The ability to provide accurate, rapid and dynamically-controlled impedance matching offers significant advantages to a wide range of present and emerging radio-frequency (RF) power applications. This work develops a new type of tunable impedance matching networks (TMN) that enables a combination of much faster and more accurate impedance matching than is available with conventional techniques. This implementation is based on a narrow-band technique, termed here phase-switched impedance modulation (PSIM), which entails the switching of passive elements at the RF operating frequency, effectively modulating their impedances. The proposed approach provides absorption of device parasitics and zero-voltage switching (ZVS) of the active devices, and we introduce control techniques that enable ZVS operation to be maintained across operating conditions. A prototype PSIM-based TMN is developed that provides a 50 Ohms match over a load impedance range suitable for inductively-coupled plasma processes. The prototype TMN operates at frequencies centered around 13.56 MHz at input RF power levels of up to 150 W.