EP0351783A2 — PWM inverter apparatus

Claim 1

Independent Claim 202 words

A PWM inverter apparatus used for driving an a.c. motor, comprising: inverter means (1) including an output part connected to said a.c. motor (3) and switching elements on-off controlled by a PWM signal; means (10) for receiving, at an interval of a given sampling period, status command information specifying a desired status of a vector of a rotating magnetic flux in said a.c. motor; means (10) for predicting, on the basis of at least said status command information received and sampled at each sampling time, the status of the vector of the rotating magnetic flux which will be produced in said a.c. motor at next sampling time; means (22) for calculating the difference between the status of the vector of the rotating magnetic flux specified by said status command information sampled at current sampling time and the predicted status of the vector of the rotating magnetic flux which will be produced at next sampling time; means (21, 23, 24) for synthesizing said difference vector using ones selected from among a plurality of predetermined reference voltage vectors; and means (30) for generating a PWM signal for controlling said switching elements of said inverter means so as to produce said selected reference voltage vectors.

Claim 2

Dependent Claim 202 words

A PWM inverter apparatus used for driving an a.c. motor, comprising: inverter means (1) including an output part connected to said a.c. motor (3) and switching elements on-off controlled by a PWM signal; means (10) for receiving, at an interval of a given sampling period, status command information specifying a desired status of a vector of a rotating magnetic flux in said a.c. motor; means (10) for predicting, on the basis of at least said status command information received and sampled at each sampling time, the status of the vector of the rotating magnetic flux which will be produced in said a.c. motor at next sampling time; means (22) for calculating the difference between the status of the vector of the rotating magnetic flux specified by said status command information sampled at current sampling time and the predicted status of the vector of the rotating magnetic flux which will be produced at next sampling time; means (21, 23, 24) for synthesizing said difference vector using ones selected from among a plurality of predetermined reference voltage vectors; and means (30) for generating a PWM signal for controlling said switching elements of said inverter means so as to produce said selected reference voltage vectors.

Claim 3

Dependent Claim 133 words

The PWM inverter according to claim 1 wherein said means (10) receive a magnetic flux command and a velocity command representing desired values of the magnitude and velocity respectively of said rotating magnetic flux vector, said means (22) calculate, at each sampling time, the difference between a preceding magnetic flux vector corresponding to a preceding magnetic flux command sampled at preceding sampling time and a current magnetic flux vector corresponding to a current magnetic flux command sampled at current sampling time, on the basis of said preceding magnetic flux vector, said current magnetic flux vector and a rotation angle between said preceding magnetic flux vector and said current magnetic flux vector, said rotation angle being calculated on the basis of a velocity command sampled at the preceding sampling time and said sampling period.

Claim 4

Dependent Claim 156 words

The PWM inverter apparatus according to claim 1, wherein said means (10) receive a magnetic flux command and a velocity command representing desired values of the magnitude and velocity respecitvely of said rotating magnetic flux vector, said means (10) are predicting, at each sampling time, a vector of a magnetic flux corresponding to a magnetic flux command which will be sampled at next sampling time, under assumption that the magnitude of the next magnetic flux vector is equal to that of a current magnetic flux vector corresponding to a magnetic flux command sampled at current sampling time and that the rotation angle between the current magnetic flux vector and the next magnetic flux vector is equal to that calculated on the basis of a velocity command sampled at the current sampling time and said sampling period, and said means (22) calculate the difference between said current magnetic flux vector and said predicted next magnetic flux vector.

Claim 5

Independent Claim 182 words

A method of generating a PWM signal in a PWM inverter apparatus which includes inverter means including an output part connected to an a.c. motor and switching elements on-off controlled by the PWM signal and which is used to drive the a.c. motor, comprising the steps of: receiving, at an interval of a given sampling period, status command information specifying a desired status of a vector of a rotating magnetic flux in said a.c. motor (3); predicting, on the basis of at least said status command information received at each sampling time, the status of the vector of the rotating magnetic flux which will be produced in said a.c. motor at next sampling time and calculating the difference between the current magnetic flux vector corresponding to said status command information sampled at current sampling time and said predicted next magnetic flux vector; synthesizing said difference vector using ones selected from among a plurality of predetermined reference voltage vectors; and generating a PWM signal for controlling said switching elements of said inverter means (1) so as to produce said selected reference voltage vectors.

Claim 6

Independent Claim 182 words

A method of generating a PWM signal in a PWM inverter apparatus which includes inverter means including an output part connected to an a.c. motor and switching elements on-off controlled by the PWM signal and which is used to drive the a.c. motor, comprising the steps of: receiving, at an interval of a given sampling period, status command information specifying a desired status of a vector of a rotating magnetic flux in said a.c. motor (3); predicting, on the basis of at least said status command information received at each sampling time, the status of the vector of the rotating magnetic flux which will be produced in said a.c. motor at next sampling time and calculating the difference between the current magnetic flux vector corresponding to said status command information sampled at current sampling time and said predicted next magnetic flux vector; synthesizing said difference vector using ones selected from among a plurality of predetermined reference voltage vectors; and generating a PWM signal for controlling said switching elements of said inverter means (1) so as to produce said selected reference voltage vectors.

Claim 7

Dependent Claim 139 words

The method according to claim 4, wherein said receiving step receives a magnetic flux command and a velocity command representing desired values of the magnitude and velocity respectively of a vector of a rotating magnetic flux in said a.c. motor (3); and said calculating step calculates at each sampling time the difference between a preceding magnetic flux vector corresponding to a preceding magnetic flux command sampled at preceding sampling time and a current magnetic flux vector corresponding to a magnetic flux command sampled at current sampling time, on the basis of said preceding magnetic flux vector, said current magnetic flux vector and a rotation angle between said preceding magnetic flux vector and said current magnetic flux vector, said rotation angle being calculated on the basis of a velocity command sampled at the preceding sampling time and said sampling period.

Claim 8

Dependent Claim 103 words

A method according to Claim 5, wherein said reference voltage vectors include six voltage unit vectors and two zero vectors ṽ 7 ,ṽ 8 determined by the combinations of on-off states of said switching elements of three-phase bridge arrangement, and said difference vector ( e ) is synthesized by the use of two voltage unit vectors ṽ i and ṽ j which are nearest in direction to said difference vector among said six voltage unit vectors and whose hold times α and β are selected to satisfy the following equations: T s = α + β where T s represents the sampling period.

Claim 9

Dependent Claim 56 words

A method according to Claim 6, wherein said difference vector (e) is synthesized also by the use of one of said zero vectors said voltage unit vectors having their hold times α, β and To selected to satisfy the following equations: Ts = α + β + T o where T s represents the sampling period.

Claim 10

Dependent Claim 57 words

A method according to Claim 7, wherein said hold times α, β and To are each divided into m sections (m: a natural number), and the values of a m , β m and T om (m = 1, 2, 3, ---, m) are selected to satisfy the following equations: where T s represents the sampling period.

Claim 11

Dependent Claim 64 words

A method according to Claim 8, wherein said zero vector ṽ o is disposed at the start point or end point of said two voltage unit vectors ṽ i and ṽ j in each of said divided sections, and the component of one phase only of said zero vector changes when said zero vector shifts to said voltage unit vector ṽ i or ṽj

Claim 12

Dependent Claim 113 words

The PWM inverter according to one of the claims 1 to 3, wherein said plural reference voltage vectors include six voltage unit vectors determined by the combinations of on-off states of said switching elements of three-phase bridge arrangement, and said difference vector synthesizing means includes means (21) for selecting two voltage unit vectors ṽ i and ṽ i nearest in direction to said difference vector e from among said six voltage unit vectors, and means (23) for calculating hold times a and of said selected voltage unit vectors ṽ i and ṽ j respectively so as to satisfy the following equations: Ts = α + β where T s represents the sampling period.

Claim 13

Dependent Claim 128 words

The PWM inverter according to Claim 10, wherein said means (23) are using said selected voltage unit vectors v i , ṽ j and one of said zero vectors ṽ o for calculating hold times a, and To of said voltage unit vectors ṽ i ṽ j and said zero vector ṽ o respectively so as to satisfy the following equations: T s - α + β + To where T s represents the sampling period, and said PWM signal generating means includes means (24) for generating said PWM signal so that said voltage unit vectors ṽ i , ṽ j and said zero vector ṽ o are arranged in the order of and have said hold times α, β and To lasting for the corresponding periods respectively.

Claim 14

Dependent Claim 47 words

The PWM inverter according to Claim 11, wherein said one zero vector ṽ o is selected so that the component of one phase only of said zero vector changes when said zero vector shifts to the adjacent one of said voltage unit vectors arranged in said order.

Claim 15

Dependent Claim 113 words

The PWM inverter according to Claim 11, wherein said hold times α, β and To are each divided by m (m: a natural number larger than 1) thereby obtaining α, β and To so as to satisfy the following equations: T s = α'm + β'm + T o 'm where T s represents the sampling period, and said PWM signal generating means includes means (24) for generating said PWM signal so that said voltage unit vectors ṽ i , ṽ j and said zero vector ṽ o are repeatedly generated for m cycles in the order of and have said hold times α, β' and To lasting for the corresponding periods respectively.

Claim 16

Dependent Claim 90 words

The PWM inverter according to claim 13, wherein said difference vector synthesizing means (22) includes means for comparing said hold time with the minimum on-duty time (T o ) min of said switching elements and permitting said hold times α, β and To to be divided by m when the relation between T o/m and (T o ) min is given by but inhibiting said hold times α, β and To from being divided by m when the relation among To, To/m and (T o ) min is given by

PWM inverter apparatus

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