro{cite:labeldate+extradate}}}
{\usebibmacro{cite:shorthand}}}
\newbibmacro*{aytcite}{%
\ifnameundef{labelname}
{\iffieldundef{shorthand}
{\usebibmacro{cite:label}%
\setunit{%
\global\booltrue{cbx:parens}%
\printdelim{nonameyeardelim}\bibopenparen}%
\ifnumequal{\value{citecount}}{1}
{\usebibmacro{prenote}}
{}%
\usebibmacro{cite:labeldate+extradate}}
{\usebibmacro{cite:shorthand}}}
{\printnames{labelname}%
\setunit{%
\global\booltrue{cbx:parens}%
\printdelim{nameyeardelim}\bibopenparen}%
\ifnumequal{\value{citecount}}{1}
{\usebibmacro{prenote}}
{}%
\usebibmacro{citeyear}}}
\newbibmacro*{cite:shorthand}{%
\printtext[bibhyperref]{\printfield{shorthand}}}
\newbibmacro*{cite:label}{%
\iffieldundef{label}
{\printtext[bibhyperref]{\printfield[citetitle]{labeltitle}}}
{\printtext[bibhyperref]{\printfield{label}}}}
\newbibmacro*{cite:labeldate+extradate}{%
\iffieldundef{labelyear}
{}
{\printtext[bibhyperref]{\printlabeldateextra}}}
\newbibmacro*{aytcite:postnote}{%
\iffieldundef{postnote}
{\ifbool{cbx:parens}
{\bibcloseparen}
{}}
{\ifbool{cbx:parens}
{\setunit{\postnotedelim}}
{\setunit{\extpostnotedelim\bibopenparen}}%
\printfield{postnote}\bibcloseparen}}
\DeclareCiteCommand{\aytcite}
{\boolfalse{cbx:parens}}
{\usebibmacro{citeindex}%
\iffirstcitekey
{\setcounter{textcitetotal}{1}}
{\stepcounter{textcitetotal}%
\textcitedelim}%
\usebibmacro{aytcite}}
{\ifbool{cbx:parens}
{\bibcloseparen\global\boolfalse{cbx:parens}}
{}}
{\usebibmacro{aytcite:postnote}}
\begin{document}
\cite{sigfridsson} or \aytcite{sigfridsson}
\printbibliography
\end{document}
style=ieee
bybibstyle=ieee,citestyle=authoryear
you'll have what you want.\citeauthor
and\citeyear
...