  Convergence bidding has been adopted in recent years by most Independent
System Operators (ISOs) in the United States as a relatively new market
mechanism to enhance market efficiency. Convergence bidding affects many
aspects of the operation of the electricity markets and there is currently a
gap in the literature on understanding how the market participants
strategically select their convergence bids in practice. To address this open
problem, in this paper, we study three years of real-world market data from the
California ISO energy market. First, we provide a data-driven overview of all
submitted convergence bids (CBs) and analyze the performance of each individual
convergence bidder based on the number of their submitted CBs, the number of
locations that they placed the CBs, the percentage of submitted supply or
demand CBs, the amount of cleared CBs, and their gained profit or loss. Next,
we scrutinize the bidding strategies of the 13 largest market players that
account for 75\% of all CBs in the California ISO market. We identify
quantitative features to characterize and distinguish their different
convergence bidding strategies. This analysis results in revealing three
different classes of CB strategies that are used in practice. We identify the
differences between these strategic bidding classes and compare their
advantages and disadvantages. We also explain how some of the most active
market participants are using bidding strategies that do not match any of the
strategic bidding methods that currently exist in the literature.
