Modulation and control methods for quasi-Z-source cascade multilevel inverters
First Claim
1. A modular multilevel space vector modulation method for a quasi-Z-source cascade multilevel inverter, comprising the steps of:
- generating a first switching signal for an upper left set of switches of each quasi-Z-source H-bridge inverter cell of a quasi-Z-source cascade multilevel inverter at a time T0/4−
Tsh/4 within a control cycle Ts of the quasi-Z-source H-bridge inverter cell, where T0 is an unmodified switching time interval of a zero state of the quasi-Z-source H-bridge inverter cell and Tsh is a time of shoot-through zero states of the quasi-Z-source H-bridge inverter cell;
comparing the first switching signal with a triangular carrier signal over the control cycle Ts and turning the upper left set of switches on if the triangular carrier signal is higher than the first switching signal and turning the upper left set of switches off if the triangular carrier signal is lower than the first switching signal;
generating a second switching signal for an upper right set of switches of the quasi-Z-source H-bridge inverter cell at a time Ts/2−
T0/4 within the control cycle Ts of the quasi-Z-source H-bridge inverter cell;
comparing the second switching signal with the triangular carrier signal over the control cycle Ts and turning the upper right set of switches on if the triangular carrier signal is higher than the second switching signal and turning the upper right set of switches off if the triangular carrier signal is lower than the second switching signal;
generating a third switching signal for a lower left set of switches of the quasi-Z-source H-bridge inverter cell at a time T0/4 within the control cycle Ts of the quasi-Z-source H-bridge inverter cell;
comparing the third switching signal with the triangular carrier signal over the control cycle Ts and turning the lower left set of switches on if the triangular carrier signal is higher than the third switching signal and turning the lower left set of switches off if the triangular carrier signal is lower than the third switching signal;
generating a fourth switching signal for a lower right set of switches of the quasi-Z-source H-bridge inverter cell at a time Ts/2−
T0/4+Tsh/4 within the control cycle Ts of the quasi-Z-source H-bridge inverter cell; and
comparing the fourth switching signal with the triangular carrier signal over the control cycle Ts and turning the lower right set of switches on if the triangular carrier signal is higher than the fourth switching signal and turning the lower right set of switches off if the triangular carrier signal is lower than the fourth switching signal.
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Abstract
The modulation methods for quasi-Z-source cascade multilevel inverters relate to control and signal modulation of quasi-Z-source cascade multilevel inverters, such as those used with photovoltaic power systems. The modulation methods for quasi-Z-source cascade multilevel inverters include a modular multilevel space vector modulation method for a photovoltaic quasi-Z-source cascade multilevel inverter for compensating for unequal voltages of separate photovoltaic modules, a pulse-width-amplitude modulation method for multilevel inverters for use in solar panel arrays attached to a three phase power grid, and a grid-connected control method for quasi-Z-source cascade multilevel inverter-based photovoltaic power generation for extracting maximum power from each Z-source cascade multilevel inverter.
8 Citations
7 Claims
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1. A modular multilevel space vector modulation method for a quasi-Z-source cascade multilevel inverter, comprising the steps of:
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generating a first switching signal for an upper left set of switches of each quasi-Z-source H-bridge inverter cell of a quasi-Z-source cascade multilevel inverter at a time T0/4−
Tsh/4 within a control cycle Ts of the quasi-Z-source H-bridge inverter cell, where T0 is an unmodified switching time interval of a zero state of the quasi-Z-source H-bridge inverter cell and Tsh is a time of shoot-through zero states of the quasi-Z-source H-bridge inverter cell;comparing the first switching signal with a triangular carrier signal over the control cycle Ts and turning the upper left set of switches on if the triangular carrier signal is higher than the first switching signal and turning the upper left set of switches off if the triangular carrier signal is lower than the first switching signal; generating a second switching signal for an upper right set of switches of the quasi-Z-source H-bridge inverter cell at a time Ts/2−
T0/4 within the control cycle Ts of the quasi-Z-source H-bridge inverter cell;comparing the second switching signal with the triangular carrier signal over the control cycle Ts and turning the upper right set of switches on if the triangular carrier signal is higher than the second switching signal and turning the upper right set of switches off if the triangular carrier signal is lower than the second switching signal; generating a third switching signal for a lower left set of switches of the quasi-Z-source H-bridge inverter cell at a time T0/4 within the control cycle Ts of the quasi-Z-source H-bridge inverter cell; comparing the third switching signal with the triangular carrier signal over the control cycle Ts and turning the lower left set of switches on if the triangular carrier signal is higher than the third switching signal and turning the lower left set of switches off if the triangular carrier signal is lower than the third switching signal; generating a fourth switching signal for a lower right set of switches of the quasi-Z-source H-bridge inverter cell at a time Ts/2−
T0/4+Tsh/4 within the control cycle Ts of the quasi-Z-source H-bridge inverter cell; andcomparing the fourth switching signal with the triangular carrier signal over the control cycle Ts and turning the lower right set of switches on if the triangular carrier signal is higher than the fourth switching signal and turning the lower right set of switches off if the triangular carrier signal is lower than the fourth switching signal. - View Dependent Claims (2)
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3. A pulse-width-amplitude modulation method for multilevel inverters, comprising the steps of:
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varying carrier amplitudes for a quasi-Z-source cascade of multilevel inverters (qZS-CMI) between top and bottom amplitudes of three-phase modulating signals for a left inverter H-bridge leg and a right inverter H-bridge leg, respectively, the left and right inverter H-bridge legs each having an upper power switch and a lower power switch; implementing boost control for a pulse-width-amplitude (PWAM) modulating signal if shoot-through references exceed predetermined minimum and maximum threshold values; using the shoot-through references and the threshold values to determine a shoot-through duty ratio; and for each of the power switches, determining a phase sector alternately presenting no switching action, shoot-through only, and shoot-through with active modulation, the phase sector determination depending on the shoot-through duty ratio. - View Dependent Claims (4, 5, 6)
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7. A grid-connected control method for quasi-Z-source cascade multilevel inverter-based photovoltaic power generator producing single-phase output, the generator having a cascade of photovoltaic (PV) array modules connected to a single-phase power grid, the method comprising the steps of:
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for each quasi-Z-source cascade multilevel inverter (qZS-CMI) PV array module of the cascade, providing a phase lock of grid voltage, vg, as a first input to a proportional integral controller of the module; for a first qZS-CMI PV array module of the cascade, providing a complex conjugate of a time derivative of grid current as a second input to the first PV array module'"'"'s controller; feeding an output of the first PV array module'"'"'s controller to an inner grid-tie current loop to provide a reference value thereof and a total voltage loop modulation reference, vmt; for a second through last qZS-CMI PV array module of the cascade, providing that module'"'"'s voltage loop as a second input to the corresponding module'"'"'s controller; for the second through a next to the last qZS-CMI PV array module of the cascade, summing an output of the corresponding PV array module'"'"'s controller with the inner grid-tie current reference value to provide space vector modulation signals vm2 through vm(n-1); for the last qZS-CMI PV array module of the cascade, summing an output of the last PV array module'"'"'s controller with the grid voltage vg to provide a last space vector modulation signal vmn; for the first qZS-CMI PV array module of the cascade, subtracting a sum of the space vector modulation signals vm2 through vmn from the total voltage loop modulation reference Vmt to provide a first space vector modulation signal vm1; and applying the first through last space vector modulation signals vm1, vm2 through vm(n-1), and vmn to H-bridge switches of the respective qZS-CMI PV array modules, whereby shoot-through duty ratios of the H-bridge switches are controlled to extract maximum power from each qZS-CMI PV array module, transfer substantially all captured PV power to the power grid at unity power factor, assure a constant DC-link peak voltage for each qZS-CMI PV array module, and assure a balanced DC-link peak voltage among the qZS-CMI PV array modules of the cascade.
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Specification