Power quality monitoring results of a modern building is presented and evaluated in this paper. Excessive current quality problems are detected, which is caused by large numbers of nonlinear loads, such as PCs, printers and TVs, in the building. In order to suppress the current harmonics and the neutral current, parallel power quality compensators should be applied. The two voltage source inverter topologies for 3-phase 4-wire compensators are compared in this paper. Results indicate that the four-leg inverter can double the neutral current compensation capability. But its phase current harmonics compensation capability is the same as three-leg center-split inverter. The initial cost and control complexity of the two kinds of inverter are compared both in 2-level and in 3-level system. And a 3-phase 4-wire parallel power quality compensator prototype is implemented. Experimental results are given to show that the current harmonics and neutral current can be compensated simultaneously.