System and method for unbalance adjustment for inverter split-phase controlling and distribution transformer current

A method for unbalance adjustment for inverter split-phase controlling and distribution transformer current, which is applied to a system for unbalance adjustment for inverter split-phase controlling and distribution transformer current,

• wherein the system comprises:
• a distribution transformer and an a-phase line, a b-phase line, a c-phase line, and a neutral line n connected to a low voltage side of the distribution transformer, wherein the system for unbalance adjustment for inverter split-phase controlling and distribution transformer current comprises:
• a distributed power supply equipped with a positive power output terminal and a negative power output terminal;
• a three-phase full-bridge inverter provided with a positive inverter input terminal, a negative inverter input terminal, an inverter a-phase output terminal, an inverter b-phase output terminal, and an inverter c-phase output terminal, wherein the positive inverter input terminal is connected to the positive power output terminal, the negative inverter input terminal is connected to the negative power output terminal, the inverter a-phase output terminal, the inverter b-phase output terminal, and the inverter c-phase output terminal are connected to the a-phase line, the b-phase line, and the c-phase line, respectively, through a three-phase reactor;
• wherein the three-phase full-bridge inverter is configured to output corresponding compensation currents to the a-phase line, the b-phase line, and the c-phase line, respectively, through the three-phase reactor, so as to perform three-phase unbalance adjustment;
• a first filter capacitor connected to the positive inverter input terminal and the positive power output terminal;
• a second filter capacitor connected in series with the first filter capacitor, wherein the second filter capacitor is connected to the negative inverter input terminal and the negative power output terminal, and the neutral line n is connected between the first filter capacitor and the second filter capacitor;
• wherein the method comprises:
• obtaining an initial unbalance degree according to an a-phase load current of the a-phase line, a b-phase load current of the b-phase line, and a c-phase load current of the c-phase line at a low-voltage side of the distribution transformer;
• when the initial unbalance degree reaches a preset starting value, obtaining an a-phase front-end load current, a b-phase front-end load current, and a c-phase front-end load current at the front-end load side of the three-phase full-bridge inverter, and an a-phase back-end load current, a b-phase back-end load current, and a c-phase back-end load current at the back-end load side of the three-phase full-bridge inverter;
• performing sequence component decomposition processing, according to the a-phase front-end load current, the b-phase front-end load current, the c-phase front-end load current, the a-phase back-end load current, the b-phase back-end load current, and the c-phase back-end load, to obtain correspondingly an a-phase negative sequence current, a b-phase negative sequence current, and a c-phase negative sequence current, and an a-phase zero-sequence current, a b-phase zero-sequence current, and a c-phase zero-sequence current;
• performing calculation to obtain an a-phase capacitor voltage control component, a b-phase capacitor voltage control component, and a c-phase capacitor voltage according to the voltage between the positive and negative terminals at the first filter capacitor and the second filter capacitor which are connected in series and a preset reference voltage;
• obtaining an a-phase compensation current reference value according to the a-phase negative sequence current, the a-phase zero sequence current, and the a-phase capacitor voltage control component, obtaining an b-phase compensation current reference value according to the b-phase negative sequence current, the b-phase zero sequence current, and the b-phase capacitor voltage control component, obtaining a c-phase compensation current reference value according to the c-phase negative sequence current, the c-phase zero sequence current, and the c-phase capacitor voltage control component;
• outputting correspondingly an a-phase compensation current, a b-phase compensation current, and a c-phase compensation current to the a-phase line, the b-phase line, and the c-phase line, respectively, and making the outputted a-phase compensation current, the outputted b-phase compensation current, and the outputted c-phase compensation current track the a-phase compensation current reference value, the b-phase compensation current reference value, and the c-phase compensation current reference value, respectively, through hysteresis controlling, so as to adjust unbalance current by phase.