This paper proposes a piezoelectric transformer based on a resonant inverter that allows varying-capacity for ozone generation. The drawback of a piezoelectric transformer (PT) lies in its limited ability to transfer power, rendering it unable to provide sufficient current. Therefore, this study proposes a resonance topology with multiple modular parallel PTs using a PT-equivalent circuit derivation, and analyzes the resulting resonance curve characteristics. The proposed resonance topology can flexibly expand the output capacity, and stabilize the resonance characteristics and mechanical frequency. These results show that the proposed device is better suited to controller design. In addition, the study embeds an asymmetrical pulse width modulation (APWM) control concept into the microprocessor control unit such that the operating power of the ozone generator can be well regulated. This method has been realized with hardware circuit verification. Results demonstrate that the proposed inverter effectively drives the ozone generator system, regulates the operation power, and achieves the zero-voltage switching. The proposed design also ensures that the output current of each PT is evenly balanced, thereby facilitating the flexible capacity operations of the approach for industrial applications.