Pulse-width modulation method for a frequency converter

• US 20050046508A1
• Filed: 08/26/2004
• Published: 03/03/2005
• Est. Priority Date: 08/28/2003
• Status: Active Grant

• Current Assignee: Vacon Oy (Danfoss A/S)
• Original Assignee: Vacon Oyj (Danfoss A/S)
• Inventors: Saren, Hannu, Luukko, Julius
• Granted Patent: US 7,190,601 B2
• Time in Patent Office: Days
• US Class Current: 332/109
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements
• CPC Class Codes: H02M 7/53876 based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times
• CPC Class Codes: H02P 21/22 Current control, e.g. using a current control loop
• CPC Class Codes: H02P 21/28 Stator flux based control
• CPC Class Codes: H02P 27/08 with pulse width modulation

Abstract

A space-vector pulse-width modulation method for a frequency converter provided with a voltage intermediate circuit, said frequency converter comprising a mains bridge (10) to be connected to an alternating current source (U_U, U_V, U_W), a direct-voltage intermediate circuit and a controlled load bridge (11) for supplying a variable-frequency alternating voltage (U_S, U_R, U_T) to a load (12), and in which method the modulator performing the modulation is given a reference. The load bridge modulator is given a reference consisting of the references for the flux linkage changes produced by the voltage vectors, the flux linkage change is calculated on the basis of measured intermediate-circuit voltage, and the currently active voltage vector is kept turned on until the reference value is reached.

Claims

1. Space-vector pulse-width modulation method for a frequency converter provided with a voltage intermediate circuit, said frequency converter comprising a mains bridge (10) to be connected to an alternating current source (U_U, U_V, U_W), a direct-voltage intermediate circuit and a controlled load bridge (11) for supplying a variable-frequency alternating voltage (U_S, U_R, U_T) to a load (12),

characterized in that

the references for the flux linkage changes produced by the voltage vectors are given as a reference to the modulator of the load bridge,

the flux linkage change is calculated on the basis of measured intermediate-circuit voltage, and

the currently active voltage vector is kept turned on until the reference value is reached.

2. Method according to claim 1,

characterized in that, in the method, a first voltage vector (V_m) is turned on and kept in the turned-on state until the flux linkage change equals half the reference (Δ

ψ

_m,ref), whereupon a second voltage vector (V_m+1) is applied and kept turned on until the flux linkage change produced by it equals half the reference Δ

ψ

_m+1,ref, whereupon a zero voltage vector (V₇) is turned on until a time (T_s/2) corresponding to half the duration of the switching period has elapsed from the beginning of the switching period, and after that the second voltage vector (V_m+1) is turned on until the remaining half of reference (Δ

ψ

_m+1,ref) for flux linkage change has been fulfilled, whereupon the first voltage vector (V_m) is again turned on and applied until the remaining half of reference (Δ

ψ

_m,ref) for flux linkage change has been fulfilled, and after that, if any time of the switching period still remains, the zero voltage vector (V₀) is additionally turned on until the end of the switching period.

3. Method according to claim 1 and 2, wherein the frequency converter'"'"'s mains bridge is also a controlled bridge,

characterized in that the mains bridge is likewise controlled using a corresponding differential space-vector pulse-width modulation (DSVPWM) method, wherein the mains bridge modulator is given a reference value consisting of imaginary references for the flux linkage change of the inductor (L_AC) connected between the power supply mains and the bridge.

4. Frequency converter, comprising a mains bridge (10) to be connected to an alternating current source (U_U, U_V, U_W), a direct-voltage intermediate circuit and a controlled load bridge (11) for supplying a variable-frequency alternating voltage (U_S, U_R, U_T) to a load (12), said load bridge being controlled by space vector pulse-width modulation by means of a modulator provided in a control unit (13),

characterized in that in the control unit (13) the reference for the mains bridge modulator consists of the references for the flux linkage changes produced by the voltage vectors, the modulator calculates the flux linkage change on the basis of measured intermediate-circuit voltage and

keeps the currently active voltage vector turned on until the reference value is reached.

5. Frequency converter according to claim 4,

characterized in that the modulator turns on a first voltage vector (V_m), which is kept turned-on until the flux linkage change equals half the reference (Δ

ψ

_m,ref) whereupon the modulator changes to a second voltage vector (V_m+1), which is kept turned-on until the flux linkage change produced by it equals half the reference Δ

ψ

_m+1,ref, whereupon the modulator turns on a zero voltage vector (V₇) until a time (T_s/2) corresponding to half the duration of the switching period has elapsed from the beginning of the switching period, and after that the modulator turns on the second voltage vector (V_m+1) until the remaining half of reference (Δ

ψ

_m+1,ref) for flux linkage change has been fulfilled, whereupon the modulator again turns on the first voltage vector (V_m), which is applied until the remaining half of reference (Δ

ψ

_m,ref) for flux linkage change has been fulfilled, and after that, if any time of the switching period still remains, the modulator additionally turns on the zero voltage vector (V₀) until the end of the switching period.

6. Frequency converter according to claim 4 and 5, in which frequency converter the mains bridge is also a controlled bridge,

characterized in that the modulator of the mains bridge controls the mains bridge by a corresponding differential space-vector pulse-width modulation (DSVPWM) method, wherein the reference value for the mains bridge modulator consists of imaginary references for the flux linkage change of the inductor (L_AC) connected between the power supply mains and the bridge.